WO2024228087A1 - 二次電池 - Google Patents

二次電池 Download PDF

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Publication number
WO2024228087A1
WO2024228087A1 PCT/IB2024/053966 IB2024053966W WO2024228087A1 WO 2024228087 A1 WO2024228087 A1 WO 2024228087A1 IB 2024053966 W IB2024053966 W IB 2024053966W WO 2024228087 A1 WO2024228087 A1 WO 2024228087A1
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active material
positive electrode
electrode active
surface layer
lithium
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French (fr)
Japanese (ja)
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山崎舜平
横溝和音
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Semiconductor Energy Laboratory Co Ltd
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Semiconductor Energy Laboratory Co Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • One aspect of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter.
  • One aspect of the present invention relates to a power storage device including a secondary battery, a semiconductor device, a display device, a light-emitting device, a lighting device, an electronic device, or a manufacturing method thereof.
  • electronic devices refer to devices that have a power storage device in general, and electro-optical devices that have a power storage device, information terminal devices that have a power storage device, etc. are all electronic devices.
  • lithium-ion secondary batteries lithium-ion capacitors
  • air batteries air batteries
  • all-solid-state batteries all-solid-state batteries.
  • demand for high-output, high-capacity lithium-ion secondary batteries in particular has expanded rapidly in line with the development of the semiconductor industry, and they have become indispensable in today's information society as a rechargeable energy source.
  • X-ray diffraction is one of the techniques used to analyze the crystal structure of positive electrode active materials.
  • XRD data can be analyzed by using the Inorganic Crystal Structure Database (ICSD) introduced in Non-Patent Document 4.
  • ICSD Inorganic Crystal Structure Database
  • the lattice constant of lithium cobalt oxide described in Non-Patent Document 5 can be referenced from ICSD.
  • the analysis program RIETAN-FP Non-Patent Document 6
  • VESTA Non-Patent Document 7 can be used as software for drawing crystal structures.
  • Non-Patent Document 8 When considering the crystal structure of oxides, Shannon's ionic radius (Non-Patent Document 8) can be referred to.
  • ImageJ (Non-Patent Documents 9 to 11) is known as an example of image processing software.
  • this software for example, the shape of the positive electrode active material can be analyzed.
  • Microelectron diffraction is also effective in identifying the crystal structure of the positive electrode active material, particularly the crystal structure of the surface layer.
  • the analysis program ReciPro can be used to analyze the electron diffraction pattern.
  • Non-Patent Document 13 The electrochemical properties of metal oxides have also been studied for a long time.
  • Lithium-ion secondary batteries have room for improvement in various aspects, such as discharge capacity, cycle characteristics, reliability, safety, and cost.
  • the surface of the positive electrode active material may be coated with an electrochemically stable oxide, but this coating may reduce the electrical conductivity and inhibit the insertion and desorption of lithium. If the electrical conductivity is reduced and/or the insertion and desorption of lithium ions is inhibited, there is concern that the characteristics of the secondary battery may be reduced, such as reduced rate characteristics and reduced charge and discharge capacity in low-temperature environments.
  • one aspect of the present invention has an object to provide a positive electrode active material that can be used in a lithium ion secondary battery and that improves electrical conductivity and/or promotes insertion and desorption of lithium ions.
  • an object of the present invention is to provide a positive electrode active material or composite oxide in which the decrease in discharge capacity in a low-temperature environment is suppressed.
  • an object of the present invention is to provide a positive electrode active material or composite oxide in which the decrease in discharge capacity during charge and discharge cycles is suppressed.
  • an object of the present invention is to provide a positive electrode active material or composite oxide whose crystal structure is not easily destroyed even after repeated charge and discharge.
  • an object of the present invention is to provide a positive electrode active material or composite oxide whose discharge capacity is large.
  • an object of the present invention is to provide a secondary battery or vehicle that is safe or highly reliable.
  • Another object of one embodiment of the present invention is to provide a positive electrode active material, a composite oxide, a power storage device, or a manufacturing method thereof.
  • one aspect of the present invention provides a positive electrode active material having an element that can become a semiconductor when it becomes an oxide in the surface layer.
  • an element that can become a semiconductor when it becomes an oxide in the surface layer.
  • one or more elements selected from nickel, titanium, ruthenium, vanadium, niobium, chromium, molybdenum, tungsten, rhenium, osmium, rhodium, iridium, lanthanum, and strontium can be used as such an element.
  • the surface layer of the positive electrode active material has an additive element that stabilizes the crystal structure.
  • the additive element that stabilizes the crystal structure for example, one or more selected from magnesium, fluorine, nickel, and aluminum can be used.
  • One aspect of the present invention is a secondary battery having a positive electrode active material, the positive electrode active material having an additive element whose oxide can become a semiconductor, magnesium, and lithium cobalt oxide, the positive electrode active material having cracks, the positive electrode active material having a surface layer portion and a crack portion, the surface layer portion being a region within 10 nm from the surface other than the crack, the crack portion being a region within 10 nm from the surface of the crack and being a region other than the surface layer portion, magnesium being detected from the surface layer portion and the crack portion, the element whose oxide can become a semiconductor being detected from the surface layer portion, and the element whose oxide can become a semiconductor being one or two selected from nickel and titanium.
  • Another embodiment of the present invention is a secondary battery having a positive electrode active material, the positive electrode active material comprising magnesium and lithium cobalt oxide, the positive electrode active material having a magnesium concentration gradient in a surface layer portion, and in EDX-ray analysis of magnesium in the positive electrode active material, when a peak width at a height that is 1 ⁇ 5 of the maximum value of the detected amount of magnesium is divided in half by a perpendicular line drawn from the maximum value to the horizontal axis, the peak width MgW core on the inner side is larger than the peak width MgW shell on the surface side.
  • Another aspect of the present invention is a secondary battery having a positive electrode active material, the positive electrode active material having an additive element whose oxide can become a semiconductor, magnesium, and lithium cobalt oxide, the positive electrode active material having cracks, the positive electrode active material having a surface layer portion and a crack portion, the surface layer portion being a region within 10 nm from the surface other than the crack, the crack portion being a region within 10 nm from the surface of the crack and being a region other than the surface layer portion, magnesium being detected from the surface layer portion and the crack portion, an element whose oxide can become a semiconductor is detected from the surface layer portion, the element whose oxide can become a semiconductor is one or two selected from titanium and nickel, the positive electrode active material has a magnesium concentration gradient in the surface layer portion, and in EDX-ray analysis of magnesium in the positive electrode active material, when a peak width at a height 1 ⁇ 5 of the maximum value of the amount of magnesium detected is divided in half by a perpendicular line drawn down from the maximum value to the horizontal axis
  • the surface layer and cracks prefferably have fluorine.
  • a positive electrode active material that can be used in a lithium ion secondary battery and that has improved electrical conductivity and/or accelerated insertion and desorption of lithium ions.
  • a positive electrode active material or composite oxide that can be used in a lithium ion secondary battery and that suppresses a decrease in discharge capacity in a low-temperature environment.
  • a positive electrode active material or composite oxide that suppresses a decrease in discharge capacity during charge and discharge cycles.
  • a secondary battery or vehicle that is safe or highly reliable.
  • one embodiment of the present invention can provide a positive electrode active material, a composite oxide, a power storage device, or a manufacturing method thereof.
  • FIG. 1A is a cross-sectional view of a positive electrode active material
  • FIG. 1B is a diagram illustrating the distribution of nickel (Ni) or titanium (Ti), as well as magnesium, fluorine, and aluminum.
  • FIG. 2 is a diagram illustrating the distribution of magnesium.
  • FIG. 3 is an example of a TEM image in which the crystal orientations are roughly consistent.
  • Fig. 4A is an example of an STEM image in which the crystal orientations are roughly consistent
  • Fig. 4B is an FFT pattern of a region of the rock-salt crystal RS
  • Fig. 4C is an FFT pattern of a region of the layered rock-salt crystal LRS.
  • FIG. 5 is a diagram illustrating the crystal structure of the positive electrode active material.
  • FIG. 5 is a diagram illustrating the crystal structure of the positive electrode active material.
  • FIG. 6 is a diagram illustrating the crystal structure of a conventional positive electrode active material.
  • FIG. 7 shows an XRD pattern calculated from the crystal structure.
  • FIG. 8 shows an XRD pattern calculated from the crystal structure.
  • 9A and 9B are diagrams showing XRD patterns calculated from the crystal structure.
  • FIG. 10 is a cross-sectional view of the positive electrode active material.
  • FIG. 11 is a diagram illustrating a method for producing a positive electrode active material.
  • 12A to 12C are diagrams illustrating a method for manufacturing a positive electrode active material.
  • 13A and 13B are diagrams illustrating a method for manufacturing a positive electrode active material.
  • FIG. 14 is a diagram showing the external appearance of a secondary battery.
  • 15A to 15C are diagrams illustrating a method for manufacturing a secondary battery.
  • 16A to 16H are diagrams illustrating an example of an electronic device.
  • 17A to 17D are diagrams illustrating an example of an electronic device.
  • 18A to 18C are diagrams illustrating an example of an electronic device.
  • 19A to 19C are diagrams illustrating an example of a vehicle.
  • the space group is expressed using short notation of the international notation (or Hermann-Mauguin notation).
  • the crystal plane and crystal direction are expressed using Miller indices.
  • the space group, crystal plane, and crystal direction are expressed by adding a superscript bar to the numbers, but in this specification, due to format restrictions, instead of adding a bar above the numbers, a - (minus sign) may be added before the numbers.
  • Individual directions that indicate directions within a crystal are expressed with [ ]
  • collective directions that indicate all equivalent directions are expressed with ⁇ >
  • individual faces that indicate crystal faces are expressed with ( )
  • collective faces with equivalent symmetry are expressed with ⁇ ⁇ .
  • trigonal crystals expressed as space group R-3m are generally sometimes expressed as a composite hexagonal lattice of hexagonal crystals for ease of understanding the structure.
  • hkl not only (hkl) but also (hkil) may be used as Miller indices.
  • i is -(h+k).
  • crystal planes and the like are represented as a compound hexagonal lattice unless otherwise specified.
  • the term "particles” does not necessarily refer to spherical shapes (cross-sectional shape being circular), but may refer to shapes such as ellipses, rectangles, trapezoids, triangles, squares with rounded corners, and asymmetric shapes in cross-section, and further may refer to shapes such as irregular shapes.
  • the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the lithium that can be inserted and removed from the positive electrode active material is removed.
  • the theoretical capacity of LiCoO2 is 274 mAh/g
  • the theoretical capacity of LiNiO2 is 275 mAh/g
  • the theoretical capacity of LiMn2O4 is 148 mAh/g.
  • the amount of lithium that can be inserted and removed from the positive electrode active material is indicated by x in the composition formula, for example, x in Li x MO 2 (where M is one or more selected from cobalt, nickel, and manganese).
  • x (theoretical capacity - charging capacity) / theoretical capacity.
  • Li 0.2 MO 2 or x 0.2.
  • x in Li x MO 2 is small means 0.1 ⁇ x ⁇ 0.24.
  • the completion of discharge here refers to a state in which the voltage is 3.0 V or 2.5 V or less at a current of 100 mA/g or less.
  • the charge capacity and/or discharge capacity used to calculate x in Li x MO 2 is preferably measured under conditions that are free of or have little influence from short circuits and/or decomposition of the electrolyte, etc. For example, data from a secondary battery that has experienced a sudden change in capacity that is considered to be due to a short circuit should not be used to calculate x.
  • the space group of a crystal structure is identified by XRD, electron diffraction, neutron diffraction, etc. Therefore, in this specification, etc., "belonging to a certain space group,” “belonging to a certain space group,” or “being a certain space group” can be rephrased as "identified with a certain space group.”
  • Cubic close packing of anions refers to a state in which the second layer of anions is arranged above the gaps of the first layer of anions, and the third layer of anions is arranged directly above the gaps of the second layer of anions, but not directly above the first layer of anions. Therefore, the anions do not have to be strictly cubic lattices. Also, since real crystals always have defects, the analysis results do not necessarily have to be theoretical. For example, in the electron diffraction pattern or FFT (fast Fourier transform) pattern of a TEM image, etc., spots may appear at positions slightly different from the theoretical positions. For example, if the orientation with respect to the theoretical positions is 5 degrees or less, or 2.5 degrees or less, it can be said to have a cubic close packing structure.
  • FFT fast Fourier transform
  • the distribution of a certain element refers to the region in which the element is continuously detected in a non-noise range using a certain continuous analytical method.
  • a region in which the element is continuously detected in a non-noise range can also be defined as a region in which the element is always detected when the analysis is performed multiple times.
  • a positive electrode active material to which an additive element that improves electrical conductivity and/or an additive element that stabilizes the crystal structure has been added may be expressed as a composite oxide, a positive electrode material, a positive electrode material, a positive electrode material for secondary batteries, etc.
  • the positive electrode active material of one embodiment of the present invention preferably has a compound.
  • the positive electrode active material of one embodiment of the present invention preferably has a composition.
  • the positive electrode active material of one embodiment of the present invention preferably has a composite.
  • the characteristics of individual particles of the positive electrode active material in the following embodiments, etc. it is not necessary that all particles have that characteristic. For example, if 50% or more, preferably 70% or more, and more preferably 90% or more of three or more randomly selected particles of the positive electrode active material have that characteristic, it can be said that there is a sufficient effect of improving the characteristics of the positive electrode active material and the secondary battery containing it.
  • the positive electrode active material of one embodiment of the present invention has a stable crystal structure even at high voltages. Because the crystal structure of the positive electrode active material is stable in the charged state, it is possible to suppress the decrease in charge/discharge capacity that accompanies repeated charging and discharging.
  • lithium-ion secondary cells and lithium-ion secondary assembled batteries (hereinafter referred to as lithium-ion secondary batteries) can be said to be in a pre-degradation state when they have a discharge capacity of 97% or more of their rated capacity.
  • the rated capacity complies with JIS C 8711:2019.
  • they are not limited to the above JIS standards, but also comply with various JIS and IEC standards for electric vehicle propulsion, industrial use, etc.
  • the state of the materials in a secondary battery before degradation is referred to as an initial product or initial state
  • the state after degradation (the state when the secondary battery has a discharge capacity of less than 97% of the rated capacity) may be referred to as a product in use or in use state, or a used product or used state.
  • Fig. 1A is a cross-section of a positive electrode active material 100 according to one embodiment of the present invention.
  • the positive electrode active material 100 has a surface layer 100a and an interior 100b.
  • a dashed line indicates the boundary between the surface layer 100a and the interior 100b.
  • (001) indicates the (001) plane in the case where the positive electrode active material 100 is LiMO 2 (wherein M is one or more selected from Co, Ni, Mn, and Fe) having a crystal structure of layered rock salt belonging to the space group R-3m.
  • the surface layer 100a of the positive electrode active material 100 refers to, for example, a region within 10 nm perpendicular or approximately perpendicular to the surface. Note that approximately perpendicular means 80° to 100°.
  • the surface layer 100a is synonymous with the surface vicinity, surface vicinity region, or shell.
  • the region that is within 10 nm perpendicular or approximately perpendicular to the surface of the crack and does not overlap with the surface portion 100a is defined as the inner wall surface portion 100c.
  • the area deeper than the surface layer 100a and the inner wall surface layer 100c of the positive electrode active material is called the interior 100b.
  • the interior 100b is synonymous with the interior region or core.
  • FIG. 1B is a schematic diagram of element concentration distribution in a cross-sectional analysis including the surface and surface layer 100a of the positive electrode active material 100, measured from the surface toward the interior 100b. Measurement from the surface toward the interior is also called measurement in the depth direction, and the X1-X2 and Y1-Y2 arrows in FIG. 1A are examples of the depth direction.
  • the surface layer 100a has an edge region and a basal region.
  • the edge region has a surface exposed in a direction intersecting with the (001) plane (also called a surface other than the (001) orientation), and the region within 10 nm perpendicular or approximately perpendicular from the surface is called the edge region.
  • intersecting means that the angle between the perpendicular to the first plane (the (001) plane) and the normal to the second plane (the surface of the positive electrode active material 100) is 10 degrees or more and 90 degrees or less, more preferably 30 degrees or more and 90 degrees or less, and even more preferably 50 degrees or more and 90 degrees or less.
  • the basal region has a surface parallel to the (001) plane (also called a (001)-oriented surface), and the region within 10 nm perpendicular or nearly perpendicular to the surface is called the basal region.
  • parallel here means that the angle between the perpendicular to the first surface (the (001) plane) and the normal to the second surface (the surface of the positive electrode active material 100) is 0 degrees or more and less than 10 degrees, preferably 0 degrees or more and 5 degrees or less, and more preferably 0 degrees or more and 2.5 degrees or less.
  • the surface of the positive electrode active material 100 refers to the surface of the composite oxide including the surface layer portion 100a and the interior portion 100b. Therefore, the positive electrode active material 100 does not include metal oxides such as aluminum oxide (Al 2 O 3 ) that do not have lithium sites that can contribute to charging and discharging, carbonates chemically adsorbed after the preparation of the positive electrode active material, hydroxyl groups, etc.
  • the attached metal oxide refers to, for example, metal oxides whose crystal orientation does not match that of the interior portion 100b.
  • the positive electrode active material 100 does not include electrolytes, organic solvents, binders, conductive materials, or compounds derived from these that are attached to the positive electrode active material 100.
  • the positive electrode active material 100 may have a grain boundary.
  • the grain boundary refers to, for example, a portion where particles of the positive electrode active material 100 are adhered to each other, a portion where the crystal orientation changes inside the positive electrode active material 100, that is, a portion where the repetition of bright and dark lines in an STEM image or the like becomes discontinuous, a portion containing many crystal defects, a portion where the crystal structure is disordered, etc.
  • the crystal defect refers to a defect that can be observed in a cross-sectional TEM (transmission electron microscope) or cross-sectional STEM image, that is, a structure in which other atoms have entered between the lattices, a cavity, etc.
  • a grain boundary can be said to be one type of planar defect.
  • the vicinity of a grain boundary refers to a region within 10 nm of the grain boundary.
  • the positive electrode active material 100 includes lithium, a transition metal M, oxygen, and an additive element whose oxide can become a semiconductor. It is preferable that the positive electrode active material 100 further includes an additive element that stabilizes the crystal structure.
  • the additive element may be simply called an additive element as a higher-level concept of the additive element whose oxide can become a semiconductor and the additive element that stabilizes the crystal structure.
  • the transition metal M is one or more selected from cobalt, nickel, manganese, and iron.
  • the positive electrode active material 100 can have, for example, a layered rock salt type crystal structure, a spinel type crystal structure, or an olivine type crystal structure. More specifically, it can have lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt aluminate (NCA) having a layered rock salt type crystal structure, LiMnO 2 having a spinel type crystal structure, or lithium iron phosphate (LFP) having an olivine type crystal structure.
  • LCO lithium cobalt oxide
  • NCM lithium nickel cobalt manganese oxide
  • NCA lithium nickel cobalt aluminate
  • LiMnO 2 having a spinel type crystal structure
  • LFP lithium iron phosphate
  • the positive electrode active material 100 is preferably a composite oxide (LiMO 2 ) of lithium and a transition metal M having a layered rock salt crystal structure to which an additive element is added.
  • the positive electrode active material of a lithium ion secondary battery must contain a transition metal capable of oxidation and reduction in order to maintain charge neutrality even when lithium ions are inserted and removed.
  • the positive electrode active material 100 preferably uses mainly cobalt as the transition metal M responsible for the oxidation and reduction reaction. If the positive electrode active material 100 contains 75 atomic % or more of cobalt, preferably 90 atomic % or more, and more preferably 95 atomic % or more of the transition metals, this is preferable because it has many advantages such as being relatively easy to synthesize, being easy to handle, and having excellent cycle characteristics.
  • the transition metal M of the positive electrode active material 100 is 75 atomic % or more, preferably 90 atomic % or more, and more preferably 95 atomic % or more
  • the stability when a large amount of lithium is desorbed by charging is superior to that of a composite oxide in which nickel such as lithium nickel oxide (LiNiO 2 ) accounts for the majority of the transition metal.
  • nickel such as lithium nickel oxide (LiNiO 2 ) accounts for the majority of the transition metal.
  • cobalt is less affected by distortion due to the Jahn-Teller effect than nickel.
  • the Jahn-Teller effect in transition metal compounds varies in strength depending on the number of electrons in the d orbital of the transition metal.
  • a layered rock salt type composite oxide in which low-spin nickel (III) in octahedral coordination such as lithium nickel oxide accounts for the majority of the transition metal M is greatly affected by the Jahn-Teller effect, and distortion is likely to occur in the layer consisting of octahedrons of nickel and oxygen. Therefore, there is an increased concern that the crystal structure will collapse during the charge and discharge cycle.
  • nickel ions are larger than cobalt ions and are close to the size of lithium ions. Therefore, in a layered rock-salt type composite oxide in which nickel occupies a majority of the transition metal M, such as lithium nickel oxide, there is a problem that cation mixing of nickel and lithium is likely to occur.
  • the additive element of the positive electrode active material 100 can be, for example, one or more selected from nickel, titanium, copper, ruthenium, vanadium, niobium, chromium, molybdenum, tungsten, rhenium, osmium, rhodium, iridium, lanthanum, and strontium.
  • the additive element of which the oxide can be a semiconductor means that the oxide of the metal has an electrical resistivity (literature value) of 1 ⁇ 10 ⁇ 8 S/cm or more and has a property of decreasing electrical resistance with increasing temperature.
  • an additive element such as nickel or titanium, whose oxide can become a semiconductor
  • the presence of an additive element in the surface layer 100a, whose oxide can become a semiconductor, is expected to reduce the impedance of the positive electrode active material 100.
  • Oxides of additive elements that stabilize the crystal structure, such as magnesium, exhibit insulating properties, but it is believed that the presence of an additive element, whose oxide can become a semiconductor, can alleviate this insulating property.
  • the concentration is too high or if the region having only the additive element whose oxide can be a semiconductor is too wide, there is a risk that the crystal structure of the positive electrode active material 100 may be distorted.
  • titanium is difficult to obtain as a stable phase layered rock salt type LiTiO 2 , so there is concern about titanium as an additive element used in a positive electrode active material having a layered rock salt type crystal structure.
  • nickel is more preferable as an additive element used in a positive electrode active material having a layered rock salt type crystal structure because nickel is relatively stable as a layered rock salt type LiNiO 2 , and therefore is less likely to distort the layered rock salt type crystal structure compared to titanium.
  • Additional elements that stabilize the crystal structure are preferably one or more selected from magnesium, aluminum, fluorine, zirconium, iron, manganese, chromium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, and beryllium.
  • the positive electrode active material 100 can include lithium cobalt oxide with added magnesium and nickel, lithium cobalt oxide with added magnesium, nickel and fluorine, lithium cobalt oxide with added magnesium, nickel, aluminum and titanium, lithium cobalt oxide with added magnesium, nickel, aluminum, titanium and fluorine, etc.
  • the additive elements that can turn the oxide into a semiconductor and the additive elements that stabilize the crystal structure are preferably dissolved in the positive electrode active material 100. Therefore, for example, when performing line analysis by STEM-EDX, the depth at which the amount of these additive elements detected increases is preferably located deeper than the depth at which the amount of transition metal M detected increases, i.e., on the inner side of the positive electrode active material 100.
  • the depth at which an element is detected in increasing amounts in STEM-EDX line analysis refers to the depth at which measurements that are not noise in terms of intensity, spatial resolution, etc., are continuously obtained.
  • additive element is synonymous with “mixture” or “part of raw material.”
  • Additive elements that can turn an oxide into a semiconductor do not necessarily have to include nickel, titanium, copper, ruthenium, vanadium, niobium, chromium, molybdenum, tungsten, rhenium, osmium, rhodium, iridium, lanthanum, or strontium. Additionally, additive elements that stabilize the crystal structure do not necessarily have to include fluorine, zirconium, iron, manganese, chromium, arsenic, zinc, silicon, sulfur, phosphorus, boron, bromine, or beryllium.
  • the positive electrode active material 100 is substantially free of manganese, the above-mentioned advantages of being relatively easy to synthesize and handle, and having excellent cycle characteristics, are even greater.
  • the weight of manganese contained in the positive electrode active material 100 is preferably, for example, 600 ppm or less, more preferably 100 ppm or less.
  • the positive electrode active material 100 has the above-mentioned additive element in the surface layer 100a. Furthermore, it is more preferable that the positive electrode active material 100 has a plurality of additive elements. Furthermore, it is preferable that the surface layer 100a has a higher concentration of one or more selected from the additive elements than the inner layer 100b. Alternatively, it is preferable that the surface layer 100a has a greater detected amount of one or more selected from the additive elements than the inner layer 100b. Furthermore, it is preferable that the one or more selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient. The detected amount refers to, for example, the count in EDX-ray analysis.
  • the distribution of the added elements in the positive electrode active material 100 differs depending on the added element, rather than all of the added elements being distributed in the same way.
  • the depth of the peak differs depending on the added element.
  • the peak refers to the maximum value of the detection amount in the surface layer 100a or within 50 nm from the surface.
  • the depth refers to the depth from the surface or a reference point in the EDX-ray analysis described below.
  • At least magnesium, nickel, or titanium among the additive elements have a higher concentration in the surface layer 100a than in the interior 100b.
  • the detection amount of the surface layer 100a is larger than the detection amount of the interior 100b.
  • the detection amount peak is in a region closer to the surface in the surface layer 100a. For example, it is preferable to have a detection amount peak on the surface or within 3 nm from the reference point. It is also preferable that the distributions of magnesium and nickel overlap.
  • the detection amount peaks of magnesium and nickel may be at the same depth, the magnesium peak may be closer to the surface, or the nickel peak may be closer to the surface.
  • the difference in depth between the detection amount peak of nickel and the detection amount peak of magnesium is preferably within 3 nm, and more preferably within 1 nm. It is also preferable that the half-width of the detection amount is narrow.
  • the distributions of magnesium and titanium overlap.
  • the peaks of the detection amounts of magnesium and titanium may be at the same depth, or the magnesium peak may be closer to the surface, or the titanium peak may be closer to the surface.
  • the difference in depth between the peak of the detection amount of titanium and the peak of the detection amount of magnesium is preferably within 3 nm, and more preferably within 1 nm. It is also preferable that the half-width of the detection amounts is narrow.
  • the difference in depth between the peak of the detected amount of titanium, the peak of the detected amount of nickel and the peak of the detected amount of magnesium is preferably within 3 nm, and more preferably within 1 nm. It is also preferable that the half-width of the detected amount is narrow.
  • the above-mentioned regions where the distributions of magnesium and nickel overlap, the regions where the distributions of magnesium and titanium overlap, or the regions where the distributions of magnesium, nickel, and titanium overlap are preferably located in edge regions of the surface layer 100a where lithium ions are inserted and removed.
  • the distribution of the added element shown in the schematic diagram of FIG. 1B is preferably observed in a depth direction analysis of the edge region such as the X1 to X2 arrows in FIG. 1A.
  • the above-mentioned overlap of the distribution of the added element is not necessarily required.
  • the amount of nickel detected in the interior 100b may be very small compared to the surface layer 100a, may not be detected, or may be less than 1 atomic %.
  • the amount of fluorine detected in the surface layer 100a is greater than the amount detected inside. It is also preferable that the surface layer 100a has a peak of the detection amount closer to the surface. For example, it is preferable that the detection amount peak is on the surface or within 3 nm from the reference point. Similarly, it is preferable that the amount of titanium, silicon, phosphorus, boron and/or calcium detected in the surface layer 100a is greater than the amount detected inside. It is also preferable that the detection amount peak is on the surface or within 3 nm from the reference point in STEM-EDX-ray analysis.
  • the magnesium concentration peak is located slightly inward from the fluorine concentration peak.
  • the fluorine concentration peak is located slightly outward from the magnesium concentration peak. This can further improve resistance to hydrofluoric acid when hydrofluoric acid is contained as an impurity in the electrolyte.
  • the magnesium concentration peak is 0.5 nm or more inward from the fluorine concentration peak, and even more preferable that it is 1.5 nm or more inward.
  • At least aluminum among the added elements, has a detection amount peak further in than magnesium and titanium.
  • the distributions of magnesium and aluminum may overlap, but there may be little overlapping area.
  • the detection amount peak of aluminum may be present in the surface layer 100a, or it may be deeper than the surface layer 100a.
  • the peak is present on the surface, or in a region of 5 nm to 30 nm from the reference point toward the inside.
  • the layered rock-salt crystal structure of the positive electrode active material 100 can be further stabilized. For example, it is expected that the change from the layered rock-salt crystal structure to the spinel crystal structure in the surface layer 100a of the positive electrode active material 100 can be suppressed.
  • the distance between the cation and oxygen is longer than that of the layered rock salt type LiAlO 2 , so aluminum is less likely to exist stably.
  • the valence change caused by Li + being replaced by Mg 2+ around cobalt can be compensated for by changing from Co 3+ to Co 2+ , thereby achieving cation balance.
  • Al can only take a trivalent state, it is thought that it is less likely to exist stably near magnesium in the rock salt type or layered rock salt type structure.
  • the positive electrode active material 100 contains manganese
  • the added element does not necessarily have to have the same concentration gradient or distribution in the entire surface layer 100a and the inner wall surface layer 100c of the positive electrode active material 100.
  • additive elements detected in the surface layer 100a may not be detected in the inner wall surface layer 100c.
  • additive elements e.g., titanium, nickel, etc.
  • the amount is 1 atomic % or less.
  • additive elements whose oxides can become semiconductors are not detected, or that the amount is 1 atomic % or less, in a deep portion of the inner wall surface layer 100c, for example, in a region 300 nm or more from the surface.
  • “Not detected” here means, for example, that the amount is below the lower detection limit in STEM-EDX analysis.
  • the cracked portion 106 is a portion where the crack may become deeper or spread as deterioration progresses. If the crack becomes deeper or spreads, the positive electrode active material 100 may break, leading to a serious capacity decrease such as a loss of the conductive path.
  • the area of the inner wall surface layer 100c facing the cracked portion 106 is much smaller than that of the surface layer 100a. Therefore, the inner wall surface layer 100c is an area where suppression of deterioration is prioritized over its function as a diffusion path for lithium ions. Therefore, it is preferable that the added element, whose oxide can become a semiconductor and which is expected to promote the insertion and removal of lithium ions, is not present in the inner wall surface layer 100c or is present in small amounts.
  • the effect on crack progression is small, so even if an additive element that can turn the oxide into a semiconductor is detected, it is not a big problem.
  • the positive electrode active material 100 has few or shallow cracks 106, and it is most preferable that no cracks 106 exist.
  • the additive element may be distributed in an island shape in the surface layer portion 100a, or the distribution tendency of the additive element may differ depending on the crystal plane.
  • the (001) oriented surface of the positive electrode active material 100 may have a different distribution of additive elements from the other surfaces.
  • the (001) oriented surface and its surface layer portion 100a may have a lower detection amount of one or more selected from additive elements compared to surfaces other than the (001) orientation.
  • the detection amount of one or more of magnesium, nickel, and titanium may be low.
  • the (001) oriented surface and its surface layer portion 100a may have one or more selected from additive elements that are not detected, or the detection amount in STEM-EDX analysis may be 1 atomic % or less. Specifically, the detection amount of nickel may be not detected, or 1 atomic % or less. In particular, in the case of an analysis method for detecting characteristic X-rays such as EDX, since the energy of K ⁇ of cobalt and K ⁇ of nickel are close, it is difficult to detect a trace amount of nickel in a material in which cobalt is the main element.
  • the (001) oriented surface and its surface layer 100a may have a peak of one or more detection amounts selected from the additive elements that is shallower from the surface than a surface other than the (001) oriented surface.
  • the peaks of the detection amounts of magnesium and aluminum may be shallower than other surfaces.
  • the MO2 layer is relatively stable, it is more stable for the surface of the positive electrode active material 100 to have a (001) orientation. The main diffusion path of lithium ions during charging and discharging is not exposed on the (001) plane.
  • the diffusion paths of lithium ions are exposed on surfaces other than those with the (001) orientation. Therefore, the surfaces and surface layer 100a other than those with the (001) orientation are important regions for maintaining the diffusion paths of lithium ions, and at the same time, they are prone to becoming unstable because they are the regions from which lithium ions are first desorbed. Therefore, reinforcing the surfaces and surface layer 100a other than those with the (001) orientation is extremely important for maintaining the crystal structure of the entire positive electrode active material 100.
  • the distribution of the added elements in the surface other than the (001) orientation and in the surface layer 100a thereof is, for example, as shown in FIG. 1B.
  • nickel in particular is preferably detected in the surface other than the (001) orientation and in the surface layer 100a thereof.
  • the concentration of the added elements may be low or absent, as described above.
  • the magnesium distribution in the (001) oriented surface and its surface layer 100a preferably has a half-width of 10 nm to 200 nm, more preferably 50 nm to 150 nm, and even more preferably 80 nm to 120 nm.
  • the magnesium distribution in the non-(001) oriented surface and its surface layer 100a preferably has a half-width of more than 200 nm to 500 nm, more preferably 200 nm to 300 nm, and even more preferably 230 nm to 270 nm.
  • the nickel distribution in the surface that is not (001) oriented and in the surface layer 100a thereof preferably has a half-width of 30 nm or more and 150 nm or less, more preferably 50 nm or more and 130 nm or less, and even more preferably 70 nm or more and 110 nm or less.
  • the additive elements spread mainly through the diffusion path of lithium ions, so that the distribution of the additive elements in the surface other than the (001) orientation and in the surface layer 100a thereof can be easily controlled to a preferred range.
  • the distribution of the added element may not be a normal distribution in the depth direction.
  • the slope may differ between the surface side and the inner side.
  • the slope may be steeper on the surface side and gentler on the inner side.
  • the peak width MgW core on the inner side may be larger than the peak width MgW shell on the surface side.
  • Magnesium is divalent, and magnesium ions are more stable at the lithium site than at the cobalt site in the layered rock salt crystal structure, so they tend to enter the lithium site.
  • the presence of magnesium at an appropriate concentration at the lithium site of the surface layer 100a makes it easier to maintain the layered rock salt crystal structure. This is presumably because the magnesium present at the lithium site functions as a pillar supporting the MO2 layers.
  • the presence of magnesium can suppress the detachment of oxygen around magnesium when x in Li x CoO 2 is, for example, 0.24 or less.
  • the presence of magnesium can be expected to increase the density of the positive electrode active material 100.
  • the magnesium concentration of the surface layer 100a is high, it can be expected that the corrosion resistance to hydrofluoric acid generated by the decomposition of the electrolyte will be improved.
  • magnesium is present at an appropriate concentration, it does not adversely affect the insertion and desorption of lithium during charging and discharging, and the above benefits can be enjoyed. However, if there is an excess of magnesium, it may have a negative effect on the insertion and desorption of lithium. Furthermore, the effect of stabilizing the crystal structure may be reduced. This is thought to be because magnesium enters the cobalt site in addition to the lithium site. In addition, unnecessary magnesium compounds (oxides, fluorides, etc.) that do not substitute for either the lithium site or the cobalt site may segregate on the surface of the positive electrode active material, and may become resistance components in the secondary battery. Furthermore, as the magnesium concentration of the positive electrode active material increases, the discharge capacity of the positive electrode active material may decrease. This is thought to be because too much magnesium enters the lithium site, reducing the amount of lithium that contributes to charging and discharging.
  • the amount of magnesium contained in the entire positive electrode active material 100 is appropriate.
  • the number of magnesium atoms is preferably 0.002 to 0.06 times the number of cobalt atoms, more preferably 0.005 to 0.03 times, and even more preferably about 0.01 times.
  • the amount of magnesium contained in the entire positive electrode active material 100 here may be a value obtained by performing an elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS, ICP-MS, etc., or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100.
  • nickel can exist in either the cobalt site or the lithium site.
  • it has a lower redox potential than cobalt, so it can be said that it is easier to release lithium and electrons during charging, for example. Therefore, it is expected that the charge and discharge speed will be faster. Therefore, even with the same charging voltage, a larger charge and discharge capacity can be obtained when the transition metal M is nickel than when it is cobalt.
  • the shift of the layered structure consisting of octahedra of cobalt and oxygen can be suppressed.
  • the change in volume accompanying charging and discharging is suppressed.
  • the elastic modulus increases, that is, the material becomes harder. This is presumably because nickel present at the lithium site also functions as a pillar supporting the MO2 layers. Therefore, it is expected that the crystal structure will be more stable, especially in a charged state at high temperatures, for example, 45°C or higher, which is preferable.
  • NiO nickel oxide
  • the order of ionization tendency is lowest for magnesium, aluminum, cobalt, and nickel (Mg>Al>Co>Ni). Therefore, nickel is thought to be less likely to dissolve into the electrolyte during charging than the other elements listed above. Therefore, it is thought to be highly effective in stabilizing the crystal structure of the surface layer when in a charged state.
  • Ni2 + is the most stable, and nickel has a higher trivalent ionization energy than cobalt. Therefore, it is known that nickel and oxygen alone do not form a spinel crystal structure. Therefore, nickel is thought to have the effect of suppressing the phase change from the layered rock salt type to the spinel type crystal structure.
  • an excess of nickel is undesirable because it increases the influence of distortion due to the Jahn-Teller effect. Also, an excess of nickel may adversely affect the insertion and extraction of lithium.
  • the positive electrode active material 100 as a whole contains an appropriate amount of nickel.
  • the number of nickel atoms contained in the positive electrode active material 100 is preferably more than 0% and not more than 7.5% of the number of cobalt atoms, more preferably 0.05% to 4%, more preferably 0.1% to 2%, and more preferably 0.2% to 1%.
  • Or more than 0% and not more than 4% is preferable.
  • Or more than 0% and not more than 2% is preferable.
  • Or more than 0.05% to 7.5% is preferable.
  • more than 0.05% to 2% is preferable.
  • Or more than 0.1% to 7.5% is preferable.
  • Or more than 0.1% to 4% is preferable.
  • the amount of nickel shown here may be, for example, a value obtained by performing an elemental analysis of the entire positive electrode active material using GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.
  • Aluminum may also be present at the cobalt site in the layered rock salt crystal structure. Since aluminum is a typical trivalent element and its valence does not change, lithium around the aluminum is unlikely to move during charging and discharging. Therefore, aluminum and its surrounding lithium function as columns and can suppress changes in the crystal structure. Therefore, as described below, even if the positive electrode active material 100 is subjected to a force that causes it to expand and contract in the c-axis direction due to the insertion and desorption of lithium ions, that is, even if a force that causes it to expand and contract in the c-axis direction is applied by changing the charging depth or charging rate, deterioration of the positive electrode active material 100 can be suppressed.
  • Aluminum also has the effect of suppressing the dissolution of surrounding cobalt and improving continuous charging resistance. Furthermore, since the Al-O bond is stronger than the Co-O bond, it can suppress the desorption of oxygen from around the aluminum. These effects improve thermal stability. Therefore, by having aluminum as an added element, it is possible to improve safety when using the positive electrode active material 100 in a secondary battery. Furthermore, it is possible to obtain a positive electrode active material 100 whose crystal structure is less likely to collapse even when repeatedly charged and discharged.
  • the amount of aluminum contained in the entire positive electrode active material 100 is appropriate.
  • the number of aluminum atoms contained in the entire positive electrode active material 100 is preferably 0.05% to 4% of the number of cobalt atoms, preferably 0.1% to 2%, and more preferably 0.3% to 1.5%.
  • 0.05% to 2% is preferable.
  • 0.1% to 4% is preferable.
  • the amount contained in the entire positive electrode active material 100 here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material 100 using GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material 100.
  • Fluorine is a monovalent anion, and when part of the oxygen in the surface layer 100a is replaced by fluorine, the lithium desorption energy is reduced. This is because the redox potential of the cobalt ion accompanying lithium desorption differs depending on the presence or absence of fluorine. In other words, when there is no fluorine, the cobalt ion changes from trivalent to tetravalent with lithium desorption. On the other hand, when there is fluorine, the cobalt ion changes from divalent to trivalent with lithium desorption. The redox potential of the cobalt ion is different between the two.
  • the positive electrode active material 100 when part of the oxygen is replaced by fluorine in the surface layer 100a of the positive electrode active material 100, it can be said that the desorption and insertion of lithium ions near the fluorine is likely to occur smoothly. Therefore, when the positive electrode active material 100 is used in a secondary battery, the charge/discharge characteristics, large current characteristics, etc. can be improved.
  • the presence of fluorine in the surface layer 100a having a surface that is in contact with the electrolyte, or the attachment of fluoride to the surface can suppress excessive reaction between the positive electrode active material 100 and the electrolyte.
  • the corrosion resistance to hydrofluoric acid can be effectively improved.
  • the melting point of the fluoride including lithium fluoride
  • it can function as a flux (also called a fluxing agent) that lowers the melting point of the other additive element source.
  • the heating temperature is preferably 742°C or higher, more preferably 830°C or higher. It may also be 800°C or higher, which is between these.
  • phosphorus is present in the surface layer portion 100a because it may be possible to suppress short circuits when x in Li x CoO 2 is kept small.
  • phosphorus is present in the surface layer portion 100a as a compound containing phosphorus and oxygen.
  • the hydrogen fluoride generated by the decomposition of the electrolyte or electrolyte reacts with the phosphorus, which may reduce the hydrogen fluoride concentration in the electrolyte, which is preferable.
  • hydrogen fluoride When the electrolyte contains LiPF 6 , hydrogen fluoride may be generated by hydrolysis. In addition, hydrogen fluoride may be generated by a reaction between polyvinylidene fluoride (PVDF), which is used as a component of the positive electrode, and an alkali.
  • PVDF polyvinylidene fluoride
  • the positive electrode active material 100 When the positive electrode active material 100 has phosphorus together with magnesium, the stability in the state where x in Li x CoO 2 is small becomes extremely high, which is preferable.
  • the number of phosphorus atoms is preferably 1% or more and 20% or less of the number of cobalt atoms, more preferably 2% or more and 10% or less, and even more preferably 3% or more and 8% or less. Or 1% or more and 10% or less is preferable. Or 2% or more and 20% or less is preferable. Or 2% or more and 8% or less is preferable. Or 3% or more and 20% or less is preferable. Or 3% or more and 10% or less is preferable.
  • the number of magnesium atoms is preferably 0.1% or more and 10% or less of the number of cobalt atoms, more preferably 0.5% or more and 5% or less, and more preferably 0.7% or more and 4% or less. Or 0.1% or more and 5% or less is preferable. Or 0.1% or more and 4% or less is preferable. Or 0.5% or more and 10% or less is preferable. Alternatively, 0.5% or more and 4% or less is preferable. Alternatively, 0.7% or more and 10% or less is preferable. Alternatively, 0.7% or more and 5% or less is preferable.
  • the phosphorus and magnesium concentrations shown here may be values obtained by performing elemental analysis of the entire positive electrode active material 100 using, for example, GD-MS, ICP-MS, or the like, or may be based on values of the composition of raw materials in the process of producing the positive electrode active material 100.
  • the progression of the cracks can be suppressed by the presence of phosphorus, or more specifically, a compound containing phosphorus and oxygen, inside the positive electrode active material with the cracks on its surface, for example, in the embedded portion.
  • magnesium is added in a process before nickel.
  • magnesium and nickel are added in the same process. Magnesium has a large ionic radius and tends to remain in the surface layer of lithium cobalt oxide regardless of the process in which it is added, whereas nickel can diffuse widely inside the lithium cobalt oxide if magnesium is not present. Therefore, if nickel is added before magnesium, there is a concern that nickel will diffuse into the lithium cobalt oxide and not remain in the desired amount in the surface layer.
  • the positive electrode active material 100 has additive elements with different distributions, it is preferable because it can stabilize the crystal structure in a wider region.
  • the positive electrode active material 100 has both magnesium and nickel distributed in a region closer to the surface of the surface layer 100a and aluminum distributed in a deeper region, it can stabilize the crystal structure in a wider region than if it had only one of them.
  • aluminum is not essential on the surface because the stabilization of the surface can be sufficiently achieved by magnesium, nickel, etc. Rather, it is preferable for aluminum to be distributed widely in a deeper region.
  • aluminum is continuously detected in a region from 1 nm to 25 nm in the depth direction from the surface. It is preferable to distribute aluminum widely in a region from 0 nm to 100 nm from the surface, preferably from 0.5 nm to 50 nm from the surface, because it can stabilize the crystal structure in a wider region.
  • the effects of the respective additive elements are synergistic and can contribute to further stabilization of the surface layer 100a.
  • the inclusion of magnesium, nickel, and aluminum is highly effective in providing a stable composition and crystal structure, and is therefore preferable.
  • the surface layer 100a is occupied only by a compound of the added element and oxygen, it is not preferable because it makes it difficult to insert and remove lithium.
  • the surface layer 100a it is not preferable for the surface layer 100a to be occupied only by MgO or a structure in which MgO and MO(II) are in solid solution.
  • the surface layer 100a must contain at least a transition metal M such as cobalt, and must also contain lithium in the discharged state, and must have a path for the insertion and removal of lithium.
  • the surface layer 100a has a higher cobalt concentration than magnesium.
  • the ratio Mg/Co of the number of magnesium atoms Mg to the number of cobalt atoms Co is preferably 0.62 or less. It is also preferable that the surface layer 100a has a higher cobalt concentration than nickel. It is also preferable that the surface layer 100a has a higher cobalt concentration than aluminum. It is also preferable that the surface layer 100a has a higher cobalt concentration than fluorine.
  • the surface layer 100a has a higher concentration of magnesium than nickel.
  • the number of nickel atoms is preferably 1/6 or less of the number of magnesium atoms.
  • some of the added elements particularly magnesium, nickel and aluminum
  • they are present randomly and dilutely in the interior 100b.
  • magnesium and aluminum are present at appropriate concentrations in the lithium sites of the interior 100b, it has the effect of making it easier to maintain the layered rock-salt crystal structure, as described above.
  • nickel is present at an appropriate concentration in the interior 100b, it is possible to suppress the shifting of the layered structure consisting of cobalt and oxygen octahedra, as described above.
  • magnesium and nickel are present together, a synergistic effect of suppressing the elution of magnesium can be expected, as described above.
  • the crystal structure changes continuously from the interior 100b toward the surface due to the concentration gradient of the added element as described above.
  • the crystal orientation of the surface layer 100a and the interior 100b are roughly consistent.
  • the crystal structure changes continuously from the interior 100b of the layered rock salt type toward the surface and surface layer 100a, which has characteristics of the rock salt type or both the rock salt type and the layered rock salt type. It is also preferable that the crystal orientation of the surface layer 100a, which has characteristics of the rock salt type or both the rock salt type and the layered rock salt type, and the interior 100b of the layered rock salt type are roughly consistent.
  • a layered rock-salt type crystal structure belonging to the space group R-3m which is possessed by a composite oxide containing lithium and a transition metal such as cobalt
  • the layered rock-salt type crystal structure may have a structure in which the lattice of the rock-salt type crystal is distorted.
  • a rock-salt crystal structure is a structure that has a cubic crystal structure, such as the space group Fm-3m, in which cations and anions are arranged alternately. Note that there may be a deficiency of cations or anions.
  • rock salt type and rock salt type crystal structure characteristics can be determined by electron diffraction, TEM images, cross-sectional STEM images, etc.
  • the rock salt type has no distinction between the cation sites, but the layered rock salt type has two types of cation sites in the crystal structure, one of which is mostly occupied by lithium and the other by a transition metal.
  • the layered structure in which two-dimensional planes of cations and two-dimensional planes of anions are alternately arranged is the same for both the rock salt type and the layered rock salt type.
  • the central spot (transmitted spot) of the bright spots of the electron diffraction pattern corresponding to the crystal planes forming this two-dimensional plane is set as the origin 000
  • the bright spot closest to the central spot is, for example, the (111) plane in the rock salt type in an ideal state, and, for example, the (003) plane in the layered rock salt type.
  • the distance between the bright spots on the (003) plane of LiCoO 2 is observed to be about half the distance between the bright spots on the (111) plane of MgO. Therefore, when the analysis region has two phases, for example, rock salt type MgO and layered rock salt type LiCoO2 , the electron beam diffraction pattern has a plane orientation in which bright spots with strong brightness and bright spots with weak brightness are arranged alternately. Bright spots common to the rock salt type and layered rock salt type have strong brightness, and bright spots occurring only in the layered rock salt type have weak brightness.
  • Layered rock salt crystals and the anions in rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in the O3' type and monoclinic O1(15) crystals described below also have a cubic close-packed structure. Therefore, when a layered rock salt crystal comes into contact with a rock salt crystal, there are crystal faces on which the cubic close-packed structure formed by the anions is oriented in the same direction.
  • Anions on the ⁇ 111 ⁇ plane of a cubic crystal structure have a triangular lattice.
  • Layered rock salt type has space group R-3m and a rhombohedral structure, but to make the structure easier to understand, it is generally represented as a compound hexagonal lattice, and the (001) plane of the layered rock salt type has a hexagonal lattice.
  • the triangular lattice of the cubic ⁇ 111 ⁇ plane has the same atomic arrangement as the hexagonal lattice of the (001) plane of the layered rock salt type. When the two lattices are compatible, it can be said that the orientation of the cubic close-packed structure is aligned.
  • the space group of layered rock salt crystals and O3' type crystals is R-3m, which is different from the space group Fm-3m (the space group of general rock salt crystals) of rock salt crystals, so the Miller indices of the crystal planes that satisfy the above conditions are different between layered rock salt crystals and O3' type crystals and rock salt crystals.
  • the crystal orientations are roughly the same.
  • the three-dimensional structural similarity in which the crystal orientations are roughly the same, or the same crystallographic orientation is called topotaxis.
  • the fact that the crystal orientations in the two regions roughly coincide can be determined from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, electron beam diffraction patterns, etc. It can also be judged from the FFT patterns of TEM images and STEM images. Furthermore, XRD (X-ray diffraction), neutron diffraction, etc. can also be used to make the judgment.
  • Figure 3 shows an example of a TEM image in which the orientation of the layered rock salt crystals LRS and the rock salt crystals RS roughly coincides.
  • Images reflecting the crystal structure can be obtained in TEM images, STEM images, HAADF-STEM images, ABF-STEM images, etc.
  • a contrast originating from a crystal plane is obtained.
  • the contrast originating from the (003) plane is obtained as a repetition of bright bands (bright strips) and dark bands (dark strips). Therefore, when a repetition of bright lines and dark lines is observed in a TEM image and the angle between the bright lines (for example, L RS and L LRS shown in FIG.
  • lithium cobalt oxide with a layered rock-salt crystal structure is observed perpendicular to the c-axis
  • the arrangement of the cobalt atoms is observed perpendicular to the c-axis as a bright line or an arrangement of highly bright dots, and the arrangements of the lithium atoms and oxygen atoms are observed as dark lines or low-brightness areas.
  • fluorine (atomic number 9) and magnesium (atomic number 12) are added to the lithium cobalt oxide.
  • Figure 4A shows an example of an STEM image in which the orientations of the layered rock-salt crystal LRS and the rock-salt crystal RS roughly match.
  • Figure 4B shows the FFT pattern of the area of the rock-salt crystal RS
  • Figure 4C shows the FFT pattern of the area of the layered rock-salt crystal LRS.
  • the composition, JCPDS card number, and the d-value and angle calculated from these are shown on the left of Figures 4B and 4C.
  • the actual measured values are shown on the right.
  • the spot marked with an O is the zeroth order diffraction.
  • the spot marked A in Figure 4B is due to the 11-1 reflection of the cubic crystal.
  • the spot marked A in Figure 4C is due to the 0003 reflection of the layered rock salt type. From Figures 4B and 4C, it can be seen that the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type roughly coincide. In other words, it can be seen that the line passing through AO in Figure 4B is roughly parallel to the line passing through AO in Figure 4C. In this case, roughly coincident and roughly parallel mean that the angle is 5 degrees or less, or 2.5 degrees or less.
  • the ⁇ 0003> orientation of the layered rock salt type may roughly match the ⁇ 11-1> orientation of the rock salt type.
  • these reciprocal lattice points are spot-like, that is, not continuous with other reciprocal lattice points.
  • a reciprocal lattice point that is spot-like and not continuous with other reciprocal lattice points indicates high crystallinity.
  • the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type are roughly the same, depending on the incidence orientation of the electron beam, a spot that is not due to the 0003 reflection of the layered rock salt type may be observed in a reciprocal lattice space different from the orientation of the 0003 reflection of the layered rock salt type.
  • the spot marked B in Figure 4C is due to the 1014 reflection of the layered rock salt type.
  • ⁇ AOB 52° to 56°
  • ⁇ AOB 52° to 56°
  • d 0.19 nm to 0.21 nm.
  • this index is just an example, and does not necessarily have to be the same.
  • a reciprocal lattice point equivalent to 0003 and 1014 may be used.
  • spots not originating from the 11-1 reflection of a cubic crystal may be observed in a reciprocal lattice space other than the orientation where the 11-1 reflection of a cubic crystal is observed.
  • the spot marked B in Figure 4B originates from the 200 reflection of a cubic crystal. This is because a diffraction spot may be observed at an angle of 54° to 56° (i.e., ⁇ AOB is 54° to 56°) from the orientation of the reflection (A in Figure 4B) originating from the 11-1 of a cubic crystal.
  • ⁇ AOB is 54° to 56°
  • this index is only an example, and does not necessarily have to match this.
  • reciprocal lattice points equivalent to 11-1 and 200 of a cubic crystal may be used.
  • layered rock-salt type positive electrode active materials such as lithium cobalt oxide
  • the (003) plane and its equivalent as well as the (104) plane and its equivalent, as crystal planes. Therefore, when observing the (003) plane, for example, with a TEM or the like, first select a particle of the positive electrode active material in which a crystal plane expected to be the (003) plane is observed with a SEM or the like, and then slice the particle of the positive electrode active material with a FIB (Focused Ion Beam) or the like so that the (003) plane can be observed with an electron beam incident at [120] in the TEM or the like. When it is desired to determine the coincidence of the crystal orientations, it is preferable to slice the layered rock-salt type so that the (003) plane can be easily observed.
  • FIB Flucused Ion Beam
  • the layered rock-salt type composite oxide has a high discharge capacity, has a two-dimensional lithium ion diffusion path, is suitable for lithium ion insertion/extraction reactions, and is excellent as a positive electrode active material for secondary batteries. Therefore, it is particularly preferable that the inner part 100b, which occupies most of the volume of the positive electrode active material 100, has a layered rock-salt type crystal structure.
  • the layered rock-salt type crystal structure is shown in FIG. 5 with R-3m O3 attached.
  • the surface layer 100a of the positive electrode active material 100 preferably has a function of reinforcing the layered structure of the transition metal M and oxygen octahedrons in the interior 100b so that it is not broken even if lithium is removed from the positive electrode active material 100 by charging.
  • the surface layer 100a preferably functions as a barrier film for the positive electrode active material 100.
  • the surface layer 100a which is the outer periphery of the positive electrode active material 100, preferably reinforces the positive electrode active material 100.
  • Reinforcement here refers to suppressing structural changes in the surface layer 100a and interior 100b of the positive electrode active material 100, such as oxygen elimination and/or shifting of the layered structure of the transition metal M and oxygen octahedrons. And/or to suppressing oxidative decomposition of the electrolyte on the surface of the positive electrode active material 100.
  • the surface layer 100a has a different crystal structure from the inner portion 100b. It is also preferable that the surface layer 100a has a composition and crystal structure that are more stable at room temperature (25°C) than the inner portion 100b. For example, it is preferable that at least a part of the surface layer 100a of the positive electrode active material 100 of one embodiment of the present invention has a rock salt type crystal structure. Alternatively, it is preferable that the surface layer 100a has both a layered rock salt type crystal structure and a rock salt type crystal structure. Alternatively, it is preferable that the surface layer 100a has the characteristics of both a layered rock salt type crystal structure and a rock salt type crystal structure.
  • the surface layer 100a is the region where lithium ions are first desorbed during charging, and is the region where the lithium concentration is likely to be lower than that of the inside 100b.
  • the atoms on the surface of the particles of the positive electrode active material 100 that the surface layer 100a has can be said to be in a state where some bonds are broken. Therefore, the surface layer 100a is likely to become unstable, and can be said to be a region where the deterioration of the crystal structure is likely to begin.
  • the crystal structure of the layered structure consisting of the transition metal M and oxygen octahedrons in the surface layer 100a is displaced, the influence is linked to the inside 100b, and the crystal structure of the layered structure is also displaced in the inside 100b, which is thought to lead to the deterioration of the crystal structure of the entire positive electrode active material 100.
  • the surface layer 100a can be sufficiently stabilized, even when x in Li x MO 2 is small, for example, even if x is 0.24 or less, the layered structure consisting of the transition metal M and oxygen octahedrons in the inside 100b can be made less likely to be broken. Furthermore, it is possible to suppress the misalignment of the layer consisting of the transition metal M and oxygen octahedrons in the inner portion 100b.
  • the interior 100b of the positive electrode active material 100 is preferably free of defects, including dislocations, or has a low density.
  • the positive electrode active material 100 preferably has a large crystallite size measured by XRD. In other words, the interior 100b is preferably highly crystalline.
  • the surface of the positive electrode active material 100 is preferably smooth.
  • Dislocations in the interior 100b can be observed, for example, with a TEM. If the density of defects, including dislocations, is sufficiently low, they may not be observed in a specific 1 ⁇ m square of the observation sample. Note that dislocations are a type of crystal defect and are different from vacancy defects.
  • the crystallite size is larger, as described later, when x in Li x CoO 2 is small, the O3′ type crystal structure is more easily maintained, and the contraction of the c-axis length is more easily suppressed.
  • the positive electrode active material When calculating the crystallite size, it is preferable to obtain the XRD diffraction pattern for the positive electrode active material alone, but it may also be obtained for the positive electrode, which includes the current collector, binder, conductive material, etc. in addition to the positive electrode active material.
  • the positive electrode active material in the positive electrode state, the positive electrode active material may be oriented due to the effects of pressure, etc., applied during the manufacturing process. If the orientation is too strong, the crystallite size may not be calculated accurately, so it is more preferable to obtain the pattern by removing the positive electrode active material layer from the positive electrode, removing some of the binder, etc., in the positive electrode active material layer using a solvent, etc., and then filling the sample holder.
  • Another method is to apply grease to a silicon non-reflective plate and attach the powder sample to it.
  • the crystallite size can be calculated using, for example, Bruker D8 ADVANCE, with CuK ⁇ as the X-ray source, 2 ⁇ between 15° and 90°, increment 0.005, and LYNXEYE XE-T as the detector, and the diffraction pattern obtained using ICSD coll. code. 172909 as the literature value of lithium cobalt oxide. Analysis can be performed using DIFFRAC. TOPAS ver. 6 as the crystal structure analysis software, and can be set, for example, as follows. Emission Profile: CuKa5.
  • LVol-IB which is the crystallite size corrected by the integral width standard calculated by the above method, as the crystallite size. Note that if the calculated Preferred Orientation is less than 0.8, the orientation of the sample may be too strong and it may not be suitable for determining the crystallite size.
  • the positive electrode active material 100 of one embodiment of the present invention preferably has a crystal structure in a state where x in Li x MO 2 is small, which is different from that of a conventional positive electrode active material, due to the distribution of the additive elements and/or the crystal structure as described above in a discharged state.
  • a small x here means that 0.1 ⁇ x ⁇ 0.24.
  • the change in the crystal structure of a conventional positive electrode active material is shown in Fig. 6.
  • the conventional positive electrode active material shown in Fig. 6 is lithium cobalt oxide ( LiCoO2 ) that does not have any added elements.
  • the change in the crystal structure of lithium cobalt oxide that does not have any added elements is described in Non-Patent Documents 1 to 3, etc.
  • lithium occupies an octahedral site, and there are three CoO 2 layers in the unit cell. Therefore, this crystal structure is sometimes called an O3 type crystal structure.
  • the CoO 2 layer refers to a structure in which an octahedral structure in which oxygen is six-coordinated to cobalt is continuous on a plane in an edge-sharing state. This is sometimes called a layer consisting of an octahedron of cobalt and oxygen.
  • conventional lithium cobalt oxide has a crystal structure that is highly symmetrical to lithium when x is about 0.5, and belongs to the monoclinic space group P2/m.
  • This structure has one CoO2 layer in the unit cell. Therefore, it is sometimes called O1 type or monoclinic O1 type.
  • the positive electrode active material has a crystal structure of the trigonal space group P-3m1, and one CoO2 layer is present in the unit cell. Therefore, this crystal structure may be called O1 type or trigonal O1 type.
  • the trigonal crystal may be converted to a composite hexagonal lattice and called hexagonal O1 type.
  • conventional lithium cobalt oxide has a crystal structure of space group R-3m.
  • This structure can be said to be a structure in which a CoO 2 structure such as trigonal O1 type and a LiCoO 2 structure such as R-3m O3 are alternately stacked. Therefore, this crystal structure may be called an H1-3 type crystal structure.
  • the number of cobalt atoms per unit cell in the H1-3 type crystal structure is twice that of other structures.
  • the c-axis of the H1-3 type crystal structure is shown in a diagram in which the c-axis is 1/2 of the unit cell.
  • the coordinates of cobalt and oxygen in the unit cell can be expressed as Co (0,0,0.42150 ⁇ 0.00016), O1 (0,0,0.27671 ⁇ 0.00045), and O2 (0,0,0.11535 ⁇ 0.00045).
  • O1 and O2 are oxygen atoms.
  • Which unit cell should be used to express the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of the XRD pattern. In this case, it is sufficient to adopt the unit cell that results in the smallest GOF (goodness of fit) value.
  • conventional lithium cobalt oxide repeatedly changes its crystal structure (i.e., undergoes a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m O 3 structure in the discharged state.
  • the difference in volume between the H1-3 crystal structure and the R-3m O3 crystal structure in a discharged state exceeds 3.5%, typically 3.9% or more.
  • the H1-3 type crystal structure has a structure in which two CoO layers are continuous, such as the trigonal O1 type, and is therefore likely to be unstable.
  • the crystal structure of conventional lithium cobalt oxide breaks down when it is repeatedly charged and discharged so that x is 0.24 or less.
  • the breakdown of the crystal structure leads to a deterioration in cycle characteristics. This is because the breakdown of the crystal structure reduces the number of sites where lithium can exist stably and makes it difficult to insert and remove lithium.
  • the change in the crystal structure between the discharged state where x in Li x MO 2 is 1 and the state where x is 0.24 or less is smaller than that of a conventional positive electrode active material. More specifically, the deviation of the MO 2 layer between the state where x is 1 and the state where x is 0.24 or less can be reduced. Also, the change in volume compared per cobalt atom can be reduced. Therefore, the positive electrode active material 100 of one embodiment of the present invention is less likely to collapse in crystal structure even when charging and discharging are repeated so that x is 0.24 or less, and excellent cycle characteristics can be realized.
  • the positive electrode active material 100 of one embodiment of the present invention can have a more stable crystal structure than a conventional positive electrode active material in the state where x in Li x MO 2 is 0.24 or less. Therefore, the positive electrode active material 100 of one embodiment of the present invention is less likely to cause a short circuit when the state where x in Li x MO 2 is 0.24 or less is maintained. In such a case, the safety of the secondary battery is further improved, which is preferable.
  • FIG. 5 shows the crystal structure of the interior 100b of the positive electrode active material 100 when x in Li x MO2 is 1, approximately 0.2, and approximately 0.15.
  • the interior 100b occupies most of the volume of the positive electrode active material 100 and is the part that contributes greatly to charge and discharge, so it can be said that the displacement of the MO2 layer and the change in volume are the most problematic parts.
  • the positive electrode active material 100 has the same crystal structure as conventional lithium cobalt oxide, R-3m O3.
  • the positive electrode active material 100 has a different crystal structure from that of conventional lithium cobalt oxide when x is 0.24 or less, for example, about 0.2 and about 0.15, in which case the lithium cobalt oxide has an H1-3 type crystal structure.
  • the symmetry of the CoO2 layer is the same as that of O3. Therefore, this crystal structure is called an O3'-type crystal structure.
  • This crystal structure is shown in FIG. 5 with R-3m O3'.
  • the coordinates of cobalt and oxygen in the unit cell can be expressed in the range of Co(0,0,0.5), O(0,0,x), 0.20 ⁇ x ⁇ 0.25.
  • the monoclinic O1(15) crystal structure has the coordinates of cobalt and oxygen in the unit cell as follows: Co1(0.5,0,0.5), Co2(0,0.5,0.5), O1 (X O1 , 0, Z O1 ), 0.23 ⁇ X O1 ⁇ 0.24, 0.61 ⁇ Z O1 ⁇ 0.65, O2( XO2,0.5 , ZO2 ),
  • this crystal structure can show the lattice constant even in the space group R-3m if a certain degree of error is allowed.
  • the coordinates of cobalt and oxygen in the unit cell are as follows: Co(0,0,0.5), O(0,0,Z O ), The range of Z O can be expressed as 0.21 ⁇ Z O ⁇ 0.23.
  • the difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the O3' type crystal structure is 2.5% or less, more specifically 2.2% or less, typically 1.8%.
  • the difference in volume per the same number of cobalt atoms between R-3m O3 in a discharged state and the monoclinic O1(15) crystal structure is 3.3% or less, more specifically 3.0% or less, typically 2.5%.
  • Table 1 shows the difference in volume per cobalt atom between R-3m O3 in a discharged state, O3', monoclinic O1(15), H1-3 type, and trigonal O1.
  • the lattice constants of each crystal structure used in the calculations in Table 1 can be found in literature values for R-3m O3 and trigonal O1 in a discharged state (ICSD coll.code.172909 and 88721).
  • H1-3 refer to Non-Patent Document 3.
  • O3' and monoclinic O1(15) can be calculated from experimental values obtained by XRD.
  • the positive electrode active material 100 of one embodiment of the present invention when x in Li x MO 2 is small, that is, when a large amount of lithium is released, the change in the crystal structure is suppressed more than in the conventional positive electrode active material. In addition, the change in volume is also suppressed when compared per the same number of cobalt atoms. Therefore, the positive electrode active material 100 does not easily lose its crystal structure even when charging and discharging are repeated such that x is 0.24 or less. Therefore, the positive electrode active material 100 suppresses a decrease in charge and discharge capacity in the charge and discharge cycle. In addition, since more lithium can be stably used than in the conventional positive electrode active material, the positive electrode active material 100 has a large discharge capacity per weight and per volume. Therefore, by using the positive electrode active material 100, a secondary battery with a high discharge capacity per weight and per volume can be manufactured.
  • the positive electrode active material 100 may have an O3' type crystal structure when x in Li x MO 2 is 0.15 or more and 0.24 or less, and it is estimated that the positive electrode active material 100 may have an O3' type crystal structure even when x is more than 0.24 and 0.27 or less. It has also been confirmed that the positive electrode active material 100 may have a monoclinic O1 (15) type crystal structure when x in Li x MO 2 is more than 0.1 and 0.2 or less, typically when x is 0.15 or more and 0.17 or less.
  • the crystal structure is not necessarily limited to the above range of x because it is affected not only by x in Li x MO 2 but also by the number of charge/discharge cycles, charge/discharge current, temperature, electrolyte, etc.
  • the positive electrode active material 100 may have only O3' type, may have only monoclinic O1 (15) type, or may have both crystal structures. Furthermore, all of the particles in the interior 100b of the positive electrode active material 100 do not have to have O3' type and/or monoclinic O1 (15) type crystal structures. They may contain other crystal structures, or may be partially amorphous.
  • the state in which x in Li x MO 2 is small can be said to be a state in which it is charged at a high charging voltage.
  • a charging voltage of 4.6 V or more based on the potential of lithium metal can be said to be a high charging voltage.
  • the charging voltage is expressed based on the potential of lithium metal.
  • the positive electrode active material 100 of one embodiment of the present invention is preferable because it can maintain a crystal structure with the symmetry of R-3m O3 even when charged at a high charging voltage, for example, a voltage of 4.6 V or more at 25°C.
  • the positive electrode active material 100 when the charging voltage is further increased, the H1-3 type crystal structure may finally be observed.
  • the crystal structure is affected by the number of charge/discharge cycles, the charge/discharge current, the temperature, the electrolyte, etc., so when the charging voltage is lower, for example, even when the charging voltage is 4.5 V or more and less than 4.6 V at 25° C., the positive electrode active material 100 of one embodiment of the present invention may be able to have the O3' type crystal structure.
  • the monoclinic O1(15) type crystal structure when charging at a voltage of 4.65 V or more and 4.7 V or less at 25° C., the monoclinic O1(15) type crystal structure may be able to be formed.
  • the voltage of the secondary battery drops by the amount of the graphite potential compared to the above.
  • the potential of graphite is about 0.05V to 0.2V based on the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, the battery has a similar crystal structure at the voltage obtained by subtracting the graphite potential from the above voltage.
  • lithium is shown to exist at all lithium sites with equal probability, but this is not limited to the above.
  • Lithium may be present biasedly at some lithium sites, or may have symmetry, for example, as in monoclinic O1( Li0.5CoO2 ) shown in Fig. 6.
  • the distribution of lithium can be analyzed, for example, by neutron diffraction.
  • the O3' and monoclinic O1(15) type crystal structures have random lithium between the layers, but are similar to the CdCl2 type crystal structure.
  • This CdCl2 type -like crystal structure is close to the crystal structure of lithium nickel oxide when it is charged to Li0.06NiO2 , but it is known that pure lithium cobalt oxide or layered rock salt type positive electrode active materials containing a large amount of cobalt do not usually have the CdCl2 type crystal structure.
  • the additive element contained in the positive electrode active material 100 of one embodiment of the present invention is distributed as described above, and at least a part of the additive element is unevenly distributed in and near the crystal grain boundaries.
  • uneven distribution refers to the concentration of an element in one area being different from that in other areas. It is synonymous with segregation, precipitation, non-uniformity, bias, or the presence of a mixture of areas of high concentration and areas of low concentration.
  • the magnesium concentration at and near the grain boundaries of the positive electrode active material 100 is higher than that at and near the grain boundaries in the interior 100b. It is also preferable that the fluorine concentration at and near the grain boundaries is higher than that at and near the grain boundaries in the interior 100b. It is also preferable that the nickel concentration at and near the grain boundaries is higher than that at and near the grain boundaries in the interior 100b. It is also preferable that the aluminum concentration at and near the grain boundaries is higher than that at and near the grain boundaries in the interior 100b.
  • Grain boundaries are a type of planar defect. As a result, they are prone to become unstable, just like particle surfaces, and changes in the crystal structure are likely to begin. Therefore, if the concentration of added elements at and near the grain boundaries is high, changes in the crystal structure can be more effectively suppressed.
  • the magnesium concentration and fluorine concentration are high at and near the grain boundaries, even if cracks occur along the grain boundaries of the positive electrode active material 100 of one embodiment of the present invention, the magnesium concentration and fluorine concentration will be high near the surface created by the cracks. Therefore, even in the positive electrode active material after cracks have occurred, the corrosion resistance to hydrofluoric acid can be improved. Also, even in the positive electrode active material after cracks have occurred, side reactions between the electrolyte and the positive electrode active material can be suppressed.
  • the particle size of the positive electrode active material 100 can be measured, for example, by a laser diffraction type particle size distribution measuring device.
  • the particle size of the positive electrode active material 100 measured by the laser diffraction type particle size distribution measuring device has a median diameter (D50) of preferably 1 ⁇ m or more and 100 ⁇ m or less, more preferably 2 ⁇ m or more and 40 ⁇ m or less, and even more preferably 5 ⁇ m or more and 30 ⁇ m or less. Or preferably 1 ⁇ m or more and 40 ⁇ m or less. Or preferably 1 ⁇ m or more and 30 ⁇ m or less. Or preferably 2 ⁇ m or more and 100 ⁇ m or less. Or preferably 2 ⁇ m or more and 30 ⁇ m or less. Or preferably 5 ⁇ m or more and 100 ⁇ m or less. Or preferably 5 ⁇ m or more and 40 ⁇ m or less.
  • Positive electrode active material 100 with a relatively small particle size is expected to have high charge/discharge rate characteristics.
  • Positive electrode active material 100 with a relatively large particle size is expected to have high charge/discharge cycle characteristics and maintain a high discharge capacity.
  • a certain positive electrode active material is the positive electrode active material 100 of one embodiment of the present invention having an O3′ type and/or monoclinic O1(15) type crystal structure when x in Li x MO 2 is small can be determined by analyzing a positive electrode having a positive electrode active material with a small x in Li x MO 2 using XRD, electron beam diffraction, neutron beam diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), or the like.
  • XRD is particularly preferred because it can analyze with high resolution the symmetry of transition metals such as cobalt contained in the positive electrode active material, it can compare the degree of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, and it can obtain sufficient accuracy even when measuring the positive electrode obtained by dismantling the secondary battery as is.
  • powder XRD can obtain diffraction peaks that reflect the crystal structure of the interior 100b of the positive electrode active material 100, which occupies the majority of the volume of the positive electrode active material 100.
  • the positive electrode active material from the positive electrode obtained by dismantling a secondary battery, prepare a powder sample, and then measure it.
  • the positive electrode active material 100 of one embodiment of the present invention is characterized in that there is little change in the crystal structure when x in Li x MO 2 is 1 and when it is 0.24 or less.
  • a material in which 50% or more of the crystal structure exhibits a large change in the crystal structure when charged at a high voltage is not preferable because it cannot withstand repeated charging and discharging at a high voltage.
  • the O3' or monoclinic O1(15) crystal structure is not obtained by simply adding an additive element.
  • lithium cobalt oxide having magnesium and fluorine, or lithium cobalt oxide having magnesium and aluminum is common, depending on the concentration and distribution of the additive element, there are cases where x in Li x MO 2 is 0.24 or less and the O3' and/or monoclinic O1(15) crystal structure accounts for 60% or more, and cases where the H1-3 crystal structure accounts for 50% or more.
  • the positive electrode active material 100 of one embodiment of the present invention Even in the case of the positive electrode active material 100 of one embodiment of the present invention, if x is too small, such as 0.1 or less, or under conditions where the charging voltage exceeds 4.9 V, an H1-3 type or trigonal O1 type crystal structure may be produced. Therefore, to determine whether or not a positive electrode active material 100 of one embodiment of the present invention is present, analysis of the crystal structure, such as XRD, and information such as the charging capacity or charging voltage are required.
  • Whether the distribution of added elements in a certain positive electrode active material is as described above can be determined by analysis using, for example, XPS, energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), etc.
  • the crystal structure of the surface layer 100a, grain boundaries, etc. can be analyzed by electron beam diffraction of a cross section of the positive electrode active material 100.
  • charging for determining whether a certain composite oxide is the positive electrode active material 100 of one embodiment of the present invention can be performed by preparing a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) with a lithium counter electrode and charging the coin cell.
  • a coin cell CR2032 type, diameter 20 mm, height 3.2 mm
  • the positive electrode can be made by coating a positive electrode current collector made of aluminum foil with a slurry of a mixture of a positive electrode active material, a conductive material, and a binder.
  • Lithium metal can be used for the counter electrode.
  • the voltage of the secondary battery and the potential of the positive electrode will differ. Unless otherwise specified, the voltage and potential in this specification refer to the potential of the positive electrode.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • a 25 ⁇ m thick polypropylene porous film can be used as the separator.
  • the positive and negative electrode cans can be made of stainless steel (SUS).
  • the coin cell prepared under the above conditions is charged at any voltage (for example, 4.5V, 4.55V, 4.6V, 4.65V, 4.7V, 4.75V, or 4.8V).
  • the charging method is not particularly limited as long as it can be charged at any voltage for a sufficient time.
  • the current in CC charging can be 20mA/g or more and 100mA/g or less.
  • CV charging can be terminated at 2mA/g or more and 10mA/g or less. In order to observe the phase change of the positive electrode active material, it is desirable to charge at such a small current value.
  • the current does not become 2mA/g or more and 10mA/g or less even after CV charging for a long time, it is considered that the current is consumed not for charging the positive electrode active material but for decomposing the electrolyte, so CV charging may be terminated when a sufficient time has passed since the start.
  • the sufficient time can be, for example, 1.5 hours or more and 3 hours or less.
  • the temperature is 25°C or 45°C.
  • XRD can be performed by sealing the cell in a sealed container in an argon atmosphere.
  • the conditions for the multiple charge/discharge cycles may be different from the above-mentioned charging conditions.
  • charging can be performed by constant current charging at a current value of 20 mA/g to 100 mA/g up to an arbitrary voltage (e.g., 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V), followed by constant voltage charging until the current value becomes 2 mA/g to 10 mA/g, and discharging can be performed at a constant current of 2.5 V and 20 mA/g to 100 mA/g.
  • an arbitrary voltage e.g., 4.6 V, 4.65 V, 4.7 V, 4.75 V, or 4.8 V
  • constant current discharge can be performed at, for example, 2.5 V and a current value of 20 mA/g or more and 100 mA/g or less.
  • the XRD measurement apparatus and conditions are not particularly limited.
  • the measurement can be performed using the following apparatus and conditions.
  • XRD device Bruker AXS, D8 ADVANCE
  • X-ray source Cu Output: 40kV, 40mA
  • Divergence angle Div. Slit, 0.5° Detector: LynxEye Scan method: 2 ⁇ / ⁇ continuous scan Measurement range (2 ⁇ ): 15° to 90° Step width (2 ⁇ ): 0.01°
  • Setting count time 1 second/step Sample stage rotation: 15 rpm It is preferable to remove the background and the CuK ⁇ 2 ray peak from the obtained XRD pattern using the analysis software DIFFRAC.EVA.
  • the measurement sample is a powder, it can be set up by placing it in a glass sample holder or sprinkling the sample on a greased silicone anti-reflective plate. If the measurement sample is a positive electrode, the positive electrode can be attached to the substrate with double-sided tape, and the positive electrode active material layer can be set to match the measurement surface required by the device.
  • Ideal powder XRD patterns calculated from the models of the O3' type crystal structure, the monoclinic O1(15) type crystal structure, and the H1-3 type crystal structure using CuK ⁇ 1 radiation are shown in Figures 7 , 8, 9A, and 9B.
  • Figures 9A and 9B show the XRD patterns of the O3' type crystal structure, the monoclinic O1(15) type crystal structure, and the H1-3 type crystal structure, with Figure 9A showing an enlarged view of the region in which 2 ⁇ is between 18° and 21°, and Figure 9B showing an enlarged view of the region in which 2 ⁇ is between 42° and 46°.
  • the patterns of LiCoO 2 (O3) and CoO 2 (O1) were created using Reflex Powder Diffraction, one of the modules of Materials Studio (BIOVIA), from crystal structure information obtained from ICSD (Inorganic Crystal Structure Database) (see Non-Patent Document 4).
  • the pattern of the H1-3 type crystal structure was created in the same manner from the crystal structure information described in Non-Patent Document 3.
  • the crystal structure patterns of the O3′ type and monoclinic O1(15) type were estimated from the XRD pattern of the positive electrode active material, and fitting was performed using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker), and XRD patterns were created in the same manner as for the others.
  • the positive electrode active material 100 of one embodiment of the present invention may have an O3'-type and/or monoclinic O1 (15)-type crystal structure when x in Li x CoO 2 is small, but not all of the particles may have an O3'-type and/or monoclinic O1 (15)-type crystal structure. Other crystal structures may be included, or a part may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, the O3'-type and/or monoclinic O1 (15)-type crystal structure is preferably 50% or more, more preferably 60% or more, and even more preferably 66% or more. If the O3'-type and/or monoclinic O1 (15)-type crystal structure is 50% or more, more preferably 60% or more, and even more preferably 66% or more, the positive electrode active material can have sufficiently excellent cycle characteristics.
  • the H1-3 type and O1 type crystal structures are 50% or less. Or, it is preferable that they are 34% or less. Or, more preferably, they are not substantially observed.
  • the O3' type and/or monoclinic O1(15) type crystal structure is preferably 35% or more, more preferably 40% or more, and even more preferably 43% or more.
  • each diffraction peak after charging is sharp, i.e., has a narrow full width at half maximum.
  • the full width at half maximum is narrow.
  • the half width varies depending on the XRD measurement conditions and the value of 2 ⁇ , even for peaks arising from the same crystal phase.
  • the full width at half maximum is preferably, for example, 0.2° or less, more preferably 0.15° or less, and even more preferably 0.12° or less. Note that not all peaks necessarily meet this requirement. If some peaks meet this requirement, it can be said that the crystallinity of that crystal phase is high. Such high crystallinity contributes sufficiently to stabilizing the crystal structure after charging.
  • the crystallite size of the O3' type and monoclinic O1 (15) crystal structures of the positive electrode active material 100 is reduced to only about 1/20 of LiCoO 2 (O3) in the discharged state. Therefore, even under the same XRD measurement conditions as the positive electrode before charging and discharging, a clear peak of the O3' type and/or monoclinic O1 (15) crystal structure can be confirmed when x in Li x CoO 2 is small.
  • the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be determined from the half-width of the XRD peak.
  • the positive electrode active material 100 has a small influence of the Jahn-Teller effect.
  • the positive electrode active material 100 may contain transition metals such as nickel and manganese as additive elements, so long as the influence of the Jahn-Teller effect is small.
  • nickel is less than 7.5 atomic % of the transition metal M contained in the positive electrode active material 100.
  • manganese is preferably 4 atomic % or less.
  • nickel concentration and manganese concentration ranges do not necessarily apply to the surface layer 100a.
  • concentrations in the surface layer 100a may be higher than those stated above.
  • the preferable range of the lattice constant was considered, and it was found that, in the positive electrode active material of one embodiment of the present invention, in the layered rock salt crystal structure of the positive electrode active material 100 in a state where no charging or discharging is performed or in a discharged state, which can be estimated from the XRD pattern, the a-axis lattice constant is preferably greater than 2.814 ⁇ 10 ⁇ 10 m and smaller than 2.817 ⁇ 10 ⁇ 10 m, and the c-axis lattice constant is preferably greater than 14.05 ⁇ 10 ⁇ 10 m and smaller than 14.07 ⁇ 10 ⁇ 10 m.
  • the state where no charging or discharging is performed may be, for example, a powder state before the positive electrode of a secondary battery is prepared.
  • the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis is greater than 0.20000 and less than 0.20049.
  • a first peak may be observed at 2 ⁇ of 18.50° or more and 19.30° or less, and a second peak may be observed at 2 ⁇ of 38.00° or more and 38.80° or less.
  • XPS X-ray photoelectron spectroscopy
  • inorganic oxides when monochromatic aluminum K ⁇ rays are used as the X-ray source, it is possible to analyze a region from the surface to a depth of about 2 to 8 nm (usually 5 nm or less), so that the concentration of each element can be quantitatively analyzed in a region about half the depth of the surface layer 100a.
  • narrow scan analysis can be used to analyze the bonding state of the elements.
  • the quantitative accuracy of XPS is often about ⁇ 1 atomic %, with a lower limit of about 1 atomic %, depending on the element.
  • the concentration of one or more selected from the additive elements is preferably higher in the surface layer 100a than in the interior 100b.
  • concentration of one or more selected from the additive elements in the surface layer 100a is preferably higher than the average of the entire positive electrode active material 100. Therefore, for example, it can be said that the concentration of one or more selected additive elements in the surface layer 100a measured by XPS or the like is preferably higher than the average concentration of the additive elements in the entire positive electrode active material 100 measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).
  • the magnesium concentration of at least a part of the surface layer 100a measured by XPS or the like is higher than the average magnesium concentration of the entire positive electrode active material 100.
  • the titanium concentration of at least a part of the surface layer 100a is higher than the average titanium concentration of the entire positive electrode active material 100.
  • the nickel concentration in at least a portion of the surface layer 100a is higher than the average nickel concentration in the entire positive electrode active material 100.
  • the aluminum concentration in at least a portion of the surface layer 100a is higher than the average aluminum concentration in the entire positive electrode active material 100.
  • the fluorine concentration in at least a portion of the surface layer 100a is higher than the average fluorine concentration in the entire positive electrode active material 100.
  • the surface and surface layer 100a of the positive electrode active material 100 do not contain carbonates, hydroxyl groups, etc. that are chemically adsorbed after the preparation of the positive electrode active material 100. They also do not contain electrolyte, binder, conductive material, or compounds derived from these that are attached to the surface of the positive electrode active material 100. Therefore, when quantifying the elements contained in the positive electrode active material, corrections may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, etc. that can be detected by surface analysis such as XPS. For example, XPS makes it possible to separate the types of bonds by analysis, and corrections may be made to exclude C-F bonds derived from the binder.
  • the positive electrode active material and the positive electrode active material layer may be washed to remove the electrolyte, binder, conductive material, or compounds derived from these that are attached to the surface of the positive electrode active material.
  • lithium may dissolve into the solvent used for washing, but even in this case, the added element is unlikely to dissolve, so this does not affect the atomic ratio of the added element.
  • the concentration of the added element in the surface layer 100a and the concentration of the added element in the positive electrode active material 100 may be compared in terms of the atomic ratio to cobalt.
  • Using the ratio to cobalt is preferable because it allows comparison while reducing the influence of carbonates and the like that are chemically adsorbed after the positive electrode active material is produced.
  • the atomic ratio Mg/Co of magnesium to cobalt as determined by XPS analysis is preferably 0.4 or more and 1.5 or less.
  • the atomic ratio Mg/Co as determined by ICP-MS analysis is preferably 0.001 or more and 0.06 or less.
  • the concentrations of lithium and cobalt in the surface layer 100a are higher than the concentrations of one or more additive elements selected from the additive elements contained in the surface layer 100a measured by XPS or the like.
  • the concentration of at least a part of the cobalt in the surface layer 100a measured by XPS or the like is higher than the concentration of at least a part of the magnesium in the surface layer 100a measured by XPS or the like.
  • the concentration of lithium is higher than the concentration of magnesium.
  • the concentration of cobalt is higher than the concentration of nickel.
  • the concentration of lithium is higher than the concentration of nickel. It is also preferable that the concentration of cobalt is higher than aluminum. It is also preferable that the concentration of lithium is higher than the concentration of aluminum. It is also preferable that the concentration of cobalt is higher than fluorine. It is also preferable that the concentration of lithium is higher than fluorine.
  • aluminum is widely distributed in a deep region, for example, on the surface, or in a region with a depth of 5 nm to 50 nm from the reference point. Therefore, although aluminum is detected in an analysis of the entire positive electrode active material 100 using ICP-MS, GD-MS, etc., it is more preferable that the concentration of aluminum is not detected by XPS, etc., or is 1 atomic % or less.
  • the number of magnesium atoms is preferably 0.4 to 1.2 times, more preferably 0.65 to 1.0 times, relative to the number of cobalt atoms.
  • the number of nickel atoms is preferably 0.15 to 0.03 times, more preferably 0.13 to 0.15 times, relative to the number of cobalt atoms.
  • the number of aluminum atoms is preferably 0.12 to 0.09 times, more preferably 0.09 to 0.3 times, more preferably 0.1 to 1.1 times, relative to the number of cobalt atoms.
  • the above ranges indicate that these additive elements are not attached to a narrow range on the surface of the positive electrode active material 100, but are widely distributed in the surface layer 100a of the positive electrode active material 100 at a preferred concentration.
  • monochromated aluminum K ⁇ rays can be used as the X-ray source.
  • the take-off angle can be set to, for example, 45°.
  • the measurement can be performed using the following apparatus and conditions.
  • the peak showing the bond energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably about 684.3 eV. This value is different from both the bond energy of lithium fluoride, 685 eV, and the bond energy of magnesium fluoride, 686 eV.
  • the peak showing the bond energy between magnesium and other elements is preferably equal to or greater than 1302 eV and less than 1304 eV, and more preferably about 1303 eV. This is a different value from the bond energy of magnesium fluoride, which is 1305 eV, and is close to the bond energy of magnesium oxide.
  • ⁇ EDX> It is preferable that one or more selected from the additive elements contained in the positive electrode active material 100 have a concentration gradient. It is more preferable that the depth from the surface of the concentration peak of the positive electrode active material 100 differs depending on the additive element.
  • the concentration gradient of the additive element can be evaluated, for example, by exposing a cross section of the positive electrode active material 100 using a focused ion beam (FIB) or the like and analyzing the cross section using energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like.
  • FIB focused ion beam
  • EDX energy dispersive X-ray spectroscopy
  • EPMA electron probe microanalysis
  • EDX area analysis In EDX measurements, performing measurements while scanning an area and evaluating the area in two dimensions is called EDX area analysis. Performing measurements while scanning linearly and evaluating the distribution of atomic concentrations within the positive electrode active material is called line analysis. Furthermore, data extracted from a linear area from EDX area analysis may be called line analysis. Measuring an area without scanning is called point analysis.
  • the concentration of the added element can be quantitatively analyzed in the surface layer 100a, the inside 100b, and the vicinity of the grain boundaries of the positive electrode active material 100.
  • concentration distribution and maximum value of the added element can be analyzed.
  • analysis using a thinned sample such as STEM-EDX is more preferable because it can analyze the concentration distribution in the depth direction from the surface to the center of the positive electrode active material in a specific region without being affected by the distribution in the depth direction.
  • the beam diameter of the electron beam also called the beam diameter, probe diameter, or probe diameter
  • the beam diameter in STEM-EDX ray analysis is preferably 0.3 nm or less, more preferably 0.2 nm or less, and even more preferably 0.1 nm or less.
  • the positive electrode active material 100 is a compound containing oxygen and a transition metal capable of inserting and removing lithium
  • the interface between the region where the transition metal M (e.g., Co, Ni, Mn, Fe, etc.) that is oxidized and reduced with the insertion and removal of lithium and oxygen is present and the region where it is not present is defined as the surface of the positive electrode active material.
  • a protective film may be attached to the surface, but the protective film is not included in the positive electrode active material.
  • the protective film a single layer or multilayer film of carbon, metal, oxide, resin, etc. may be used.
  • the graph of the amount of detection of characteristic X-rays of the element does not change sharply, and it may be difficult to determine the surface strictly. Therefore, in the analysis of the positive electrode active material in STEM-EDX-ray analysis, etc., the point where the amount of detection of characteristic X-rays of the transition metal M is 50% of the sum of the average value M AVE of the amount of detection of characteristic X-rays of the transition metal M in the interior and the average value M BG of the amount of detection of characteristic X-rays of the transition metal M in the background is taken as the reference point of the surface.
  • the point where the amount of detection of characteristic X-rays of oxygen is 50% of the sum of the average value O AVE of the amount of detection of characteristic X-rays of oxygen in the interior and the average value O BG of the amount of detection of characteristic X-rays of oxygen in the background is taken as the reference point of the surface. Note that if the two points are different, it is considered that this is due to the influence of metal oxides, carbonates, etc. containing oxygen attached to the surface, so the point based on the transition metal M can be adopted as the reference point. In the case of a positive electrode active material having a plurality of transition metals M, the reference point can be found using the M AVE and M BG of the element that has the largest amount of characteristic X-rays detected inside.
  • the average background value M BG of the transition metal M can be obtained by averaging a range of 2 nm or more, preferably 3 nm or more, outside the positive electrode active material, for example, avoiding the vicinity where the detected amount of the transition metal M starts to increase.
  • the average internal detected amount M AVE can be obtained by averaging a range of 2 nm or more, preferably 3 nm or more, in a region where the counts of the transition metal M and oxygen are saturated and stable, for example, a portion that is 30 nm or more, preferably 50 nm deep from the region where the detected amount of the transition metal M starts to increase.
  • the average background value O BG of oxygen and the average internal detected amount of oxygen O AVE can also be obtained in the same manner.
  • the surface of the positive electrode active material 100 in a cross-sectional STEM (scanning transmission electron microscope) image or the like is the boundary between an area where an image originating from the crystal structure of the positive electrode active material is observed and an area where it is not observed, and is the outermost area where atomic columns originating from the atomic nuclei of metal elements having atomic numbers larger than lithium among the metal elements that make up the positive electrode active material are confirmed.
  • the surface in an STEM image or the like may be determined in conjunction with an analysis with higher spatial resolution.
  • a peak in STEM-ED X-ray analysis refers to a convex maximum value that appears in a graph of the characteristic X-ray intensity for each element, or the maximum value of the characteristic X-ray for each element.
  • noise in STEM-ED X-ray analysis can be a measured value with a half-width less than the spatial resolution (R), for example, less than R/2.
  • the effects of noise can be reduced by scanning the same location multiple times under the same conditions.
  • the integrated values measured over six scans can be used as the detection value for each element.
  • the number of scans is not limited to six, and more can be performed and the average can be used as the detection value for each element.
  • STEM-EDX analysis can be performed, for example, as follows.
  • a protective film is deposited on the surface of the positive electrode active material.
  • carbon can be deposited using an ion sputtering device (Hitachi High-Tech MC1000).
  • the positive electrode active material is sliced to prepare a STEM cross-sectional sample.
  • the slice processing can be performed using a FIB-SEM device (Hitachi High-Tech XVision 200TBS).
  • the pickup is performed using an MPS (micro-probing system), and the finishing processing conditions can be, for example, an acceleration voltage of 10 kV.
  • STEM-EDX-ray analysis for example, a STEM device (Hitachi High-Tech HD-2700) can be used, and an EDAX Octane T Ultra W (two-wire) can be used as the EDX detector.
  • the emission current of the STEM device is set to 6 ⁇ A or more and 10 ⁇ A or less, and a portion of the sliced sample with minimal depth and unevenness is measured.
  • the magnification is, for example, about 150,000 times.
  • the conditions for EDX-ray analysis can be drift correction, line width 42 nm, pitch 0.2 nm, and frame number 6 or more.
  • the concentration of each added element, particularly added element X, in the surface layer portion 100a is higher than that in the interior portion 100b.
  • the magnesium concentration in the surface layer 100a is higher than the magnesium concentration in the interior 100b.
  • the peak of the magnesium concentration in the surface layer 100a is preferably present on the surface of the positive electrode active material 100 or at a depth of 3 nm from the reference point toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm.
  • the magnesium concentration decays to 60% or less of the peak at a point 1 nm deep from the peak top.
  • the magnesium concentration decays to 30% or less of the peak at a point 2 nm deep from the peak top.
  • the peak concentration here refers to the maximum value of the concentration.
  • the maximum value of the magnesium concentration (detected amount of magnesium/(sum of detected amounts of magnesium, oxygen, cobalt, fluorine, aluminum, titanium, and nickel) in the surface layer 100a is preferably 0.5 Atomic% or more and 10 Atomic% or less, and more preferably 1 Atomic% or more and 5 Atomic% or less.
  • the maximum titanium concentration (detected amount of titanium/(sum of detected amounts of magnesium, oxygen, cobalt, fluorine, aluminum, titanium, and nickel) in the surface layer 100a is preferably 0.2 Atomic% or more and 5 Atomic% or less, and more preferably 0.5 Atomic% or more and 2 Atomic% or less.
  • the maximum nickel concentration (detected amount of nickel/(sum of detected amounts of magnesium, oxygen, cobalt, fluorine, aluminum, titanium, and nickel) in the surface layer 100a is preferably 0.2 Atomic% or more and 5 Atomic% or less, and more preferably 0.5 Atomic% or more and 3 Atomic% or less.
  • the distribution of fluorine has an overlapping region with the distribution of magnesium.
  • the difference in the depth direction between the peak of the fluorine concentration and the peak of the magnesium concentration is preferably within 10 nm, more preferably within 3 nm, and even more preferably within 1 nm.
  • the peak of the fluorine concentration in the surface layer 100a is preferably present on the surface of the positive electrode active material 100 or at a depth of up to 3 nm from the reference point toward the center, more preferably at a depth of up to 1 nm, and even more preferably at a depth of up to 0.5 nm.
  • the fluorine concentration peak it is more preferable for the fluorine concentration peak to be slightly closer to the surface than the magnesium concentration peak, as this increases resistance to hydrofluoric acid.
  • it is more preferable for the fluorine concentration peak to be 0.5 nm or more closer to the surface than the magnesium concentration peak, and even more preferable for it to be 1.5 nm or more closer to the surface.
  • the peak of the nickel concentration in the surface layer 100a is preferably present at a depth of up to 3 nm from the surface or reference point of the positive electrode active material 100 toward the center, more preferably at a depth of up to 1 nm, and even more preferably at a depth of up to 0.5 nm.
  • the distribution of nickel has an overlapping region with the distribution of magnesium.
  • the difference in depth between the peak of nickel concentration and the peak of magnesium concentration is preferably within 3 nm, and more preferably within 1 nm.
  • the peak of the titanium concentration in the surface layer 100a is preferably present at a depth of up to 3 nm from the surface or reference point of the positive electrode active material 100 toward the center, more preferably at a depth of up to 1 nm, and even more preferably at a depth of up to 0.5 nm.
  • the distribution of titanium has an overlapping region with the distribution of magnesium.
  • the difference in depth between the peak of titanium concentration and the peak of magnesium concentration is preferably within 3 nm, and more preferably within 1 nm.
  • the magnesium, nickel or fluorine concentration peak is closer to the surface than the aluminum concentration peak of the surface layer 100a when EDX-ray analysis is performed.
  • the aluminum concentration peak is present on the surface of the positive electrode active material 100, or at a depth of 0.5 nm to 50 nm from the reference point toward the center, and more preferably at a depth of 5 nm to 50 nm.
  • a battery using the positive electrode active material 100 can achieve both "high cycle characteristics” that suppress deterioration of discharge capacity during repeated high voltage charging (e.g., charging with an upper limit of 4.6 V) and discharging, and "high low temperature characteristics” that provide a large discharge capacity at low temperatures (e.g., 0°C, -20°C, -40°C).
  • the ratio of the number of atoms of magnesium Mg to cobalt Co (Mg/Co) at the peak of the magnesium concentration is preferably 0.05 or more and 0.6 or less, more preferably 0.1 or more and 0.4 or less.
  • the ratio of the number of atoms of aluminum Al to cobalt Co (Al/Co) at the peak of the aluminum concentration is preferably 0.05 or more and 0.6 or less, more preferably 0.1 or more and 0.45 or less.
  • the ratio of the number of atoms of nickel Ni to cobalt Co (Ni/Co) at the peak of the nickel concentration is preferably 0 or more and 0.2 or less, more preferably 0.01 or more and 0.1 or less.
  • the ratio of the number of atoms of fluorine F to cobalt Co (F/Co) at the peak of the fluorine concentration is preferably 0 or more and 1.6 or less, more preferably 0.1 or more and 1.4 or less.
  • the ratio of the number of atoms of the added element to cobalt Co in the vicinity of the grain boundary is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. Even more preferably, it is 0.030 or more and 0.20 or less. Or it is preferably 0.020 or more and 0.30 or less. Or it is preferably 0.020 or more and 0.20 or less. Or it is preferably 0.025 or more and 0.50 or less. Or it is preferably 0.025 or more and 0.20 or less. Or it is preferably 0.030 or more and 0.50 or less. Or it is preferably 0.030 or more and 0.30 or less.
  • the ratio of the number of magnesium atoms to cobalt atoms (Mg/Co) near the grain boundaries is preferably 0.020 or more and 0.50 or less. Further preferably, it is 0.025 or more and 0.30 or less. Further preferably, it is 0.030 or more and 0.20 or less. Or it is preferably 0.020 or more and 0.30 or less. Or it is preferably 0.020 or more and 0.20 or less. Or it is preferably 0.025 or more and 0.50 or less. Or it is preferably 0.025 or more and 0.20 or less. Or it is preferably 0.030 or more and 0.50 or less.
  • the additive element is not attached to a narrow area on the surface of the positive electrode active material 100, but is widely distributed at a preferred concentration in the surface layer 100a of the positive electrode active material 100.
  • EPMA Electro Probe Microanalysis
  • Area analysis can analyze the distribution of each element.
  • EPMA surface analysis is performed on a cross section of the positive electrode active material 100 of one embodiment of the present invention
  • one or more selected from the added elements have a concentration gradient, similar to the results of the EDX analysis. It is also more preferable that the depth from the surface of the concentration peak differs depending on the added element. The preferred range of the concentration peak of each added element is also the same as in the case of EDX.
  • EPMA analyzes a region from the surface to a depth of about 1 ⁇ m. Therefore, the quantitative values of each element may differ from the measurement results obtained using other analytical methods. For example, when the surface analysis of the positive electrode active material 100 is performed using EPMA, the concentration of each added element present in the surface layer 100a may be lower than the results of XPS.
  • ⁇ Raman spectroscopy> As described above, it is preferable that at least a part of the surface layer 100a of the positive electrode active material 100 of one embodiment of the present invention has a rock salt type crystal structure. Therefore, when the positive electrode active material 100 and a positive electrode having the same are analyzed by Raman spectroscopy, it is preferable that a cubic crystal structure such as a rock salt type is also observed along with the layered rock salt crystal structure.
  • peaks are observed at 470 cm -1 to 490 cm -1 and 580 cm -1 to 600 cm-1 in layered rock salt LiCoO2, while a peak (vibration mode: A1g ) is observed at 665 cm -1 to 685 cm -1 in cubic CoOx ( 0 ⁇ x ⁇ 1) (rock salt Co1 - yO (0 ⁇ y ⁇ 1 ) or spinel Co3O4 ).
  • the integrated intensity of each peak is defined as I1 from 470 cm -1 to 490 cm -1 , I2 from 580 cm -1 to 600 cm -1 , and I3 from 665 cm -1 to 685 cm -1 , it is preferable that the value of I3/I2 is 1% or more and 10% or less, and more preferably 3% or more and 9% or less.
  • the surface layer 100a of the positive electrode active material 100 has a rock salt type crystal structure in a preferred range.
  • the characteristics of the rock salt type crystal structure are observed in the electron microbeam diffraction pattern as well as the layered rock salt crystal structure.
  • the characteristics of the rock salt type crystal structure are not too strong in the surface layer 100a, especially in the outermost surface (for example, 1 nm deep from the surface), taking into account the above-mentioned difference in sensitivity. This is because the presence of an additive element such as magnesium in the lithium layer while maintaining the layered rock salt type crystal structure can ensure a diffusion path for lithium and has a stronger function of stabilizing the crystal structure than when the outermost surface is covered with a rock salt type crystal structure.
  • a micro-electron beam diffraction pattern is obtained from a region having a depth of 1 nm or less from the surface, and a micro-electron beam diffraction pattern is obtained from a region having a depth of 3 nm to 10 nm, it is preferable that the difference in the lattice constant calculated from these patterns is small.
  • the difference in lattice constant calculated from a measurement point at a depth of 1 nm or less from the surface and a measurement point at a depth of 3 nm to 10 nm is preferably 0.1 ⁇ or less for the a-axis, and 1.0 ⁇ or less for the c-axis. It is more preferable that the difference is 0.05 ⁇ or less for the a-axis, and more preferably 0.6 ⁇ or less for the c-axis. It is even more preferable that the difference is 0.04 ⁇ or less for the a-axis, and even more preferably 0.3 ⁇ or less for the c-axis.
  • the positive electrode active material 100 preferably has a smooth surface with few irregularities.
  • a smooth surface with few irregularities indicates that the effect of the flux described below is sufficiently exerted to melt the surfaces of the additive element source and the lithium cobalt oxide. Therefore, this is one factor indicating that the distribution of the additive element in the surface layer portion 100a is good.
  • That the surface is smooth and has few irregularities can be determined, for example, from a cross-sectional SEM image or cross-sectional TEM image of the positive electrode active material 100, the specific surface area of the positive electrode active material 100, etc.
  • the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 as follows:
  • the cathode active material 100 is processed by FIB or the like to expose the cross section. At this time, it is preferable to cover the cathode active material 100 with a protective film, a protective agent, or the like.
  • an SEM image of the interface between the protective film or the like and the cathode active material 100 is taken.
  • the interface is extracted using the image processing software.
  • the interface line between the protective film or the like and the cathode active material 100 is selected using an automatic selection tool or the like, and the data is extracted to a spreadsheet software or the like.
  • this surface roughness is the surface roughness at least at 400 nm from the outer periphery of the particle of the cathode active material.
  • the particle surface of the positive electrode active material 100 of this embodiment preferably has a root mean square (RMS) surface roughness, which is an index of roughness, of less than 3 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.
  • RMS root mean square
  • the image processing software used for noise processing, interface extraction, etc. is not particularly limited, but for example, "ImageJ" described in Non-Patent Documents 8 to 10 can be used.
  • Spreadsheet software, etc. is also not particularly limited, but for example, Microsoft Office Excel can be used.
  • the surface smoothness of the positive electrode active material 100 can also be quantified from the ratio of the actual specific surface area S R measured by a constant volume gas adsorption method to the ideal specific surface area S i .
  • the ideal specific surface area S i is calculated assuming that all particles have the same diameter D50, the same weight, and an ideal spherical shape.
  • the median diameter D50 can be measured using a particle size distribution meter that uses the laser diffraction/scattering method.
  • the specific surface area can be measured using a specific surface area measuring device that uses the gas adsorption method by the constant volume method, for example.
  • the ratio S R /S i of the ideal specific surface area S i determined from the median diameter D50 to the actual specific surface area S R is preferably 2.1 or less.
  • the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 by the following method.
  • a surface SEM image of the positive electrode active material 100 is obtained.
  • a conductive coating may be applied as a pretreatment before observation. It is preferable that the observation surface is perpendicular to the electron beam. When comparing multiple samples, the measurement conditions and observation area should be the same.
  • a grayscale image contains luminance (brightness information).
  • the change in luminance can be quantified in relation to the number of gradations. This numerical value is called the grayscale value.
  • a histogram is a three-dimensional representation of the gradation distribution in the target area, and is also called a brightness histogram. Obtaining a brightness histogram makes it possible to visually evaluate the unevenness of the positive electrode active material in an easily understandable way.
  • the difference between the maximum and minimum values of the above grayscale value is preferably 120 or less, more preferably 115 or less, and even more preferably 70 to 115.
  • the standard deviation of the grayscale value is preferably 11 or less, more preferably 8 or less, and even more preferably 4 to 8.
  • the particle size distribution of the positive electrode active material 100 can also be calculated from a cross-sectional SEM image of the positive electrode active material 100 by the method described below.
  • an analysis region is cut out from the acquired cross-sectional SEM image.
  • a range of 50 ⁇ m or more ⁇ 100 ⁇ m or more can be cut out as a range having a sufficient area for image analysis, but this is not limited to this.
  • a smaller area or a larger area may be cut out.
  • functions of image processing software may be used to cut out the cross-sectional SEM image.
  • ImageJ may be used as the image processing software, and the image may be cut out using its crop function.
  • the first image is binarized using image processing software and particle analysis is performed.
  • Image processing software that can be used is, for example, ImageJ.
  • the binarization process is explained below.
  • a first image shown in a 256-value grayscale is used as a frequency graph excluding black (value 0) and white (value 255), and the low value side (HWHM_L) and high value side (HWHM_H) are obtained as the half-width at half maximum (HWHM) of the maximum peak in the frequency graph.
  • HWHM_L low value side
  • HWHM_H high value side
  • the minimum value a of the range that is twice the width of HWHM_L on the low value side from the value that is the peak top (maximum frequency) of the maximum peak and the maximum value b of the range that is twice the width of HWHM_H on the high value side are determined.
  • binarization is performed so that the range of values less than a is white, the range of values between a and b is black, and the range of values greater than b is white.
  • binarization is performed as Threshold (a, b) using ImageJ's Threshold function.
  • the particle size distribution of each particle can be calculated from the cross-sectional SEM image.
  • Performing the above analysis is called performing particle size distribution analysis using a cross-sectional SEM image of the positive electrode.
  • a coating portion may be attached to at least a portion of the surface of the positive electrode active material 100.
  • Figure 10 shows an example of a positive electrode active material 100 with a coating portion 104 attached.
  • the coating portion 104 is preferably formed by, for example, accumulating decomposition products of the electrolyte and the organic electrolyte solution with charging and discharging.
  • the coating portion 104 preferably has, for example, carbon, oxygen, and fluorine.
  • the coating portion 104 having one or more selected from boron, nitrogen, sulfur, and fluorine may be a good quality coating portion and is preferable.
  • the coating portion 104 does not have to cover the entire positive electrode active material 100. For example, it is sufficient to cover 50% or more of the surface of the positive electrode active material 100, more preferably 70% or more, and even more preferably 90% or more.
  • the positive electrode active material 100 according to one embodiment of the present invention has a stable crystal structure even at high voltage.
  • the stable crystal structure of the positive electrode active material in the charged state can suppress the decrease in charge/discharge capacity associated with repeated charging and discharging.
  • As a feature of the positive electrode active material 100 having the above-mentioned excellent properties it has been explained in the above ⁇ XRD>> that when x in Li x CoO 2 is small, it has an O3' type and/or monoclinic O1(15) type crystal structure.
  • the positive electrode active material 100 according to one embodiment of the present invention is also characterized by the volume resistivity of the powder.
  • the volume resistivity of the powder of the positive electrode active material 100 at a pressure of 64 MPa is preferably 1.0 ⁇ 10 8 ⁇ cm or more and 1.0 ⁇ 10 10 ⁇ cm or less, and more preferably 5.0 ⁇ 10 8 ⁇ cm or more and 1.5 ⁇ 10 9 ⁇ cm or less.
  • the positive electrode active material 100 having the above volume resistivity has a stable crystal structure even at high voltages, and can be used as an indicator that the surface layer 100a, which is important for the crystal structure of the positive electrode active material to be stable in the charged state, has been well formed.
  • This section describes a method for measuring the volume resistivity of powder of the positive electrode active material 100 according to one embodiment of the present invention.
  • the measurement of the volume resistivity of a powder preferably has an instrument part having a terminal for resistance measurement and a mechanism for applying pressure to the powder to be measured.
  • the terminal for resistance measurement preferably has four terminals (also called four probes).
  • MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd. can be used as a measurement device having a terminal for resistance measurement and a mechanism for applying pressure to the powder (sample) to be measured.
  • the resistance measurement device can be a low resistance measurement device Loresta GP or a high resistance measurement device Hiresta GP. Loresta GP can be used to measure low resistance samples, and Hiresta GP can be used to measure high resistance samples.
  • the measurement environment is preferably a stable environment such as a dry room.
  • the dry room environment is preferably, for example, a temperature environment of 25°C and a dew point environment of -40°C or less.
  • the electrical resistance decreases due to the influence of moisture in the air, and the original physical property value may not be obtained.
  • the measuring section is structured so that the powder sample comes into contact with a terminal for measuring resistance, and is structured so that pressure can be applied to the powder sample.
  • the measuring section also has a structure for measuring the volume of the powder sample in the measuring section. Specifically, the measuring section has a cylindrical space, and the powder sample is set in this space.
  • the structure for measuring the volume of the powder sample described above can measure the height of the powder set in the space, thereby measuring the volume occupied by the powder at that time.
  • the electrical resistance of the powder and the volume of the powder are measured while pressure is applied to the powder.
  • the pressure applied to the powder can be measured under a number of conditions.
  • the electrical resistance and volume of the powder can be measured under pressure conditions of 16 MPa, 25 MPa, 38 MPa, 51 MPa, and 64 MPa.
  • the volume resistivity of the powder can be calculated from the measured electrical resistance and volume of the powder.
  • the volume resistivity of the powder of the positive electrode active material 100 of one embodiment of the present invention is 1.0 ⁇ 10 8 ⁇ cm or more and 1.0 ⁇ 10 10 ⁇ cm or less when measured under a pressure of 64 MPa, favorable cycle characteristics are exhibited in a charge-discharge cycle test under high charging voltage conditions, and if the volume resistivity is 5.0 ⁇ 10 8 ⁇ cm or more and 1.5 ⁇ 10 9 ⁇ cm or less, even more favorable cycle characteristics are exhibited in a charge-discharge cycle test under high voltage conditions.
  • volume resistivity measured as above is the volume resistivity of the powder.
  • ⁇ Ion Chromatography> A method for measuring the powder of the positive electrode active material 100 according to one embodiment of the present invention by ion chromatography will be described.
  • the measurement by ion chromatography involves a pretreatment step of dissolving the powder of the positive electrode active material 100 in an acid to obtain a solution for measurement, and a measurement step of measuring the solution.
  • the ion chromatography device and conditions are not particularly limited.
  • the measurement can be performed using the following device and conditions.
  • an ion chromatography device for example, the Dionex ICS-2100 ion chromatography system manufactured by Thermo Fisher Scientific can be used.
  • ion chromatography is performed using the second mixed solution obtained by the above pretreatment.
  • anion analysis and cation analysis it is preferable to perform anion analysis and cation analysis.
  • An example of the conditions for anion analysis is shown below.
  • Anion analysis can be performed at 35°C using a Dionex IonPac AG20 (2 x 50 mm) or Dionex IonPac AS20 (2 x 250 mm) column.
  • a KOH aqueous solution is used as the eluent, and the flow rate should be set to 0.44 ml/min. It is preferable to perform gradient measurement so that the concentration of the KOH aqueous solution gradually increases.
  • An electrical conductivity detector is used as the detector, and a mixed anion standard solution manufactured by Kanto Chemical Co., Ltd. can be used to create a calibration curve.
  • Cation analysis can be performed at 30°C using a Dionex IonPac CG16 (3 x 50 mm) or Dionex IonPac CS16 (3 x 250 mm) column.
  • the eluent should be an aqueous solution of methanesulfonic acid (MSA), and the flow rate should be 0.36 ml/min. It is recommended that isocratic measurements be performed with the concentration of the MSA aqueous solution kept constant.
  • An electrical conductivity detector is used as the detector, and a mixed cation standard solution manufactured by Kanto Chemical Co., Ltd. can be used to create a calibration curve.
  • the ion chromatography measurements described above allow for quantitative measurement of anions such as fluorine (F) and chlorine (Cl), and for cations such as lithium (Li), magnesium (Mg), cobalt (Co), and nickel (Ni).
  • anions such as fluorine (F) and chlorine (Cl)
  • cations such as lithium (Li), magnesium (Mg), cobalt (Co), and nickel (Ni).
  • the weight of fluorine relative to the weight of the powder is preferably 100 ppm or more and 1000 ppm or less, and more preferably 100 ppm or more and 200 ppm or less.
  • This embodiment can be used in combination with other embodiments.
  • the method of adding the added elements is important. At the same time, it is also important that the crystallinity of the interior 100b is good.
  • cobalt is mainly used as the transition metal M of the positive electrode active material 100
  • the annealing temperature is too high, cation mixing occurs, increasing the possibility that an added element, such as magnesium, will enter the cobalt site.
  • Magnesium present at the cobalt site has no effect of maintaining the layered rock salt type crystal structure of R-3m when x in Li x CoO 2 is small.
  • the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium being evaporated.
  • a material that functions as a flux with the additive element source.
  • Any material that has a lower melting point than lithium cobalt oxide can function as a flux.
  • fluorine compounds such as lithium fluoride are suitable. Adding a flux lowers the melting point of the additive element source and lithium cobalt oxide. Lowering the melting point makes it easier to distribute the additive element well at a temperature where cation mixing is unlikely to occur.
  • a lithium source (Li source) and a transition metal M source (M source) are prepared as starting materials, that is, lithium and transition metal M, respectively.
  • Li source Li source
  • M source transition metal M source
  • cobalt cobalt is used as the transition metal M
  • the lithium source it is preferable to use a compound containing lithium, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. It is preferable that the lithium source has high purity, for example, a material with a purity of 99.99% or more.
  • cobalt source it is preferable to use a compound containing cobalt, for example, cobalt oxide such as tricobalt tetroxide, cobalt hydroxide, etc.
  • cobalt oxide such as tricobalt tetroxide, cobalt hydroxide, etc.
  • the cobalt source is preferably of high purity, for example, a material with a purity of 3N (99.9%) or more, preferably 4N (99.99%) or more, more preferably 4N5 (99.995%) or more, and even more preferably 5N (99.999%) or more may be used.
  • a high purity material impurities in the positive electrode active material can be controlled. As a result, the capacity of the secondary battery is increased and/or the reliability of the secondary battery is improved.
  • the cobalt source has high crystallinity, for example, single crystal grains.
  • the crystallinity of the cobalt source can be evaluated using TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc., or evaluation using X-ray diffraction (XRD), electron beam diffraction, neutron beam diffraction, etc.
  • XRD X-ray diffraction
  • the above methods for evaluating crystallinity can be applied not only to cobalt sources, but also to evaluating the crystallinity of other sources.
  • step S12 the lithium source and the cobalt source are pulverized and mixed to prepare a mixed material.
  • the pulverization and mixing can be performed in a dry or wet manner.
  • the wet method is preferable because it can be crushed into smaller particles.
  • a solvent is prepared.
  • ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. can be used. It is more preferable to use an aprotic solvent that is less likely to react with lithium.
  • dehydrated acetone with a purity of 99.5% or more is used. It is preferable to mix the lithium source and the cobalt source with dehydrated acetone with a purity of 99.5% or more, in which the moisture content is suppressed to 10 ppm or less, and then pulverize and mix them.
  • dehydrated acetone with the above-mentioned purity it is possible to reduce impurities that may be mixed in.
  • a ball mill, a bead mill, or the like can be used as a means for grinding and mixing.
  • a ball mill it is recommended to use aluminum oxide balls or zirconium oxide balls as the grinding media. Zirconium oxide balls are preferable because they emit fewer impurities.
  • the peripheral speed is set to 100 mm/s or more and 2000 mm/s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 838 mm/s (rotation speed 400 rpm, ball mill diameter 40 mm).
  • step S13 shown in FIG. 11 the mixed material is heated.
  • the heating is preferably performed at 800° C. or more and 1100° C. or less, more preferably at 900° C. or more and 1000° C. or less, and even more preferably at about 950° C. If the temperature is too low, the decomposition and melting of the lithium source and the cobalt source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to lithium transpiration from the lithium source and/or cobalt being excessively reduced. For example, cobalt may change from trivalent to divalent, inducing oxygen defects, etc.
  • the heating time should be between 1 hour and 100 hours, and more preferably between 2 hours and 20 hours.
  • the heating rate depends on the heating temperature reached, but it is recommended to set it to between 80°C/h and 250°C/h. For example, if heating at 1000°C for 10 hours, the heating rate should be 200°C/h.
  • the heating is preferably performed in an atmosphere with little water, such as dry air, for example, an atmosphere with a dew point of ⁇ 50° C. or less, more preferably an atmosphere with a dew point of ⁇ 80° C. or less.
  • the heating is performed in an atmosphere with a dew point of ⁇ 93° C.
  • the impurity concentrations of CH 4 , CO, CO 2 , H 2 , and the like in the heating atmosphere should each be 5 ppb (parts per billion) or less.
  • the heating atmosphere is preferably an atmosphere containing oxygen.
  • the heating atmosphere is preferably an atmosphere containing oxygen.
  • the flow rate of the dry air is preferably 10 L/min.
  • the method of continuously introducing oxygen into the reaction chamber and having oxygen flow through the reaction chamber is called flow.
  • the heating atmosphere is an atmosphere containing oxygen
  • a method that does not allow flow may be used.
  • the reaction chamber may be depressurized and then filled with oxygen (or purged) to prevent the oxygen from entering or leaving the reaction chamber.
  • the reaction chamber may be depressurized to -970 hPa and then filled with oxygen to 50 hPa.
  • the material After heating, the material can be allowed to cool naturally, but it is preferable that the time it takes to cool from the specified temperature to room temperature is between 10 and 50 hours. However, cooling to room temperature is not always necessary, as long as the material is cooled to a temperature that is acceptable for the next step.
  • the heating in this process may be performed using a rotary kiln or roller hearth kiln. Heating using a rotary kiln can be performed while stirring, whether it is a continuous or batch type.
  • the crucible used for heating is preferably made of aluminum oxide.
  • Aluminum oxide crucibles are made of a material that does not easily release impurities. In this embodiment, an aluminum oxide crucible with a purity of 99.9% is used. It is preferable to place a lid on the crucible when heating. This prevents the material from volatilizing.
  • a new crucible refers to one that has undergone the process of putting in and heating materials containing lithium, transition metal M, and/or additive elements two or less times.
  • a crucible that has been used multiple times refers to one that has undergone the process of putting in and heating materials containing lithium, transition metal M, and/or additive elements three or more times. This is because, when a new crucible is used, there is a risk that some of the materials, including lithium fluoride, may be absorbed, diffused, moved, and/or attached to the sheath during heating.
  • the material After heating, the material may be crushed and sieved as necessary. When recovering the heated material, it may be transferred from the crucible to a mortar and then recovered. It is preferable to use agate or partially stabilized zirconium oxide for the mortar. Note that the same heating conditions as those in step S13 can be applied to the heating steps other than step S13 described below.
  • Step S14 By the above steps, lithium cobalt oxide (LiCoO 2 ) can be synthesized as shown in step S14 in FIG.
  • the composite oxide may also be produced by a coprecipitation method.
  • the composite oxide may also be produced by a hydrothermal method.
  • pre-synthesized lithium cobalt oxide may be used in step S14.
  • steps S11 to S13 can be omitted.
  • step S15 By carrying out step S15 on pre-synthesized lithium cobalt oxide, lithium cobalt oxide with a smooth surface can be obtained.
  • step S20 it is preferable to add an additive element to the lithium cobalt oxide.
  • the additive element is added in a plurality of steps, so that the additive element added first in the flow shown in Fig. 11 is described as A1, the additive element added second time is A2, and the additive element added third time is A3.
  • the step of adding the additive element A1 will be described with reference to Fig. 12A.
  • an additive element source (A1 source) to be added to lithium cobalt oxide is prepared.
  • a lithium source may be prepared together with the A1 source.
  • the additive element A1 can be any of the additive elements described in the previous embodiment. Specifically, one or more elements selected from magnesium, fluorine, nickel, aluminum, titanium, zirconium, vanadium, iron, manganese, chromium, niobium, arsenic, zinc, silicon, sulfur, phosphorus, and boron can be used. Also, one or two elements selected from bromine and beryllium can be used.
  • the source of the additive element can be called a magnesium source.
  • the magnesium source can be magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, or the like.
  • multiple magnesium sources described above can be used.
  • the dopant element source can be referred to as a fluorine source.
  • the fluorine source that can be used include lithium fluoride (LiF), magnesium fluoride ( MgF2 ), aluminum fluoride ( AlF3 ), titanium fluoride ( TiF4 ), cobalt fluoride ( CoF2 , CoF3 ), nickel fluoride ( NiF2 ), zirconium fluoride ( ZrF4 ), vanadium fluoride ( VF5 ), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride ( ZnF2 ), calcium fluoride ( CaF2 ), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride ( BaF2 ), cerium fluoride ( CeF3 , CeF4 ), lanthanum fluoride ( LaF3 ), and sodium aluminum hexafluoride (LiF), magnesium fluoride ( MgF
  • Magnesium fluoride can be used as both a fluorine source and a magnesium source. Lithium fluoride can also be used as a lithium source. Other lithium sources that can be used in step S21 include lithium carbonate.
  • the fluorine source may be a gas, such as fluorine ( F2 ), carbon fluoride , sulfur fluoride, oxygen fluoride ( OF2 , O2F2 , O3F2 , O4F2 , O5F2 , O6F2 , O2F ) , nitrogen trifluoride ( NF3 ), or the like , which may be mixed into the atmosphere in the heating step described below.
  • F2 fluorine
  • carbon fluoride sulfur fluoride
  • oxygen fluoride OF2 , O2F2 , O3F2 , O4F2 , O5F2 , O6F2 , O2F
  • NF3 nitrogen trifluoride
  • magnesium and fluorine are used as the additive element A1.
  • Lithium fluoride (LiF) is prepared as a fluorine source
  • magnesium fluoride (MgF 2 ) is prepared as a fluorine source and a magnesium source.
  • the amount of lithium fluoride increases, there is a concern that the lithium becomes too excessive and the cycle characteristics deteriorate.
  • the term “nearby” refers to a value that is greater than 0.9 times and smaller than 1.1 times the value.
  • Step S22> 12A the magnesium source and the fluorine source are pulverized and mixed. This step can be performed under the pulverization and mixing conditions selected from those described in step S12.
  • step S23 shown in Fig. 12A the above-mentioned crushed and mixed materials can be collected to obtain the A1 source.
  • the A1 source shown in step S23 has a plurality of starting materials and can be called a mixture.
  • the particle size of the mixture is preferably D50 (median diameter) 600 nm to 10 ⁇ m, more preferably 1 ⁇ m to 5 ⁇ m. Even when a single material is used as the source of the additive element, the D50 (median diameter) is preferably 600 nm to 10 ⁇ m, more preferably 1 ⁇ m to 5 ⁇ m.
  • Such a finely powdered mixture makes it easier to uniformly attach the mixture to the surface of the lithium cobalt oxide particles when mixed with the lithium cobalt oxide in a later process. If the mixture is uniformly attached to the surface of the lithium cobalt oxide particles, this is preferable because it makes it easier to uniformly distribute or diffuse the additive element in the surface layer 100a of the composite oxide after heating.
  • lithium cobalt oxide and an Al source are mixed together.
  • the mixing conditions in step S31 are preferably milder than those in step S12 so as not to destroy the shape of the lithium cobalt oxide particles.
  • dry mixing is a milder method than wet mixing.
  • a ball mill, bead mill, etc. can be used for mixing.
  • zirconium oxide balls it is preferable to use zirconium oxide balls as the media.
  • the materials are mixed dry in a ball mill using zirconium oxide balls with a diameter of 1 mm at 150 rpm for 1 hour.
  • the mixing is carried out in a dry room with a dew point of -100°C or higher and -10°C or lower.
  • Step S32> 11 the mixed material is collected to obtain a mixture 901.
  • the material may be crushed and then sieved, if necessary.
  • step S33 shown in Fig. 11 the mixture 901 is heated.
  • the heating conditions can be selected from those described in step S13.
  • the heating time is preferably 2 hours or more.
  • the pressure inside the furnace may be higher than atmospheric pressure in order to increase the oxygen partial pressure of the heating atmosphere. This is because if the oxygen partial pressure of the heating atmosphere is insufficient, cobalt, etc. will be reduced, and lithium cobalt oxide, etc. may not be able to maintain the layered rock salt type crystal structure.
  • the lower limit of the heating temperature in step S33 must be equal to or higher than the temperature at which the reaction between the lithium cobalt oxide and the additive element source proceeds.
  • the temperature at which the reaction proceeds may be any temperature at which mutual diffusion of elements contained in the lithium cobalt oxide and the additive element source occurs, and may be lower than the melting temperature of these materials.
  • An oxide is used as an example for explanation, and it is known that solid-phase diffusion occurs at a temperature 0.757 times the melting temperature Tm (Tammann temperature Td ). Therefore, the heating temperature in step S33 may be 650°C or higher.
  • the reaction proceeds more easily if the temperature is equal to or higher than the melting temperature of one or more of the materials contained in the mixture 901.
  • the eutectic point of LiF and MgF2 is around 742°C, so that the lower limit of the heating temperature in step S33 is preferably set to 742°C or higher.
  • the lower limit of the heating temperature is more preferably 830° C. or higher.
  • the upper limit of the heating temperature is below the decomposition temperature of lithium cobalt oxide (1130°C). At temperatures close to the decomposition temperature, there is concern that lithium cobalt oxide may decompose, albeit only in small amounts. Therefore, a temperature of 1000°C or less is more preferable, 950°C or less is even more preferable, and 900°C or less is even more preferable.
  • the heating temperature in step S33 is preferably 650°C to 1130°C, more preferably 650°C to 1000°C, even more preferably 650°C to 950°C, and even more preferably 650°C to 900°C.
  • 742°C to 1130°C is preferred, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C.
  • 800°C to 1100°C, 830°C to 1130°C is preferred, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C.
  • some materials for example LiF, which is a fluorine source, may function as a flux.
  • This function allows the heating temperature to be lowered below the decomposition temperature of lithium cobalt oxide, for example to between 742°C and 950°C, and additive elements such as magnesium can be distributed in the surface layer to produce a positive electrode active material with good characteristics.
  • LiF has a lower specific gravity in a gaseous state than oxygen
  • LiF may volatilize or sublime when heated, and if it volatilizes, the amount of LiF in the mixture 901 will decrease. This weakens its function as a flux. Therefore, it is necessary to heat while suppressing the volatilization of LiF.
  • LiF is not used as the fluorine source, etc.
  • Li on the LiCoO2 surface may react with F of the fluorine source to produce LiF, which may volatilize. Therefore, even if a fluoride with a melting point higher than LiF is used, it is necessary to suppress the volatilization in the same way.
  • the heating in this process is preferably performed so that the particles of mixture 901 do not stick to each other. If the particles of mixture 901 stick to each other during heating, the contact area with oxygen in the atmosphere decreases, and the route along which the added elements (e.g., fluorine) diffuse is blocked, which may result in poor distribution of the added elements (e.g., magnesium and fluorine) in the surface layer.
  • the added elements e.g., fluorine
  • the additive element e.g., fluorine
  • a smooth positive electrode active material with few irregularities can be obtained. Therefore, in order to maintain the smooth state of the surface after the heating in step S15 in this process or to make it even smoother, it is better for the particles of mixture 901 not to stick together.
  • the flow rate of the oxygen-containing atmosphere in the kiln When heating in a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere in the kiln. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to first purge the atmosphere and not flow the atmosphere after introducing the oxygen atmosphere into the kiln. Flowing oxygen can cause the fluorine source to evaporate, which is not preferable in terms of maintaining the smoothness of the surface.
  • the mixture 901 can be heated in an atmosphere containing LiF, for example, by placing a lid on a container containing the mixture 901.
  • the heating time varies depending on conditions such as the heating temperature, the size of the lithium cobalt oxide in step S14, and the composition. When the lithium cobalt oxide is small, a lower temperature or a shorter heating time may be more preferable than when the lithium cobalt oxide is large.
  • the heating temperature is preferably, for example, 650° C. or more and 950° C. or less.
  • the heating time is preferably, for example, 3 hours or more and 60 hours or less, more preferably 10 hours or more and 30 hours or less, and even more preferably about 20 hours.
  • the cooling time after heating is preferably, for example, 10 hours or more and 50 hours or less.
  • the heating temperature is preferably, for example, 650° C. or higher and 950° C. or lower.
  • the heating time is preferably, for example, 1 hour or higher and 10 hours or lower, and more preferably about 5 hours.
  • the cooling time after heating is preferably, for example, 10 hours or higher and 50 hours or lower.
  • step S34 shown in FIG. 11 the heated material is recovered and crushed as necessary to obtain a composite oxide 902.
  • an additive element source (A2 source) is required.
  • the additive element A2 can be the additive element described in step S21.
  • nickel and aluminum are used as the additive element A2.
  • Nickel oxide, nickel hydroxide, etc. can be used as the nickel source.
  • Aluminum oxide, aluminum hydroxide, etc. can be used as the aluminum source.
  • steps S41 to S43 of FIG. 12B the nickel source and the aluminum source can be crushed to obtain the A2 source.
  • the conditions of step S22 can be referred to for the crushing conditions.
  • Step S51> 11 the composite oxide 902 is mixed with the A2 source.
  • the description of step S31 can be referred to for the mixing conditions.
  • Step S52> 11 the mixed material is recovered to obtain a mixture 903.
  • the material may be crushed and then sieved, if necessary.
  • Step S53> 11 the mixture 903 is heated.
  • the heating conditions can be found in the description of step S33.
  • Step S54 Next, in step S54 shown in FIG. 11, the heated material is recovered and crushed as necessary to obtain a composite oxide 904.
  • an additive element source (A3 source) is required.
  • the additive element A3 can be the additive element described in step S21.
  • titanium is used as the additive element A3.
  • Lithium titanate, titanium oxide, titanium hydroxide, etc. can be used as the titanium source.
  • the titanium source can be pulverized to obtain the A3 source.
  • the pulverization conditions can refer to the conditions in step S22.
  • Step S71> 11 the composite oxide 904 is mixed with the A3 source.
  • the description of step S31 can be referred to for the mixing conditions.
  • Step S72> 11 the mixed material is recovered to obtain a mixture 905.
  • the material may be crushed and then sieved, if necessary.
  • Step S73> 11 the mixture 905 is heated.
  • the heating conditions can be found in the description of step S33.
  • step S74 shown in Fig. 11 the heated material is collected and crushed as necessary to obtain the positive electrode active material 100. At this time, it is preferable to further sieve the collected particles.
  • the positive electrode active material 100 of one embodiment of the present invention can be produced.
  • the positive electrode active material of one embodiment of the present invention has a smooth surface.
  • the positive electrode active material 100 with a smooth surface may be more resistant to physical destruction caused by pressure, etc., than a positive electrode active material that does not have a smooth surface.
  • the positive electrode active material 100 is less likely to be destroyed in a test involving the application of pressure, such as a nail penetration test, and as a result, safety may be increased.
  • the initial heating causes lithium to be released from part of the surface layer 100a of the lithium cobalt oxide, resulting in a better distribution of the added elements.
  • the distribution of the additive elements can be easily differentiated by initial heating through the following mechanism.
  • lithium is released from a part of the surface layer 100a by initial heating.
  • the lithium cobalt oxide having the lithium-deficient surface layer 100a is mixed with additive element sources such as nickel source, aluminum source, and magnesium source and heated.
  • additive element sources such as nickel source, aluminum source, and magnesium source and heated.
  • magnesium is a typical divalent element
  • nickel is a transition metal but is prone to becoming a divalent ion. Therefore, a rock salt phase containing Mg 2+ and Ni 2+ , and Co 2+ reduced by the deficiency of lithium is formed in a part of the surface layer 100a.
  • this phase is formed in a part of the surface layer 100a, it may not be clearly confirmed in an electron microscope image such as STEM and an electron beam diffraction pattern.
  • nickel is likely to dissolve and diffuse to the interior 100b when the surface layer 100a is a layered rock-salt type lithium cobalt oxide, but is likely to remain in the surface layer 100a when part of the surface layer 100a is of the rock-salt type. Therefore, by performing initial heating, it is possible to make it easier for divalent additive elements such as nickel to remain in the surface layer 100a.
  • the effect of this initial heating is particularly large on the surface other than the (001) orientation of the positive electrode active material 100 and on its surface layer 100a.
  • the Me-O distance in rock salt Ni0.5Mg0.5O is 2.09 ⁇
  • the Me - O distance in rock salt MgO is 2.11 ⁇ .
  • the Me-O distance in spinel NiAl2O4 is 2.0125 ⁇
  • the Me-O distance in spinel MgAl2O4 is 2.02 ⁇ .
  • the bond distance between metals other than lithium and oxygen is shorter than the above.
  • the Al-O distance in layered rock salt type LiAlO2 is 1.905 ⁇ (Li-O distance is 2.11 ⁇ ).
  • the Co-O distance in layered rock salt type LiCoO2 is 1.9224 ⁇ (Li-O distance is 2.0916 ⁇ ).
  • Non-Patent Document 8 the ionic radius of hexacoordinated aluminum is 0.535 ⁇ , and the ionic radius of hexacoordinated oxygen is 1.4 ⁇ , the sum of which is 1.935 ⁇ .
  • Initial heating is also expected to have the effect of increasing the crystallinity of the layered rock salt type crystal structure in the interior 100b.
  • a method 2 for producing a positive electrode active material which is one embodiment of the present invention and is different from the method 1 for producing a positive electrode active material, will be described with reference to Fig. 13A and Fig. 13B.
  • the method 2 for producing a positive electrode active material differs from the method 1 for producing a positive electrode active material mainly in the number of times that an additive element is added. For other descriptions, the description of the method 1 can be referred to.
  • the preparation method in which the additive element is added only after LiMO2 is prepared has been described, but the present invention is not limited to the above method.
  • the additive element may be added at another timing or multiple times. The timing may be changed depending on the element.
  • an additive element may be added to the lithium source and the cobalt source in step S11, that is, at the stage of the starting material for the composite oxide.
  • the additive element source added at this time is shown as the A0 source in FIG. 13A.
  • step S13 lithium cobalt oxide containing the additive element can be obtained.
  • steps S11 to S14 there is no need to separate the steps S11 to S14 from the steps S21 to S23. This can be said to be a simple and highly productive method.
  • lithium cobalt oxide that already contains some of the added elements.
  • steps S11 to S14 and some of the steps in step S20 can be omitted. This is a simple and highly productive method.
  • Additional elements may also be added to lithium cobalt oxide to which magnesium and fluorine have already been added.
  • This embodiment can be used in combination with other embodiments.
  • Example of secondary battery configuration The following description will be given taking as an example a secondary battery shown in FIG. 14 in which a positive electrode, a negative electrode, and an electrolyte are enclosed in an exterior body.
  • the positive electrode includes a positive electrode active material layer and a positive electrode current collector.
  • the positive electrode active material layer includes a positive electrode active material, and may include a conductive material (synonymous with a conductive additive) and a binder.
  • the positive electrode active material is prepared by the method described in the above embodiment.
  • the positive electrode active material described in the previous embodiment may be mixed with other positive electrode active materials.
  • positive electrode active material examples include composite oxides having an olivine type crystal structure, a layered rock salt type crystal structure, or a spinel type crystal structure, such as LiFePO4 , LiFeO2 , LiNiO2 , LiMn2O4 , V2O5 , Cr2O5 , and MnO2 .
  • LiNiO2 or LiNi1 - xMxO2 (0 ⁇ x ⁇ 1 ) (M Co, Al, etc. ) )
  • LiMn2O4 lithium nickel oxide
  • the characteristics of the secondary battery can be improved.
  • the conductive material is also called a conductive agent or conductive assistant, and is made of a carbon material.
  • attaching does not only refer to the physical adhesion between the active material and the conductive material, but also includes the case where a covalent bond is formed, the case where the conductive material is bonded by van der Waals forces, the case where the conductive material covers a part of the surface of the active material, the case where the conductive material is embedded in the surface irregularities of the active material, and the case where the two materials are electrically connected even if they are not in contact with each other.
  • the active material layers such as the positive electrode active material layer and the negative electrode active material layer, preferably contain a conductive material.
  • the conductive material for example, one or more of the following can be used: carbon black such as acetylene black and furnace black; graphite such as artificial graphite and natural graphite; carbon fibers such as carbon nanofibers and carbon nanotubes; and graphene compounds.
  • carbon fiber for example, mesophase pitch-based carbon fiber, isotropic pitch-based carbon fiber, etc. can be used.
  • carbon nanofiber or carbon nanotube can be used as the carbon fiber. Carbon nanotube can be produced, for example, by vapor phase growth method.
  • graphene compounds include graphene, multi-layer graphene, multi-graphene, graphene oxide, multi-layer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc.
  • Graphene compounds have carbon, have a shape such as a plate or sheet, and have a two-dimensional structure formed of six-membered carbon rings. The two-dimensional structure formed of six-membered carbon rings may be called a carbon sheet.
  • Graphene compounds may have functional groups.
  • graphene compounds preferably have a curved shape.
  • graphene compounds may be rolled up to resemble carbon nanofibers.
  • graphene oxide refers to a material that contains carbon and oxygen, has a sheet-like shape, and has functional groups, particularly epoxy groups, carboxy groups, or hydroxy groups.
  • reduced graphene oxide refers to a material that has carbon and oxygen, has a sheet-like shape, and has a two-dimensional structure formed of six-membered carbon rings. Although reduced graphene oxide can function as a single sheet, multiple sheets may be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic% and the oxygen concentration is 2 atomic% or more and 15 atomic% or less. By setting such carbon and oxygen concentrations, it can function as a highly conductive conductive material even in small amounts. In addition, reduced graphene oxide preferably has an intensity ratio G/D of the G band and the D band in the Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive conductive material even in small amounts.
  • Graphene compounds may have excellent electrical properties, such as high electrical conductivity, and excellent physical properties, such as high flexibility and high mechanical strength.
  • graphene compounds have a sheet-like shape.
  • Graphene compounds may have a curved surface, enabling surface contact with low contact resistance.
  • the graphene compound may cover 80% or more of the area of the active material. It is preferable that the graphene compound is wrapped around at least a part of the active material particles.
  • the graphene compound is overlapped on at least a part of the active material particles. It is also preferable that the shape of the graphene compound matches at least a part of the shape of the active material particles.
  • the shape of the active material particles refers to, for example, the unevenness of a single active material particle or the unevenness formed by multiple active material particles. It is also preferable that the graphene compound surrounds at least a part of the active material particles.
  • the graphene compound may also have holes.
  • active material particles with a small particle size for example, active material particles of 1 ⁇ m or less
  • the specific surface area of the active material particles is large, and more conductive paths connecting the active material particles are required.
  • Rapid charging and rapid discharging characteristics may be required for secondary batteries for two- or four-wheeled vehicles and secondary batteries for drones. Rapid charging characteristics may also be required for mobile electronic devices. Rapid charging and discharging refers to charging and discharging at 200 mA/g, 400 mA/g, or 1000 mA/g or more per weight of the positive electrode active material.
  • the multiple graphenes or graphene compounds are formed so as to partially cover the multiple granular positive electrode active materials or to be attached to the surfaces of the multiple granular positive electrode active materials, and therefore are preferably in surface contact with each other.
  • a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed by bonding multiple graphenes or graphene compounds together.
  • the graphene net can also function as a binder that bonds the active materials together. This allows the amount of binder to be reduced or not used at all, thereby improving the ratio of active material to the electrode volume and electrode weight. In other words, the discharge capacity of the secondary battery can be increased.
  • a material used in forming the graphene compound may be mixed with the graphene compound and used in the active material layer.
  • particles used as a catalyst in forming the graphene compound may be mixed with the graphene compound.
  • catalysts used in forming the graphene compound include particles having silicon oxide (SiO 2 , SiO x (x ⁇ 2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc.
  • the particles preferably have a median diameter (D50) of 1 ⁇ m or less, more preferably 100 nm or less.
  • the content of the conductive material relative to the total amount of the active material layer is preferably 1 wt% or more and 10 wt% or less, and more preferably 1 wt% or more and 5 wt% or less.
  • graphene compounds Unlike granular conductive materials such as carbon black, which make point contact with the active material, graphene compounds enable surface contact with low contact resistance, so a smaller amount than normal conductive materials can improve the electrical conductivity between the granular active material and the graphene compound. This makes it possible to increase the ratio of active material in the active material layer, thereby increasing the discharge capacity of the battery.
  • Particulate carbon-containing compounds such as carbon black and graphite, or fibrous carbon-containing compounds such as carbon nanotubes, tend to enter tiny spaces.
  • a tiny space refers to, for example, the area between multiple active materials.
  • the density of the electrode can be increased and an excellent conductive path can be formed.
  • a battery obtained by the manufacturing method of one embodiment of the present invention has a high capacity density and is stable, making it effective as an in-vehicle battery.
  • Binder As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Also, as the binder, fluororubber can be used.
  • SBR styrene-butadiene rubber
  • fluororubber can be used as the binder.
  • a water-soluble polymer as the binder.
  • polysaccharides can be used as the water-soluble polymer.
  • the polysaccharide one or more of cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, and starch can be used.
  • CMC carboxymethyl cellulose
  • methyl cellulose methyl cellulose
  • ethyl cellulose methyl cellulose
  • hydroxypropyl cellulose diacetyl cellulose
  • regenerated cellulose regenerated cellulose
  • polystyrene polymethyl acrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose as the binder.
  • PVDF polyvinylidene fluoride
  • PAN polyacrylonitrile
  • the current collector As the current collector, a material having high electrical conductivity, such as metals such as stainless steel, gold, platinum, aluminum, and titanium, and alloys thereof, can be used. In addition, it is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. In addition, an aluminum alloy to which an element that improves heat resistance, such as silicon, titanium, neodymium, scandium, or molybdenum, is added can be used. In addition, it may be formed of a metal element that reacts with silicon to form a silicide.
  • Examples of metal elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel.
  • the current collector can be appropriately used in a shape such as a foil, plate, sheet, mesh, punched metal, or expanded metal. It is preferable to use a current collector having a thickness of 5 ⁇ m or more and 30 ⁇ m or less.
  • the additive element whose oxide can become a semiconductor, as described in the first embodiment may be attached to the surface of the negative electrode and/or positive electrode active material. Specifically, it may be attached to the surface of the active material as particles of nickel oxide (NiO), copper oxide, copper, or the like. This can increase the contact area between the particles containing the additive element and the active material and the current collector. This is expected to reduce the impedance of the positive electrode and/or negative electrode.
  • soft copper which is a type of copper, is expected to have a large effect because it has good elongation and excellent conductivity.
  • the negative electrode includes a negative electrode active material layer and a negative electrode current collector.
  • the negative electrode active material layer may include a conductive material and a binder.
  • Negative electrode active material for example, an alloy-based material and/or a carbon-based material can be used.
  • an element capable of carrying out a charge/discharge reaction by alloying/dealloying reaction with lithium can be used.
  • a material containing one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used.
  • Such elements have a larger charge/discharge capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh/g. For this reason, it is preferable to use silicon as the negative electrode active material. Compounds containing these elements may also be used.
  • Examples include SiO , Mg2Si , Mg2Ge , SnO, SnO2 , Mg2Sn , SnS2 , V2Sn3 , FeSn2, CoSn2 , Ni3Sn2 , Cu6Sn5, Ag3Sn , Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7 , CoSb3 , InSb , SbSn , etc.
  • elements capable of carrying out charge/discharge reactions by alloying/dealloying reactions with lithium, and compounds containing such elements may be referred to as alloy - based materials.
  • SiO refers to, for example, silicon monoxide.
  • SiO can be expressed as SiO x .
  • x preferably has a value close to 1.
  • x is preferably 0.2 or more and 1.5 or less, more preferably 0.3 or more and 1.2 or less.
  • x is preferably 0.2 or more and 1.2 or less.
  • x is preferably 0.3 or more and 1.5 or less.
  • Carbon-based materials that can be used include graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc.
  • Graphite includes artificial graphite, natural graphite, etc.
  • artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, etc.
  • MCMB mesocarbon microbeads
  • spherical graphite having a spherical shape can be used as the artificial graphite.
  • MCMB may have a spherical shape, which is preferable.
  • it is relatively easy to reduce the surface area of MCMB which may be preferable.
  • natural graphite include flake graphite, spheroidized natural graphite, etc.
  • graphite When lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed), graphite exhibits a low potential (0.05 V to 0.3 V vs. Li/Li + ) similar to that of lithium metal. This allows lithium ion secondary batteries to exhibit a high operating voltage. Furthermore, graphite is preferable because it has the advantages of a relatively high charge/discharge capacity per unit volume, a relatively small volume expansion, low cost, and high safety compared to lithium metal.
  • oxides such as titanium dioxide ( TiO2 ), lithium titanium oxide ( Li4Ti5O12 ), lithium- graphite intercalation compound ( LixC6 ), niobium pentoxide ( Nb2O5 ), tungsten oxide ( WO2 ), and molybdenum oxide ( MoO2 ) can be used.
  • Li2.6Co0.4N3 is preferable because it shows a large charge/discharge capacity (900mAh/g, 1890mAh/ cm3 ).
  • the composite nitride of lithium and a transition metal When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, and therefore it is preferable that the composite nitride of lithium and a transition metal can be combined with a material that does not contain lithium ions as a positive electrode active material, such as V 2 O 5 or Cr 3 O 8. Even when a material that contains lithium ions is used as the positive electrode active material, the composite nitride of lithium and a transition metal can be used as the negative electrode active material by desorbing the lithium ions contained in the positive electrode active material in advance.
  • a material that undergoes a conversion reaction can be used as the negative electrode active material.
  • a transition metal oxide that does not form an alloy with lithium such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO) may be used as the negative electrode active material.
  • materials that undergo a conversion reaction include oxides such as Fe2O3 , CuO, Cu2O , RuO2 , and Cr2O3 , sulfides such as CoS0.89 , NiS, and CuS, nitrides such as Zn3N2 , Cu3N , and Ge3N4 , phosphides such as NiP2 , FeP2 , and CoP3 , and fluorides such as FeF3 and BiF3 .
  • oxides such as Fe2O3 , CuO, Cu2O , RuO2 , and Cr2O3
  • sulfides such as CoS0.89 , NiS, and CuS
  • nitrides such as Zn3N2 , Cu3N , and Ge3N4
  • phosphides such as NiP2 , FeP2 , and CoP3
  • fluorides such as FeF3 and BiF3 .
  • the conductive material and binder that the negative electrode active material layer can have can be the same materials as the conductive material and binder that the positive electrode active material layer can have.
  • the negative electrode current collector may be made of the same material as the positive electrode current collector, but it is preferable that the negative electrode current collector is made of a material that does not form an alloy with carrier ions such as lithium.
  • an electrolyte solution having a solvent and an electrolyte dissolved in the solvent can be used.
  • the electrolyte solution has a solvent and a lithium salt.
  • an aprotic organic solvent is preferable, and for example, one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, ⁇ -butyrolactone, ⁇ -valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide,
  • a mixed organic solvent containing a fluorinated cyclic carbonate (sometimes written as a fluorinated cyclic carbonate) or a fluorinated chain carbonate (sometimes written as a fluorinated chain carbonate) can be used as the electrolyte.
  • the mixed organic solvent contains both a fluorinated cyclic carbonate and a fluorinated chain carbonate. Both the fluorinated cyclic carbonate and the fluorinated chain carbonate have a substituent that exhibits electron-withdrawing properties, and are preferable because they lower the solvation energy of lithium ions. Therefore, both the fluorinated cyclic carbonate and the fluorinated chain carbonate are suitable for the electrolyte, and these mixed organic solvents are suitable.
  • fluorinated cyclic carbonates examples include fluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), and tetrafluoroethylene carbonate (F4EC).
  • DFEC has isomers such as cis-4,5 and trans-4,5. All of the fluorinated cyclic carbonates have electron-withdrawing substituents, so the solvation energy of lithium ions is thought to be low. In FEC, the electron-withdrawing substituent is an F group.
  • a fluorinated chain carbonate is methyl 3,3,3-trifluoropropionate.
  • the abbreviation for methyl 3,3,3-trifluoropropionate is "MTFP.”
  • MTFP the electron-withdrawing substituent is a CF3 group.
  • FEC is one of the cyclic carbonates and has a high dielectric constant, so when used in an organic solvent, it has the effect of promoting the dissociation of lithium salts.
  • FEC has a substituent that shows electron-withdrawing properties, so it is easier to desolvate with lithium ions than ethylene carbonate (EC).
  • EC ethylene carbonate
  • the solvation energy of lithium ions in FEC is smaller than that of EC that does not have a substituent that shows electron-withdrawing properties. Therefore, it is easier to separate lithium ions on the surface of the positive electrode active material and the surface of the negative electrode active material, and the internal resistance of the secondary battery can be reduced.
  • FEC has a deep highest occupied molecular orbital (HOMO)
  • HOMO deep highest occupied molecular orbital
  • FEC has a high viscosity. Therefore, it is recommended to use a mixed organic solvent that further contains MTFP in the electrolyte, rather than just FEC.
  • MTFP is a type of chain carbonate, and can reduce the viscosity of the electrolyte, or maintain the viscosity at room temperature (typically 25°C) even at low temperatures (typically 0°C).
  • MTFP has a smaller solvation energy than methyl propionate (abbreviated as "MP"), which does not have a substituent that exhibits electron-withdrawing properties, it may form a solvate with lithium ions when used in an electrolyte.
  • MP methyl propionate
  • the organic solvent described above is preferably highly purified with a low content of granular dust or molecules other than the constituent molecules of the organic solvent (hereinafter simply referred to as "impurities", including oxygen (O2), water (H2O) or moisture). It is also preferable that the reaction by-products during synthesis are suppressed through appropriate purification.
  • the impurities in the electrolyte are 100 ppm or less, preferably 50 ppm or less, and more preferably less than 10 ppm.
  • the concentration of moisture among the impurities can be detected by Karl Fischer titration.
  • the above-mentioned organic solvent has almost no peaks due to impurities confirmed by NMR measurement or the like. Almost no peaks can be confirmed includes a ratio of the integrated area of the peak due to the impurity to the integrated area of the peak due to the main component (simply referred to as integral ratio) of 0.005 or less, preferably 0.002 or less.
  • integral ratio a ratio of the integrated area of the peak due to the impurity to the integrated area of the peak due to the main component (simply referred to as integral ratio) of 0.005 or less, preferably 0.002 or less.
  • the total content of the mixed organic solvent containing FEC and MTFP having such physical properties is 100 vol%, and it is recommended to mix them so that the volume ratio is x:100-x (where 5 ⁇ x ⁇ 30, preferably 10 ⁇ x ⁇ 20). In other words, it is recommended to mix them so that there is more MTFP than FEC in the mixed organic solvent.
  • the ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion.
  • Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations.
  • Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.
  • lithium salts also called electrolytes
  • examples of lithium salts (also called electrolytes) dissolved in the above- mentioned solvent include LiPF6 , LiClO4 , LiAsF6 , LiBF4 , LiAlCl4 , LiSCN, LiBr , LiI, Li2SO4 , Li2B10Cl10, Li2B12Cl12 , LiCF3SO3 , LiC4F9SO3 , LiC ( CF3SO2 ) 3 , LiC ( C2F5SO2 ) 3 , LiN (CF3SO2 ) 2 , LiN ( C4F9SO2 ) ( CF3SO2 ) , LiN ( C2F5SO2 ) .
  • the lithium salt may be 0.5 mol/L or more and 3.0 mol/L or less relative to the solvent.
  • fluorides such as LiPF 6 and LiBF 4 improves the safety of the lithium ion secondary battery.
  • the above-mentioned electrolyte is preferably a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities").
  • impurities a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities").
  • the weight ratio of impurities to the electrolyte is 1 wt% or less, preferably 0.1 wt% or less, and more preferably 0.01 wt% or less.
  • the electrolyte may contain an additive.
  • the additive can suppress the reactive decomposition of the electrolyte that may occur on the positive electrode surface or the negative electrode surface when the secondary battery is operated at high voltage and/or high temperature.
  • vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), and lithium bis(oxalate)borate (LiBOB) can be used as the additive.
  • LiBOB is particularly preferred because it is easy to form a good coating.
  • VC or FEC is preferred because it can form a good coating on the negative electrode during aging or charging in the early stages of use of the secondary battery, thereby improving the cycle characteristics.
  • one or more dinitrile compounds can be used as the additive.
  • dinitrile compounds include succinonitrile, glutaronitrile, adiponitrile (ADN), and ethylene glycol bis(propionitrile) ether (EGBE).
  • fluorobenzene may be added to the organic solvent.
  • concentration of the additive may be, for example, 0.1 wt% or more and 5 wt% or less with respect to the entire electrolyte.
  • PS or EGBE are preferable because they form a good coating on the positive electrode during charging and discharging, improving cycle characteristics.
  • FB is preferable because it improves the wettability of the organic solvent to the positive electrode and negative electrode.
  • Dinitrile compounds are preferable because the nitrile groups are oriented to the positive electrode and negative electrode, inhibiting the oxidative decomposition of the organic solvent, improving voltage resistance.
  • dinitrile compounds are preferable because they can prevent copper dissolution during overdischarge when a current collector having copper is used for the negative electrode. Considering the use of secondary batteries at high voltages, it is preferable to add a nitrile compound.
  • Gel electrolyte As the gel electrolyte, a polymer gel in which a polymer is swollen with an electrolytic solution may be used. By using a polymer gel electrolyte, a semi-solid electrolyte layer can be provided, and safety against leakage and the like can be improved. In addition, it is possible to make the secondary battery thinner and lighter.
  • Polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, fluorine-based polymer gel, etc.
  • polymer for example, a polymer having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and copolymers containing these can be used.
  • PEO polyethylene oxide
  • PVDF-HFP which is a copolymer of PVDF and hexafluoropropylene (HFP)
  • the polymer formed may also have a porous shape.
  • Solid electrolyte instead of the electrolyte, a solid electrolyte having an inorganic material such as a sulfide or oxide, or a solid electrolyte having a polymer material such as a PEO (polyethylene oxide) can be used.
  • a solid electrolyte When a solid electrolyte is used, the installation of a separator and/or a spacer becomes unnecessary.
  • the entire battery can be solidified, there is no risk of leakage, and safety is dramatically improved.
  • the secondary battery preferably has a separator.
  • the separator may be made of, for example, paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic, polyolefin, or polyurethane.
  • the separator is preferably processed into an envelope shape and disposed so as to encase either the positive electrode or the negative electrode.
  • the separator may have a multi-layer structure.
  • an organic material film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture of these.
  • ceramic materials that can be used include aluminum oxide particles and silicon oxide particles.
  • fluorine materials that can be used include PVDF and polytetrafluoroethylene.
  • polyamide materials that can be used include nylon and aramid (meta-aramid, para-aramid).
  • Coating with ceramic-based materials improves oxidation resistance, suppressing the deterioration of the separator during high-voltage charging and improving the reliability of the secondary battery. Coating with fluorine-based materials also makes it easier for the separator and electrodes to adhere to each other, improving output characteristics. Coating with polyamide-based materials, especially aramid, improves heat resistance, improving the safety of the secondary battery.
  • both sides of a polypropylene film may be coated with a mixture of aluminum oxide and aramid.
  • the surface of the polypropylene film that comes into contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the surface that comes into contact with the negative electrode may be coated with a fluorine-based material.
  • the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, so the discharge capacity per volume of the secondary battery can be increased.
  • the exterior body of the secondary battery can be made of, for example, a metal material such as aluminum and/or a resin material.
  • a film-shaped exterior body can also be used.
  • the film for example, a three-layer structure film can be used in which a thin metal film having excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film such as a polyamide-based resin or polyester-based resin is further provided on the thin metal film as the outer surface of the exterior body.
  • Fig. 14 and Fig. 15 show a positive electrode 503 having a positive electrode current collector 501 and a positive electrode active material layer 502, a negative electrode 506 having a negative electrode current collector 504 and a negative electrode active material layer 505, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.
  • the laminated secondary battery has a flexible structure, when it is mounted in an electronic device having at least a part having flexibility, the secondary battery can also be bent in accordance with the deformation of the electronic device.
  • An example of a method for manufacturing the laminated secondary battery will be described with reference to Figs. 15A to 15C.
  • FIG. 15B shows the laminated negative electrode 506, separator 507, and positive electrode 503.
  • an example is shown in which five sets of negative electrodes and four sets of positive electrodes are used.
  • the tab regions of the positive electrodes 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode.
  • ultrasonic welding may be used for the joining.
  • the tab regions of the negative electrodes 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.
  • the negative electrode 506, separator 507, and positive electrode 503 are placed on the exterior body 509.
  • the exterior body 509 is folded at the portion indicated by the dashed line. After that, the outer periphery of the exterior body 509 is joined.
  • the joining for example, thermocompression bonding or the like may be used.
  • an area (hereinafter referred to as an inlet) that is not joined is provided on a part (or one side) of the exterior body 509 so that the electrolyte can be introduced later.
  • an electrolyte (not shown) is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509.
  • the electrolyte is preferably introduced under a reduced pressure atmosphere or an inert atmosphere.
  • the inlet is joined. In this manner, a laminated secondary battery 500 can be produced.
  • FIGs. 16A to 16G An example of mounting a secondary battery having the positive electrode active material described in the previous embodiment in an electronic device is shown in Figs. 16A to 16G.
  • Examples of electronic devices to which secondary batteries are applied include television devices (also called televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game machines, personal digital assistants, audio playback devices, and large game machines such as pachinko machines.
  • secondary batteries with a flexible shape can be incorporated into the interior or exterior walls of houses and buildings, and along the curved surfaces of the interior or exterior of automobiles.
  • FIG. 16A shows an example of a mobile phone.
  • the mobile phone 7400 includes a display portion 7402 built into a housing 7401, operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like.
  • the mobile phone 7400 includes a secondary battery 7407.
  • the secondary battery of one embodiment of the present invention as the secondary battery 7407, a lightweight mobile phone with a long life can be provided.
  • FIG. 16B shows the mobile phone 7400 in a bent state.
  • the secondary battery 7407 installed inside is also bent.
  • FIG. 16C shows the state of the bent secondary battery 7407 at that time.
  • the secondary battery 7407 is a thin storage battery.
  • the secondary battery 7407 is fixed in a bent state.
  • the secondary battery 7407 has a lead electrode electrically connected to the current collector.
  • the current collector is copper foil, and a part of it is alloyed with gallium to improve adhesion with the active material layer in contact with the current collector, resulting in a configuration with high reliability when the secondary battery 7407 is bent.
  • FIG. 16D shows an example of a bangle-type display device.
  • the portable display device 7100 includes a housing 7101, a display unit 7102, an operation button 7103, and a secondary battery 7104.
  • FIG. 16E shows a bent secondary battery 7104.
  • the housing deforms, and the curvature of the secondary battery 7104 changes in part or in whole.
  • the degree of bending at any point on the curve expressed by the value of the radius of the corresponding circle is called the radius of curvature, and the reciprocal of the radius of curvature is called the curvature.
  • the housing or the main surface of the secondary battery 7104 changes in part or in whole when the radius of curvature is in the range of 40 mm to 150 mm. If the radius of curvature on the main surface of the secondary battery 7104 is in the range of 40 mm to 150 mm, high reliability can be maintained.
  • a secondary battery of one embodiment of the present invention as the secondary battery 7104, a lightweight portable display device with a long life can be provided.
  • FIG. 16F shows an example of a wristwatch-type mobile information terminal.
  • the mobile information terminal 7200 includes a housing 7201, a display portion 7202, a band 7203, a buckle 7204, operation buttons 7205, an input/output terminal 7206, and the like.
  • the portable information terminal 7200 can execute various applications such as mobile phone calls, e-mail, text browsing and creation, music playback, Internet communications, and computer games.
  • the display surface of the display unit 7202 is curved, and display can be performed along the curved display surface.
  • the display unit 7202 also has a touch sensor, and can be operated by touching the screen with a finger or a stylus. For example, an application can be started by touching an icon 7207 displayed on the display unit 7202.
  • the operation button 7205 can have various functions, such as time setting, power on/off operation, wireless communication on/off operation, silent mode activation/cancellation, and power saving mode activation/cancellation.
  • the functions of the operation button 7205 can be freely set by an operating system built into the mobile information terminal 7200.
  • the mobile information terminal 7200 is also capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless headset to enable hands-free calling.
  • the portable information terminal 7200 also includes an input/output terminal 7206, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input/output terminal 7206. Note that charging can also be performed by wireless power supply without using the input/output terminal 7206.
  • the display portion 7202 of the mobile information terminal 7200 includes a secondary battery of one embodiment of the present invention.
  • a lightweight mobile information terminal with a long life can be provided.
  • the secondary battery 7104 shown in FIG. 16E can be incorporated in a curved state inside the housing 7201 or in a bendable state inside the band 7203.
  • the mobile information terminal 7200 preferably has a sensor.
  • the mobile information terminal 7200 is equipped with a fingerprint sensor, a pulse sensor, a human body sensor such as a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, etc.
  • FIG. 16G shows an example of an armband-type display device.
  • the display device 7300 has a display portion 7304 and a secondary battery of one embodiment of the present invention.
  • the display device 7300 can also be provided with a touch sensor in the display portion 7304 and can also function as a portable information terminal.
  • the display surface of the display unit 7304 is curved, and display can be performed along the curved display surface.
  • the display device 7300 can change the display status by using standardized short-range wireless communication, etc.
  • the display device 7300 also has an input/output terminal, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the input/output terminal. Note that charging can also be performed by wireless power supply without using the input/output terminal.
  • a lightweight display device with a long life can be provided.
  • a secondary battery according to one embodiment of the present invention as a secondary battery in everyday electronic devices, it is possible to provide products that are lightweight and have a long life.
  • examples of everyday electronic devices include electric toothbrushes, electric shavers, and electric beauty devices.
  • the secondary batteries used in these products it is desirable to have a stick-shaped secondary battery that is easy for users to hold, is small, lightweight, and has a large discharge capacity.
  • the electronic cigarette 7500 is composed of an atomizer 7501 including a heating element, a secondary battery 7504 that supplies power to the atomizer, and a cartridge 7502 including a liquid supply bottle and a sensor.
  • a protection circuit that prevents overcharging and/or over-discharging of the secondary battery 7504 may be electrically connected to the secondary battery 7504.
  • the secondary battery 7504 shown in FIG. 16H has an external terminal so that it can be connected to a charging device. Since the secondary battery 7504 is the tip part when held, it is desirable that the total length is short and the weight is light.
  • the secondary battery of one embodiment of the present invention has a high discharge capacity and good cycle characteristics, so that a small and lightweight electronic cigarette 7500 that can be used for a long period of time can be provided.
  • FIG. 17A shows an example of a wearable device.
  • Wearable devices use secondary batteries as a power source. Furthermore, when used by a user at home or outdoors, there is a demand for wearable devices that can be charged wirelessly as well as via wired charging, with an exposed connector, in order to improve splash-proof, water-resistant, or dust-proof performance.
  • a secondary battery according to one embodiment of the present invention can be mounted on a glasses-type device 4000 as shown in FIG. 17A.
  • the glasses-type device 4000 has a frame 4000a and a display unit 4000b.
  • the glasses-type device 4000 can be made lightweight, well-balanced in weight, and capable of long continuous use.
  • a configuration can be realized that can accommodate space-saving features associated with a smaller housing.
  • the headset type device 4001 can be equipped with a secondary battery which is one embodiment of the present invention.
  • the headset type device 4001 has at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c.
  • a secondary battery can be provided in the flexible pipe 4001b and/or the earphone unit 4001c.
  • the secondary battery according to one embodiment of the present invention can be mounted on the device 4002 that can be directly attached to the body.
  • the secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002.
  • the secondary battery according to one embodiment of the present invention can be mounted on the device 4003 that can be attached to clothing.
  • the secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003.
  • the belt-type device 4006 can be equipped with a secondary battery according to one embodiment of the present invention.
  • the belt-type device 4006 has a belt portion 4006a and a wireless power receiving portion 4006b, and a secondary battery can be mounted inside the belt portion 4006a.
  • a configuration that can accommodate space saving associated with a smaller casing can be realized.
  • the secondary battery of one embodiment of the present invention can be mounted on the wristwatch device 4005.
  • the wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and a secondary battery can be provided on the display portion 4005a or the belt portion 4005b.
  • the display unit 4005a can display not only the time, but also various other information such as incoming emails and phone calls.
  • the wristwatch-type device 4005 is a wearable device that is worn directly on the arm, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's amount of exercise and health can be accumulated to manage the user's health.
  • FIG. 17B shows an oblique view of the wristwatch device 4005 removed from the wrist.
  • FIG. 17C shows a state in which a secondary battery 913 is built in.
  • the secondary battery 913 is the secondary battery described in embodiment 4.
  • the secondary battery 913 is provided in a position overlapping with the display portion 4005a, and is small and lightweight.
  • FIG. 17D shows an example of a wireless earphone.
  • a wireless earphone having a pair of main bodies 4100a and 4100b is illustrated, but this does not necessarily have to be a pair.
  • the main bodies 4100a and 4100b each have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. They also preferably have a substrate on which a circuit such as a wireless IC is mounted, a charging terminal, and the like. They may also have a microphone.
  • the case 4110 has a secondary battery 4111. It also preferably has a board on which circuits such as a wireless IC and a charging control IC are mounted, and a charging terminal. It may also have a display unit, buttons, etc.
  • Main units 4100a and 4100b can wirelessly communicate with other electronic devices such as smartphones. This allows sound data and the like sent from other electronic devices to be played on main units 4100a and 4100b. Furthermore, if main units 4100a and 4100b have a microphone, sound picked up by the microphone can be sent to the other electronic device, and the sound data after processing by the electronic device can be sent back to main units 4100a and 4100b for playback. This allows them to be used as, for example, a translation machine.
  • the secondary battery 4103 in the main body 4100a can be charged from the secondary battery 4111 in the case 4110.
  • the coin-type secondary battery, cylindrical secondary battery, or the like in the previous embodiment can be used as the secondary battery 4111 and the secondary battery 4103.
  • a secondary battery using the positive electrode active material 100 obtained in embodiment 1 as the positive electrode has a high energy density, and by using it for the secondary battery 4103 and the secondary battery 4111, a configuration that can accommodate space saving associated with miniaturization of wireless earphones can be realized.
  • FIG. 18A shows an example of a cleaning robot.
  • the cleaning robot 6300 has a display unit 6302 arranged on the top surface of a housing 6301, multiple cameras 6303 arranged on the side, brushes 6304, operation buttons 6305, a secondary battery 6306, various sensors, and the like.
  • the cleaning robot 6300 is equipped with tires, a suction port, and the like.
  • the cleaning robot 6300 can move by itself, detect dirt 6310, and suck up the dirt from a suction port arranged on the bottom surface.
  • the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, if an object that may become entangled in the brush 6304, such as a wire, is detected by image analysis, the rotation of the brush 6304 can be stopped.
  • the cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component therein. By using the secondary battery 6306 according to one embodiment of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be an electronic device with long operating time and high reliability.
  • FIG. 18B shows an example of a robot.
  • the robot 6400 shown in FIG. 18B includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.
  • the microphone 6402 has a function of detecting the user's voice and environmental sounds.
  • the speaker 6404 has a function of emitting sound.
  • the robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.
  • the display unit 6405 has a function of displaying various information.
  • the robot 6400 can display information desired by the user on the display unit 6405.
  • the display unit 6405 may be equipped with a touch panel.
  • the display unit 6405 may also be a removable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer are possible.
  • the upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. Furthermore, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the moving mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.
  • the robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or electronic component.
  • a secondary battery according to one embodiment of the present invention in the robot 6400, the robot 6400 can be an electronic device with long operating time and high reliability.
  • FIG. 18C shows an example of an aircraft.
  • the aircraft 6500 shown in FIG. 18C has a propeller 6501, a camera 6502, a secondary battery 6503, etc., and has the ability to fly autonomously.
  • the flying object 6500 includes therein a secondary battery 6503 according to one embodiment of the present invention.
  • the flying object 6500 can be an electronic device with a long operating time and high reliability.
  • next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized.
  • HVs hybrid vehicles
  • EVs electric vehicles
  • PVs plug-in hybrid vehicles
  • FIG. 19 illustrates an example of a vehicle using a secondary battery according to one embodiment of the present invention.
  • the automobile 8400 illustrated in FIG. 19A is an electric automobile that uses an electric motor as a power source for running. Alternatively, it is a hybrid automobile that can use an electric motor and an engine as a power source for running. By using one embodiment of the present invention, a vehicle with a long cruising distance can be realized.
  • the automobile 8400 also has a secondary battery.
  • secondary battery modules can be arranged on the floor of the vehicle interior. The secondary battery can not only drive the electric motor 8406, but also supply power to light-emitting devices such as the headlight 8401 and room light (not shown).
  • the secondary battery can also supply power to display devices such as a speedometer and a tachometer that the automobile 8400 has.
  • the secondary battery can also supply power to semiconductor devices such as a navigation system that the automobile 8400 has.
  • the automobile 8500 shown in FIG. 19B can charge the secondary battery of the automobile 8500 by receiving power supply from an external charging facility by a plug-in method and/or a non-contact power supply method.
  • FIG. 19B shows a state in which a secondary battery 8024 mounted on the automobile 8500 is being charged from a ground-mounted charging device 8021 via a cable 8022.
  • the charging method and connector standards may be appropriately performed using a predetermined method such as CHAdeMO (registered trademark) or Combo.
  • the charging device 8021 may be a charging station installed in a commercial facility or a home power source.
  • the secondary battery 8024 mounted on the automobile 8500 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.
  • a power receiving device can be mounted on the vehicle and power can be supplied contactlessly from a ground power transmission device for charging.
  • this contactless power supply method by incorporating a power transmission device into the road and/or exterior wall, charging can be performed not only while the vehicle is stopped but also while it is moving.
  • This contactless power supply method can also be used to send and receive power between vehicles.
  • solar cells can be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped and/or moving. Electromagnetic induction and/or magnetic field resonance methods can be used for such contactless power supply.
  • FIG. 19C is an example of a two-wheeled vehicle using a secondary battery of one embodiment of the present invention.
  • a scooter 8600 shown in FIG. 19C includes a secondary battery 8602, a side mirror 8601, and a turn signal light 8603.
  • the secondary battery 8602 can supply electricity to the turn signal light 8603.
  • the scooter 8600 shown in FIG. 19C can store a secondary battery 8602 in the under-seat storage 8604.
  • the secondary battery 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small.
  • the secondary battery 8602 is removable, and when charging, the secondary battery 8602 can be carried indoors, charged, and stored before riding.
  • the cycle characteristics of the secondary battery are improved, and the discharge capacity of the secondary battery can be increased. Therefore, the secondary battery itself can be made smaller and lighter. If the secondary battery itself can be made smaller and lighter, it will contribute to reducing the weight of the vehicle, and the cruising distance can be improved.
  • the secondary battery installed in the vehicle can be used as a power supply source for something other than the vehicle. In this case, for example, it is possible to avoid using a commercial power source during peak power demand. If it is possible to avoid using a commercial power source during peak power demand, it can contribute to energy conservation and reduction of carbon dioxide emissions. Furthermore, if the cycle characteristics are good, the secondary battery can be used for a long period of time, and the amount of rare metals used, including cobalt, can be reduced.

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WO2022189889A1 (ja) * 2021-03-09 2022-09-15 株式会社半導体エネルギー研究所 複合酸化物の作製方法、正極、リチウムイオン二次電池、電子機器、蓄電システム、及び移動体

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JP2018206747A (ja) * 2016-07-05 2018-12-27 株式会社半導体エネルギー研究所 正極活物質、正極活物質の作製方法、および二次電池
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