US20170155135A1 - Positive electrode active material and lithium ion secondary cell using same - Google Patents

Positive electrode active material and lithium ion secondary cell using same Download PDF

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US20170155135A1
US20170155135A1 US15/363,677 US201615363677A US2017155135A1 US 20170155135 A1 US20170155135 A1 US 20170155135A1 US 201615363677 A US201615363677 A US 201615363677A US 2017155135 A1 US2017155135 A1 US 2017155135A1
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positive electrode
active material
electrode active
oxide
base portion
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Ryuta SUGIURA
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Toyota Motor Corp
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Toyota Motor Corp
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Publication of US20170155135A1 publication Critical patent/US20170155135A1/en
Priority to US16/666,701 priority Critical patent/US11430986B2/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a positive electrode active material and a lithium ion secondary cell using the same.
  • Japanese Patent Application Publication No. 2001-266879 indicates that thermal stability of a cell in a charged state can be improved by coating the surface of positive electrode active material particles (base active material) with a layered electroconductive oxide.
  • the electroconductive oxide such as disclosed in Japanese Patent Application Publication No. 2001-266879 generally has a large anisotropy of electroconductivity.
  • the investigation conducted by the inventors has revealed that when a material (for example, a layered compound) with a large anisotropy of electroconductivity is used as a base active material, where the electroconductive direction of the base active material is not matched with the electroconductive direction of the electroconductive oxide, the cell resistance is greatly increased.
  • Another drawback is that the electroconductive oxide peels off from the surface of the base active material and durability decreases as a result of the base active material expansion and contraction when the cell is charged and discharged.
  • the present invention has been created to resolve such problems, and it is an object of the present invention to provide a positive electrode active material in which the effect of coating the surface of a base active material with an electroconductive oxide is advantageously demonstrated. Another related object is to provide a lithium ion secondary cell that is provided with the positive electrode active material and excels in input-output characteristic and durability.
  • the present invention provides a positive electrode active material for a lithium ion secondary cell, including a base portion including a lithium transition metal complex oxide having a layered crystal structure, and a coating portion formed on a surface of the base portion, and including an electroconductive oxide having a layered crystal structure.
  • a stacking plane direction of the layered crystal structure in the lithium transition metal complex oxide is represented by a first virtual line
  • a stacking plane direction of the layered crystal structure in the electroconductive oxide is represented by a second virtual line
  • a smaller angle ⁇ formed by the first virtual line and the second virtual line satisfies the following conditions: an average angle ⁇ ave. obtained by arithmetically averaging the angle ⁇ satisfies 0° ⁇ ave. ⁇ 60°; and a ratio of points in which the angle ⁇ is greater than 60° is 39% or less.
  • the effect of coating the surface of the base portion with the coating portion is demonstrated to a higher degree.
  • compounds with a layered structure generally have a large anisotropy of electroconductivity, and the electroconductivity in the stacking plane direction (direction perpendicular to the stacking direction) tends to be high. Therefore by matching the stacking plane direction of the base portion with the stacking plane direction of the coating portion, it is possible to demonstrate the effect of improving the electroconductivity at a high level. Further, the coating portion easily relaxes stresses in the crystals in the stacking direction.
  • the positive electrode active material of such a configuration makes it possible to realize a lithium ion secondary cell with excellent input-output characteristic and durability.
  • the ⁇ ave. satisfies 0° ⁇ ave. ⁇ 23°.
  • the degree of matching of the electroconductive direction of the base portion and the electroconductive direction of the coating portion can thus be further improved.
  • the cell resistance can be further decreased and further improvement of the input-output characteristic can be realized.
  • the ratio of points in which the angle ⁇ is greater than 60° is 10% or less.
  • the degree of matching of the electroconductive direction of the base portion and the electroconductive direction of the coating portion can thus be further improved.
  • the cell resistance can be further decreased and further improvement of the input-output characteristic can be realized.
  • a lithium ion secondary cell equipped with the positive electrode active material.
  • Such a lithium ion secondary cell for example, has a low initial resistance and a high durability such that the cell capacity is unlikely to decrease even in repeated charging and charging over a long period of time.
  • FIG. 1 is a schematic diagram illustrating the cross section of the positive electrode active material according to one embodiment
  • FIG. 2 is a partial enlarged view in (II) in FIG. 1 ;
  • FIG. 3A is a schematic diagram illustrating the crystal structure of lithium-nickel-cobalt-manganese oxide
  • FIG. 3B is a schematic diagram illustrating the crystal structure of yttrium-barium-copper oxide
  • FIG. 4 is a schematic diagram illustrating the vertical sectional view of the lithium ion secondary cell according to one embodiment.
  • a positive electrode active material disclosed herein and a lithium ion secondary cell using the same will be explained herein with reference to appropriate drawings.
  • Features other than those specifically described in the present specification for example, the composition and shape of the positive electrode active material), but necessary for implementing the present invention (for example, constituent elements of the cell other than the positive electrode active material and general process for manufacturing the cell) can be considered as design matters for a person skilled in the art that are based on the conventional techniques in the pertinent field.
  • the positive electrode active material disclosed herein and the lithium ion secondary cell using the same can be implemented on the basis of the contents disclosed in the present specification and common technical knowledge in the pertinent field.
  • FIG. 1 is a schematic diagram illustrating the cross section of the positive electrode active material 1 according to one embodiment.
  • FIG. 2 is a partial enlarged view in which part of the surface of the positive electrode active material 1 is depicted on an enlarged scale.
  • the particle of the positive electrode active material 1 depicted in FIG. 1 has a base portion 2 serving as a nucleus of the positive electrode active material 1 and a coating portion 4 that covers the surface of the base portion 2 .
  • the base portion 2 is in the form of the so-called hollow structure. That is, the base portion 2 has a ring-shaped substantive portion formed by aggregation (association) of primary particles of a lithium transition metal complex oxide and a hollow portion (void portion) formed inside thereof.
  • the base portion 2 has the hollow structure, but such the structure is not limiting.
  • the base portion 2 may have a common porous structure or solid structure in which the substantive portion and void portion are present homogeneously throughout the entire base portion 2 .
  • the base portion 2 includes a lithium transition metal complex oxide having a layered crystal structure.
  • the substantive portion is configured by aggregation of primary particles of the lithium transition metal complex oxide.
  • the lithium transition metal complex oxide includes a lithium element and one or two or more transition metal elements. It is preferred that the lithium transition metal complex oxide include at least one of Ni, Co, and Mn as the transition metal element.
  • lithium transition metal complex oxide examples include a lithium-nickel complex oxide, a lithium-cobalt complex oxide, a lithium-nickel-manganese complex oxide, a lithium-nickel-cobalt-manganese complex oxide, a lithium-nickel-cobalt-aluminum complex oxide, and a lithium-iron-nickel-manganese complex oxide.
  • the “lithium-nickel-cobalt-manganese complex oxide”, as referred to in the present specification, is a term inclusive not only of oxides having Li, Ni, Co, Mn, and O as constituent elements, but also of oxides including one or two or more other additional elements.
  • additional elements include transition metal elements and typical metal elements such as Na, Mg, Ca, Ba, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Zn, Al, and Ga.
  • the additional elements may be also semimetal elements such as B, C, Si, and P, and non-metal elements such as S, F, Cl, Br, and I.
  • lithium-nickel complex oxide lithium-cobalt complex oxide
  • lithium-nickel-manganese complex oxide lithium-nickel-cobalt-aluminum complex oxide
  • lithium-iron-nickel-manganese complex oxide lithium-nickel-cobalt-aluminum complex oxide
  • lithium-iron-nickel-manganese complex oxide lithium-nickel-cobalt-aluminum complex oxide
  • lithium-iron-nickel-manganese complex oxide lithium-iron-nickel-manganese complex oxide
  • the lithium transition metal complex oxide is a lithium-nickel-cobalt-manganese complex oxide represented by the following formula (I).
  • M and A may or may not be included.
  • M is one or two or more elements among Zr, Mo, W, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, and B.
  • A is one or two or more elements among F, Cl, and Br.
  • y, z, and (1-y-z) may be about the same (for example, the difference therebetween may be 0.1 or less).
  • the composition ratio of Ni, Co, and Mn may be about the same.
  • Such a lithium-nickel-cobalt-manganese complex oxide has a high energy density and also excels in thermal stability. For this reason, the effect of the technique disclosed herein can be demonstrated at a higher level.
  • the lithium transition metal complex oxide has a layered crystal structure.
  • the crystal structure (whether it is layered) of the lithium transition metal complex oxide can be determined, for example, by well-known conventional X-ray diffraction measurements, or the like.
  • the lithium transition metal complex oxide has an X-ray diffraction peak attributable to a hexagonal crystal structure of a space group R3-m and/or a monoclinic crystal structure of a space group C2/m.
  • X-ray diffraction peak attributable to a hexagonal crystal structure of a space group R3-m and/or a monoclinic crystal structure of a space group C2/m.
  • smooth introduction and release of lithium ions are possible, but the anisotropy of electroconductivity tends to increase. Therefore, in the lithium transition metal complex oxide having such X-ray diffraction peaks, the effect of the technique disclosed herein can be demonstrated at a higher level.
  • FIG. 3A is a schematic diagram illustrating the crystal structure of the lithium-nickel-cobalt-manganese complex oxide.
  • the lithium-nickel-cobalt-manganese complex oxide has a layered rock-salt structure in which oxide layers and lithium (Li) layers are stacked alternately in a predetermined stacking direction.
  • the stacking direction of the lithium-nickel-cobalt-manganese complex oxide is the up-down direction in FIG. 3A .
  • oxygen octahedral structures are contiguous in the stacking plane direction (direction perpendicular to the stacking direction; the left-right direction in FIG.
  • the oxygen octahedral structure is formed by transition metals, namely, Ni, Co, and Mn, serving as central elements, and by six oxygen elements surrounding the periphery of the central elements.
  • transition metals namely, Ni, Co, and Mn
  • the stacking plane direction is an “electroconductive direction” with a high electroconductivity.
  • the electroconductive direction of the base portion 2 is represented by straight lines. That is, in FIGS. 1 and 2 , directions extending radially from the central side (side of the hollow portion) of the base portion 2 to the surface side (side of the coating portion 4 ) are electroconductive directions.
  • the size (average particle diameter) of the base portion 2 is not particularly limited, but may be about 0.1 ⁇ m or more, for example, 1 ⁇ m or more with consideration for handleability and operability during molding of the coating portion 4 . Further, from the standpoint of forming a dense and homogeneous positive electrode active material layer, the size may be about 50 ⁇ m or less, typically 30 ⁇ m or less, for example, 20 ⁇ m or less. A particle diameter (D 50 particle diameter) corresponding to cumulative 50%, from the fine particle side with a small particle diameter, in a volume-standard particle size distribution obtained by particle size distribution measurements based on the general laser diffraction-light scattering method can be used as the average particle diameter.
  • the coating portion 4 includes an electroconductive oxide having a layered crystal structure.
  • electroconductive oxide means an oxide having electroconductivity in a temperature range (for example, 0° C. to 50° C.) in which the cell is used. Among them, oxides which are generally known as superconductive materials are preferred. Typical examples of electroconductive oxides include perovskite-type electroconductive oxides, pyrochlore-type electroconductive oxides, and K 2 NiF 4 -type electroconductive oxides.
  • YBa 2 Cu 3 O 7 YBCO
  • Bi 2 Sr 2 Ca 2 Cu 3 O 10 Hg 12 Tl 3 Ba 30 Ca 30 Cu 45 O 127
  • La 2 ⁇ x Sr x CuO 4 LSCO, where 0 ⁇ x ⁇ 2
  • LaFePO LaFeAsO
  • LaFeAsO 1 ⁇ x F x where 0 ⁇ x ⁇ 1
  • composition ratio of oxygen (O) is represented by integers for the sake of convenience, but these numerical values need not to be interpreted strictly, and fluctuations (for example, fluctuations of about ⁇ 20%) thereof associated with stability of crystal structure, or the like, can be allowed.
  • the electroconductive oxide has a layered crystal structure.
  • the crystal structure (whether it is layered) of the electroconductive oxide can be determined, for example, by well-known conventional X-ray diffraction measurements, or the like.
  • the electroconductive oxide has a two-dimensional plane (electroconductive surface) responsible for electron conduction in the crystal structure.
  • a CuO 2 plane and FeAs plane are known as electroconductive surfaces.
  • FIG. 3B is a schematic diagram of the crystal structure of yttrium-barium-copper oxide (YBa 2 Cu 3 O 7 ).
  • This oxide has a layered structure in which an insulating layer, which is called “block layer”, and a CuO 2 plane are stacked in a predetermined stacking direction (up-down direction in FIG. 3B ).
  • block layer an insulating layer
  • CuO 2 plane are stacked in a predetermined stacking direction (up-down direction in FIG. 3B ).
  • a CuO layer and a BaO layer are stacked in the stacking direction.
  • Cu and O are arranged in a square lattice shape and have a sheet-shaped form in a stacking plane direction (left-right direction in FIG.
  • the stacking plane direction is an “electroconductive direction” with a high electroconductivity.
  • Yttrium (Y) atoms are disposed in a space sandwiched between two CuO 2 planes.
  • the electroconductive directions in the coating portion 4 are represented by straight lines.
  • the electroconductive direction of the lithium transition metal complex oxide in the base portion 2 and the electroconductive direction of the electroconductive oxide in the coating portion 4 are advantageously matched. This will be described in greater detail with reference to FIG. 2 .
  • an interface of the base portion 2 and the coating portion 4 is at the surface of the positive electrode active material 1 .
  • the base portion 2 and the coating portion 4 each have an oxide (layered oxide) of a layered structure.
  • the stacking plane directions of the layered oxides are represented by lines.
  • the stacking plane direction of the layered oxide in the base portion 2 is taken as a first virtual line Lb and a stacking plane direction of the layered oxide in the coating portion 4 is represented by a second virtual line Lc
  • the first virtual line Lb and the second virtual line Lc intersect at the interface of the base portion 2 and the coating portion 4 .
  • the smaller of the angles formed by the two straight lines is denoted by ⁇ .
  • the angle ⁇ is 0° at a minimum and 90° at a maximum.
  • the stacking plane directions of the base portion 2 and the coating portion 4 can be said to coincide at a higher level as the angle ⁇ becomes smaller.
  • the average angle ⁇ ave. is preferably 40° or less, more preferably 31° or less, and even more preferably 23° or less. As a result, the effects of the technique disclosed herein can be stably demonstrated at an even higher level. Meanwhile, the time required for producing the positive electrode active material 1 with a smaller average angle ⁇ ave. tends to increase. Therefore, from the standpoint of productivity and cost, the average angle ⁇ ave. may be 5° or more, for example, 12° or more. Likewise, the ratio of points in which the angle ⁇ is greater than 60° is preferably 22% or less, more preferably 16% or less, in particular 10% or less. Further, the ratio of points in which the angle ⁇ is greater than 60° may be, for example, 7% or more.
  • the angle ⁇ can be measured, for example, in the following manner. First, the cross section of the positive electrode active material 1 is sliced by focused ion beam (FIB) processing or the like. Then, electron microscope observations of the positive electrode active material 1 are performed 10 or more times so that the base portion 2 and the coating portion 4 are present in the same field of view. For example, a transmission electron microscope (TEM) can be used as the electron microscope. Then, electron beam diffraction measurements are performed separately for the base portion 2 and the coating portion 4 in the same field of view, and electron beam diffraction images are acquired.
  • FIB focused ion beam
  • the crystal orientation of the layered oxide in the base portion 2 and the crystal orientation of the layered oxide in the coating portion 4 are then analyzed from the obtained electron beam diffraction images, and the respective stacking plane directions are determined. A smaller angle among the angles formed by the two stacking plane directions which are thus determined can be taken as the angle ⁇ .
  • the ratio of the surface of the base portion 2 coated by the coating portion 4 is not particularly limited. From the standpoint of exhibiting the effect of improving the electroconductivity at a high level, about 10% or more, typically 20% or more, for example, 30% or more of the entire surface of the base portion 2 may be coated with the coating portion 4 . Meanwhile, from the standpoint of maintaining and increasing the easiness of Li ion introduction and release, about 90% or less, for example, 80% or less of the entire surface of the base portion 2 may be coated with the coating portion 4 .
  • the coverage ratio of the surface of the base portion 2 can be determined, for example, by calculating the ratio (%) of the outer peripheral length of the base portion 2 where the coating portion 4 has been formed in the electron microscope observation image of the cross section of the positive electrode active material 1 , the entire outer peripheral length of the base portion 2 being taken as 100%.
  • the average thickness of the coating portion 4 is not particularly limited, but from the standpoint of productivity, or the like, the average thickness may be about 100 nm or less, typically 0.5 nm to 20 nm, for example, about 1 nm to 5 nm.
  • the average thickness of the coating portion 4 can be determined by measuring the shortest distance from any position on the inner surface of the coating portion 4 to the outer surface of the coating portion 4 in the electron microscope observation image of the cross section of the positive electrode active material 1 .
  • the average particle diameter (secondary particle diameter) of the positive electrode active material 1 is not particularly limited, but with consideration for handleability and operability, the average particle diameter may be about 0.1 ⁇ m or more, for example, 1 ⁇ m or more. From the standpoint of forming a dense and homogeneous positive electrode active material layer, the average particle diameter may be about 50 ⁇ m or less, typically 30 ⁇ m or less, for example 20 ⁇ m or less.
  • the shape of the positive electrode active material 1 is not particularly limited.
  • the shape is substantially spherical.
  • the term “substantially spherical” used herein is inclusive of spherical, rugby ball, and polygonal shapes, and the average aspect ratio (the ratio of the length in the long-axis direction to the length in the short-axis direction in the smallest rectangle circumscribing the particle) is about 1 to 2, for example, 1 to 1.5.
  • a method for manufacturing the positive electrode active material 1 is not particularly limited.
  • a liquid-phase method such as a sol-gel method and a co-precipitation method can be used.
  • An example of the preferred manufacturing method includes a step of preparing a lithium transition metal complex oxide as the base portion 2 and a step of forming the coating portion 4 by applying an electroconductive oxide to the surface of the prepared lithium transition metal complex oxide.
  • a supply source of a metal element, other than Li, that constitutes the lithium transition metal complex oxide is prepared.
  • a metal salt such as a nickel salt, a cobalt salt, and a manganese salt can be used as a supply source of a metal element other than Li.
  • the anions of these metal salts may be selected to obtain the desired solubility of respective salts in water.
  • the anions of the metal salts can be a sulfate ion, a nitrate ion, and a carbonate ion.
  • the supply source of the metal element is then weighed to obtain the desired composition ratio and mixed with a water-based solvent to prepare an aqueous solution.
  • a basic aqueous solution with pH 11 to 14 is added to neutralize the aqueous solution, a hydroxide including the metal element is precipitated, and a sol-like starting material hydroxide is obtained.
  • a basic aqueous solution with pH 11 to 14 is added to neutralize the aqueous solution, a hydroxide including the metal element is precipitated, and a sol-like starting material hydroxide is obtained.
  • an aqueous solution of sodium hydroxide or ammonia water can be used as the basic aqueous solution.
  • the starting material hydroxide is precipitated slowly over time by stepwise adjusting the pH and amount added of the basic aqueous solution.
  • a lithium transition metal complex oxide with adjusted crystal structure and crystal orientation for example such as depicted in FIG. 1 , can be advantageously realized.
  • This starting material hydroxide is then mixed with a lithium supply source, and the mixture is calcined and then cooled.
  • a lithium supply source for example, lithium carbonate, lithium hydroxide, and lithium nitrate can be used as the lithium supply source.
  • the obtained calcined material is pulverized, as appropriate, to prepare a lithium transition metal complex oxide serving as the base portion 2 .
  • the supply source of the metal element constituting the electroconductive oxide is prepared.
  • the supply source of the metal element is then weighed to obtain the desired composition ratio and mixed with a water-based solvent to prepare an aqueous solution.
  • the aqueous solution is then mixed with the prepared lithium transition metal complex oxide at a desirable ratio and the solvent is then removed by drying.
  • the powder obtained is calcined.
  • the electroconductive oxide is directly fused to the surface of the lithium transition metal complex oxide, and the positive electrode active material 1 in the form in which the base portion 2 and the coating portion 4 are strongly combined together can be manufactured.
  • the temperature increase rate in a temperature range in which the epitaxial growth advances may be set to about 10° C./h to 100° C./h.
  • the positive electrode active material 1 in which the electroconductive directions in the base portion 2 and the coating portion 4 are matched for example such as depicted in FIG. 1 , can be manufactured.
  • the above-described positive electrode active material is used as a positive electrode for a lithium ion secondary cell.
  • a positive electrode for the lithium ion secondary cell typically includes a positive electrode collector and a positive electrode active material layer including the positive electrode active material and formed on the positive electrode collector.
  • An electroconductive material composed of a metal with good electric conductivity (for example, aluminum) can be advantageously used as the positive electrode collector.
  • the positive electrode active material layer can include other optional components such as an electroconductive material, a binder, and a dispersant.
  • a carbon material such as carbon black can be used as the electroconductive material.
  • a halogenated vinyl resin such as polyvinylidene fluoride (PVdF) can be used as the binder.
  • a lithium ion secondary cell is constructed by accommodating the positive electrode together with a negative electrode and a nonaqueous electrolyte in a cell case.
  • the negative electrode typically includes a negative electrode collector and a negative electrode active material layer formed on the negative electrode collector.
  • the negative electrode active material layer can include a negative electrode active material and other optional components (for example, a binder and a thickening agent).
  • An electroconductive member composed of a metal with good electric conductivity (for example, copper) can be used as the negative electrode collector.
  • a carbon material such as graphite can be used as the negative electrode active material.
  • SBR styrene butadiene rubber
  • CMC carboxymethyl cellulose
  • An electrolyte in which a support salt is included in a nonaqueous solvent is preferred as the nonaqueous electrolyte.
  • a lithium salt such as LiPF 6 and LiBF 4 can be used as the support salt.
  • an aprotic solvent such as a carbonate, an ester, and an ether can be used as the organic solvent.
  • FIG. 4 is a schematic diagram illustrating the vertical sectional structure of the lithium ion secondary cell according to one embodiment.
  • a lithium ion secondary cell 100 is provided with a flat wound electrode body 80 , a nonaqueous electrolyte (not depicted in the figure), and a cell case 50 in the form of a flat rectangular parallelepiped in which the wound electrode body 80 and the nonaqueous electrolyte are accommodated.
  • the cell case 50 is provided with a case main body 52 in the form of a flat rectangular parallelepiped open at the upper end and a lid 54 that closes the opening of the case main body 52 .
  • the material of the cell case 50 is, for example, a lightweight metal such as aluminum.
  • the shape of the cell case is not particularly limited and can be, for example, a rectangular parallelepiped or a cylinder.
  • a positive electrode terminal 70 and a negative electrode terminal 72 for external connection are provided at the upper surface of the cell case 50 (that is, the lid 54 ). Parts of the terminals 70 , 72 protrude to the surface side of the lid 54 .
  • the positive electrode terminal 70 is electrically connected to the positive electrode of the wound electrode body 80 on the cell case 50 side.
  • the negative electrode terminal 72 is electrically connected to the negative electrode of the wound electrode body 80 on the cell case 50 side.
  • the lid 54 is also provided with a safety valve 55 for releasing the gas generated inside the cell case 50 to the outside.
  • the wound electrode body 80 is provided with an elongated positive electrode sheet 10 and an elongated negative electrode sheet 20 .
  • the positive electrode sheet 10 is provided with an elongated positive electrode collector and a positive electrode active material layer 14 formed along the longitudinal direction on the surface (typically on both surfaces) of the positive electrode collector.
  • the positive electrode active material layer 14 is provided with the above-described positive electrode active material 1 .
  • the negative electrode sheet 20 is provided with an elongated negative electrode collector and a negative electrode active material layer 24 formed along the longitudinal direction on the surface (typically on both surfaces) of the negative electrode collector.
  • the wound electrode body 80 depicted in FIG. 4 is also provided with two elongated separator sheets 40 .
  • the positive electrode active material layer 14 of the positive electrode sheet 10 and the negative electrode active material layer 24 of the negative electrode sheet 20 are insulated from each other by the separator sheets 40 .
  • the material of the separator sheet 40 is, for example, a resin such as polyethylene (PE), polypropylene (PP), and polyesters.
  • a porous heat-insulating layer including inorganic compound particles (inorganic filler) may be provided on the surface of the separator sheets 40 with the object of preventing a short circuit, and the like.
  • the wound electrode body 80 of the present embodiment has a flat shape, but a suitable shape (for example, a cylindrical shape or a stacked shape) can be selected, as appropriate, according to the shape of the cell case or usage objective.
  • a suitable shape for example, a cylindrical shape or a stacked shape
  • the lithium ion secondary cell including the positive electrode active material disclosed herein is superior to the conventional products in both the input-output characteristic and the durability. Therefore, the lithium ion secondary cell is suitable for a variety of applications and can be advantageously used for applications requiring a high input-output density and applications requiring long-term continuous used without replacement.
  • An example of such applications is a power source (drive power supply) for a motor installed on a vehicle.
  • the type of the vehicle is not particularly limited, but the vehicle is typically an automobile, for example, a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), and an electric vehicle (EV).
  • PGV plug-in hybrid vehicle
  • HV hybrid vehicle
  • EV electric vehicle
  • Such lithium ion secondary cells are typically used in the form of a cell pack in which a plurality of the cells are connected in series and/or parallel.
  • Base portion LiNi 1/3 Co 1/3 Mn 1/3 O 2 ; Coating portion: YBa 2 Cu 3 O 6.8 >>
  • nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved as sources of metals other than Li in water so as to obtain the above composition of the base portion.
  • Sodium hydroxide was added thereto and stirring was performed while neutralizing the system, to obtain the starting material hydroxide according to Example 1.
  • the starting material hydroxide was mixed with lithium carbonate, and the mixture was calcined for 15 h at 900° C. under an air atmosphere.
  • the calcined material was pulverized in a ball mill to obtain a lithium-nickel-cobalt-manganese complex oxide (LiNi 1/3 Co 1/3 Mn 1/3 O 2 ) with an average particle diameter of 10 ⁇ m.
  • yttrium sulfate, barium sulfate, and copper sulfate as metal sources were dissolved in water to obtain the composition of the coating portion.
  • the obtained lithium-nickel-cobalt-manganese oxide was then added and the components were mixed. The amount added at this time was adjusted such that the total number of moles of the metals (Y, Ba, Cu) constituting the electroconductive oxide was 2 per 100 moles of all metals (Ni, Co, Mn), except for lithium, of the lithium-nickel-cobalt-manganese oxide.
  • the mixture was then heated to 60° to remove the solvent, and a particulate powder was obtained in which the reaction precursor of the coating portion was attached to the surface of the lithium-nickel-cobalt-manganese complex oxide.
  • a positive electrode active material was then obtained by calcining the obtained particulate powder according to a predetermined calcination pattern.
  • the calcination pattern was set to involve raising the temperature at a temperature increase rate of 200° C./h from room temperature to 300° C., raising the temperature at a temperature increase rate of 10° C./h from 300° C. to 450° C., raising the temperature at a temperature increase rate of 50° C./h from 450° C. to 550° C., and holding for 5 h after reaching 550° C.
  • Example 2 the positive electrode active materials were obtained in the same manner as in Example 1, except that the temperature increase rate from 300° C. to 450° C. was set to increase little by little within a range from 15° C./h to 100° C./h.
  • the positive electrode active materials were obtained in the same manner as in Example 1, except that the temperature increase rate from 300° C. to 450° C. was set to increase little by little within a range from 100° C./h to 200° C./h.
  • Lithium ion secondary cells were constructed using the obtained positive electrode active materials (Examples 1 to 8 and Reference Examples 1 to 4).
  • the fabricated positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, acetylene black as an electroconductive materials, and a dispersant were weighed to obtain a mass ratio of 80:8:2:0.2.
  • a composition for forming a positive electrode active material layer was prepared by mixing these materials in N-methyl-2-pyrrolidone (NMP) to obtain a solid fraction of 56 mass %.
  • NMP N-methyl-2-pyrrolidone
  • a positive electrode sheet (Examples 1 to 8, Reference Examples 1 to 4) having a positive electrode active material layer on the positive electrode collector was fabricated by applying the composition to both surfaces of an aluminum foil (positive electrode collector) by using a die coater, drying, and then pressing.
  • a graphite material as a negative electrode active material as a negative electrode active material
  • a styrene-butadiene copolymer (SBR) as a binder and carboxymethyl cellulose (CMC) as a thickening agent were weighed to obtain a mass ratio of 98:1:1.
  • a composition for forming a negative electrode active material layer was then prepared by mixing these materials in water.
  • a negative electrode sheet having a negative electrode active material layer on the negative electrode collector was fabricated by applying the composition to both surfaces of a copper foil (negative electrode collector), drying, and then pressing.
  • a wound electrode body was then fabricated by winding the positive electrode sheet and the negative electrode sheet together with a separator sheet.
  • a porous resin sheet in which a polypropylene layer was laminated on both sides of a polyethylene layer was used as the separator sheet.
  • Current-collecting members were welded to both end portions (non-formation portions of active material layers) in the lateral direction of the wound electrode body, and the wound electrode body was then accommodated in a cell case in the form of a rectangular parallelepiped.
  • ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:4:3 to prepare a mixed solvent.
  • a nonaqueous electrolytic solution was prepared by dissolving LiPF 6 as a support salt at a concentration of 1.1 mol/L in the mixed solvent.
  • Lithium ion secondary cells (Examples 1 to 8, Reference Examples 1 to 4) were then constructed by pouring the nonaqueous electrolytic solution into the cell case and then sealing the cell case with the lid.
  • the fabricated lithium ion secondary cells were constant-current (CC) charged at a rate of 1/3 C to a voltage of 4.2 V under a temperature environment of 25° C. and then constant-voltage (CV) charged to a current value of 1/50 C to obtain a fully charged state (state with a state of charge (SOC) of 100%).
  • the cells were then constant-current (CC) discharged at a rate of 1/3 C to a voltage of 3 V under a temperature environment of 25° C., and the CC discharge capacity at this time was taken as the initial capacity.
  • 1 C means the current value at which the capacity (Ah) of the cell which is estimated from the theoretic capacity of the active material can be charged within 1 h.
  • each lithium ion secondary cell was adjusted to 3.70 V.
  • Each lithium ion secondary cell was CC discharged at a discharge rate of 10 C to a voltage of 3.00 V under a temperature environment of 25° C.
  • a resistance value (5-sec value) was then calculated from the discharge current value and the terminal voltage value at a fifth second after the start of discharge. The results are shown in the appropriate column in Table 1.
  • the values in Table 1 were obtained by normalization in which the resistance value for the lithium ion secondary cell of Example 1 was taken as a reference (100).
  • Each lithium ion secondary cell was subjected to 200 cycles of repeated charging and discharging under a temperature condition of 60° C., and the cell capacity (CC discharge capacity) after each cycle was measured in the same manner as the initial capacity.
  • the charging-discharging conditions of one cycle during the high-temperature cycle test were as follows: CC charging to a voltage of 4.3 V at a charge rate of 2 C and then CC discharging to a voltage of 3.0 V at a discharge rate of 2 C.
  • the capacity retention ratio (%) was then calculated by dividing the cell capacity after 200 cycles by the initial capacity and multiplying by 100. The results are shown in the appropriate column in Table 1.
  • the average angle ⁇ ave. was small and the ratio of points in which the angle ⁇ was greater than 60° was also small. This is apparently because the epitaxial growth of the electroconductive oxide advanced advantageously due to a gradual increase of temperature in the calcination temperature region in which the crystal growth of the electroconductive oxide advanced.
  • Example 9 to 11 the electroconductive oxides with the composition ratios shown in Table 2 were used for the coating portion. Specifically, the metal sources were dissolved in water so as to obtain the compositions shown in Table 2, and then the lithium-nickel-cobalt-manganese complex oxide was added and mixed. The temperature increase rate from 300° C. to 450° C. was set to 15° C./h. Positive electrode active materials were obtained in the same manner as in Example 1, except for the above-described changes.
  • positive electrode active materials were obtained in the same manner as in Examples 9 to 11, except that the temperature increase rate from 300° C. to 450° C. was set to 120° C./h.
  • Example 12 and 13 the electroconductive oxides with the composition ratios shown in Table 3 were used for the base portion. Specifically, the metal sources other than Li were dissolved in water so as to obtain the compositions shown in Table 3, and then sodium hydroxide was added, and stirring was performed while neutralizing the system, to obtain starting material hydroxides. The temperature increase rate from 300° C. to 450° C. was set to 15° C./h. Positive electrode active materials were obtained in the same manner as in Example 1, except for the above-described changes.
  • positive electrode active materials were obtained in the same manner as in Examples 12 and 13, except that the temperature increase rate from 300° C. to 450° C. was set to 120° C./h.
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