WO2025028061A1 - 正極活物質、正極、非水電解質二次電池、および正極活物質の製造方法 - Google Patents

正極活物質、正極、非水電解質二次電池、および正極活物質の製造方法 Download PDF

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WO2025028061A1
WO2025028061A1 PCT/JP2024/022567 JP2024022567W WO2025028061A1 WO 2025028061 A1 WO2025028061 A1 WO 2025028061A1 JP 2024022567 W JP2024022567 W JP 2024022567W WO 2025028061 A1 WO2025028061 A1 WO 2025028061A1
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positive electrode
active material
electrode active
lithium
composite oxide
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French (fr)
Japanese (ja)
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正悟 江崎
浩史 川田
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Panasonic Intellectual Property Management Co Ltd
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Panasonic Intellectual Property Management Co Ltd
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Priority to JP2025537722A priority patent/JPWO2025028061A1/ja
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • 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
    • 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

  • This disclosure relates to a positive electrode active material, a positive electrode, a non-aqueous electrolyte secondary battery, and a method for producing a positive electrode active material.
  • the positive electrode active material has a significant effect on battery performance such as input/output characteristics, capacity, and durability, and therefore positive electrode active materials have been the subject of much research.
  • lithium transition metal composite oxides containing transition metal elements such as Ni and Mn are used as positive electrode active materials.
  • the type and amount of elements contained in the lithium transition metal composite oxide, as well as the crystal structure of the composite oxide have a significant effect on battery performance, and even slight changes in these physical properties may make it impossible to achieve the desired performance.
  • Patent Documents 1 to 3 disclose improvements to the crystal structure of positive electrode active materials of specific compositions with the aim of improving battery performance such as increasing capacity.
  • Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used as power sources for driving vehicles, and there is a demand for even higher capacity and improved initial charge/discharge efficiency.
  • the positive electrode active materials of Patent Documents 1 to 3 still have a lot of room for improvement in terms of higher capacity and improved initial charge/discharge efficiency.
  • a positive electrode active material is a positive electrode active material used in a non-aqueous electrolyte secondary battery, the positive electrode active material having a crystal structure belonging to the space group R-3m and represented by the composition formula Li x Na y Ni 1-a-b Mn a X b O c , in which X is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, Ni, and Mn, 0.80 ⁇ x ⁇ 1.15, 0 ⁇ y ⁇ 0.20, 0.80 ⁇ x+y ⁇ 1.20, 0 ⁇ 1-a-b ⁇ 1, 0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1, and c are values that satisfy electrical neutrality, and when the non-aqueous electrolyte secondary battery is initially charged, an X-ray diffraction pattern obtained by X-ray diffraction has a peak derived from a compound different from the compound represented by the composition formula in a range of a diffraction angle 2 ⁇ of 15.7° or more and 18.0
  • a method for producing a positive electrode active material is a method for producing a positive electrode active material for use in a non-aqueous electrolyte secondary battery, and includes the steps of: synthesizing a Na composite oxide represented by a composition formula Na e Ni 1-f- g Mn f X g O h (wherein X is at least one element selected from metal elements other than Li, Na, Ni, and Mn, and e ⁇ 1.15, 0 ⁇ 1-f-g ⁇ 1, 0 ⁇ f ⁇ 1, 0 ⁇ g ⁇ 1, and h is a value that satisfies electrical neutrality); and reacting the Na composite oxide with a lithium compound to exchange a portion of Na in the Na composite oxide for Li, wherein the lithium compound includes at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium hydrogen carbonate.
  • the positive electrode of one aspect of the present disclosure is characterized by including the above-mentioned positive electrode active material.
  • the nonaqueous electrolyte secondary battery which is one aspect of the present disclosure, is characterized by having the above-mentioned positive electrode, a negative electrode, and a nonaqueous electrolyte.
  • the positive electrode active material disclosed herein can increase the capacity of non-aqueous electrolyte secondary batteries and improve the initial charge/discharge efficiency.
  • 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention
  • 1A and 1B are diagrams showing X-ray diffraction patterns of the positive electrode active material prepared in Example 1, in which (a) is an overall view from 10° to 80°, and (b) is an enlarged view from 10° to 30°
  • 1A and 1B are diagrams showing X-ray diffraction patterns of the positive electrode active material prepared in Example 2, in which (a) is an overall view from 10° to 80°, and (b) is an enlarged view from 10° to 30°.
  • 1A and 1B are diagrams showing X-ray diffraction patterns of the positive electrode active material prepared in Example 3, in which (a) is an overall view from 10° to 80°, and (b) is an enlarged view from 10° to 30°.
  • 1A and 1B are diagrams showing X-ray diffraction patterns of the positive electrode active material prepared in Example 4, in which (a) is an overall view from 10° to 80°, and (b) is an enlarged view from 10° to 30°.
  • 1 shows X-ray diffraction patterns of the positive electrode active material prepared in Example 5, where (a) is an overall view from 10° to 80° and (b) is an enlarged view from 10° to 30°.
  • FIG. 1 shows the X-ray diffraction pattern of the positive electrode active material prepared in Comparative Example 1, where (a) is an overall view from 10° to 80°, and (b) is an enlarged view from 10° to 30°.
  • 1A and 1B are diagrams showing X-ray diffraction patterns of the positive electrode active material prepared in Comparative Example 2, in which (a) is an overall view from 10° to 80°, and (b) is an enlarged view from 10° to 30°.
  • FIG. 2 is a diagram showing charge/discharge curves of test cells of an example and a comparative example.
  • FIG. 13A and 13B are diagrams showing X-ray diffraction patterns of the positive electrode active material prepared in Example 7, in which (a) is an overall view from 10° to 80°, and (b) is an enlarged view from 10° to 30°.
  • 13A and 13B are diagrams showing X-ray diffraction patterns of the positive electrode active material prepared in Example 8, in which (a) is an overall view from 10° to 80°, and (b) is an enlarged view from 10° to 30°.
  • a positive electrode active material for a non-aqueous electrolyte secondary battery which has a crystal structure belonging to space group R-3m and is represented by a composition formula Li x Na y Ni 1-a- b Mn a X b O c (wherein X is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, Ni, and Mn, and 0.80 ⁇ x ⁇ 1.15, 0 ⁇ y ⁇ 0.20, 0.80 ⁇ x+y ⁇ 1.20, 0 ⁇ 1-a-b ⁇ 1, 0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1, and c is a value that satisfies electrical neutrality), and in an X-ray diffraction pattern when the non-aqueous electrolyte secondary battery is initially charged, a peak derived from a compound different from the compound represented by the above composition formula is found to be in the range of a diffraction angle 2 ⁇ of 15.7° or more and
  • Na complex oxide sodium transition metal complex oxide
  • Li-Na complex oxide lithium sodium transition metal complex oxide
  • a cylindrical battery in which a wound electrode body 14 is housed in a cylindrical exterior body 16 with a bottom is exemplified as a nonaqueous electrolyte secondary battery, but the exterior body of the battery is not limited to a cylindrical exterior body.
  • the nonaqueous electrolyte secondary battery according to the present disclosure may be, for example, a prismatic battery with a prismatic exterior body, a coin battery with a coin-shaped exterior body, or a pouch-type battery with an exterior body composed of a laminate sheet including a metal layer and a resin layer.
  • the electrode body is not limited to a wound type, and may be a laminated type electrode body in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween.
  • the design of the nonaqueous electrolyte secondary battery according to the present disclosure is not limited to the design of the exemplified nonaqueous electrolyte secondary battery, and a known nonaqueous electrolyte secondary battery design may be applied.
  • the nonaqueous electrolyte secondary battery 10 includes a wound electrode body 14, a nonaqueous electrolyte, and an exterior body 16 that contains the electrode body 14 and the nonaqueous electrolyte.
  • the electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape with the separator 13 interposed therebetween.
  • the exterior body 16 is a cylindrical metal container with a bottom that is open on one axial side, and the opening of the exterior body 16 is closed by a sealing body 17.
  • the sealing body 17 side of the battery is referred to as the top
  • the bottom side of the exterior body 16 is referred to as the bottom.
  • the positive electrode 11, negative electrode 12, and separator 13 that constitute the electrode body 14 are all rectangular, elongated bodies that are spirally wound in the longitudinal direction and stacked alternately in the radial direction of the electrode body 14.
  • the separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other.
  • the two separators 13 are arranged, for example, to sandwich the positive electrode 11.
  • the electrode body 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.
  • the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction
  • the transverse direction of the positive electrode 11 and the negative electrode 12 is the axial direction. That is, the transverse end faces of the positive electrode 11 and the negative electrode 12 form the axial end faces of the electrode body 14.
  • Insulating plates 18, 19 are arranged above and below the electrode body 14.
  • the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes outside the insulating plate 19 and extends toward the bottom side of the exterior body 16.
  • the positive electrode lead 20 is connected to the underside of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal.
  • the negative electrode lead 21 is connected to the inner bottom inner surface of the exterior body 16 by welding or the like, and the exterior body 16 serves as the negative electrode terminal.
  • a gasket 28 is provided between the exterior body 16 and the sealing body 17 to ensure airtightness inside the battery.
  • the exterior body 16 has a grooved portion 22 that supports the sealing body 17, with part of the side surface protruding inward.
  • the grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior body 16, and supports the sealing body 17 on its upper surface.
  • the sealing body 17 is fixed to the top of the exterior body 16 by the grooved portion 22 and the open end of the exterior body 16 that is crimped to the sealing body 17.
  • the sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked.
  • Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to each other.
  • the lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges.
  • the positive electrode 11 has a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core.
  • a foil of a metal such as aluminum, an aluminum alloy, stainless steel, or titanium that is stable in the potential range of the positive electrode 11, or a film having such a metal disposed on the surface layer can be used.
  • the positive electrode mixture layer preferably contains a positive electrode active material, a conductive agent, and a binder, and is provided on both sides of the positive electrode core.
  • the positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core, drying the coating, and then compressing it to form a positive electrode mixture layer on both sides of the positive electrode core.
  • Examples of the conductive agent contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powders, conductive whiskers, etc.
  • the conductive agent may be used alone or in combination with multiple types.
  • the content of the conductive agent is not particularly limited, but is, for example, 0.1% by mass or more and 5% by mass or less with respect to the mass of the positive electrode mixture layer.
  • binder contained in the positive electrode mixture layer examples include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer, and acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer. These resins may also be used in combination with carboxymethylcellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.
  • CMC carboxymethylcellulose
  • PEO polyethylene oxide
  • One type of binder may be used alone, or multiple types may be used in combination.
  • the content of the binder is not particularly limited, but is, for example, 0.1% by mass or more and 5% by mass or less with respect to the mass of the positive electrode mixture layer.
  • the positive electrode active material has a crystal structure belonging to the space group R-3m and contains a lithium sodium transition metal composite oxide (Li-Na composite oxide) represented by the composition formula Li x Na y Ni 1-a-b Mn a X b O c .
  • Li-Na composite oxide Li x Na y Ni 1-a-b Mn a X b O c .
  • X is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, Ni, and Mn, and 0.80 ⁇ x ⁇ 1.15, 0 ⁇ y ⁇ 0.20, 0.80 ⁇ x+y ⁇ 1.20, 0 ⁇ 1-a-b ⁇ 1, 0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1, and c is a value that satisfies electrical neutrality.
  • the composite oxide constituting the positive electrode active material contains Li, Na, and Ni as essential elements, and preferably further contains Mn.
  • the contents of Li, Na, Ni, Mn and X contained in the positive electrode active material can be measured using an ICP emission spectrometer (for example, CIROS-120 manufactured by SPECTRO).
  • the molar ratio of Na (y) may be more than 0 and less than 0.2 (0 ⁇ y ⁇ 0.2), but is preferably 0.02 or more, more preferably 0.05 or more, and even more preferably 0.07 or more.
  • the molar ratio of Na (y) is 0.02 ⁇ y ⁇ 0.2, or 0.05 ⁇ y ⁇ 0.2, or 0.07 ⁇ y ⁇ 0.2, a peak appears prominently in the X-ray diffraction pattern at the time of the initial charge and discharge in the range of a diffraction angle 2 ⁇ of 15.7° or more and 18.0° or less.
  • a plateau region appears in the initial charge and discharge curve, and the improvement effect of the charge and discharge capacity and the initial charge and discharge efficiency becomes more prominent.
  • the molar ratio (y) of Na is preferably 0.15 or less, more preferably 0.14 or less, and even more preferably 0.13 or less.
  • the molar ratio (y) of Na is 0 ⁇ y ⁇ 0.15, or 0 ⁇ y ⁇ 0.14, or 0 ⁇ y ⁇ 0.13, it is considered that the layered structure of the complex oxide is stabilized, and the improvement effect of the charge/discharge capacity and the initial charge/discharge efficiency becomes more remarkable.
  • the molar ratio (y) of Na exceeds 0.2, Na ions are extracted to the positive electrode during charging, and the extracted Na ions may be occluded in the negative electrode.
  • an example of a suitable range for the molar ratio (y) of Na is 0.02 ⁇ y ⁇ 0.15, or 0.05 ⁇ y ⁇ 0.14, or 0.06 ⁇ y ⁇ 0.13.
  • the molar ratio of Li (x) may be 0.80 or more and 1.15 or less (0.80 ⁇ x ⁇ 1.15), but is preferably 0.82 or more, more preferably 0.84 or more.
  • the upper limit of the molar ratio of Li (x) is preferably 1.00, more preferably 0.95.
  • An example of a suitable range of the molar ratio of Li (x) is 0.80 ⁇ x ⁇ 1.00, 0.80 ⁇ x ⁇ 0.95, 0.82 ⁇ x ⁇ 1.15, 0.82 ⁇ x ⁇ 1.00, 0.82 ⁇ x ⁇ 0.95, 0.84 ⁇ x ⁇ 1.15, 0.84 ⁇ x ⁇ 1.00, or 0.84 ⁇ x ⁇ 0.95.
  • the molar ratio (x) of Li is within this range, the effects of improving the charge/discharge capacity and the initial charge/discharge efficiency become more significant.
  • the total molar ratio of Li and Na (x+y) may be more than 0.80 and 1.20 or less (0.80 ⁇ x+y ⁇ 1.20), but is preferably 0.85 or more, more preferably 0.90 or more, and even more preferably 0.95 or more.
  • the upper limit of the total molar ratio of Li and Na (x+y) is preferably 1.10, more preferably 1.05.
  • An example of a suitable range of the total molar ratio (x+y) of Li and Na is 0.80 ⁇ x+y ⁇ 1.10, 0.80 ⁇ x+y ⁇ 1.05, 0.85 ⁇ x+y ⁇ 1.20, 0.85 ⁇ x+y ⁇ 1.10, 0.85 ⁇ x+y ⁇ 1.05, 0.90 ⁇ x+y ⁇ 1.20, 0.90 ⁇ x+y ⁇ 1.10, 0.90 ⁇ x+y ⁇ 1.05, 0.95 ⁇ x+y ⁇ 1.20, 0.95 ⁇ x+y ⁇ 1.10, or 0.95 ⁇ x+y ⁇ 1.05. If the total molar ratio (x+y) of Li and Na is within this range, the improvement effect of the charge/discharge capacity and the initial charge/discharge efficiency becomes more remarkable.
  • the molar ratio of Ni (1-a-b) may be 1 or less (0 ⁇ 1-a-b ⁇ 1), but is preferably 0.82 or less, more preferably 0.70 or less.
  • the molar ratio of Ni (1-a-b) is preferably 0.30 or more, more preferably 0.40 or more. Therefore, an example of a suitable range of the molar ratio of Ni (1-a-b) is 0.30 ⁇ 1-a-b ⁇ 0.82, or 0.40 ⁇ 1-a-b ⁇ 0.70. In this case, the improvement effect of the charge-discharge capacity and the initial charge-discharge efficiency becomes more remarkable.
  • the positive electrode active material preferably contains Mn.
  • the molar ratio (a) of Mn is preferably 0.75 or less, more preferably 0.65 or less.
  • the molar ratio (a) of Mn is preferably 0.20 or more, more preferably 0.25 or more.
  • An example of a suitable range of the molar ratio (a) of Mn is 0.20 ⁇ a ⁇ 0.75, or 0.25 ⁇ a ⁇ 0.65. In this case, the improvement effect of the charge/discharge capacity and the initial charge/discharge efficiency becomes more remarkable.
  • X may be at least one element selected from Mg, Ca, Sr, Ba, Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, Sb, B, Ga, In, P, Zr, Hf, Nb, Ta, Mo, W, Co, and Al.
  • the molar ratio (b) of X is preferably 0.10 or less (0 ⁇ b ⁇ 0.10), more preferably 0.08 or less (0 ⁇ b ⁇ 0.08), and even more preferably 0.05 or less (0 ⁇ b ⁇ 0.05).
  • X is preferably at least one selected from Al, Co, and Zr, and among them, Al or Co is preferable.
  • Al is contained in the positive electrode active material
  • an example of a suitable range of the molar ratio (b) of Al is 0.005 ⁇ b ⁇ 0.025.
  • Co is contained in the positive electrode active material
  • an example of a suitable range of the molar ratio (b) of Co is 0.005 ⁇ b ⁇ 0.1.
  • the molar ratio of O (c) is a value that satisfies electrical neutrality.
  • the molar ratio of O (c) is a value that satisfies the valence of O in the positive electrode active material.
  • the layered rock salt structure has a structure in which oxygen is deficient.
  • the layered rock salt structure has an excess of oxygen.
  • the electron conductivity of the positive electrode active material is improved by oxygen deficiency, but if the oxygen deficiency increases, the crystal structure belonging to the space group R-3m cannot be maintained, which is thought to cause a decrease in charge/discharge capacity and cycle characteristics.
  • the electron conductivity of the positive electrode active material is improved by the presence of oxygen between the lattices, but if the amount of excess oxygen increases, the valence of Ni and Mn in the positive electrode active material increases, and it is thought that the charge capacity is greatly reduced. Therefore, for example, when the sum of the molar ratios of Ni, Mn, and X is 1, the molar ratio (c) of O is preferably 1.8 or more and 2.3 or less, more preferably 1.85 or more and 2.25 or less.
  • the oxygen amount of the positive electrode active material can be measured using an oxygen/nitrogen analyzer (e.g., EMGA-920 manufactured by Horiba, Ltd.).
  • the Li-Na composite oxide is, for example, a secondary particle formed by agglomeration of a plurality of primary particles.
  • An example of the volume-based median diameter (D50) of the Li-Na composite oxide is 1 ⁇ m or more and 30 ⁇ m or less, or 3 ⁇ m or more and 20 ⁇ m or less.
  • the D50 of the composite oxide is a particle size at which the volume integrated value is 50% in the particle size distribution measured by the laser diffraction scattering method.
  • the BET specific surface area of the Li-Na composite oxide is, for example, 0.1 m 2 /g or more and 10 m 2 /g or less, or 0.5 m 2 /g or more and 5 m 2 /g or less.
  • the BET specific surface area of the composite oxide is measured according to the BET method (nitrogen adsorption method) described in JIS R1626. If the D50 and the BET specific surface area are within the range, it is easy to increase the capacity.
  • the positive electrode active material is mainly composed of the Li-Na composite oxide.
  • the main component means the component with the highest mass ratio among the components of the positive electrode active material.
  • the mixture layer of the positive electrode 11 may contain a composite oxide other than the Li-Na composite oxide as the positive electrode active material, but the content of the Li-Na composite oxide is preferably 50 mass% or more, and may be substantially 100 mass%.
  • the Li-Na composite oxide has a peak at a diffraction angle 2 ⁇ in the range of 15.7° or more and 18.0° or less, which is derived from a compound different from the compound represented by the composition formula Li x Na y Ni 1-a-b Mn a X b O c , in an X-ray diffraction pattern obtained by X-ray diffraction when a nonaqueous electrolyte secondary battery is initially charged.
  • X is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, Ni, and Mn, and 0.80 ⁇ x ⁇ 1.15, 0 ⁇ y ⁇ 0.20, 0.80 ⁇ x+y ⁇ 1.20, 0 ⁇ 1-a-b ⁇ 1, 0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1, and c is a value that satisfies electrical neutrality.
  • the nonaqueous electrolyte secondary battery when the nonaqueous electrolyte secondary battery is initially charged refers to the case where the nonaqueous electrolyte secondary battery is initially charged, the initial charging being performed on the nonaqueous electrolyte secondary battery that is composed of a positive electrode containing a positive electrode active material made of the Li-Na composite oxide described above, a negative electrode made of lithium metal foil, and a nonaqueous electrolyte, and the specific conditions are as described in the examples described later.
  • the charging voltage during the initial charging is not particularly limited as long as it is a voltage at which the peak appears, but is, for example, 3.8 V or more, or may be 4.0 V or more, or may be 4.2 V or more.
  • Figure 2 shows the X-ray diffraction patterns of the Li-Na composite oxide of this embodiment during charging and discharging.
  • Figure 2 shows the X-ray diffraction patterns of the Li-Na composite oxide synthesized in Example 1 described below before charging and discharging and during the first charging and discharging.
  • Figure 2(a) is an overall view from 10° to 80°
  • Figure 2(b) is an enlarged view from 10° to 30°.
  • the Li-Na composite oxide of Example 1 has a peak in the 2 ⁇ range of 18.1° or more and 18.8° or less in the X-ray diffraction pattern before charging and discharging.
  • the diffraction peak appearing in the 2 ⁇ range of 18.1° or more and 18.8° or less is referred to as the first peak.
  • "a diffraction peak appearing in the range of numerical value (A)° or more and numerical value (B)° or less” means a diffraction peak having a peak top in the range of numerical value (A)° or more and numerical value (B)° or less.
  • the first peak is a diffraction peak of the (003) plane of the crystalline phase (hereinafter, the first crystalline phase ) of the Li-Na composite oxide represented by the composition formula Li x Na y Ni 1-a-b Mn a X b O c (wherein X is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, Ni, and Mn, and 0.80 ⁇ x ⁇ 1.15, 0 ⁇ y ⁇ 0.20, 0.80 ⁇ x+y ⁇ 1.20, 0 ⁇ 1-a-b ⁇ 1, 0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1, and c is a value that satisfies electrical neutrality).
  • the Li-Na composite oxide of Example 1 does not have a peak in the range of 2 ⁇ of 15.7° or more and 18.0 or less in the state before charging and discharging.
  • X is at least one selected from the group consisting of transition metal elements and typical elements other than Na, Ni, and Mn, and 0 ⁇ 1- ⁇ - ⁇ 1, 0 ⁇ 1, 0 ⁇ 1, and ⁇ is a value that satisfies electrical neutrality.
  • ⁇ is a value that satisfies electrical neutrality.
  • the intensity of the second peak increases.
  • the second peak does not appear in the X-ray diffraction pattern before charging. From this, it can be said that the second crystal phase does not exist in the positive electrode active material before charging, the second crystal phase appears when the charging voltage is increased, and the proportion of the second crystal phase present in the positive electrode active material increases when the charging voltage is further increased. Also, when the nonaqueous electrolyte secondary battery is charged up to 4.5 V and then discharged for the first time, the intensity of the second peak decreases.
  • the proportion of the second crystal phase present in the positive electrode active material decreases when discharging is performed. Furthermore, when discharging is performed with a lowered voltage, the second peak does not appear. Therefore, it is presumed that the crystal structure of the Li-Na composite oxide of Example 1 is the same as the crystal structure before charging, even when charging and discharging are performed.
  • the third peak is presumably a diffraction peak of the (003) plane of a Li-poor Li-Na composite oxide from which Li has been desorbed by charging.
  • the charge/discharge reaction proceeds in a state in which the first crystal phase and a Li-poor Li-Na composite oxide crystal phase (hereinafter, the third crystal phase) represented by a composition formula different from that of the first crystal phase coexist.
  • the intensity of the first peak attributable to the first crystal phase decreases, while the intensity of the third peak attributable to the third crystal phase increases.
  • the first crystal phase and the third crystal phase change their abundance ratio as charging and discharging proceeds.
  • a plateau region appears in which there is almost no change in voltage, and it is possible to realize a high capacity non-aqueous electrolyte secondary battery and an improvement in the initial charge and discharge efficiency.
  • Li-Na composite oxide is used as the positive electrode active material, which is represented by the composition formula Li x Na y Ni 1-a-b Mn a X b O c (wherein X is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, Ni, and Mn, and 0.80 ⁇ x ⁇ 1.15, 0 ⁇ y ⁇ 0.20, 0.80 ⁇ x+y ⁇ 1.20, 0 ⁇ 1-a-b ⁇ 1, 0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1, and c is a value that satisfies electrical neutrality), and in the X-ray diffraction pattern when the nonaqueous electrolyte secondary battery is initially charged, the diffraction angle 2 ⁇ has a peak in the range of 15.7° or more and 18.0° or less.
  • the effect of the present disclosure cannot be obtained if the X-ray diffraction pattern before the nonaqueous electrolyte secondary battery is initially charged, that is, at the time when the positive electrode active material is synthesized, has a peak in the range of the diffraction angle 2 ⁇ of 15.7° or more and 18.0° or less.
  • the X-ray diffraction pattern of the complex oxide is obtained using a desktop X-ray diffractometer (manufactured by Rigaku Corporation, product name "MiniFlex600") Diffracted X-rays are detected by a high-speed one-dimensional detector (D/teX Ultra 2).
  • the measurement conditions using the above X-ray diffraction device are as follows.
  • X-ray source CuK ⁇ ray Tube voltage: 40 kV Tube current: 15mA
  • the positive electrode active material which is an example of an embodiment, can be manufactured by the following method. Note that the manufacturing method described here is only one example, and the manufacturing method of the positive electrode active material is not limited to this method.
  • the Li-Na composite oxide is produced through a process of (1) mixing and calcining a sodium raw material and a nickel raw material to synthesize a Na composite oxide, and (2) reacting the Na composite oxide with a lithium compound to exchange a part of the Na in the Na composite oxide for Li.
  • a manganese raw material it is preferable to further add a manganese raw material, and a raw material containing an element X may be added, and a Na composite oxide is synthesized that is represented by the composition formula Na e Ni 1-f-g Mn f X g O h , where X is at least one element selected from metal elements other than Li, Na, Ni, and Mn, and e ⁇ 1.15, 0 ⁇ 1-f-g ⁇ 1, 0 ⁇ f ⁇ 1, 0 ⁇ g ⁇ 1, and h is a value that satisfies electrical neutrality.
  • the sodium raw material is at least one selected from the group consisting of metallic sodium and sodium compounds.
  • the sodium compound is not particularly limited as long as it contains Na, and examples thereof include acetates such as CH 3 COONa and CH 3 COONa.3H 2 O, nitrates such as NaNO 3 , sulfates such as Na 2 SO 4 , carbonates such as Na 2 CO 3 , hydrogen carbonates such as NaHCO 3 , hydroxides such as NaOH, and oxides such as Na 2 O and Na 2 O 2.
  • Na 2 CO 3 , NaHCO 3 , NaOH, and NaNO 3 are preferred.
  • the nickel raw material is at least one selected from the group consisting of metallic nickel and nickel compounds.
  • the nickel compound is not particularly limited as long as it contains Ni, and examples thereof include oxides such as NiO, hydroxides such as Ni(OH) 2 and NiOOH, nitrates such as NiNO 3 , carbonates such as NiCO 3 and Ni 4 CO 3 (OH) 6 (H 2 O) 4 , and sulfates such as NiSO 4. Among them, Ni(OH) 2 is preferred.
  • the manganese raw material is at least one selected from the group consisting of metallic manganese and manganese compounds.
  • the manganese compound is not particularly limited as long as it contains Mn, and examples thereof include oxides such as MnO, Mn2O3 , Mn3O4 , and MnO2, hydroxides such as Mn(OH) 2 and MnOOH, carbonates such as MnCO3 , nitrates such as Mn ( NO3 ) 2 , and sulfates such as MnSO4 .
  • Mn(OH) 2 is preferred.
  • the raw material containing element X at least one selected from the group consisting of element X and compounds of element X is used.
  • the compound containing element X is not particularly limited as long as it contains X, and examples thereof include oxides, hydroxides, carbonates, nitrates, and sulfates. Note that as the raw material for the Na composite oxide, a compound containing Ni and Mn, a compound containing Ni and X, a compound containing Mn and X, or a compound containing Ni, Mn, and X may be used.
  • the mixing ratio of the raw materials for the Na complex oxide may be set appropriately and is not particularly limited.
  • the molar ratio of Na in the mixture of raw materials for the Na complex oxide is e
  • the molar ratio of Ni is 1-f-g
  • the molar ratio of Mn is f
  • the molar ratio of element X is g
  • the ratios are set so that 0.90 ⁇ e ⁇ 1.15, 0.4 ⁇ 1-f-g ⁇ 0.82, 0.25 ⁇ f ⁇ 0.65, and 0.005 ⁇ g ⁇ 0.05.
  • the method for mixing the raw materials is not particularly limited as long as it can mix the raw materials uniformly, and mixing using a known mixer such as a mixer is an example.
  • the mixture of the raw materials is fired in a firing furnace in the air or in an oxygen stream.
  • the firing temperature is preferably 700°C or higher and 900°C or lower, and more preferably 750°C or higher and 850°C or lower.
  • the heating rate is preferably slow, for example, 0.3°C/min or higher and 5.0°C/min or lower, or 0.5°C/min or higher and 3.0°C/min or lower.
  • the firing time is preferably 20 hours or longer.
  • the firing time means the time from when the temperature of the firing furnace reaches the firing temperature to when the firing ends and cooling begins.
  • the fired product is, for example, rapidly cooled in the air by being removed from the firing furnace.
  • step (2) a part of the Na in the Na composite oxide is exchanged with Li. That is, it is necessary to exchange Li so that a predetermined amount of Na remains.
  • a suitable method of exchanging Na with Li includes a method of adding a molten salt of a lithium compound (hereinafter referred to as "lithium molten salt") to the Na composite oxide and heating it.
  • lithium hydroxide for example, at least one selected from the group consisting of lithium hydroxide, lithium carbonate, lithium hydrogen carbonate, lithium nitrate, lithium sulfate, lithium chloride, lithium iodide, and lithium bromide is used as the lithium molten salt, but it is preferable to use at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium hydrogen carbonate, and it is more preferable to use lithium hydroxide.
  • lithium hydroxide may be anhydrous or hydrated.
  • the molar ratio of lithium hydroxide to the total moles of the lithium molten salt is preferably 5 mol% or more, more preferably 25 mol% or more, even more preferably 50 mol% or more, and even more preferably 75 mol% or more.
  • the lithium molten salt may essentially be composed of only lithium hydroxide.
  • the mixing ratio of the Na composite oxide and the lithium molten salt can be set appropriately.
  • the mixing ratio of the Na composite oxide and the lithium molten salt is preferably such that the molar ratio (Li/Na) of Li in the lithium molten salt to Na in the Na composite oxide is 0.9 or more, more preferably 1.0 or more, and even more preferably 1.5 or more.
  • (Li/Na) is preferably 15 or less, preferably 10 or less, and even more preferably 8 or less.
  • the mixing ratio of the Na composite oxide and the lithium molten salt is preferably such that (Li/Na) is 0.9 or more and 15 or less, more preferably 1.0 or more and 10 or less, and even more preferably 1.5 or more and 8 or less.
  • the heating temperature in the Li exchange process is preferably 200°C or higher and 400°C or lower, and more preferably 250°C or higher and 350°C or lower. If the heating temperature exceeds 400°C, the reaction may proceed too rapidly, resulting in a non-uniform reaction. On the other hand, if the heating temperature is lower than 200°C, the reaction may not proceed sufficiently, and excess Na may remain.
  • the heating treatment time is set to 3 hours or higher and 10 hours or lower, for example, after the desired heating treatment temperature is reached by increasing the temperature at a rate of 3.0°C/min or higher and 8.0°C/min or lower. After the heating treatment, the material is cooled.
  • the cooling method is not particularly limited, and may be, for example, natural cooling (cooling in a furnace).
  • the resulting product is thoroughly washed with water, ethanol, or methanol, and then dried to obtain Li-Na composite oxide.
  • the atmosphere for drying after washing is either air or vacuum, and is not particularly limited. After washing, another heating treatment or another washing treatment may also be performed.
  • the negative electrode 12 may have, for example, a negative electrode core and a negative electrode mixture layer formed on the surface of the negative electrode core, or a metal Li foil may be used as the negative electrode 12.
  • the negative electrode 12 may have a negative electrode core, and lithium metal may be precipitated on the surface of the negative electrode core by charging.
  • the negative electrode 12 has a negative electrode mixture layer, the negative electrode mixture layer is preferably formed on both sides of the negative electrode core.
  • a foil of a metal stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film in which the metal is disposed on the surface layer may be used.
  • the thickness of the negative electrode core is, for example, 5 ⁇ m or more and 30 ⁇ m or less.
  • the negative electrode mixture layer includes, for example, a negative electrode active material and a binder.
  • the thickness of the negative electrode mixture layer is, for example, 10 ⁇ m or more and 150 ⁇ m or less on one side of the negative electrode core.
  • the negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. to the surface of a negative electrode core body, drying the coating, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode core body.
  • the negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly absorb and release lithium ions, and generally carbon materials such as graphite are used.
  • Graphite may be any of natural graphite such as scaly graphite, lump graphite, and earthy graphite, lump artificial graphite, and artificial graphite such as graphitized mesophase carbon microbeads.
  • metals that are alloyed with Li such as Si and Sn, metal compounds containing Si and Sn, and lithium titanium composite oxides may be used as the negative electrode active material.
  • those provided with a carbon coating may be used.
  • Si-containing compound represented by SiO x (0.5 ⁇ x ⁇ 1.6) or a Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by Li 2y SiO (2+y) (0 ⁇ y ⁇ 2) may be used in combination with graphite.
  • Binders contained in the negative electrode mixture layer include, for example, styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or it may be a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more types.
  • SBR styrene butadiene rubber
  • NBR nitrile butadiene rubber
  • CMC carboxymethyl cellulose
  • PAA polyacrylic acid
  • PAA-Na polyacrylic acid
  • PAA-K polyvinyl alcohol
  • PVA polyvinyl alcohol
  • a porous sheet having ion permeability and insulating properties is used for the separator 13.
  • the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric.
  • the material of the separator 13 is preferably a polyolefin such as polyethylene or polypropylene, or cellulose.
  • the separator 13 may have a single layer structure or a multi-layer structure.
  • a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.
  • a filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.
  • inorganic fillers include oxides and phosphate compounds containing metal elements such as Ti, Al, Si, and Mg.
  • the filler layer can be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13.
  • Non-aqueous electrolyte has ion conductivity (for example, lithium ion conductivity).
  • the non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.
  • the liquid electrolyte contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.
  • the non-aqueous solvent examples include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these.
  • the non-aqueous solvent may contain a halogen-substituted product in which at least a portion of the hydrogen of these solvents is replaced with a halogen atom such as fluorine.
  • halogen-substituted product examples include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylates such as methyl fluoropropionate (FMP).
  • FEC fluoroethylene carbonate
  • FMP fluorinated chain carboxylates
  • FEC fluoroethylene carbonate
  • FMP fluorinated chain carboxylates
  • esters examples include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylate esters such as gamma-butyrolactone (GBL) and gamma-valerolactone (GVL); and chain carboxylate esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).
  • cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate
  • chain carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC
  • ethers examples include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane ethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, Examples of such chain ethers include ethyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene,
  • the electrolyte salt is preferably a lithium salt.
  • the lithium salt include LiClO4 , LiBF4, LiPF6 , LiAlCl4 , LiSbF6 , LiSCN , LiCF3SO3 , LiCF3CO2 , LiAsF6 , LiB10Cl10 , lower aliphatic lithium carboxylate, LiCl, LiBr, LiI, phosphates, borates, and imide salts.
  • the phosphates include lithium difluorophosphate ( LiPO2F2 ) , lithium difluorobis(oxalato ) phosphate (LiDFBOP), and lithium tetrafluoro(oxalato)phosphate.
  • borates examples include lithium bis(oxalato)borate (LiBOB), and lithium difluoro(oxalato)borate (LiDFOB).
  • imide salt lithium bisfluorosulfonylimide (LiN(FSO 2 ) 2 ), lithium bistrifluoromethanesulfonate imide (LiN(CF 3 SO 2 ) 2 ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF 3 SO 2 )(C 4 F 9 SO 2 )), lithium bispentafluoroethanesulfonate imide (LiN(C 2 F 5 SO 2 ) 2 ), etc. are used.
  • the concentration of the lithium salt may be, for example, 4 mol or less per 1 L of nonaqueous solvent, may be 3 mol or less, preferably 1.8 mol or less, and more preferably 0.8 mol or more and 1.8 mol or less.
  • the non-aqueous electrolyte may contain an additive.
  • the additive include unsaturated carbonate esters, acid anhydrides, phenol compounds, benzene compounds, nitrile compounds, isocyanate compounds, sultone compounds, sulfate compounds, borate ester compounds, phosphate ester compounds, and phosphite ester compounds.
  • unsaturated cyclic carbonates examples include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate.
  • One type of unsaturated cyclic carbonate may be used alone, or two or more types may be used in combination. In the unsaturated cyclic carbonate, some of the hydrogen atoms may be substituted with fluorine atoms.
  • the acid anhydride may be an anhydride in which multiple carboxylic acid molecules are condensed intermolecularly, but is preferably an acid anhydride of a polycarboxylic acid.
  • acid anhydrides of polycarboxylic acids include succinic anhydride, maleic anhydride, and phthalic anhydride.
  • Phenol compounds include, for example, phenol and hydroxytoluene.
  • Benzene compounds include, for example, fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).
  • Nitrile compounds include adiponitrile, pimelonitrile, propionitrile, succinonitrile, etc.
  • Isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), bisisocyanatomethylcyclohexane (BIMCH), etc.
  • Sultone compounds include propane sultone, propene sultone, etc.
  • Sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, lithium fluorosulfate, etc.
  • Boron ester compounds include trimethyl borate, tris(trimethylsilyl)borate, etc.
  • Phosphate ester compounds include trimethyl phosphate, tris(trimethylsilyl)phosphate, etc.
  • Phosphite ester compounds include trimethyl phosphite, tris(trimethylsilyl)phosphite, etc.
  • the solid electrolyte for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used.
  • the inorganic solid electrolyte a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used.
  • the polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer.
  • the matrix polymer for example, a polymer material that absorbs a non-aqueous solvent and gels is used.
  • the polymer material for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.
  • Li-Na composite oxide was analyzed using an ICP optical emission spectrometer (CIROS-120 manufactured by SPECTRO) and an oxygen/nitrogen analyzer (EMGA-920 manufactured by HORIBA , Ltd.). It was confirmed that the Li-Na composite oxide was represented by the composition formula Li0.843Na0.122Ni0.503Mn0.497O1.93 .
  • the Li-Na composite oxide was used as the positive electrode active material.
  • the positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a solid content mass ratio of 92:5:3, and a positive electrode mixture slurry was prepared using N-methyl-2-pyrrolidone (NMP) as a dispersion medium.
  • NMP N-methyl-2-pyrrolidone
  • a non-aqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF 6 ) in a mixed solvent prepared by mixing fluoroethylene carbonate (FEC) and methyl propionate (FMP) in a volume ratio of 1:3 to a concentration of 1 mol/L.
  • LiPF 6 lithium hexafluorophosphate
  • FEC fluoroethylene carbonate
  • FMP methyl propionate
  • a lithium metal foil was used as the negative electrode, and the positive and negative electrodes were arranged to face each other with a separator interposed therebetween to prepare an electrode assembly.
  • the electrode assembly and the nonaqueous electrolyte were placed in a coin-shaped outer can, and the opening of the outer can was sealed with a gasket and a sealer to prepare a test cell (nonaqueous electrolyte secondary battery).
  • FIG. 3 shows the X-ray diffraction patterns of the Li-Na composite oxide synthesized in Example 2 before and during the initial charge and discharge.
  • a lithium molten salt was used, which was prepared by mixing lithium hydroxide, lithium nitrate, and lithium chloride in a molar ratio of 50:44:6.
  • the above-mentioned lithium molten salt and the Na composite oxide
  • composition formula of the prepared Li-Na composite oxide was Li 0.914 Na 0.0735 Ni 0.504 Mn 0.496 O 1.929 .
  • FIG. 4 shows the X-ray diffraction patterns of the Li-Na composite oxide synthesized in Example 3 before and during the initial charge and discharge.
  • a lithium molten salt was used, which was prepared by mixing lithium hydroxide, lithium nitrate, and lithium chloride in a molar ratio of 75:22:3.
  • the above-mentioned lithium molten salt and the Na composite oxide were mixed
  • composition formula of the prepared Li-Na composite oxide was Li 0.897 Na 0.0861 Ni 0.505 Mn 0.495 O 1.859 .
  • FIG. 5 shows the X-ray diffraction patterns of the Li-Na composite oxide synthesized in Example 4 before and during the initial charge and discharge.
  • a lithium molten salt was used, which was prepared by mixing lithium hydroxide, lithium nitrate, and lithium chloride in a molar ratio of 25:66:9.
  • the above-mentioned lithium molten salt and the Na composite oxide were mixed
  • composition formula of the prepared Li-Na composite oxide was Li 0.915 Na 0.0652 Ni 0.506 Mn 0.494 O 1.861 .
  • FIG. 6 shows the X-ray diffraction patterns of the Li-Na composite oxide synthesized in Example 5 before and during the initial charge and discharge.
  • the complex oxides of Examples 1 to 5 and Comparative Examples 1 and 2 have a first peak attributable to the (003) plane of the complex oxide in the range of 2 ⁇ of 18.1° or more and 18.8° or less in the X-ray diffraction patterns before charging and discharging.
  • the first peaks of the complex oxides of Examples 1 to 5 and Comparative Example 2 appear at lower angles than the first peak of the complex oxide of Comparative Example 1. This is because Na has a larger lattice constant than Li, and therefore the lattice constants of the complex oxides of Examples 1 to 5 and Comparative Example 2 that contain Na are larger than the lattice constant of the complex oxide of Comparative Example 1.
  • the second peak belonging to the (003) plane of the Na composite oxide appears within the range of 2 ⁇ of 15.7° or more and 18.0° or less.
  • the third peak belonging to the (003) plane of the Li-poor Li-Na composite oxide appears within the range of 2 ⁇ of 19.0° or more and 21.0° or less. That is, the first peak and the second peak appear simultaneously at some voltages, the first peak, the second peak, and the third peak appear simultaneously at some voltages, or the second peak and the third peak appear simultaneously at some voltages.
  • the second peak when the charging voltage is 3.8 V or more, the second peak does not appear, and even when the charging voltage is 4.32 V or more, the third peak does not appear. Furthermore, in the composite oxide of Comparative Example 2, the second peak does not appear when the charging voltage is 3.8 V or higher, and the third peak appears when the charging voltage is 4.32 V or higher, but the first and third peaks do not appear simultaneously.
  • Table 1 shows the charge capacity, discharge capacity, and initial charge/discharge efficiency of the test cells of Examples 1 to 5 and Comparative Examples 1 and 2.
  • Table 1 also shows the composition of the composite oxide, the type of lithium molten salt, and the presence or absence of a second peak during initial charging.
  • Figure 9 shows the initial charge/discharge curves of the test cells of Examples 1 to 3 and Comparative Example 1.
  • the test cells of Examples 1 to 5 have higher capacity and improved initial charge/discharge efficiency compared to the test cells of Comparative Examples 1 and 2.
  • a positive electrode active material that contains a predetermined amount of Na and has a peak in the diffraction angle 2 ⁇ range of 15.7° or more and 18.0° or less in the X-ray diffraction pattern obtained by X-ray diffraction when the nonaqueous electrolyte secondary battery is initially charged, it is possible to achieve high battery capacity and improved initial charge/discharge efficiency.
  • the positive electrode active material of Comparative Example 2 which uses lithium bromide as the lithium molten salt, contains almost no Na, so the second peak does not appear during charging and the battery does not achieve high capacity.
  • the test cells of Examples 1 to 3 have a plateau region where there is almost no change in voltage when the charge voltage and discharge voltage are around 4.3 V. This is presumably because, as described above, the first crystal phase and the third crystal phase coexist at a certain voltage, and charging and discharging proceeds while changing their abundance ratio.
  • the test cell of Comparative Example 1 does not have a plateau region when the charge voltage and discharge voltage are around 4.3 V. This is consistent with the fact that the test cell of Comparative Example 1 did not have a third peak belonging to the (003) plane of the third crystal phase in the X-ray diffraction pattern.
  • test cell of Comparative Example 2 does not have a plateau region when the charge voltage and discharge voltage are around 4.3 V, similar to the test cell of Comparative Example 1. That is, the test cell of Comparative Example 2 has a peak in the X-ray diffraction pattern that is attributed to the (003) plane of the third crystal phase, but no plateau region appears at charge and discharge voltages of around 4.3 V. This is presumably because charge and discharge proceed without the first and third crystal phases coexisting. Therefore, it is presumed that the second crystal phase that appears during charge and discharge acts as a medium for allowing the first and third crystal phases to coexist, and creates a plateau region in which charge and discharge proceed while changing the abundance ratio of each.
  • the test cells of Examples 4 and 5, like Examples 1 to 3, have higher capacities and improved initial charge/discharge efficiency compared to the test cells of Comparative Examples 1 and 2. This is due to the use of a positive electrode active material that contains a predetermined amount of Na and has a peak in the diffraction angle 2 ⁇ range of 15.7° or more and 18.0° or less in the X-ray diffraction pattern obtained by X-ray diffraction when the non-aqueous electrolyte secondary battery is initially charged. Furthermore, it was confirmed that the test cells of Examples 4 and 5 show a plateau region in which there is almost no change in voltage at charge and discharge voltages of around 4.3 V in the initial charge/discharge curves, like the test cells of Examples 1 to 3.
  • Li-Na composite oxide Li 0.897 Na 0.0944 Ni 0.596 Mn 0.404 O 2.
  • a positive electrode was prepared, a test cell was prepared, the charge/discharge capacity and the initial charge/discharge efficiency were evaluated, and X-ray diffraction measurements were performed.
  • the Li-Na composite oxide of Example 6 shows the X-ray diffraction patterns of the Li-Na composite oxide synthesized in Example 6 before and during the initial charge/discharge. As shown in FIG. 10, the Li-Na composite oxide of Example 6 has a second peak in the range of 2 ⁇ of 15.7° or more and 18.0° or less when the charge voltage is 4.0 V or more.
  • Example 11 shows the X-ray diffraction pattern of the Li-Na composite oxide synthesized in Example 7 before charge and discharge, and during the initial charge and discharge.
  • the second peak appeared within the range of 2 ⁇ of 15.7° or more and 18.0° or less.
  • Example 12 shows the X-ray diffraction patterns of the Li-Na composite oxide synthesized in Example 8 before and during the initial charge and discharge. As shown in FIG. 12, in the Li—Na composite oxide of Example 7, when the charging voltage was 4 V or higher, a second peak appeared within the range of 2 ⁇ of 15.7° or more and 18.0° or less.
  • the composition formula of the prepared composite oxide was Li1.0Ni0.596Mn0.404O2 .
  • Tables 2, 3, and 4 show the composition of the composite oxide, the type of lithium molten salt, and the presence or absence of a second peak during initial charging.
  • test cells of Examples 6, 7, and 8 have higher capacities and improved initial charge/discharge efficiencies compared to the test cells of Comparative Examples 3, 4, and 5.
  • the effects of the present disclosure are achieved even when the Ni content of the composite oxide is increased.
  • Configuration 1 A positive electrode active material for use in a non-aqueous electrolyte secondary battery, the positive electrode active material having a crystal structure belonging to space group R-3m and represented by a composition formula Li x Na y Ni 1-a-b Mn a X b O c , in which X is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, Ni, and Mn, 0.80 ⁇ x ⁇ 1.15, 0 ⁇ y ⁇ 0.20, 0.80 ⁇ x+y ⁇ 1.20, 0 ⁇ 1-a-b ⁇ 1, 0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1, and c are values that satisfy electrical neutrality, and when the non-aqueous electrolyte secondary battery is initially charged, an X-ray diffraction pattern obtained by X-ray diffraction has a peak derived from a compound other than the compound represented by the composition formula in a diffraction angle 2 ⁇ range of 15.7° or more and 18.0°
  • Configuration 2 The positive electrode active material according to configuration 1, wherein the charging voltage in the initial charging is 3.8 V or more.
  • Configuration 3 The positive electrode active material according to configuration 1 or 2, wherein the peak is a peak attributable to a compound belonging to space group R-3m and represented by a composition formula NaNi 1- ⁇ - ⁇ Mn ⁇ X ⁇ O ⁇ , in which X is at least one selected from the group consisting of transition metal elements and typical elements other than Na, Ni, and Mn, and 0 ⁇ 1- ⁇ - ⁇ 1, 0 ⁇ 1, 0 ⁇ 1, and ⁇ is a value that satisfies electrical neutrality.
  • Aspect 4 The positive electrode active material according to any one of Aspects 1 to 3, wherein in the composition formula Li x Na y Ni 1-ab Mn a X b O c , the molar ratio of Na (y) is 0.02 ⁇ y ⁇ 0.15.
  • Aspect 5 The positive electrode active material according to any one of aspects 1 to 4, wherein in the composition formula Li x Na y Ni 1-ab Mn a X b O c , the molar ratio of Na (y) is 0.06 ⁇ y ⁇ 0.13.
  • Aspect 6 The positive electrode active material according to any one of aspects 1 to 5, wherein in the composition formula Li x Na y Ni 1-ab Mn a X b O c , the molar ratio of Ni (1-ab) is 0.3 ⁇ 1-bc ⁇ 0.82.
  • Structure 7 The positive electrode active material according to any one of structures 1 to 6, wherein in the composition formula Li x Na y Ni 1-a-b Mn a X b O c , X is at least one selected from Mg, Ca, Sr, Ba, Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, Sb, B, Ga, In, P, Zr, Hf, Nb, Ta, Mo, W, Co, and Al.
  • Constitution 8 The positive electrode active material according to any one of constitutions 1 to 7, wherein in the composition formula Li x Na y Ni 1-ab Mn a X b O c , X is at least one selected from Al and Co.
  • Configuration 9 A method for producing a positive electrode active material for use in a non-aqueous electrolyte secondary battery, comprising the steps of : synthesizing a Na composite oxide represented by a composition formula NaeNi1 -f-gMnfXgOh (wherein X is at least one element selected from metal elements other than Li, Na, Ni , and Mn, and e ⁇ 1.15, 0 ⁇ 1-f-g ⁇ 1, 0 ⁇ f ⁇ 1, 0 ⁇ g ⁇ 1, and h is a value that satisfies electrical neutrality); and reacting the Na composite oxide with a lithium compound to exchange a portion of Na in the Na composite oxide for Li, wherein the lithium compound includes at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium
  • Configuration 10 A positive electrode comprising the positive electrode active material of any one of configurations 1 to 8.
  • Aspect 11 A nonaqueous electrolyte secondary battery comprising the positive electrode according to aspect 10, a negative electrode, and a nonaqueous electrolyte.

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PCT/JP2024/022567 2023-07-31 2024-06-21 正極活物質、正極、非水電解質二次電池、および正極活物質の製造方法 Pending WO2025028061A1 (ja)

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JP2017174558A (ja) 2016-03-22 2017-09-28 本田技研工業株式会社 リチウム複合酸化物およびその製造方法、二次電池用正極活物質ならびに二次電池
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KR20030047456A (ko) * 2001-12-10 2003-06-18 학교법인 한양학원 리튬 2차 전지용 층상 망간 양극 활물질, 그의 제조방법및 그를 포함하는 리튬 2차 전지
JP2004323331A (ja) * 2003-04-28 2004-11-18 Tosoh Corp リチウム−ニッケル−マンガン複合酸化物及びその製造方法並びにその用途
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