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EP-4738440-A1 - POSITIVE ELECTRODE ACTIVE MATERIAL, BATTERY, AND METHOD OF PRODUCING POSITIVE ELECTRODE ACTIVE MATERIAL

EP4738440A1EP 4738440 A1EP4738440 A1EP 4738440A1EP-4738440-A1

Abstract

A positive electrode active material comprises secondary particles (1), wherein each of the secondary particles includes primary particles, each of the primary particles includes an olivine-type phosphate compound, carbon and lithium phosphate are adhered to at least part of a surface of the secondary particle (1), in a cross section of the secondary particle (1), the secondary particle (1) is composed of a central portion (1a), an intermediate portion (1b), and an outer peripheral portion (1c), a relationship of 1.05≤C LPO /X LPO is satisfied, where C LPO represents an amount-of-substance concentration of lithium phosphate in the outer peripheral portion (1c), and X LPO represents an average value of amount-of- substance concentrations of lithium phosphate in the central portion (1a), the intermediate portion (1b), and the outer peripheral portion (1c).

Inventors

  • ISHIGAKI, Yuki
  • EGUCHI, TATSUYA
  • KIMIJIMA, Takeshi

Assignees

  • TOYOTA JIDOSHA KABUSHIKI KAISHA

Dates

Publication Date
20260506
Application Date
20251001

Claims (11)

  1. A positive electrode active material comprising: secondary particles (1), wherein each of the secondary particles includes primary particles, each of the primary particles includes an olivine-type phosphate compound, carbon and lithium phosphate are adhered to at least part of a surface of the secondary particle (1), in a cross section of the secondary particle (1), the secondary particle (1) is composed of a central portion (1a), an intermediate portion (1b), and an outer peripheral portion (1c), and a relationship of 1.05≤C LPO /X LPO is satisfied, where C LPO represents an amount-of-substance concentration of lithium phosphate in the outer peripheral portion (1c), and X LPO represents an average value of amount-of- substance concentrations of lithium phosphate in the central portion (1a), the intermediate portion (1b), and the outer peripheral portion (1c).
  2. The positive electrode active material according to claim 1, wherein a relationship of 1.5≤C LPO /X LPO is satisfied.
  3. The positive electrode active material according to claim 1, wherein a relationship of C LPO /X LPO ≤7.0 is satisfied.
  4. The positive electrode active material according to claim 1, wherein a relationship of C LPO /X LPO ≤4.5 is satisfied.
  5. The positive electrode active material according to claim 1, wherein a relationship of C LPO /X LPO ≤3.0 is satisfied.
  6. The positive electrode active material according to claim 1, wherein the surface of the secondary particle (1) includes a first adhesion portion (4) and a second adhesion portion (5), carbon is adhered to the first adhesion portion (4), and carbon and lithium phosphate are adhered to the second adhesion portion (5).
  7. The positive electrode active material according to claim 1, wherein the olivine-type phosphate compound is lithium manganese iron phosphate.
  8. A battery comprising the positive electrode active material according to any one of claims 1 to 7.
  9. The battery according to claim 8, having a bipolar structure.
  10. A method of producing a positive electrode active material, the method comprising: (a) mixing a manganese compound, a first lithium compound, a first phosphate compound, a carbon material, and a first solvent to form a first slurry; (b) forming precursor particles by drying the first slurry; (c) performing heat treatment of the precursor particles to form first particles; (d) mixing the first particles, a second lithium compound, a second phosphate compound, and a second solvent to form a second slurry; and (e) drying the second slurry to produce second particles.
  11. The method of producing a positive electrode active material according to claim 10, wherein a concentration of the second lithium compound in the second slurry is more than 0.1% and not more than 0.5% in mass fraction, and a concentration of the second phosphate compound in the second slurry is more than 0.3% and not more than 1.5% in mass fraction.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This nonprovisional application is based on Japanese Patent Application No. 2024-191444 filed on October 31, 2024, with the Japan Patent Office, the entire contents of which are hereby incorporated by reference. BACKGROUND Field The present disclosure relates to a positive electrode active material, a battery, and a method of producing a positive electrode active material. Description of the Background Art Japanese Patent Laying-Open No. 2019-175764 discloses a positive electrode material for a lithium-ion secondary battery wherein the surface of an olivine-type phosphate compound is covered with carbon. SUMMARY As a positive electrode active material, olivine-type phosphate compounds have been developed. Conventionally, suggestions have been made for enhancing electronic conductivity by covering an olivine-type phosphate compound with carbon. However, there is room for improvement in endurance. An object of the present disclosure is to improve endurance. Hereinafter, the technical configuration and effects of the present disclosure will be described. It should be noted that the action mechanism according to the present disclosure includes presumption. The action mechanism does not limit the technical scope of the present disclosure. A positive electrode active material comprising: secondary particles, whereineach of the secondary particles includes primary particles,each of the primary particles includes an olivine-type phosphate compound,carbon and lithium phosphate are adhered to at least part of a surface of the secondary particle,in a cross section of the secondary particle, the secondary particle is composed of a central portion, an intermediate portion, and an outer peripheral portion, anda relationship of 1.05≤CLPO/XLPO is satisfied, whereCLPO represents an amount-of-substance concentration of lithium phosphate in the outer peripheral portion, andXLPO represents an average value of amount-of- substance concentrations of lithium phosphate in the central portion, the intermediate portion, and the outer peripheral portion. When only carbon is adhered to the surface of a secondary particle, an olivine-type phosphate compound included in the secondary particle degrades during charge-discharge cycles, and as a result, capacity degradation may be facilitated. Hence, there is a chance that sufficient endurance may not be obtained. In the present disclosure, not only carbon but also lithium phosphate (Li3PO4, which may be simply called "LPO" hereinafter) are adhered to the surface of a secondary particle. Moreover, in the present disclosure, carbon and LPO are adhered to not only the surface but also the inside of a secondary particle. It is conceivable that when the amount-of-substance concentration (concentration in terms of amount of substance) of LPO at the surface of a secondary particle is higher than the amount-of-substance concentration of LPO inside the secondary particle, especially when the relationship of 1.05<CLPO/XLPO is satisfied, degradation of the olivine-type phosphate compound included in the secondary particle may be inhibited. As a result, endurance is expected to be improved. The positive electrode active material according to [1], wherein a relationship of 1.5≤CLPO/XLPO is satisfied. When the relationship of 1.5≤CLPO/XLPO is satisfied, endurance is expected to be further improved. The positive electrode active material according to [1] or [2], wherein a relationship of CLPO/XLPO≤7.0 is satisfied. The greater the CLPO/XLPO is, the more improved the endurance is expected to be. However, when CLPO/XLPO is great, specific capacity tends to be degraded. When the relationship of CLPO/XLPO≤7.0 is satisfied, endurance and specific capacity are expected to be well balanced. The positive electrode active material according to any one of [1] to [3], wherein a relationship of CLPO/XLPO≤4.5 is satisfied. When the relationship of CLPO/XLPO≤4.5 is satisfied, endurance and specific capacity are expected to be balanced even better. The positive electrode active material according to any one of [1] to [4], wherein a relationship of CLPO/XLPO≤3.0 is satisfied. The positive electrode active material according to any one of [1] to [5], wherein the surface of the secondary particle includes a first adhesion portion and a second adhesion portion,carbon is adhered to the first adhesion portion, andcarbon and lithium phosphate are adhered to the second adhesion portion. The positive electrode active material according to any one of [1] to [6], wherein the olivine-type phosphate compound is lithium manganese iron phosphate. A battery comprising the positive electrode active material according to any one of [1] to [7]. The battery according to [8], having a bipolar structure. A method of producing a positive electrode active material, the method comprising: (a) mixing a manganese compound, a first lithium compound, a first phosphate compound, a carbon material, and a first