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US-12620593-B2 - Positive electrode active material, positive electrode having the same and lithium secondary battery

US12620593B2US 12620593 B2US12620593 B2US 12620593B2US-12620593-B2

Abstract

The invention relates to a process for the preparation of carbon-deposited alkali metal oxyanion and the use thereof as cathode material in lithium secondary batteries wherein the process comprises synthesis of partially reacted alkali metal oxyanion, a wet-based nanomilling step, a drying step and a subsequent carbon deposition step performed by a thermal CVD process. The invention also relates to carbon deposited alkali metal oxyanion with less than 80 ppm of sulfur impurities for the preparation of a cathode of lithium secondary batteries with exceptional high-temperature electrochemical properties.

Inventors

  • Christophe Michot

Assignees

  • Christophe Michot

Dates

Publication Date
20260505
Application Date
20240601

Claims (20)

  1. 1 . A process for the preparation of a carbon deposited lithium metal phosphate of formula LiMPO 4 , said process comprising the steps: a) performing a wet or dry milling of LiMPO 4 precursors, comprising at least one lithium source, at least one M source, at least one phosphorous source, and at least one organic carbon source, drying the milled precursors if milling is performed as a wet milling to obtain a solid compound; heat treating the milled precursors under a protective atmosphere to obtain a heat treated material, wherein; the sources of lithium, M, and phosphorous is optionally introduced, in whole or in part, in the form of compounds with more than one source element; M comprises at least 95% at. of Fe (II), or Mn (II), or mixture thereof; Fe, or Mn, or mixture thereof in the heat treated material is in 2+ oxidation state; conversion rate of the heat treated material as olivine structure LiMPO 4 is between 30 and 99 mol %; b) subjecting the material obtained in step a) to at least one water-based or alcohol-based bead milling to obtain a milled suspension of particles of said material having a median size to less than 500 nm; c) drying the milled suspension obtained in step b) to obtain a solid compound; d) subjecting the solid compound obtained in step c) to at least one thermal chemical vapor deposition process with a gas-phase carbon source to obtain a carbon deposit.
  2. 2 . A process according to claim 1 wherein the heat treatment of step a) is carried out at a temperature between 550 to 650° C.
  3. 3 . A process according to claim 1 wherein the bead milling of step b) is performed in water as fluid carrier.
  4. 4 . A process according to claim 1 wherein the bead milling of step b) is performed in alcohol as fluid carrier.
  5. 5 . A process according to claim 1 wherein the bead milling of step b) is performed in a stir bead mills, with beads having a mean diameter between 50 and 800 μm.
  6. 6 . A process according to claim 1 wherein the bead milling of step b) is performed in presence of an amount of a reductant of less than 10000 ppm, relatively to the mass of the heat treated material of step a).
  7. 7 . A process according to claim 6 wherein the reductant is selected from the group consisting of hydrazine, hydroquinone, formic acid, ascorbic acid, and mixture thereof.
  8. 8 . A process according to claim 1 wherein after the bead milling of step b) the heat treated material of step a) is obtained in the form of primary particles having a median size comprised between 25 and 250 nm.
  9. 9 . A process according to claim 1 wherein the drying of step c) is performed by spray drying.
  10. 10 . A process according to claim 1 wherein the gas-phase carbon source is selected from the group consisting of benzene, propylene, acetylene, and mixture thereof, and wherein thermal CVD step is performed at a temperature between 60° and 750° C.
  11. 11 . A process according to claim 1 wherein the water content of the carbon deposited LiMPO 4 is less than 200 ppm, based on total weight of carbon deposited LiMPO 4 .
  12. 12 . A process according to claim 1 wherein the carbon deposit content is less than 2.5 wt. %, based on total weight of carbon deposited LiMPO 4 .
  13. 13 . A process according to claim 1 wherein the carbon deposited LiMPO 4 is in the form of carbon deposited spherical secondary agglomerates of LiMPO 4 primary particles.
  14. 14 . A process according to claim 13 , wherein the porosity of the secondary agglomerates is between 5 and 40%.
  15. 15 . A process according to claim 13 , wherein the secondary agglomerates press density is comprised between 2.4 and 3 g/cm 3 .
  16. 16 . A process according to claim 1 , wherein the electronic conductivity of the carbon deposited lithium metal phosphate of formula LiMPO 4 is more than 10 −1 S·cm −1 .
  17. 17 . A process according to claim 1 , wherein the carbon deposit is in the form of a continuous, adherent, and uniform deposit.
  18. 18 . A process according to claim 1 wherein LiMPO 4 is LiFePO 4 .
  19. 19 . A process according to claim 1 wherein lithium source is lithium carbonate, M and phosphorous source is FePO 4 ·xH 2 O, x is 0≤x≤4.
  20. 20 . A process according to claim 1 wherein M comprises one or more other metals, comprising Ni, or Co, or aliovalent or isovalent metals selected from the group consisting of Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru, Ga, Sr, Ba, B and W.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a divisional of U.S. patent application Ser. No. 18/203,027, filed May 29, 2023 (now U.S. Pat. No. 12,040,487), which is a divisional of U.S. patent application Ser. No. 16/802,551, filed Feb. 26, 2020 (now U.S. Pat. No. 11,721,808), which claims the benefit of U.S. Provisional Application 62/810,872 filed Feb. 26, 2019, the contents of which are herein incorporated by reference in their entirety. FIELD OF THE INVENTION The present invention relates to a carbon-deposited alkali metal oxyanion, as well as to a multi-step process for preparing same, and the use thereof of said carbon-deposited alkali metal oxyanion as cathode material in lithium secondary batteries. BACKGROUND OF THE INVENTION Olivine-type LiFePO4 has become an important cathode material for lithium ion batteries as a result of its superior capacity retention, thermal stability, nontoxicity and safety. But olivine LiFePO4 suffers from significant disadvantages, such as low intrinsic and ionic conductivity. Coating with carbon can improve electrical conductivity, and poor lithium ion diffusion can be addressed by the synthesis of small particles. In the specific case of a carbon-deposited lithium ferrous phosphate, referred to as C—LiFePO4, several processes have been proposed to manufacture the material, either by pyrolysis of a carbon precursor on LiFePO4 or by simultaneous reaction of lithium, iron and PO4 sources and a carbon precursor. For example, EP 1 049 182 A3 and US 2002/0195591 A1 describe solid-state thermal processes allowing synthesis of C—LiFePO4 including through the following reaction: Fe(III)⁢PO4+Li⁢‐⁢source+carbon⁢ precursor→C⁢‐⁢LiFe(II)⁢PO4 in which the carbon precursor is an organic material that forms a carbon deposit through pyrolysis while generating reducing gases that efficiently reduce the iron (III). US 2007/0054187 A1 discloses the preparation of lithium metal phosphate LiMPO4 through the reaction of a Li-source, at least one M-source (M can be Fe, Mn, Co, Ni) and at least one PO4-source under hydrothermal conditions at a temperature between 10° and 250° C. and at a pressure from 1 to 40 bar. The disclosed process comprises mixing LiMPO4 with a carbon precursor, drying and calcining the obtained mixture, allowing synthesis of C-LiMPO4. The implementation of such processes at an industrial scale presents challenges as they involve a number of simultaneously occurring chemical, electrochemical, gas-phase, gas-solid reactions, sintering, and carbon deposition. The electrochemical properties of an alkali metal oxyanion electrode material having a carbon deposit are thus dependent on numerous parameters such as surface properties, wettability, surface area, porosity, particle size distribution, water-content, crystal structure, carbon deposit conductivity, as well as the raw materials chemistry, reactor feed rate, flow of gas, etc. All those properties are difficult to control in a very precise fashion during the reaction, which results in the obtaining of non-stoichiometric materials, the incompleteness of the reaction and the remaining of impurities in the obtained materials. Problems therefore remain to find a simple and optimized process for making higher quality cathode materials for battery applications. SUMMARY OF THE INVENTION Therefore it is the object of the present invention to provide an alternative process for manufacturing carbon-deposited alkali metal oxyanion as cathode material, which shows similar if not better electrochemical performance than materials of the prior art when the carbon-deposited alkali metal oxyanion according to the present invention is used as active electrode material in lithium secondary batteries. Furthermore, it is the object of the present invention to provide a versatile process for the preparation of carbon-deposited alkali metal oxyanion comprising only a few synthesis steps, which can be conducted easily for manufacturing various grades of high-performance and cost-effective cathode materials. Moreover, at each steps, process allows efficient control and optimization of the precursors, impurities susceptible to reactions that are detrimental to battery operation, particle morphology and quality of carbon deposit. The object is achieved by a multi-step process for the preparation of a carbon-deposited alkali metal oxyanion. In the specific case of a carbon-deposited lithium ferrous phosphate, referred to as C—LiFePO4, said process preferably comprising the steps: a) mixing, preferably milling, starting material compounds comprising at least one lithium source, at least one ferric phosphate source, and at least one organic carbon source, and heating the starting material to obtain a carbon-deposited lithium ferrous phosphate, preferably comprising a ferrous phosphate or pyrophosphate phase;b) subjecting the material obtained in step a): PROCESS A: to at least one water-based bead nanomilling step, preferably