Composite-coated solid-state battery cathode material, preparation method and solid-state battery

Abstract

The application provides a composite-coated solid-state battery positive electrode material, a preparation method and a solid-state battery. The preparation method comprises the following steps: a mixed metal salt solution containing a single crystal directing agent is mixed with an ammonia alkali mixed solution and is passed into a reaction kettle in a parallel flow to perform a co-precipitation reaction, so as to obtain a positive electrode precursor; the positive electrode precursor, a lithium-rich spinel powder, a first fast ion conductor powder and a first lithium salt are subjected to a first sintering treatment to obtain a positive electrode intermediate; the positive electrode intermediate is subjected to liquid phase coating treatment with a second fast ion conductor powder, a zirconium source and a second lithium salt, and after a second sintering treatment, the composite-coated solid-state battery positive electrode material is obtained. When the composite-coated solid-state battery positive electrode material provided by the application is applied to a solid-state battery, the interface impedance between the solid-state electrolyte and the positive electrode can be significantly reduced, the lithium ion transmission efficiency is improved, and thus the interface stability and long cycle life of the solid-state battery are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, specifically relating to a composite-coated solid-state battery cathode material, its preparation method, and a solid-state battery. Background Technology

[0002] Solid-state batteries, as a new generation of power battery technology, are increasingly demonstrating their core advantages. Replacing traditional liquid electrolytes with solid electrolytes, they possess significant characteristics such as high energy density, strong safety, and long cycle life, making them widely applicable to diverse scenarios including new energy vehicles, energy storage systems, and low-altitude aircraft. With the rapid development of solid-state batteries, the demand for cathode and precursor materials is also growing rapidly, and the high-nickelization of ternary cathode materials has become a crucial aspect of solid-state battery technology development.

[0003] However, high-nickel ternary cathode materials have two main drawbacks in practical applications of solid-state batteries: First, the volume of high-nickel ternary cathode materials shrinks / expands during cycling, easily leading to mechanical degradation or void formation at the solid-solid interface, affecting interfacial mechanical stability. Second, due to the high surface oxidation state of high-nickel ternary cathode materials, especially at high charging potentials, the solid electrolyte is prone to chemical and electrochemical interfacial side reactions with the cathode material, affecting interfacial chemical and electrochemical stability. Currently, although researchers have proposed using surface coating and other techniques to improve the interfacial compatibility between the cathode and the solid electrolyte, the passive physical isolation effect of traditional coating techniques (such as Al2O3 coating layers) is limited, and rigid coating layers are prone to cracking and failure under volume expansion; at the same time, some coating materials have poor electronic conductivity, resulting in a large interfacial impedance between the two.

[0004] Therefore, how to further solve the problems of poor compatibility of high-nickel ternary cathode materials with solid electrolytes, incompatibility of coating layer interfaces, and large interface impedance remains the main challenge currently faced by those skilled in the art. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a composite-coated solid-state battery cathode material and its preparation method. When this composite-coated solid-state battery cathode material is applied to a solid-state battery, it can significantly reduce the interfacial impedance between the solid electrolyte and the cathode, improve the lithium-ion transport efficiency, and thus greatly improve the interfacial stability and long cycle life of the solid-state battery.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a composite-coated solid-state battery cathode material, the method comprising the following steps: A mixed metal salt solution containing a single-crystal directing agent and a mixed ammonia-alkali solution are fed into a reactor in parallel to carry out a co-precipitation reaction to obtain a positive electrode precursor. The cathode precursor, lithium-rich spinel powder, first fast ion conductor powder and first lithium salt are subjected to a first sintering process to obtain a cathode intermediate. The cathode intermediate is subjected to liquid-phase coating with a second fast ion conductor powder, a zirconium source, and a second lithium salt. After a second sintering process, the composite-coated solid-state battery cathode material is obtained.

[0007] This invention effectively solves the problems of poor compatibility of high-nickel ternary cathode materials with solid electrolytes, incompatibility of coating layer interfaces, and high impedance by adopting a synergistic strategy that combines a highly crystalline single-crystal cathode precursor with a double-layer functional coating layer.

[0008] Specifically, on the one hand, the preparation method provided by the present invention enables the functional coating layer to be effectively bonded to the high-nickel ternary cathode material matrix, further enhancing the structural and chemical stability of the composite cathode material, effectively suppressing material oxidation, gas generation and surface residual lithium side reactions, reducing capacity decay during cycling, and thus extending the material's service life. On the other hand, the present invention first constructs an inner coating layer containing the first fast ion conductor powder on the surface of the highly crystalline single-crystal cathode precursor, which can accelerate lithium ion transport and improve the material interface stability. At the same time, the high-valence metal elements in the first fast ion conductor powder enter the material lattice through bulk doping, which has the following technical effects: (1) High-valence doped ions (such as Ta) 5+ 、Nb 5+ or Zr 4+ Ni can be suppressed through charge compensation. 2+ Migration to the lithium layer significantly reduces the degree of cation mixing and effectively alleviates the severe lattice shrinkage caused by the harmful H2-H3 phase transition during charging and discharging, fundamentally reducing the generation of microcracks and ensuring the structural integrity of the material during long-term cycling; (2) Doping ions (especially Zr) 4+ Ti 4+ The ionic radius of the ions is larger than that of the replaced transition metal ions. After entering the lattice, the interlayer spacing of the layered structure increases, which widens the fast migration channel of lithium ions and significantly reduces the transport resistance of lithium ions in the bulk phase; (3) After the high-valence doped ions enter the lattice, lithium vacancies will be induced in the lithium layer in order to maintain charge balance. These lithium vacancies provide "vacancy sites" for neighboring lithium ions to jump to, which significantly reduces the energy barrier required for lithium ion migration; at the same time, doping also regulates Ni 3+ / Ni 2+By optimizing the electronic structure, the diffusion coefficient of lithium ions within the cathode phase is further improved. Then, this invention successfully constructs a multi-component synergistic outer coating layer on the surface of the cathode intermediate, further reducing the interfacial impedance between the solid electrolyte and the cathode, and effectively preventing side reactions with sulfide solid electrolytes, thus ensuring that the resulting composite-coated solid-state battery cathode material perfectly meets the requirements of solid electrolyte applications.

[0009] Preferably, the single-crystal directing agent comprises citric acid and sodium gluconate.

[0010] Preferably, the mass percentage of the single crystal guiding agent is 2% to 5%, based on the total mass of the metal elements in the mixed metal salt solution as 100%. For example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0011] In this invention, by controlling the specific type and mass percentage of the single-crystal directing agent, the nucleation and crystal growth kinetics can be better controlled, promoting anisotropic growth and inhibiting polycrystalline nucleation, thereby obtaining single-crystal morphology or single-crystal-like high-crystallinity cathode precursor particles.

[0012] Preferably, the mass ratio of citric acid to sodium gluconate is 1:(1~2), for example, it can be 1:1, 1:1.2, 1:1.5, 1:1.8 or 1:2, etc., not limited to the listed values. Other unlisted values ​​within this range are also applicable, which is conducive to forming "quasi-single crystal" spherical secondary particles with consistent internal atomic arrangement.

[0013] Preferably, the total concentration of transition metal ions in the mixed metal salt solution is 1.5 mol / L to 2.5 mol / L, for example, it can be 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L or 2.5 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] Preferably, the mixed metal salt solution contains nickel, cobalt, and M, wherein the M element exemplarily includes manganese and / or aluminum.

[0015] Preferably, the concentration of ammonia in the ammonia-alkali mixed solution is 0.1 mol / L to 0.3 mol / L, for example, it can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L or 0.3 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the concentration of alkali in the ammonia-alkali mixed solution is 1.0 mol / L to 2.0 mol / L, for example, it can be 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L or 2.0 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] As an example, the base may be sodium hydroxide.

[0018] Preferably, the pH value of the coprecipitation reaction is 10.8 to 11.2, for example, it can be 10.8, 10.9, 11.0, 11.1 or 11.2, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the temperature of the coprecipitation reaction is 55℃~60℃, for example, 55℃, 57℃, 59℃ or 60℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the D of the primary particles in the positive electrode precursor v The particle size of 50 is 0.5μm to 1.5μm, for example, it can be 0.5μm, 0.8μm, 1μm, 1.2μm or 1.5μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the D of the secondary particles in the positive electrode precursor v The particle size is 7μm to 9μm, for example, it can be 7μm, 7.5μm, 8μm, 8.5μm or 9μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the lithium-rich spinel powder has the chemical formula Li. 1+a Ni 0.5-a Mn 1.5+a O4, where 0 < a ≤ 0.15, and a can be, for example, 0.02, 0.05, 0.08, 0.1, 0.12 or 0.15, etc., not limited to the listed values, and other unlisted values ​​within this range also apply.

[0023] Preferably, based on the total mass of the positive electrode precursor as 100%, the mass percentage of the lithium-rich spinel powder is 3% to 5%, for example, it can be 3%, 3.5%, 4%, 4.5% or 5%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] In this invention, by controlling the mass percentage of lithium-rich spinel powder, the lithium-rich spinel powder and the matrix are more tightly bonded, forming a uniform spinel layered heterostructure, thereby improving the structural stability and electrochemical performance of the composite cathode material.

[0025] Preferably, the first fast ion conductor powder comprises a first sulfide fast ion conductor powder.

[0026] Preferably, the first sulfide fast ion conductor powder includes Li a M x P y S5Cl, wherein M is selected from at least one of Ta, Nb, Zr or Ti, 5.5≤a≤7.0, 0<x≤0.4, and 0.6≤y≤1.0.

[0027] Specifically, 'a' can be, for example, 5.5, 6.0, 6.5, or 7.0, 'x' can be, for example, 0.1, 0.2, 0.3, or 0.4, and 'y' can be, for example, 0.6, 0.7, 0.8, 0.9, or 1.0.

[0028] Preferably, the particle size of the first fast ion conductor powder is 0.2μm to 0.5μm, for example, it can be 0.2μm, 0.3μm, 0.4μm or 0.5μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, based on the total mass of the positive electrode precursor as 100%, the mass percentage of the first fast ion conductor powder is 0.5% to 1%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] In this invention, by controlling the mass percentage of the first fast ion conductor powder, not only can a rapid diffusion channel for lithium ions be provided, but the relative stability of the material structure can also be maintained.

[0031] Preferably, the first lithium salt includes, for example, lithium hydroxide or lithium carbonate.

[0032] Preferably, the molar ratio of lithium in the first lithium salt to transition metal in the positive electrode precursor is (1.01~1.10):1, for example, it can be 1.01:1, 1.02:1, 1.05:1, 1.08:1 or 1.10:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the first sintering process includes sequential A sintering and B sintering.

[0034] Preferably, the sintering temperature of A is 420℃~490℃, and the sintering time of A is 4h~6h.

[0035] Specifically, the sintering temperature of A can be, for example, 420℃, 450℃, 480℃ or 490℃, and the sintering time of A can be, for example, 4h, 5h or 6h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0036] Preferably, the sintering temperature of B is 750℃~780℃, and the sintering time of B is 8h~12h.

[0037] Specifically, the sintering temperature of B can be, for example, 750℃, 760℃, 770℃ or 780℃, and the sintering time of B can be, for example, 8h, 10h or 12h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0038] Preferably, the first sintering process is carried out in an oxygen-containing atmosphere, which exemplarily includes air or oxygen.

[0039] Preferably, after the first sintering treatment is completed and before the liquid phase coating treatment, the following steps are further included: Prepare a dilute solution of saturated lithium carbonate (concentration of 0.05 mol / L to 0.1 mol / L). The positive electrode intermediate was mixed with a dilute solution of saturated lithium carbonate at a solid-liquid ratio of 1 g: 10 mL, and the mixture was stirred and washed at 50 °C for 0.5 h to 1 h, with the washing endpoint controlled at pH ≤ 8.5. After washing, the mixture was filtered, rinsed 3 to 4 times with deionized water, and then vacuum dried at 80 °C to 100 °C for 6 h to 8 h to obtain an activated material with a clean surface and no residual alkali.

[0040] Preferably, the second fast ion conductor powder comprises a second sulfide fast ion conductor powder.

[0041] Preferably, the second sulfide fast ion conductor powder includes Li a M x P y S5Cl, wherein M is selected from at least one of Ta, Nb, Zr or Ti, 5.5≤a≤7.0, 0<x≤0.4, and 0.6≤y≤1.0.

[0042] Specifically, 'a' can be, for example, 5.5, 6.0, 6.5, or 7.0, 'x' can be, for example, 0.1, 0.2, 0.3, or 0.4, and 'y' can be, for example, 0.6, 0.7, 0.8, 0.9, or 1.0.

[0043] Preferably, the particle size of the second fast ion conductor powder is ≤200nm, for example, it can be 50nm, 80nm, 100nm, 120nm, 150nm, 180nm or 200nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] Preferably, the zirconium source includes ZrOCl2·8H2O.

[0045] Preferably, the zirconium source has a particle size ≤100nm, such as 20nm, 40nm, 50nm, 60nm, 80nm or 100nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, the second lithium salt comprises lithium phosphate.

[0047] Preferably, the mass ratio of the second fast ion conductor powder, the zirconium source, and the second lithium salt is (1.8~2.2):1:(0.7~0.8), for example, it can be 1.8:1:0.7, 1.9:1:0.72, 2:1:0.75, 2.1:1:0.78, or 2.2:1:0.8, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable, thereby better improving the diffusion ability of lithium ions, reducing interfacial impedance, and reducing the occurrence of interfacial side reactions, which is beneficial to improving the long-term cycle stability of the battery.

[0048] In this invention, the second fast ion conductor powder itself has ultra-high ion conductivity (10). -2 ~10 -3 The S / cm ratio significantly reduces the interfacial impedance between the positive electrode and the solid electrolyte, and the second fast ion conductor powder hardly reacts with the zirconium source and the second lithium salt. Furthermore, the zirconium source acts as a protective layer to prevent side reactions between the sulfide solid electrolyte and the positive electrode, and the second lithium salt can supplement lithium and accelerate lithium-ion conduction.

[0049] Preferably, based on the total mass of the positive electrode intermediate as 100%, the total mass percentage of the second fast ion conductor powder, the zirconium source, and the second lithium salt is 1.5% to 2.0%, for example, it can be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] Preferably, the temperature of the second sintering treatment is 550℃~600℃, and the time of the second sintering treatment is 4h~6h.

[0051] Specifically, the temperature of the second sintering treatment can be, for example, 550℃, 560℃, 580℃ or 600℃, and the time of the second sintering treatment can be, for example, 4h, 5h or 6h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0052] In this invention, by controlling the specific conditions of the second sintering process to carry it out at a lower temperature, it is possible to achieve the densification transformation of the outer coating layer (transforming the liquid-phase coated precursor into a multi-component synergistic coating layer with a thickness of 20nm~50nm), while releasing the lattice stress accumulated during the first sintering process, making the distribution of doped elements more uniform.

[0053] In summary, this invention forms a three-level gradient strengthening system of "doped phase stability - inner coating layer protection - outer coating layer isolation" by controlling the temperature gradient design of the first and second sintering (low temperature pretreatment → high temperature sintering → medium temperature secondary sintering).

[0054] Preferably, after the second sintering treatment is completed, the following steps are further included: The material obtained after the second sintering treatment was kept at 120℃~150℃ in a nitrogen atmosphere for 2h~4h to thoroughly remove any possible residual trace organic matter and impurities; then it was sieved using a standard sieve, and D was taken. v The composite-coated solid-state battery cathode material is obtained by collecting 50 particles with a particle size of 7μm~9μm and a uniform particle size distribution.

[0055] In a second aspect, the present invention provides a composite-coated solid-state battery cathode material, wherein the composite-coated solid-state battery cathode material is prepared by the preparation method of the composite-coated solid-state battery cathode material according to the first aspect, and the composite-coated solid-state battery cathode material includes a cathode material core and a first coating layer and a second coating layer disposed sequentially from the inside to the outside on the surface of the cathode material core.

[0056] Preferably, the thickness of the first coating layer is 5nm to 15nm, for example, it can be 5nm, 8nm, 10nm, 12nm or 15nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] Preferably, the thickness of the second coating layer is 20nm to 50nm, for example, it can be 20nm, 30nm, 40nm or 50nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] Thirdly, the present invention provides a solid-state battery, the solid-state battery comprising a positive electrode, a negative electrode and a solid electrolyte, wherein the positive electrode active material of the positive electrode comprises the solid-state battery positive electrode material with composite coating according to the second aspect.

[0059] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0060] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing a composite-coated solid-state battery cathode material. By adopting a synergistic strategy that combines a highly crystalline single-crystal cathode precursor with a double-layer functional coating layer, it effectively solves the problems of poor compatibility of high-nickel ternary cathode materials with solid electrolytes, incompatibility of coating layer interfaces, and high impedance.

[0061] Specifically, on the one hand, the preparation method provided by this invention enables the functional coating layer to be effectively bonded to the high-nickel ternary cathode material matrix, further enhancing the structural and chemical stability of the composite cathode material, effectively suppressing material oxidation, gas generation, and surface residual lithium side reactions, reducing capacity decay during cycling, and thus extending the material's service life. On the other hand, this invention first constructs an inner coating layer containing a first fast ion conductor powder on the surface of a highly crystalline single-crystal cathode precursor, which can accelerate lithium-ion transport and improve material interface stability. Simultaneously, the high-valence metal elements in the first fast ion conductor powder are doped into the material lattice, stabilizing the structure, expanding the interlayer spacing, and promoting lithium-ion diffusion kinetics. Then, this invention successfully constructs a multi-component synergistic outer coating layer on the surface of the cathode intermediate, further reducing the interfacial impedance between the solid electrolyte and the cathode, and effectively preventing side reactions with sulfide solid electrolytes, making the resulting composite-coated solid-state battery cathode material perfectly suited to the requirements of solid electrolyte applications. Detailed Implementation

[0062] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0063] Example 1 This embodiment provides a composite-coated solid-state battery cathode material and its preparation method. The composite-coated solid-state battery cathode material includes a cathode material core and a first coating layer (10 nm thick) and a second coating layer (35 nm thick) sequentially disposed on the surface of the cathode material core from the inside out. The corresponding preparation method includes the following steps: (1) NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O were mixed in a ratio of Ni, Co and Mn of 0.90:0.05:0.05 to prepare a nickel-cobalt-manganese mixed metal salt solution with a total metal ion concentration of 2 mol / L. Citric acid and sodium gluconate were added to the nickel-cobalt-manganese mixed metal salt solution as a single crystal guiding agent (based on the total mass of metal elements in the nickel-cobalt-manganese mixed metal salt solution being 100%, the mass percentage of the single crystal guiding agent being 3.5%, and the mass ratio of citric acid to sodium gluconate being 1:1.5).

[0064] A mixed ammonia-alkali solution was prepared, with the concentration of free ammonia controlled at 0.2 mol / L and the concentration of sodium hydroxide at 1.5 mol / L. A nickel-cobalt-manganese mixed metal salt solution containing a single-crystal guiding agent was added to the reaction vessel in parallel with the ammonia-alkali solution. The temperature was controlled at a constant 58℃, and a co-precipitation reaction was carried out under constant pH 11.0. The growth rate was controlled to obtain the D-type primary particles. v 50 secondary particles with a diameter of 1.0 μm have a D v 50 products with a particle size of 8μm were obtained. After the coprecipitation reaction was completed, the product was washed and vacuum dried to obtain a spherical, highly crystalline single-crystal cathode precursor.

[0065] (2) The spherical high-crystallinity single-crystal cathode precursor obtained in step (1) and lithium-rich spinel powder (Li 1.07 Ni 0.43 Mn 1.57 O4), Li 6.2 P 0.8 Zr 0.2 S5Cl (particle size 0.35 μm) and LiOH·H2O were dry-mixed and pre-calcined at 450℃ for 5 h in an oxygen atmosphere, then directly heated to 760℃ for sintering for 10 h, followed by furnace cooling to obtain a highly crystalline single-crystal cathode intermediate. The lithium-rich spinel powder comprised 4% of the total mass of the spherical highly crystalline single-crystal cathode precursor (100%), and Li... 6.2 P 0.8 Zr 0.2 The mass percentage of S5Cl is 0.7%, and the molar ratio of lithium in LiOH·H2O to transition metal elements in the spherical highly crystalline single-crystal cathode precursor is 1.05:1.

[0066] (3) The highly crystalline single-crystal cathode intermediate obtained in step (2) was mixed with a dilute solution of saturated lithium carbonate with a concentration of 0.07 mol / L at a solid-liquid ratio of 1 g: 10 mL. The mixture was stirred and washed at 50 °C for 0.7 h, and the washing endpoint was controlled to be pH ≤ 8.5. After washing, the mixture was filtered, rinsed three times with deionized water, and then vacuum dried at 90 °C for 7 h to obtain an activated material with a clean surface and no residual alkali.

[0067] (4) The material treated in step (3) and the coating raw material are wet-mixed in anhydrous ethanol (solid-liquid ratio of 1:8), stirred evenly, and then dried under a nitrogen atmosphere from 40°C to 70°C until no solvent residue remains, to obtain the mixed and dried material. The mixed and dried material is then transferred to a tube furnace and sintered at 580°C for 5 hours. The coating raw material is Li. 6.2 P 0.8 Zr 0.2 A mixture of S5Cl (particle size 150 nm), ZrOCl2·8H2O (particle size 80 nm), and lithium phosphate (Li 6.2 P 0.8 Zr 0.2 The mass ratio of S5Cl, ZrOCl2·8H2O to lithium phosphate is 2:1:0.75. Based on the total mass of the material after treatment in step (3) as 100%, the mass percentage of the coating raw material is 1.7%.

[0068] (5) The material obtained in step (4) is kept at 135℃ in a nitrogen atmosphere for 3 hours to completely remove any trace organic matter and impurities that may remain; then it is sieved using a standard sieve, and D is taken. v The composite-coated solid-state battery cathode material was obtained by using 50 particles with a diameter of 8 μm and uniform particle size distribution.

[0069] Example 2 This embodiment provides a composite-coated solid-state battery cathode material and its preparation method. The composite-coated solid-state battery cathode material includes a cathode material core and a first coating layer (5 nm thick) and a second coating layer (20 nm thick) sequentially disposed on the surface of the cathode material core from the inside out. The corresponding preparation method includes the following steps: (1) NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O were mixed in a ratio of Ni, Co and Mn of 0.90:0.05:0.05 to prepare a nickel-cobalt-manganese mixed metal salt solution with a total metal ion concentration of 1.5 mol / L. Citric acid and sodium gluconate were added to the nickel-cobalt-manganese mixed metal salt solution as a single crystal guiding agent (based on the total mass of metal elements in the nickel-cobalt-manganese mixed metal salt solution being 100%, the mass percentage of the single crystal guiding agent being 2%, and the mass ratio of citric acid to sodium gluconate being 1:1).

[0070] A mixed ammonia-alkali solution was prepared, with the concentration of free ammonia controlled at 0.1 mol / L and the concentration of sodium hydroxide at 1.0 mol / L. A nickel-cobalt-manganese mixed metal salt solution containing a single-crystal guiding agent was added to the reaction vessel in parallel with the ammonia-alkali solution. The temperature was controlled at a constant 55℃, and a co-precipitation reaction was carried out under constant pH 10.8. The growth rate was controlled to obtain the D-type primary particles.v 50 secondary particles with a diameter of 0.5 μm have a D v 50 products with a particle size of 7μm were obtained. After the coprecipitation reaction was completed, the product was washed and vacuum dried to obtain a spherical, highly crystalline single-crystal cathode precursor.

[0071] (2) The spherical high-crystallinity single-crystal cathode precursor obtained in step (1) and lithium-rich spinel powder (Li 1.02 Ni 0.48 Mn 1.52 O4), Li 6.1 P 0.9 Zr 0.1 S5Cl (particle size 0.2 μm) and LiOH·H2O were dry-mixed and pre-calcined at 420℃ for 6 h in an oxygen atmosphere, then directly heated to 750℃ for sintering for 12 h, followed by furnace cooling to obtain a highly crystalline single-crystal cathode intermediate. The lithium-rich spinel powder comprised 3% of the total mass of the spherical highly crystalline single-crystal cathode precursor (100%), and Li... 6.1 P 0.9 Zr 0.1 The mass percentage of S5Cl is 0.5%, and the molar ratio of lithium in LiOH·H2O to transition metal in the spherical highly crystalline single-crystal cathode precursor is 1.01:1.

[0072] (3) The highly crystalline single-crystal cathode intermediate obtained in step (2) was mixed with a dilute solution of saturated lithium carbonate with a concentration of 0.07 mol / L at a solid-liquid ratio of 1 g: 10 mL. The mixture was stirred and washed at 50 °C for 0.7 h, and the washing endpoint was controlled to be pH ≤ 8.5. After washing, the mixture was filtered, rinsed three times with deionized water, and then vacuum dried at 90 °C for 7 h to obtain an activated material with a clean surface and no residual alkali.

[0073] (4) The material treated in step (3) and the coating material are wet-mixed in anhydrous ethanol (solid-liquid ratio of 1:8), stirred evenly, and then dried under a nitrogen atmosphere from 40°C to 70°C until no solvent residue remains, to obtain the mixed and dried material. The mixed and dried material is then transferred to a tube furnace and sintered at 550°C for 6 hours. The coating material is Li. 6.1 P 0.9 Zr 0.1 S5Cl (particle size 100 nm), ZrOCl2·8H2O (particle size 50 nm), and lithium phosphate (Li) 6.1 P 0.9 Zr 0.1 The mass ratio of S5Cl, ZrOCl2·8H2O to lithium phosphate is 1.8:1:0.7. Based on the total mass of the material after treatment in step (3) as 100%, the mass percentage of the coating raw material is 1.5%.

[0074] (5) The material obtained in step (4) is kept at 135℃ in a nitrogen atmosphere for 3 hours to completely remove any trace organic matter and impurities that may remain; then it is sieved using a standard sieve, and D is taken. v The composite-coated solid-state battery cathode material was obtained by using 50 particles with a diameter of 7 μm and uniform particle size distribution.

[0075] Example 3 This embodiment provides a composite-coated solid-state battery cathode material and its preparation method. The composite-coated solid-state battery cathode material includes a cathode material core and a first coating layer (15 nm thick) and a second coating layer (50 nm thick) sequentially disposed on the surface of the cathode material core from the inside out. The corresponding preparation method includes the following steps: (1) NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O were mixed in a ratio of Ni, Co and Mn of 0.90:0.05:0.05 to prepare a nickel-cobalt-manganese mixed metal salt solution with a total metal ion concentration of 2.5 mol / L. Citric acid and sodium gluconate were added to the nickel-cobalt-manganese mixed metal salt solution as a single crystal guiding agent (based on the total mass of metal elements in the nickel-cobalt-manganese mixed metal salt solution being 100%, the mass percentage of the single crystal guiding agent being 5%, and the mass ratio of citric acid to sodium gluconate being 1:2).

[0076] A mixed ammonia-alkali solution was prepared, with the concentration of free ammonia controlled at 0.3 mol / L and the concentration of sodium hydroxide at 2.0 mol / L. A nickel-cobalt-manganese mixed metal salt solution containing a single-crystal guiding agent was added to the reaction vessel in parallel with the ammonia-alkali solution. The temperature was controlled at a constant 60℃, and a co-precipitation reaction was carried out under constant pH 11.2. The growth rate was controlled to obtain the D-type primary particles. v 50 secondary particles with a diameter of 1.5 μm have a D v 50 products with a particle size of 9 μm were obtained. After the co-precipitation reaction was completed, the product was washed and vacuum dried to obtain a spherical, highly crystalline single-crystal cathode precursor.

[0077] (2) The spherical high-crystallinity single-crystal cathode precursor obtained in step (1) and lithium-rich spinel powder (Li 1.15 Ni 0.35 Mn 1.65 O4), Li 6.4 P 0.6 Zr 0.4S5Cl (particle size 0.5 μm) and LiOH·H2O were dry-mixed and pre-calcined at 490℃ for 4 h in an oxygen atmosphere, followed by direct heating to 780℃ for sintering for 8 h, and then cooled in the furnace to obtain a highly crystalline single-crystal cathode intermediate. The intermediate consisted of 5% lithium-rich spinel powder (based on the total mass of the spherical highly crystalline single-crystal cathode precursor as 100%), and Li... 6.4 P 0.6 Zr 0.4 The mass percentage of S5Cl is 1%, and the molar ratio of lithium in LiOH·H2O to transition metal in the spherical highly crystalline single-crystal cathode precursor is 1.10:1.

[0078] (3) The highly crystalline single-crystal cathode intermediate obtained in step (2) was mixed with a dilute solution of saturated lithium carbonate with a concentration of 0.07 mol / L at a solid-liquid ratio of 1 g: 10 mL. The mixture was stirred and washed at 50 °C for 0.7 h, and the washing endpoint was controlled to be pH ≤ 8.5. After washing, the mixture was filtered, rinsed three times with deionized water, and then vacuum dried at 90 °C for 7 h to obtain an activated material with a clean surface and no residual alkali.

[0079] (4) The material treated in step (3) and the coating material are wet-mixed in anhydrous ethanol (solid-liquid ratio of 1:8), stirred evenly, and then dried under a nitrogen atmosphere from 40°C to 70°C until no solvent residue remains, to obtain the mixed and dried material. The mixed and dried material is then transferred to a tube furnace and sintered at 600°C for 4 hours. The coating material is Li. 6.4 P 0.6 Zr 0.4 S5Cl (particle size 200 nm), ZrOCl2·8H2O (particle size 100 nm), and lithium phosphate (Li) 6.4 P 0.6 Zr 0.4 The mass ratio of S5Cl, ZrOCl2·8H2O to lithium phosphate is 2.2:1:0.8. Based on the total mass of the material after step (3) treatment as 100%, the mass percentage of the coating raw material is 2%.

[0080] (5) The material obtained in step (4) is kept at 135℃ in a nitrogen atmosphere for 3 hours to completely remove any trace organic matter and impurities that may remain; then it is sieved using a standard sieve, and D is taken. v The composite-coated solid-state battery cathode material was obtained by using 50 particles with a diameter of 9 μm and uniform particle size distribution.

[0081] Example 4 The difference between this embodiment and embodiment 1 is that in step (1), the mass ratio of citric acid to sodium gluconate is 1:4, while all other aspects are the same as in embodiment 1.

[0082] Example 5 The difference between this embodiment and embodiment 1 is that in step (1), the mass ratio of citric acid to sodium gluconate is 1:0.2, while all other aspects are the same as in embodiment 1.

[0083] Example 6 The difference between this embodiment and embodiment 1 is that in step (2), the total mass of the spherical high crystallinity single crystal cathode precursor is 100%, the mass percentage of lithium-rich spinel powder is 1%, and everything else is the same as in embodiment 1.

[0084] Example 7 The difference between this embodiment and Embodiment 1 is that, in step (2), with the total mass of the spherical high-crystallinity single-crystal cathode precursor as 100%, Li 6.2 P 0.8 Zr 0.2 The mass percentage of S5Cl is 3%, and everything else is the same as in Example 1.

[0085] Example 8 The difference between this embodiment and embodiment 1 is that, in step (4), Li 6.2 P 0.8 Zr 0.2 The mass ratio of S5Cl, ZrOCl2·8H2O to lithium phosphate is 1:1:0.5, and all other aspects are the same as in Example 1.

[0086] Example 9 The difference between this embodiment and embodiment 1 is that, in step (4), Li 6.2 P 0.8 Zr 0.2 The mass ratio of S5Cl, ZrOCl2·8H2O to lithium phosphate is 3:2:1, and all other aspects are the same as in Example 1.

[0087] Comparative Example 1 The difference between this comparative example and Example 1 is that, in step (1), the single crystal guiding agent composed of citric acid and sodium gluconate was not added to the nickel-cobalt-manganese mixed metal salt solution, that is, the step of adding the single crystal guiding agent composed of citric acid and sodium gluconate to the nickel-cobalt-manganese mixed metal salt solution was omitted, and both are the same as in Example 1.

[0088] Comparative Example 2 The difference between this comparative example and Example 1 is that, in step (2), Li is not added. 6.2 P 0.8 Zr 0.2 S5Cl (particle size 0.35μm) is the spherical, highly crystalline single-crystal cathode precursor obtained in step (1) and lithium-rich spinel powder (Li). 1.07 Ni0.43 Mn 1.57 O4) and LiOH·H2O were dry-mixed and pre-calcined at 450°C for 5 hours in an oxygen atmosphere, then directly heated to 760°C for sintering for 10 hours and cooled in the furnace to obtain a highly crystalline single-crystal cathode intermediate. All other aspects were the same as in Example 1.

[0089] Comparative Example 3 The difference between this comparative example and Example 1 is that in step (4), the coating material is only lithium phosphate. The mass percentage of the coating material is 1% based on the total mass of the material after treatment in step (3) as 100%. Everything else is the same as in Example 1.

[0090] Comparative Example 4 The difference between this comparative example and Example 1 is that in step (4), the coating material only includes ZrOCl2·8H2O and lithium phosphate in a mass ratio of 3:0.75. The mass percentage of the coating material is 1% based on the total mass of the material after treatment in step (3) as 100%. All other aspects are the same as in Example 1.

[0091] Comparative Example 5 The difference between this comparative example and Example 1 is that in step (4), the material after step (3) is coated with liquid phase without sintering, that is, the step of transferring the mixed and dried material into a tube furnace and sintering at 580°C for 5 hours is omitted. All other steps are the same as in Example 1.

[0092] Lithium-ion batteries were prepared using the highly crystalline single-crystal composite cathode materials provided in Examples 1-9 and Comparative Examples 1-5, and then their performance was tested, as follows: Preparation of positive electrode sheet: The high crystallinity single crystal composite positive electrode material, Super P conductive agent and polyvinylidene fluoride binder provided in the above examples and comparative examples are mixed in a mass ratio of 8:1:1. N-methylpyrrolidone is added and stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry is then coated onto aluminum foil, dried and rolled to obtain a positive electrode sheet.

[0093] Preparation of lithium-ion batteries: The above-mentioned positive electrode sheets were assembled with solid electrolyte and metallic lithium to form CR2032 coin cells. After standing for 48 hours, electrochemical performance tests were conducted at a constant temperature of 25℃. The tests were performed at a rate of 0.2C and a voltage range of 2.0V to 4.8V. The capacity retention rate after 200 cycles was tested, and the AC internal resistance of the battery was measured using electrochemical impedance spectroscopy (EIS) at a frequency range of 1Hz to 10Hz. 6 Hz, voltage amplitude is 5mV.

[0094] The test results are shown in Table 1.

[0095] Table 1 As shown in Table 1, as can be seen from Examples 1 to 3, the composite-coated solid-state battery cathode material prepared by the present invention, through the synergistic strategy of "high crystallinity single crystal structure core + bulk phase doping reinforcement + dual fast ion conductor stepwise coating", enables the lithium-ion battery made with this composite-coated solid-state battery cathode material to retain a capacity of 93.8%~94.5% after 200 cycles at 25℃ and 0.2C, and the internal resistance is as low as 19.2mΩ~20.1mΩ.

[0096] Comparing Examples 1 with Examples 4-5, it can be seen that by controlling the mass ratio of citric acid to sodium gluconate within the range of 1:(1-2), it is beneficial to form "quasi-single-crystal" spherical secondary particles with uniform internal atomic arrangement. If the ratio between the two is unbalanced, the chelation-dispersion synergy will be disrupted, leading to a decrease in the size uniformity of the primary particles of the cathode precursor, a reduction in the degree of single crystallization, and the introduction of additional grain boundaries, which will affect the cycle performance of the battery.

[0097] Comparing Examples 1 with Examples 6-7, it can be seen that in Example 6, due to the low mass percentage of lithium-rich spinel powder, the inner coating layer is incomplete, and part of the positive electrode substrate surface is exposed. In Example 7, due to the high mass percentage of the first fast ion conductor powder, an excessively thick inner coating layer (thickness > 15 nm) is easily formed, increasing the resistance to lithium ion passage. Furthermore, excessive doping elements may lead to lattice distortion or the formation of second-phase impurities.

[0098] Comparing Example 1 with Examples 8-9, it can be seen that Example 8, due to Li 6.2 P 0.8 Zr 0.2 The low content of S5Cl, ZrOCl2·8H2O, and lithium phosphate prevented the successful formation of a multi-component synergistic coating layer, making it difficult to reduce interfacial impedance. In Example 9, the thicker coating layer became an additional barrier to lithium-ion diffusion, and the low electronic conductivity of the zirconium-based compound further increased electron transport resistance.

[0099] Comparing Example 1 with Comparative Example 1, it can be seen that the absence of single-crystal directing agent (citric acid + sodium gluconate) makes the cathode precursor a conventional polycrystalline spherical particle with a large number of grain boundaries inside. During battery cycling, anisotropic lattice strain causes microcracks to be generated at the grain boundaries, which further accelerates structural degradation.

[0100] Comparing Example 1 and Comparative Example 2, it can be seen that the absence of the first fast ion conductor powder causes the material to lose the dual protection of the bulk doping source and the inner coating layer at the same time, which prevents high-valence metal elements from entering the crystal lattice, resulting in the inability to expand the interlayer spacing, the disappearance of the cation mixing inhibition effect, and the absence of MO bond reinforcement, causing the material structure to degrade rapidly during cycling.

[0101] Comparing Example 1 with Comparative Examples 3-4, it can be seen that the ionic conductivity of lithium phosphate in Comparative Example 3 (coating material is only lithium phosphate) is much lower than that of fast ion conductors, and it cannot form a stable zirconium-based interface phase. Comparative Example 4 (coating material is only zirconium source + lithium phosphate, without a second fast ion conductor) mainly forms the Li2ZrO3 phase after sintering, and its ionic conductivity (approximately 10) is also lower. -6 The S / cm ratio is much lower than that of the second fastest ion conductor (approximately 10). -3 (S / cm), making it impossible to construct a high-speed lithium-ion transport channel.

[0102] Comparing Example 1 and Comparative Example 5, it can be seen that without the second sintering treatment, the liquid phase coating precursor cannot be transformed into a dense crystalline coating layer, resulting in a loose and porous outer coating layer, which further aggravates the interfacial side reactions. In addition, the coating layer lacks chemical bonding and has poor adhesion to the substrate, making it easy to peel off during battery cycling.

[0103] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a composite-coated solid-state battery cathode material, characterized in that, The preparation method includes the following steps: A mixed metal salt solution containing a single-crystal directing agent and a mixed ammonia-alkali solution are fed into a reactor in parallel to carry out a co-precipitation reaction to obtain a positive electrode precursor. The cathode precursor, lithium-rich spinel powder, first fast ion conductor powder and first lithium salt are subjected to a first sintering process to obtain a cathode intermediate. The cathode intermediate is subjected to liquid-phase coating with a second fast ion conductor powder, a zirconium source, and a second lithium salt. After a second sintering process, the composite-coated solid-state battery cathode material is obtained.

2. The preparation method according to claim 1, characterized in that, The single-crystal directing agent includes citric acid and sodium gluconate; Preferably, the mass percentage of the single-crystal guiding agent is 2% to 5%, based on the total mass of the metal elements in the mixed metal salt solution being 100%. Preferably, the mass ratio of citric acid to sodium gluconate is 1:(1~2).

3. The preparation method according to claim 1 or 2, characterized in that, The concentration of ammonia in the ammonia-alkali mixed solution is 0.1 mol / L to 0.3 mol / L; Preferably, the concentration of alkali in the ammonia-alkali mixed solution is 1.0 mol / L to 2.0 mol / L; Preferably, the pH value of the coprecipitation reaction is 10.8~11.2; Preferably, the temperature of the coprecipitation reaction is 55℃~60℃.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The primary particles in the positive electrode precursor have D v 50 particles have a diameter of 0.5μm to 1.5μm; Preferably, the D of the secondary particles in the positive electrode precursor v The particle size of 50 particles is 7μm~9μm.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The chemical formula of the lithium-rich spinel powder is Li 1+a Ni 0.5-a Mn 1.5+a O4, where 0 < a ≤ 0.15; Preferably, based on the total mass of the cathode precursor, the mass percentage of the lithium-rich spinel powder is 3% to 5%. Preferably, the first fast ion conductor powder comprises a first sulfide fast ion conductor powder; Preferably, the first sulfide fast ion conductor powder includes Li a M x P y S5Cl, wherein M is selected from at least one of Ta, Nb, Zr or Ti, 5.5≤a≤7.0, 0<x≤0.4, and 0.6≤y≤1.0; Preferably, the particle size of the first fast ion conductor powder is 0.2 μm to 0.5 μm; Preferably, based on the total mass of the positive electrode precursor as 100%, the mass percentage of the first fast ion conductor powder is 0.5% to 1%; Preferably, the first sintering process includes sequential A sintering and B sintering; Preferably, the sintering temperature of A is 420℃~490℃, and the sintering time of A is 4h~6h; Preferably, the sintering temperature of B is 750℃~780℃, and the sintering time of B is 8h~12h.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The second fast ion conductor powder includes a second sulfide fast ion conductor powder; Preferably, the second sulfide fast ion conductor powder includes Li a M x P y S5Cl, wherein M is selected from at least one of Ta, Nb, Zr or Ti, 5.5≤a≤7.0, 0<x≤0.4, and 0.6≤y≤1.0; Preferably, the particle size of the second fast ion conductor powder is ≤200nm; Preferably, the zirconium source comprises ZrOCl2·8H2O; Preferably, the zirconium source has a particle size ≤100nm; Preferably, the second lithium salt comprises lithium phosphate; Preferably, the mass ratio of the second fast ion conductor powder, the zirconium source, and the second lithium salt is (1.8~2.2):1:(0.7~0.8); Preferably, based on the total mass of the positive electrode intermediate as 100%, the total mass percentage of the second fast ion conductor powder, the zirconium source, and the second lithium salt is 1.5% to 2.0%.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The temperature of the second sintering treatment is 550℃~600℃, and the time of the second sintering treatment is 4h~6h.

8. A composite-coated solid-state battery cathode material, characterized in that, The composite-coated solid-state battery cathode material is prepared by the method for preparing the composite-coated solid-state battery cathode material according to any one of claims 1-7. The composite-coated solid-state battery cathode material includes a cathode material core and a first coating layer and a second coating layer disposed sequentially from the inside to the outside on the surface of the cathode material core.

9. The composite-coated solid-state battery cathode material according to claim 8, characterized in that, The thickness of the first coating layer is 5nm~15nm; Preferably, the thickness of the second coating layer is 20nm~50nm.

10. A solid-state battery, characterized in that, The solid-state battery includes a positive electrode, a negative electrode, and a solid electrolyte, wherein the positive electrode active material of the positive electrode includes the composite-coated solid-state battery positive electrode material according to claim 8 or 9.

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