A cathode material for solid-state batteries, its preparation method and application

Abstract

This invention discloses a cathode material for solid-state batteries, its preparation method, and its applications. The cathode material has a core-shell structure, comprising an active core and an amorphous lithium-ion conductive shell coating the surface of the active core. This cathode material is prepared by a mechanochemical reaction between a cathode material matrix with residual lithium salt on its surface and van der Waals crystals. While consuming the residual lithium salt on the surface of the cathode material matrix, the amorphous lithium-ion conductive shell is generated in situ. This invention, through an integrated strategy of "mechanochemical reaction consumption - in-situ construction," effectively removes harmful residual lithium salt from the cathode material surface while simultaneously constructing an amorphous protective layer with high ionic conductivity and high interfacial stability, significantly improving the interfacial compatibility between the cathode material and the solid electrolyte. The preparation method is simple, environmentally friendly, and easy to scale up. When the resulting cathode material is used in solid-state batteries, it can effectively improve the battery's cycle life, rate performance, and coulombic efficiency.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a cathode material for solid-state batteries, its preparation method and application. Specifically, it relates to a method for removing residual lithium salts from the surface of a cathode material and simultaneously constructing an ultra-high ion conductivity layer, as well as the resulting cathode material for solid-state batteries and a lithium-ion battery containing the material. Background Technology

[0002] With the increasing demand for energy density from new energy vehicles and consumer electronics, solid-state batteries based on solid-state electrolytes are considered one of the core directions of next-generation energy storage technology. Solid-state batteries use non-flammable inorganic solid electrolytes to replace traditional liquid electrolytes, offering higher safety and the potential to match lithium metal anodes, potentially increasing battery energy density by more than 30%. However, the commercialization of solid-state batteries is facing more severe interface challenges, among which the problem of residual lithium salts on the surface of the cathode material is particularly prominent. On the one hand, residual lithium salts on the surface of the cathode material, such as LiOH / Li2CO3, are lithium-ion insulating materials, leading to an increase in the impedance of the cathode / electrolyte interface. Furthermore, under certain conditions, the residual lithium salts may undergo side reactions with the electrolyte layer, further increasing the interface impedance and severely restricting the cycle life and rate performance of solid-state batteries.

[0003] The conventional industrial method for dealing with residual lithium salts on the surface of cathode materials is water washing, which dissolves the residual lithium salts with deionized water. However, water washing is cumbersome, costly, and can easily damage the crystal structure of the cathode material, introducing defects and even causing lithium ion loss from the material itself. In addition, surface coating of the cathode material is also a common method for dealing with residual lithium salts. For example, Chinese patent CN116072876A uses nano-Co(OH)2 to coat the cathode material. Although this can convert the residual lithium salts on the surface into a LiCoO2 coating layer, Co(OH)2 is expensive and has poor compatibility with solid electrolytes such as sulfides, leading to increased interfacial impedance and battery failure after cycling. Chinese patent CN121546036A describes a method that involves mixing ammonium fluoride and ammonium chloride with the cathode material and then heat-treating to eliminate residual alkali on the surface while simultaneously constructing a LiF protective layer in situ on the cathode material surface. This significantly reduces the residual alkali content, and the lithium-ion permeability of LiF further reduces interfacial impedance and polarization. However, LiF has low ionic conductivity, making it difficult to improve the rate performance of the battery. Therefore, effectively removing residual lithium salts and improving the interface without sacrificing material performance and simplifying the process is crucial for the commercial application of high-energy-density lithium-ion battery technology. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a cathode material for solid-state batteries with high ionic conductivity and high interface stability, as well as its preparation method and application.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A cathode material for solid-state batteries includes an active core and an amorphous lithium-ion conductive shell covering the surface of the active core; the cathode material is generated by a cathode material matrix and van der Waals crystals through a mechanochemical reaction, the surface of the cathode material matrix has residual lithium salt, and the mechanochemical reaction consumes the residual lithium salt while generating the amorphous lithium-ion conductive shell in situ on the surface of the cathode material matrix.

[0006] The design concept of the above technical solution lies in the fact that this invention constructs a unique "active core-amorphous shell" core-shell structure, enabling the cathode material to possess both high capacity and excellent interfacial stability. The active core is responsible for providing electrochemical capacity, while the amorphous lithium-ion conductor shell plays multiple key roles: firstly, this shell layer effectively isolates the cathode material from direct contact with commonly used solid electrolytes such as sulfides, suppressing interfacial side reactions; secondly, the amorphous structure eliminates grain boundary impedance, providing isotropic lithium-ion transport channels, enabling rapid lithium-ion conduction; furthermore, this shell layer originates from the in-situ conversion of harmful residual lithium salts on the surface of the cathode material, achieving resource utilization by "turning waste into treasure."

[0007] The amorphous lithium-ion conductive shell has an amorphous structure, which has advantages such as isotropy, no grain boundary impedance, tight bonding with the substrate, and adaptability to volume changes during charging and discharging. This is beneficial for the rapid transport of lithium ions and the long-term stability of the interface structure. In mechanical force (such as mechanical ball milling) chemical reactions, the strong mechanical force causes interlayer delamination, lattice distortion, and chemical bond breakage in van der Waals crystals, generating a large number of fresh surfaces and active sites. Simultaneously, residual lithium salts such as LiOH / Li2CO3 on the surface of the cathode material substrate are activated, and the two undergo a solid-phase reaction. The reaction products are deposited in situ on the surface of the cathode material substrate, forming a uniform and dense coating layer. This integrated "reaction consumption-in-situ construction" strategy effectively removes harmful residual lithium salts while simultaneously constructing a protective layer with high ionic conductivity.

[0008] Specifically, the amorphous lithium-ion conductive shell has high lithium-ion conductivity. The positive electrode material is prepared by ball milling a positive electrode material matrix with residual lithium hydroxide and / or lithium carbonate on the surface and van der Waals crystals. The van der Waals crystals react with the residual lithium salts on the surface of the positive electrode material under the mechanical force of ball milling. While consuming the residual lithium salts, an amorphous lithium-ion conductive shell is generated in situ on the surface of the positive electrode material.

[0009] As a further preferred embodiment of the above technical solution, the van der Waals crystal is a type of zero-dimensional, one-dimensional, or two-dimensional material in which atoms are stacked together by van der Waals forces; its general chemical formula is M. a Xb Y c Where M is selected from transition metal elements (such as Mo, W, Ti, Ru, Ta, Zr, Nb, Al, etc.), X is selected from chalcogen elements (S, Se) or halogen elements (Cl, Br, I), Y is selected from oxygen or nitrogen, and a, b, c are non-negative integers, satisfying a>0, b≥1, c≥0. Preferably, the van der Waals crystal is one or more of molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2), tungsten diselenide (WSe2), titanium disulfide (TiS2), titanium dichloride (TiCl2), ruthenium trichloride (RuCl3), tantalum pentachloride (TaCl5), zirconium tetrachloride (ZrCl4), niobium pentachloride (NbCl5), aluminum trichloride (AlCl3), or niobium oxychloride (NbOCl3). The above-mentioned van der Waals crystals have unique structures and chemical reactivity, and can undergo efficient reactions under mechanical force, making them particularly suitable for the scheme of this invention.

[0010] As a further preferred embodiment of the above technical solution, the cathode material matrix is ​​a lithium transition metal oxide with residual lithium hydroxide and / or lithium carbonate on its surface, including at least one of lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (NCM111, NCM523, NCM622, NCM811), lithium nickel cobalt aluminum oxide (NCA), lithium-rich manganese-based materials (xLi2MnO3·(1-x)LiMO2), or lithium iron phosphate (LiFePO4); the above-mentioned cathode materials are prone to generating residual lithium salts on the surface during the high-nickelization or lithium-richization process, which is particularly suitable for the solution of the present invention.

[0011] As a further preferred embodiment of the above technical solution, the thickness of the amorphous lithium-ion conductive shell is 1 nm to 200 nm. A preferred shell thickness range is 2 nm to 50 nm, and more preferably 5 nm to 20 nm. If the shell is too thin (<2 nm), it cannot completely cover the substrate surface, making it difficult to effectively suppress side reactions; if the shell is too thick, it will reduce the energy density of the cathode material.

[0012] As a further preferred embodiment of the above technical solution, the particle size of the positive electrode material is 0.1μm to 30μm, and more preferably 1μm to 15μm.

[0013] As a further preferred embodiment of the above technical solution, the content of lithium halides (LiCl, LiBr, etc.) and / or chalcogenide lithium salts (Li2S, Li2Se, etc.) in the amorphous lithium-ion conductor shell needs to be strictly controlled, and their total mass percentage of the shell layer mass should be less than 5%, preferably less than 1%, and more preferably trace level (<0.1%). This is because, although LiCl, Li2S, etc. themselves have a certain lithium-ion conductivity, if they exist as the main components of the shell layer, it will bring the following adverse effects: (1) Poor hygroscopicity and chemical stability: Lithium halides (especially LiCl) are extremely hygroscopic and easily absorb moisture from the air, causing deliquescence, which leads to a decrease in the storage stability of the material and may release HCl inside the battery to corrode the electrodes. Chalcogenide lithium salts (such as Li2S) are extremely sensitive to moisture and are easily hydrolyzed to produce toxic H2S gas.

[0014] (2) Increased interface impedance: Although LiCl, Li2S and other materials have certain lithium-ion conductivity, their ionic conductivity is relatively low compared to the amorphous lithium-ion conductor shell. Excessive content will hinder the transport of lithium ions.

[0015] Therefore, the key to this invention is that it does not simply generate lithium halides or chalcogenide lithium salts, but rather controls the reaction conditions and the selection of van der Waals crystals so that the reaction products exist mainly in the form of complex amorphous halides or sulfides or oxyhalides / oxysulfides solid solutions.

[0016] Based on the same technical concept, the present invention also provides a method for preparing the above-mentioned positive electrode material for solid-state batteries, comprising the following steps: (1) The cathode material precursor is mixed with lithium salt and then sintered to obtain the cathode material matrix; (2) The positive electrode material substrate and van der Waals crystal are mechanically ball-milled to cause the van der Waals crystal to undergo a mechanochemical reaction with the residual lithium salt on the surface of the positive electrode material substrate. While consuming the residual lithium salt, an amorphous lithium-ion conductive shell is generated in situ on the surface of the positive electrode material substrate.

[0017] This preparation method is simple, low-cost, and easy to scale up. First, a cathode material matrix is ​​prepared using a traditional solid-state sintering method. A certain amount of lithium salt, such as LiOH / Li₂CO₃, naturally remains on the surface of this matrix. Then, the cathode material matrix is ​​mixed with a small amount of van der Waals crystals, and a solid-state reaction is induced by mechanical ball milling. During ball milling, mechanical energy is converted into chemical energy, driving the van der Waals crystals to react with the residual lithium salts. The reaction products are then coated in situ onto the surface of the cathode material matrix, forming a conductive shell. The entire process requires no solvents, no subsequent heat treatment, and generates no wastewater, making it a green and environmentally friendly modification method.

[0018] As a further preferred embodiment of the above technical solution, the amount of van der Waals crystal added accounts for 0.05% to 5% of the mass of the cathode material matrix. Too little addition will not completely consume the residual lithium salt, potentially resulting in an incomplete conductive shell; too much addition will lead to over-reaction, requiring strict control. The mechanical ball milling speed is 100 rpm to 1000 rpm, preferably 200 rpm to 500 rpm; the ball milling time is 0.5 h to 20 h, preferably 2 h to 8 h; the ball milling media are zirconium oxide balls or agate balls, with a ball-to-material ratio of 5 to 50:1, preferably 10 to 30:1. The ball milling process can be carried out under an inert atmosphere (such as argon or nitrogen) to prevent the van der Waals crystal from absorbing moisture or oxidizing, while also avoiding side reactions between the cathode material and CO2 / H2O in the air. By optimizing the ball milling process parameters (time, speed, ball-to-material ratio), the degree of reaction can be controlled, avoiding excessive reaction leading to excessive enrichment of lithium halides or chalcogenide lithium salts, ensuring that the shell layer exists in a stable amorphous composite form.

[0019] Based on the same technical concept, the present invention also provides an application of the above-mentioned solid-state battery cathode material or the solid-state battery cathode material prepared by the above-mentioned preparation method. The solid-state battery cathode material is used to make solid-state batteries, especially sulfide-based all-solid-state batteries. The lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte membrane. The preparation steps of the positive electrode sheet include: mixing the solid-state battery cathode material with a solid electrolyte, a conductive agent, and a binder through a dry or wet process to obtain a cathode mixture, and then laminating it with aluminum foil. If a wet process is used, the composite is dried, and then rolled and cut to obtain the positive electrode sheet.

[0020] Because the cathode material prepared by this invention has an amorphous lithium-ion conductor shell formed in situ on its surface, and the content of free lithium halide / lithium chalcogenide salts in this shell layer is strictly controlled, it exhibits good chemical compatibility and interfacial stability with sulfide solid electrolytes, and can be directly used in dry or wet processes for solid-state batteries. The preferred dry process avoids potential damage to the interfacial layer by solvents, thus preserving the structural integrity of the shell layer to the greatest extent possible.

[0021] Compared with the prior art, the advantages of the present invention are as follows: (1) The solid-state battery cathode material of the present invention is generated by a mechanochemical reaction between a cathode material matrix and van der Waals crystals. During the mechanochemical reaction, harmful residual lithium salts on the surface of the cathode material matrix react with the van der Waals crystals and are consumed, which is equivalent to removing residual lithium salts in situ. This completely solves the side reaction problem between residual lithium salts and sulfide electrolytes, and avoids a series of process and performance problems such as HF generation, gas production, and gelation. At the same time, the reaction between residual lithium salts and van der Waals crystals generates an amorphous lithium-ion conductive shell on the surface of the cathode material matrix that combines high ionic conductivity and interface stability, i.e., an amorphous composite. It itself has high lithium-ion conductivity (due to the presence of Li). + It combines high ionic conductivity with high interfacial stability, eliminating grain boundary impedance and exhibiting far superior chemical and electrochemical stability compared to free LiCl or Li₂S. Furthermore, the amorphous structure of the conductive shell offers multiple advantages, including isotropy, tight bonding with the substrate, and adaptability to volume changes during charge and discharge, thus enhancing long-term cycle stability.

[0022] (2) The method for preparing the cathode material for solid-state batteries of the present invention is simple and environmentally friendly. It is completed in one step by mechanical ball milling, without the need for solvents, subsequent heat treatment, or wastewater generation. It has a wide process window and is easy to scale up for production. By precisely controlling the reaction parameters, the composition of the outer shell layer can be regulated to better ensure the electrical performance of the cathode material.

[0023] (3) The cathode material for solid-state batteries of the present invention is adapted to solid-state batteries, and is particularly suitable for all-solid-state battery systems. The stable lithium-ion conductive shell constructed on its surface can effectively suppress the interfacial side reactions between the cathode and the solid electrolyte, and significantly improve the cycle life, rate performance and coulombic efficiency of solid-state batteries.

[0024] In summary, this invention utilizes an integrated strategy of "mechanical-chemical-reaction consumption-in-situ construction-composition regulation" to simultaneously remove residual lithium salts from the surface of cathode materials and construct an ultra-high ionic conductivity interface. More importantly, the process employed is simple, efficient, and environmentally friendly. Attached Figure Description

[0025] Figure 1 This is a SEM image of the solid cathode material prepared in Example 7 of the present invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the materials and instruments used in the following embodiments are commercially available.

[0027] Example 1: A solid-state battery cathode material of the present invention includes an active core and an amorphous lithium-ion conductive shell. The cathode material substrate is a high-nickel single-crystal NCM622 cathode material (D50 particle size of 10 μm, surface residual lithium content of approximately 5000 ppm based on surface residual alkali content); the shell layer generated by in-situ reaction has a thickness of approximately 20 nm and is an amorphous lithium-ion conductive layer (i.e., conductive layer) formed by a mechanochemical reaction between tungsten disulfide (WS2) and residual lithium salt.

[0028] A method for preparing a positive electrode material for a solid-state battery according to this embodiment includes the following steps: (1) Material preparation: Commercial high-nickel single crystal NCM622 cathode material (surface residual alkali content is about 5000ppm) was selected, and tungsten disulfide (WS2) was selected as the reactant.

[0029] (2) Mechanical ball milling: NCM622 and WS2 were added to a planetary ball mill at a mass ratio of 97.5:2.5. The ball milling jar was made of zirconium oxide, and the ball milling media were zirconium oxide balls (3 mm in diameter). The ball-to-material ratio was 20:1. Under the protection of argon atmosphere, the mixture was ball milled at 300 rpm for 4 hours to obtain the cathode material for solid-state batteries.

[0030] Example 2: A solid-state battery cathode material of the present invention includes an active core and an amorphous lithium-ion conductive shell. The cathode material matrix is ​​a lithium-rich manganese-based cathode material (LLO, chemical formula 0.5Li₂MnO₃·0.5LiNi). 0.33 Co 0.33 Mn 0.33 O2, D50 particle size is 8μm); the shell generated by the in-situ reaction is about 25nm thick, which is an amorphous lithium-ion conductor layer generated by the mechanochemical reaction of aluminum trichloride (AlCl3) and residual lithium salt.

[0031] A method for preparing a positive electrode material for a solid-state battery according to this embodiment includes the following steps: (1) Material preparation: Lithium-rich manganese-based cathode material (LLO) was selected, with a residual alkali content of about 8000 ppm on the surface. Aluminum trichloride (AlCl3) was selected as the reactant.

[0032] (2) Mechanical ball milling: LLO and AlCl3 were added to a planetary ball mill at a mass ratio of 98:2. The ball mill jar was made of zirconium oxide, the ball milling media was zirconium oxide balls, and the ball-to-material ratio was 15:1. Under the protection of argon atmosphere, the mixture was ball milled at 250 rpm for 6 hours to obtain the cathode material for solid-state batteries.

[0033] Example 3: A solid-state battery cathode material of the present invention includes an active core and an amorphous lithium-ion conductive shell. The cathode material substrate is a high-nickel NCM811 cathode material (D50 particle size of 12 μm, surface residual alkali content of approximately 12000 ppm); the shell layer generated by in-situ reaction has a thickness of approximately 60 nm and is an amorphous lithium-ion conductive layer generated by a mechanochemical reaction between molybdenum disulfide (MoS2) and residual lithium salt.

[0034] A method for preparing a positive electrode material for a solid-state battery according to this embodiment includes the following steps: (1) Material preparation: Commercial high-nickel NCM811 cathode powder was selected. Molybdenum disulfide (MoS2) powder was selected as the reactant.

[0035] (2) Mechanical ball milling: NCM811 and MoS2 were added to a planetary ball mill at a mass ratio of 96:4. The ball mill jar was made of zirconium oxide, the grinding media was zirconium oxide balls, and the ball-to-material ratio was 25:1. Under the protection of argon atmosphere, the mixture was ball milled at 350 rpm for 3 hours to obtain the cathode material for solid-state batteries.

[0036] Example 4: A solid-state battery cathode material of the present invention includes an active core and an amorphous lithium-ion conductive shell. The cathode material substrate is a single-crystal NCM523 cathode material (D50 particle size of 5 μm, surface residual alkali content of about 3000 ppm); the shell layer generated by in-situ reaction has a thickness of about 6 nm and is an amorphous lithium-ion conductive layer generated by a mechanochemical reaction between titanium disulfide (TiS2) and residual lithium salt.

[0037] A method for preparing a positive electrode material for a solid-state battery according to this embodiment includes the following steps: (1) Material preparation: Commercial single-crystal NCM523 cathode material was selected. Titanium disulfide (TiS2) nanosheets were selected as reactants.

[0038] (2) Mechanical ball milling: NCM523 and TiS2 were added to a planetary ball mill at a mass ratio of 99.4:0.6. The ball mill jar was made of zirconium oxide, the grinding media was zirconium oxide balls, and the ball-to-material ratio was 10:1. Under the protection of argon atmosphere, the mixture was ball milled at 200 rpm for 8 hours to obtain the cathode material for solid-state batteries.

[0039] Example 5: A solid-state battery cathode material of the present invention includes an active core and an amorphous lithium-ion conductive shell. The cathode material matrix is ​​lithium iron phosphate (LiFePO4, D50 particle size of 2μm, surface residual alkali content of about 800ppm); the shell layer generated by in-situ reaction has a thickness of about 2nm and is an amorphous lithium-ion conductive layer generated by mechanochemical reaction of tantalum pentachloride (TaCl5) and residual lithium salt.

[0040] A method for preparing a positive electrode material for a solid-state battery according to this embodiment includes the following steps: (1) Material preparation: Commercial lithium iron phosphate cathode material was selected. Tantalum pentachloride (TaCl5) powder was selected as the reactant.

[0041] (2) Mechanical ball milling: LiFePO4 and TaCl5 were added to a planetary ball mill at a mass ratio of 99.5:0.5. The ball mill jar was made of zirconium oxide, the ball milling media was zirconium oxide balls, and the ball-to-material ratio was 30:1. Under the protection of argon atmosphere, the mixture was ball milled at 400 rpm for 2 hours to obtain the cathode material for solid-state batteries.

[0042] Example 6: A solid-state battery cathode material of the present invention includes an active core and an amorphous lithium-ion conductive shell. The cathode material matrix is ​​a high-nickel NCA cathode material (LiNi). 0.8 Co 0.15 Al 0.05 O2, D50 particle size is 10μm, surface residual alkali content is about 9000ppm); the shell layer generated by the in-situ reaction is about 40nm thick, which is an amorphous lithium-ion conductor layer generated by the mechanochemical reaction of zirconium tetrachloride (ZrCl4) and residual lithium salt.

[0043] A method for preparing a positive electrode material for a solid-state battery according to this embodiment includes the following steps: (1) Material preparation: Commercial high-nickel NCA cathode material was selected. Zirconium tetrachloride (ZrCl4) powder was selected as the reactant.

[0044] (2) Mechanical ball milling: NCA and ZrCl4 were added to a planetary ball mill at a mass ratio of 96:4. The ball mill jar was made of zirconium oxide, the ball milling media was zirconium oxide balls, and the ball-to-material ratio was 20:1. Under the protection of argon atmosphere, the mixture was ball milled at 300 rpm for 5 hours to obtain the cathode material for solid-state batteries.

[0045] Example 7: A solid-state battery cathode material of the present invention includes an active core and an amorphous lithium-ion conductive shell. The cathode material substrate is a high-nickel NCM811 cathode material (D50 particle size of 12 μm, surface residual alkali content of approximately 12000 ppm); the shell layer generated by in-situ reaction has a thickness of approximately 50 nm and is an amorphous lithium-ion conductive layer generated by a mechanochemical reaction between niobium pentachloride (NbCl5) and residual lithium salt.

[0046] A method for preparing a positive electrode material for a solid-state battery according to this embodiment includes the following steps: (1) Material preparation: Commercial high-nickel NCM811 cathode powder was selected. Niobium pentachloride (NbCl5) powder was selected as the reactant.

[0047] (2) Mechanical ball milling: NCM811 and NbCl5 were added to a planetary ball mill at a mass ratio of 97:3. The ball milling jar was made of zirconium oxide, the ball milling media was zirconium oxide balls, and the ball-to-material ratio was 25:1. Under the protection of argon atmosphere, the mixture was ball milled at 350 rpm for 4 hours to obtain the cathode material for solid-state batteries.

[0048] Figure 1 The image shows a SEM image of the solid cathode material prepared in this embodiment. It can be seen from the image that the shell thickness generated by the in-situ reaction is about 50 nm.

[0049] Example 8: A positive electrode material for solid-state batteries according to the present invention includes an active core and an amorphous lithium-ion conductive shell. The positive electrode material matrix is ​​lithium cobalt oxide (LiCoO2, D50 particle size of 15 μm, surface residual alkali content of about 2000 ppm); the shell layer generated by in-situ reaction has a thickness of about 15 nm and is an amorphous lithium-ion conductive layer generated by mechanochemical reaction between niobium oxychloride (NbOCl3) and residual lithium salt.

[0050] A method for preparing a positive electrode material for a solid-state battery according to this embodiment includes the following steps: (1) Material preparation: Commercial lithium cobalt oxide cathode material was selected. Niobium trichloride (NbOCl3) powder was selected as the reactant.

[0051] (2) Mechanical ball milling: LiCoO2 and NbOCl3 were added to a planetary ball mill at a mass ratio of 99.8:0.2. The ball mill jar was made of zirconium oxide, the ball milling media was zirconium oxide balls, and the ball-to-material ratio was 15:1. Under the protection of argon atmosphere, the mixture was ball milled at 250 rpm for 6 hours to obtain the cathode material for solid-state batteries.

[0052] Comparative Example 1: A positive electrode material for solid-state batteries is prepared by the following method: The NCM622 material was treated using the same traditional water washing process as in Example 1. The specific steps were as follows: the NCM622 cathode material was added to deionized water, stirred for 10 minutes, then filtered, dried, and sintered at 750°C for 5 hours in an oxygen atmosphere.

[0053] Comparative Example 2: A positive electrode material for solid-state batteries is prepared by the following method: The NCM622 cathode material used in Example 1 was mixed with nano-Al2O3 powder at a mass ratio of 99.5:0.5 and heat-treated at 500°C for 5 hours to obtain an Al2O3-coated cathode material. The residual alkali content on the surface of this material was still as high as 4000ppm, and the Al2O3 coating layer was an insulating layer.

[0054] Residual lithium content is characterized, specifically by the residual alkali Li2CO3 content: The residual lithium content of samples from Examples 1-8 and Comparative Examples 1-2 was tested. The test method was potentiometric titration: 5g of sample was weighed and dispersed in 100ml of deionized water, stirred for 10 minutes, filtered, and the filtrate was titrated with 0.1mol / L hydrochloric acid to pH=4.5. The residual lithium content (calculated as Li2CO3) was calculated. The test results are shown in Table 1.

[0055] Table 1. Test results of residual lithium content in cathode materials of Examples 1-8 and Comparative Examples 1-2

[0056] As can be seen from Table 1, the residual alkali content (i.e. residual lithium content) of the cathode materials in each embodiment of the present invention is significantly reduced compared with that before treatment, and the removal rate is all above 81%, which is much higher than the 20% residual lithium content removal rate of Al2O3 coated cathode material in Comparative Example 2. Although Comparative Example 1 achieved a residual lithium content removal rate of 86%, the traditional water washing process has many defects: it generates a large amount of polluted wastewater, and after water washing and drying, it still needs to be sintered at 750°C for 5 hours, which is energy-intensive, cumbersome, costly, and easily damages the crystal structure of the cathode material, introduces defects, and even causes the loss of lithium ions in the material body.

[0057] Battery performance characterization: The cathode materials used in each embodiment and comparative example were respectively prepared into coin cells for performance testing. The testing methods are as follows: (1) Battery fabrication: Each positive electrode material was mixed with vapor-grown carbon fiber (VGCF) and sulfide electrolyte (Li6PS5Cl) at a mass ratio of 70:5:25. The mixture was then pressed into a positive electrode sheet in a mold with a diameter of 10 mm under a pressure of 200 MPa. Sulfide electrolyte (Li6PS5Cl) powder was added to one side of the positive electrode sheet. Then, a pressure of 200 MPa was applied to obtain a positive electrode / electrolyte composite structure. Finally, a Li-In composite negative electrode sheet was added to assemble the mold battery. The battery performance was tested under a pressure of 200 MPa.

[0058] (2) Battery evaluation: The electrical performance of each battery was tested, including the initial discharge capacity at 0.1C, the 1C rate performance (1C / 0.1C capacity ratio), and the capacity retention rate after 100 cycles at 1C. The test results are shown in Table 2. Table 2 Performance test results of coin cells with different cathode materials

[0059] As shown in Table 2, the solid-state battery cathode materials of the various embodiments of the present invention exhibit significant improvements in rate performance and cycle stability compared to the comparative examples. The rate efficiencies of Examples 1-8 all exceed 91%, and the capacity retention after 100 cycles is all above 94%, significantly superior to Comparative Example 1 (water washing treatment) and Comparative Example 2 (Al2O3 coating). This indicates that the present invention, through an integrated mechanochemical "reaction consumption-in-situ construction" strategy, effectively removes residual lithium salts while forming an amorphous in-situ reaction layer with excellent lithium-ion conductivity, significantly improving interfacial kinetic performance.

[0060] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A positive electrode material for solid-state batteries, characterized in that, It includes an active core and an amorphous lithium-ion conductive shell covering the surface of the active core; the positive electrode material is generated by a positive electrode material matrix and van der Waals crystal through a mechanochemical reaction, the surface of the positive electrode material matrix has residual lithium salt, and the mechanochemical reaction consumes the residual lithium salt while generating an amorphous lithium-ion conductive shell in situ on the surface of the positive electrode material matrix.

2. The positive electrode material for solid-state batteries according to claim 1, characterized in that, The van der Waals crystal is a type of zero-dimensional, one-dimensional, or two-dimensional material composed of atoms stacked together by van der Waals forces, with the general chemical formula M. a X b Y c Where M is selected from transition metal elements, X is selected from chalcogens or halogens, Y is selected from oxygen or nitrogen, and a, b, and c are non-negative integers, satisfying a>0, b≥1, and c≥0.

3. The positive electrode material for solid-state batteries according to claim 2, characterized in that, The transition metal element is at least one of Mo, W, Ti, Ru, Ta, Zr, Nb, and Al; the chalcogenide element is S or Se; and the halogen element is at least one of Cl, Br, and I.

4. The positive electrode material for solid-state batteries according to claim 3, characterized in that, The van der Waals crystal is one or more of molybdenum disulfide, tungsten disulfide, molybdenum diselenide, tungsten diselenide, titanium disulfide, titanium dichloride, ruthenium trichloride, tantalum pentachloride, zirconium tetrachloride, niobium pentachloride, aluminum trichloride, or niobium oxychloride.

5. The positive electrode material for solid-state batteries according to claim 1, characterized in that, The cathode material matrix is ​​a lithium transition metal oxide with residual lithium hydroxide and / or lithium carbonate on its surface; the lithium transition metal oxide includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, or lithium iron phosphate.

6. The positive electrode material for solid-state batteries according to claim 1, characterized in that, The thickness of the amorphous lithium-ion conductive shell is 1 nm to 200 nm; and / or the particle size of the positive electrode material is 0.1 μm to 30 μm.

7. The positive electrode material for solid-state batteries according to any one of claims 1 to 6, characterized in that, The total mass of lithium halides and chalcogenide lithium salts in the amorphous lithium-ion conductive shell accounts for less than 5% of the total mass of the amorphous lithium-ion conductive shell.

8. A method for preparing a positive electrode material for a solid-state battery as described in any one of claims 1 to 7, characterized in that, Includes the following steps: (1) The cathode material precursor is mixed with lithium salt and then sintered to obtain the cathode material matrix; (2) The positive electrode material matrix and van der Waals crystal are mechanically ball-milled to cause the van der Waals crystal to undergo a mechanochemical reaction with the residual lithium salt on the surface of the positive electrode material matrix.

9. The preparation method according to claim 8, characterized in that, The amount of van der Waals crystals is 0.05% to 5% of the mass of the cathode material matrix. The rotation speed of the mechanical ball mill is 100 rpm to 1000 rpm, and the milling time is 0.5 h to 20 h. The milling media are zirconia balls or agate balls, and the ball-to-material ratio is 5 to 50:

1.

10. The application of a solid-state battery cathode material as described in any one of claims 1 to 7, or a solid-state battery cathode material prepared by the preparation method described in claim 8 or 9, characterized in that, The positive electrode material is used to manufacture a solid-state battery; the solid-state battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte membrane; the preparation steps of the positive electrode sheet include: mixing the positive electrode material with a solid electrolyte, a conductive agent, and a binder through a dry or wet process to obtain a positive electrode mixture, then laminating it with aluminum foil; if a wet process is used, the mixture is dried after lamination, and then rolled and cut to obtain the positive electrode sheet.

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