Composite positive electrode material, preparation method and application thereof, and simulation evaluation method of interface stress distribution of composite positive electrode material

Abstract

The invention belongs to the technical field of solid-state batteries, and particularly relates to a composite positive electrode material, a preparation method and application thereof, and a simulation evaluation method of interface stress distribution of the composite positive electrode material. The composite positive electrode material comprises a modified positive electrode material and sulfide type solid electrolyte, the modified positive electrode material comprises positive electrode active particles and a coating layer coating the surfaces of the positive electrode active particles; and the material of the coating layer is a polymer-lithium salt composite material with an elastic modulus of 0.1-5.0 GPa or a lithium-containing oxide material with an elastic modulus of 120-200 GPa. The key point of the invention is that the surfaces of the positive active particles are coated with a polymer-lithium salt composite material or a lithium-containing oxide material with a specific elastic modulus, so that the obtained composite positive electrode material enables the lithium ion solid-state battery to show remarkably improved rate capability and cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery technology, specifically relating to a composite cathode material, its preparation method and application, as well as a simulation evaluation method for the interfacial stress distribution of the composite cathode material. Background Technology

[0002] With the rapid development of new energy and electronic technologies, lithium-ion batteries are widely used in many fields such as new energy vehicles. During use, their capacity inevitably decreases, mainly due to the particle breakage of composite cathode materials caused by expansion and contraction during cycling. Therefore, mitigating the mechanical failure of cathode materials is a key issue in improving battery performance, especially important for solid-state battery design. Currently, there is an urgent need to find methods to alleviate the stress on cathode materials. Summary of the Invention

[0003] One of the objectives of this invention is to address the problem that existing cathode materials are prone to mechanical failure during use, leading to severe performance degradation of lithium-ion batteries. This invention provides a composite cathode material that significantly reduces the interfacial stress of the cathode during charging and discharging by coating the surface of the cathode particles with a specific material layer, thereby improving the performance of lithium-ion batteries.

[0004] Specifically, the composite cathode material includes a modified cathode material and a sulfide-type solid electrolyte; the modified cathode material includes cathode active particles and a coating layer covering the surface of the cathode active particles; the coating layer material is a polymer-lithium salt composite material with an elastic modulus of 0.1~5.0 GPa or a lithium oxide-containing material with an elastic modulus of 120~200 GPa; the polymer in the polymer-lithium salt composite material is selected from at least one of polyethylene oxide, polycarbonate, polymethyl methacrylate, and polystyrene.

[0005] In a preferred embodiment, the positive electrode active particles are selected from at least one of lithium nickel cobalt manganese oxide particles, lithium nickel cobalt aluminum oxide particles, and lithium manganese iron phosphate particles.

[0006] In a preferred embodiment, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide and / or lithium hexafluorophosphate.

[0007] In a preferred embodiment, the lithium oxide material is selected from at least one of lithium niobate, lithium lanthanum zirconium oxide, and lithium lanthanum titanium oxide.

[0008] In a preferred embodiment, the mass ratio of the modified cathode material to the sulfide-type solid electrolyte is 1:(0.3~0.5).

[0009] In a preferred embodiment, the mass ratio of the coating material to the positive electrode active particles is (1~3):100.

[0010] In a preferred embodiment, the mass ratio of polymer to lithium salt in the polymer-lithium salt composite material is 5:(1~3).

[0011] A second objective of this invention is to provide a method for preparing the aforementioned composite cathode material. The preparation method includes the following steps: S1. Dissolve lithium salt and polymer in a first organic solvent to form a mixture, and then subject the mixture to a first ball milling process with the first positive electrode active particles to obtain a first modified positive electrode material with a polymer-lithium salt composite coating layer on the surface. Alternatively, the lithium oxide is dispersed in a second organic solvent to form a dispersion, and then the dispersion is subjected to a second ball milling treatment with the second positive electrode active particles to obtain a second modified positive electrode material with a lithium oxide coating layer on the surface. S2. The first modified cathode material or the second modified cathode material is subjected to a third ball milling treatment with a sulfide-type solid electrolyte to obtain a composite cathode material.

[0012] In a preferred embodiment, in step S1, the mass ratio of the lithium salt to the polymer is (1~3):5.

[0013] In a preferred embodiment, in step S1, the mass ratio of the first positive electrode active particle to the polymer in the mixture is 100:(1~3).

[0014] In a preferred embodiment, in step S1, the mass ratio of the second positive electrode active particle to the lithium oxide-containing dispersion is 100:(1~3).

[0015] In a preferred embodiment, in step S1, the conditions for the first ball milling treatment and the second ball milling treatment each independently include: a rotation speed of 150~2000 rpm and a time of 6~10 h.

[0016] In a preferred embodiment, in step S1, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide and / or lithium hexafluorophosphate.

[0017] In a preferred embodiment, in step S1, the first positive electrode active particle and the second positive electrode active particle are each independently selected from at least one of lithium nickel cobalt manganese oxide particles, lithium nickel cobalt aluminum oxide particles, and lithium manganese iron phosphate particles.

[0018] In a preferred embodiment, in step S1, the first organic solvent and the second organic solvent are each independently selected from at least one of acetonitrile, methanol, ethanol, isopropanol, acetone, and dimethylformamide.

[0019] In a preferred embodiment, in step S2, the mass ratio of the first modified cathode material or the second modified cathode material to the sulfide-type solid electrolyte is 1:(0.3~0.5).

[0020] In a preferred embodiment, in step S2, the conditions for the third ball milling process include: a rotation speed of 150-200 rpm and a time of 1-3 h.

[0021] The third objective of this invention is to provide a composite cathode material prepared by the above method.

[0022] The fourth objective of this invention is to provide the application of the above-mentioned composite cathode material in solid-state batteries.

[0023] The fifth objective of this invention is to provide a simulation evaluation method for the interfacial stress distribution of composite cathode materials. The evaluation method includes: mixing the composite cathode material and a binder via ball milling to form an electrode sheet; performing a CT scan on the electrode sheet; importing the obtained CT images into image processing software for processing to obtain a three-dimensional microstructure model of the composite cathode material; importing the obtained three-dimensional microstructure model into simulation software; inputting battery simulation parameters and electrochemical model control equations and stress model control equations to construct an electrochemical field-mechanical field coupled simulation model. The coupling principle is based on the fact that the deformation of the mechanical field is driven by the chemical strain caused by the change in lithium ion concentration in the electrochemical field; setting charge-discharge test parameters for simulation testing; obtaining an interfacial stress distribution cloud map and calculating the maximum value, average value, and standard deviation of the interfacial stress as quantitative indicators for evaluating stress level and uniformity.

[0024] Beneficial Effects: The key to this invention lies in coating the surface of positive electrode active particles with a polymer-lithium salt composite material or lithium oxide-containing material with a specific elastic modulus, and then combining it with a sulfide-type solid electrolyte to prepare a composite positive electrode material. This composite positive electrode material enables lithium-ion solid-state batteries to exhibit better rate performance and cycle performance. This may be because the polymer-lithium salt composite coating layer with an elastic modulus of 0.1~5.0 GPa has high hardness and good mechanical support, which can uniformly disperse the external stacking pressure applied during battery assembly and the stress generated during cycling to a larger contact area, avoiding excessive stress concentration at local points, thereby maintaining the interface. Physical integrity; lithium oxides with an elastic modulus of 120~200 GPa utilize their high elasticity and high deformation capacity to effectively absorb local stress concentration caused by the volume change of positive electrode active material particles during charging and discharging, thereby delaying the generation and propagation of interfacial microcracks and improving the cycle stability of the battery. Moreover, multiphysics simulation tests have also verified that polymer-lithium salt composite materials and lithium oxide materials with specific elastic moduli can effectively alleviate stress accumulation and stress concentration caused by the expansion and contraction of active particles during charging and discharging, improve mechanical failure problems, and thus improve the electrochemical performance and stability of the battery. Attached Figure Description

[0025] Figure 1 The discharge curves of the PEO@NCM-LPSC composite cathode material prepared in Example 1 at different rates are shown.

[0026] Figure 2 The discharge curves of the LiNbO3@NCM-LPSC composite cathode material prepared in Example 2 at different discharge rates are shown.

[0027] Figure 3 The discharge curves of the NCM-LPSC reference cathode material prepared in Comparative Example 1 at different discharge rates are shown.

[0028] Figure 4 These are rate performance diagrams for PEO@NCM-LPSC, LiNbO3@NCM-LPSC, and NCM-LPSC materials.

[0029] Figure 5 These are half-cell models for NCM-LPSC, LiNbO3@NCM-LPSC, and PEO@NCM-LPSC materials.

[0030] Figure 6Figures show the stress distribution of NCM-LPSC, LiNbO3@NCM-LPSC, and PEO@NCM-LPSC materials during the discharge process. Figures (a) to (c) show the stress distribution of NCM-LPSC at discharge depths of 0%, 50%, and 100% (DoD); Figures (d) to (f) show the stress distribution of LiNbO3@NCM-LPSC at discharge depths of 0%, 50%, and 100% (DoD); and Figures (g) to (i) show the stress distribution of PEO@NCM-LPSC at discharge depths of 0%, 50%, and 100% (DoD). Detailed Implementation

[0031] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Furthermore, unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present invention.

[0032] The composite cathode material provided by this invention includes a modified cathode material and a sulfide-type solid electrolyte. The modified cathode material comprises cathode active particles and a coating layer covering the surface of the cathode active particles. The coating layer material is a polymer-lithium salt composite material with an elastic modulus of 0.1~5.0 GPa or a lithium oxide-containing material with an elastic modulus of 120~200 GPa. The polymer in the polymer-lithium salt composite material is selected from at least one of polyethylene oxide (PEO), polycarbonate (PC), polymethyl methacrylate (PMMA), and polystyrene (PS). The elastic modulus of the polymer-lithium salt composite material can be 0.1 GPa, 0.5 GPa, 1.0 GPa, 2.0 GPa, 3.0 GPa, 4.0 GPa, 5.0 GPa, or any value between them. The elastic modulus of the lithium oxide-containing material can be 120 GPa, 150 GPa, 180 GPa, 200 GPa, or any value between them.

[0033] In this invention, the positive electrode active particles can be selected from at least one of lithium nickel cobalt manganese oxide particles (NCM), lithium nickel cobalt aluminum oxide particles (NCA), and lithium manganese iron phosphate particles (LMFP), more preferably lithium nickel cobalt manganese oxide particles (NCM), such as NCM811, NCM523, NCM622, NCM721, etc., and particularly preferably NCM811 (Ni:Co:Mn=8:1:1).

[0034] In this invention, the sulfide-type solid electrolyte can be any one of the prior art, and is particularly preferred to be Li6PS5Cl(LPSC).

[0035] In this invention, the lithium oxide material can be any compound containing lithium with an elastic modulus in the range of 120~200GPa, and specific examples include, but are not limited to, at least one of lithium niobate, lithium lanthanum zirconium oxide, and lithium lanthanum titanium oxide.

[0036] In this invention, the mass ratio of the modified cathode material to the sulfide-type solid electrolyte is preferably 1:(0.3~0.5), such as 1:0.3, 1:0.4, 1:0.5 or any ratio therebetween.

[0037] In this invention, the preferred mass ratio of the coating material to the positive electrode active particles is (1~3):100, such as 1:100, 2:100, 3:100 or any ratio therebetween.

[0038] In this invention, the preferred mass ratio of polymer to lithium salt in the polymer-lithium salt composite material is 5:(1~3), such as 5:1, 5:1.5, 5:2, 5:2.5, 5:3 or any value between them.

[0039] The method for preparing the composite cathode material provided by this invention includes the following steps: S1. Dissolve lithium salt and polymer in a first organic solvent to form a mixture, and then subject the mixture to a first ball milling process with the first positive electrode active particles to obtain a first modified positive electrode material with a polymer-lithium salt composite coating layer on the surface. Alternatively, the lithium oxide is dispersed in a second organic solvent to form a dispersion, and then the dispersion is subjected to a second ball milling treatment with the second positive electrode active particles to obtain a second modified positive electrode material with a lithium oxide coating layer on the surface. S2. The first modified cathode material or the second modified cathode material is subjected to a third ball milling treatment with a sulfide-type solid electrolyte to obtain a composite cathode material.

[0040] In this invention, in step S1, the preferred mass ratio of the lithium salt to the polymer is (1~3):5, such as 1:5, 1.5:5, 2:5, 2.5:5, 3:5 or any ratio between them.

[0041] In this invention, in step S1, the mass ratio of the first positive electrode active particle to the polymer in the mixture is preferably 100:(1~3), such as 100:1, 100:1.5, 100:2, 100:2.5, 100:3 or any value between them.

[0042] In this invention, in step S1, the mass ratio of the second positive electrode active particle to the lithium oxide-containing dispersion is preferably 100:(1~3), such as 100:1, 100:1.5, 100:2, 100:2.5, 100:3 or any value between them.

[0043] In this invention, in step S1, the conditions for the first ball milling treatment and the second ball milling treatment each preferably include: a rotation speed of 150~200 rpm, such as 150 rpm, 180 rpm, 200 rpm or any value between them; and a time of 6~10 h, such as 6 h, 7 h, 8 h, 9 h, 10 h or any value between them.

[0044] In this invention, in step S1, the lithium salt is preferably lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and / or lithium hexafluorophosphate (LiPF6).

[0045] In this invention, in step S1, the first positive electrode active particle and the second positive electrode active particle are each independently preferred from at least one of lithium nickel cobalt manganese oxide particles, lithium nickel cobalt aluminum oxide particles, and lithium manganese iron phosphate particles, more preferably lithium nickel cobalt manganese oxide particles (NCM), such as NCM811, NCM523, NCM622, NCM721, etc., and particularly preferably NCM811.

[0046] In this invention, in step S1, the first organic solvent and the second organic solvent are each independently preferred from at least one of acetonitrile, methanol, ethanol, isopropanol, acetone, and dimethylformamide.

[0047] In this invention, in step S2, the mass ratio of the first modified cathode material or the second modified cathode material to the sulfide-type solid electrolyte is preferably 1:(0.3~0.5), such as 1:0.3, 1:0.4, 1:0.5 or any ratio therebetween.

[0048] In this invention, the conditions for the third ball milling process in step S2 preferably include: a rotation speed of 150~200 rpm, such as 150 rpm, 180 rpm, 200 rpm or any value between them; and a time of 1~3 h, such as 1 h, 2 h, 3 h or any value between them.

[0049] The simulation evaluation method for the interfacial stress distribution of composite cathode materials provided by this invention includes: mixing the composite cathode material and binder by ball milling to form an electrode sheet; performing CT scanning on the electrode sheet; importing the obtained CT images into image processing software for processing to obtain a three-dimensional microstructure model of the composite cathode material; importing the obtained three-dimensional microstructure model into simulation software; inputting battery simulation parameters and electrochemical model control equations and stress model control equations to construct an electrochemical field-mechanical field coupled simulation model; the coupling principle is based on the fact that the deformation of the mechanical field is driven by the chemical strain caused by the change in lithium ion concentration in the electrochemical field; setting charge and discharge test parameters for simulation testing; obtaining the interfacial stress distribution cloud map and calculating the maximum value, average value, and standard deviation of the interfacial stress as quantitative indicators for evaluating stress level and uniformity.

[0050] The present invention will be described in detail below through specific embodiments. These embodiments are intended to explain the invention and should not be construed as limiting it. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0051] Example 1 LiTFSI and PEO (purchased from Aladdin Reagents, catalog number P101345) were mixed with 10 mL of anhydrous acetonitrile at a mass ratio of 2:5 and stirred on a magnetic stirrer for 24 h, then allowed to stand for 24 h to form a PEO solution. NCM811 and the PEO solution were ball-milled at a mass ratio of NCM811:PEO = 100:1 for 8 h at a speed of 150 rpm to obtain PEO-lithium composite-coated NCM powder. This powder was then ball-milled with LPSC at a mass ratio of 7:3 for 1 h at a speed of 180 rpm to obtain a composite cathode powder, denoted as PEO@NCM-LPSC.

[0052] Example 2 Lithium niobate (LiNbO3) was mixed with 10 mL of anhydrous acetonitrile and stirred on a magnetic stirrer for 12 h, followed by ultrasonic dispersion for 12 h to form a lithium niobate dispersion. NCM811 and the lithium niobate dispersion were ball-milled at a mass ratio of NCM811:lithium niobate = 100:1 for 8 h at 150 rpm to obtain lithium niobate-coated NCM powder. This powder was then ball-milled with LPSC at a mass ratio of 7:3 for 1 h at 180 rpm to obtain a composite cathode powder, denoted as LiNbO3@NCM-LPSC.

[0053] Comparative Example 1 NCM811 and LPSC were ball-milled at a mass ratio of 7:3 for 1 hour at a speed of 150 rpm to obtain a reference cathode powder, denoted as NCM-LPSC.

[0054] Test case (1) Performance test of lithium-ion solid-state battery: The composite cathode materials obtained in the examples and comparative examples were ball-milled with PTFE binder at a mass ratio of 98:2 and pressed into cathode sheets. The cathode sheets were then assembled with LPSC solid electrolyte and Li-In anode to form a solid-state battery. The sample preparation pressure was 250 MPa and the assembly pressure was 50 MPa.

[0055] Rate performance testing: At 25℃, the assembled solid-state battery was first charged to 100% SOC using a constant current. Then, it was discharged at constant current rates of 0.05C, 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, and 1C to 2.1V. The voltage change during discharge was recorded. The battery capacity was calculated and accumulated using Q(mAh / g) = I(mA)*t(h) / m(g). Each rate was tested three times, and the next rate was tested after completing one rate test. The results are shown below. Figures 1-3 The discharge curve shown and Figure 4 The total discharge capacity performance at different rates is shown.

[0056] Cyclic performance test: At 25℃, the assembled solid-state battery was charged to 3.6V at a constant current of 0.1C, allowed to stand for 5 minutes, and then discharged to 2.1V at a constant current of 0.1C. The discharge capacity at this point was recorded, which is the discharge capacity of the first cycle. The solid-state battery was subjected to cyclic charge-discharge tests according to the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the solid-state battery after 100 cycles at 25℃ = discharge capacity after 100 cycles / discharge capacity of the first cycle * 100%. The results are shown in Table 1.

[0057] Depend on Figures 1-4 As shown in Table 1, compared with the uncoated Comparative Example 1, the composite cathode materials obtained in Examples 1-2 exhibit better capacity performance, rate performance, and cycle stability.

[0058] Table 1

[0059] (2) Simulation test based on multiphysics field: The composite cathode materials obtained in the examples and comparative examples were ball-milled with PTFE binder at a mass ratio of 98:2 and pressed into cathode sheets. The prepared electrode samples were fixed firmly on a rotating stage, and then CT equipment was used to take pictures. After obtaining CT images, the original images were imported into AVIZO software. According to the different gray values ​​of the images, the images were divided into two phases: the active material phase and the electrolyte phase. A particle was selected for manual phase separation as a coating layer to obtain the three-dimensional microstructure model required for simulation. The obtained three-dimensional microstructure model was imported into COMSOL software, and then a cuboid was constructed and placed on top of the electrode as the electrolyte. The battery simulation parameters and the electrochemical model control equation and stress model control equation in Table 2 were input. The meaning of the symbols in each equation is shown in Table 3. Thus, the electrochemical field-mechanical field coupled simulation model was constructed. The half-cell simulation models of Examples 1-2 and Comparative Example 1 are as follows. Figure 5As shown; in the constructed electrochemical-mechanical field coupled simulation model, the specific values ​​of the electrochemical and mechanical parameters are input, and the boundary and initial conditions are set. Then, stress simulation tests are started, and the results are as follows. Figure 6 The diagram shows the interface stress distribution contour plot. For Figure 6 The results were analyzed, and 11 points were determined in the model. The maximum stress at each of these 11 points was recorded during the discharge process. The average of the sum of the maximum stresses at these 11 points was calculated as the average stress during the discharge process. Finally, the average stress of NCM-LPSC was calculated to be 1146 MPa, the average stress of LiNbO3@NCM-LPSC was 774 MPa, and the average stress of PEO@NCM-LPSC was 294 MPa. It can be seen that the composite cathode material with a specific coating layer structure provided by this invention can effectively improve the mechanical properties of electrode particles, reduce stress, and thus improve battery performance.

[0060] Table 2

[0061] Table 3

[0062]

[0063] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A composite cathode material, characterized in that, The composite cathode material includes a modified cathode material and a sulfide-type solid electrolyte; the modified cathode material includes cathode active particles and a coating layer covering the surface of the cathode active particles; the coating layer material is a polymer-lithium salt composite material with an elastic modulus of 0.1~5.0 GPa or a lithium oxide-containing material with an elastic modulus of 120~200 GPa; the polymer in the polymer-lithium salt composite material is selected from at least one of polyethylene oxide, polycarbonate, polymethyl methacrylate, and polystyrene.

2. The composite cathode material according to claim 1, characterized in that, The positive electrode active particles are selected from at least one of lithium nickel cobalt manganese oxide particles, lithium nickel cobalt aluminum oxide particles, and lithium manganese iron phosphate particles. Preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide and / or lithium hexafluorophosphate; Preferably, the lithium oxide material is selected from at least one of lithium niobate, lithium lanthanum zirconium oxide, and lithium lanthanum titanium oxide.

3. The composite cathode material according to claim 1, characterized in that, The mass ratio of the modified cathode material to the sulfide-type solid electrolyte is 1:(0.3~0.5); Preferably, the mass ratio of the coating material to the positive electrode active particles is (1~3):100; Preferably, the mass ratio of polymer to lithium salt in the polymer-lithium salt composite material is 5:(1~3).

4. The method for preparing the composite cathode material according to any one of claims 1 to 3, characterized in that, The preparation method includes the following steps: S1. Dissolve lithium salt and polymer in a first organic solvent to form a mixture, and then subject the mixture to a first ball milling process with the first positive electrode active particles to obtain a first modified positive electrode material with a polymer-lithium salt composite coating layer on the surface. Alternatively, the lithium oxide is dispersed in a second organic solvent to form a dispersion, and then the dispersion is subjected to a second ball milling treatment with the second positive electrode active particles to obtain a second modified positive electrode material with a lithium oxide coating layer on the surface. S2. The first modified cathode material or the second modified cathode material is subjected to a third ball milling treatment with a sulfide-type solid electrolyte to obtain a composite cathode material.

5. The method for preparing the composite cathode material according to claim 4, characterized in that, In step S1, the mass ratio of the lithium salt to the polymer is (1~3):5; Preferably, the mass ratio of the first positive electrode active particle to the polymer in the mixture is 100:(1~3); Preferably, the mass ratio of the second positive electrode active particles to the lithium oxide-containing dispersion is 100:(1~3); Preferably, the conditions for the first ball milling treatment and the second ball milling treatment each independently include: The rotation speed is 150~200 rpm, and the time is 6~10 hours.

6. The method for preparing the composite cathode material according to claim 4, characterized in that, In step S1, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide and / or lithium hexafluorophosphate; Preferably, the first positive electrode active particle and the second positive electrode active particle are each independently selected from at least one of lithium nickel cobalt manganese oxide particles, lithium nickel cobalt aluminum oxide particles, and lithium manganese iron phosphate particles. Preferably, the first organic solvent and the second organic solvent are each independently selected from at least one of acetonitrile, methanol, ethanol, isopropanol, acetone, and dimethylformamide.

7. The method for preparing the composite cathode material according to claim 4, characterized in that, In step S2, the mass ratio of the first modified cathode material or the second modified cathode material to the sulfide-type solid electrolyte is 1:(0.3~0.5); Preferably, the conditions for the third ball milling process include: a rotation speed of 150~200 rpm and a time of 1~3 h.

8. The composite cathode material prepared by the method according to any one of claims 4 to 7.

9. The application of the composite cathode material according to any one of claims 1 to 3 and claim 8 in solid-state batteries.

10. A simulation evaluation method for interfacial stress distribution in composite cathode materials, characterized in that, The evaluation method includes: mixing the composite cathode material and binder by ball milling to form an electrode sheet; performing CT scanning on the electrode sheet; importing the obtained CT images into image processing software for processing to obtain a three-dimensional microstructure model of the composite cathode material; importing the obtained three-dimensional microstructure model into simulation software; inputting battery simulation parameters and electrochemical model control equations and stress model control equations to construct an electrochemical field-mechanical field coupled simulation model. The coupling principle is based on the fact that the deformation of the mechanical field is driven by the chemical strain caused by the change in lithium ion concentration in the electrochemical field; setting charge and discharge test parameters to conduct simulation tests; obtaining the interface stress distribution cloud map and calculating the maximum value, average value, and standard deviation of the interface stress as quantitative indicators for evaluating stress level and uniformity.

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