Composite positive electrode material, preparation method thereof, positive electrode plate and solid-state lithium ion battery

Abstract

The invention discloses a composite positive electrode material, a preparation method thereof, a positive electrode plate and a solid-state lithium ion battery, and belongs to the technical field of secondary batteries. The composite positive electrode material comprises a lithium-rich positive electrode material, a halide solid electrolyte and high-voltage lithium cobalt oxide which are ball-milled and mixed. And the ratio of D90 of the lithium-rich positive electrode material to D90 of the high-voltage lithium cobalt oxide is 1: (1-5). The mass ratio of the lithium-rich positive electrode material to the high-voltage lithium cobalt oxide is (0.5-9.5): (9.5-0.5), and the halide solid electrolyte accounts for 5%-30% of the mass of the composite positive electrode material. When the composite positive electrode material is used for preparing the solid-state lithium ion battery, the discharge median voltage and the discharge specific capacity of the solid-state lithium ion battery can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and more particularly, to a composite cathode material, a method for preparing the same, a cathode electrode sheet, and a solid-state lithium-ion battery. Background Art

[0002] Rich lithium cathode materials are considered to be an ideal choice for the new generation of high-energy density power lithium batteries due to their advantages such as high specific capacity, high working voltage, low cost, and high safety, and are the key technology for the energy density of power lithium batteries to break through 400 Wh / kg.

[0003] However, solid-state lithium-ion batteries prepared using rich lithium cathode materials often have problems such as low first-cycle Coulombic efficiency, low charge-discharge specific capacity, severe voltage decay, or poor rate performance, and these problems become more prominent in solid-state lithium-ion batteries, seriously hindering the industrial application of rich lithium cathode materials in solid-state lithium-ion batteries. Summary of the Invention

[0004] The present application provides a composite cathode material, a method for preparing the same, a cathode electrode sheet, and a solid-state lithium-ion battery to improve the discharge specific capacity of the solid-state lithium-ion battery.

[0005] The present application is implemented as follows:

[0006] In a first aspect, an example of the present application provides a composite cathode material, including a rich lithium cathode material, a halide solid electrolyte, and lithium cobaltate with high pressure, which are ball-milled and mixed. The ratio of D90 of the rich lithium cathode material to D90 of the lithium cobaltate with high pressure is 1:(1-5). The mass ratio of the rich lithium cathode material to the lithium cobaltate with high pressure is (0.5-9.5):(9.5-0.5), and the mass percentage of the halide solid electrolyte in the composite cathode material is 5%-30%.

[0007] In the above implementation process, the rich lithium cathode material has a relatively high theoretical specific capacity (250 mAh / g) and a relatively high working voltage (>4.8 V), the halide solid electrolyte has a high oxidation-resistant voltage (>5 V) and good electrochemical compatibility with the rich lithium cathode material, the lithium cobaltate with high pressure (>4.8 V) has a working voltage matching that of the rich lithium cathode material, and the lithium cobaltate with high pressure has relatively high ionic conductivity and electronic conductivity. Adding a specific mass ratio of the halide solid electrolyte and the lithium cobaltate with high pressure to modify the rich lithium cathode material, and through the particle size matching of the rich lithium cathode material and the lithium cobaltate with high pressure, the tap density of the composite cathode material can be improved, and the solid-state lithium-ion battery prepared can promote the release of the electric quantity of the rich lithium cathode material while maintaining a relatively high discharge median voltage, thereby improving the discharge specific capacity of the solid-state lithium-ion battery.

[0008] In combination with the first aspect, in an alternative embodiment of the present application, the chemical general formula of the lithium-rich cathode material is xLi2MnO3·(1-x)LiMO2, where M is at least one of Fe, Ni, Co, and Mn, and 0 < x < 1.

[0009] Optionally, the lithium-rich cathode material includes Li 1.2 Ni 0.17 Co 0.1 Mn 0.53 O2, Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, Li 1.2 Mn 0.54 Ni 0.13 O2 or Li 1.44 Ni 0.16 Mn 0.56 O2 or any combination of at least two of them.

[0010] In the above implementation process, the above lithium-rich cathode material has characteristics such as a high specific capacity of more than about 250 mAh / g, a high working voltage of about 4.8 V, low cost, and high safety, and can improve the working voltage, discharge specific capacity, and safety of the prepared solid-state lithium-ion battery.

[0011] In combination with the first aspect, in an alternative embodiment of the present application, the chemical general formula of the halide solid electrolyte is Li a MX b , where M is at least one of In, Y, Yb, Er, Hf, Sc, Mg, Zr, Mn, or Zn, X is at least one of F, Cl, I, or Br, 1 ≤ a ≤ 8, and 2 ≤ b ≤ 10.

[0012] Optionally, the halide solid electrolyte includes any one or a combination of at least two of Li3InCl6, Li3YCl6, Li2MnCl4, Li2ZnCl4, or Li3YCl6.

[0013] In the above implementation process, the above halide solid electrolyte has good electrochemical compatibility with the lithium-rich cathode material, while sulfide electrolytes and polymer electrolytes are limited by their low oxidation potential (<4.0 V), that is, the electrolyte undergoes a decomposition reaction at a high working voltage and cannot match the lithium-rich cathode material to meet the normal operation of the lithium-rich cathode material. When the halide electrolyte is paired with the lithium-rich cathode material, it can improve the ionic conductivity of the lithium-rich cathode material while maintaining good structural stability of the electrolyte itself, and thus can improve the discharge specific capacity and cycle stability of the prepared solid-state lithium-ion battery.

[0014] In combination with the first aspect, in an alternative embodiment of the present application, the ratio of D90 of the lithium-rich cathode material to D90 of the high-voltage lithium cobaltate is 1:(2 - 3).

[0015] Optionally, the D90 of the lithium-rich cathode material is 1 - 5 μm, and the D90 of the high-voltage lithium cobaltate is 3 - 25 μm.

[0016] In the above implementation process, the ratio of D90 of the lithium-rich cathode material to D90 of the high-voltage lithium cobaltate in the composite cathode material is 1:(2 - 3). When preparing the cathode electrode sheet using this composite cathode material, the compaction density of the cathode electrode sheet can be increased, the release of the electric quantity of the cathode active material can be further promoted, and thus the discharge specific capacity of the solid-state lithium-ion battery can be further improved.

[0017] In combination with the first aspect, in an alternative embodiment of the present application, the mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate is 1:(1 - 3).

[0018] And / or, the mass proportion of the halide solid electrolyte in the composite cathode material is 5% - 20%.

[0019] In the above implementation process, the mass proportion of the halide solid electrolyte in the composite cathode material is 5% - 20%, and the mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate is 1:(1 - 3). While improving the electronic conductivity and ionic conductivity of the lithium-rich cathode material, the addition of non-cathode active materials such as the halide solid electrolyte can be reduced, the release of the electric quantity of the cathode active material can be promoted, and thus the discharge specific capacity of the prepared solid-state lithium-ion battery can be improved.

[0020] In the second aspect, an example of the present application provides a preparation method of the composite cathode material provided in the first aspect, including: ball-milling and mixing the lithium-rich cathode material, the halide solid electrolyte, and the high-voltage lithium cobaltate.

[0021] In the above implementation process, ball-milling and mixing the lithium-rich cathode material, the halide solid electrolyte, and the high-voltage lithium cobaltate can improve the mixing uniformity of the lithium-rich cathode material, the halide solid electrolyte, and the high-voltage lithium cobaltate in the composite cathode material, can improve the compaction density and the release degree of the electric quantity of the cathode active material, and improve the discharge specific capacity of the solid-state lithium-ion battery.

[0022] In combination with the second aspect, in some possible implementation manners, the method of ball-milling and mixing includes:

[0023] Under an inert atmosphere, wet ball-mill the lithium-rich cathode material and the halide solid electrolyte, then perform drying and annealing treatments to obtain a lithium-rich cathode material coated with the halide solid electrolyte. Dry ball-mill the lithium-rich cathode material coated with the halide solid electrolyte and the high-voltage lithium cobaltate to obtain a mixed cathode material.

[0024] In the above implementation process, a halide solid electrolyte coating layer is first formed on the surface of the lithium-rich cathode material by wet coating. The halide solid electrolyte has good electrochemical compatibility with the lithium-rich cathode material, and the halide solid electrolyte has good ionic conductivity, which can improve the ionic conductivity of the lithium-rich cathode material while reducing the influence of the solid electrolyte on the electrochemical performance of the lithium-rich cathode material. Then, the lithium-rich cathode material coated with the halide solid electrolyte is dry ball-milled with lithium cobaltate under high pressure to obtain a composite cathode material in which lithium cobaltate under high pressure and the lithium-rich cathode material coated with the halide solid electrolyte are uniformly mixed. In this composite cathode material, lithium cobaltate under high pressure has a relatively high voltage platform, as well as relatively high ionic conductivity and electronic conductivity, which can improve the ionic conductivity and electronic conductivity of the composite cathode material while ensuring that the composite cathode material has a relatively high specific capacity and working voltage. Mixing in the order of wet ball milling first and then dry ball milling can further improve the mixing uniformity, increase the compaction density, and increase the discharge specific capacity of the prepared solid-state lithium-ion battery.

[0025] Combined with the second aspect, in some possible implementation manners, the solvent used for wet ball milling includes any one or a combination of at least two of isopentane, n-pentane, petroleum ether, hexane, cyclohexane, isooctane, trifluoroacetic acid, trimethylpentane, cyclopentane, heptane, butyl chloride, trichloroethylene, carbon tetrachloride, trichlorotrifluoroethane, propyl ether, toluene, p-xylene, chlorobenzene, benzene, isobutanol, or diethyl ether.

[0026] Optionally, the drying temperature is 80 - 250 °C, and the annealing temperature is 200 - 400 °C.

[0027] Optionally, the drying temperature is 200 - 250 °C, and the annealing temperature is 300 - 350 °C.

[0028] Optionally, the ball-to-material ratio for ball milling is (20 - 5):1, the rotation speed is 50 - 300 r / min, and the time is 0.5 - 4 h.

[0029] Optionally, the rotation speed is 100 - 200 r / min.

[0030] In the above implementation process, wet ball milling is performed on the lithium-rich cathode material and the halide solid electrolyte using the above solvent, which can not only improve the mixing uniformity of the materials, but also reduce the influence of the solvent on the electrochemical performance of the halide solid electrolyte and the lithium-rich cathode material during ball milling. Moreover, after drying at a temperature of 80-250 °C for a certain period of time and then annealing at a temperature of 200-400 °C, it can not only reduce the residual amount of the solvent in the composite cathode material, but also improve the crystallinity of the halide electrolyte, thereby affecting the ionic conductivity of the halide electrolyte. Appropriate drying temperature and annealing temperature can reduce the influence on the performance of the halide solid electrolyte, and also help the cathode active material to fully release the electric charge, improving the discharge specific capacity of the prepared solid-state lithium-ion battery.

[0031] In addition, when the ball-to-material ratio of ball milling is (20-5):1 and the rotation speed is 50-300 r / min for ball milling for 0.5-4 h, the lithium-rich cathode material, the halide solid electrolyte and the high-voltage lithium cobaltate can be mixed evenly, and the probability of particle breakage or phase change of the cathode active material and the halide solid electrolyte can also be reduced. Appropriate ball-to-material ratio and ball milling rotation speed can further improve the electrochemical performance of the composite cathode material and the discharge capacity of the prepared solid-state lithium-ion battery.

[0032] In a third aspect, an example of the present application provides a positive electrode plate, which includes a positive electrode current collector and a positive electrode active material layer provided on at least a part of the surface of the positive electrode current collector. The positive electrode active material layer includes the composite cathode material provided in the first aspect.

[0033] Optionally, the mass ratio of the composite cathode material in the positive electrode active material layer is 90-95%.

[0034] In the above implementation process, using the composite cathode material provided in the first aspect of the example of the present application to prepare the positive electrode plate, this composite cathode material not only has a high working voltage and high specific capacity, but also has good electronic conductivity and ionic conductivity, can reduce the addition of other non-cathode active materials except the composite cathode material, and also has a high tap density, which can improve the discharge specific capacity of the prepared solid-state lithium-ion battery and alleviate the attenuation of its voltage.

[0035] In a fourth aspect, an example of the present application provides a solid-state lithium-ion battery, which includes the positive electrode plate provided in the third aspect.

[0036] In the above implementation process, using the positive electrode plate provided in the third aspect of the example of the present application to prepare the solid-state lithium-ion battery can make the solid-state lithium-ion battery have a high discharge median voltage, areal capacity and discharge specific capacity. Description of the Drawings

[0037] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0038] Figure 1 Schematic diagram of the composite cathode material provided by the embodiment of the present application;

[0039] Figure 2 Charge and discharge curve graph provided by Embodiment 1 of the present application;

[0040] Figure 3 Cycling performance test graph provided by Embodiment 1 of the present application;

[0041] Figure 4 Charge and discharge curve graph provided by Comparative Example 1 of the present application.

[0042] Icons: 100 - composite cathode material; 101 - lithium-rich cathode material; 102 - halide solid electrolyte; 103 - high-voltage lithium cobaltate. Detailed implementation manners

[0043] The following will describe the implementation schemes of the present application in detail in conjunction with the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are adopted. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0044] Please refer to Figure 1 , the embodiment of the present application provides a composite cathode material 100, including a lithium-rich cathode material 101, a halide solid electrolyte 102, and a high-voltage lithium cobaltate 103.

[0045] Among them, the ratio of D90 of the lithium-rich cathode material to D90 of the high-voltage lithium cobaltate is 1:(1 - 5). The mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate is (0.5 - 9.5):(9.5 - 0.5), and the mass proportion of the halide solid electrolyte in the composite cathode material is 5% - 30%.

[0046] In the above-mentioned composite cathode material 100, the lithium-rich cathode material 101 has a high theoretical specific capacity and a high working voltage. The halide solid electrolyte 102 has good electrochemical compatibility with the lithium-rich cathode material. The high-voltage lithium cobaltate 103 has a working voltage matching that of the lithium-rich cathode material 101, and the halide solid electrolyte 102 has a high ionic conductivity. The high-voltage lithium cobaltate 103 has a high ionic conductivity and an electronic conductivity. Modifying the lithium-rich cathode material 101 by adding a specific mass ratio of the halide solid electrolyte 102 and the high-voltage lithium cobaltate 103, and through the particle size matching of the lithium-rich cathode material 101 and the high-voltage lithium cobaltate 103, can enable the solid-state lithium-ion battery to maintain a high discharge median voltage while promoting the full release of the charge of the cathode active material and improving the discharge specific capacity of the solid-state lithium-ion battery.

[0047] In the embodiments of the present application, the "lithium-rich cathode material" refers to a type of material with a lithium content higher than that of traditional cathode materials. Its core principle is to introduce more lithium ions into the cathode material to increase the energy density of the battery.

[0048] In some embodiments, the lithium-rich cathode material includes a lithium-rich manganese-based cathode material. The chemical general formula of the lithium-rich cathode material is xLi2MnO3·(1-x)LiMO2, where M is at least one of Fe, Ni, Co, or Mn, and 0 < x < 1.

[0049] As an example, the lithium-rich cathode material includes Li 1.2 Ni 0.17 Co 0.1 Mn 0.53 O2, Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, Li 1.2 Mn 0.54 Ni 0.13 O2 or Li 1.44 Ni 0.16 Mn 0.56 O2, or any one or at least two combinations thereof.

[0050] Traditional cathode materials, such as LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25O2 (which can also be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 085 Co 015 Al 005 O2), etc., the molar content of lithium ions in which is lower than that of the xLi2MnO3·(1 - x)LiMO2 lithium-rich cathode material in the embodiments of the present application.

[0051] The lithium-rich cathode material has a high lithium content and a high theoretical energy density. However, the lithium-rich cathode material has poor electronic and ionic conductivities, poor structural stability, poor initial capacity and cycling performance. Therefore, in step S1 of the embodiments of the present application, a halide solid electrolyte and high-voltage lithium cobaltate are added and mixed and ball-milled with the lithium-rich cathode material, which can make up for the deficiencies of the poor electronic and ionic conductivities of the lithium-rich cathode material by utilizing the high ionic conductivity of the halide solid electrolyte and the high ionic and electronic conductivities of high-voltage lithium cobaltate, and improve the electrochemical performance of the composite cathode material.

[0052] The halide solid electrolyte and the lithium-rich cathode material have good electrochemical compatibility. By using the halide solid electrolyte and the lithium-rich cathode material in combination, the halide electrolyte maintains good structural stability and ionic conductivity at a high working voltage (>4.2V), and can maintain the normal operation of the lithium-rich cathode material. If other solid electrolytes other than the halide solid electrolyte are mixed with the lithium-rich cathode material, for example, a sulfide solid electrolyte or a polymer electrolyte is combined with the lithium-rich cathode material, the sulfide electrolyte or the polymer electrolyte will decompose at a high working voltage, which will affect the power release of the lithium-rich cathode material and even make it unable to work.

[0053] In some possible embodiments, the chemical general formula of the halide solid electrolyte is Li a MX b , at least one of In, Y, Yb, Er, Hf, Sc, Mg, Zr, Mn or Zn, X is at least one of F, Cl, I or Br, 1≤a≤8, 2≤b≤10.

[0054] Exemplarily, the halide solid electrolyte includes any one or a combination of at least two of Li3InCl6, Li3YCl6, Li2MnCl4, Li2ZnCl4 or Li3YCl6.

[0055] "High-voltage lithium cobaltate" refers to the material obtained by modifying lithium cobaltate. Compared with ordinary lithium cobaltate, high-voltage lithium cobaltate has a higher voltage. The working voltage of high-voltage lithium cobaltate is approximately 2.5 - 4.8V, while that of ordinary lithium cobaltate is 2.5 - 4.2V. The maximum working voltage of high-voltage lithium cobaltate is higher than that of ordinary lithium cobaltate.

[0056] By using high-voltage lithium cobaltate in combination with a lithium-rich cathode material instead of ordinary lithium cobaltate, it is possible to improve the ionic conductivity and electronic conductivity of the composite cathode material while ensuring the structural stability of lithium cobaltate during high-voltage operation. At the same time, the high-voltage lithium cobaltate and the lithium-rich cathode in the composite cathode material can synergistically release electricity, increasing the median discharge voltage and discharge specific capacity of the composite cathode material.

[0057] In the embodiments of this application, the mass ratio of the lithium-rich cathode material to high-voltage lithium cobaltate is (0.5 - 9.5):(9.5 - 0.5), and the mass proportion of the halide solid electrolyte in the composite cathode material is 5% - 30%. Adding high-voltage lithium cobaltate and halide solid electrolyte in specific mass ratios can improve the ionic conductivity and electronic conductivity of the composite cathode material while also increasing the degree of electricity release of the cathode active material in the composite cathode material, and can improve the discharge specific capacity of the solid-state lithium-ion battery.

[0058] If the content of high-voltage lithium cobaltate is too high, the capacity of the composite cathode material will be reduced. If the content of high-voltage lithium cobaltate is too low, the electricity of the lithium-rich cathode material cannot be fully released, which will also lead to a reduction in the discharge specific capacity of the solid-state lithium-ion battery prepared from the composite cathode material.

[0059] If the content of the halide solid electrolyte is too high, it will lead to an increase in the content of non-cathode active substances in the cathode electrode sheet and also reduce the capacity of the solid-state lithium-ion battery.

[0060] As an example, the mass ratio of the lithium-rich cathode material to high-voltage lithium cobaltate can be one of 0.5:9.5, 1:9, 1.5:8.5, 2:8, 2.5:7.5, 3:7, 3.5:6.5, 4:6, 4.5:5.5, 5:5, 5.5:4.5, 6.5:3.5, 7:3, 7.5:2.5, 8:2, 8.5:1.5, 9:1 or 9.5:0.5 or any range between any two of them.

[0061] As an example, the mass proportion of the halide solid electrolyte in the composite cathode material can be one of 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25% or 30% or any range between any two of them.

[0062] Further, in some embodiments, the mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate can be 1:(1-3).

[0063] As an example, the mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate can be 1:1. Alternatively, the mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate can be 1:3.

[0064] Alternatively, the mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate can be 3:1.

[0065] Further, in some embodiments, the mass percentage of the halide solid electrolyte in the composite cathode material is 5%-20%.

[0066] Further, in some embodiments, the mass percentage of the halide solid electrolyte in the composite cathode material is 5%-15%. Alternatively, in some embodiments, the mass percentage of the halide solid electrolyte in the composite cathode material is 5%-10%.

[0067] In the embodiments of the present application, by using a lithium-rich cathode material with a specific particle size in combination with a high-voltage lithium cobaltate with a specific particle size, the tap density of the composite cathode material can be increased, and the release degree of the performance such as the electricity of the positive electrode active material can be further improved.

[0068] As an example, the ratio of D90 of the lithium-rich cathode material to D90 of the high-voltage lithium cobaltate can be one of 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5 or the range between any two of them.

[0069] Further, in some possible embodiments, the ratio of D90 of the lithium-rich cathode material to D90 of the high-voltage lithium cobaltate is 1:(2-3).

[0070] In some embodiments, D90 of the lithium-rich cathode material is 1-5 μm, and D90 of the high-voltage lithium cobaltate is 3-25 μm.

[0071] As an example, D90 of the lithium-rich cathode material can be one of 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm or the range between any two of them.

[0072] As an example, D90 of the high-voltage lithium cobaltate can be one of 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm or 25 μm or the range between any two of them.

[0073] In the composite cathode material provided by the embodiments of the present application, the lithium-rich cathode material, the halide solid electrolyte, and the high-voltage lithium cobaltate are uniformly mixed. The composite cathode material has a relatively high tap density.

[0074] Furthermore, the embodiments of the present application also provide a preparation method of a composite cathode material, including:

[0075] S1. Ball-mill and mix the lithium-rich cathode material, the halide solid electrolyte, and the high-voltage lithium cobaltate.

[0076] Furthermore, in some embodiments, in step S1, the method of ball-mill mixing includes:

[0077] S11. Under an inert atmosphere, wet ball-mill the lithium-rich cathode material and the halide solid electrolyte, and then perform drying and annealing treatments to obtain a lithium-rich cathode material coated with the halide solid electrolyte.

[0078] S12. Dry ball-mill the lithium-rich cathode material coated with the halide solid electrolyte and the high-voltage lithium cobaltate to obtain a composite cathode material.

[0079] Adopting the ball-milling process of first wet ball-milling the lithium-rich cathode material and the halide solid electrolyte, and then dry ball-milling the lithium-rich cathode material coated with the halide solid electrolyte and the high-voltage lithium cobaltate can further improve the mixing uniformity, increase the tap density, and increase the discharge capacity of the prepared solid-state lithium-ion battery. If the lithium-rich cathode material, the halide solid electrolyte, and the high-voltage lithium cobaltate are directly wet ball-milled and mixed, the discharge specific capacity of the prepared solid-state lithium-ion battery will be reduced. If the lithium-rich cathode material and the halide solid electrolyte are first dry ball-milled, and then the ball-milled product and the high-voltage lithium cobaltate are dry ball-milled, the discharge specific capacity of the prepared solid-state lithium-ion battery will be reduced. If the lithium-rich cathode material and the high-voltage lithium cobaltate are first wet ball-milled and then dry ball-milled, it will affect the ionic conductivity and electronic conductivity of the composite cathode and reduce the discharge specific capacity of the solid-state lithium-ion battery.

[0080] Furthermore, in some embodiments, during wet and dry ball-milling, the ball-to-material ratio for ball-milling is (20 - 5):1, the rotation speed is 50 - 300 r / min, and the time is 0.5 - 4 h.

[0081] During wet and dry ball-milling, appropriate ball-to-material ratio, ball-milling rotation speed, and ball-milling time can, while improving the mixing uniformity of the composite cathode material, also reduce the probability of reactions such as decomposition or phase change of the lithium-rich cathode material, the halide solid electrolyte, or the high-voltage lithium cobaltate material during ball-milling, and improve the electrochemical performance of the composite cathode material.

[0082] As an example, the ball-to-material ratio can be one of 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1, or within the range between any two of them.

[0083] As an example, the rotation speed of ball milling can be one of 50 r / min, 100 r / min, 150 r / min, 200 r / min, 250 r / min or 300 r / min, or within the range between any two of them.

[0084] As an example, the ball milling time can be one of 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h or 4 h, or within the range between any two of them.

[0085] Furthermore, in some possible embodiments, the rotation speed of ball milling can be 100 - 200 r / min.

[0086] Furthermore, in some possible embodiments, in step S1, the solvent used for wet ball milling includes any one or a combination of at least two of isopentane, n-pentane, petroleum ether, hexane, cyclohexane, isooctane, trifluoroacetic acid, trimethylpentane, cyclopentane, heptane, butyl chloride, trichloroethylene, carbon tetrachloride, trichlorotrifluoroethane, propyl ether, toluene, p-xylene, chlorobenzene, benzene, isobutanol or diethyl ether.

[0087] Using the above solvents to perform wet ball milling on the halide solid electrolyte and the lithium-rich cathode material can reduce the particle size of the halide solid electrolyte, improve the uniformity of coating the lithium-rich cathode material, and at the same time reduce the probability of chemical reaction between the solvent and the halide solid electrolyte during the wet ball milling process.

[0088] After wet ball milling, it is necessary to dry the milled product. Since in the wet ball milling process, the above solvents are in full contact and infiltration with the lithium-rich cathode material and the halide solid electrolyte, even after drying for a long time, there will still be a certain amount of solvent residue. In order to further reduce the solvent residue in the milled product, it is necessary to perform annealing treatment after drying for a certain time. Appropriate drying temperature and annealing temperature can not only improve the preparation efficiency of the composite cathode material, but also reduce the solvent residue in the composite cathode material and reduce the influence of the solvent on the electrochemical performance of the halide solid electrolyte material and the lithium-rich cathode material.

[0089] If the annealing temperature is too high, the halide solid electrolyte or the lithium-rich cathode material may decompose or undergo a phase change reaction. If the annealing temperature is too low, the adverse effect of the solvent on the electrochemical performance of the halide solid electrolyte is difficult to recover, which is not conducive to improving the electrochemical performance of the composite cathode material.

[0090] As an example, the drying temperature can be one of 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C or 250°C, or a range between any two of them.

[0091] As an example, the annealing temperature can be one of 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C, or a range between any two of them.

[0092] Further, in some embodiments, the drying temperature can be 200 - 250°C, and the annealing temperature can be 300 - 350°C.

[0093] Further, the embodiments of the present application provide a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active material layer provided on at least a part of the surface of the positive electrode current collector. The positive electrode active material layer includes a composite positive electrode material prepared according to the above preparation method.

[0094] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0095] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0096] Further, in some possible embodiments, the mass ratio of the composite positive electrode material in the positive electrode active material layer is 90 - 95%.

[0097] The composite positive electrode material provided by the embodiments of the present application has high ionic conductivity and electronic conductivity. When preparing the positive electrode sheet, the addition of other non-positive electrode active materials such as conductive carbon can be reduced. In the positive electrode sheet, the content of the positive electrode active material is relatively high, which can further improve the electrochemical performance such as the discharge specific capacity of the solid-state lithium-ion battery.

[0098] As an example, the mass ratio of the composite cathode material in the cathode active material layer can be one of 90%, 91%, 92%, 93%, 94% or 95%, or within the range between any two of them.

[0099] In some embodiments, the cathode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0100] In some embodiments, in addition to the composite cathode material, the cathode active material layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] In some embodiments, the cathode electrode sheet can be prepared by the following method: dispersing the above components for preparing the cathode electrode sheet, such as the composite cathode material, conductive agent, binder, and any other components, in a solvent (such as N - methylpyrrolidone) to form a cathode slurry; coating the cathode slurry on the cathode current collector, and after processes such as drying and cold pressing, the cathode electrode sheet can be obtained.

[0102] Furthermore, the embodiment of the present application also provides a solid - state lithium - ion battery, including the cathode electrode sheet provided by the embodiment of the present application.

[0103] In some embodiments, the solid - state lithium - ion battery further includes an anode electrode sheet and a solid - state electrolyte layer disposed between the cathode electrode sheet and the anode electrode sheet.

[0104] As an example, the anode electrode sheet includes an anode current collector and an anode active material layer disposed on at least a part of the surface of the anode current collector.

[0105] The anode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0106] The negative electrode active material layer contains a negative electrode active material, and the negative electrode active material can be a negative electrode active material for solid-state lithium-ion batteries known in the art. As an example, the negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc.

[0107] In some embodiments, the negative electrode active material layer may further optionally include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0108] In some embodiments, the negative electrode active material layer may further optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] The solid electrolyte layer contains a solid electrolyte material. As an example, the solid electrolyte material is selected from oxide-based solid electrolyte materials, polymer-based solid electrolyte materials, halide-based solid electrolyte materials, or sulfide solid electrolyte materials.

[0110] The composite cathode material of the present application will be further described in detail below in conjunction with embodiments.

[0111] Example 1

[0112] Example 1 provides a composite cathode material, and its preparation method is as follows:

[0113] (1) Mixing of halide solid electrolyte and lithium-rich cathode material:

[0114] First, 40 g of halide solid electrolyte (Li2ZrCl6, D90 = 1 μm) and 80 g of lithium-rich cathode material (Li 1.2 Ni 0.17 Co 0.1 Mn 0.53 O2, D90 = 2 μm) are placed in a ball milling jar, 50 g of isopentane (purity: 99.9%) solvent is added, and they are mixed at a rotation speed of 100 r / min for 2 h to obtain a mixture of halide solid electrolyte and lithium-rich cathode material.

[0115] (2) Removal of organic solvent:

[0116] The mixture obtained in step (1) is placed in an oven and baked at a temperature of 200 °C for 5 h. Then, the dried mixture is placed in a muffle furnace and annealed at a temperature of 300 °C for 2 h to obtain a lithium-rich cathode material coated with a halide solid electrolyte.

[0117] (3) Preparation of composite cathode material:

[0118] Take the lithium-rich cathode material coated with halide solid electrolyte obtained in step (3) and 80 g of high-voltage lithium cobaltate (LiCoO₂, working voltage 2.5 - 4.8 V, D90 = 4 μm) and place them in a ball milling jar. Mix them at a rotation speed of 100 r / min for 2 h to obtain a composite cathode material. The mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate is 1:1. The ratio of the particle size D90 of the lithium-rich cathode material to that of the high-voltage lithium cobaltate is 1:2. See Table 1 for some process parameters.

[0119] Example 2

[0120] Example 2 provides a composite cathode material, which is different from Example 1 in that:

[0121] In step (1), the mass of the lithium-rich cathode material is 40 g; in step (3), the mass of the high-voltage lithium cobaltate is 120 g. The mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate is 1:3. See Table 1 for some process parameters.

[0122] Example 3

[0123] Example 3 provides a composite cathode material, which is different from Example 1 in that:

[0124] In step (1), the mass of the lithium-rich cathode material is 120 g; in step (3), the mass of the high-voltage lithium cobaltate is 40 g. The mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate is 3:1. See Table 1 for some process parameters.

[0125] Example 4

[0126] Example 4 provides a composite cathode material, which is different from Example 1 in that:

[0127] In step (1), the particle size D90 of the lithium-rich cathode material is 2 μm; in step (3), the particle size D90 of the high-voltage lithium cobaltate is 10 μm. The ratio of the particle size D90 of the lithium-rich cathode material to that of the high-voltage lithium cobaltate is 1:5. See Table 1 for some process parameters.

[0128] Example 5

[0129] Example 5 provides a composite cathode material, which is different from Example 1 in that:

[0130] In step (2), the drying temperature is 100 °C and the annealing temperature is 200 °C. See Table 1 for some process parameters.

[0131] Example 6

[0132] Example 6 provides a composite cathode material, which is different from that of Example 1 in that:

[0133] In steps (1) and (3), the rotation speed of ball milling is 300 r / min. See Table 1 for some process parameters.

[0134] Example 7

[0135] Example 7 provides a composite cathode material, and the preparation method is as follows:

[0136] Put 40 g of halide solid electrolyte (Li2ZrCl6, D90 = 1 μm), 80 g of lithium-rich cathode material (Li 1.2 Ni 0.17 Co 0.1 Mn 0.53 O2, D90 = 2 μm) and 80 g of high-voltage lithium cobaltate (LiCoO2, D90 = 4 μm) into a ball milling jar, add 50 g of isopentane (purity: 99.9%) solvent, and mix at a rotation speed of 100 r / min for 2 h to obtain a mixture.

[0137] Then, place the mixture in an oven and bake it at a temperature of 150 °C for 5. Place the dried mixture in a muffle furnace and anneal it at a temperature of 250 °C for 2 h to obtain the composite cathode material. See Table 1 for some process parameters.

[0138] Example 8

[0139] Example 8 provides a composite cathode material, which is different from that of Example 1 in that:

[0140] In step (1), no organic solvent is added, and the halide solid electrolyte and the lithium-rich cathode material are dry ball milled. Step (2) is not carried out. See Table 1 for some process parameters.

[0141] Example 9

[0142] Example 9 provides a composite cathode material, which is different from that of Example 1 in that: no ball milling is carried out, and the halide solid electrolyte, the lithium-rich cathode material and the high-voltage lithium cobaltate are placed in a mortar and ground and mixed. See Table 1 for some process parameters.

[0143] Comparative Example 1

[0144] Comparative Example 1 provides a composite cathode material, which is different from that of Example 1 in that:

[0145] Step (3) is not carried out, and the prepared composite cathode material does not contain high-voltage lithium cobaltate. See Table 1 for some process parameters.

[0146] Comparative Example 2

[0147] Comparative Example 2 provides a composite cathode material, which is different from that of Example 1 in that:

[0148] In step (1), 40 g of halide solid electrolyte was replaced with 40 g of sulfide solid electrolyte (chemical formula: Li6PS5Cl, D90 = 1 μm). For some process parameters, please refer to Table 1.

[0149] Comparative Example 3

[0150] Comparative Example 3 provides a composite cathode material, which is different from that of Example 1 in that:

[0151] In step (3), 80 g of high-voltage lithium cobaltate (LiCoO2) was replaced with 80 g of ordinary lithium cobaltate (Xiamen Tungsten New Energy Materials Co., Ltd., working voltage: 2.5 - 4.2 V). For some process parameters, please refer to Table 1.

[0152] Table 1

[0153]

[0154]

[0155] Test Example 1

[0156] The tap density of the composite cathode materials provided in Examples 1 - 9 and Comparative Examples 1 - 3 was measured. The test method was as follows: The composite cathode material was placed in a circular mold with a diameter of 1 cm, and an axial pressure of 500 MPa was applied. The area, thickness, and mass of the electrode sheet were measured, and the tap density was calculated. The statistical results are shown in Table 2.

[0157] Test Example 2

[0158] The electrical properties of the composite cathode materials provided in Examples 1 - 9 and Comparative Examples 1 - 3 were tested. The test method was as follows:

[0159] A solid-state battery was assembled using a mold, and its electrochemical properties were tested. The positive electrode sheet, solid electrolyte membrane sheet, and negative electrode sheet pressed from the composite cathode material were sequentially placed in the mold battery, and a pressure of 500 MPa was applied and maintained at this pressure to test its charge-discharge performance. The charge-discharge test parameters were: charge and discharge at a rate of 0.1C. After two charge-discharge cycles, cycle at a rate of 0.3C.

[0160] The charge-discharge test curve and cycle performance curve of Example 1 are respectively shown in Figure 2 and Figure 3 , and the charge-discharge curve of Comparative Example 1 is as shown in Figure 4 . The test results are shown in Table 2.

[0161] Table 2

[0162]

[0163] Result analysis:

[0164] As can be seen from Table 1, the composite cathode materials provided in Examples 1-9 of the present application have a high tap density, and also have a high discharge median voltage, areal capacity, and discharge specific capacity. In Comparative Example 1, the tap density, discharge specific capacity, and median voltage are all low.

[0165] Combining Examples 1, 2, and 3, it can be seen that in Example 1, the mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate is 1:1, in Example 2, the mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate is 1:3, and in Example 3, the mass ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate is 3:1. The solid-state lithium-ion battery prepared in Example 1 has the highest discharge specific capacity, which is higher than that of Examples 2 and 3, indicating that although the lithium-rich cathode material has a high theoretical specific capacity, the actual discharge specific capacity of the prepared solid-state lithium-ion battery does not increase with the increase in the content of the lithium-rich cathode material. If the ratio of the lithium-rich cathode material to the high-voltage lithium cobaltate is not appropriate, the discharge specific capacity of the solid-state lithium-ion battery will be reduced.

[0166] Combining Examples 1 and 4, it can be seen that in Example 1, the D90 particle size of the lithium-rich cathode material is 2 μm, and the D90 particle size of the high-voltage lithium cobaltate is 4 μm, and the particle size ratio is 1:2, and the tap density is 2.7 g / cm 3 , and the discharge median voltage is 4.1 V, and the discharge specific capacity is 241 mAh / cm 2 . In Example 4, the D90 particle size of the lithium-rich cathode material is 2 μm, and the D90 particle size of the high-voltage lithium cobaltate is 10 μm, and the particle size ratio is 1:5, and the tap density is 2.0 g / cm 3 , and the discharge median voltage is 4.4 V, and the discharge specific capacity is 190 mAh / cm 2 , indicating that the particle size ratio of the lithium-rich cathode material and the high-voltage lithium cobaltate has a great influence on the tap density. A low tap density is also not conducive to the release of the charge of the lithium-rich cathode material, and will reduce the discharge specific capacity of the solid-state lithium-ion battery.

[0167] Combining Examples 1 and 5, it can be seen that in Example 1, the solvent removal temperature and the annealing temperature are 200 °C and 300 °C respectively, and the discharge specific capacity of the obtained solid-state lithium-ion battery is 235 mAh / g. In Example 5, the solvent removal temperature and the annealing temperature are 100 °C and 200 °C respectively, and the discharge specific capacity of the obtained solid-state lithium-ion battery is 178 mAh / g, indicating that the solvent removal temperature and the annealing temperature have a great influence on the performance of the halide solid electrolyte. Appropriate solvent removal temperature and annealing temperature are helpful for the release of the charge of the lithium-rich cathode material and can improve the discharge specific capacity of the solid-state lithium-ion battery.

[0168] Combining Example 1 and Example 6, it can be seen that the ball milling speed in Example 1 is 100 r / min, and the ball milling speed in Example 6 is 300 r / min. The tap density, discharge median voltage and areal capacity of the composite cathode materials prepared in Example 1 and Example 6 are not significantly different, but the discharge specific capacity of Example 6 is lower than that of Example 1, indicating that during the ball milling process, too high a speed will cause the particles of the cathode active material or the halide solid electrolyte to break or undergo a phase change, and an appropriate ball milling speed can further improve the discharge specific capacity of the composite cathode material.

[0169] Combining Example 1, Example 7, Example 8 and Example 9, it can be seen that following the mixing sequence of Example 1 helps to improve the mixing uniformity, increase the tap density, promote the release of the charge of the lithium-rich cathode material, and can increase the discharge specific capacity of the solid-state lithium-ion battery to 234 mAh / g. In Example 7, directly wet ball milling and mixing the lithium-rich cathode material, the halide solid electrolyte and the high-voltage cobaltate will affect the release of the charge of the lithium-rich cathode material, and the discharge specific capacity of its solid-state lithium-ion battery is 202 mAh / g, lower than that of Example 1. In Example 8, dry ball milling the halide solid electrolyte and the lithium-rich cathode material will reduce the tap density of the composite cathode material and inhibit the release of the charge of the lithium-rich cathode material, and the discharge specific capacity of the prepared solid-state lithium-ion battery is 211 mAh / g, lower than that of Example 1. In Example 9, grinding and mixing the halide solid electrolyte, the lithium-rich cathode material and the high-voltage cobaltate in a mortar results in a lower tap density of the prepared composite cathode material, and the discharge specific capacity of the prepared solid-state lithium-ion battery is 183 mAh / g, lower than that of Example 1. It shows that the mixing process of Example 1 of the present application, which first wet ball mills the lithium-rich cathode material and the halide solid electrolyte, then dries and anneals the wet ball milling product at a specific temperature, and then adds the high-voltage cobaltate for dry ball milling, can further increase the tap density, promote the release of the charge of the lithium-rich cathode material, and can increase the discharge specific capacity of the prepared solid-state lithium-ion battery.

[0170] From Comparative Example 1, Comparative Proportion 1, Comparative Proportion 2 and Comparative Proportion 3, it can be seen that in Comparative Proportion 1, the high-voltage lithium cobaltate is not added to modify the lithium-rich cathode material, and the discharge specific capacity of the prepared solid-state lithium-ion battery is relatively low. From Comparative Example 1 and Comparative Proportion 2, it can be seen that in Comparative Proportion 2, the sulfide solid electrolyte is used to modify the lithium-rich cathode material, which is not conducive to the normal operation of the lithium-rich cathode material, and the discharge specific capacity of the prepared solid-state lithium-ion battery is lower than that of Example 1, only 32 mAh / g. In Comparative Proportion 3, the high-voltage lithium cobaltate is replaced with ordinary lithium cobaltate, which is not conducive to the release of the electric quantity of the lithium-rich cathode material, and the discharge specific capacity of the prepared solid-state lithium-ion battery is lower than that of Example 1. It shows that the modification of the composite cathode material with a specific mass ratio of sulfide solid electrolyte and high-voltage lithium cobaltate in the embodiments of the present application can promote the full release of the electric quantity of the lithium-rich cathode material and improve the discharge specific capacity of the prepared solid-state lithium-ion battery.

[0171] In summary, according to the preparation method provided by the embodiments of the present application, by regulating the addition amount of high-voltage lithium cobaltate and its particle size ratio to the lithium-rich cathode material, and cooperating with the halide solid electrolyte with a specific mass content, the lithium-rich cathode material is modified, and the tap density and discharge specific capacity of the prepared composite cathode material can be improved. Moreover, by adopting a multi-step mixing process of wet ball milling first and then dry ball milling, drying and annealing at a specific temperature, and ball milling at a specific ball milling speed, the uniformity of material mixing and the release degree of the electric quantity of the lithium-rich cathode material are both greatly improved.

[0172] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A composite positive electrode material, characterized in that: It includes ball-milled mixed lithium-rich positive electrode material, halide solid electrolyte and high-pressure lithium cobalt oxide; the ratio of D90 of the lithium-rich positive electrode material to the D90 of the high-pressure lithium cobalt oxide is 1:(1-5); the mass ratio of the lithium-rich positive electrode material to the high-pressure lithium cobalt oxide is (0.5-9.5):(9.5-0.5), and the mass proportion of the halide solid electrolyte in the composite positive electrode material is 5% to 30%.

2. The composite positive electrode material according to claim 1, characterized in that The general chemical formula of the lithium-rich positive electrode material is xLi2MnO3·(1-x)LiMO2, wherein M is at least one of Fe, Ni, Co or Mn, <x<1; Optionally, the lithium-rich cathode material includes Li 1.2 Ni 0.17 Co 0.1 Mn 0.53 O2、Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2、Li 1.2 Mn 0.54 Ni 0.13 O2 or Li 1.44 Ni 0.16 Mn 0.56 Any one or a combination of at least two of O2.

3. The composite positive electrode material according to claim 1, characterized in that: The chemical formula of the halide solid electrolyte is Li a MX b , wherein M is at least one of In, Y, Yb, Er, Hf, Sc, Mg, Zr, Mn or Zn, X is at least one of F, Cl, I or Br, 1≤a≤8, 2≤b≤10; Optionally, the halide solid electrolyte includes any one of Li3InCl6, Li3YCl6, Li2MnCl4, Li2ZnCl4 or Li3YCl6, or a combination of at least two thereof.

4. The composite positive electrode material according to claim 1, characterized in that The ratio of D90 of the lithium-rich positive electrode material to D90 of the high-pressure lithium cobalt oxide is 1:(2-3); Optionally, the D90 of the lithium-rich positive electrode material is 1 to 5 μm, and the D90 of the high-pressure lithium cobalt oxide is 3 to 25 μm.

5. The composite positive electrode material according to claim 1, characterized in that: The mass ratio of the lithium-rich positive electrode material to the high-voltage lithium cobalt oxide is 1:(1-3); And / or, the mass proportion of the halide solid electrolyte in the composite positive electrode material is 5% to 20%.

6. A method for preparing a composite positive electrode material according to any one of claims 1 to 5, characterized in that: The lithium-rich positive electrode material, the halide solid electrolyte and the high-voltage lithium cobalt oxide are ball-milled and mixed.

7. The preparation method according to claim 6, characterized in that: The ball milling mixing method comprises: Under an inert atmosphere, wet ball milling the lithium-rich cathode material and the halide solid electrolyte is performed, followed by drying and annealing to obtain a lithium-rich cathode material coated with the halide solid electrolyte; The lithium-rich positive electrode material coated with the halide solid electrolyte and high-pressure lithium cobalt oxide are dry-milled to obtain the composite positive electrode material.

8. The preparation method according to claim 7, characterized in that: The solvent for wet ball milling includes any one of isopentane, n-pentane, petroleum ether, hexane, cyclohexane, isooctane, trifluoroacetic acid, trimethylpentane, cyclopentane, heptane, butyl chloride, trichloroethylene, carbon tetrachloride, trichlorotrifluoroethane, propyl ether, toluene, p-xylene, chlorobenzene, benzene, isobutyl alcohol or diethyl ether, or a combination of at least two thereof; Optionally, the drying temperature is 80-250° C., and the annealing temperature is 200-400° C.; Optionally, the drying temperature is 200-250°C, and the annealing temperature is 300-350°C.

9. A positive electrode sheet, characterized in that: It comprises a positive electrode current collector and a positive electrode active material layer disposed on at least a portion of the surface of the positive electrode current collector; the positive electrode active material layer comprises the composite positive electrode material according to any one of claims 1 to 5; Optionally, the composite positive electrode material accounts for 90-95% by mass in the positive electrode active material layer.

10. A solid-state lithium-ion battery, characterized in that: Including the positive electrode sheet as described in claim 9.

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