Cathode materials and their preparation methods, solid-state batteries

Abstract

This application discloses a cathode material and its preparation method, as well as a solid-state battery, belonging to the field of battery technology. The cathode material includes a layered oxide active material and a coating layer covering the surface of the layered oxide active material. The coating layer includes lithium fluoride, lithium borate, and lithium phosphate. The cathode material provided by this application can combine the properties of chemical isolation, fast ion conduction, and strong interfacial bonding, reducing side reactions and space charge layers in the cathode material, significantly reducing interfacial impedance. When applied to batteries, it can improve the battery's long-cycle stability, high-rate performance, and overall safety performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a cathode material and its preparation method, and a solid-state battery. Background Technology

[0002] Sulfide solid electrolytes have become a focus of research and development for next-generation energy storage technologies due to their superior safety and high energy density potential. Using layered oxide materials as cathode materials is an effective way to improve battery operating voltage and energy density. However, the interfacial compatibility between layered oxide cathode materials and sulfide solid electrolytes is poor. The two materials are mismatched in terms of chemical stability, crystal structure, and lithium-ion migration mechanisms, leading to side reactions and physical contact failures at the interface, severely restricting the overall performance of the battery. High voltage (≥4.5V) further exacerbates this problem.

[0003] To address the aforementioned issues, current strategies primarily focus on surface coating of layered oxide cathode materials to improve the solid-solid interface between them and sulfide electrolytes. Related technologies mainly employ the construction of single-component crystalline coating layers (such as Li₂ZrO₃ layers, Li₂SiO₃ layers, Li...) on the surface of the layered oxide cathode material. 1.3 Al 0.3 Ti 1.7 The method of (PO4)3 layers. However, the thermal expansion coefficients of these rigid crystalline coatings are mismatched with those of the layered oxide cathode material, which easily leads to cracks during cycling. A single chemical composition is difficult to synergistically meet the dual requirements of physical isolation reaction and providing a fast lithium-ion channel, and has limited effect on reducing interface impedance and improving battery capacity decay. Summary of the Invention

[0004] This application provides a cathode material and its preparation method, as well as a solid-state battery, which can combine the properties of chemical isolation, fast ion conduction and strong interfacial bonding, reduce the side reactions and space charge layer of the cathode material, and significantly reduce the interfacial impedance. When applied to a battery, it can improve the battery's long-cycle stability, high-rate performance and overall safety performance.

[0005] According to a first aspect of this application, a positive electrode material is provided, the positive electrode material comprising a layered oxide active material and a coating layer covering the surface of the layered oxide active material; The coating layer includes lithium fluoride, lithium borate, and lithium phosphate.

[0006] In the cathode material provided in this application, the layered oxide active material ensures good energy density. Within the coating layer covering the surface of the layered oxide active material, lithium fluoride acts as a highly stable chemical barrier, effectively isolating interfacial side reactions under high voltage (≥4.5V) conditions. Lithium borate acts as a fast ion conductor, constructing an efficient lithium-ion transport channel, thereby reducing the space charge effect. Lithium phosphate forms a strong bond with the surface of the layered oxide active material through its PO bonds, ensuring a tight bond between the coating layer and the layered oxide active material, and fixing the surface lattice oxygen in the layered oxide active material. Through the synergistic effect of lithium fluoride, lithium borate, and lithium phosphate in the coating layer, a structure combining chemical isolation, fast ion conduction, and strong interfacial bonding can be constructed on the surface of the layered oxide active material. This reduces side reactions and the space charge layer in the cathode material, significantly lowering interfacial impedance. When applied to batteries, this improves the battery's long-cycle stability, high-rate performance, and overall safety performance.

[0007] Optionally, the mass ratio of the coating layer to the layered oxide active material is (0.5-3):100.

[0008] Maintaining the mass ratio of the coating layer to the layered oxide active material within the aforementioned range ensures effective coating, allowing lithium fluoride, lithium borate, and lithium phosphate in the coating layer to perform their respective functions, reducing side reactions, optimizing lithium-ion transport performance, lowering interfacial impedance, and minimizing the impact of the coating layer on the energy density of the cathode material. Maintaining the mass ratio of lithium fluoride, lithium borate, and lithium phosphate within the aforementioned range also balances the various properties of the coating layer, resulting in a cathode material that possesses excellent chemical stability, ion conductivity, and mechanical strength.

[0009] Optionally, the particle size D50 of the layered oxide active material is 2μm-20μm; And / or, the thickness of the coating layer is 3nm-10nm.

[0010] By ensuring the particle size D50 of the layered oxide active material is within the aforementioned range, a balance can be struck between ion transport performance and mechanical stability, guaranteeing good energy density and rate performance. By ensuring the coating thickness is within the aforementioned range, the impact on the energy density of the cathode material can be reduced while maintaining good coating performance, providing sufficient chemical isolation, fast ion conduction, and strong interfacial bonding.

[0011] Optionally, the coating layer includes a first coating layer and a second coating layer, wherein the first coating layer coats the surface of the layered oxide active material, and the second coating layer coats the surface of the first coating layer; The first coating layer includes lithium phosphate, and the second coating layer includes lithium fluoride and lithium borate.

[0012] The lithium phosphate included in the first coating layer creates a relatively stable interfacial environment, providing sufficient protection for the layered oxide active material, reducing the probability of side reactions, and maintaining good mechanical stability. The lithium fluoride and lithium borate included in the second coating layer provide a stable chemical barrier through lithium fluoride, enhancing chemical isolation, and provide good fast ion conduction through lithium borate. The combination of the first and second coating layers ensures the various performance characteristics of the cathode material and leverages their synergistic effect to improve process compatibility and balance the performance of each component.

[0013] Optionally, the mass ratio of the first coating layer to the second coating layer is (0.8-1.2):1.

[0014] By keeping the mass ratio of the first coating layer and the second coating layer within the above range, the various properties of the coating layer can be balanced, so that the cathode material has good chemical stability, ion conductivity and mechanical strength.

[0015] Optionally, the layered oxide active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and ternary materials; The molecular formula of the ternary material is LiNi x Mn y Co z O2, x+y+z=1, and 0.6≤x≤0.9.

[0016] Lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and ternary materials all have high energy density and layered structures, which can ensure good cycle stability. By adding the above-mentioned coating layers to lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and ternary materials, the cathode material can be guaranteed to have high energy density while also having the functions of chemical isolation, fast ion conduction, and strong interfacial bonding.

[0017] According to a second aspect of this application, a method for preparing a cathode material is provided, comprising: The phosphate solution and the layered oxide active material are dispersed in a first solvent to obtain a mixed solution; A lithium compound solution is added to a mixed solution, and after reaction and drying, lithium phosphate is formed on the surface of the layered oxide active material to obtain the first coating material. The first coating material and lithium tetrafluoroborate are mixed, and the lithium tetrafluoroborate is coated on the surface of the first coating material to obtain the second coating material; The second coating material is annealed in an oxygen-containing atmosphere to form lithium fluoride and lithium borate, thus obtaining the cathode material.

[0018] The method for preparing the cathode material provided in this application possesses all the beneficial effects of the cathode material described above, which will not be repeated here. Coating via a liquid-phase reaction improves the uniformity of the coating and ensures thorough bonding between the coating layer and the layered oxide active material. The method for preparing the cathode material provided in this application can form an amorphous coating layer on the surface of the layered oxide active material. Compared to the crystalline coating layer in traditional technologies, this reduces cracking caused by grain boundary stress, lowers the risk of direct contact between the layered oxide active material and the external environment, and can adapt to volume changes during charging and discharging. This achieves a balance between interface stability, high-speed ion conduction, and mechanical integrity, thereby improving cycle performance and rate performance.

[0019] Optionally, the phosphate solution contains 0.5%-2% by mass of phosphate. And / or, the phosphate includes at least one of ammonium dihydrogen phosphate, ammonium phosphate, trimethyl phosphate and triethyl phosphate; And / or, the lithium compound includes at least one of lithium hydroxide, lithium nitrate and lithium acetate.

[0020] By controlling the mass percentage of the phosphate solution within the aforementioned range, the reaction rate and the amount of lithium phosphate produced can be precisely controlled, ensuring process stability. The use of ammonium dihydrogen phosphate ensures good solubility and dispersibility. Optionally, mixing the first coating material and lithium tetrafluoroborate, and coating the surface of the first coating material with lithium tetrafluoroborate, includes: The first coating material is added to the second solvent, and then lithium tetrafluoroborate is added and mixed. The solvent is then removed so that lithium tetrafluoroborate coats the surface of the first coating material.

[0021] The above method enables lithium tetrafluoroborate to be fully dispersed and uniformly coated on the surface of the first coating material. The process is simple, improves coating efficiency, and ensures that the microstructure of the coated surface is controllable.

[0022] Optionally, the second coating material is annealed in an oxygen-containing atmosphere, including: The second coating material is annealed in air at 300℃-500℃ for 2h-6h.

[0023] By annealing the second coating material in air at 300℃-500℃, LiBF4 reacts with oxygen at higher temperatures to form lithium borate and lithium fluoride. This results in a uniform second coating layer, while lithium borate provides fast ion conductivity, and lithium fluoride provides chemical stability. Setting the temperature to 300℃-500℃ ensures efficient reaction between LiBF4 and oxygen. Using an air atmosphere reduces costs, and setting the annealing time to 2h-6h ensures complete reaction and controls process costs.

[0024] According to a third aspect of this application, a solid-state battery is provided, the solid-state battery including a positive electrode sheet, the positive electrode sheet including a positive electrode material and a sulfide solid electrolyte; The positive electrode material includes the positive electrode material as described above, and / or the positive electrode material prepared by the method described above.

[0025] The solid-state battery provided in this application has all the advantages of the cathode material described above, which will not be repeated here. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a transmission electron microscope (TEM) scan of the cathode material in Embodiment 1 of this application; Figure 2 This is a transmission electron microscope (TEM) scan of lithium cobalt oxide in Comparative Example 1. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] This application provides a positive electrode material and its preparation method, as well as a solid-state battery. Detailed descriptions are provided below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0030] In a first aspect, embodiments of this application provide a cathode material, which includes a layered oxide active material and a coating layer covering the surface of the layered oxide active material. The coating layer includes lithium fluoride, lithium borate, and lithium phosphate.

[0031] In the cathode material provided in this application embodiment, the layered oxide active material can ensure good energy density. In the coating layer covering the surface of the layered oxide active material, lithium fluoride acts as a highly stable chemical barrier, effectively isolating interfacial side reactions under high voltage (≥4.5V) conditions. Lithium borate acts as a fast ion conductor, constructing an efficient lithium-ion transport channel, thereby reducing the space charge effect. Lithium phosphate forms a strong bond with the surface of the layered oxide active material through its PO bonds, ensuring a tight bond between the coating layer and the layered oxide active material, and fixing the surface lattice oxygen in the layered oxide active material. Through the synergy of lithium fluoride, lithium borate, and lithium phosphate in the coating layer, a structure with chemical isolation, fast ion conduction, and strong interfacial bonding functions can be constructed on the surface of the layered oxide active material, reducing side reactions and the space charge layer of the cathode material, significantly reducing interfacial impedance. When applied to batteries, this improves the battery's long-cycle stability, high-rate performance, and overall safety performance.

[0032] In some embodiments, the mass ratio of the coating layer to the layered oxide active material is (0.5-3):100.

[0033] By maintaining the mass ratio of the coating layer to the layered oxide active material within the aforementioned range, the coating effect can be guaranteed, allowing lithium fluoride, lithium borate, and lithium phosphate in the coating layer to play their respective roles, reducing side reactions, optimizing lithium-ion transport performance, reducing interfacial impedance, and minimizing the impact of the coating layer on the energy density of the cathode material.

[0034] For example, the mass ratio of the coating layer to the layered oxide active material can be 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1:100, 1.1:100, 1.2:100, 1.3:100, 1.4:100, 1.5:100, 1.6:100, 1.7:100, 1.8:100, 1.9:100, 2:100, 2.1:100, 2.2:100, 2.3:100, 2.4:100, 2.5:100, 2.6:100, 2.7:100, 2.8:100, 2.9:100, or 3:100.

[0035] In some embodiments, the particle size D50 of the layered oxide active material is 2 μm-20 μm.

[0036] By ensuring that the particle size D50 of the layered oxide active material is within the above-mentioned range, it is possible to balance ion transport performance and mechanical stability, thereby guaranteeing good energy density and rate performance.

[0037] By ensuring that the particle size D50 of the layered oxide active material is within the above-mentioned range, it is possible to balance ion transport performance and mechanical stability, thereby guaranteeing good energy density and rate performance.

[0038] For example, the particle size D50 of the layered oxide active material can be 2 μm, 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 or 20 μm.

[0039] In some embodiments, the layered oxide active material is a single-crystal material. Compared to polycrystalline materials, single-crystal materials have better lithium-ion transport performance, stronger mechanical stability, and better rate performance and stability.

[0040] In some embodiments, the thickness of the coating layer is 3nm-10nm.

[0041] By keeping the thickness of the coating layer within the above range, the impact on the energy density of the cathode material can be reduced while ensuring good coating effect and providing sufficient chemical isolation, fast ion conduction and strong interfacial bonding.

[0042] For example, the thickness of the coating layer can be 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm or 10nm.

[0043] In some embodiments, the coating layer includes a first coating layer and a second coating layer. The first coating layer coats the surface of the layered oxide active material, and the second coating layer coats the side of the first coating layer facing away from the layered oxide active material. The first coating layer includes lithium phosphate, and the second coating layer includes lithium fluoride and lithium borate.

[0044] The lithium phosphate included in the first coating layer creates a relatively stable interfacial environment, providing sufficient protection for the layered oxide active material, reducing the probability of side reactions, and maintaining good mechanical stability. The lithium fluoride and lithium borate included in the second coating layer provide a stable chemical barrier through lithium fluoride, enhancing chemical isolation, and provide good fast ion conduction through lithium borate. The combination of the first and second coating layers ensures the various performance characteristics of the cathode material and leverages their synergistic effect to improve process compatibility and balance the performance of each component.

[0045] In some embodiments, the mass ratio of the first coating layer to the second coating layer is (0.8-1.2):1.

[0046] By maintaining the mass ratio of lithium fluoride, lithium borate, and lithium phosphate in the coating layer within the aforementioned range, the various properties of the coating layer can be balanced, resulting in a cathode material that possesses both excellent chemical stability, ion conductivity, and mechanical strength.

[0047] For example, the relative mass ratio of the first coating layer to the second coating layer in the coating layer can be: 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1.

[0048] In some embodiments, the layered oxide active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and ternary materials. The molecular formula of the ternary material is LiNi. x Mn y Co z O2, x+y+z=1, and 0.6≤x≤0.9.

[0049] Lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and ternary materials all have high energy density and layered structures, which can ensure good cycle stability. By adding the above-mentioned coating layers to lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and ternary materials, the cathode material can be guaranteed to have high energy density while also having the functions of chemical isolation, fast ion conduction, and strong interfacial bonding.

[0050] The molecular formula of the lithium-rich manganese-based material is xLi2MnO3·(1-x)LiMO2, where 0 < x < 1, and M represents at least one of Ni, Co, and Mn.

[0051] Secondly, embodiments of this application provide a method for preparing a cathode material, used to prepare the cathode material as described above, comprising: The phosphate solution and the layered oxide active material are dispersed in a first solvent to obtain a mixed solution; A lithium compound solution is added to a mixed solution, and after reaction and drying, lithium phosphate is formed on the surface of the layered oxide active material to obtain the first coating material. The first coating material and lithium tetrafluoroborate are mixed, and the lithium tetrafluoroborate is coated on the surface of the first coating material to obtain the second coating material; The second coating material is annealed in an oxygen-containing atmosphere to form lithium fluoride and lithium borate, thus obtaining the cathode material.

[0052] The method for preparing the cathode material provided in this application has all the beneficial effects of the cathode material described above, which will not be repeated here. Coating via a liquid-phase reaction improves the uniformity of the coating and ensures thorough bonding between the coating layer and the applied oxide active material. The method for preparing the cathode material provided in this application can form an amorphous coating layer on the surface of the layered oxide active material. Compared to the crystalline coating layer in traditional technologies, this reduces cracking caused by grain boundary stress, lowers the risk of direct contact between the layered oxide active material and the external environment, and can adapt to volume changes during charging and discharging. This achieves a balance between interface stability, high-speed ion conduction, and mechanical integrity, thereby improving cycle performance and rate performance.

[0053] In some embodiments, the phosphate solution contains 0.5%-2% by mass of phosphate.

[0054] By controlling the mass percentage of the phosphate solution within the above range, the reaction rate and the amount of lithium phosphate generated can be precisely controlled, ensuring process stability.

[0055] For example, the mass percentage of phosphate in the phosphate solution may be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%.

[0056] In some embodiments, the phosphate includes at least one of ammonium dihydrogen phosphate, ammonium phosphate, trimethyl phosphate, and triethyl phosphate.

[0057] In some embodiments, the lithium compound includes at least one of lithium hydroxide, lithium nitrate, and lithium acetate.

[0058] For example, a phosphate solution and a layered oxide active material are dispersed in a first solvent to obtain a mixed solution, comprising: Add diammonium hydrogen phosphate to the first solvent (such as deionized water), then add the layered oxide active material, ultrasonically disperse for 10 min, and stir at 500 rpm at room temperature for 2 h to obtain a mixed solution.

[0059] A lithium compound solution is added to a mixed solution, followed by reaction and drying to form lithium phosphate on the surface of the layered oxide active material, yielding a first coating material comprising: A lithium hydroxide monohydrate solution was added dropwise to the mixed solution, and then stirred at room temperature for 30 minutes at 500 rpm. The mixture was then heated to 90°C and stirred until dry, forming lithium phosphate on the surface of the layered oxide active material, thus obtaining the first coating material.

[0060] In some embodiments, mixing a first coating material and lithium tetrafluoroborate, and coating the surface of the first coating material with lithium tetrafluoroborate, includes: The first coating material is added to the second solvent, and then lithium tetrafluoroborate is added and mixed. The second solvent is then removed so that lithium tetrafluoroborate coats the surface of the first coating material.

[0061] The above method enables LiBF4 to be fully dispersed and uniformly coated on the surface of the first coating material. The process is simple, improves coating efficiency, and ensures that the microstructure of the coated surface is controllable.

[0062] For example, the second solvent can be anhydrous ethanol, and the above steps can be as follows: after grinding and dispersing the first coating material, transfer it into anhydrous ethanol, then add LiBF4 to the solution at a mass percentage of 0.5%-2%, then sonicate for 20 minutes, and then evaporate the anhydrous ethanol at a speed of 500 rpm and a temperature of 60°C, so that LiBF4 can be uniformly coated on the surface of the first coating material.

[0063] In some embodiments, annealing the second coating material in an oxygen-containing atmosphere includes: The second coating material is annealed in air at 300℃-500℃ for 2h-6h.

[0064] By annealing the second coating material in air at 300℃-500℃, LiBF4 reacts with oxygen at higher temperatures to form lithium borate and lithium fluoride. This results in a uniform second coating layer, while lithium borate provides fast ion conductivity, and lithium fluoride provides chemical stability. Setting the temperature to 300℃-500℃ ensures efficient reaction between LiBF4 and oxygen. Using an air atmosphere reduces costs, and setting the treatment time to 2h-6h ensures complete reaction and controls process costs.

[0065] For example, the annealing temperature can be set to 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃ or 500℃, and the annealing time can be set to 2h, 3h, 4h, 5h or 6h.

[0066] Thirdly, embodiments of this application provide a solid-state battery, which includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode material and a sulfide solid electrolyte; The positive electrode material includes the positive electrode material as described above, and / or the positive electrode material prepared by the method described above.

[0067] The solid-state battery provided in this application has all the advantages of the cathode material described above, which will not be repeated here.

[0068] In some embodiments, the positive electrode sheet further includes a conductive agent, and the mass percentage of the positive electrode material, the sulfide solid electrolyte, and the conductive agent can be (60-75):(24.5-37.5):(0.5-2.5).

[0069] For example, the sulfide solid electrolyte can be lithium phosphorus sulfide chlorine (Li6PS5Cl), and the conductive agent can be carbon fiber (VGCF).

[0070] For example, a method for preparing a solid-state battery can be as follows: Inside an argon glove box, the cathode material, Li6PS5Cl, and VGCF were mixed in a mass ratio of 68.5:30:1.5, and then ground and mixed evenly to obtain cathode powder. Weigh 80mg-120mg of Li6PS5Cl and add it to the model battery. Then, press it at 400MPa for more than 5 minutes in a tablet press to obtain a solid electrolyte layer. Weigh 10mg-15mg of positive electrode powder and add it to one side of the model battery. Then, cold press it in a tablet press at a pressure of 400MPa for more than 10 minutes to obtain the positive electrode sheet. Weigh 60mg-120mg of lithium indium alloy powder and add it to the other side of the model battery. Then, press it in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain the negative electrode sheet. Then, the solid electrolyte layer, positive electrode, and negative electrode are assembled into a solid-state battery.

[0071] The embodiments of this application are further illustrated below with reference to specific examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to the conditions recommended by the manufacturer.

[0072] Example 1 (1) Dissolve 0.0437 g of ammonium dihydrogen phosphate in 70 mL, then weigh 10 g of lithium cobalt oxide powder (particle size D50 is 10 μm), add it to the above solution, ultrasonically disperse for 10 min, and stir at room temperature for 2 h at a speed of 500 rpm to obtain a mixed solution; (2) Dissolve 0.0865 g of lithium hydroxide monohydrate in 100 mL of deionized water to obtain a lithium hydroxide monohydrate solution. Slowly add the lithium hydroxide monohydrate solution to the mixed solution, stir at room temperature at 500 rpm for 30 min, and then heat to 90 °C and stir to dry to obtain the first coating material. (3) The first coating material was ground and dispersed in an agate mortar, then transferred to 60 mL of anhydrous ethanol, 0.0356 g of LiBF4 was added, and then sonicated for 20 min. The anhydrous ethanol was evaporated at 500 rpm and 60 °C to obtain the second coating material. (4) The second coating material is transferred into a tube furnace and annealed in an air atmosphere at 450°C for 3 hours to obtain a positive electrode material with a total coating content of 1%; wherein, the surface of the positive electrode material includes a coating layer, and the coating layer includes lithium fluoride, lithium borate and lithium phosphate. (5) In an argon glove box, the positive electrode materials Li6PS5Cl and VGCF are mixed in a mass ratio of 68.5:30:1.5 and then ground and mixed evenly to obtain composite positive electrode powder; 100mg of composite positive electrode powder is weighed and added to the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain a solid electrolyte layer; 10mg of positive electrode powder is weighed and added to one side of the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 10 minutes; 90mg of lithium indium alloy powder is weighed and added to the other side of the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain a solid electrolyte layer, a positive electrode layer and a negative electrode layer assembled into a solid battery.

[0073] Example 2 (1) Dissolve 0.0219 g of ammonium dihydrogen phosphate in 70 mL, then weigh 10 g of lithium cobalt oxide powder (particle size D50 is 10 μm), add it to the above solution, ultrasonically disperse for 10 min, and stir at room temperature for 2 h at a speed of 500 rpm to obtain a mixed solution; (2) Dissolve 0.0433 g of lithium hydroxide monohydrate in 100 mL of deionized water to obtain a lithium hydroxide monohydrate solution. Slowly add the lithium hydroxide monohydrate solution to the mixed solution and stir at room temperature for 30 min at 500 rpm. Then heat to 90 °C and stir to dry to obtain the first coating material. (3) The first coating material was ground and dispersed in an agate mortar, then transferred to 60 mL of anhydrous ethanol, 0.0178 g of LiBF4 was added, and then sonicated for 20 min. The anhydrous ethanol was evaporated at 500 rpm and 60 °C to obtain the second coating material. (4) The second coating material is transferred into a tube furnace and annealed in an air atmosphere at 450°C for 3 hours to obtain a positive electrode material with a total coating content of 0.5%; wherein the surface of the positive electrode material includes a coating layer, and the coating layer includes lithium fluoride, lithium borate and lithium phosphate. (5) In an argon glove box, the positive electrode materials Li6PS5Cl and VGCF are mixed in a mass ratio of 68.5:30:1.5 and then ground and mixed evenly to obtain composite positive electrode powder; 100mg of composite positive electrode powder is weighed and added to the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain a solid electrolyte layer; 10mg of positive electrode powder is weighed and added to one side of the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 10 minutes; 90mg of lithium indium alloy powder is weighed and added to the other side of the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain a solid electrolyte layer, a positive electrode layer and a negative electrode layer assembled into a solid battery.

[0074] Example 3 (1) Dissolve 0.0656 g of ammonium dihydrogen phosphate in 70 mL, then weigh 10 g of lithium cobalt oxide powder (particle size D50 is 10 μm), add it to the above solution, ultrasonically disperse for 10 min, and stir at room temperature for 2 h at a speed of 500 rpm to obtain a mixed solution; (2) Dissolve 0.1297 g of lithium hydroxide monohydrate in 100 mL of deionized water to obtain a lithium hydroxide monohydrate solution. Slowly add the lithium hydroxide monohydrate solution to the mixed solution and stir at room temperature for 30 min at 500 rpm. Then heat to 90 °C and stir to dry to obtain the first coating material. (3) The first coating material was ground and dispersed in an agate mortar, then transferred to 60 mL of anhydrous ethanol, 0.535 g of LiBF4 was added, and then sonicated for 20 min. The anhydrous ethanol was evaporated at 500 rpm and 60 °C to obtain the second coating material. (4) The second coating material is transferred into a tube furnace and annealed in an air atmosphere at 450°C for 3 hours to obtain a positive electrode material with a total coating content of 1.5%; wherein the surface of the positive electrode material includes a coating layer, and the coating layer includes lithium fluoride, lithium borate and lithium phosphate. (5) In an argon glove box, the positive electrode materials Li6PS5Cl and VGCF are mixed in a mass ratio of 68.5:30:1.5 and then ground and mixed evenly to obtain composite positive electrode powder; 100mg of composite positive electrode powder is weighed and added to the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain a solid electrolyte layer; 10mg of positive electrode powder is weighed and added to one side of the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 10 minutes; 90mg of lithium indium alloy powder is weighed and added to the other side of the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain a solid electrolyte layer, a positive electrode layer and a negative electrode layer assembled into a solid battery.

[0075] Example 4 (1) Dissolve 0.1093 g of ammonium dihydrogen phosphate in 70 mL, then weigh 10 g of lithium cobalt oxide powder (particle size D50 is 10 μm), add it to the above solution, ultrasonically disperse for 10 min, and stir at room temperature for 2 h at a speed of 500 rpm to obtain a mixed solution; (2) Dissolve 0.2162 g of lithium hydroxide monohydrate in 100 mL of deionized water to obtain a lithium hydroxide monohydrate solution. Slowly add the lithium hydroxide monohydrate solution to the mixed solution and stir at room temperature at 500 rpm for 30 min. Then heat to 90 °C and stir to dry to obtain the first coating material. (3) The first coating material was ground and dispersed in an agate mortar, then transferred to 60 mL of anhydrous ethanol, 0.0891 g of LiBF4 was added, and then sonicated for 20 min. The anhydrous ethanol was evaporated at 500 rpm and 60 °C to obtain the second coating material. (4) The second coating material is transferred into a tube furnace and annealed in an air atmosphere at 450°C for 3 hours to obtain a positive electrode material with a total coating content of 2.5%; wherein the surface of the positive electrode material includes a coating layer, and the coating layer includes lithium fluoride, lithium borate and lithium phosphate. (5) In an argon glove box, the positive electrode materials Li6PS5Cl and VGCF are mixed in a mass ratio of 68.5:30:1.5 and then ground and mixed evenly to obtain composite positive electrode powder; 100mg of composite positive electrode powder is weighed and added to the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain a solid electrolyte layer; 10mg of positive electrode powder is weighed and added to one side of the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 10 minutes; 90mg of lithium indium alloy powder is weighed and added to the other side of the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain a solid electrolyte layer, a positive electrode layer and a negative electrode layer assembled into a solid battery.

[0076] Example 5 (1) Dissolve 0.1312 g of ammonium dihydrogen phosphate in 70 mL, then weigh 10 g of lithium cobalt oxide powder (particle size D50 is 10 μm), add it to the above solution, ultrasonically disperse for 10 min, and stir at room temperature for 2 h at a speed of 500 rpm to obtain a mixed solution; (2) Dissolve 0.2595g of lithium hydroxide monohydrate in 100mL of deionized water to obtain a lithium hydroxide monohydrate solution. Slowly add the lithium hydroxide monohydrate solution to the mixed solution and stir at room temperature at 500rpm for 30min. Then heat to 90℃ and stir to dry to obtain the first coating material. (3) The first coating material was ground and dispersed in an agate mortar, then transferred to 60 mL of anhydrous ethanol, 0.1069 g of LiBF4 was added, and then sonicated for 20 min. The anhydrous ethanol was evaporated at 500 rpm and 60 °C to obtain the second coating material. (4) The second coating material is transferred into a tube furnace and annealed in an air atmosphere at 450°C for 3 hours to obtain a positive electrode material with a total coating content of 3%; wherein, the surface of the positive electrode material includes a coating layer, and the coating layer includes lithium fluoride, lithium borate and lithium phosphate. (5) In an argon glove box, the positive electrode materials Li6PS5Cl and VGCF are mixed in a mass ratio of 68.5:30:1.5 and then ground and mixed evenly to obtain composite positive electrode powder; 100mg of composite positive electrode powder is weighed and added to the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain a solid electrolyte layer; 10mg of positive electrode powder is weighed and added to one side of the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 10 minutes; 90mg of lithium indium alloy powder is weighed and added to the other side of the model battery, and then cold-pressed in a tablet press at a pressure of 400MPa for more than 5 minutes to obtain a solid electrolyte layer, a positive electrode layer and a negative electrode layer assembled into a solid battery.

[0077] Example 6 The difference between this embodiment and Example 1 is that lithium cobalt oxide is replaced with an equal amount of lithium nickel oxide (molecular formula LiNiO2, particle size D50 is 10μm), while all other conditions remain the same as in Example 1.

[0078] Example 7 The difference between this embodiment and Embodiment 1 is that lithium cobalt oxide is replaced with an equal amount of lithium nickel manganese oxide (molecular formula LiNi). 0.5 Mn 0.5 O2 (particle size D50 is 10 μm), and all other conditions are the same as in Example 1.

[0079] Example 8 The difference between this embodiment and Example 1 is that lithium cobalt oxide is replaced with an equal amount of lithium-rich manganese-based material (molecular formula Li2MnO3·LiNiO2, particle size D50 is 10μm), while all other conditions remain the same as in Example 1.

[0080] Example 9 The difference between this embodiment and Embodiment 1 is that lithium cobalt oxide is replaced with an equal amount of ternary material (molecular formula LiNi). 0.6 Mn 0.2 Co 0.2 O2 (particle size D50 is 10 μm), and all other conditions are the same as in Example 1.

[0081] Example 10 The difference between this embodiment and Embodiment 1 is that lithium cobalt oxide is replaced with an equal amount of ternary material (molecular formula LiNi). 0.6 Co 0.2 Al 0.2 O2 (particle size D50 is 10 μm), and all other conditions are the same as in Example 1.

[0082] Comparative Example 1 The difference between this comparative example and Example 1 is that the positive electrode material is replaced by an equal amount of lithium cobalt oxide powder (particle size D50 is 10μm), and no coating treatment is performed. All other conditions are the same as in Example 1.

[0083] Comparative Example 2 (1) Dissolve 0.0990 g of ammonium dihydrogen phosphate in 70 mL, then weigh 10 g of lithium cobalt oxide powder (particle size D50 is 10 μm), add it to the above solution, ultrasonically disperse for 10 min, and stir at room temperature for 2 h at a speed of 500 rpm to obtain a mixed solution; (2) Dissolve 0.1090 g of lithium hydroxide monohydrate in 100 mL of deionized water to obtain a lithium hydroxide monohydrate solution. Slowly add the lithium hydroxide monohydrate solution to the mixed solution, stir at room temperature at 500 rpm for 30 min, and then heat to 90 °C and stir to dry to obtain the coating material. (3) The coating material was transferred into a tube furnace and annealed in an air atmosphere at 450°C for 3 hours to obtain a cathode material coated with 1% lithium phosphate. (4) In an argon glove box, the positive electrode materials Li6PS5Cl and VGCF are mixed in a mass ratio of 68.5:30:1.5, and then ground and mixed evenly to obtain positive electrode powder; 100mg of the positive electrode powder is added to the model battery and pressed at 400MPa for more than 5 minutes in a tablet press to obtain a solid electrolyte layer; 10mg of the positive electrode powder is added to one side of the model battery and pressed at 400MPa for more than 10 minutes in a tablet press to obtain a positive electrode sheet; 90mg of lithium indium alloy powder is added to the other side of the model battery and pressed at 400MPa for more than 5 minutes in a tablet press to obtain a solid electrolyte layer, a positive electrode sheet and a negative electrode sheet assembled into a solid battery.

[0084] Comparative Example 3 (1) 10g of lithium cobalt oxide powder (particle size D50 is 10μm) was ground and dispersed in an agate mortar, then transferred to 60mL of anhydrous ethanol, 0.0510g of LiBF4 was added, and then sonicated for 20min. The anhydrous ethanol was evaporated at 500rpm and 60℃ to obtain the coating material. (2) The coating material was transferred into a tube furnace and annealed in an air atmosphere at 450°C for 3 hours to obtain a cathode material coated with 1% lithium borate and lithium fluoride. (3) In an argon glove box, the positive electrode materials Li6PS5Cl and VGCF are mixed in a mass ratio of 68.5:30:1.5 and then ground and mixed evenly to obtain positive electrode powder; 100mg of the positive electrode powder is added to the model battery and pressed at 400MPa for more than 5 minutes in a tablet press to obtain a solid electrolyte layer; 12.5mg of the positive electrode powder is added to one side of the model battery and pressed at 400MPa for more than 10 minutes in a tablet press to obtain a positive electrode sheet; 90mg of lithium indium alloy powder is added to the other side of the model battery and pressed at 400MPa for more than 5 minutes in a tablet press to obtain a solid electrolyte layer, a positive electrode sheet and a negative electrode sheet assembled into a solid battery.

[0085] The cathode materials (i.e., coated lithium cobalt oxide and uncoated lithium cobalt oxide) in Example 1 and Comparative Example 1 were observed under a transmission electron microscope, as shown below. Figures 1-2 As shown.

[0086] like Figures 1-2 As shown, in Example 1, the positive electrode material has a coating layer formed on the surface of the lithium cobalt oxide particles, while in Comparative Example 1, the lithium cobalt oxide powder does not have a coating layer on its surface.

[0087] Cycle performance, rate performance, and storage performance of the solid-state batteries in Examples 1-10 and Comparative Examples 1-3 were tested respectively. Except for Example 8, the tests for the other examples and comparative examples were conducted under a pressure of 100 MPa and a voltage range of 2.6V-4.5V (vs. Li / Li). + The corresponding lithium-indium alloy counter electrode voltage is 2.0V-3.9V (vs. In / Li). + The tests in Example 8 were conducted under a pressure of 100 MPa and a voltage range of 2.8V-4.8V (vs. Li / Li). + The corresponding lithium-indium alloy electrode voltage is 1.38V-4.18V (vs. In / Li). + The cycle performance test method is as follows: Charge and discharge are performed at 0.1C, and the first charge capacity and first discharge capacity are obtained respectively, and the initial coulombic efficiency is calculated; the first cycle capacity is tested at a current of 0.5C, and the capacity retention rate after 300 cycles is calculated. The rate performance test method is as follows: the average discharge specific capacity of the solid-state battery after 3 cycles is tested at charging currents of 0.1C, 0.2C, 0.33C, 0.5C, 1C, and 3C respectively. The storage performance test method is as follows: with the solid-state battery at 100% SOC, it is placed at a temperature of 60℃ for 7 days, 14 days, and 21 days respectively, and the capacity retention rate and capacity recovery rate are tested. The test results are shown in Tables 1-3. Table 1

[0088] Table 2

[0089] Table 3

[0090] As can be seen from Tables 1, 2, and 3, compared to the uncoated lithium cobalt oxide application in Comparative Example 1, the coated lithium cobalt oxide batteries in Examples 1-5 of this application show significant improvements in initial efficiency, capacity retention, discharge specific capacity, and capacity recovery rate. Furthermore, the coated lithium nickel oxide in Example 6, the coated lithium nickel manganese oxide in Example 7, the coated lithium-rich manganese-based material in Example 8, and the coated ternary materials in Examples 9 and 10 also exhibit good long-term cycle stability and high-rate performance.

[0091] Furthermore, the total mass percentage of the coating material in Examples 1, 2, and 3 is 1%. However, the coating layer in Example 1 includes lithium phosphate, lithium borate, and lithium fluoride, while the coating layer in Comparative Example 2 only includes lithium phosphate, and the coating layer in Comparative Example 3 only includes lithium fluoride and lithium borate. Comparing the test results of Examples 1, 2, and 3, it can be seen that the battery using the cathode material in Example 1 exhibits significant improvements in initial efficiency, capacity retention, discharge specific capacity, and capacity recovery rate. This indicates that lithium phosphate, lithium borate, and lithium fluoride in the coating layer of Example 1 of this application work synergistically, constructing a layered oxide active material surface that combines chemical isolation, fast ion conduction, and strong interfacial bonding. This reduces side reactions and space charge layers in the cathode material, significantly lowers interfacial impedance, and improves the battery's long-cycle stability, high-rate performance, and overall safety.

[0092] The test results from Examples 1-5 show that as the proportion of total coating increases, the battery's initial efficiency, 0.5C cycle performance, and average three-cycle discharge specific capacity exhibit a trend of first increasing and then decreasing, while the capacity retention rate and capacity recovery rate show an increasing trend. The test results from Examples 1 and 6-10 show that, compared to coated lithium nickel oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and ternary materials, the coated lithium cobalt oxide in Example 1, when applied to the battery, shows a more significant improvement in the battery's initial efficiency, capacity retention rate, discharge specific capacity, and capacity recovery rate. This is mainly because, compared to lithium nickel oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and ternary materials, lithium cobalt oxide has better electronic conductivity and lithium-ion conductivity, resulting in excellent rate performance. After being coated with layers including lithium fluoride, lithium borate, and lithium phosphate, the cathode material exhibits more significant improvements in long-cycle stability, high-rate performance, and overall safety performance.

[0093] In summary, the cathode material provided in this application, through a coating layer including lithium fluoride, lithium borate, and lithium phosphate, can improve the battery's long-cycle stability, high-rate performance, and overall safety performance.

[0094] The foregoing has provided a detailed description of a cathode material and its preparation method, as well as a solid-state battery, provided by the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A positive electrode material, characterized in that, The positive electrode material includes a layered oxide active material and a coating layer covering the surface of the layered oxide active material; The coating layer includes lithium fluoride, lithium borate, and lithium phosphate.

2. The cathode material according to claim 1, characterized in that, The mass ratio of the coating layer to the layered oxide active material is (0.5-3):

100.

3. The cathode material according to claim 1, characterized in that, The particle size D50 of the layered oxide active material is 2μm-20μm; And / or, the thickness of the coating layer is 3nm-10nm.

4. The cathode material according to any one of claims 1-3, characterized in that, The coating layer includes a first coating layer and a second coating layer. The first coating layer coats the surface of the layered oxide active material, and the second coating layer coats the side of the first coating layer that is away from the layered oxide active material. The first coating layer includes the lithium phosphate, and the second coating layer includes the lithium fluoride and the lithium borate.

5. The positive electrode material according to claim 4, characterized in that, The mass ratio of the first coating layer to the second coating layer is (0.8-1.2):

1.

6. The cathode material according to any one of claims 1-3, characterized in that, The layered oxide active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, and ternary materials. The molecular formula of the ternary material is LiNi. x Mn y Co z O2, x+y+z=1, and 0.6≤x≤0.

9.

7. A method for preparing a cathode material, used to prepare the cathode material as described in any one of claims 1-6, characterized in that, include: The phosphate solution and the layered oxide active material are dispersed in the first solution to obtain a mixed solution; A lithium compound solution is added to the mixed solution, and after reaction and drying, lithium phosphate is formed on the surface of the layered oxide active material to obtain the first coating material. The first coating material and lithium tetrafluoroborate are mixed, and the lithium tetrafluoroborate is coated on the surface of the first coating material to obtain the second coating material; The second coating material is annealed in an oxygen-containing atmosphere to form lithium fluoride and lithium borate, thus obtaining the cathode material.

8. The method for preparing the cathode material according to claim 7, characterized in that, In the phosphate solution, the mass percentage of the phosphate is 0.5%-2%; And / or, the phosphate includes at least one of ammonium dihydrogen phosphate, ammonium phosphate, trimethyl phosphate, and triethyl phosphate; And / or, the lithium compound includes at least one of lithium hydroxide, lithium nitrate, and lithium acetate.

9. The method for preparing the cathode material according to claim 7, characterized in that, The step of mixing the first coating material and lithium tetrafluoroborate, and coating the surface of the first coating material with the lithium tetrafluoroborate, includes: The first coating material is added to the second solvent, and then the lithium tetrafluoroborate is added and mixed. The solvent is then removed so that the lithium tetrafluoroborate coats the surface of the first coating material.

10. The method for preparing the cathode material according to any one of claims 7-9, characterized in that, The annealing treatment of the second coating material in an oxygen-containing atmosphere includes: The second coating material is annealed in air at 300℃-500℃ for 2h-6h.

11. A solid-state battery, characterized in that, The solid-state battery includes a positive electrode sheet, which includes a positive electrode material and a sulfide solid electrolyte. The cathode material includes the cathode material as described in any one of claims 1-6, and / or the cathode material prepared by the method described in any one of claims 7-10.

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