Lithium cobalt oxide cathode material for sulfide all-solid-state battery and preparation method thereof

Abstract

This invention discloses a lithium cobalt oxide cathode material for sulfide-based all-solid-state batteries and its preparation method, belonging to the field of solid-state battery technology. To address the problems of poor interfacial compatibility, poor electrochemical window, and side reactions between lithium cobalt oxide cathodes and sulfide-based solid electrolytes, this invention optimizes interfacial stability through a double-layer coating structure consisting of an inner high-stability coating and an outer fast-ion conductor. Simultaneously, the inner and outer coating layers coordinate the electrochemical window between the cathode material and the solid electrolyte, suppressing side reactions and the formation of a space charge layer, thereby improving the battery's energy density and cycle life. This lithium cobalt oxide cathode material achieves inner and outer coating through a three-stage sintering process, ensuring efficient ion diffusion and interfacial stability, and exhibiting a wide applicable voltage range.

Description

Technical Field

[0001] This invention relates to a lithium cobalt oxide cathode material for sulfide all-solid-state batteries and its preparation method, belonging to the field of solid-state battery technology. Background Technology

[0002] As people become increasingly reliant on electronic products and electric vehicles, higher expectations are being placed on batteries—longer driving range and greater safety. However, the energy density of traditional liquid batteries is already close to their theoretical value, and safety issues remain. Therefore, all-solid-state batteries, with their high safety performance and theoretical energy density, are receiving increasing attention. Compared to traditional liquid lithium-ion batteries, all-solid-state batteries use solid electrolytes instead of the flammable, explosive, and volatile organic liquid electrolytes found in liquid batteries. Furthermore, all-solid-state batteries can utilize batteries with the most negative equilibrium potential (-3.04 V relative to the standard hydrogen electrode) and a higher theoretical capacity (3860 mAhg). -1 With a lithium metal anode, the energy density will be greatly improved. In theory, all-solid-state batteries also have a wide electrochemical stability window, which can suppress the formation of lithium dendrites and reduce the self-discharge behavior of the battery.

[0003] Despite the numerous theoretical advantages of all-solid-state batteries, they still exhibit several shortcomings in experimental applications. Firstly, some solid-state electrolytes have low room-temperature lithium-ion conductivity, and solid-to-solid contact generates significant interfacial impedance. These two factors directly limit the rate performance and energy density of all-solid-state batteries. Currently, sulfur-based solid-state electrolytes possess high room-temperature lithium-ion conductivity, suitable Young's modulus, and good deformability, effectively addressing the aforementioned two issues. However, sulfur-based solid-state electrolytes will introduce new interfacial problems with the cathode material. The mismatch between the cathode and electrolyte interface can lead to a space charge layer and an unstable solid electrolyte layer, resulting in capacity reduction and increased interfacial impedance. These drawbacks will accelerate the performance degradation of all-solid-state batteries.

[0004] One effective method is to coat the surface of a metal oxide cathode with a transition layer having a suitable chemical potential. These coating layers possess high ionic conductivity and electronic insulation properties, and can effectively suppress lithium-ion consumption at the cathode-electrolyte interface, thereby reducing interfacial impedance. The selected coating materials are mostly metal oxides, such as LiNbO3, Li3PO4, Li3BO3, and Li4Ti5O. 12Examples of active materials include Li₂ZrO₃, LiTaO₃, LiAlO₂, and Li₂WO₄. For instance, patent application number 202111063477.0 discloses a sulfide-based lithium cobalt oxide cathode material for all-solid-state batteries and its preparation method. This method increases the contact area between the cathode material and the solid electrolyte and reduces the internal resistance of the cathode active material by preparing a uniform electrolyte layer with a gradient of ionic conductivity on the surface of the cathode material in situ. However, it does not solve the problem of contact point failure between the cathode material and the solid electrolyte caused by volume changes during cycling. Another example is patent application number 202080022173.7, which discloses sulfide-based cathode active material particles for all-solid-state batteries. This method reduces the active material and improves the cathode performance by coating and passivating the surface of the cathode material. However, currently, a single coating layer cannot completely cover the electrochemical window between the cathode material and the sulfide-based solid electrolyte. This patent still fails to provide battery performance at high voltages (>4.5V), resulting in insufficient capacity utilization. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium cobalt oxide cathode material for sulfide all-solid-state batteries and its preparation method. Through the synergistic effect of the inner high-stability coating and the outer ionic conductor, the interfacial compatibility between lithium cobalt oxide and sulfur-based solid electrolyte is optimized, side reactions and space charge layer formation are suppressed, and good structural reversibility is achieved under high voltage, which significantly improves the energy density and cycle life of all-solid-state batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] A lithium cobalt oxide cathode material for sulfide all-solid-state batteries, with the chemical formula Li x Co 1-y M y O2, where 0.99≤x<1.03, 0≤y<0.01, and the doping element M includes multiple types of Mg, Al, B, P, Ti, La, Y, Ni, Mn, Sn, Zn, Nb, Ta, Zr, and W, and contains a double-layer coating structure consisting of an inner coating layer and an outer coating layer.

[0008] Furthermore, the lithium cobalt oxide cathode material has a particle size of 1~10 μm, and the inner coating layer includes Li4Ti5O. 12 It contains at least one of Li2ZrO3, LiAlO2, and Li2WO4, and the outer coating layer includes at least one of Li3BO3, LiNbO3, Li3PO4, and LiTaO3.

[0009] A method for preparing a lithium cobalt oxide cathode material for a sulfide all-solid-state battery includes the following steps: Cobalt precursor particles, lithium carbonate, and a type of additive are mixed evenly, sintered once, cooled to room temperature, crushed and sieved to obtain primary particles. The obtained primary particles are mixed with secondary additives and sintered twice to coat the primary particles with an inner coating layer. After cooling to room temperature, the particles are crushed and sieved to obtain secondary particles. The obtained secondary particles are mixed with three types of additives and sintered three times. An outer coating layer is then applied to the inner coating layer. After cooling to room temperature, the mixture is crushed and sieved to obtain lithium cobalt oxide cathode material.

[0010] Furthermore, the cobalt precursor includes at least one of Co3O4, Co(OH)2, CoO, and Co2O3.

[0011] Furthermore, the additive contains at least one element of Mg, Al, Ti, Zr, Y, Sn, La, Ni, and Mn.

[0012] Furthermore, the two types of additives contain at least one coating element of Ti, Zr, Al, and W.

[0013] Furthermore, the three types of additives contain at least one coating element of B, Nb, P, and Ta.

[0014] Furthermore, the Class I, Class II, and Class III additives are in the form of compounds of oxides, alkalis, and salts.

[0015] Furthermore, the inner coating layer comprises Li4Ti5O 12 At least one of Li2ZrO3, LiAlO2, and Li2WO4.

[0016] Furthermore, the outer coating layer includes at least one of Li3BO3, LiNbO3, Li3PO4, and LiTaO3.

[0017] Furthermore, the coating element content of the inner coating layer is 500-50000ppm.

[0018] Furthermore, the coating element content of the outer coating layer is 500-50000ppm.

[0019] Furthermore, the mixing methods of the primary product particles and the secondary additives, and the mixing methods of the secondary product particles and the tertiary additives, employ dry coating, wet coating, ALD process, fluidized bed process, and spray drying process.

[0020] Furthermore, the sintering conditions are as follows: first, pre-fire at 400-750℃ for 2-7 hours, and then sinter at 800-1200℃ for 10-30 hours.

[0021] Furthermore, the conditions for the secondary sintering are: temperature of 250-900℃ and time of 3-10h.

[0022] Furthermore, the conditions for the three sintering processes are: a temperature of 250-900℃ and a time of 3-10h.

[0023] Furthermore, a 300-mesh sieve was used for all three sieving processes.

[0024] The present invention achieves the following technical effects.

[0025] 1. The lithium cobalt oxide prepared by this invention is in the O3 phase, which ensures capacity utilization, increases effective contact with sulfur-based solid electrolyte, and prepares a dense, highly stable inner coating layer and a highly ion-diffusion outer coating layer through a two-stage coating process, which optimizes interface compatibility, suppresses side reactions and space charge layer formation, and improves battery energy density and cycle life.

[0026] 2. The present invention employs an improved double-coating process, which achieves a denser surface coating effect, optimizes the interfacial stability between lithium cobalt oxide and sulfur-based solid electrolyte, and broadens the applicable voltage range of all-solid-state batteries.

[0027] 3. Compared with ternary cathodes, lithium cobalt oxide of the present invention can provide higher energy density and a wider secondary heat treatment temperature range as a cathode material; at the same time, limiting the micron-sized particles can reduce particle breakage during pressurization, increase effective contact with solid electrolyte, and alleviate the volume effect during charging and discharging.

[0028] 4. The present invention is simple to operate, has low raw material costs, and is easy to industrialize. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating a method for preparing lithium cobalt oxide cathode material for a sulfide all-solid-state battery according to the present invention.

[0030] Figure 2 The image shows a SEM image of the lithium cobalt oxide cathode material prepared in Example 1.

[0031] Figure 3 This is a SEM image of the lithium cobalt oxide cathode material prepared in Example 2.

[0032] Figure 4 This is a SEM image of the lithium cobalt oxide cathode material prepared in Example 3.

[0033] Figure 5 The image shows a SEM image of the lithium cobalt oxide cathode material prepared in Comparative Example 1.

[0034] Figure 6This is a TEM image of the lithium cobalt oxide cathode material prepared in Example 1.

[0035] Figure 7 This is a TEM image of the lithium cobalt oxide cathode material prepared in Example 2.

[0036] Figure 8 This is a TEM image of the lithium cobalt oxide cathode material prepared in Comparative Example 1.

[0037] Figure 9 The image shows the XPS pattern of the lithium cobalt oxide cathode material prepared in Example 1.

[0038] Figure 10 XPS image of the lithium cobalt oxide cathode material prepared in Example 2.

[0039] Figure 11 The first charge-discharge curve of the lithium cobalt oxide cathode material prepared in Example 1 in a sulfur-based solid-state battery system is shown. Detailed Implementation

[0040] To make the various technical features, advantages, or effects of the present invention more apparent and understandable, detailed descriptions are provided below through embodiments.

[0041] One specific embodiment of the present invention provides a lithium cobalt oxide cathode material for sulfide all-solid-state batteries, with the chemical formula Li. x Co 1-y M y O2, where 0.99≤x<1.03, 0≤y<0.01, and the doping element M includes multiple types of Mg, Al, B, P, Ti, La, Y, Ni, Mn, Sn, Zn, Nb, Ta, Zr, and W, and contains a double-layer coating structure consisting of an inner coating layer and an outer coating layer.

[0042] In another specific embodiment of the present invention, the lithium cobalt oxide cathode material has a particle size of 1~10 μm, and the inner coating layer includes Li4Ti5O. 12 It contains at least one of Li2ZrO3, LiAlO2, and Li2WO4, and the outer coating layer includes at least one of Li3BO3, LiNbO3, Li3PO4, and LiTaO3.

[0043] A specific embodiment of the present invention provides a method for preparing lithium cobalt oxide cathode material for sulfide all-solid-state batteries, such as... Figure 1 As shown, it includes the following steps: Cobalt precursor particles, lithium carbonate, and a type of additive are mixed evenly, sintered once, cooled to room temperature, crushed and sieved to obtain primary particles. The obtained primary particles are mixed with secondary additives and sintered twice to coat the primary particles with an inner coating layer. After cooling to room temperature, the particles are crushed and sieved to obtain secondary particles. The obtained secondary particles are mixed with three types of additives and sintered three times. An outer coating layer is then applied to the inner coating layer. After cooling to room temperature, the mixture is crushed and sieved to obtain lithium cobalt oxide cathode material.

[0044] In another specific embodiment of the present invention, the proportions of the cobalt precursor particles, lithium carbonate, and a type of additive should be calculated with reference to the elemental proportions of the chemical formula of the lithium cobalt oxide cathode material and the amount of inner and outer coating layers added. For example, the total amount of the required elements in the type of additive can be 500-1500 ppm, but is not limited thereto.

[0045] In another specific embodiment of the present invention, the cobalt precursor includes at least one of Co3O4, Co(OH)2, CoO, and Co2O3.

[0046] In another specific embodiment of the present invention, the additive contains at least one element of Mg, Al, Ti, Zr, Y, Sn, La, Ni, and Mn.

[0047] In another specific embodiment of the present invention, the two types of additives contain at least one coating element of Ti, Zr, Al, and W.

[0048] In another specific embodiment of the present invention, the three types of additives contain at least one coating element of B, Nb, P, and Ta.

[0049] In another specific embodiment of the present invention, the first-class additive, the second-class additive, and the third-class additive are in the form of compounds of oxides, alkalis, and salts.

[0050] In another specific embodiment of the present invention, the inner coating layer comprises Li4Ti5O 12 At least one of Li2ZrO3, LiAlO2, and Li2WO4.

[0051] In another specific embodiment of the present invention, the outer coating layer includes at least one of Li3BO3, LiNbO3, Li3PO4, and LiTaO3.

[0052] In another specific embodiment of the present invention, the coating element content of the inner coating layer is 500-50000ppm.

[0053] In another specific embodiment of the present invention, the coating element content of the outer coating layer is 500-50000ppm.

[0054] In another specific embodiment of the present invention, the mixing method of the primary product particles and the secondary additives, and the mixing method of the secondary product particles and the tertiary additives, adopt dry coating, wet coating, ALD process, fluidized bed process, and spray drying process.

[0055] In another specific embodiment of the present invention, the sintering conditions are as follows: first, pre-fire at 400-750℃ for 2-7 hours, and then sinter at 800-1200℃ for 10-30 hours.

[0056] In another specific embodiment of the present invention, the conditions for the secondary sintering are: temperature of 250-900℃ and time of 3-10h.

[0057] In another specific embodiment of the present invention, the conditions for the three sintering processes are: temperature of 250-900℃ and time of 3-10h.

[0058] In another specific embodiment of the present invention, a 300-mesh sieve is used for all three sieving processes.

[0059] The following are some specific examples.

[0060] Example 1 (1) Small particles of Co3O4, lithium carbonate (lithium metal ratio 0.99), basic magnesium carbonate, Al2O3, and Mn(OH)2 (with Mg, Al, and Mn contents of 500ppm each) are mixed evenly and pre-calcined at 550℃ for 3 h. Then, the temperature is raised to 800℃ and sintered for 10 h. After cooling to room temperature, the material blocks are crushed using an air jet mill and sieved through a 300-mesh sieve to obtain primary particles containing Mg doping.

[0061] (2) The primary particles were mixed with the additive TiO2 by dry coating. The content of the coating element Ti was 500 ppm. The holding temperature for the secondary sintering was 250℃ and the holding time was 5h. After cooling to room temperature, the material blocks were crushed by air jet mill and sieved through a 300-mesh sieve to obtain secondary particles with Li2TiO3 as the inner coating layer.

[0062] (3) The secondary product particles and additive B2O5 were mixed by dry coating. The content of the coating element Ta was 500ppm. The holding temperature for the third sintering was 250℃ and the holding time was 5h. After cooling to room temperature, the material blocks were crushed by air jet mill and sieved through a 300-mesh sieve to obtain lithium cobalt oxide cathode material with Li3BO3 as the outer coating layer.

[0063] Example 2 (1) Small particles of Co3O4, small particles of Co(OH)2, lithium carbonate (lithium metal ratio 0.99), Al2O3, TiO2, and SnO2 (each of which contains 500 ppm of Al, Ti, and Sn) are mixed evenly and then pre-calcined at 550°C for 3 h. Then the temperature is raised to 850°C and sintered for 30 h. After cooling to room temperature, the material blocks are crushed using an air jet mill and sieved through a 300-mesh sieve to obtain primary particles containing Al, Ti, and Sn dopants.

[0064] (2) The primary particles were mixed with additive ZrO2 by dry coating. The content of Zr in the coating element was 1000ppm. The holding temperature for the secondary sintering was 550℃ and the holding time was 5h. After cooling to room temperature, the material blocks were crushed by air jet mill and sieved through a 300-mesh sieve to obtain secondary particles with Li2ZrO3 as the inner coating layer.

[0065] (3) The secondary particles were coated with (NH4)H2PO4 using the ALD process. The content of the coating element P was 1000ppm. The holding temperature for the three sinterings was 550℃ and the holding time was 3h. After cooling to room temperature, the material was crushed using an air jet mill and sieved through a 300-mesh sieve to obtain the lithium cobalt oxide cathode material with Li3PO4 as the outer coating layer.

[0066] Example 3 (1) Small particles of CoO, lithium carbonate (lithium metal ratio 1.025), Ni(OH)2, Mg(OH)2, and Al2O3 (with Ni, Al, and Mg content of 1000ppm each) are mixed evenly and pre-calcined at 550℃ for 3 h. Then, the temperature is raised to 900℃ and sintered for 20 h. After cooling to room temperature, the material blocks are crushed using an air jet mill and sieved through a 300-mesh sieve to obtain primary particles doped with Ni, Mn, and Mg.

[0067] (2) The primary product particles were mixed with the additive WO3 by wet coating. The content of the coating element W was 5000ppm. The holding temperature for the secondary sintering was 550℃ and the holding time was 8h. After cooling to room temperature, the material blocks were crushed by air jet mill and sieved through a 300-mesh sieve to obtain secondary product particles with Li2WO4 as the inner coating layer.

[0068] (3) The secondary product particles were mixed with the additive Ta2O5 by wet coating. The content of the coating element Ta was 5000ppm. The holding temperature for the second sintering was 550℃ and the holding time was 8h. After cooling to room temperature, the material was crushed by air jet mill and sieved through a 300-mesh sieve to obtain lithium cobalt oxide cathode material with Li2ZrO3 as the outer coating layer.

[0069] Example 4 (1) Small particles of Co3O4, lithium carbonate (lithium metal ratio 1.02), Y2O3, La2O3, Mg(OH)2, and MnO2 (where the content of La, Y, Mn, and Mg is 1000ppm each) are mixed evenly and pre-calcined at 400℃ for 7 h. Then, the temperature is raised to 950℃ and sintered for 20 h. After cooling to room temperature, the material blocks are crushed using an air jet mill and sieved through a 300-mesh sieve to obtain primary particles containing La, Y, Mn, and Mg dopants.

[0070] (2) Al2O3 was coated onto the primary particles using a fluidized bed process. The content of the coating element Al was 10,000 ppm. The holding temperature for the secondary sintering was 650℃ and the holding time was 8h. After cooling to room temperature, the material blocks were crushed using an air jet mill and sieved through a 300-mesh sieve to obtain secondary particles with LiAlO2 coating.

[0071] (3) Nb2O5 was coated onto the secondary particles using a fluidized bed process. The content of the coated element Nb was 10,000 ppm. The holding temperature for the secondary sintering was 650℃ and the holding time was 8h. After cooling to room temperature, the material was crushed using an air jet mill and sieved through a 300-mesh sieve to obtain lithium cobalt oxide cathode material with LiNbO3 as the coating layer.

[0072] Example 5 (1) Small particles of Co3O4, lithium carbonate (lithium metal ratio 1.05), MnO2, SnO2, Y2O3, and La2O3 (of which the contents of Mn, Sn, La, and Y are 1500ppm each) are mixed evenly and pre-calcined at 750℃ for 2h. Then the temperature is raised to 1020℃ and sintered for 30h. After cooling to room temperature, the material blocks are crushed using an air jet mill and sieved through a 300-mesh sieve to obtain primary particles doped with Mn, Sn, La, and Y.

[0073] (2) Li2ZrO3 was coated onto the primary particles using a spray drying process. The content of the coating element Zr was 20,000 ppm. The holding temperature for the secondary sintering was 750℃ and the holding time was 10 h. After cooling to room temperature, the material blocks were crushed using an air jet mill and sieved through a 300-mesh sieve to obtain secondary particles with Li2ZrO3 as the inner coating layer.

[0074] (3) Using a fluidized bed process, Ta2O5 and Li3PO4 are coated onto the secondary particles. The content of the coating elements Ta and P is 20,000 ppm. The holding temperature for the secondary sintering is 750℃ and the holding time is 10h. After cooling to room temperature, the material is crushed using an air jet mill and sieved through a 300-mesh sieve to obtain lithium cobalt oxide cathode material with LiTaO3 and Li3PO4 as the outer coating layer.

[0075] Example 6 (1) Small particles of Co3O4, lithium carbonate (lithium metal ratio 1.05), SnO2, La2O3, ZnO, and MnO2 (with Zn, Mn, Sn, and La content 1500ppm) were mixed evenly and pre-calcined at 550℃ for 3 h. Then, the temperature was raised to 1020℃ and sintered for 30 h. After cooling to room temperature, the material blocks were crushed using an air jet mill and sieved through a 300-mesh sieve to obtain primary particles containing Zn, Mn, Sn, and La dopants.

[0076] (2) Using the ALD process, LiAlO3 and Li2WO4 were uniformly coated onto the primary particles. The content of the coating elements Al and W was 50,000 ppm. The holding temperature for the secondary sintering was 900℃ and the holding time was 3h. After cooling to room temperature, the material blocks were crushed using an air jet mill and sieved through a 300-mesh sieve to obtain secondary particles with the coating layer being LiAlO3 and Li2WO4.

[0077] (3) Using a fluidized bed process, Ta2O5 and Nb2O5 are uniformly coated onto the secondary particles. The content of the coating elements Ta and Nb is 50,000 ppm. The holding temperature for the secondary sintering is 900℃ and the holding time is 10h. After cooling to room temperature, the material blocks are crushed using an air jet mill and sieved through a 300-mesh sieve to obtain lithium cobalt oxide cathode material with LiNbO3 and LiTaO3 as the coating layers.

[0078] Comparative Example 1 Small particles of Co3O4 and lithium carbonate (lithium metal ratio 0.99) were mixed evenly and pre-calcined at 550℃ for 3 h, then heated to 800℃ for sintering for 10 h. After cooling to room temperature, the material was crushed using an air jet mill and sieved through a 300-mesh sieve to obtain undoped lithium cobalt oxide cathode material.

[0079] Comparative Example 2 (1) Mix small particles of Co3O4, lithium carbonate (lithium metal ratio 0.99), and basic magnesium carbonate (Mg content 1000ppm) evenly and pre-calcine at 600℃ for 3 h, then heat to 1000℃ and sinter for 10 h. After cooling to room temperature, crush the material blocks using an air jet mill and sieve through a 300 mesh screen to obtain primary particles containing Mg doping.

[0080] (2) The primary product particles and additive Al2O3 were mixed by dry coating. The content of Al in the coating element was 500 ppm. The holding temperature for the secondary sintering was 250℃ and the holding time was 10 h. After cooling to room temperature, the material was crushed by air jet mill and sieved through a 300 mesh screen to obtain lithium cobalt oxide cathode material with LiAlO2 coating layer.

[0081] Figure 2 This is a SEM image of the lithium cobalt oxide cathode material prepared in Example 1. Figure 3This is a SEM image of the lithium cobalt oxide cathode material prepared in Example 2. Figure 4 This is a SEM image of the lithium cobalt oxide cathode material prepared in Example 3. Figure 5 The SEM image of the lithium cobalt oxide cathode material prepared in Comparative Example 1 shows that the surface of the coated lithium cobalt oxide particles is smoother and rounder, indicating that the surface coating layer uniformly coats the lithium cobalt oxide particles.

[0082] Figure 6 This is a TEM image of the lithium cobalt oxide cathode material prepared in Example 1. Figure 7 This is a TEM image of the lithium cobalt oxide cathode material prepared in Example 2. Figure 8 The image shows a TEM image of the lithium cobalt oxide cathode material prepared in Comparative Example 1. It can be seen that the surface of the lithium cobalt oxide cathode material prepared in the example has a coating layer with a thickness of about 5~10nm, and the interior is a layered lithium cobalt oxide structure.

[0083] Figure 9 The image shows the XPS pattern of the lithium cobalt oxide cathode material prepared in Example 1. Figure 10 The XPS image of the lithium cobalt oxide cathode material prepared in Example 2 shows that signal peaks of B and Ta were detected in the surface coating layer, which is consistent with the technical solution of the present invention.

[0084] The lithium cobalt oxide cathode materials prepared in the above embodiments and comparative examples were tested in an all-solid-state battery system.

[0085] First, the prepared lithium cobalt oxide powder and Li6PS5Cl sulfur-based solid electrolyte were added to a mortar at a mass ratio of 7.5:2.5, mixed and ground evenly to form a composite positive electrode material, with Li6PS5Cl as the solid electrolyte and Li-In alloy as the negative electrode.

[0086] Next, battery assembly was performed. First, 100 mg of Li6PS5Cl was placed into a mold and pressed into a solid electrolyte sheet under a pressure of 300 MPa. Then, 8 mg of composite cathode powder was placed on one side of the intermediate electrolyte layer and pressed together with the electrolyte under a pressure of 250 MPa. Finally, Li-In foil was attached to the other side, and the battery was finally pressed into an all-solid-state lithium battery under a pressure of 75 MPa. The assembled all-solid-state lithium battery was a powder-pressed mold battery with a diameter of 10 mm. In the all-solid-state lithium battery, the areal density of the cathode was approximately 10.5 mg cm⁻¹. -2 (The areal density corresponding to the active substance is approximately 7.8 mg cm⁻¹) -2 All battery assembly was carried out in a glove box filled with Ar, with water and oxygen content both below 0.1 ppm.

[0087] Furthermore, after the all-solid-state battery was assembled, the electrochemical performance of the secondary-coated lithium cobalt oxide cathode material was studied at 25°C. The charge-discharge voltage range was set to 1.98-3.96V vs. Li-In (corresponding to 2.6-4.58V vs. Li+ / Li, since the potential of Li-In alloy is 0.62V vs. Li+ / Li), and the cycle was performed at 0.1C / 0.1C for 2 cycles and at 0.33C / 0.33C for 50 cycles.

[0088] Figure 11 The first charge-discharge curve of the lithium cobalt oxide cathode material prepared in Example 1 in a sulfur-based solid-state battery system is shown.

[0089] The test data for all-solid-state batteries are shown in Table 1 below.

[0090] Table 1. Charge-discharge specific capacity and cycle data for the first cycle. Compared to Comparative Example 1 without coating treatment, Examples 1-6 show significant improvements in capacity and cycle life. Among them, Examples 1-4, compared to Examples 5-6, only use two elements for coating, which is relatively less effective in compensating for the difference in electrochemical window between the lithium cobalt oxide cathode and the sulfur-based solid electrolyte, resulting in poorer cycle performance.

[0091] Although the present invention has been disclosed above with reference to embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention should be covered within the protection scope of the present invention, which is defined by the claims.

Claims

1. A lithium cobalt oxide cathode material for a sulfide all-solid-state battery, characterized in that, The chemical formula is Li x Co 1-y M y O2, where 0.99≤x<1.03, 0≤y<0.01, and the doping element M includes multiple types of Mg, Al, B, P, Ti, La, Y, Ni, Mn, Sn, Zn, Nb, Ta, Zr, and W, and contains a double-layer coating structure consisting of an inner coating layer and an outer coating layer.

2. The lithium cobalt oxide cathode material for a sulfide all-solid-state battery as described in claim 1, characterized in that, The lithium cobalt oxide cathode material has a particle size of 1~10 μm, and the inner coating layer includes Li4Ti5O. 12 The coating layer comprises at least one of Li2ZrO3, LiAlO2, and Li2WO4, and the outer coating layer comprises at least one of Li3BO3, LiNbO3, Li3PO4, and LiTaO3.

3. A method for preparing lithium cobalt oxide cathode material for a sulfide all-solid-state battery as described in claim 1 or 2, characterized in that, Includes the following steps: Cobalt precursor particles, lithium carbonate, and a type of additive are mixed evenly, sintered once, cooled to room temperature, crushed and sieved to obtain primary particles. The obtained primary particles are mixed with secondary additives and sintered twice to coat the primary particles with an inner coating layer. After cooling to room temperature, the particles are crushed and sieved to obtain secondary particles. The obtained secondary particles are mixed with three types of additives and sintered three times. An outer coating layer is then applied to the inner coating layer. After cooling to room temperature, the mixture is crushed and sieved to obtain lithium cobalt oxide cathode material.

4. The method as described in claim 3, characterized in that, The cobalt precursor includes at least one of Co3O4, Co(OH)2, CoO, and Co2O3.

5. The method as described in claim 3, characterized in that, The first type of additive contains at least one element of Mg, Al, Ti, Zr, Y, Sn, La, Ni, and Mn; the second type of additive contains at least one coating element of Ti, Zr, Al, and W; and the third type of additive contains at least one coating element of B, Nb, P, and Ta.

6. The method as described in claim 5, characterized in that, The Class I, Class II, and Class III additives are in the form of compounds of oxides, alkalis, and salts.

7. The method as described in claim 5, characterized in that, The inner coating layer includes Li4Ti5O 12 The outer coating layer comprises at least one of Li2ZrO3, LiAlO2, and Li2WO4; the outer coating layer comprises at least one of Li3BO3, LiNbO3, Li3PO4, and LiTaO3.

8. The method as described in claim 5, characterized in that, The inner coating layer has a coating element content of 500-50000ppm; the outer coating layer has a coating element content of 500-50000ppm.

9. The method as described in claim 3, characterized in that, The mixing methods of the primary product particles and the secondary additives, and the mixing methods of the secondary product particles and the tertiary additives, employ dry coating, wet coating, ALD process, fluidized bed process, and spray drying process.

10. The method as described in claim 3, characterized in that, The first sintering conditions are: pre-firing at 400-750℃ for 2-7 hours, then sintering at 800-1200℃ for 10-30 hours; the second sintering conditions are: temperature 250-900℃, time 3-10 hours; the third sintering conditions are: temperature 250-900℃, time 3-10 hours.

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