Double-layer coated ternary positive electrode material for solid-state battery as well as preparation method and application of double-layer coated ternary positive electrode material

Abstract

The invention discloses a double-layer coated ternary positive electrode material for a solid-state battery as well as a preparation method and application of the double-layer coated ternary positive electrode material, and relates to the technical field of batteries. The method comprises the following steps: mixing a nickel-cobalt-manganese-containing ternary positive electrode precursor, spinel powder and a first lithium salt, and pre-sintering and annealing in an oxygen atmosphere to obtain a lithium-rich spinel-coated ternary positive electrode material; and mixing the lithium-rich spinel coated ternary positive electrode material with an alkali solution, carrying out alkali washing, carrying out solid-liquid separation, drying, and forming a lithium-deficient spinel structure and an alkali metal carbonate protection layer on the surface of the lithium-rich spinel coated ternary positive electrode material. The prepared double-layer coated ternary positive electrode material for the solid-state battery has a continuous Li < + > transmission channel, and the cycle performance, the rate capability and the thermal stability are remarkably improved. The double-layer coated ternary positive electrode material for the solid-state battery can be widely applied to preparation of the solid-state battery.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a double-layer coated ternary positive electrode material for solid-state batteries, and a preparation method and application thereof. Background Art

[0002] As the global demand for clean energy grows, the application of traditional lithium-ion batteries in fields such as electric vehicles and energy storage faces many challenges, including the flammability of liquid electrolytes, poor temperature adaptability and environmental risks.

[0003] Solid-state batteries have become a promising alternative due to their high safety, energy density and cycle stability brought by solid electrolytes. However, the key material of solid-state batteries - nickel-rich ternary cathodes - still faces industrial challenges, such as high-temperature thermal runaway, Li + / Ni 2+ Structural degradation caused by intercalation and capacity decay due to interfacial side reactions seriously impact the battery's cycle life and rate performance. Therefore, improving the structural stability of cathode materials and inhibiting interfacial side reactions are key breakthroughs in advancing solid-state battery technology.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a double-layer coated ternary positive electrode material for solid-state batteries and its preparation method and application, so as to improve the structural stability of the positive electrode material, inhibit interfacial side reactions, and improve the cycle performance, rate performance and thermal stability of the positive electrode material.

[0006] The present invention is achieved in that: In a first aspect, the present invention provides a method for preparing a double-layer coated ternary cathode material for a solid-state battery, comprising: A ternary positive electrode precursor containing nickel, cobalt and manganese, spinel powder and a first lithium salt are mixed and then pre-sintered and annealed in an oxygen atmosphere to obtain a lithium-rich spinel-coated ternary positive electrode material; The lithium-rich spinel-coated ternary positive electrode material is mixed with an alkaline solution and subjected to alkaline washing, solid-liquid separation and then drying to form a lithium-deficient spinel structure and an alkali metal carbonate protective layer on the surface of the lithium-rich spinel-coated ternary positive electrode material.

[0007] In an optional embodiment, the amount of the spinel powder added is 0.1% to 3% of the mass of the ternary positive electrode precursor; And / or, the first lithium salt is added in an amount such that the molar ratio of the lithium element in the first lithium salt to the nickel, cobalt and manganese elements in the ternary positive electrode precursor is 1.01-1.10.

[0008] In an optional embodiment, the pre-calcination temperature is 400-500° C. and the time is 3-5 hours; And / or, the annealing temperature is 700-800° C. and the time is 6-10 h; And / or, after the annealing, the temperature is lowered to room temperature at a rate of 3-8°C / min.

[0009] In an optional embodiment, the method for preparing the spinel powder includes: mixing a nickel source, a manganese source and a second lithium salt to form a dispersion, grinding the dispersion to a particle size D50 = 0.2-1 μm in the slurry, then drying to obtain a spinel precursor, and sintering the spinel precursor to obtain the spinel powder.

[0010] In an optional embodiment, the spinel powder has the general formula Li 1+x Ni 0.5-x Mn 1.5+x O4, wherein -0.2≤x≤0.2, the nickel source, the manganese source and the second lithium salt are mixed in a molar ratio of Li:(Ni+Mn)=0.4-0.6, and the solid-liquid ratio is 1 kg:2-10 L; And / or, the grinding includes sand grinding, and the sand grinding time is 0.5 to 5 hours; And / or, the drying comprises spray drying, the air flow rate of the spray drying is 4-6m 3 / h, outlet temperature 90~110℃, and spinel precursor of 0.5~1μm; And / or, the sintering temperature is 650-750° C. and the sintering time is 5-12 hours.

[0011] In an optional embodiment, the first lithium salt and the second lithium salt are independently selected from one or more of lithium sulfate, lithium nitrate, lithium acetate and lithium chloride; And / or, the nickel source is selected from one or more of nickel oxide, nickel hydroxide, nickel sulfate, nickel nitrate, nickel acetate and nickel chloride; And / or, the manganese source is selected from one or more of manganese oxide, manganese hydroxide, manganese sulfate, manganese nitrate, manganese acetate and manganese chloride.

[0012] In an optional embodiment, the alkaline solution includes at least one of potassium hydroxide and sodium hydroxide; And / or, the concentration of the alkaline solution is 0.01 mol / L~1 mol / L; the solid-liquid ratio of the lithium-rich spinel-coated ternary cathode material to the alkaline solution is 1 kg:1-10 L; And / or, the solid-liquid separation is suction filtration; And / or, the drying is vacuum drying, and the temperature of the vacuum drying is 80-120°C.

[0013] In an optional embodiment, the preparation method of the ternary positive electrode precursor includes a co-precipitation method, a sol-gel method, a hydrothermal method, a solvothermal method, a spray pyrolysis method or a solid phase method.

[0014] In a second aspect, the present invention provides a double-layer coated ternary positive electrode material for a solid-state battery, which is prepared using the preparation method of the double-layer coated ternary positive electrode material for a solid-state battery as described in any of the aforementioned embodiments.

[0015] In a third aspect, the present invention provides the use of the double-layer coated ternary positive electrode material for solid-state batteries as described in the aforementioned embodiment in the preparation of solid-state batteries.

[0016] The present invention has the following beneficial effects: The present invention provides a method for preparing a double-layer coated ternary cathode material for solid-state batteries. The method ensures the continuity of the interface lattice by directly coating the surface of the ternary cathode precursor with spinel powder, realizes seamless interface coupling between the spinel phase and the layered phase through crystal structure matching design, and subsequently generates alkali metal carbonate on the surface to replace part of Li2CO3 by alkali washing, thereby improving the purity and chemical stability of the surface spinel phase, protecting the outer surface from the decomposition of the electrolyte in the high-voltage area, and effectively inhibiting the volume expansion and oxygen release of the ternary cathode material. The spinel and alkali metal carbonate double block direct contact with the electrolyte. The obtained double-layer coated ternary cathode material for solid-state batteries has continuous Li + The transmission channel significantly improves the cycle performance, rate performance and thermal stability. This double-layer coated ternary cathode material for solid-state batteries can be widely used in the preparation of solid-state batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 An SEM image of the lithium-rich spinel-coated ternary cathode material provided in step (3) of Example 1 of the present application; Figure 2 A magnified TEM image of the surface of the lithium-rich spinel-coated ternary cathode material provided in step (3) of Example 1 of the present application; Figure 3 XPS-C of the lithium-rich spinel-coated ternary cathode material provided in step (4) of Example 1 of this application 1sSpectrum (a) and XPS-C of NCM high nickel cathode material with spinel and K2CO3 double coating after KOH treatment 1s Spectrum (b); Figure 4 This is the SEM image of the spinel-coated ternary positive electrode material provided in Comparative Example 2 of this application. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0020] The present invention provides a method for preparing a double-layer coated ternary cathode material for a solid-state battery, which comprises: S1. Prepare spinel powder.

[0021] A nickel source, a manganese source and a second lithium salt are mixed to form a dispersion, the dispersion is ground to a particle size D50 of 0.2-1 μm in a slurry, and then dried to obtain a spinel precursor, and the spinel precursor is sintered to obtain spinel powder.

[0022] Among them, the general formula of spinel powder is Li 1+x Ni 0.5-x Mn 1.5+x O4, where -0.2≤x≤0.2, the nickel source, manganese source, and second lithium salt are mixed at a molar ratio of Li:(Ni+Mn)=0.4-0.6, with a solid-to-liquid ratio of 1kg:2-10L; the nickel source includes but is not limited to one or more of nickel oxide, nickel hydroxide, nickel sulfate, nickel nitrate, nickel acetate, and nickel chloride; and / or the manganese source includes but is not limited to one or more of manganese oxide, manganese hydroxide, manganese sulfate, manganese nitrate, manganese acetate, and manganese chloride. And / or the second lithium salt includes but is not limited to one or more of lithium sulfate, lithium nitrate, lithium acetate, and lithium chloride.

[0023] In the present invention, a nickel source, a manganese source, and a second lithium salt are used as raw materials to prepare spinel powder, wherein the nickel source, the manganese source, and the second lithium salt are first mixed to form a dispersion and then ground, thereby ensuring the particle size and mixing uniformity of the slurry, compared to directly mixing the nickel source, the manganese source, and the second lithium salt in a solid state, which will result in poor mixing uniformity. Among them, the grinding method includes but is not limited to sand milling, ball milling, etc., as long as the particle size of the particles in the slurry can be ground to D50 = 0.2-1 μm, in some typical but non-limiting examples, the grinding method is sand milling, and the sand milling time is 0.5 to 5 hours.

[0024] In the present invention, the ground slurry is dried in various ways, including but not limited to spray drying, oven drying, air drying, etc., as long as the slurry can be dried. In some typical but non-limiting examples, spray drying is used to dry the slurry, and the air flow rate of the spray drying is 4-6m 3 / h, with an outlet temperature of 90-110°C, to produce spinel precursors with a diameter of 0.5-1μm. Spray drying allows the slurry to be directly dried into micron-sized spherical powders after atomization, eliminating the multi-step process of "precipitation-filtration-washing-drying" required by the traditional co-precipitation method. This method enables 24-hour uninterrupted operation, increasing production efficiency by over 30% (e.g., throughput can reach tons per hour). Compared to the long, high-temperature sintering required by the solid-phase method, spray drying reduces energy consumption by approximately 20%. The metal salt solution is uniformly mixed at the atomic level during atomization, avoiding the localized segregation problems associated with the solid-phase method. Furthermore, the spinel precursors obtained by spray drying are spherical particles with a porous structure and more uniform particle size. Furthermore, the spray drying process is fully enclosed, with N2 / Ar protection to prevent Ni²⁺ oxidation. The lack of a washing step prevents the introduction of Na⁺ and SO⁄²⁻.

[0025] In the present invention, the spinel precursor is sintered at a temperature of 650-750°C for 5-12 hours. This sintering process can preliminarily produce spinel powder with low crystallinity. Annealing during subsequent coating further improves the crystallinity of the spinel coating layer.

[0026] S2. Prepare the ternary positive electrode precursor.

[0027] In the present invention, the ternary cathode precursor is applicable to various types of ternary cathode materials commonly available on the market. In some typical but non-limiting examples, the ternary cathode precursor includes but is not limited to a nickel-cobalt-manganese precursor.

[0028] Among them, there are also many methods for preparing ternary positive electrode precursors. Conventional processes can be used as long as they can synthesize ternary positive electrode precursors. For example, conventional synthesis methods such as co-precipitation method, sol-gel method, hydrothermal method, solvent thermal method, spray pyrolysis method or solid phase method can be used as methods for preparing ternary positive electrode precursors in this application. The present invention does not make specific limitations on this.

[0029] S3. Prepare lithium-rich spinel-coated ternary positive electrode materials.

[0030] A ternary positive electrode precursor containing nickel, cobalt and manganese, spinel powder and a first lithium salt are mixed and then pre-sintered and annealed in an oxygen atmosphere to obtain a lithium-rich spinel-coated ternary positive electrode material.

[0031] The spinel powder is added in an amount of 0.1% to 3% of the mass of the ternary cathode precursor. The first lithium salt is added in an amount such that the molar ratio of the lithium element in the first lithium salt to the nickel, cobalt, and manganese elements in the ternary cathode precursor is 1.01 to 1.10. The first lithium salt includes, but is not limited to, one or more of lithium sulfate, lithium nitrate, lithium acetate, or lithium chloride.

[0032] In the present invention, the ternary positive electrode precursor, spinel powder and the first lithium salt are mixed in advance to introduce the spinel powder in the precursor stage, rather than coating the synthesized positive electrode material. In the present invention, the mixture is pre-sintered and annealed in an oxygen atmosphere to form a tighter bond between the spinel powder and the matrix, forming a uniform spinel-layered heterostructure, thereby improving the structural stability and electrochemical performance of the material.

[0033] The pre-calcination temperature is 400-500°C for 3-5 hours. This pre-calcination removes volatile components such as moisture, residual solvents, or lithium salt decomposition products from the ternary cathode precursor, spinel powder, and first lithium salt, thereby preventing structural defects in the material due to rapid volatilization during the high-temperature stage. At lower temperatures, the lithium salt (such as LiOH or Li2CO3) begins to partially melt and reacts initially with the surface of the ternary cathode precursor, forming localized lithiated products and providing a uniform reaction foundation for subsequent annealing. Pre-calcination achieves initial stabilization of the surface contact between the spinel powder and the ternary cathode precursor. A preliminary solid-phase reaction forms a progressive interface between the spinel and the layered precursor, relieving interfacial stress, reducing the lattice mismatch between the two phases, and lowering the diffusion driving force of Mn at high temperatures, thereby inhibiting the conversion of the surface spinel to a layered structure in an oxygen atmosphere. Oxygen can inhibit the reduction of transition metals (such as Ni²⁺, Co³⁺) at low temperature, maintain high valence, and promote the valence stability of Mn in spinel (such as Mn³⁺ / Mn 4 ⁺), preventing the formation of oxygen vacancies.

[0034] Annealing is performed at 700-800°C for 6-10 hours. This process fully lithiates the ternary precursor, forming a layered structure. Simultaneously, the spinel and layered phases form a tightly bound heterostructure through high-temperature solid-phase diffusion. At high temperatures, atomic-level interdiffusion occurs between the spinel particles and the layered matrix, forming chemically bonded interfaces (e.g., spinel embedded within layered grain boundaries). This enhances structural coherence and inhibits phase transformation and crack propagation during cycling. Annealing redistributes transition metals (Ni, Co, and Mn) between the spinel and layered phases. For example, Mn migrates from the spinel to the layered surface, creating a concentration gradient that suppresses cation mixing of Ni²⁺ in the layered phase and improves structural stability. At high temperatures, oxygen maintains a high oxidation state, ensuring a near-ideal oxygen stoichiometry in the material (e.g., reducing oxygen vacancies) while suppressing Jahn-Teller distortion of Mn³⁺ in the spinel phase, thereby enhancing cycling stability.

[0035] After annealing, the material is cooled to room temperature at a rate of 3-8°C / min. This cooling process allows the two-phase interface formed at high temperature to further fuse during the slow cooling process, reducing interfacial dislocations or microcracks and enhancing structural stability. This gives atoms sufficient time to relax, forming a more complete lattice arrangement, improving the material's crystallinity and ionic conductivity.

[0036] S4. Preparation of double-layer coated ternary positive electrode materials for solid-state batteries.

[0037] The lithium-rich spinel-coated ternary positive electrode material is mixed with an alkaline solution for alkaline washing, and then dried after solid-liquid separation to form a lithium-deficient spinel structure and an alkali metal carbonate protective layer on the surface of the lithium-rich spinel-coated ternary positive electrode material.

[0038] Wherein, the alkaline solution includes but is not limited to at least one of potassium hydroxide and sodium hydroxide; it should be understood that the alkaline solution in the present invention does not include a lithium salt solution (such as lithium hydroxide). This is because the present invention requires the use of an alkaline washing process to partially replace the alkali metal elements in the alkaline solution with the Li on the surface of the lithium-rich spinel-coated ternary positive electrode material. + Lithium salt solutions cannot achieve the above purpose. Therefore, the alkaline solution in the present invention does not include lithium salt solutions. And / or, the concentration of the alkaline solution is 0.01 mol / L to 1 mol / L; the solid-to-liquid ratio of the lithium-rich spinel-coated ternary cathode material to the alkaline solution is 1 kg: 1-10 L, and the mixing time is 10-120 minutes.

[0039] In the present invention, the lithium-rich spinel-coated ternary positive electrode material is alkaline washed with an alkaline solution. The alkaline solution can wash away the residual alkali (such as LiOH, Li2CO3) remaining on the surface of the lithium-rich spinel-coated ternary positive electrode material during the annealing process, thereby forming a lithium-deficient spinel structure and enhancing the migration and storage capacity of Li+. The alkali metal in the alkaline solution will enter the surface of the lithium-rich spinel-coated ternary positive electrode material, that is, enter the spinel coating layer, so that the alkali metal (such as K and Na) in the alkaline solution will replace part of the Li in the spinel coating layer. At the same time, in the process of washing away the residual alkali, the alkaline solution will react with the carbon dioxide in the water to generate alkali metal carbonate. Taking the alkaline solution as KOH as an example, the reaction process is: 2KOH + CO2→K2CO3+ H2O. The generated alkali metal carbonate can be coated on at least part of the surface of the lithium-rich spinel-coated ternary positive electrode material, by removing the adsorbed H2O molecules in the subsequent drying process and forming K2CO3 on the outer surface. The outer surface is protected from chemical decomposition of the electrolyte in the high-voltage area by partially replacing Li2CO3 with K2CO3. It should be understood that the alkali metal carbonate protective layer in the present invention means that the surface of the lithium-rich spinel-coated ternary positive electrode material is at least partially coated with an alkali metal carbonate protective layer.

[0040] There are various methods for solid-liquid separation, including but not limited to filtration, suction filtration, centrifugation, etc., with suction filtration being preferred. There are also various methods for drying, including but not limited to oven drying, air drying, or heating, with vacuum drying being preferred, wherein the vacuum drying temperature is 80-120°C.

[0041] The double-layer coated ternary cathode material for solid-state batteries, prepared by the above-mentioned preparation method, has a double coating of lithium-rich spinel coating layer and alkali metal carbonate protective layer, achieving interfacial lattice continuity, effectively suppressing the volume expansion and oxygen release of the NCM material, and the double coating layer blocks direct contact with the electrolyte. The resulting material has a continuous Li+ transmission channel, significantly improving the cycle performance, rate performance, and thermal stability.

[0042] The above-mentioned double-layer coated ternary positive electrode material for solid-state batteries can be widely used in the preparation of solid-state batteries.

[0043] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0044] Example 1 This embodiment provides a method for preparing a double-layer coated ternary cathode material for a solid-state battery, which comprises the following steps: Step (1): Mix nickel source (nickel oxide), manganese source (manganese tetraoxide), and lithium salt (lithium carbonate) in a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.5, add solvent water in a solid-liquid ratio of 1kg:5L, sand grind to a particle size D50 of about 0.2μm in the slurry, and then spray dry with an air flow rate of 5m 3 / h, outlet temperature 100 °C, and a spinel precursor with a particle size of about 1 μm was obtained; Step (2): sintering the spinel precursor obtained in step (1) at 650° C. for 12 h to obtain spinel powder; Step (3): Mix the ternary NCM high nickel precursor (structural formula Ni0.9Mn0.05C0.05(OH)2) prepared by the co-precipitation method, spinel powder and lithium salt at high speed, wherein the amount of spinel powder added is 0.75wt% of the mass of the ternary high nickel precursor, and the amount of lithium salt added is added according to the molar ratio of lithium element in the lithium salt and nickel, cobalt and manganese in the ternary positive electrode precursor Li: (Ni+ Co+Mn) = 1.05. Gradient sintering is carried out in an oxygen atmosphere; pre-sintering at 450℃ for 4h, annealing at 750℃ for 8h, and finally cooling to room temperature at a rate of 5℃ / min to obtain a lithium-rich spinel-coated ternary positive electrode material. Figure 1 As shown in Figure 2, the sample has a single crystal structure with a smooth surface and no impurities, which is consistent with the typical characteristics of highly crystalline materials. Figure 2As shown, Example 1 uses direct coating of nano-spinel powder combined with KOH treatment process to successfully construct a spinel coating layer with a smooth surface and uniform thickness (13 nm).

[0045] Step (4): The cathode material obtained in step (3) is mixed with the diluted KOH solution (concentration of 0.5 mol / L) at a solid-liquid ratio of 1kg:5L and stirred for 60 minutes. The mixture is then washed with deionized water, filtered, and dried under vacuum at 120°C to obtain an NCM high-nickel cathode material with a double coating layer of spinel and K2CO3. Figure 3 The C=O bond peak in K2CO3 corresponds to a characteristic 288.6 eV peak, while the C=O peak in Li2CO3 is 289.3 eV. Because the electronegativity of K⁺ (0.82) is lower than that of Li⁺ (0.98), the electron binding energy of the C=O bond is weakened. Therefore, the C=O peak after KOH treatment shifts significantly to the right, closer to the C=O peak of K2CO3. At the same time, the K2CO3 coating causes the C=O peak to increase from 23% to 37%, indicating an increase in the surface carbonate content.

[0046] Example 2 This embodiment provides a method for preparing a double-layer coated ternary cathode material for a solid-state battery, which comprises the following steps: Step (1): Mix nickel source (nickel oxide), manganese source (manganese tetraoxide), and lithium salt (lithium carbonate) in a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.4, add solvent water in a solid-liquid ratio of 1kg:2L, sand grind to a particle size D50 of about 0.5μm in the slurry, and then spray dry with an air flow rate of 4m 3 / h, outlet temperature 110℃, and a spinel precursor with a particle size of about 1μm was obtained; Step (2): sintering the spinel precursor obtained in step (1) at 650° C. for 12 h to obtain spinel powder; Step (3): The ternary NCM high-nickel precursor (structural formula: Ni0.9Mn0.05C0.05(OH)2) prepared by the coprecipitation method, spinel powder and lithium salt are mixed at high speed, wherein the amount of spinel powder added is 0.1wt% of the mass of the ternary high-nickel precursor, and the amount of lithium salt added is added according to the molar ratio of lithium in the lithium salt to nickel, cobalt and manganese in the ternary positive electrode precursor: Li:(Ni+Co+Mn)=1.01. Gradient sintering is carried out in an oxygen atmosphere; pre-sintering at 400℃ for 5h, annealing at 700℃ for 10h, and finally cooling to room temperature at a rate of 3℃ / min to obtain a lithium-rich spinel-coated ternary positive electrode material.

[0047] Step (4): The positive electrode material obtained in step (3) is mixed with the diluted KOH solution (concentration of 0.01 mol / L) at a solid-liquid ratio of 1 kg:1 L and stirred for 30 minutes, then washed with deionized water, filtered, and vacuum-dried at 80°C to obtain an NCM high-nickel positive electrode material with a double coating layer of spinel and K2CO3.

[0048] Example 3 This embodiment provides a method for preparing a double-layer coated ternary cathode material for a solid-state battery, which comprises the following steps: Step (1): Mix nickel source (nickel oxide), manganese source (manganese oxide), and lithium salt (lithium hydroxide) in a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.6, add solvent water in a solid-liquid ratio of 1kg:10L, sand grind to a particle size D50 of about 1μm in the slurry, and then spray dry with an air flow rate of 6m 3 / h, outlet temperature 90℃, and a spinel precursor with a particle size of about 1μm was obtained; Step (2): sintering the spinel precursor obtained in step (1) at 750° C. for 6 h to obtain spinel powder; Step (3): The ternary NCM high-nickel precursor (structural formula: Ni0.9Mn0.05C0.05(OH)2) prepared by the coprecipitation method, spinel powder, and lithium salt are mixed at high speed, wherein the amount of spinel powder added is 3wt% of the mass of the ternary high-nickel precursor, and the amount of lithium salt added is added according to the molar ratio of lithium in the lithium salt to nickel, cobalt, and manganese in the ternary positive electrode precursor: Li:(Ni+Co+Mn)=1.10. Gradient sintering is performed in an oxygen atmosphere; pre-sintering at 500℃ for 3h, annealing at 800℃ for 6h, and finally cooling to room temperature at a rate of 8℃ / min to obtain a lithium-rich spinel-coated ternary positive electrode material.

[0049] Step (4): The positive electrode material obtained in step (3) is mixed with the diluted KOH solution (concentration of 1 mol / L) at a solid-liquid ratio of 1 kg:10 L and stirred for 120 min, then washed with deionized water, filtered, and vacuum-dried at 100°C to obtain an NCM high-nickel positive electrode material with a double coating layer of spinel and K2CO3.

[0050] Example 4 This embodiment is basically the same as embodiment 1, except that, in step (3) of this embodiment, the amount of lithium salt added is based on the molar ratio of lithium in the lithium salt to nickel, cobalt and manganese in the ternary positive electrode precursor, Li: (Ni + Co + Mn) = 1.02.

[0051] Example 5 This embodiment is basically the same as embodiment 1, with the only difference being that, in step (3) of this embodiment, the amount of spinel powder added is 0.5 wt% of the mass of the ternary high nickel precursor.

[0052] Example 6 This embodiment is basically the same as embodiment 1, except that in step (3) of this embodiment, the annealing temperature is 800° C. and the annealing time is 8 h.

[0053] Example 7 This embodiment is basically the same as embodiment 1, except that in step (4) of this embodiment, the vacuum drying temperature is 100°C.

[0054] Example 8 This embodiment is basically the same as embodiment 1, except that in step (4) of this embodiment, the solid-liquid ratio of the positive electrode material to the diluted KOH solution is 1 kg:10 L.

[0055] Example 9 This embodiment is basically the same as Example 1, except that in step (4) of this embodiment, the base is NaOH, and the obtained product is an NCM high-nickel positive electrode material having a double coating layer of spinel and Na2CO3.

[0056] Example 10 This embodiment is substantially the same as embodiment 1, with the only difference being that, in step (4) of this embodiment, the mixing time of the positive electrode material and the diluted KOH solution is 120 min.

[0057] Example 11 This embodiment is basically the same as embodiment 1, with the only difference being that in step (3) of this embodiment, the cooling rate after annealing is 10°C / min.

[0058] Example 12 This embodiment is basically the same as embodiment 1, except that in step (4) of this embodiment, the alkaline solution is NH4OH.

[0059] Comparative Example 1 This comparative example is substantially the same as Example 1, except that the KOH treatment step is omitted and no K2CO3 protective layer is formed on the surface. The specific preparation method comprises the following steps: Step (1): Nickel source (nickel oxide), manganese source (manganese tetraoxide), and lithium salt (lithium carbonate) are mixed in a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.5, and solvent water is added in a solid-liquid ratio of 1kg:5L. The mixture is sand-ground to a particle size D50 of about 0.2μm in the slurry, and then spray-dried to obtain a spinel precursor with a particle size of about 1μm.

[0060] Step (2): sintering the spinel precursor obtained in step (1) at 650° C. for 12 h to obtain spinel powder; Step (3): The ternary NCM high-nickel precursor (structural formula: Ni0.9Mn0.05C0.05(OH)2) prepared by the coprecipitation method, spinel powder and lithium salt are mixed at high speed, wherein the amount of spinel powder added is 0.75wt% of the mass of the ternary high-nickel precursor, and the amount of lithium salt added is added according to the molar ratio of lithium element in the lithium salt to nickel, cobalt and manganese in the ternary positive electrode precursor, Li:(Ni+ Co+Mn)=1.05. Gradient sintering is carried out in an oxygen atmosphere; pre-sintering at 450℃ for 4h, annealing at 750℃ for 8h, and finally cooling to room temperature at a rate of 5℃ / min to obtain a positive electrode material with spinel coating.

[0061] Comparative Example 2 This comparative example is essentially the same as Example 1, with the main difference being that in this comparative example, the spinel is coated on the surface of the NCM cathode material intermediate rather than the precursor. The specific preparation method includes the following steps: Step (1): Mix nickel source (nickel oxide), manganese source (manganese tetraoxide), and lithium salt (lithium carbonate) in a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.5, add solvent water in a solid-liquid ratio of 1kg:5L, sand grind to a particle size D50 of about 0.2μm in the slurry, and then spray dry with an air flow rate of 5m 3 / h, outlet temperature 100 ° C, to obtain a spinel precursor with a particle size of about 1 μm; step (2): sintering the spinel precursor obtained in step (1) at 600 ° C for 12 hours to obtain spinel powder; Step (3): The ternary NCM high nickel precursor and lithium salt are mixed at a high speed according to Li: (Ni + Co + Mn) = 1.05, sintered at a high temperature of 750 ° C / 8h in an oxygen atmosphere, and cooled to room temperature to obtain the NCM positive electrode material.

[0062] Step (4): The positive electrode material obtained in step (3) and the 0.75 wt% spinel powder obtained in step (2) are mixed at high speed.

[0063] Step (5): The product obtained in step (4) is subjected to a second high-temperature sintering at 800°C / 4h, and after cooling to room temperature, a ternary positive electrode material with a spinel coating layer is obtained.

[0064] Step (6): The positive electrode material obtained in step (3) is mixed with the diluted KOH solution (concentration of 0.5 mol / L) at a solid-liquid ratio of 1kg:5L and stirred for 60 minutes, then washed with deionized water, filtered, and vacuum-dried at 120°C to obtain an NCM high-nickel positive electrode material with a double coating layer of spinel and K2CO3.

[0065] Comparative Example 3 This comparative example is basically the same as Example 1, except that an acid wash process is adopted in this comparative example instead of an alkaline wash process. The specific preparation method comprises the following steps: Step (1): Mix nickel source (nickel oxide), manganese source (manganese tetraoxide), and lithium salt (lithium carbonate) in a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.5, add solvent water in a solid-liquid ratio of 1kg:5L, sand grind to a particle size D50 of about 0.2μm in the slurry, and then spray dry with an air flow rate of 5m 3 / h, outlet temperature 100 ° C, to obtain a spinel precursor with a particle size of about 1 μm; step (2): sintering the spinel precursor obtained in step (1) at 650 ° C for 12 hours to obtain spinel powder; Step (3): The ternary NCM high-nickel precursor (structural formula: Ni0.9Mn0.05C0.05(OH)2) prepared by the coprecipitation method, spinel powder and lithium salt are mixed at high speed, wherein the amount of spinel powder added is 0.75wt% of the mass of the ternary high-nickel precursor, and the amount of lithium salt added is added according to the molar ratio of lithium element in the lithium salt to nickel, cobalt and manganese in the ternary positive electrode precursor: Li:(Ni+ Co+Mn)=1.05. Gradient sintering is carried out in an oxygen atmosphere; pre-sintering at 450℃ for 4h, annealing at 750℃ for 8h, and finally cooling to room temperature at a rate of 5℃ / min to obtain a lithium-rich spinel-coated ternary positive electrode material. Step (4): The positive electrode material obtained in step (3) was mixed with the diluted citric acid solution (concentration of 0.5 mol / L) at a solid-liquid ratio of 1kg:5L and stirred for 60 minutes, then washed with deionized water, filtered, and vacuum-dried at 120°C to obtain a spinel-coated NCM high-nickel positive electrode material.

[0066] Comparative Example 4 This comparative example is basically the same as Example 1, except that the preparation and coating of spinel powder are omitted in this comparative example, i.e., there is no spinel coating layer in this comparative example. The specific preparation method includes the following steps: Step (1): The ternary NCM high nickel precursor and lithium salt are mixed at a high speed according to Li: (Ni + Co + Mn) = 1.05, sintered at 750 ° C for 8 hours in an oxygen atmosphere, and cooled to room temperature to obtain the ternary high nickel positive electrode material.

[0067] Step (2): The ternary high-nickel cathode material obtained in step (1) is subjected to a second high-temperature sintering at 800° C. for 4 h, and then cooled to room temperature to obtain the ternary high-nickel cathode material.

[0068] Step (3): The positive electrode material obtained in step (3) was mixed with the diluted KOH solution (concentration of 0.5 mol / L) at a solid-liquid ratio of 1kg:5L and stirred for 60 minutes, then washed with deionized water, filtered, and vacuum-dried at 120°C to obtain a K2CO3-coated NCM high-nickel positive electrode material.

[0069] Comparative Example 5 This comparative example is basically the same as Example 1, except that the spinel powder in this comparative example is magnesium aluminum spinel. The specific preparation method includes: Step (1): Mix magnesium acetate and aluminum acetate in a molar ratio of 1:2, add solvent water according to a solid-liquid ratio of 1kg:5L, sand grind to a particle size D50 of about 0.2μm in the slurry, and then spray dry with an air flow rate of 5m 3 / h, outlet temperature 100 °C, and a spinel precursor with a particle size of about 1 μm was obtained; Step (2): sintering the spinel precursor obtained in step (1) at 650° C. for 12 h to obtain spinel powder; Step (3): The ternary NCM high-nickel precursor (structural formula: Ni0.9Mn0.05C0.05(OH)2) prepared by the coprecipitation method, spinel powder and lithium salt are mixed at high speed, wherein the amount of spinel powder added is 0.75wt% of the mass of the ternary high-nickel precursor, and the amount of lithium salt added is added according to the molar ratio of lithium in the lithium salt to nickel, cobalt and manganese in the ternary positive electrode precursor, Li:(Ni+Co+Mn)=1.05. Gradient sintering is carried out in an oxygen atmosphere; pre-sintering at 450℃ for 4h, annealing at 750℃ for 8h, and finally cooling to room temperature at a rate of 5℃ / min to obtain a lithium-rich spinel-coated ternary positive electrode material.

[0070] Step (4): The positive electrode material obtained in step (3) is mixed with the diluted KOH solution (concentration of 0.5 mol / L) at a solid-liquid ratio of 1kg:5L and stirred for 60 minutes, then washed with deionized water, filtered, and vacuum-dried at 120°C to obtain an NCM high-nickel positive electrode material with a double coating layer of spinel and K2CO3.

[0071] Comparative Example 6 This comparative example is basically the same as Example 1, except that the coating method of the spinel powder in this comparative example is different. The specific preparation method includes: Step (1): Add the ternary NCM high-nickel precursor (structural formula: Ni0.9Mn0.05C0.05(OH)2) prepared by the co-precipitation method, nickel source (nickel sulfate), manganese source (manganese sulfate), and lithium salt (lithium sulfate) in the amount of Example 1, mix them evenly, heat and stir, evaporate the solvent, and dry to obtain the spinel-coated ternary NCM high-nickel precursor, and then perform gradient sintering in an oxygen atmosphere; pre-sinter at 450°C for 4h, then anneal at 750°C for 8h, and finally cool to room temperature at a rate of 5°C / min to obtain a lithium-rich spinel-coated ternary positive electrode material.

[0072] Step (2): The positive electrode material obtained in step (1) is mixed with the diluted KOH solution (concentration of 0.5 mol / L) at a solid-liquid ratio of 1kg:5L and stirred for 60 minutes, then washed with deionized water, filtered, and vacuum-dried at 120°C to obtain an NCM high-nickel positive electrode material with a double coating layer of spinel and K2CO3.

[0073] Comparative Example 7 This comparative example is substantially the same as Example 1, except that the alkali washing time in this comparative example is different. The specific preparation method comprises: Step (1): Mix nickel source (nickel oxide), manganese source (manganese tetraoxide), and lithium salt (lithium carbonate) in a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.5, add solvent water in a solid-liquid ratio of 1kg:5L, sand grind to a particle size D50 of about 0.2μm in the slurry, and then spray dry with an air flow rate of 5m 3 / h, outlet temperature 100 °C, and a spinel precursor with a particle size of about 1 μm was obtained; Step (2): sintering the spinel precursor obtained in step (1) at 650° C. for 12 h to obtain spinel powder; Step (3): The ternary NCM high-nickel precursor (structural formula: Ni0.9Mn0.05C0.05(OH)2) prepared by the coprecipitation method, spinel powder and lithium salt are mixed at high speed, wherein the amount of spinel powder added is 0.75wt% of the mass of the ternary high-nickel precursor, and the amount of lithium salt added is added according to the molar ratio of lithium in the lithium salt to nickel, cobalt and manganese in the ternary positive electrode precursor, Li:(Ni+Co+Mn)=1.05. Gradient sintering is carried out in an oxygen atmosphere; pre-sintering at 450℃ for 4h, annealing at 750℃ for 8h, and finally cooling to room temperature at a rate of 5℃ / min to obtain a lithium-rich spinel-coated ternary positive electrode material.

[0074] Step (4): The positive electrode material obtained in step (3) was mixed with the diluted KOH solution (concentration of 0.5 mol / L) at a solid-liquid ratio of 1kg:5L and stirred for 10 minutes, then washed with deionized water, filtered, and vacuum-dried at 120°C to obtain an NCM high-nickel positive electrode material.

[0075] Experimental example The positive electrode materials obtained in the above Examples 1-12 and Comparative Examples 1-7 are prepared to form solid-state batteries.

[0076] The entire process was performed in a glove box: the positive electrode material, solid electrolyte, and conductive agent were weighed and manually ground in a weight ratio of 70:27.5:25. After grinding for 30 minutes, 16-18 mg was weighed. 100±0.5 mg of solid electrolyte was weighed, and indium powder and solid electrolyte were weighed in a weight ratio of 3:7. After grinding for 30 minutes, 100±0.5 mg was weighed as the indium negative electrode intermediate layer. These were added to the mold battery cavity and assembled and compacted with the lithium-copper negative electrode. The mold battery was removed from the glove box, connected to the positive and negative electrode cables, and the test began. The capacity retention rate after 100 cycles was measured at a charge and discharge voltage of 2.6-4.3 V.

[0077] The electrochemical performance was tested. The test results are shown in Table 1.

[0078]

[0079] Through comparative analysis of the performance of the comparative examples and the embodiments, it can be seen that the uniformity and structural integrity of the spinel coating layer have a decisive influence on the electrochemical performance of the NCM positive electrode material.

[0080] The spinel layer + K2CO3 modified layer formed by epitaxial growth in the embodiment of the present invention has the following advantages: (1) low lattice mismatch, effectively alleviating the volume expansion during the charge and discharge process; (2) forming a continuous Li + transmission channel to ensure ionic conductivity; (3) completely isolate the electrodes from direct contact with the electrolyte, inhibiting transition metal dissolution and electrolyte oxidation side reactions. Therefore, the first discharge specific capacity of Example 1-12 can reach above 232.7 mAh / g, and the capacity retention rate reaches above 91.8% after 100 cycles at a 0.5C rate, which is significantly better than that of Comparative Examples 1-7.

[0081] In contrast, the traditional coating process has obvious defects: Comparative Example 1 does not have a KOH treatment step, and no K2CO3 protective layer is formed on the surface, and the capacity retention rate is only 83.4%; the dry coating of Comparative Example 2 forms an island distribution ( Figure 4), so that a large area of ​​the matrix is ​​exposed, and the capacity retention rate drops to 86.4%; Comparative Example 3 is an acid pickling process, and no K2CO3 protective layer is formed on the surface, and the capacity retention rate is 82.7%. Comparative Example 4 is in direct contact with the NCM matrix and KOH. Due to the lack of the protection of the spinel layer, the matrix Li will be separated, thereby increasing the residual lithium, and the capacity retention rate is reduced to 88.3%. Comparative Example 5 uses magnesium aluminum spinel for coating, but it is not as resistant to alkali washing as nickel manganese spinel, and the capacity retention rate is slightly reduced to 87.4%. Comparative Example 6 does not pre-form spinel powder, but forms a spinel coating by directly adding the raw materials for forming spinel powder when mixing with the NCM high-nickel precursor. However, the spinel coating prepared by this method is not uniform and dense enough, and the capacity retention rate is only 84.6%. Comparative Example 7 does not have enough alkali washing time, and does not generate enough K2CO3 on the surface, and the capacity retention rate is 83.2%.

[0082] Experimental data confirms that the uniform and dense spinel layer + K2CO3 protective layer achieved through optimized coating process can simultaneously improve the structural stability and interfacial chemical stability of the material, which is the key to achieving excellent cycle performance (>91.8% capacity retention) and rate performance.

[0083] In summary, the preparation method of the double-layer coated ternary positive electrode material for solid-state batteries provided by the present invention ensures the continuity of the interface lattice by directly coating the surface of the ternary positive electrode precursor with spinel powder, realizes the seamless interface coupling of the spinel phase and the layered phase by crystal structure matching design, and subsequently generates alkali metal carbonate on the surface to replace part of Li2CO3 by alkali washing, thereby improving the purity and chemical stability of the surface spinel phase, protecting the outer surface from the decomposition of the electrolyte in the high-pressure area, and effectively inhibiting the volume expansion and oxygen release of the ternary positive electrode material. The spinel and alkali metal carbonate double block the direct contact of the electrolyte. The obtained double-layer coated ternary positive electrode material for solid-state batteries has continuous Li + The transmission channel significantly improves the cycle performance, rate performance and thermal stability. This double-layer coated ternary cathode material for solid-state batteries can be widely used in the preparation of solid-state batteries.

[0084] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a double-layer coated ternary cathode material for solid-state batteries, characterized in that: It includes: A ternary positive electrode precursor containing nickel, cobalt and manganese, spinel powder and a first lithium salt are mixed and then pre-sintered and annealed in an oxygen atmosphere to obtain a lithium-rich spinel-coated ternary positive electrode material; The lithium-rich spinel-coated ternary positive electrode material is mixed with an alkaline solution and subjected to alkaline washing, solid-liquid separation and then drying to form a lithium-deficient spinel structure and an alkali metal carbonate protective layer on the surface of the lithium-rich spinel-coated ternary positive electrode material.

2. The method for preparing a double-layer coated ternary cathode material for a solid-state battery according to claim 1, characterized in that: The amount of spinel powder added is 0.1% to 3% of the mass of the ternary cathode precursor; And / or, the first lithium salt is added in an amount such that the molar ratio of the lithium element in the first lithium salt to the nickel, cobalt and manganese elements in the ternary positive electrode precursor is 1.01-1.

10.

3. The method for preparing a double-layer coated ternary cathode material for a solid-state battery according to claim 1, characterized in that: The pre-calcination temperature is 400-500°C and the time is 3-5h; And / or, the annealing temperature is 700-800° C. and the time is 6-10 h; And / or, after the annealing, the temperature is lowered to room temperature at a rate of 3-8°C / min.

4. The method for preparing a double-layer coated ternary cathode material for a solid-state battery according to claim 1, characterized in that: The preparation method of the spinel powder includes: mixing a nickel source, a manganese source and a second lithium salt to form a dispersion, grinding the dispersion to a particle size D50 of 0.2-1 μm in the slurry, then drying to obtain a spinel precursor, and sintering the spinel precursor to obtain the spinel powder.

5. The method for preparing a double-layer coated ternary cathode material for a solid-state battery according to claim 4, characterized in that: The general formula of the spinel powder is Li 1+x Ni 0.5-x Mn 1.5+x O4, wherein -0.2≤x≤0.2, the nickel source, the manganese source and the second lithium salt are mixed in a molar ratio of Li:(Ni+Mn)=0.4-0.6, and the solid-liquid ratio is 1kg:2-10L; And / or, the grinding includes sand grinding, and the sand grinding time is 0.5 to 5 hours; And / or, the drying comprises spray drying, the air flow rate of the spray drying is 4-6m 3 / h, outlet temperature 90~110℃, and spinel precursor of 0.5~1μm; And / or, the sintering temperature is 650-750° C. and the sintering time is 5-12 hours.

6. The method for preparing a double-layer coated ternary cathode material for a solid-state battery according to claim 4, characterized in that: The first lithium salt and the second lithium salt are independently selected from one or more of lithium sulfate, lithium nitrate, lithium acetate and lithium chloride; And / or, the nickel source is selected from one or more of nickel oxide, nickel hydroxide, nickel sulfate, nickel nitrate, nickel acetate and nickel chloride; And / or, the manganese source is selected from one or more of manganese oxide, manganese hydroxide, manganese sulfate, manganese nitrate, manganese acetate and manganese chloride.

7. The method for preparing a double-layer coated ternary cathode material for a solid-state battery according to claim 1, characterized in that: The alkaline solution includes at least one of potassium hydroxide and sodium hydroxide; And / or, the concentration of the alkaline solution is 0.01 mol / L~1 mol / L; the solid-liquid ratio of the lithium-rich spinel-coated ternary cathode material to the alkaline solution is 1 kg:1-10 L; And / or, the alkali washing time is 10-120min; And / or, the solid-liquid separation is suction filtration; And / or, the drying is vacuum drying, and the temperature of the vacuum drying is 80-120°C.

8. The method for preparing a double-layer coated ternary cathode material for a solid-state battery according to claim 1, characterized in that: The preparation method of the ternary positive electrode precursor includes a co-precipitation method, a sol-gel method, a hydrothermal method, a solvothermal method, a spray pyrolysis method or a solid phase method.

9. A double-layer coated ternary cathode material for solid-state batteries, characterized in that: It is prepared by the preparation method of the double-layer coated ternary positive electrode material for solid-state batteries according to any one of claims 1 to 8.

10. Use of the double-layer coated ternary cathode material for solid-state batteries according to claim 9 in the preparation of solid-state batteries.

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