A double-layer coated ternary positive electrode material for solid-state batteries and a preparation method and application thereof

Abstract

The application discloses a double-layer coated ternary positive electrode material for solid-state batteries and a preparation method and application thereof, and relates to the technical field of batteries. The method comprises the following steps: mixing a ternary positive electrode precursor containing nickel, cobalt and manganese, spinel powder and a first lithium salt, and then pre-burning and annealing in an oxygen atmosphere to obtain a lithium-rich spinel coated ternary positive electrode material; mixing the lithium-rich spinel coated ternary positive electrode material with an alkali solution to perform alkali washing, drying after solid-liquid separation, and forming 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. The double-layer coated ternary positive electrode material for solid-state batteries obtained by preparation has continuous Li + transport channels, and significantly improves the cycle performance, rate performance and thermal stability. The double-layer coated ternary positive electrode material for solid-state batteries can be widely applied in the preparation of solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a double-layer coated ternary cathode material for solid-state batteries, its preparation method, and its application. Background Technology

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

[0003] Solid-state batteries, with their high safety, energy density, and cycle stability due to solid-state electrolytes, have become a highly promising alternative. However, the key material for solid-state batteries—nickel-rich ternary cathodes—still faces industrialization challenges, such as high-temperature thermal runaway and Li... + / Ni 2+ Structural degradation caused by mixed electrode materials and capacity decay caused by interfacial side reactions severely impact the cycle life and rate performance of batteries. Therefore, improving the structural stability of cathode materials and suppressing interfacial side reactions have become key breakthroughs in promoting the development of solid-state battery technology.

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

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

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a double-layer coated ternary cathode material for solid-state batteries, comprising: A ternary cathode precursor containing nickel, cobalt, and manganese, spinel powder, and a first lithium salt were mixed and pre-calcined and annealed in an oxygen atmosphere to obtain a lithium-rich spinel-coated ternary cathode material. The lithium-rich spinel-coated ternary cathode material is mixed with an alkaline solution for alkaline washing, followed by solid-liquid separation and drying. This process forms a lithium-deficient spinel structure and an alkali metal carbonate protective layer on the surface of the lithium-rich spinel-coated ternary cathode material.

[0007] In an optional embodiment, 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 such a way that the molar ratio of lithium in the first lithium salt to nickel, cobalt and manganese in the ternary cathode precursor is 1.01-1.10.

[0008] In an optional embodiment, the pre-firing temperature is 400-500℃ and the time is 3-5 hours; And / or, the annealing temperature is 700-800℃ and the time is 6-10h; And / or, after annealing, the temperature is reduced 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 until the particle size D50 in the slurry is 0.2-1 μm, drying it 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 milling, the sand milling time being 0.5 to 5 hours; And / or, the drying includes spray drying, wherein the air flow rate of the spray drying is 4-6 m³ / h. 3 / h, with an outlet temperature of 90~110℃, a spinel precursor of 0.5~1μm is obtained; And / or, the sintering temperature is 650~750℃ and the time is 5~12h.

[0011] In an optional embodiment, the first lithium salt and the second lithium salt are each 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 to 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 vacuum filtration; And / or, the drying is vacuum drying, and the temperature of the vacuum drying is 80-120°C.

[0013] In optional embodiments, the preparation methods of the ternary cathode precursor include coprecipitation, sol-gel, hydrothermal, solvothermal, spray pyrolysis, or solid-phase methods.

[0014] Secondly, the present invention provides a double-layer coated ternary cathode material for solid-state batteries, which is prepared by the preparation method of double-layer coated ternary cathode material for solid-state batteries as described in any of the foregoing embodiments.

[0015] Thirdly, the present invention provides the application of the double-layer coated ternary cathode material for solid-state batteries as described in the foregoing embodiments in the preparation of solid-state batteries.

[0016] The present invention has the following beneficial effects: This invention provides a method for preparing a double-layered ternary cathode material for solid-state batteries. By directly coating spinel powder onto the surface of the ternary cathode precursor, interfacial lattice continuity is ensured. Seamless interfacial coupling between the spinel phase and the layered phase is achieved through crystal structure matching design. Subsequently, alkali washing generates alkali metal carbonates on the surface, replacing some of the Li₂CO₃, thus improving the purity and chemical stability of the surface spinel phase. This protects the outer surface from electrolyte decomposition under high-voltage conditions, effectively suppressing volume expansion and oxygen release of the ternary cathode material. The spinel and alkali metal carbonates provide a dual barrier, preventing direct contact between the spinel and the electrolyte. The resulting double-layered ternary cathode material for solid-state batteries exhibits continuous Li₂CO₃ lattice. + The improved transport channels significantly enhance cycle performance, rate performance, and thermal stability. This double-layer-coated ternary cathode material for solid-state batteries can be widely used in their fabrication. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 SEM image of the lithium-rich spinel-coated ternary cathode material provided in step (3) of Example 1 of this 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 this application; Figure 3 XPS-C, the lithium-rich spinel-coated ternary cathode material provided in step (4) of Embodiment 1 of this application. 1sImage (a) and XPS-C of NCM high-nickel cathode material with spinel and K2CO3 double coating after KOH treatment. 1s Map (b); Figure 4 This is a SEM image of the spinel-coated ternary cathode material provided in Comparative Example 2 of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] This invention provides a method for preparing a double-layer coated ternary cathode material for solid-state batteries, comprising: 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 then ground until the particle size D50 in the slurry is 0.2-1 μm. The dispersion is then dried to obtain a spinel precursor. The spinel precursor is then 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-liquid ratio of 1 kg: 2-10 L; 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 this invention, nickel source, manganese source, and a second lithium salt are used together as raw materials to prepare spinel powder. The method of first mixing the nickel source, manganese source, and second lithium salt to form a dispersion and then grinding it ensures the particle size and mixing uniformity of the slurry. This is in contrast to directly mixing the nickel source, manganese source, and second lithium salt in a solid state, which results in poor mixing uniformity. The grinding method includes, but is not limited to, sand milling and ball milling, as long as the particle size in the slurry can be ground to D50 = 0.2-1 μm. In some typical but non-limiting examples, sand milling is used, and the milling time is 0.5-5 hours.

[0024] In this invention, the ground slurry is dried. Various drying methods are available, including but not limited to spray drying, oven drying, and air drying, as long as the slurry can be dried. In some typical but non-limiting examples, spray drying is used to dry the slurry, with an air flow rate of 4-6 m³ / h. 3 At an outlet temperature of 90-110℃, a spinel precursor with a particle size of 0.5-1μm is obtained. Spray drying directly dries the atomized slurry into micron-sized spherical powder, eliminating the multi-step "precipitation-filtration-washing-drying" process of traditional co-precipitation methods. It can operate continuously for 24 hours, increasing production efficiency by over 30% (e.g., hourly throughput can reach tons). Compared to the long-duration high-temperature sintering of solid-state methods, spray drying reduces energy consumption by approximately 20%. The metal salt solution achieves atomic-level uniform mixing during atomization, avoiding the localized segregation problem of solid-state methods. Furthermore, the spinel precursor obtained by spray drying is spherical with a porous structure and more uniform particle size. In addition, the entire spray drying process is closed, allowing for N2 / Ar protection to prevent Ni²⁺ oxidation, and eliminates the need for washing steps, avoiding the introduction of Na⁺ and SO₄²⁻.

[0025] In this invention, the spinel precursor is sintered at a temperature of 650-750°C for 5-12 hours. Sintering allows for the pre-obtaining of spinel powder with low crystallinity, which, when annealed during subsequent coating, further improves the crystallinity of the spinel coating layer.

[0026] S2. Preparation of ternary cathode precursor.

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

[0028] There are various methods for preparing ternary cathode precursors. Any conventional process that can synthesize ternary cathode precursors is acceptable. For example, conventional synthesis methods such as coprecipitation, sol-gel, hydrothermal, solvothermal, spray pyrolysis, or solid-phase methods can all be used as methods for preparing ternary cathode precursors in this application. This invention does not impose any specific limitations on these methods.

[0029] S3. Preparation of lithium-rich spinel-coated ternary cathode material.

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

[0031] The amount of spinel powder added is 0.1% to 3% of the mass of the ternary cathode precursor; the amount of the first lithium salt added is based on a molar ratio of lithium in the first lithium salt to nickel, cobalt, and manganese in the ternary cathode precursor of 1.01-1.10. 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 this invention, the ternary cathode precursor, spinel powder, and first lithium salt are pre-mixed to introduce spinel powder at the precursor stage, rather than coating it onto the synthesized cathode material. In this invention, the mixture is pre-fired and annealed in an oxygen atmosphere to make the spinel powder and the matrix form a tighter bond, 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℃, and the time is 3-5 hours. 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, preventing material structural defects caused by rapid volatilization during the high-temperature stage. At a lower temperature, the lithium salt (such as LiOH or Li2CO3) begins to partially melt and react initially with the surface of the ternary cathode precursor, forming localized lithiation products, providing a uniform reaction basis for subsequent annealing. Pre-calcination achieves initial stabilization of the surface contact between the spinel powder and the ternary cathode precursor. Through preliminary solid-phase reaction, a progressive interface is formed between the spinel and the layered precursor, relieving interfacial stress, reducing lattice mismatch between the two phases, reducing the diffusion driving force of Mn at high temperatures, and thus inhibiting the transformation of surface spinel into a layered structure in an oxygen atmosphere. Oxygen can inhibit the reduction of transition metals (such as Ni²⁺ and Co³⁺) at low temperatures, maintaining their high valence states, while simultaneously promoting the valence stability of Mn in spinel (such as Mn³⁺ / Mn). 4 ⁺), to prevent the formation of oxygen vacancies.

[0034] The annealing temperature is 700-800℃, and the time is 6-10 hours. Annealing enables complete lithiation of the ternary precursor, forming a layered structure. Simultaneously, the spinel phase and the layered phase form a tightly bonded heterostructure through high-temperature solid-state diffusion. At high temperatures, spinel particles undergo atomic-level interdiffusion with the layered matrix, forming chemically bonded interfaces (e.g., spinel phase embedded in the grain boundaries of the layered phase), enhancing structural coherence and suppressing phase transformations and crack propagation during cycling. Annealing redistributes transition metals (Ni, Co, Mn) between the spinel and layered phases; for example, Mn migrates from the spinel to the surface of the layered phase, creating a gradient concentration, thereby suppressing Ni²⁺ cation mixing in the layered phase and improving structural stability. At high temperatures, oxygen maintains a high oxidation state, ensuring that the stoichiometry of oxidation in the material is close to the ideal value (e.g., reducing oxygen vacancies), while suppressing the Jahn-Teller distortion of Mn³⁺ in the spinel phase, improving cycling stability.

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

[0036] S4. Preparation of double-layer coated ternary cathode material for solid-state batteries.

[0037] The lithium-rich spinel-coated ternary cathode material is mixed with an alkaline solution for alkaline washing, followed by solid-liquid separation and drying. This process forms a lithium-deficient spinel structure and an alkali metal carbonate protective layer on the surface of the lithium-rich spinel-coated ternary cathode material.

[0038] 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 this invention does not include lithium salt solutions (e.g., lithium hydroxide), because this invention requires the use of an alkaline washing process to partially replace the Li₂ on the surface of the lithium-rich spinel-coated ternary cathode material with alkali metal elements from the alkaline solution. + However, lithium salt solutions cannot achieve the above objectives; therefore, the alkaline solution in this 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-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 min.

[0039] In this invention, the lithium-rich spinel-coated ternary cathode material is alkali-washed with an alkaline solution. The alkaline solution can wash away the residual alkali (such as LiOH, Li2CO3) left on the surface of the lithium-rich spinel-coated ternary cathode material during the annealing process, thereby forming a lithium-deficient spinel structure and enhancing the migration and storage capacity of Li+. The alkali metals in the alkaline solution will enter the surface of the lithium-rich spinel-coated ternary cathode material, that is, enter the spinel coating layer. Thus, the alkali metals (such as K and Na) in the alkaline solution will replace part of the Li in the spinel coating layer. Simultaneously, during the washing away of residual alkali, the alkaline solution reacts with carbon dioxide in the water to generate alkali metal carbonates. Taking KOH as an example, the reaction process is: 2KOH + CO2 → K2CO3 + H2O. The generated alkali metal carbonates can at least coat a portion of the surface of the lithium-rich spinel-coated ternary cathode material. By removing the adsorbed H2O molecules during the subsequent drying process and forming K2CO3 on the outer surface, the outer surface is protected from the chemical decomposition of electrolyte in the high-voltage zone by partially replacing Li2CO3 with K2CO3. It should be understood that the alkali metal carbonate protective layer in this invention means that the surface of the lithium-rich spinel-coated ternary cathode 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, vacuum filtration, and centrifugation, with vacuum filtration being the preferred method. There are also various drying methods, including but not limited to baking, air drying, or heating, with vacuum drying being the preferred method, wherein the temperature for vacuum drying is 80-120℃.

[0041] The solid-state battery double-layer coated ternary cathode material prepared by the above-described method features a lithium-rich spinel coating and an alkali metal carbonate protective layer, achieving interfacial lattice continuity, effectively suppressing NCM material volume expansion and oxygen release, and the double coating layer blocks direct contact with the electrolyte. The resulting material possesses continuous Li+ transport channels, significantly improving cycle performance, rate performance, and thermal stability.

[0042] The aforementioned double-layer coated ternary cathode 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 will be further described in detail below with reference to embodiments.

[0044] Example 1 This embodiment provides a method for preparing a double-layer coated ternary cathode material for solid-state batteries, which includes the following steps: Step (1): Mix nickel source (nickel oxide), manganese source (manganese tetroxide), and lithium salt (lithium carbonate) at a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.5. Add solvent water at a solid-liquid ratio of 1kg:5L. Grind the mixture until the particle size D50 in the slurry is approximately 0.2μm, then spray dry it at a gas flow rate of 5m³ / h. 3 / h, with an outlet temperature of 100℃, spinel precursors with a particle size of about 1μm were obtained; Step (2): The spinel precursor obtained in step (1) is sintered 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 co-precipitation method, spinel powder, and lithium salt are mixed at high speed. The amount of spinel powder added is 0.75 wt% of the mass of the ternary high-nickel precursor, and the amount of lithium salt added is based on the molar ratio of lithium element in the lithium salt to nickel, cobalt, and manganese in the ternary cathode precursor, Li:(Ni+Co+Mn)=1.05. Gradient sintering is carried out in an oxygen atmosphere; after pre-firing at 450℃ for 4 h, annealing is performed at 750℃ for 8 h, and finally cooling to room temperature at a rate of 5℃ / min, the lithium-rich spinel-coated ternary cathode material can be obtained. Figure 1 As shown, the sample has a smooth, impurity-free single-crystal structure, 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 to successfully construct a spinel coating layer with a smooth surface and uniform thickness (13nm).

[0045] Step (4): The cathode material obtained in step (3) is mixed with a diluted KOH solution (concentration of 0.5 mol / L) at a solid-liquid ratio of 1 kg: 5 L and stirred for 60 min. Then, it is washed with deionized water, filtered, and vacuum dried at 120 °C to obtain the NCM high-nickel cathode material with a spinel and K2CO3 double coating. Please refer to [link to relevant documentation]. Figure 3 The C=O bond peak in K₂CO₃ corresponds to a characteristic value of 288.6 eV, 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, becoming closer to the C=O peak of K₂CO₃. Simultaneously, the K₂CO₃ capping layer increases the proportion of the C=O peak from 23% to 37%, indicating an increase in surface carbonate content.

[0046] Example 2 This embodiment provides a method for preparing a double-layer coated ternary cathode material for solid-state batteries, which includes the following steps: Step (1): Mix nickel source (nickel oxide), manganese source (manganese tetroxide), and lithium salt (lithium carbonate) at a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.4. Add solvent water at a solid-liquid ratio of 1kg:2L. Grind the mixture until the particle size D50 in the slurry is approximately 0.5μm, then spray dry it at a gas flow rate of 4m³ / h. 3 / h, with an outlet temperature of 110℃, spinel precursors with a particle size of about 1μm were obtained; Step (2): The spinel precursor obtained in step (1) is sintered 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 co-precipitation method, spinel powder, and lithium salt are mixed at high speed. The amount of spinel powder added is 0.1 wt% of the mass of the ternary high-nickel precursor, and 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 cathode precursor, Li:(Ni+Co+Mn)=1.01. Gradient sintering is carried out in an oxygen atmosphere; after pre-firing at 400℃ for 5 h, it is annealed at 700℃ for 10 h, and finally cooled to room temperature at a rate of 3℃ / min to obtain the lithium-rich spinel-coated ternary cathode material.

[0047] Step (4): The cathode 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 min. Then, it is washed with deionized water, filtered, and dried under vacuum at 80 °C to obtain the NCM high-nickel cathode material with spinel and K2CO3 double coating layers.

[0048] Example 3 This embodiment provides a method for preparing a double-layer coated ternary cathode material for solid-state batteries, which includes the following steps: Step (1): Mix nickel source (nickel oxide), manganese source (manganese oxide), and lithium salt (lithium hydroxide) at a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.6. Add solvent water at a solid-liquid ratio of 1kg:10L. Grind the mixture until the particle size D50 in the slurry is approximately 1μm, then spray dry it at a gas flow rate of 6m³ / h. 3 / h, with an outlet temperature of 90℃, spinel precursors with a particle size of about 1μm were obtained; Step (2): The spinel precursor obtained in step (1) is sintered at 750°C for 6 hours to obtain spinel powder; Step (3): The ternary NCM high-nickel precursor (structural formula Ni0.9Mn0.05C0.05(OH)2) prepared by co-precipitation method, spinel powder, and lithium salt are mixed at high speed. 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 based on the molar ratio of lithium in the lithium salt to nickel, cobalt, and manganese in the ternary cathode precursor, Li:(Ni+Co+Mn)=1.10. Gradient sintering is carried out in an oxygen atmosphere; after pre-firing at 500℃ for 3h, it is annealed at 800℃ for 6h, and finally cooled to room temperature at a rate of 8℃ / min to obtain the lithium-rich spinel-coated ternary cathode material.

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

[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 cathode precursor, Li:(Ni+Co+Mn)=1.02.

[0051] Example 5 This embodiment is basically the same as that of embodiment 1, except 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℃ and the annealing time is 8h.

[0053] Example 7 This embodiment is basically the same as embodiment 1, except that in step (4) of this embodiment, the temperature of vacuum drying 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 1kg:10L.

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

[0056] Example 10 This embodiment is basically the same as embodiment 1, except that in step (4) of this embodiment, the stirring time for mixing the positive electrode material with the diluted KOH solution is 120 min.

[0057] Example 11 This embodiment is basically the same as embodiment 1, except that in step (3) of this embodiment, the cooling rate after annealing is 10℃ / min.

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

[0059] Comparative Example 1 This comparative example is basically the same as Example 1, the main difference being that the KOH treatment step is omitted in this comparative example, and a K2CO3 protective layer is not formed on the surface. The specific preparation method includes the following steps: Step (1): Nickel source (nickel oxide), manganese source (manganese tetroxide), and lithium salt (lithium carbonate) are mixed in a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.5. Solvent water is added at a solid-liquid ratio of 1kg:5L. The mixture is sand-milled until the particle size D50 in the slurry is about 0.2μm, and then spray-dried to obtain a spinel precursor with a particle size of about 1μm.

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

[0061] Comparative Example 2 This comparative example is basically the same as Example 1, the main difference being that spinel is coated on the surface of the NCM cathode material intermediate, rather than on the precursor. The specific preparation method includes the following steps: Step (1): Mix nickel source (nickel oxide), manganese source (manganese tetroxide), and lithium salt (lithium carbonate) at a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.5. Add solvent water at a solid-liquid ratio of 1kg:5L. Grind the mixture until the particle size D50 in the slurry is approximately 0.2μm, then spray dry it at a gas flow rate of 5m³ / h. 3 / h, outlet temperature 100℃, to obtain spinel precursor with a particle size of about 1μm; Step (2): sinter the spinel precursor obtained in step (1) at 600℃ for 12h to obtain spinel powder. Step (3): The ternary NCM high-nickel precursor and lithium salt are mixed at high speed with Li:(Ni+Co+Mn)=1.05, and sintered at high temperature for 750℃ / 8h in an oxygen atmosphere. After cooling to room temperature, the NCM cathode material can be obtained.

[0062] Step (4): The cathode material obtained in step (3) is mixed at high speed with the 0.75wt% spinel powder obtained in step (2).

[0063] Step (5): The product obtained in step (4) is subjected to a second high-temperature sintering at 800℃ / 4h. After cooling to room temperature, a ternary cathode material with a spinel coating is obtained.

[0064] Step (6): 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 1 kg: 5 L and stirred for 60 min. Then, it is washed with deionized water, filtered, and dried under vacuum at 120 °C to obtain the NCM high-nickel cathode material with spinel and K2CO3 double coating layers.

[0065] Comparative Example 3 This comparative example is basically the same as Example 1, the main difference being that an acid washing process is used in this comparative example instead of an alkaline washing process. The specific preparation method includes the following steps: Step (1): Mix nickel source (nickel oxide), manganese source (manganese tetroxide), and lithium salt (lithium carbonate) at a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.5. Add solvent water at a solid-liquid ratio of 1kg:5L. Grind the mixture until the particle size D50 in the slurry is approximately 0.2μm, then spray dry it at a gas flow rate of 5m³ / h. 3 / h, outlet temperature 100℃, to obtain spinel precursor with a particle size of about 1μm; Step (2): sinter the spinel precursor obtained in step (1) at 650℃ for 12h to obtain spinel powder. Step (3): The ternary NCM high-nickel precursor (structural formula Ni0.9Mn0.05C0.05(OH)2) prepared by co-precipitation method, spinel powder, and lithium salt are mixed at high speed. The amount of spinel powder added is 0.75 wt% of the mass of the ternary high-nickel precursor, and the amount of lithium salt added is based on the molar ratio of lithium element in the lithium salt to nickel, cobalt, and manganese in the ternary cathode precursor, Li:(Ni+Co+Mn)=1.05. Gradient sintering is carried out in an oxygen atmosphere; after pre-firing at 450℃ for 4 h, it is annealed at 750℃ for 8 h, and finally cooled to room temperature at a rate of 5℃ / min to obtain the lithium-rich spinel-coated ternary cathode material. Step (4): The cathode material obtained in step (3) is mixed with a diluted citric acid solution (concentration of 0.5 mol / L) at a solid-liquid ratio of 1 kg: 5 L and stirred for 60 min. Then, it is washed with deionized water, filtered, and dried under vacuum at 120 °C to obtain NCM high-nickel cathode material with spinel coating.

[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; that is, 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 high speed with Li:(Ni+Co+Mn)=1.05, and sintered at 750℃ for 8 hours in an oxygen atmosphere. After cooling to room temperature, the ternary high-nickel cathode material can be obtained.

[0067] Step (2): The ternary high-nickel cathode material obtained in step (1) is subjected to a second high-temperature sintering at 800℃ for 4 hours. After cooling to room temperature, the ternary high-nickel cathode material can be obtained.

[0068] Step (3): The cathode material obtained in step (3) is mixed with diluted KOH solution (concentration of 0.5 mol / L) at a solid-liquid ratio of 1 kg: 5 L and stirred for 60 min. Then, it is washed with deionized water, filtered, and dried under vacuum at 120 °C to obtain K2CO3-coated NCM high-nickel cathode 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 at a molar ratio of 1:2, add solvent water at a solid-liquid ratio of 1 kg: 5 L, mill until the particle size D50 in the slurry is about 0.2 μm, then spray dry with an air flow rate of 5 m³ / h. 3 / h, with an outlet temperature of 100℃, spinel precursors with a particle size of about 1μm were obtained; Step (2): The spinel precursor obtained in step (1) is sintered 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 co-precipitation method, spinel powder, and lithium salt are mixed at high speed. The amount of spinel powder added is 0.75 wt% of the mass of the ternary high-nickel precursor, and 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 cathode precursor, Li:(Ni+Co+Mn)=1.05. Gradient sintering is carried out in an oxygen atmosphere; after pre-firing at 450℃ for 4 h, it is annealed at 750℃ for 8 h, and finally cooled to room temperature at a rate of 5℃ / min to obtain the lithium-rich spinel-coated ternary cathode material.

[0070] 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 1 kg: 5 L and stirred for 60 min. Then, it is washed with deionized water, filtered, and dried under vacuum at 120 °C to obtain the NCM high-nickel cathode material with spinel and K2CO3 double coating.

[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): The ternary NCM high-nickel precursor (structure Ni0.9Mn0.05C0.05(OH)2) prepared by co-precipitation method, nickel source (nickel sulfate), manganese source (manganese sulfate), and lithium salt (lithium sulfate) were added according to the addition amount in Example 1. After mixing evenly, the mixture was heated and stirred to evaporate the solvent. After drying, spinel-coated ternary NCM high-nickel precursor was obtained. Then, gradient sintering was carried out in an oxygen atmosphere. After pre-firing at 450℃ for 4h, it was annealed at 750℃ for 8h. Finally, it was cooled to room temperature at a rate of 5℃ / min to obtain lithium-rich spinel-coated ternary cathode material.

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

[0073] Comparative Example 7 This comparative example is basically the same as Example 1, except that the alkaline washing time is different in this comparative example. The specific preparation method includes: Step (1): Mix nickel source (nickel oxide), manganese source (manganese tetroxide), and lithium salt (lithium carbonate) at a molar ratio of Ni:Mn=1:3 and Li:(Ni+Mn)=0.5. Add solvent water at a solid-liquid ratio of 1kg:5L. Grind the mixture until the particle size D50 in the slurry is approximately 0.2μm, then spray dry it at a gas flow rate of 5m³ / h. 3 / h, with an outlet temperature of 100℃, spinel precursors with a particle size of about 1μm were obtained; Step (2): The spinel precursor obtained in step (1) is sintered 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 co-precipitation method, spinel powder, and lithium salt are mixed at high speed. The amount of spinel powder added is 0.75 wt% of the mass of the ternary high-nickel precursor, and 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 cathode precursor, Li:(Ni+Co+Mn)=1.05. Gradient sintering is carried out in an oxygen atmosphere; after pre-firing at 450℃ for 4 h, it is annealed at 750℃ for 8 h, and finally cooled to room temperature at a rate of 5℃ / min to obtain the lithium-rich spinel-coated ternary cathode material.

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

[0075] Experimental Example Solid-state batteries were fabricated using the cathode materials obtained in Examples 1-12 and Comparative Examples 1-7.

[0076] The entire process was conducted inside a glove box: Weigh the positive electrode material, solid electrolyte, and conductive agent in a weight ratio of 70:27.5:25 and manually grind them for 30 minutes. Weigh 16-18 mg of this mixture. Weigh 100±0.5 mg of the solid electrolyte. Weigh indium powder and solid electrolyte in a weight ratio of 3:7 and grind for 30 minutes. Weigh 100±0.5 mg of this mixture as the indium anode intermediate layer. Add these materials separately to the mold battery cavity and assemble them with the lithium copper anode, compacting them firmly. Remove the mold battery from the glove box, connect the positive and negative wires, and begin testing. Measure the capacity retention after 100 charge / discharge cycles at a voltage of 2.6-4.3V.

[0077] Electrochemical performance was tested, and the test results are shown in Table 1.

[0078]

[0079] The performance comparison analysis between the examples and the embodiments shows that the uniformity and structural integrity of the spinel coating layer have a decisive influence on the electrochemical performance of the NCM cathode material.

[0080] The embodiments of the present invention, through epitaxial growth of a spinel layer + K2CO3 modified layer, have the following advantages: (1) low lattice mismatch, effectively alleviating volume expansion during charging and discharging; (2) forming continuous Li + The transmission channel ensures ionic conductivity; (3) it completely isolates the electrode from direct contact with the electrolyte, suppressing the dissolution of transition metals and the side reaction of electrolyte oxidation. Therefore, the initial discharge specific capacity of Examples 1-12 can reach more than 232.7 mAh / g, and the capacity retention rate after 100 cycles at 0.5C rate is more than 91.8%, which is significantly better than Comparative Examples 1-7.

[0081] In contrast, traditional coating processes have significant drawbacks: Comparative Example 1 lacks a KOH treatment step, failing to form a K2CO3 protective layer on the surface, resulting in a capacity retention rate of only 83.4%; Comparative Example 2's dry coating process forms island-like distributions (…). Figure 4The large-area exposure of the substrate in Comparative Example 3 resulted in a capacity retention rate of 86.4%. Comparative Example 4 involved a pickling process, which did not form a K2CO3 protective layer on the surface, resulting in a capacity retention rate of 82.7%. Comparative Example 4 involved direct contact between the NCM substrate and KOH. Due to the lack of a spinel layer, Li in the substrate detached, leading to increased residual lithium and a capacity retention rate of 88.3%. Comparative Example 5 used magnesium aluminum spinel coating, but lacked the alkali resistance of nickel manganese spinel, resulting in a slightly reduced capacity retention rate of 87.4%. Comparative Example 6 did not pre-form spinel powder; instead, it formed spinel coating by directly adding the raw material for spinel powder formation during mixing with the high-nickel NCM precursor. However, the spinel coating layer prepared by this method was not uniform and dense enough, resulting in a capacity retention rate of only 84.6%. Comparative Example 7 had insufficient alkali washing time, failing to generate enough K2CO3 on the surface, resulting in a capacity retention rate of 83.2%.

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

[0083] In summary, the method for preparing a double-layered ternary cathode material for solid-state batteries provided by this invention ensures interfacial lattice continuity by directly coating spinel powder onto the surface of the ternary cathode precursor. Seamless interfacial coupling between the spinel phase and the layered phase is achieved through crystal structure matching design. Subsequent alkaline washing generates alkali metal carbonates on the surface, replacing some of the Li₂CO₃, thus improving the purity and chemical stability of the surface spinel phase. This protects the outer surface from electrolyte decomposition under high-voltage conditions, effectively suppressing volume expansion and oxygen release of the ternary cathode material. The spinel and alkali metal carbonates provide a dual barrier against direct electrolyte contact. The resulting double-layered ternary cathode material for solid-state batteries exhibits continuous Li₂CO₃ lattice continuity. + The improved transport channels significantly enhance cycle performance, rate performance, and thermal stability. This double-layer-coated ternary cathode material for solid-state batteries can be widely used in their fabrication.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included 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 cathode precursor containing nickel, cobalt, and manganese, spinel powder, and a first lithium salt were mixed and pre-calcined and annealed in an oxygen atmosphere to obtain a lithium-rich spinel-coated ternary cathode material. 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 until the particle size D50 in the slurry is 0.2-1 μm; subsequently drying to obtain a spinel precursor; and sintering the spinel precursor to obtain the spinel powder; the general formula of the spinel powder is Li. 1+x Ni 0.5-x Mn 1.5+x O4, where -0.2 ≤ x ≤ 0.2; The lithium-rich spinel-coated ternary cathode material is mixed with an alkaline solution for alkaline washing. The alkaline solution includes at least one of potassium hydroxide and sodium hydroxide. The alkaline washing time is 10-120 minutes. After solid-liquid separation, the material is dried to form a lithium-deficient spinel structure and an alkali metal carbonate protective layer on the surface of the lithium-rich spinel-coated ternary cathode material.

2. The method for preparing a double-layer coated ternary cathode material for solid-state batteries 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 such a way that the molar ratio of lithium in the first lithium salt to nickel, cobalt and manganese in the ternary cathode precursor is 1.01-1.

10.

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

4. The method for preparing a double-layer coated ternary cathode material for solid-state batteries according to claim 1, characterized in that, The nickel source, the manganese source, and the second lithium salt are mixed at 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 milling, the sand milling time being 0.5 to 5 hours; And / or, the drying includes spray drying, wherein the air flow rate of the spray drying is 4-6 m³ / h. 3 / h, with an outlet temperature of 90~110℃, a spinel precursor of 0.5~1μm is obtained; And / or, the sintering temperature is 650~750℃ and the time is 5~12h.

5. The method for preparing a double-layer coated ternary cathode material for solid-state batteries according to claim 1, characterized in that, The first lithium salt and the second lithium salt are each 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.

6. The method for preparing a double-layer coated ternary cathode material for solid-state batteries according to claim 1, characterized in that, The concentration of the alkaline solution is 0.01 mol / L to 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 vacuum filtration; And / or, the drying is vacuum drying, and the temperature of the vacuum drying is 80-120℃.

7. The method for preparing a double-layer coated ternary cathode material for solid-state batteries according to claim 1, characterized in that, The preparation methods of the ternary cathode precursor include coprecipitation, sol-gel, solvothermal, spray pyrolysis, or solid-phase methods.

8. A double-layer coated ternary cathode material for solid-state batteries, characterized in that, It is prepared using the preparation method of the solid-state battery double-layer coated ternary cathode material as described in any one of claims 1-7.

9. The application of the double-layer coated ternary cathode material for solid-state batteries as described in claim 8 in the preparation of solid-state batteries.

Images