Alumina coating and method of making and use thereof

Abstract

This invention relates to the field of battery materials technology, specifically to an alumina coating, its preparation method, and its application. The alumina coating includes a positive electrode coating slurry formed on the surface of a positive electrode and / or a negative electrode coating slurry formed on the surface of a negative electrode. The positive electrode coating slurry includes nano-alumina powder, a first solid electrolyte, a first film-forming aid, a first binder, a first dispersant, and a first solvent. The negative electrode coating slurry includes nano-alumina powder, a second solid electrolyte, a second film-forming aid, a second binder, a second dispersant, and a second solvent. The preparation method includes: providing positive / negative electrode sheets to be coated; preparing positive / negative electrode coating slurries of a preset viscosity; and applying the slurries to the electrode surface using an atomization spraying method to form an alumina coating. This invention significantly improves the adhesion between the coating and the electrode, interface uniformity, and ionic conductivity by combining differentiated positive and negative electrode formulations with a semi-dry atomization spraying process.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to an alumina coating, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in new energy vehicles, portable electronic devices, and power tools due to their superior performance, including high energy density, long cycle life, and low self-discharge rate. However, as the scale of lithium-ion battery applications continues to expand, their safety performance issues are becoming increasingly prominent. In particular, under extreme conditions such as internal short circuits, overcharging, and over-discharging, thermal runaway can easily occur, even leading to battery fires and explosions. Furthermore, traditional lithium-ion battery cathode materials, such as lithium cobalt oxide and lithium manganese oxide, while meeting high energy density requirements, often suffer from poor safety.

[0003] To improve the safety performance of lithium-ion batteries, researchers have explored various methods. One common approach is to coat the electrode surface with a functional coating. Alumina (Al₂O₃), an inorganic oxide with excellent thermal stability, chemical inertness, insulation, and mechanical strength, is widely used for surface modification of battery electrodes. Forming an alumina coating on the electrode surface can effectively enhance battery safety performance, such as inhibiting electrolyte decomposition, reducing lithium dendrite growth, improving electrode-electrolyte interface stability, and enhancing the electrode's thermal barrier properties at high temperatures. Furthermore, the alumina coating can improve electrode wettability and enhance the interfacial contact between the electrode and electrolyte, thereby optimizing the battery's rate performance.

[0004] However, despite the numerous advantages of alumina coatings, existing coating components and processes still face several technical bottlenecks that limit their large-scale application in high-end battery products. In traditional spraying processes, alumina is typically applied after rolling, resulting in weak adhesion between the coating and the active material layer. This makes the coating prone to peeling or detachment during battery charge-discharge cycles or mechanical vibrations, leading to increased interfacial impedance and even localized short circuits. Furthermore, existing spraying equipment has high requirements for the surface roughness and flatness of the electrode sheets, making it difficult to adapt to novel electrodes with high porosity, porous structures, or micron-level unevenness (such as 3D structure electrodes and fiber-reinforced electrodes), resulting in poor coating adhesion or incomplete coverage. Therefore, developing a novel alumina coating preparation method that overcomes these problems is of great significance for improving the safety and performance of lithium-ion batteries. Summary of the Invention

[0005] To address the problems in existing technologies, such as weak adhesion between the alumina coating and the electrode substrate, poor adaptability to electrode surface morphology, and difficulty in precisely controlling coating thickness and uniformity, this invention aims to provide an alumina coating, its preparation method, and its applications to solve these problems.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides an alumina coating, comprising a positive electrode coating slurry formed on the surface of a positive electrode sheet and a negative electrode coating slurry formed on the surface of a negative electrode sheet; The raw material components and weight parts of the positive electrode coating slurry include: nano alumina powder, first solid electrolyte, first film-forming aid, first binder, first dispersant, and first solvent; The raw material components and weight parts of the negative electrode coating slurry include: nano alumina powder, second solid electrolyte, second film-forming aid, second binder, second dispersant, and second solvent.

[0007] As a preferred embodiment of the present invention, the raw material components of the positive electrode coating slurry are as follows by weight: 20-50 parts of nano-alumina powder, 20-30 parts of the first solid electrolyte, 20-30 parts of the first film-forming aid, 0.2-1.5 parts of the first binder, 0.05-1 part of the first dispersant, and the solid content of the positive electrode coating slurry is 5-20%. The raw material components of the negative electrode coating slurry are as follows by weight: 20-50 parts of nano alumina powder, 20-30 parts of the second solid electrolyte, 20-30 parts of the second film-forming aid, 0.2-1.5 parts of the second binder, 0.05-1 part of the second dispersant, and the solid content of the negative electrode coating slurry is 5-20%.

[0008] As a preferred embodiment of the present invention, the positive electrode coating slurry has at least one of the following characteristics a1) to a7): a1) The particle size of the nano-alumina powder is 5-100 nm; a2) The first solid electrolyte includes one or more of lithium aluminum titanium phosphate powder (LATP), lithium lanthanum zirconium oxide (LLZO) powder, and lithium aluminum germanium phosphate (LAGP) powder, with a particle size of 100-200 nm. a3) The first film-forming aid includes one or more of lithium fluoride powder and lithium phosphate powder, with a particle size of 100-150 nm; a4) The first adhesive comprises polyvinylidene fluoride (PVDF); a5) The first dispersant includes one or more of polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP); a6) The first solvent includes N-methylpyrrolidone (NMP); a7) The dry film thickness of the positive electrode coating slurry is 0.1 to 1 μm.

[0009] As a preferred embodiment of the present invention, the negative electrode coating slurry has at least one of the following features b1) to b7): b1) The particle size of the nano-alumina powder is 5-100 nm; b2) The second solid electrolyte includes one or more of lithium lanthanum zirconium oxide (LLZO) powder and lithium superion conductor (LISICON) powder, with a particle size of 100-200 nm; b3) The second film-forming aid includes one or more of lithium fluoride powder and lithium phosphate powder, with a particle size of 100-150 nm; b4) The second adhesive includes one or more of carboxymethyl cellulose (CMC) and polyacrylic acid (PAA); b5) The second dispersant includes one or more of polyethylene glycol and polyvinylpyrrolidone; b6) The second solvent includes water; b7) The dry film thickness of the negative electrode coating slurry is 0.1 to 1 μm.

[0010] The nano-alumina powder has a particle size of 50–100 nm, exhibiting good dispersibility to prevent nozzle clogging and providing good mechanical support. The particle sizes of both the first and second solid electrolytes must be controlled below 200 nm to ensure ion conduction and coating continuity; excessively fine particles are prone to agglomeration, affecting conductivity. The particle sizes of the first and second film-forming agents (100–150 nm) are moderate, reducing agglomeration and preventing nozzle clogging.

[0011] Secondly, the present invention provides a method for preparing the aforementioned alumina coating, comprising the following steps: Provide the positive / negative electrode sheets to be coated; Prepare positive / negative electrode coating slurries with a preset viscosity, and apply the positive / negative electrode coating slurries to the surface of the positive / negative electrode sheets respectively to form an alumina coating.

[0012] As a preferred embodiment of the present invention, the preset viscosity of the positive / negative electrode coating slurry is 30000-100000 mPa·s.

[0013] As a preferred embodiment of the present invention, the step of applying the positive / negative electrode coating slurry to the positive / negative electrode sheet surface respectively specifically involves: using an atomizing spraying method to uniformly spray the positive / negative electrode coating slurry onto the positive / negative electrode sheet surface respectively.

[0014] As a preferred technical solution of the present invention, the atomized spraying is selected from air atomized spraying or ultrasonic atomized spraying. During the spraying process, the height of the nozzle from the surface of the positive / negative electrode is 10-20 mm, and the spraying speed is 0.01-5 L / min.

[0015] Thirdly, the present invention provides an electrode sheet comprising a positive / negative current collector, a positive / negative active material coating formed on the surface of the positive / negative current collector, and an alumina coating as described above formed on the surface of the positive / negative active material coating.

[0016] Fourthly, the present invention provides a lithium-ion battery, characterized in that it includes the electrode sheets as described above.

[0017] This invention addresses the industry pain points of existing alumina coatings, such as weak adhesion to electrodes, poor surface morphology adaptability, difficulty in controlling thickness uniformity, and limited functionality. Through two core technological innovations—a differentiated multifunctional composite slurry formulation for both positive and negative electrodes and a semi-dry atomized spraying preparation process—it achieves a comprehensive breakthrough in coating reliability, overall battery performance, and industrial applicability. The specific beneficial effects can be summarized as follows: 1. This invention pioneers a core process of atomized spraying when the positive / negative electrode coating slurry is not completely dry, but in a semi-dry state (slurry viscosity is 30,000–100,000 mPa·s). The slurry still possesses certain adhesion and fluidity. Combined with the binder components (PVDF for positive electrode, CMC for negative electrode) in the slurry system, the sprayed alumina coating can embed into the micropores and depressions on the surface of the active material layer, forming a mechanically interlocked and in-situ bonded structure. This solution is completely different from the traditional roll-pressing and spraying process, fundamentally solving the industry pain points of poor coating-substrate adhesion and easy peeling in traditional technologies. It significantly improves the coating-electrode interface bonding force, effectively avoiding the risk of increased interface impedance and localized short circuits caused by coating detachment during battery charge-discharge cycles and mechanical vibration, greatly improving the long-term reliability of the battery.

[0018] 2. This invention employs an air atomization / ultrasonic atomization spraying process, precisely controlling the nozzle distance from the electrode to the electrode at 10–20 mm and the spraying speed at 0.01–5 L / min. The atomized slurry particles are fine and uniformly distributed, eliminating the need for pretreatment such as grinding or leveling the electrode surface. It can directly adapt to and penetrate novel electrodes with high porosity, porous structures, and micron-level uneven surfaces (such as 3D structure electrodes and fiber-reinforced electrodes). This technology overcomes the stringent limitations of traditional coating / spraying processes on the flatness and roughness of the electrode surface, breaking the application barrier that traditional alumina coatings can only be applied to conventional flat electrodes, and significantly expanding the applicable scenarios of the technology.

[0019] 3. This invention precisely controls the viscosity of the positive and negative electrode coating slurry to 30,000–100,000 mPa·s, combined with refined process control of atomized spraying, to stably and accurately control the dry film thickness of the positive and negative electrode coatings within the range of 0.1–1 μm. The coatings achieve complete coverage and excellent areal density and thickness uniformity. This solution solves the problems of large coating thickness fluctuations and incomplete local coverage in traditional processes, ensuring stable coating function, significantly reducing the scrap rate in battery production, and achieving high consistency in battery cell performance, fully meeting the quality control requirements of large-scale mass production.

[0020] 4. This invention overcomes the limitations of traditional alumina coatings that only provide physical barrier function. Through differentiated composite slurry formulations for the positive and negative electrodes, a functionalized interface layer integrating thermal barrier, ion conduction, and interface stability is constructed, achieving synergistic optimization of battery performance. Dedicated solid electrolytes are matched to the positive and negative electrodes: lithium aluminum titanium phosphate (LATP) is added to the positive electrode, and lithium lanthanum zirconium oxide (LLZO) is added to the negative electrode. While retaining the core advantages of alumina's insulation and thermal barrier properties, this significantly improves the interfacial lithium-ion conductivity, substantially optimizes battery rate performance, and effectively suppresses lithium plating at the negative electrode. The introduction of film-forming aids such as lithium fluoride allows for the in-situ formation of an artificial SEI film on the electrode surface, effectively suppressing electrolyte side reactions and improving the battery's initial coulombic efficiency and long-term cycle stability. The synergistic effect of nano-alumina, solid electrolyte, and film-forming aids resolves the contradiction between improving safety and sacrificing electrochemical performance in traditional technologies, achieving simultaneous upgrades in battery safety, rate performance, and cycle life.

[0021] 5. This invention directly embeds the alumina coating spraying process into the conventional lithium battery coating process, eliminating the need for additional processes such as rolling, electrode surface pretreatment, and high-temperature sintering. It also eliminates the need for new large-scale specialized equipment and is highly compatible with existing lithium battery mass production lines. This solution significantly shortens battery production turnaround time, reduces energy consumption and equipment investment costs, while offering high process flexibility to adapt to the production of electrodes of different sizes and types. It demonstrates excellent feasibility for large-scale mass production and economic benefits, solving the problems of difficult industrialization and high costs associated with traditional modification processes.

[0022] 6. This invention fundamentally improves the safety performance of lithium-ion batteries through multi-dimensional technological synergy involving materials, interfaces, and structures: Nano-alumina itself possesses excellent thermal stability, chemical inertness, insulation, and mechanical strength. Combined with a complete composite coating with strong interfacial adhesion, it effectively suppresses the spread of thermal runaway and prevents direct contact between the positive and negative electrodes under extreme conditions such as internal short circuits, overcharge, and over-discharge. Simultaneously, it inhibits electrolyte decomposition and reduces lithium dendrite growth. This technology provides reliable electrode surface modification technology support for high-end lithium battery products with high energy density and high safety requirements, such as those used in new energy vehicles and energy storage systems, helping high-end lithium batteries achieve the core goals of intrinsic safety and long lifespan. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, these should not be construed as limiting the present invention and are merely examples.

[0024] Unless otherwise specified, the test methods or experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are obtained from conventional commercial sources or prepared by conventional methods.

[0025] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0026] Example 1 This embodiment provides a method for preparing an alumina coating on a positive electrode sheet, including: (1) Provide the positive electrode sheet to be coated.

[0027] (2) Prepare the positive electrode coating slurry by atomizing the slurry in a semi-dry state onto the surface of the positive electrode to form an alumina coating. During the spraying process, the nozzle is 15 mm above the surface of the positive electrode and the spraying speed is 2 L / min.

[0028] The raw material components of the positive electrode coating slurry are as follows by weight: 40 parts of nano alumina powder, 25 parts of LATP, 25 parts of LiF, 1 part of PVDF, 0.5 parts of PVP, and an appropriate amount of NMP is added and mixed evenly to make the viscosity of the positive electrode coating slurry 60000mPa·s.

[0029] Example 2 The difference between this embodiment and Embodiment 1 is that the raw material components of the positive electrode coating slurry, by weight, are: 30 parts of nano-alumina powder, 20 parts of LATP, 20 parts of Li3PO4, 1 part of PVDF, 0.5 parts of PEG, with an appropriate amount of NMP added and mixed evenly to achieve a viscosity of 50000 mPa·s for the positive electrode coating slurry. The rest is the same as in Embodiment 1.

[0030] Example 3 The difference between this embodiment and Embodiment 1 is that the raw material components of the positive electrode coating slurry, by weight, are: 50 parts of nano-alumina powder, 30 parts of LLZO, 30 parts of LiF, 1.5 parts of PVDF, and 1 part of PVP, with an appropriate amount of NMP added and mixed evenly to achieve a viscosity of 70000 mPa·s for the positive electrode coating slurry. The rest is the same as in Embodiment 1.

[0031] Example 4 The difference between this embodiment and Embodiment 1 is that the raw material components of the positive electrode coating slurry, by weight, are: 40 parts of nano-alumina powder, 25 parts of LAGP, 25 parts of LiF, 0.5 parts of PVDF, and 0.2 parts of PEG. An appropriate amount of NMP is added and mixed evenly to make the viscosity of the positive electrode coating slurry 65000 mPa·s. The rest is the same as in Embodiment 1.

[0032] Example 5 The difference between this embodiment and Embodiment 1 is that the raw material components of the positive electrode coating slurry, by weight, are: 40 parts of nano-alumina powder, 25 parts of LATP, 25 parts of Li3PO4, 1 part of PVDF, 0.5 parts of PVP, with an appropriate amount of NMP added and mixed evenly to achieve a viscosity of 80000 mPa·s for the positive electrode coating slurry. The rest is the same as in Embodiment 1.

[0033] Example 6 This embodiment provides a method for preparing an alumina coating on a negative electrode sheet, including: (1) Provide the negative electrode sheet to be coated.

[0034] (2) Prepare the negative electrode coating slurry by atomizing the slurry in a semi-dry state onto the surface of the negative electrode sheet to form an alumina coating. During the spraying process, the nozzle is 15 mm above the surface of the negative electrode sheet and the spraying speed is 2 L / min.

[0035] The raw material components of the negative electrode coating slurry are as follows by weight: 40 parts of nano alumina powder, 25 parts of LLZO, 25 parts of LiF, 1 part of CMC, 0.5 parts of PVP, and an appropriate amount of NMP is added and mixed evenly to make the viscosity of the negative electrode coating slurry 60000mPa·s.

[0036] Example 7 The difference between this embodiment and Embodiment 6 is that the raw material components of the negative electrode coating slurry, by weight, are: 30 parts of nano-alumina powder, 20 parts of LLZO, 20 parts of Li3PO4, 1 part of PAA, and 0.5 parts of PEG. An appropriate amount of NMP is added and mixed evenly to make the viscosity of the negative electrode coating slurry 50000 mPa·s. The rest is the same as in Embodiment 6.

[0037] Example 8 The difference between this embodiment and Embodiment 6 is that the raw material components of the negative electrode coating slurry, by weight, are: 50 parts of nano-alumina powder, Li 14 30 parts Zn(GeO4)4, 30 parts LiF, 1.5 parts CMC, 1 part PVP, and an appropriate amount of NMP were added and mixed evenly to make the viscosity of the negative electrode coating slurry 70000 mPa·s. The rest was the same as in Example 6.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that LATP powder is not added to the positive electrode coating slurry, while other conditions are the same as in Example 1.

[0039] Comparative Example 2 The difference between this comparative example and Example 1 is that LiF powder is not added to the positive electrode coating slurry, while other conditions are the same as in Example 1.

[0040] Comparative Example 3 The difference between this comparative example and Example 1 is that the viscosity of the positive electrode coating slurry is controlled to be only 10,000 mPa·s when spraying the slurry, while other conditions are the same as in Example 1.

[0041] Comparative Example 4 The difference between this comparative example and Example 1 is that the viscosity of the positive electrode coating slurry during spraying is 150,000 mPa·s, while other conditions are the same as in Example 1.

[0042] Comparative Example 5 The difference between this comparative example and Example 1 is that the coating method is a traditional coating method, in which the electrode is rolled and then coated with a coating layer on the surface, and then dried.

[0043] Experimental Example The combined conductivity and rate performance were demonstrated in the cycle life when tested with coin cells. The electrodes prepared in the examples and comparative examples were used as working electrodes and assembled into CR2032 type coin half cells for testing. The test results are shown in Table 1.

[0044] Battery Assembly: After being rolled, the electrode sheets are punched into working electrode sheets. Electrolyte Preparation: A 1.0 mol / L LiPF6 EC / DEC / EMC solution (volume ratio 1:1:1) containing 2% fluoroethylene carbonate. In an argon-filled glove box (water and oxygen content <0.1 ppm), assemble the following components in sequence: negative electrode shell, lithium sheet, Celgard 2400 separator, electrolyte, working electrode (coated side down), gasket, spring, and positive electrode shell, and seal with a sealing machine.

[0045] Coulomb efficiency test: At 25℃, the first charge and discharge test is performed at a rate of 0.1C within a voltage range of 2.5~3.65V. The capacity is recorded and the first coulomb efficiency and specific capacity are calculated.

[0046] Long-cycle performance (>500 cycles) testing: After activating the battery for 2 cycles at 0.1C rate, a constant current charge-discharge long-cycle test was conducted at 1C rate, with a voltage range of 2.5-3.65V. The discharge capacity was recorded, and the capacity retention rate at 500 cycles was calculated based on the discharge capacity of the second cycle.

[0047] The negative electrode detection voltage range is 0.001V-2V, and everything else is the same as the positive electrode.

[0048] Table 1 Based on the performance test data from Examples 1-8, Comparative Examples 1-5, and Table 1, the following conclusions can be drawn: 1. The positive electrode coating groups of Examples 1-5 exhibit a specific capacity of 159-163 mAh / g at 0.1C discharge, an initial coulombic efficiency of 96.0-96.6%, and a capacity retention rate of 82.0-86.2% after 500 cycles. The negative electrode coating groups of Examples 6-8 exhibit a specific capacity of 350-355 mAh / g at 0.1C discharge, an initial coulombic efficiency of 93.5-94.1%, and a capacity retention rate of 82.5-85.3% after 500 cycles. Taking the positive electrode as an example, the core performance indicators of Examples 1-5 are significantly better than those of the comparative examples, verifying that the technical solution of this invention has outstanding application effects on the modification of positive electrode sheets.

[0049] 2. Compared to Example 1, Comparative Example 1, without the addition of LATP solid electrolyte, showed a decrease in 0.1C discharge capacity to 158 mAh / g, an initial coulombic efficiency to 95.8%, and a significant reduction in capacity retention after 500 cycles to 77.0%. These results demonstrate that introducing a solid electrolyte compatible with the positive and negative electrode systems into the coating can significantly improve the lithium-ion conductivity at the coating interface and reduce interfacial impedance while retaining the core advantages of alumina's thermal barrier and insulation properties. This not only improves the battery's specific capacity and initial charge-discharge efficiency but also effectively mitigates interfacial degradation during cycling, greatly enhancing the battery's long-term cycle stability.

[0050] 3. Compared to Example 1, Comparative Example 2, without the addition of LiF film-forming aids, showed a decrease in initial coulombic efficiency to 95.9%, a capacity retention rate of only 79.5% after 500 cycles, and a significant decrease in discharge specific capacity. These results confirm that film-forming aids can form a stable artificial SEI film in situ on the electrode surface, effectively suppressing side reactions between the electrolyte and electrode active materials, reducing irreversible capacity loss during the first charge-discharge cycle, and preventing impedance increases caused by continuous interfacial film growth during cycling, thus significantly improving battery cycle life.

[0051] 4. Comparative Examples 3 and 4 had their slurry viscosities adjusted to 10,000 mPa·s and 150,000 mPa·s, respectively, both deviating from the preset viscosity range of the present invention. Although their discharge specific capacity and initial coulombic efficiency were only slightly different from Example 1, their capacity retention rates after 500 cycles were only 73.0% and 74.0%, respectively, far lower than the 86.2% of Example 1. This result indicates that when the viscosity is too low, the slurry has excessive fluidity, making it impossible to form a uniform and dense coating structure, which easily leads to problems such as sagging and uneven thickness; when the viscosity is too high, the slurry has poor atomization effect, making it unable to embed into the micropores on the electrode surface to form a mechanical interlocking structure, resulting in insufficient adhesion between the coating and the electrode, which easily leads to peeling and detachment during cycling, ultimately causing a significant decrease in the cycle stability of the battery.

[0052] 5. Comparative Example 5, employing a traditional roll-pressing followed by spraying process, exhibited the lowest 0.1C discharge specific capacity and initial coulombic efficiency among the positive electrode groups, with a capacity retention rate of only 65.0% after 500 cycles, significantly lower than all other example groups. This result fully demonstrates that the semi-dry atomized spraying process of the present invention enables the coating to form a mechanically interlocked and in-situ bonded structure with the active material layer of the electrode, greatly improving the interfacial adhesion between the coating and the electrode. This effectively avoids problems such as increased interfacial impedance and localized short circuits caused by coating detachment during battery charge-discharge cycles, and is crucial for achieving long-term stable battery cycling.

[0053] In summary, this invention, through the synergistic formulation design of nano-alumina, solid electrolyte, and film-forming aids, combined with the core process of semi-dry atomization spraying, effectively overcomes the technical bottlenecks of weak adhesion, poor ion conductivity, and insufficient interface stability of traditional alumina coatings. Simultaneously, it achieves a comprehensive improvement in the specific capacity, initial coulombic efficiency, and long cycle life of lithium-ion batteries, fully verifying the scientific nature, effectiveness, and large-scale industrial application value of the technical solution of this invention.

[0054] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An alumina coating, characterized in that, This includes a positive electrode coating slurry formed on the surface of the positive electrode sheet and / or a negative electrode coating slurry formed on the surface of the negative electrode sheet; The raw material components and weight parts of the positive electrode coating slurry include: nano alumina powder, first solid electrolyte, first film-forming aid, first binder, first dispersant, and first solvent; And / or, the raw material components and weight parts of the negative electrode coating slurry include: nano alumina powder, second solid electrolyte, second film-forming aid, second binder, second dispersant, and second solvent.

2. The alumina coating according to claim 1, characterized in that, The raw material components of the positive electrode coating slurry, by weight, are: 20-50 parts of nano-alumina powder, 20-30 parts of the first solid electrolyte, 20-30 parts of the first film-forming aid, 0.2-1.5 parts of the first binder, 0.05-1 part of the first dispersant, and the solid content of the positive electrode coating slurry is 5-20%. And / or, the raw material components of the negative electrode coating slurry are, by weight, 20-50 parts of nano alumina powder, 20-30 parts of the second solid electrolyte, 20-30 parts of the second film-forming aid, 0.2-1.5 parts of the second binder, 0.05-1 part of the second dispersant, and the solid content of the negative electrode coating slurry is 5-20%.

3. The alumina coating according to claim 1, characterized in that, The positive electrode coating slurry has at least one of the following characteristics a1) to a7): a1) The particle size of the nano-alumina powder is 5-100 nm; a2) The first solid electrolyte includes one or more of lithium titanium aluminum phosphate powder, lithium lanthanum zirconium oxide powder, and lithium aluminum germanium phosphate powder, with a particle size of 100-200 nm. a3) The first film-forming aid includes one or more of lithium fluoride powder and lithium phosphate powder, with a particle size of 100-150 nm; a4) The first adhesive comprises polyvinylidene fluoride; a5) The first dispersant includes one or more of polyethylene glycol and polyvinylpyrrolidone; a6) The first solvent includes N-methylpyrrolidone; a7) The dry film thickness of the positive electrode coating slurry is 0.1 to 1 μm.

4. The alumina coating according to claim 1, characterized in that, The negative electrode coating slurry has at least one of the following characteristics b1) to b7): b1) The particle size of the nano-alumina powder is 5-100 nm; b2) The second solid electrolyte includes one or more of lithium lanthanum zirconium oxide powder and lithium superion conductor powder, with a particle size of 100-200 nm. b3) The second film-forming aid includes one or more of lithium fluoride powder and lithium phosphate powder, with a particle size of 100-150 nm; b4) The second adhesive includes one or more of carboxymethyl cellulose and polyacrylic acid; b5) The second dispersant includes one or more of polyethylene glycol and polyvinylpyrrolidone; b6) The second solvent includes water; b7) The dry film thickness of the negative electrode coating slurry is 0.1 to 1 μm.

5. A method for preparing an alumina coating as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Provide the positive / negative electrode sheets to be coated; Prepare positive / negative electrode coating slurries with a preset viscosity, and apply the positive / negative electrode coating slurries to the surface of the positive / negative electrode sheets respectively to form an alumina coating.

6. The preparation method according to claim 5, characterized in that, The preset viscosity of the positive / negative electrode coating slurry is 30,000-100,000 mPa·s.

7. The preparation method according to claim 5, characterized in that, The step of applying the positive and negative electrode coating slurry to the positive and negative electrode sheet surfaces respectively is specifically: using an atomized spraying method, the positive and negative electrode coating slurry is uniformly sprayed onto the positive and negative electrode sheet surfaces respectively.

8. The preparation method according to claim 7, characterized in that, The atomized spraying is selected from air atomized spraying or ultrasonic atomized spraying. During the spraying process, the distance between the nozzle and the surface of the positive / negative electrode is 10-20 mm, and the spraying speed is 0.01-5 L / min.

9. An electrode sheet, characterized in that, It includes positive / negative current collectors, positive / negative active material coatings formed on the surface of the positive / negative current collectors, and an alumina coating as described in claim 1 formed on the surface of the positive / negative active material coating.

10. A lithium-ion battery, characterized in that, Including the electrode as described in claim 9.

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