Preparation method and application of oxide-based ionic conductor coating material

Abstract

The invention provides a preparation method and application of an oxide-based ionic conductor coating material. The preparation method comprises the following steps: dispersing nano-scale oxide-based ion conductor particles in a liquid electrolyte solvent containing a lithium salt additive, inducing particle recrystallization at 120-150 DEG C and 1-3 MPa, and controlling the mass fraction of the micron-scale blocky structure to be 10-40%; adding polyamide acid and a nanoscale inorganic modified material, dispersing uniformly, and grinding; adding a dehydrating agent and a catalyst for thermal imidization; washing the product with pure water, and replacing the original solvent; and finally, adding an auxiliary agent to form the coating material, and coating the battery diaphragm with the coating material. According to the present invention, the solid electrolyte material is adopted as the diaphragm coating, and the ion transmission advantage of the liquid electrolyte is combined, such that the needling safety test and the low temperature cycle performance of the current secondary lithium battery are significantly improved, and the problems of low initial efficiency and poor lithium stability of the oxide electrolyte coating diaphragm are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin film preparation, and in particular relates to a preparation method and application of an oxide-based ion conductor coating material. Background Art

[0002] With the continuous growth of energy demand, lithium-ion batteries (Li-ion batteries) have attracted widespread attention as efficient and environmentally friendly energy storage devices. Battery separators, a key component of Li-ion batteries, must possess not only excellent mechanical properties and chemical stability but also good ionic conductivity. As the global energy structure shifts, Li-ion batteries, as one of the most mature energy storage technologies, are widely used in consumer electronics, electric vehicles, and large-scale energy storage. However, traditional liquid Li-ion batteries present safety risks and energy density bottlenecks.

[0003] The application of lithium-ion batteries (Li-ion batteries) continues to expand, but significant room for improvement remains in terms of energy density and safety. Improving Li-ion battery performance is inextricably linked to the development of the electrolyte materials used, which has evolved from traditional organic liquid electrolytes to hybrid solid-liquid electrolytes and finally to pure solid electrolytes. Li-ion batteries primarily utilize organic liquid electrolytes, and gel electrolytes play a role in improving battery safety. Hybrid solid-liquid electrolytes, as a compatible form of liquid and solid, combine the characteristics of both liquid and solid electrolytes and demonstrate significant application potential. All-solid-state batteries are considered a key direction for next-generation battery technology due to their high safety and energy density. As a core component of all-solid-state batteries, the performance of solid electrolytes directly impacts the overall performance of the battery. Solid-state electrolytes are primarily classified into four types: polymers, oxides, sulfides, and halides. Their high safety, high energy density, and long lifespan present new development opportunities for the next generation of Li-ion batteries. However, the path to industrialization of solid electrolyte materials remains challenging, facing high costs and the need for comprehensive production process upgrades. Currently, no true industrial implementation solution has been identified. Combining solid-state electrolytes with existing commercial separators to improve the performance of current secondary lithium batteries is a good solution.

[0004] The battery separator is a key component that affects battery performance. It needs to have good chemical stability, mechanical strength, and excellent ion conductivity. Commercial lithium-ion battery separators mostly use polyolefin microporous membranes (such as PE and PP), but their thermal stability is poor (melting point 130-165°C), which easily leads to short circuit risks. Existing technologies improve performance by coating the separator surface with ceramic materials such as Al2O3, but there are problems such as high hardness, large processing wear, and inability to suppress lithium dendrites. In addition, they only have the function of maintaining the dimensional stability of the separator at high temperatures and lack excellent electrochemical functions.

[0005] Oxide solid electrolyte materials (such as LATP and LLTO) have high ionic conductivity and thermal stability, but their direct use in all-solid-state batteries faces challenges such as high interfacial impedance and complex processes. NASICON-type ion conductors (represented by LATP) and LISICON-type ion conductors (represented by LAGP) can be used for aqueous system coating, but direct coating cannot form a uniform and effective solid interface film at the interface, and the material advantages cannot be brought into play. In addition, a large amount of Li+ will be consumed when the interface film is formed, resulting in a large decrease in the first efficiency of the battery, affecting battery performance. LATP-type solid electrolytes are unstable to lithium and cannot be directly applied to lithium metal negative electrode batteries. Garnet-type ion conductors (represented by LLZO) and perovskite-type ion conductors (represented by LLTO) are unstable to water and cannot be directly applied to aqueous coating systems.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of the present invention is to provide a preparation method and application of an oxide-based ion conductor coating material. By using a solid electrolyte material as a diaphragm coating and combining it with the ion transport advantages of a liquid electrolyte, the current secondary lithium battery needle puncture safety test and low-temperature cycle performance are significantly improved. At the same time, the problems of low initial efficiency and poor lithium stability of oxide electrolyte coated diaphragms are solved.

[0008] In order to achieve the above objectives, the present invention particularly adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing an oxide-based ion conductor coating material, comprising the following steps:

[0010] S1: Nano-sized oxide-based ion conductor particles are dispersed in a liquid electrolyte solvent containing a lithium salt additive. The solution is placed in a low-pressure reactor and induced to recrystallize at 120-150°C and 1-3 MPa. The crystallization time is controlled to 2-4 hours and the cooling rate is 2-15°C / min, forming a micron-sized block structure. By controlling the crystallization time and cooling rate, the grain boundary density and ion transport channels are optimized, the grain boundary resistance is reduced, and the lithium ion diffusion coefficient is improved.

[0011] Optionally, the nano-scale oxide-based ion conductor includes one or more of garnet-type, NASICON-type, LISICON-type, and perovskite-type oxide ion conductors.

[0012] Optionally, the liquid electrolyte solvent includes one or more of low alkyl ether, nitrile, pyridine, ester, ketone or alcohol.

[0013] Optionally, the lithium salt additive includes one or more of lithium trifluoromethanesulfinate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium difluorooxalatoborate (LiDFOB), lithium difluorophosphate (LiDFP / LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDODFP), lithium tetrafluoroborate (LiBF4), lithium bis(oxalatoborate) (LiBOB), lithium trifluoromethanesulfonate (LiCF3SO3), lithium hexafluorophosphate (LiPF6) or polymer lithium.

[0014] Preferably, the solid content of the liquid electrolyte solvent containing the lithium salt additive is 2-10%.

[0015] Furthermore, the ratio of the nano-scale oxide-based ion conductor particles to the total mass of the liquid electrolyte solvent containing the lithium salt additive is 10-80%.

[0016] S2: adding electrolyte solvent to the product of step S1, and controlling the mass fraction of the micron-sized block structure to be 10-40%.

[0017] S3: Add polyamic acid (PAA) and nano-scale inorganic modified materials to the product of step S2, disperse them evenly, and grind them.

[0018] Furthermore, the added amount of the polyamic acid accounts for 1-10% by mass of the product of step S2.

[0019] Optionally, the nano inorganic modifying material comprises one or more of MoS2, boron nitride, barium titanate, aluminum oxide or boehmite. Furthermore, the amount of the nano inorganic modifying material added is 0.5-55% by mass of the product of step S2.

[0020] Preferably, the particle size Dv50 of the nano-inorganic modified material is 0.01-0.5 μm; further, after the grinding, the particle size Dv50 of the product of step S3 is controlled to be 0.1-1 μm.

[0021] S4: adding a dehydrating agent and a catalyst to the product of step S3 for thermal imidization.

[0022] Optionally, the dehydrating agent includes acetic anhydride; and the catalyst includes pyridine.

[0023] Furthermore, the molar ratio of the polyamic acid, the dehydrating agent and the catalyst is 1:(2-8):(1-3); preferably 1:4:2.

[0024] Furthermore, the thermal imidization comprises stirring the reaction at room temperature for 2-4 hours, and then gradually raising the temperature to 50-80° C. and continuing the reaction for 1-2 hours.

[0025] The lithium salt and electrolyte solvent system used in the grain boundary modification process can shorten the reaction time and reduce the difficulty of imidization of PAA materials during the imidization stage. This is a first discovered and implemented in the industry. Step S1 not only modifies the grain boundaries of the ionic conductor, but the residual solvent system also significantly increases the imidization reaction rate during this step by enhancing solubility, catalyzing dehydration ring closure, promoting water removal, and synergistic heating. This reduces the reaction temperature by over 40% and increases the reaction rate by over 50%, shortening the reaction time from the traditional 3-4 hours to as little as 0.5-1.5 hours, thus resolving the difficulties of the imidization process.

[0026] After imidization, the unique coating layer combines the performance advantages of nano-inorganic modified materials. It not only provides flexibility and fatigue resistance, but also buffers the volume expansion of the ion conductor and prevents thermal expansion from causing electrical performance degradation. It also provides the hardness of inorganic particles, forming a physical barrier to prevent lithium dendrites from penetrating the electrolyte and reducing the risk of short circuits. By coating oxide-based ion conductors, the interface stability is significantly improved, resolving the interface issues commonly found in oxide-based ion conductors.

[0027] At the same time, through the coating of multiple materials, the microstructure of the coating layer is regulated, so that the coating layer has an extremely microscopic nano-scale porous design, which can minimize the obstruction to lithium ion migration while ensuring interface protection.

[0028] The coating layer combined with inorganic particles such as MoS2 after imidization can also effectively reduce the occurrence of side reactions of ion conductor materials in the battery system. The unique coating layer combined with the two-phase materials can guide lithium ions to diffuse along a specific path, promote uniform deposition, and avoid dendrite growth caused by local current concentration.

[0029] S5: Wash the product of step S4 with pure water to replace the original solvent.

[0030] Furthermore, the replacement of the original solvent controls the residual original solvent to be less than 1%.

[0031] Furthermore, the solid content of the final product in step S5 is controlled to be 5-55%.

[0032] S6: Adding an auxiliary agent to the product of step S5 to form the coating material.

[0033] Optionally, the auxiliary agent includes one or more of an anti-settling agent, a dispersant, an adhesive or a wetting agent.

[0034] Preferably, after adding the auxiliary agent, dispersion is carried out by sand milling and / or stirring.

[0035] Optionally, the anti-settling agent includes one or more of CMC, CMC-Li, polyethylene glycol, polyvinyl alcohol or polyethylene oxide; further, the amount of the anti-settling agent added accounts for 0.2-8% by mass of the product of step S5.

[0036] Optionally, the dispersant includes one or more of anionic dispersants, nonionic dispersants, cationic dispersants or polymeric dispersants; further, the added amount of the dispersant accounts for 0.5-6% by mass of the product of step S5.

[0037] Optionally, the adhesive includes one or more of an emulsion-type acrylate-based polymer, a solution-type acrylate-based polymer, a polyurethane polymer, a polyacrylamide polymer, a polyimide polymer or a polyamide polymer; further, the amount of the adhesive added accounts for 1-20% by mass of the product of step S5.

[0038] Optionally, the wetting agent includes one or more of an organosilicon-modified wetting agent, a polyether wetting agent, an acetylene alcohol wetting agent or an alcohol wetting agent; further, the amount of the wetting agent added accounts for 0.05-5% by mass of the product of step S5.

[0039] In a second aspect, the present invention further provides a battery separator coated with the oxide-based ion conductor coating material obtained by the preparation method.

[0040] The coating material can also be directly coated on the outside of the positive and negative electrode sheets.

[0041] Optionally, the battery separator can be a wet-process polyolefin porous membrane, a dry-process polyolefin porous membrane, a spun composite porous membrane, a non-woven porous membrane, or the like.

[0042] Optionally, the coating method can be any of micro-concave roller coating, anilox roller coating, spray coating, dot coating, dip coating, slot coating, screw extrusion coating, etc. After coating, the product is dried, rolled, and cut into pieces. During the drying process, the oven temperature is preferably in the range of 40-90°C.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) Reduce grain boundary resistance and improve ionic conductivity through grain boundary modification. Lithium salt penetrates into the grain boundary region of oxide-based ion conductor particles, fills the pores and defects at the grain boundaries, and forms a continuous and dense grain boundary network. Promote close contact between particles and reduce grain boundary resistance (can be reduced by 30%-50%). At the same time, when the electrolyte membrane is formed at the negative electrode, the consumption of free Li in the electrolyte can be reduced, and the first efficiency of the battery can be improved by more than 10% (the first efficiency of the untreated oxide-based ion conductor coated membrane battery is greatly reduced, at the level of 80-85%, and the first efficiency of the present invention can reach more than 95%).

[0045] A lithium-rich layer is formed at the grain boundary, and a low-energy-barrier ion transmission channel is constructed at the grain boundary, which reduces the activation energy of lithium ions crossing the grain boundary and increases the ion conductivity by more than double. The ion conductivity of the diaphragm product of the present invention can reach the level of (1-9)*10-3S / cm.

[0046] (2) Further optimize the interfacial impedance and improve the ionic conductivity through multi-component coating. A specific polymer-inorganic multi-component coating layer design is used to improve the interfacial impedance between oxide ion conductor particles.

[0047] (3) Multi-element coating improves the environmental and electrochemical stability of oxide-based ion conductors, and various types of oxide-based ion conductors can be applied to water-based coating systems. At the same time, the improvement of structural stability and electrochemical stability brings about improvements in safety and cycle performance. Using the diaphragm product or coating product of the present invention, the hot needle puncture temperature is increased to above 200°C; the cycle stability is improved by more than 90%, and the capacity is maintained at more than 85% after 500 cycles; the low-temperature cycle performance is improved by more than 80%, and the overall battery life is increased by 1.5 times.

[0048] This invention utilizes grain boundary modification and multi-material co-coating for oxide-based ion conductors to enhance the stability of oxides in both conventional and electrochemical environments, resolving existing challenges in the application of oxide-based ion conductor materials in aqueous coating systems. The separators described herein are widely applicable to high-energy-density lithium-ion batteries (such as power batteries and energy storage batteries), particularly those with metallic lithium anodes or high-nickel ternary cathodes, significantly improving safety and cycle life. DETAILED DESCRIPTION

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0050] It should be noted that the raw materials used in the present invention are all commercially available products. Any ratios not specified in the present invention may be any ratio. The units of the ratios not specified in the present invention are all mass ratios. Any technical details not specified in the present invention are all prior art.

[0051] The performance testing methods in the embodiments and comparative examples are as follows:

[0052] (1) Cycle performance: The test condition is 3.8-4.0V cycle 1500 times capacity retention rate; the test method is to use a charge and discharge cycle tester at room temperature, charge and discharge the battery for 50 and 500 cycles at 3.8-4.0V voltage conditions, and record its capacity retention rate.

[0053] (2) Low-temperature discharge performance: The evaluation parameter is the -10°C 1C capacity retention rate. The test method is to place the battery in a specific low-temperature environment and cool it to -20°C. Then, use a charge and discharge cycle tester to discharge the battery at a constant current of 1C and record its capacity retention rate.

[0054] (3) Extrusion safety test: A semi-cylinder with a radius of 75 mm is pressed perpendicularly to the battery cell plate at a speed of no more than 2 mm / s. Extrusion is stopped when the voltage reaches 0 V, the deformation reaches 15%, or the extrusion force reaches 100 kN or 1000 times the mass of the test object (if any of these conditions are met, the requirements are met and extrusion can be stopped). Maintain the current position for 10 minutes. After completing the above test, observe at the test environment temperature for 1 hour. The battery is required not to catch fire or explode.

[0055] Example 1

[0056] (1) LATP particles with a 200 nm gradient of Dv50 were dispersed in a liquid electrolyte solvent containing LiPF6 (the electrolyte was ethylene carbonate and dimethyl carbonate in a ratio of 1:1, the LiPF6 solid content was 4.2%, and LATP accounted for 60% of the total system mass). The particles were induced to recrystallize at 130°C and 1.8 MPa pressure to form a micron-sized block structure. The crystallization time was controlled to 4 hours and the cooling rate was 4°C / min.

[0057] (2) The corresponding electrolyte solvent (the electrolyte is ethylene carbonate and dimethyl carbonate in a ratio of 1:1) is added to the product obtained in step (1), and the mass fraction of the modified nano-oxide micron-sized block structure is controlled to be 32%.

[0058] (3) To the product obtained in step (2), 6% by mass of polyamic acid (PAA) and 4% by mass of MoS2 with a Dv50 of 40 nm were added in sequence while stirring, and the mixture was dispersed by high-speed stirring and ground using a sand mill to obtain a final product particle size Dv50 of 0.2 μm.

[0059] (4) Acetic anhydride and pyridine were added to the dispersion slurry of step (3) in sequence, with a molar ratio of PAA repeating unit: Ac2O:Py=1:4:2, and the mixture was stirred at room temperature for 2.5 hours, and then the temperature was gradually increased to 70°C and the reaction was continued for 2 hours.

[0060] (5) The product of step (4) is washed with pure water, the solvent is replaced until the solvent residue is less than 1%, and the solid content of the final product aqueous dispersion is controlled to be 20%.

[0061] (6) 0.4% by mass of CMC-Li, 0.6% by mass of polyacrylic acid amine dispersant, and 2% by mass of methyl methacrylate and ethyl methacrylate copolymer water emulsion type rubber (methyl methacrylate and ethyl methacrylate polymerization molar ratio of 65:35) were added to the slurry obtained in step (5) in sequence, and stirred and dispersed for 2 hours to form a coating slurry.

[0062] The coating slurry was applied to a 9µm thick PE base film, dried at 80°C, rolled, and slit to produce a coated separator with a double-sided coating thickness of 1µm. The separators were then assembled into full batteries, and both separator and electrical properties were tested.

[0063] The final separator shrinks by 1.2% in TD and 1.2% in MD at 130°C. The separator also exhibits an AC impedance of 1.1Ω and an ionic conductivity of 4.25ms / cm. The material interface impedance is 980Ω. After assembly, the battery exhibits an initial cycle efficiency of 95%, a capacity retention rate of 90% after 50 cycles, and a capacity retention rate of 86% after 500 cycles. The low-temperature discharge capacity retention rate at -10°C is 90%, and the extrusion safety test pass rate is 100%.

[0064] Example 2

[0065] (1) LLZO particles with a Dv50 gradient of 400 nm were dispersed in a liquid electrolyte solvent containing LiTFSI (the electrolyte was dimethyl carbonate, the solid content of LiTFSI was 2.0%, and LLZO accounted for 55% of the total system mass). The particles were induced to recrystallize at 140°C and 2.8 MPa pressure to form a micron-sized block structure. The crystallization time was controlled to 4 hours and the cooling rate was 3°C / min.

[0066] (2) The corresponding electrolyte solvent (the electrolyte is dimethyl carbonate) is added to the product obtained in step (1) to control the mass fraction of the modified nano-oxide micron-sized block structure to 20%.

[0067] (3) 8% by mass of polyamic acid (PAA) and 10% by mass of γ-crystalline alumina with a Dv50 of 10 nm were sequentially added to the product obtained in step (2) while stirring, and the mixture was dispersed by high-speed stirring and ground using a sand mill. The final product had a particle size Dv50 of 0.5 μm.

[0068] (4) Acetic anhydride and pyridine were added to the dispersion slurry of step (3) in sequence, with a molar ratio of PAA repeating unit: Ac2O:Py=1:4:2, and the mixture was stirred at room temperature for 2 hours, and then the temperature was gradually increased to 80°C and the reaction was continued for 1.5 hours.

[0069] (5) The product of step (4) is washed with pure water, the solvent is replaced until the solvent residue is less than 1%, and the solid content of the final product aqueous dispersion is controlled to be 18%.

[0070] (6) 0.3% by mass of CMC-Li, 0.8% by mass of polyacrylic acid amine dispersant, and 4% by mass of methyl methacrylate and ethyl methacrylate copolymer water emulsion type rubber (methyl methacrylate and ethyl methacrylate polymerization molar ratio of 65:35) were added to the slurry obtained in step (5) in sequence, and stirred and dispersed for 2 hours to form a coating slurry.

[0071] The coating slurry was applied to a 9µm thick PE base film, dried at 80°C, rolled, and slit to produce a coated separator with a double-sided coating thickness of 1µm. The separators were then assembled into full batteries, and both separator and electrical properties were tested.

[0072] The final separator shrinks by 2.2% in TD and 2.6% in MD at 130°C. The separator has an AC impedance of 0.8Ω and an ionic conductivity of 7.67ms / cm. The material interface impedance is 690Ω. After assembly, the battery exhibits an initial cycle efficiency of 92%, a capacity retention rate of 88% after 50 cycles, and a capacity retention rate of 86% after 500 cycles. The low-temperature discharge capacity retention rate at -10°C is 78%, and the extrusion safety test pass rate is 100%.

[0073] Example 3

[0074] (1) LATP particles with a 200 nm gradient of Dv50 were dispersed in a liquid electrolyte solvent containing LiTFSI (the electrolyte was dimethyl carbonate, the solid content of LiTFSI was 2.0%, and LATP accounted for 60% of the total system mass). The particles were induced to recrystallize at 135°C and 2.5 MPa pressure to form a micron-sized block structure. The crystallization time was controlled to 3 hours and the cooling rate was 5°C / min.

[0075] (2) The corresponding electrolyte solvent (the electrolyte is dimethyl carbonate) is added to the product obtained in step (1) to control the mass fraction of the modified nano-oxide micron-sized block structure to be 25%.

[0076] (3) To the product obtained in step (2), 5% by mass of polyamic acid (PAA) and 12% by mass of MoS2 with a Dv50 of 10 nm were added in sequence while stirring, and the mixture was dispersed by high-speed stirring and ground using a sand mill. The final product had a particle size Dv50 of 0.5 μm.

[0077] (4) Acetic anhydride and pyridine were added to the dispersion slurry of step (3) in sequence, with a molar ratio of PAA repeating unit: Ac2O:Py=1:4:2, and the mixture was stirred at room temperature for 4 hours, and then the temperature was gradually increased to 75°C and the reaction was continued for 2 hours.

[0078] (5) The product of step (4) is washed with pure water, the solvent is replaced until the solvent residue is less than 1%, and the solid content of the final product aqueous dispersion is controlled to be 25%.

[0079] (6) 0.5% by mass of CMC-Li, 1% by mass of polyacrylic acid amine dispersant, and 5% by mass of methyl methacrylate and ethyl methacrylate copolymer aqueous emulsion type rubber (methyl methacrylate and ethyl methacrylate polymerization molar ratio of 65:35) were added to the slurry obtained in step (5) in sequence, and stirred and dispersed for 2 hours to form a coating slurry.

[0080] The coating slurry was applied to a 9µm thick PE base film, dried at 80°C, rolled, and slit to produce a coated separator with a double-sided coating thickness of 1µm. The separators were then assembled into full batteries, and both separator and electrical properties were tested.

[0081] The final separator exhibited thermal shrinkage of 1.8% in TD and 1.8% in MD at 130°C. The separator also exhibited an AC impedance of 0.9Ω and an ionic conductivity of 6.53ms / cm. The material interface impedance was 720Ω. After assembly, the battery demonstrated an initial cycle efficiency of 94%, a capacity retention of 87% after 50 cycles, and an 84% capacity retention after 500 cycles. The low-temperature discharge capacity retention at -10°C was 80%, and the extrusion safety test passed 100%.

[0082] Comparative Example 1

[0083] Use 9um thick PE base film and apply conventional aluminum oxide coating.

[0084] The separator shrinks by 1.2% in TD and 2.3% in MD at 130°C. Its AC impedance is 11.4Ω, and its ionic conductivity is 0.099ms / cm. The material interface impedance is 3980Ω. After assembly, the battery exhibits an initial cycle efficiency of 89%, a capacity retention rate of 78.4% after 50 cycles, and a capacity retention rate of 69% after 500 cycles. The low-temperature discharge capacity retention rate at -10°C is 46%, and the extrusion safety test pass rate is 70%.

[0085] Comparative Example 2

[0086] Use 9um thick PE base film and apply ordinary LATP coating.

[0087] The separator shrinks by 4.2% in TD and 5.3% in MD at 130°C. Its AC impedance is 1.4Ω, and its ionic conductivity is 1.25ms / cm. The material interface impedance is 1180Ω. After assembly, the battery exhibits an initial cycle efficiency of 82%, a capacity retention rate of 79.4% after 50 cycles, and a capacity retention rate of 72% after 500 cycles. The low-temperature discharge capacity retention rate at -10°C is 72%, and the extrusion safety test pass rate is 85%.

[0088] Comparative Example 3

[0089] The difference from Example 1 is that Dv50 LATP particles with a gradient of 200 nm are directly dispersed in a liquid electrolyte solvent (the electrolyte is ethylene carbonate and dimethyl carbonate in a ratio of 1:1, and LATP accounts for 60% of the total system mass), and the mass fraction of the modified nano-oxide micron-sized block structure is controlled to be 32%. Steps (3) to (6) are then performed. In step (4), acetic anhydride and pyridine are sequentially added to the dispersion slurry of step (3) in a molar ratio of PAA repeating unit: Ac2O:Py=1:4:2. However, the imidization time and temperature need to be increased to maintain the normal progress of the imidization process. The reaction is stirred at room temperature for 5 hours, and the temperature is gradually increased to 90°C and the reaction is continued for 5 hours before use. The reaction temperature and reaction time are increased, but the degree of imidization is indeed lower than that of Example 1.

[0090] The degree of imidization can be tested by infrared spectroscopy (FTIR) by comparing the characteristic peak ratio of the imide ring (1780 cm -1 C=O symmetrical expansion and contraction, 1380cm -1 CN stretching) and benzene ring reference peak (1500cm -1 The imidization degree of Example 1 can reach 96-99%, while the imidization degree of Comparative Example 3 can only reach 90-94% under the conditions of increased temperature and time.

[0091] The separator's thermal shrinkage at 130°C was 3.2% (TD) and 5.1% (MD). The separator's AC impedance was 1.6Ω, and its ionic conductivity was 2.93ms / cm. The material interface impedance was 1200Ω. After assembly, the battery's initial cycle efficiency was 89%, its capacity retention after 50 cycles was 82%, and its capacity retention after 500 cycles was 74%. Its low-temperature discharge capacity retention at -10°C was 80%, and its extrusion safety test pass rate was 85%.

[0092] It can be seen that compared with the conventional alumina coating in Comparative Example 1, the present invention has the heat resistance of the alumina coating; at the same time, due to the unique oxide-based ion conductor coating design, the ion conductivity of the diaphragm is significantly improved; and a unique electrolyte membrane is constructed at the interface between the diaphragm and the electrode, which has obvious improvement effects in cycling, low-temperature cycling stability, and extrusion safety testing.

[0093] Compared with the ordinary LATP coating in Comparative Example 2, the present invention has certain advantages in ionic conductivity because it has modified and optimized the LATP ion conductor. At the same time, the material is more stable and has a more uniform microscopic interface than conventional LATP, which reduces the consumption of lithium in constructing the interface electrolyte membrane and has more advantages in the first efficiency of the battery. The interface membrane structure is more stable, so it also has a greater improvement in battery cycle performance and extrusion safety.

[0094] Compared to the modification of the lithium salt and electrolyte solvent system in Comparative Example 3, which does not use this system, the present invention can significantly reduce the imidization temperature and shorten the imidization time, while also achieving a higher degree of imidization in a faster time. Comparative Example 3, which does not use a lithium salt and electrolyte solvent system, has an imidization degree that is approximately 5% lower, resulting in certain raw material losses and coating weaknesses. Coating weaknesses can reduce the stability of the oxide electrolyte material, making it more likely to cause side reactions in the battery, negatively impacting the battery's electrical performance and safety. Comparison shows that Comparative Example 3 is inferior to Example 1 in terms of separator thermal stability, battery electrical performance, and extrusion safety.

[0095] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will appreciate that the technical solutions described in the aforementioned embodiments may be modified, or some or all of the technical features therein may be replaced with equivalents. Such modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the various embodiments of the present invention. Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, the combination of features from different embodiments is intended to be within the scope of the present invention and to form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background technology of the present invention and should not be construed as an admission or any form of implication that such information constitutes prior art already known to those skilled in the art.

Claims

1. A method for preparing an oxide-based ion conductor coating material, characterized in that: The steps include: S1: Nano-sized oxide-based ion conductor particles are dispersed in a liquid electrolyte solvent containing a lithium salt additive, and the particles are induced to recrystallize at 120-150°C and 1-3 MPa. The crystallization time is controlled to be 2-4 hours, and the cooling rate is 2-15°C / min to form a micron-sized block structure. S2: adding electrolyte solvent to the product of step S1, and controlling the mass fraction of the micron-sized block structure to be 10-40%; S3: adding polyamic acid and nano-scale inorganic modified material to the product of step S2, dispersing them evenly, and grinding them; S4: adding a dehydrating agent and a catalyst to the product of step S3 to perform thermal imidization; S5: Wash the product of step S4 with pure water to replace the original solvent; S6: Adding an auxiliary agent to the product of step S5 to form the coating material.

2. The preparation method according to claim 1, characterized in that In step S1, the nano-scale oxide-based ion conductor includes one or more of garnet-type, NASICON-type, LISICON-type, and perovskite-type oxide ion conductors; and / or, the liquid electrolyte solvent comprises one or more of lower alkyl ether, nitrile, pyridine, ester, ketone or alcohol; And / or, the lithium salt additive includes one or more of lithium trifluoromethanesulfinate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium difluorooxalatoborate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium trifluoromethanesulfonate, lithium hexafluorophosphate or polymer lithium.

3. The preparation method according to claim 1 or 2, characterized in that In step S1, the solid content of the liquid electrolyte solvent containing the lithium salt additive is 2-10%; And / or, the ratio of the nano-scale oxide-based ion conductor particles to the total mass of the nano-scale oxide-based ion conductor particles and the liquid electrolyte solvent containing the lithium salt additive is 10-80%.

4. The preparation method according to claim 1, characterized in that In step S3, the amount of polyamic acid added is 1-10% by mass of the product of step S2; and / or, the nano inorganic modified material comprises one or more of MoS2, boron nitride, barium titanate, aluminum oxide or boehmite; And / or, the amount of the nano-inorganic modified material added is 0.5-55% by mass of the product of step S2; And / or, the particle size Dv50 of the nano inorganic modified material is 0.01-0.5 μm; And / or, after the grinding, the particle size Dv50 of the product of step S3 is controlled to be 0.1-1 μm.

5. The preparation method according to claim 1, characterized in that In step S4, the dehydrating agent includes acetic anhydride; And / or, the catalyst comprises pyridine.

6. The preparation method according to claim 1 or 5, characterized in that In step S4, the molar ratio of the polyamic acid, the dehydrating agent and the catalyst is 1:(2-8):(1-3); And / or, the thermal imidization comprises stirring the reaction at room temperature for 2-4 hours, and then gradually raising the temperature to 50-80° C. and continuing the reaction for 1-2 hours.

7. The preparation method according to claim 1, characterized in that In step S5, the original solvent is replaced to control the residual original solvent to be less than 1%; And / or, the solid content of the final product in step S5 is controlled to be 5-55%.

8. The preparation method according to claim 1, characterized in that In step S6, the auxiliary agent includes one or more of an anti-settling agent, a dispersant, an adhesive or a wetting agent; And / or, after adding the auxiliary agent, dispersion is carried out by sand milling and / or stirring.

9. The preparation method according to claim 8, characterized in that In step S6, the anti-settling agent includes one or more of CMC, CMC-Li, polyethylene glycol, polyvinyl alcohol or polyethylene oxide; And / or, the amount of the anti-settling agent added is 0.2-8% by mass of the product of step S5; and / or, the dispersant comprises one or more of anionic dispersants, nonionic dispersants, cationic dispersants or polymeric dispersants; And / or, the amount of the dispersant added is 0.5-6% by mass of the product of step S5; And / or, the adhesive includes one or more of an emulsion-type acrylate-based polymer, a solution-type acrylate-based polymer, a polyurethane-based polymer, a polyacrylamide-based polymer, a polyimide-based polymer or a polyamide-based polymer; And / or, the amount of the adhesive added is 1-20% by mass of the product of step S5; and / or, the wetting agent comprises one or more of an organosilicon-modified wetting agent, a polyether wetting agent, an acetylene alcohol wetting agent or an alcohol wetting agent; And / or, the amount of the wetting agent added is 0.05-5% by mass of the product of step S5.

10. A battery separator, characterized in that: The invention is coated with an oxide-based ion conductor coating material prepared by the preparation method according to claims 1 to 9.