Lithium metal negative electrode and preparation method thereof, electrolyte and solid-state battery

Abstract

The invention discloses a lithium metal negative electrode, a preparation method of the lithium metal negative electrode, an electrolyte and a solid-state battery, and relates to the technical field of solid-state batteries. The ultraviolet curing protective layer is formed on at least one surface of the lithium metal matrix; the ultraviolet light curing protective layer is formed by ultraviolet light curing of protective layer precursor slurry containing polymerizable monomers and photoinitiators, and the thickness of the ultraviolet light curing protective layer ranges from 1 m to 50 m. According to the lithium metal negative electrode, a layer of compact, thin and stable protective film is rapidly constructed on the surface of lithium metal through ultraviolet curing, the stability of the lithium metal in air is remarkably improved, an electrolyte precursor solution is designed to have good compatibility and wettability with an ultraviolet curing protective layer, and under thermal initiation, the lithium metal negative electrode can be applied to the lithium battery. And the two react together to form a continuous and compact integrated interface layer with an unblocked ion transmission channel, so that low interface impedance and stable circulation are realized in a final battery cell.

Description

Technical Field

[0001] This invention relates to solid-state batteries, specifically to a lithium metal anode and its preparation method, an electrolyte, and a solid-state battery. Background Technology

[0002] Lithium-ion batteries are among the most important electrochemical energy storage devices, boasting advantages such as high energy density and long lifespan, and are widely used in consumer electronics, power tools, medical electronics, and grid energy storage systems. However, existing lithium-ion batteries based on graphite anodes (such as LiFePO4||graphite batteries) are limited by the theoretical capacity of the electrode materials, with energy densities rarely exceeding 300 Wh kg⁻¹. -1 However, this cannot meet the ever-increasing demand for high energy density, especially in the electric vehicle market. Compared to graphite anodes, lithium metal anodes offer very high specific capacity, low density, and low electrochemical potential. Battery systems using lithium metal as the anode can provide >400 Wh / kg capacity. -1 Even higher energy densities.

[0003] However, the commercialization of lithium metal batteries is hampered by the critical issue of the instability of lithium metal anodes in air. Lithium metal is easily oxidized in air, which not only reduces its electrochemical performance but also leads to serious safety hazards. Furthermore, existing lithium metal anode manufacturing processes are complex and costly, further limiting the widespread application of lithium metal batteries. Current solutions primarily involve coating the lithium metal surface with protective layers, such as alumina, to improve its stability in air. Additionally, some research has explored forming a solid electrolyte interface film on the lithium metal surface to prevent reaction between lithium metal and oxygen in the air. However, while these methods can improve lithium metal stability to some extent, they still cannot completely solve the oxidation problem in air, and the preparation of these protective layers is complex and costly.

[0004] A Chinese invention patent discloses a method for preparing an air-stable lithium metal anode and its application. The method involves immersing lithium metal in a molten protective layer material to coat the lithium metal surface with a protective layer. The protective layer components can be rosin resin, rosin glycerol ester, etc., and additives can be one or more polymers such as polyetherketone, polymethyl methacrylate, polyvinylidene fluoride, and polytetrafluoroethylene. By constructing a dense protective layer on the lithium metal surface, various gases in the air can be prevented from diffusing to the lithium metal surface, giving lithium extremely high air stability and allowing it to be stored in air for extended periods. While the patent considers the improvement in air stability of lithium metal by the polymer protective layer, it does not consider the impact of the protective layer thickness on lithium metal performance. The thickness of the protective layer in the patent is preferably greater than 50 μm, but in practical applications, the thickness of the lithium metal anode is less than 50 μm. An excessively thick protective layer will affect lithium-ion transport inside the battery, thus severely reducing battery performance. Furthermore, the high melting temperature of the protective layer during preparation poses a significant safety hazard.

[0005] A Chinese invention patent discloses a method for constructing and applying an air-stable, dendrite-free, high-efficiency lithium metal anode. This method utilizes an oligomer with hydrophobic and oxygen-barrier properties to construct a uniform coating as a protective layer on the surface of the lithium metal anode, resulting in a highly stable and efficient lithium metal anode in atmospheric environments. This air-stable high-efficiency lithium metal anode can undergo in-situ electropolymerization during application, forming a uniform and stable solid electrolyte interface film on the lithium metal anode surface. This film stabilizes the lithium anode interface, effectively inhibiting chemical corrosion and dendrite growth, improving coulombic efficiency, and consequently enhancing the battery's electrochemical performance. However, the natural drying of this polymer coating on the lithium metal anode surface involves a long process of organic solvent evaporation, which can easily cause environmental pollution.

[0006] Therefore, it is necessary to develop a method for preparing lithium metal anodes that can rapidly form a thin protective layer and have excellent air stability. This method, combined with a permeable electrolyte precursor solution, allows the lithium metal anode surface coating to fuse with the electrolyte after thermal curing, forming a solid electrolyte and improving battery cycle performance. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide a simple and efficient lithium metal anode. A thin protective layer can be rapidly constructed on the lithium metal surface through ultraviolet light curing. The lithium metal with this thin protective coating exhibits excellent air stability, reducing the stringent environmental requirements during lithium metal processing and significantly lowering the cost of battery production. Furthermore, this air-stable polymer coating, combined with a permeable electrolyte precursor solution, can be thermally cured to form a solid electrolyte, further improving battery cycle performance.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a lithium metal anode, comprising a lithium metal substrate; and A UV-curable protective layer formed on at least one surface of the lithium metal substrate; The UV-curable protective layer is formed by UV curing of a protective layer precursor slurry containing polymerizable monomers and photoinitiators, and its thickness is from 1 µm to 50 µm.

[0009] Preferably, the polymerizable monomer is selected from one or more of the following: 2,2,3,4,4,4-hexafluorobutyl acrylate, hexafluorobutyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 2,2,2-trifluoroethyl acrylate, trifluoroethyl methacrylate, 2-trifluoromethyl-2-acrylate, butyl acrylate, hydroxyethyl methacrylate, 2-phenoxyethyl acrylate, 1,4-cyclohexanediethanol divinyl ether, and triethylene glycol divinyl ether.

[0010] Preferably, the photoinitiator is selected from one or more of 1-hydroxycyclohexylphenyl ketone, 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide, and 2-hydroxy-2-methylphenylpropanone; The photoinitiator has a mass of 0.5% to 3% of the polymer monomer mass.

[0011] More preferably, the photoinitiator has a mass of 1% of the polymerizable monomer mass.

[0012] More preferably, the thickness of the UV-curable protective layer is 10 µm to 30 µm.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned lithium metal anode, comprising the following steps: In an inert atmosphere, a protective layer precursor slurry containing polymerizable monomers and photoinitiators is coated onto a lithium metal substrate. Using wavelengths of 250–420 nm and intensity of 1000–8000 mW / cm 2 The coated lithium metal substrate is cured by irradiation with ultraviolet light to form an ultraviolet-cured protective layer.

[0014] Preferably, the inert atmosphere is an argon atmosphere or a nitrogen atmosphere with both water and oxygen content below 0.1 ppm.

[0015] Preferably, a wavelength of 365nm and an intensity of 1500~4500 mW / cm are used. 2 Ultraviolet light.

[0016] Preferably, the protective layer precursor slurry is stirred at a speed of 200-500 rpm for 60-180 minutes to form a uniform slurry, and the protective layer precursor slurry is subjected to vacuum degassing treatment before coating.

[0017] Preferably, firstly, the coating and irradiation curing steps are performed on one surface of the lithium metal substrate to form a first protective layer; if a protective layer also needs to be formed on the other surface, the coating and irradiation curing steps are repeated on the other surface of the lithium metal substrate to form a second protective layer.

[0018] Thirdly, the present invention provides an electrolyte precursor solution for use in conjunction with the aforementioned lithium metal anode, comprising: Polymer monomers, organic solvents, lithium salts, and thermal initiators. The volume ratio of the polymeric monomer to the organic solvent is 1:1 to 10, the mass of the lithium salt is 5% to 100% of the total mass of the polymeric monomer and the organic solvent, and the mass of the thermal initiator is 0.5% to 3% of the mass of the polymeric monomer.

[0019] Preferably, the polymeric monomers include one or more selected from the following: 2,2,3,4,4,4-hexafluorobutyl acrylate, hexafluorobutyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 2,2,2-trifluoroethyl acrylate, trifluoroethyl methacrylate, 2-trifluoromethyl-2-acrylate, butyl acrylate, hydroxyethyl methacrylate, 2-phenoxyethyl acrylate, 1,4-cyclohexanediethanol divinyl ether, and triethylene glycol divinyl ether. The organic solvent includes one or more of the following: fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxypropane, dimethoxymethane, ethylene glycol dimethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0020] Preferably, the lithium salt includes one or more of lithium difluorophosphate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluoromethanesulfonyl)imide. The thermal initiator includes one or more of azobisisobutyronitrile and azobisisoheptanenitrile.

[0021] Fourthly, the present invention provides a method for preparing a solid-state battery, comprising the following steps: The lithium metal anode, cathode, and separator described above are assembled into a bare cell, and the bare cell is placed in a battery case. The electrolyte precursor solution described above is injected into the battery casing. The casing is left to stand to allow the electrolyte precursor solution to impregnate the UV-curable protective layer. The casing is then subjected to heat curing treatment at 40°C to 60°C for 4 to 12 hours, so that the impregnated electrolyte precursor solution and the UV-curable protective layer react together to form an integrated solid electrolyte in situ.

[0022] Fifthly, the present invention provides a solid-state battery, which is prepared by the above-described preparation method.

[0023] The beneficial effects of this invention are: 1. A UV-curable protective layer is formed on the surface of lithium metal. This is achieved by coating a specially formulated protective layer precursor slurry onto the lithium metal surface and then curing it under ultraviolet (UV) light. Its function is to rapidly construct a dense, thin, and stable protective film on the lithium metal surface, significantly improving the stability of lithium metal in air and reducing processing environmental requirements.

[0024] 2. The UV curing process takes a very short time (from a few seconds to a few minutes). Compared with natural drying or heat drying processes, production efficiency is significantly improved, and the environmental and safety problems caused by long-term evaporation of organic solvents are avoided, making it very suitable for continuous industrial production.

[0025] 3. The electrolyte precursor solution is designed to have good compatibility and wettability with the UV-curable protective layer. After the solution penetrates into the porous or polymer network structure of the protective layer, the active monomers / polymer segments of both can undergo cross-linking reaction under thermal initiation to form a continuous, dense, and unobstructed integrated interface layer with ion transport channels, thereby achieving low interfacial impedance and stable cycling in the final battery cell.

[0026] 4. The electrolyte precursor solution and the negative electrode protective layer of the present invention have consistent chemical composition, which ensures that the two are fused into a whole after thermosetting polymerization, eliminating the problem of poor solid-solid interface contact between traditional rigid coatings and subsequently added electrolytes, thereby achieving tight interface contact and excellent interface ion transport, significantly improving the cycle performance and safety of the battery. Attached Figure Description

[0027] Figure 1 This is a flowchart of the solid-state battery fabrication process of the present invention. Figure 2 This is a surface morphology image of the lithium metal anode with a UV-curable protective layer prepared in Example 1 of the present invention.

[0028] Figure 3 This is a comparison diagram of the state of the lithium metal wafer prepared in Example 1 of the present invention after being exposed to air for 30 minutes.

[0029] Figure 4This is a cycle performance curve of the soft-pack battery assembled in Embodiments 1, 2, and 3 of the present invention and Comparative Example 1 at a rate of 0.5C. Detailed Implementation

[0030] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0031] To address the inherent air instability of lithium metal anodes, the severe ion transport hindrance caused by excessively thick existing protective layers, and the challenge of balancing environmental friendliness and efficiency in the production process, this invention provides an integrated solution. Its core lies in forming a UV-curable protective layer on the surface of a lithium metal substrate, along with a compatible electrolyte precursor solution. During subsequent thermal curing, the protective layer and the electrolyte precursor fuse together to form a uniform electrolyte with low interfacial impedance.

[0032] The key to this invention's ability to achieve in-situ formation of an integrated solid electrolyte lies in the fact that the polymerizable monomers in the electrolyte precursor solution and the polymerizable monomers in the UV-curable protective layer are chemically identical or extremely similar. During the pre-curing static setting process, the electrolyte precursor solution can fully wet the interior of the polymer protective layer. During curing, the precursor solution can polymerize and connect the layers together, rather than simply engaging in physical contact. Ultimately, at the microstructure level, the original protective layer and the subsequently formed electrolyte form a dense whole, eliminating clear physical interfaces and significantly reducing interfacial impedance, thus achieving highly efficient ion transport.

[0033] The overall preparation process of this invention is as follows: Figure 1 As shown, the process clearly demonstrates the sequence and inherent relationship between the three core steps: thin-layer protection of the lithium metal anode, preparation of the electrolyte solution, and integrated molding of the battery.

[0034] I. Preparation of Lithium Metal Anodes S1. Preparation of protective layer precursor slurry The polymerizable monomer and photoinitiator mixture is stirred at 200-500 rpm for 60-120 minutes to form a uniform protective layer precursor slurry. The solution needs to be degassed under vacuum before coating.

[0035] S2, Coating and UV Curing A spraying machine dissolves and sprays the precursor onto the surface of a lithium metal strip. A precision applicator then evenly coats the lithium metal strip with the solution. A conveyor belt transports the coated lithium strip to a UV curing chamber, where the UV lamps have wavelengths of 250–420 nm and intensities of 1000–8000 mW / cm². 2 If double-sided coating is required, the other side of the lithium metal strip undergoes the same operation as above.

[0036] The preparation, coating, and curing of the above slurry are carried out in an argon-filled glove box (with water and oxygen content conditions of H2O < 0.1 ppm and O2 < 0.1 ppm) or an inert environment that meets the same water and oxygen conditions.

[0037] In some preferred embodiments of the present invention, the polymerizable monomer is selected from one or more of the following: 2,2,3,4,4,4-hexafluorobutyl acrylate, hexafluorobutyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 2,2,2-trifluoroethyl acrylate, trifluoroethyl methacrylate, 2-trifluoromethyl-2-acrylate, butyl acrylate, hydroxyethyl methacrylate, 2-phenoxyethyl acrylate, 1,4-cyclohexanediethanol divinyl ether, and triethylene glycol divinyl ether.

[0038] In some preferred embodiments of the present invention, the photoinitiator is selected from one or more of 1-hydroxycyclohexylphenyl ketone, 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide, and 2-hydroxy-2-methylphenylpropanone; the mass of the photoinitiator is 0.5% to 3% of the mass of the polymerizable monomer.

[0039] II. Preparation of Electrolyte Precursor Solution S1. Prepare raw materials Component 1 - Polymer monomers, including one or more of the following: 2,2,3,4,4,4-hexafluorobutyl acrylate, hexafluorobutyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 2,2,2-trifluoroethyl acrylate, trifluoroethyl methacrylate, 2-trifluoromethyl-2-acrylate, butyl acrylate, hydroxyethyl methacrylate, 2-phenoxyethyl acrylate, 1,4-cyclohexanediethanol divinyl ether, and triethylene glycol divinyl ether; Component 2 - an organic solvent, including one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxypropane, dimethoxymethane, ethylene glycol dimethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran, wherein the volume ratio of component 2 to component 1 is 10:1 to 1:1.

[0040] Component 3 - lithium salt, including one or more of lithium difluorophosphate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, wherein the mass of component 3 is 5 to 100% of the total mass of (component 1 + component 2), and preferably 10 to 30% in some embodiments of the present invention.

[0041] Component 4 - thermal initiator, including one or more of azobisisobutyronitrile and azobisisoheptanenitrile, wherein the mass of component 4 is 0.5% to 3% of the mass of the polymer monomer, preferably 0.6% to 1.8% in some embodiments of the present invention.

[0042] S2, monomers, organic solvents, and lithium salts are mixed and stirred at 200-500 rpm for 40-80 minutes. Then, a thermal initiator is added and stirred at 200-500 rpm for 40-80 minutes to obtain an electrolyte precursor solution.

[0043] III. Battery Assembly and Curing Steps The positive electrode (lithium iron phosphate, ternary, etc.), separator, and the prepared lithium metal negative electrode are stacked or wound in sequence to form a bare cell. The bare cell is placed in a battery case (aluminum-plastic film, aluminum case, button cell) to assemble the battery. The prepared electrolyte precursor solution containing monomers and thermal initiator is precisely injected into the battery case with the cell assembled. After injection, the battery needs to stand for several hours (4-12 hours) to allow the electrolyte precursor solution to fully penetrate and wet the electrodes and separator. The fully settled battery is placed in a high-temperature oven or incubator, and a specific temperature and time program is set according to the characteristics of the thermal initiator used for thermal curing, for example, maintaining at 40°C-60°C for 4-12 hours, so that the wetted electrolyte precursor solution reacts with the ultraviolet light-cured protective layer to form an integrated solid electrolyte in situ.

[0044] During battery assembly, if the lithium metal negative electrode is protected on one side only, the side with the protective layer should face the separator. If it is protected on both sides, its orientation is not restricted, and both sides can serve as effective electrochemical interfaces for reaction with the electrolyte.

[0045] In some preferred embodiments of the present invention, thermosetting is performed by holding at 50°C for 4 to 8 hours.

[0046] The present invention will be further illustrated by specific embodiments below.

[0047] Example 1 Preparation of lithium metal anode: 2,2,3,4,4,4-hexafluorobutyl acrylate (polymerizable monomer) and hydroxycyclohexylphenyl ketone (photoinitiator) were mixed at a mass ratio of 100:1 and stirred at 300 rpm for 60 minutes to form a uniform protective layer precursor slurry. Before coating, the slurry was degassed in a vacuum for 5 minutes. The precursor was dissolved and sprayed onto the surface of the lithium metal strip using a sprayer. A precision coater was used to uniformly coat the lithium metal strip surface. The coated lithium strip was then transferred to a UV curing chamber with UV lamps at a wavelength of 365 nm and an intensity of 1500 mW / cm². 2 The curing time was 2 minutes. After curing, a smooth, dense, and uniformly thick polymer protective layer, i.e., the UV-cured protective layer, was obtained, with a coating thickness of approximately 20 μm. In this embodiment, the polymer protective layer was disposed on one side of the lithium metal substrate, and the microstructure is shown in the figure below. Figure 1 As shown. The treated lithium strip was cut into 4×5cm negative electrode sheets and 12mm diameter discs. The lithium discs were exposed to air for 30 minutes; the lithium metal surface showed no significant change, exhibiting good air stability. The surface conditions before and after exposure were as follows. Figure 2 As shown in the left and right images.

[0048] Preparation of electrolyte precursor solution: Using a pipette, take 1 mL of 2,2,3,4,4,4-hexafluorobutyl acrylate, 2 mL of ethylene carbonate, 2 mL of diethyl carbonate, and 0.2 mL of fluoroethylene carbonate. The volume ratio of organic solvent to monomer is 4.2:1. Weigh 0.7 g of lithium hexafluorophosphate and 0.1 g of lithium difluorooxalate borate using a balance. Add the above components sequentially to the sample vial and stir at 400 rpm for 60 minutes to obtain a clear solution. Then weigh 0.01 g of azobisisobutyronitrile and add it to the above solution. Stir at 400 rpm for 60 minutes to obtain a clear solution.

[0049] Battery fabrication: Prepare the positive electrode sheet, negative electrode sheet, separator, aluminum-plastic film, and positive and negative electrode tabs in advance, and assemble them into a pouch cell. Inject the electrolyte precursor solution into the pouch cell, and then use a sealing machine to vacuum seal the pouch cell. Let the assembled battery stand for 6 hours to allow the electrolyte to fully wet the separator. After standing, transfer the pouch cell to a 50°C oven for heat curing for 12 hours. After the treatment, perform electrochemical testing on the battery.

[0050] Example 2 Preparation of lithium metal anode: 2-trifluoromethyl-2-acrylic acid and 2,2,2-trifluoroethyl ester (mass ratio 1:1) are used as monomers. The monomers and 2-hydroxy-2-methylphenylacetone (photoinitiator) are mixed at a mass ratio of 100:1 and stirred at 300 rpm for 60 minutes to form a uniform protective layer precursor slurry. Before coating, the protective layer precursor slurry is degassed in a vacuum for 5 minutes. A sprayer dissolves and sprays the precursor onto the surface of the lithium metal strip. A precision coater is used to uniformly coat the lithium metal strip surface. The coated lithium strip is then transferred to a UV curing chamber with UV lamps at a wavelength of 365 nm and an intensity of 4500 mW / cm². 2 The curing time is 2 minutes. After curing, a smooth, dense, and uniformly thick polymer protective layer of lithium metal is obtained. In this embodiment, the polymer protective layer is set on one side of the lithium metal substrate, and the thickness is the same as in Example 1. The treated lithium strip is cut into 4×5cm negative electrode sheets.

[0051] Preparation of electrolyte precursor solution: Using a pipette, take 1 mL of 2,2,2-trifluoroethyl acrylate, 1 mL of ethylene carbonate, 1 mL of diethyl carbonate, and 1 mL of methyl ethyl carbonate, with a volume ratio of organic solvent to monomer of 3:1. Weigh 1 g of lithium hexafluorophosphate using a balance. Add the above components sequentially to the sample vial and stir at 400 rpm for 60 minutes to obtain a clear solution. Then weigh 0.015 g of azobisisobutyronitrile and add it to the above solution, stirring at 400 rpm for 60 minutes to obtain a clear electrolyte precursor solution.

[0052] Battery fabrication: Prepare the positive electrode, negative electrode, separator, aluminum-plastic film, and positive and negative electrode tabs in advance, and assemble them into a pouch cell. Inject the electrolyte precursor solution into the pouch cell, and then use a sealing machine to vacuum seal the pouch cell. Let the assembled battery stand for 6 hours to allow the electrolyte to fully wet the separator. After standing, transfer the pouch cell to a 45°C oven and cure for 12 hours. After the curing process, the battery can be subjected to electrochemical testing.

[0053] Example 3 Preparation of lithium metal anode: Butyl acrylate (polymerizable monomer) and 2-hydroxy-2-methylphenylacetone (photoinitiator) were mixed at a mass ratio of 100:1 and stirred at 300 rpm for 60 minutes to form a uniform protective layer precursor slurry. Before coating, the solution was degassed in a vacuum for 5 minutes. The precursor was dissolved and sprayed onto the surface of the lithium metal strip using a sprayer. A precision coater was used to uniformly coat the lithium metal strip surface. The coated lithium strip was then transferred to a UV curing chamber with UV lamps at a wavelength of 365 nm and an intensity of 2000 mW / cm². 2The curing time is 5 minutes. After curing, a smooth, dense, and uniformly thick polymer protective layer of lithium metal is obtained. In this embodiment, the polymer protective layer is set on one side of the lithium metal substrate, and the thickness is the same as in Example 1. The treated lithium strip is cut into negative electrode sheets with a shape of 4×5 cm.

[0054] Preparation of electrolyte precursor solution: Using a pipette, take 1 mL of 2,2,2-trifluoroethyl acrylate, 3 mL of ethylene glycol dimethyl ether, and 2 mL of 1,2-dimethoxypropane (volume ratio of organic solvent to monomer = 5:1). Weigh 1.5 g of lithium bis(trifluoromethanesulfonyl)imide using a balance. Add the above components sequentially to the sample vial and stir at 400 rpm for 60 minutes to obtain a clear solution. Then weigh 0.02 g of azobisisobutyronitrile and add it to the above solution, stirring at 400 rpm for 60 minutes to obtain a clear electrolyte precursor solution.

[0055] Prepare the positive electrode, negative electrode, separator, aluminum-plastic film, and positive and negative electrode tabs in advance, and assemble them into a pouch cell. Inject the electrolyte precursor solution into the pouch cell, and then use a sealing machine to vacuum seal the pouch cell. Let the assembled cell stand for 6 hours to allow the electrolyte to fully wet the separator. After standing, transfer the pouch cell to a 45°C oven and cure for 12 hours. After the treatment is complete, the cell can be subjected to electrochemical testing.

[0056] Comparative Example 1: Methylpyrrolidone and polyvinylidene fluoride were mixed at a mass ratio of 20:1 and stirred at 300 rpm for 300 minutes at 40°C to form a homogeneous slurry. Before coating, the solution was degassed in a vacuum for 10 minutes. The solution was transferred to the surface of a lithium metal strip and uniformly coated (single-sided) with the same thickness as in Example 1 using a precision coater. The coated lithium metal was then heated on a heating stage at 80°C for 6 hours until the solvent completely evaporated. The treated lithium metal was then cut into 4×5 cm negative electrode sheets.

[0057] Preparation of electrolyte precursor solution: Using a pipette, take 1 mL of 2,2,3,4,4,4-hexafluorobutyl acrylate, 2 mL of ethylene carbonate, 2 mL of diethyl carbonate, and 0.2 mL of fluoroethylene carbonate. Weigh 0.7 g of lithium hexafluorophosphate and 0.1 g of lithium difluorooxalate borate using a balance. Add the above components sequentially to the sample vial and stir at 400 rpm for 60 minutes to obtain a clear solution. Then weigh 0.01 g of azobisisobutyronitrile and add it to the above solution, stirring at 400 rpm for 60 minutes to obtain a clear solution.

[0058] Prepare the positive electrode sheet, negative electrode sheet, separator, aluminum-plastic film, and positive and negative electrode tabs in advance, and assemble them into a pouch cell. Inject the electrolyte precursor solution into the pouch cell, and then use a sealing machine to vacuum seal the pouch cell. Let the assembled cell stand for 6 hours to allow the electrolyte to fully wet the separator. After standing, transfer the pouch cell to a 50°C oven and cure for 12 hours. After the treatment, the control cell can be subjected to electrochemical testing.

[0059] Performance testing Figure 2 This is a microscopic schematic diagram of the lithium metal anode prepared in Example 1. A smooth, dense and uniformly thick polymer protective layer is formed on the lithium metal substrate, with a coating thickness of approximately 20 μm.

[0060] Figure 3 The image shows the state of the lithium metal anode prepared in Example 1 before and after being exposed to air for 30 minutes. The lithium metal surface showed no obvious changes, indicating good air stability.

[0061] Figure 4 The graph shows the cycling data of pouch cells assembled in Examples 1, 2, and 3 and Comparative Example 1 using ternary NCM622 as the positive electrode at 0.5 C. Examples 1-3 exhibit good cycling performance; Examples 1-2 showed almost no capacity decay after 100 cycles, and Example 3 retained approximately 90% of its capacity. However, the comparative example battery failed to reach its normal capacity, with a discharge capacity less than 70% of that of the examples, and experienced rapid capacity decay. The poor cycling performance was attributed to the thick polyvinylidene fluoride (PVDF) layer on the lithium metal surface, which hindered direct contact between the electrolyte and lithium metal; furthermore, PVDF itself had poor ion conductivity.

Claims

1. A lithium metal anode, characterized by, Comprising: a lithium metal substrate; and an ultraviolet light cured protective layer formed on at least one surface of the lithium metal substrate; the ultraviolet light cured protective layer is formed by ultraviolet light curing a protective layer precursor slurry comprising a polymerizable monomer and a photoinitiator, and has a thickness of 1 µm to 50 µm.

2. The lithium metal anode of claim 1, wherein, the polymerizable monomer is selected from one or more of 2,2,3,4,4,4-hexafluorobutyl acrylate, hexafluorobutyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 2,2,2-trifluoroethyl acrylate, trifluoroethyl methacrylate, 2-trifluoromethyl-2-propenoic acid 2,2,2-trifluoroethyl ester, butyl acrylate, hydroxyethyl methacrylate, 2-phenoxyethyl acrylate, 1,4-cyclohexanedimethanol divinyl ether, and triethylene glycol divinyl ether.

3. The lithium metal anode of claim 1, wherein, the photoinitiator is selected from one or more of 1-hydroxycyclohexyl phenyl ketone, 2,4,6(trimethylbenzoyl)diphenyl phosphine oxide, and 2-hydroxy-2-methylphenyl propionone; the photoinitiator has a mass of 0.5% to 3% of the mass of the polymerizable monomer.

4. A method for producing a lithium metal negative electrode, for producing the lithium metal negative electrode according to any one of claims 1 to 3, characterized by, comprising the following steps: coating a protective layer precursor slurry comprising a polymerizable monomer and a photoinitiator on a lithium metal substrate under an inert atmosphere; The coated lithium metal substrate is irradiated and cured using ultraviolet light having a wavelength of 250 to 420 nm and an intensity of 1000 to 8000 mW / cm 2 to form an ultraviolet light-cured protective layer.

5. The method of claim 4, wherein the lithium metal anode is prepared by, the protective layer precursor slurry is stirred at a speed of 200 to 500 rpm for 60 to 180 minutes to form a uniform slurry, and the protective layer precursor slurry is subjected to vacuum degassing treatment before being coated.

6. An electrolyte precursor solution characterized in that, for use with the lithium metal anode of any one of claims 1 to 3, comprising: a polymerizable monomer, an organic solvent, a lithium salt, and a thermal initiator, wherein the volume ratio of the polymerizable monomer to the organic solvent is 1:1 to 10, the mass of the lithium salt is 5% to 100% of the total mass of the polymerizable monomer and the organic solvent, and the mass of the thermal initiator is 0.5% to 3% of the mass of the polymerizable monomer.

7. The electrolyte precursor solution of claim 6, wherein: the polymerizable monomer comprises one or more of 2,2,3,4,4,4-hexafluorobutyl acrylate, hexafluorobutyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 2,2,2-trifluoroethyl acrylate, trifluoroethyl methacrylate, 2-trifluoromethyl-2-propenoic acid 2,2,2-trifluoroethyl ester, butyl acrylate, hydroxyethyl methacrylate, 2-phenoxyethyl acrylate, 1,4-cyclohexanedimethanol divinyl ether, and triethylene glycol divinyl ether; the organic solvent comprises one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1, 2-dimethoxypropane, dimethoxymethane, ethylene glycol dimethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran.

8. The electrolyte precursor solution of claim 6, wherein: The lithium salt comprises one or more of lithium difluorophosphate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluoro oxalate borate, lithium bistrifluoromethanesulfonimide, lithium bisfluoromethanesulfonimide; The thermal initiator comprises one or more of azobisisobutyronitrile, azobisisoheptyl nitrile.

9. A method of producing a solid-state battery, characterized by, The method comprises the following steps: The lithium metal negative electrode, the positive electrode and the separator as claimed in any one of claims 1 to 3 are assembled into a bare battery cell, and the bare battery cell is placed in a battery shell; The electrolyte precursor solution as claimed in any one of claims 6 to 8 is injected into the battery shell, and the electrolyte precursor solution is allowed to soak into the ultraviolet light-cured protective layer, and heat curing treatment is performed at 40°C to 60°C for 4 to 12 hours, so that the electrolyte precursor solution and the ultraviolet light-cured protective layer react together to form an integrated solid-state electrolyte in situ.

10. A solid-state battery, characterized by, The solid-state battery is prepared by the method as claimed in claim 9.

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