CN117175035A - A lithium metal anode bipolar artificial SEI film and its preparation method and application - Google Patents

Abstract

The artificial SEI film has high ion conductivity and high ion migration number, and contains bipolar functional groups, so that desolvation of lithium ions is promoted, and solvent-induced lithium negative electrode corrosion is reduced; but also can adsorb anions to improve the migration efficiency of lithium ions. The artificial SEI film can reduce concentration polarization of lithium ions, realize uniform deposition of lithium metal ions and inhibit generation of lithium metal dendrites. The artificial SEI film is a self-supporting film formed by mixing a polar polymer, a carbonic ester solvent, lithium salt, a polymer prepolymer and a photoinitiator and then in-situ curing. The artificial SEI film prepared by the method can effectively protect a lithium metal anode; the method has the advantages of simple preparation process, easy obtainment of raw materials by using conventional equipment, safety and no pollution, and is suitable for large-scale batch production. When the artificial SEI film is used for a lithium metal battery, the artificial SEI film can be matched with a high-voltage positive electrode material, and has good cycle performance.

Description

A lithium metal anode bipolar artificial SEI film and its preparation method and application

Technical field

The invention relates to a lithium metal negative electrode bipolar artificial SEI film and its preparation method and application. The artificial SEI film is used to protect lithium metal negative electrode materials in lithium metal batteries, and belongs to the technical field of metal lithium batteries.

Background technique

Metal lithium has ultra-high theoretical specific capacity (3860mAhg ^-1 ) and extremely low redox potential (-3.040V vs. standard hydrogen electrode), making it the best negative electrode for high-energy-density lithium metal batteries (>500Wh Kg ^-1 ). Material. However, due to the high reactivity of metallic lithium with commercial carbonate electrolytes, an uneven organic/inorganic solid electrolyte interface layer (SEI film) is formed. Controlling the interface of metallic lithium anode is an effective strategy to inhibit the failure of metallic lithium anode, including electrolyte modification and artificial SEI film construction. Among them, there are three main methods of electrolyte modification: high-concentration electrolytes regulate the composition of the SEI film on the lithium surface, use additives to regulate the uniform deposition of lithium ions, and promote the formation of a stable SEI film on the surface of metallic lithium. However, during the battery cycle, electrolyte additives, lithium salts, etc. are gradually consumed, resulting in uneven composition and surface structure of the subsequently generated SEI film, which in turn triggers uneven deposition of lithium and the generation of lithium dendrites. Therefore, it is of great significance to explore efficient artificial SEI films with uniform structure, good strength and toughness, high ion conductivity and surface electronic insulation.

Currently, the method of using artificial SEI films can effectively avoid uncontrollable lithium dendrite growth and regulate the uniform diffusion of lithium ions. Huang Yunhui's research group at Huazhong University of Science and Technology reported a cationic polymer artificial SEI membrane, which has a high ion migration number and can effectively improve the stable cycling of lithium-ion batteries in carbonate electrolyte systems (1mA cm ^-2 , 700h). However, this artificial SEI The membrane's low ionic conductivity and inevitable solvent corrosion limit its further applications. (Adv.Mater.2021, 33, 2007428) Li Hong’s research group at the Institute of Physics, Chinese Academy of Sciences reported that a photocurable polymer artificial SEI film isolates the electrolyte from direct contact with metallic lithium, avoiding solvent corrosion of the lithium anode and ineffective protection of metallic lithium. Negative electrode, and lithium-lithium symmetrical battery can cycle stably for 700h in carbonate electrolyte system (0.5mA cm ^-2 ,1mA h cm ^-2 ). (Nano Energy 95(2022)106983) However, the low ion conductivity and ion migration number of the artificial SEI membrane make the battery have poor cycle stability at high rates, which still limits its further application. The research groups of Zhang Qiang of Tsinghua University and Huang Jiaqi of Beijing Institute of Technology reported an organic-inorganic composite artificial SEI membrane, which is a high ion migration number artificial SEI prepared from LLZTO inorganic particles and lithiated perfluorosulfonic acid resin. film (t _Li+ =0.82). The composite protective layer is directly coated on the surface of the metallic lithium electrode, which can effectively inhibit the formation of lithium dendrites. However, the low room temperature ionic conductivity (3.0×10 ^-5 S cm ^-1 ) significantly reduces its lithium metal performance at room temperature. Applications in batteries. (Adv.Mater.2019,1808392) Therefore, it is urgent to provide a lithium metal anode artificial SEI film material that can be widely used in lithium secondary batteries, has both high ionic conductivity and high ion migration number, can isolate solvents and is stable The stripping/deposition process of lithium ions inhibits the growth of lithium metal dendrites, thereby improving the safety performance and cycle performance of lithium metal batteries.

Contents of the invention

In view of this, the present invention provides a lithium metal anode bipolar artificial SEI film that has both high ion conductivity and high ion migration number, and provides a method for preparing the artificial SEI film and a method for preparing a lithium metal battery. The method has a simple process, easy-to-obtain raw materials, is safe and pollution-free, and is suitable for large-scale batch production.

The second object of the present invention is to provide a method for preparing a lithium metal negative electrode bipolar artificial SEI film; the method has a simple preparation process, easily available raw materials, is safe and pollution-free, and is suitable for large-scale mass production.

The third object of the present invention is to provide a metal lithium battery. The artificial SEI film of the metal lithium battery is a lithium metal negative electrode bipolar artificial SEI film according to the present invention.

In order to achieve the purpose of the present invention, the following technical solutions are provided.

A lithium metal negative electrode bipolar artificial SEI film. The artificial SEI film is composed of carbonate, polar polymer, polymer prepolymer, photoinitiator and salt. After being mixed evenly in the dark, it is directly applied with lithium metal. The surface is prepared by direct UV curing under a protective atmosphere; the protective gas is an inert gas or nitrogen.

The carbonate is ethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, difluoroethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dicarbonate Propyl ester, diphenyl carbonate, butylene carbonate, dibutyl carbonate, tetrabutanol dicarbonate, glyceryl carbonate alcohol difluoroacetate, glyceryl carbonate alcohol trifluoroacetate, glyceryl carbonate alcohol One or more of the ester ethanesulfonate esters.

The polar polymer is at least one of polyacrylonitrile, polyvinyl alcohol, poly-N-cyanomethacrylamide and polyvinyl alcohol-β-cyanoethyl ether.

The lithium salt is lithium perchlorate, lithium bistrifluorosulfonimide, lithium bis(fluorosulfonyl)amine, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bisoxaloborate, lithium dioxaloborate, and lithium tetrafluoroborate , lithium phosphate, and lithium difluorophosphate.

The polymer prepolymers are polyethylene glycol diacrylate, butyl acrylate, polyethylene glycol methyl ether methacrylate, ethoxylated trihydroxymethylpropane triacrylate, and trimethylolpropylene triacrylate. Glycidyl ether, one or more of N, N-dimethylbisacrylamide and N-cyanomethacrylamide. Preferably, the polymer prepolymer has a number average molecular weight of 100 to 1,000.

The photoinitiator is 2-hydroxy-2-methylpropiophenone, 2,2-dimethoxy-2-phenylacetophenone, benzophenone peroxide, 2-hydroxy-2-methyl- One or more of 1-[4-(2-hydroxyethoxy)phenyl]-1-propanone and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Among them, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone is already commercially available, such as Irgacure 2529 produced by Ciba Specialty Chemicals; Bis(2 ,4,6-Trimethylbenzoyl)-phenylphosphine oxide is already commercially available, such as Irgacure 819 produced by Ciba Specialty Chemicals.

Preferably, the mass ratio of polar polymer, carbonate solvent, lithium salt, polymer prepolymer, and photoinitiator is 1 to 10: 20 to 75: 1 to 15: 5 to 25: 0.01 to 0.5.

A method for preparing a lithium metal negative electrode bipolar artificial SEI film according to the present invention. The steps of the method are as follows:

(1) In the temperature range of 20 to 55°C and in a dry inert atmosphere, the artificial SEI membrane prepolymerization solvent is 1 to 10 wt% of the polar polymer and 20 to 75 wt of the carbonate solvent in terms of mass percentage. %, lithium salt 1~15wt%, polymer prepolymer 5~25wt% and photoinitiator 0.01~0.5wt% after mixing evenly; (2) Under protective gas protection, in a nearly anhydrous and oxygen-free environment, The mixture prepared in step (1) is directly coated on the surface of the lithium metal negative electrode with a scraper; the coating thickness of the mixture is 0.1 μm to 10 μm; it is cured by ultraviolet light irradiation to obtain a lithium metal negative electrode bipolar electrode according to the present invention. Artificial SEI membrane.

Wherein, the protective gas is an inert gas or nitrogen, and the purity is greater than or equal to 99%.

The preferred coating thickness of the mixture is 0.1 μm to 10 μm.

The preferred wavelength of the ultraviolet lamp is 365 nm to 400 nm.

It is preferred to irradiate the UV lamp for 1 to 5 minutes for curing.

beneficial effects

1. The present invention provides a lithium metal negative electrode bipolar artificial SEI film. The electrolyte uses polar polymers as components, and enhances ion conductivity through carbonate solvents and lithium salts; through polar cyano groups ( -C≡N) functional group and the anion ion-dipole interaction, as well as the hydrogen bonding interaction between the alcoholic hydroxyl functional group and the carbonate solvent molecule, promote the desolvation of lithium ions, improve the lithium ion migration ability, and isolate the free carbonate Molecules come into contact with the lithium negative electrode. The introduction of polymer prepolymers and photoinitiators participates in and promotes the formation of a polymer-derived SEI film organic layer on the surface of lithium metal through the interaction between functional groups and lithium metal, making the artificial SEI film tightly adhere to the surface of the lithium metal anode, which can Form a stable lithium metal anode-artificial SEI film interface.

2. The present invention provides a lithium metal negative electrode bipolar artificial SEI film. The bipolar artificial SEI film has both high ion conductivity and high ion migration number, effectively prevents corrosion of free carbonate solvents, and can stabilize The process of stripping/deposition of metallic lithium inhibits the growth of lithium dendrites caused by lithium ion concentration polarization, and exhibits lower overpotential and long-term cycle stability during galvanostatic polarization, which can significantly improve metallic lithium. Battery electrochemical performance and safety.

3. The present invention provides a method for preparing a lithium metal negative electrode bipolar artificial SEI film. The preparation process of the method is simple, all conventional equipment is used, the raw materials are easily available, and it is safe and pollution-free, and does not require the use of organic materials. Solvents such as N,N-dimethylformamide (DMF), acetonitrile, etc. are suitable for large-scale batch production.

Description of drawings

Figure 1 is a scanning electron microscope image of a lithium metal negative electrode bipolar artificial SEI film prepared in Example 1.

Figure 2 is an ion migration number diagram of a lithium metal anode bipolar artificial SEI film prepared in Example 1.

Figure 3 shows a lithium-lithium symmetrical battery using a lithium metal negative electrode bipolar artificial SEI film prepared in Example 1.

Galvanostatic plating/stripping diagram at 5mA/ ^cm2 current density.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. It should be noted that the following embodiments are for the convenience of skilled persons in understanding the present invention and are not intended to limit the scope of protection of the present invention. Those of ordinary skill in the art will not deviate from the present invention. Improvements made based on the basic concept of the invention shall fall within the protection scope of the invention.

In the following examples:

The argon gas is all argon gas with a purity of greater than or equal to 99%.

A polar polymer network gel electrolyte prepared in the following examples was tested as follows:

(1) Use a scanning electron microscope to observe the morphology of the bipolar artificial SEI film.

Test instrument: Hitachi S4800

(2) Use AC impedance-steady-state current coupling to test the ion migration number of the bipolar artificial SEI membrane of the electrolyte to assemble the test system into a bipolar artificial SEI membrane@lithium metal│electrolyte│bipolar artificial The SEI film@lithium metal symmetrical battery was tested using linear voltammetry on the CHI660E electrochemical workstation. The impedance test frequency range was 0.1Hz~10 ⁵ Hz; the IT test polarization voltage was 10mV.

Testing instrument: CHI660E electrochemical workstation, Shanghai Chenhua

(3)Electrochemical performance test

Assembly of lithium symmetrical battery: In a glove box filled with argon gas with a purity greater than or equal to 99%, put the bipolar artificial SEI film@lithium metal, separator, electrolyte and bipolar artificial SEI film@lithium metal in sequence with the model number 2025 into a button battery shell, and then use a tablet press to compact and fasten the two battery shells to obtain a symmetrical lithium-lithium battery; after the assembled lithium battery was left to stand at 30°C for 48 hours, the electrochemical performance test was performed.

The LAND battery test system was used to conduct the deposition/stripping test of metallic lithium and sodium. The test constant current density was 5mA/cm2 and the deposition surface capacity was 1mAh/cm2.

Testing instrument: LAND battery test system, model CT2001A, Wuhan Jinnuo Electronics Co., Ltd.

Example 1:

The lithium negative electrode bipolar artificial SEI film provided in this embodiment includes 5wt% polyvinyl alcohol-β-cyanoethyl ether, 55wt% ethylene carbonate, 15wt% lithium bistrifluorosulfonyl imide, 25wt% Polyethylene glycol diacrylate (Mn=400) and 0.02 wt% 2-hydroxy-2-methylpropiophenone.

The preparation method is as follows: in a glove box filled with argon, in which H ₂ O is less than 0.1ppm; O ₂ is less than 0.1ppm, at a temperature of 55°C, 15wt% bistrifluorosulfonate is sequentially added to 55wt% ethylene carbonate. Lithium imide, 5wt% polyvinyl alcohol-β-cyanoethyl ether, 25wt% polyethylene glycol diacrylate (Mn=400) and 0.02wt% 2-hydroxy-2-methylpropiophenone, and then added Stir thoroughly during the process to mix evenly, and use a scraper to apply it directly on the surface of the lithium metal anode; the coating thickness is 5.0 μm, the wavelength of the ultraviolet lamp is 365nm ~ 400nm, and the bipolarity is obtained by irradiation for 5 minutes and light curing. Artificial SEI membrane.

A polar polymer network gel electrolyte prepared in this example was tested as follows:

(1) Observe the morphology of the lithium anode bipolar artificial SEI film using a scanning electron microscope

The thickness of the lithium negative bipolar artificial SEI film is 3.7 μm

(2) Measurement results of the ion migration number of the lithium anode bipolar artificial SEI film using AC impedance-steady-state current coupling: the ion migration number of the lithium anode bipolar artificial SEI film is 0.86, such as As shown in Figure 2.

(3)Electrochemical performance test

Test results: When the lithium-lithium symmetrical battery has a current density of 10mA/ ^cm2 and a surface capacity of 2mAh/ ^cm2 , it can cycle stably for 300h without short circuit, as shown in Figure 3.

Example 2:

The lithium negative electrode bipolar artificial SEI film provided in this embodiment includes 7wt% polyvinyl alcohol-β-cyanoethyl ether and polyvinyl alcohol complex, 60wt% fluoroethylene carbonate, and 10wt% dioxalic acid Lithium borate, 23wt% polyethylene glycol diacrylate (Mn=400) and 0.02wt% photoinitiator.

The preparation method is as follows: in a glove box filled with argon, in which H ₂ O is less than 0.1ppm; O ₂ is less than 0.1ppm, at a temperature of 55°C, 10wt% dihydrogen is added in sequence to 60wt% fluoroethylene carbonate. Lithium oxalate borate, 7wt% polyvinyl alcohol-β-cyanoethyl ether and polyvinyl alcohol complex, 23wt% polyethylene glycol diacrylate (Mn=500) and 0.02wt% photoinitiator, and then added Stir thoroughly during the process to mix evenly, and use a scraper to apply it directly on the surface of the lithium metal anode; the coating thickness of the mixture is 3.0 μm, the wavelength of the ultraviolet lamp is 365nm ~ 400nm, and the irradiation is 5min ~ 15min for light curing to obtain the above Artificial SEI film for lithium metal batteries.

A polar polymer network gel electrolyte prepared in this example was tested as follows:

(1) Observe the morphology of the lithium anode bipolar artificial SEI film using a scanning electron microscope

The thickness of the lithium negative bipolar artificial SEI film is 1.8 μm

(2) Measurement results of the ion migration number of the lithium anode bipolar artificial SEI film using AC impedance-steady-state current coupling: the ion migration number of the lithium anode bipolar artificial SEI film is 0.89.

(3)Electrochemical performance test

Test results: At a current density of 10mA/ ^cm2 and a surface capacity of 2mAh/ ^cm2 , the lithium-lithium symmetrical battery can cycle stably for 500h without short circuit.

Example 3:

The lithium negative electrode bipolar artificial SEI film provided in this embodiment includes 1wt% polyacrylonitrile and polyvinyl alcohol complex, 75wt% ethyl methyl carbonate, 5wt% lithium hexafluorophosphate, and 19wt% polyethylene glycol diacrylate. and 0.02 wt% 2,2-dimethoxy-2-phenylacetophenone.

The preparation method is as follows: in a glove box filled with argon, in which H ₂ O is less than 0.1 ppm; O ₂ is less than 0.1 ppm, at a temperature of 55° C., add 5 wt % lithium hexafluorophosphate and 1 wt % lithium hexafluorophosphate in sequence to 75 wt % carbonate solvent. Polyacrylonitrile and polyvinyl alcohol compound, 19wt% polyethylene glycol diacrylate and 0.02wt% 2,2-dimethoxy-2-phenylacetophenone, and stir thoroughly during the addition process. Mix evenly and apply it directly on the surface of the lithium metal negative electrode with a spatula; the coating thickness of the mixture is 7.0 μm, the wavelength of the ultraviolet lamp is 365nm to 400nm, and the artificial SEI film of the lithium metal battery is obtained by irradiation for 5min to 15min for light curing.

A polar polymer network gel electrolyte prepared in this example was tested as follows:

(1) Observe the morphology of the lithium anode bipolar artificial SEI film using a scanning electron microscope

The thickness of the lithium negative bipolar artificial SEI film is 5.1 μm

(2) Measurement results of the ion migration number of the lithium anode bipolar artificial SEI film using AC impedance-steady-state current coupling: the ion migration number of the lithium anode bipolar artificial SEI film is 0.66.

(3)Electrochemical performance test

Test results: When the lithium-lithium symmetrical battery has a current density of 10mA/ ^cm2 and a surface capacity of 2mAh/ ^cm2 , it can cycle stably for 300h without short circuit.

Example 4:

The lithium negative electrode bipolar artificial SEI film provided in this embodiment includes 5wt% polyvinyl alcohol-β-cyanoethyl ether, 70wt% fluoroethylene carbonate, and 15wt% lithium bistrifluorosulfonimide , 10wt% polymer prepolymer and 0.02wt% photoinitiator.

The preparation method is as follows: in a glove box filled with argon, in which H ₂ O is less than 0.1ppm; O ₂ is less than 0.1ppm, at a temperature of 50°C, 15wt% dihydrogen is added in sequence to 70wt% fluoroethylene carbonate. Lithium fluorophosphate, 5wt% polar polymer, 10wt% polymer prepolymer and 0.02% photoinitiator, stir thoroughly during the addition process to mix evenly, and apply directly to the lithium metal anode with a spatula. Surface; the coating thickness of the mixture is 10 μm, the wavelength of the ultraviolet lamp is 365 nm to 400 nm, and the artificial SEI film of the lithium metal battery is obtained by irradiation for 5 min to 15 min of light curing.

A polar polymer network gel electrolyte prepared in this example was tested as follows:

(1) Observe the morphology of the lithium anode bipolar artificial SEI film using a scanning electron microscope

The thickness of the lithium negative bipolar artificial SEI film is 8.3 μm

(2) Measurement results of the ion migration number of the lithium anode bipolar artificial SEI film using AC impedance-steady-state current coupling: the ion migration number of the lithium anode bipolar artificial SEI film is 0.78.

(3)Electrochemical performance test

Test results: When the lithium-lithium symmetrical battery has a current density of 10mA/ ^cm2 and a surface capacity of 2mAh/ ^cm2 , it can cycle stably for 360h without short circuit.

Example 5:

The lithium negative electrode bipolar artificial SEI film provided in this embodiment includes 10wt% poly-N-cyanomethacrylamide and polyvinyl alcohol complex, 55wt% ethylene carbonate, and 10wt% bis(fluorosulfonyl) Lithium amine, 25 wt% polymer prepolymer and 0.02 wt% photoinitiator (2-hydroxy-2-methylpropiophenone).

The preparation method is as follows: in a glove box filled with argon, in which H ₂ O is less than 0.1ppm; O ₂ is less than 0.1ppm, at a temperature of 50°C, 10wt% bis(fluorosulfonate) is sequentially added to 55wt% ethylene carbonate. Lithium amide, 10wt% poly-N-cyanomethacrylamide and polyvinyl alcohol complex, 25wt% polymer prepolymer and 0.05wt% 2-hydroxy-2-methylpropiophenone, and after adding Stir thoroughly during the process to mix evenly, and apply it directly on the surface of the lithium metal negative electrode with a scraper; the coating thickness of the mixture is 1 μm, the wavelength of the ultraviolet lamp is 365nm~400nm, and the lithium metal battery is obtained by irradiation for 5min~15min for light curing. Artificial SEI membrane.

A polar polymer network gel electrolyte prepared in this example was tested as follows:

(1) Observe the morphology of the lithium anode bipolar artificial SEI film using a scanning electron microscope

The thickness of the lithium negative bipolar artificial SEI film is 0.3 μm

(2) Measurement results of the ion migration number of the lithium anode bipolar artificial SEI film using AC impedance-steady-state current coupling: the ion migration number of the lithium anode bipolar artificial SEI film is 0.83.

(3)Electrochemical performance test

Test results: When the lithium-lithium symmetrical battery has a current density of 10mA/ ^cm2 and a surface capacity of 2mAh/ ^cm2 , it can cycle stably for 300h without short circuit.

Claims (9)

1. A lithium metal negative electrode bipolar artificial SEI film and a preparation method and application thereof are characterized in that the artificial SEI film comprises the following components: 1 to 10 weight percent of polar polymer, 20 to 75 weight percent of carbonate solvent, 1 to 15 weight percent of lithium (sodium/potassium) salt, 5 to 25 weight percent of polymer prepolymer and 0.01 to 0.5 weight percent of photoinitiator.

2. The lithium metal anode bipolar artificial SEI film according to claim 1, wherein at least one of the polar polymers: polyacrylonitrile, polyvinyl alcohol, poly-N-cyanomethacrylamide and polyvinyl alcohol- β -cyanoethyl ether.

3. The lithium metal anode bipolar artificial SEI film according to claim 1, wherein the carbonate solvent comprises at least one of: ethylene carbonate, fluoroethylene carbonate, propylene trifluorocarbonate, difluoroethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, dipropyl carbonate, diphenyl carbonate carbon, butylene carbonate, dibutyl carbonate, tetrabutol dicarbonate, glycerol carbonate alcohol difluoroacetate, glycerol carbonate alcohol trifluoroacetate, glycerol carbonate alcohol ethanesulfonate.

4. The lithium metal negative electrode bipolar artificial SEI film according to claim 1, wherein the lithium salt comprises at least one of: lithium perchlorate, lithium bis (fluorosulfonyl) amide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis (oxalato) borate, lithium dioxaoxalato borate, lithium tetrafluoroborate, lithium phosphate, and lithium difluorophosphate.

5. The lithium metal anode bipolar artificial SEI film according to claim 1, wherein the polymer pre-polymer comprises at least one of: polyethylene glycol diacrylate, butyl acrylate, polyethylene glycol methyl ether methacrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane triglycidyl ether, N, N-dimethyl bisacrylamide, N-cyanomethacrylamide.

6. The lithium metal negative electrode bipolar artificial SEI film according to claim 1, wherein the photoinitiator comprises at least one of: 2-hydroxy-2-methylpropionyl ketone, 2-dimethoxy-2-phenylacetophenone, benzophenone peroxide, 2-hydroxy-2-methyl-1- [4- (2-hydroxyethoxy) phenyl ] -1-propanone and bis (2, 4, 6-trimethylbenzoyl) -phenylphosphine oxide.

7. A preparation method of a bipolar artificial SEI film for a lithium metal negative electrode is characterized by comprising the steps of uniformly mixing 1-10wt% of polar polymer, 20-75wt% of carbonate solvent, 1-15wt% of lithium salt, 5-25wt% of polymer prepolymer and 0.01-0.5wt% of photoinitiator in a dry inert atmosphere (or nitrogen) at a temperature range of 20-50 ℃.

8. The method for preparing the bipolar artificial SEI film for the lithium metal negative electrode, according to claim 7, is characterized in that: directly coating the surface of the lithium metal negative electrode by using a scraper; the thickness of the mixture coating is 0.1-10 mu m; the wavelength of the ultraviolet lamp is 365 nm-400 nm, and the artificial SEI film of the lithium metal battery is obtained after irradiation for 1 min-5 min for photo-curing.

9. A lithium metal battery, characterized in that the lithium metal battery comprises a lithium metal negative electrode, an artificial SEI bipolar artificial SEI film, an electrolyte, a separator and a positive electrode, wherein the artificial SEI film is the lithium metal negative electrode bipolar artificial SEI film according to any one of claims 1 to 6.