Lithium sheet with lithium tin alloy, lithium bromide and polymer composite artificial interface layer and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium metal artificial interface layer materials, and particularly relates to a lithium sheet with a lithium tin alloy, lithium bromide and polymer composite artificial interface layer and a preparation method and application of the lithium sheet. The preparation method comprises the following steps: immersing a lithium sheet into a tin bromide solution, taking out the lithium sheet after reaction, heating, adding a poly (vinylidene fluoride-co-hexafluoropropylene) solution onto the lithium sheet, and heating and drying to form a lithium tin alloy, lithium bromide and polymer composite artificial interface layer on the surface of the lithium sheet. The lithium tin alloy, lithium bromide and polymer composite artificial interface layer on the lithium sheet not only can improve the mechanical strength of a lithium metal interface, but also can improve the diffusivity of lithium ions on the interface, and can also improve the hydrophobicity of lithium metal, so that the interface condition between the lithium metal and an electrolyte is improved, the stability of the lithium metal in air is improved, and the service life of the lithium sheet is prolonged. The uniform and stable deposition of the lithium metal is facilitated, and the growth of lithium dendrites is inhibited, so that the electrochemical performance and safety of the lithium metal battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium metal artificial interface layer materials, and specifically relates to a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer, and a preparation method and application thereof. Background Art

[0002] With the continuous development of science and technology, traditional lithium-ion batteries with low theoretical energy density (387Wh / kg) can no longer meet the urgent demand for high-energy-density batteries in electronic devices and electric vehicles. Therefore, there is an urgent need to explore new high-energy-density energy storage systems. Lithium metal batteries can well meet people's demand for high-energy-density batteries. This is because lithium metal has the following advantages: First, lithium metal has an ultra-high theoretical specific capacity of 3860mAh / g; second, lithium metal has the lowest redox potential (-3.04Vvs. standard hydrogen electrode); third, lithium metal has a low volume density (0.534g / cm 3 ).

[0003] However, the practical application of existing lithium metal batteries still faces many obstacles. This is because the high reactivity of lithium metal leads to irreversible side reactions with liquid electrolytes, forming an unstable solid electrolyte interface (SEI), resulting in poor battery cycle life and low coulombic efficiency (CE). In addition, uncontrolled lithium dendrite growth can penetrate the separator, causing internal short circuits and even triggering serious safety issues such as thermal runaway.

[0004] Up to now, in order to improve the unstable interface problem between lithium metal and electrolyte, the commonly used method is to construct an artificial interface layer (such as polymers, two-dimensional materials, metal oxides and alloys, etc.) between the lithium metal negative electrode and the electrolyte to optimize the lithium metal negative electrode, thereby reducing the side reactions between metallic lithium and the electrolyte. However, the artificial interface layer in the existing technology still has problems such as unevenness and fragility. These problems not only lead to uneven performance of the artificial interface layer, affecting its stability and reliability in various scenarios, but also greatly limit the further application and expansion of related technologies. Therefore, there is an urgent need to develop new types of artificial interface layers to break through the bottleneck of existing technologies and promote the sustainable development of related industries. Summary of the Invention

[0005] To overcome the deficiencies of the prior art, the present invention provides a method for preparing a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide, and a polymer. The method comprises: first immersing the lithium sheet in a tin bromide solution, heating the sheet to form a lithium sheet having an artificial interface layer of lithium-tin alloy and lithium bromide; then dropping a poly(vinylidene fluoride-co-hexafluoropropylene) solution onto the lithium sheet having the artificial interface layer of lithium-tin alloy and lithium bromide; and heating and drying the sheet to form a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide, and a polymer. The lithium sheet having the composite artificial interface layer has a simple synthesis process, and the lithium-tin alloy can increase the affinity of the composite interface for lithium ions, reduce the nucleation overpotential of lithium ions, and promote uniform deposition of lithium ions; lithium bromide is a lithium halide material with a high mechanical modulus, which can provide a certain strength support for the composite interface, thereby improving the mechanical stability of the composite interface; and poly(vinylidene fluoride-co-hexafluoropropylene) is a hydrophobic material, which can increase the hydrophobicity of the lithium sheet, thereby making the lithium sheet stable in air. Therefore, this lithium sheet with a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer can be used as the negative electrode of a lithium metal battery. The lithium metal battery prepared after the electrode is placed in the air for half an hour has the advantages of good cycle stability and excellent rate performance.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a method for preparing a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer, the method comprising the following steps:

[0008] S1. Add tin bromide to dimethyl sulfoxide solution and dissolve to obtain a white mixed solution;

[0009] S2, immersing the lithium sheet in the white mixed solution of step S1, and generating tin and lithium bromide on the surface of the lithium sheet after reaction;

[0010] S3, taking out the lithium sheet, wiping and drying it, and then heating it to form a composite artificial interface layer of lithium-tin alloy and lithium bromide on the surface of the lithium sheet;

[0011] S4, adding poly(vinylidene fluoride-co-hexafluoropropylene) to the dimethyl sulfoxide solution and dissolving the poly(vinylidene fluoride-co-hexafluoropropylene) to obtain a white mixed solution;

[0012] S5, dropping the white mixed solution of step S4 onto the lithium sheet of step S3, and forming a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer on the surface of the lithium sheet after heating and drying.

[0013] The present invention immerses a lithium sheet in a stannic bromide solution, generating tin and lithium bromide on the surface of the lithium sheet after reaction. The lithium sheet is then removed and heated to form an artificial interface layer of lithium-tin alloy and lithium bromide on the surface of the lithium sheet. A poly(vinylidene fluoride-co-hexafluoropropylene) solution is then added to the lithium sheet, and after heating and drying, a composite artificial interface layer of lithium-tin alloy, lithium bromide, and polymer is formed on the surface of the lithium sheet. The composite artificial interface layer of lithium-tin alloy, lithium bromide, and polymer on the lithium sheet not only improves the mechanical strength of the lithium metal interface, but also increases the diffusion capacity of lithium ions on the interface and improves the hydrophobicity of the lithium metal, thereby improving the interface between the lithium metal and the electrolyte and enhancing the stability of the lithium metal in air. This facilitates the uniform and stable deposition of the lithium metal, inhibits the growth of lithium dendrites, and thus enhances the electrochemical performance and safety of the lithium metal battery.

[0014] Preferably, in the white mixed solution of step S1, the concentration of tin bromide is 0.3-0.5 g / 20-50 mL.

[0015] Preferably, in step S1, a magnetic stirrer is used to dissolve tin bromide, the stirring speed is 200-1000 rpm, and the stirring time is 3-10 hours.

[0016] Preferably, in step S2, the immersion reaction time is 15-50 minutes.

[0017] Preferably, in step S3, after the lithium sheet is taken out, it is wiped 2-5 times with dust-free paper and dried for 20-30 hours.

[0018] Preferably, in step S3, the heating treatment temperature is 150-180° C. and the time is 20-50 min.

[0019] Preferably, in the white mixed solution of step S4, the concentration of poly(vinylidene fluoride-co-hexafluoropropylene) is 1-2 g / 15-40 mL.

[0020] Preferably, in step S5, the temperature of the heating and drying treatment is 40-70° C., and the time is 20-30 hours.

[0021] The present invention also provides a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer, which is prepared by the above preparation method.

[0022] The present invention also provides the use of the lithium sheet having the lithium-tin alloy, lithium bromide and polymer composite artificial interface layer as a negative electrode of a lithium metal battery.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides a method for preparing a lithium sheet having a composite artificial interface layer of a lithium-tin alloy, lithium bromide, and a polymer. The method comprises first immersing a lithium sheet in a tin bromide solution and heating the sheet to produce a lithium sheet having the artificial interface layer of the lithium-tin alloy and lithium bromide. Then, a poly(vinylidene fluoride-co-hexafluoropropylene) solution is added to the lithium sheet having the artificial interface layer of the lithium-tin alloy and lithium bromide, and then heating and drying the sheet to produce a lithium sheet having the artificial interface layer of the lithium-tin alloy, lithium bromide, and polymer. The lithium sheet having the composite artificial interface layer has simple and efficient synthesis steps.

[0025] The present invention first immerses a lithium sheet in a tin bromide solution to prepare a lithium sheet having a lithium-tin alloy and lithium bromide artificial interface layer, then drips a poly(vinylidene fluoride-co-hexafluoropropylene) solution onto the lithium sheet having the lithium-tin alloy and lithium bromide artificial interface layer, and after subsequent heating and drying treatment, prepares a lithium sheet having a lithium-tin alloy, lithium bromide and polymer composite artificial interface layer. The lithium-tin alloy can improve the affinity of the composite interface for lithium ions, reduce the nucleation overpotential of lithium ions, and promote the uniform deposition of lithium ions; lithium bromide is a lithium halide material with a high mechanical modulus, which can provide a certain strength support for the composite interface, thereby improving the mechanical stability of the composite interface; and poly(vinylidene fluoride-co-hexafluoropropylene) has high hydrophobicity, which can make the lithium sheet hydrophobic, thereby maintaining stability in air. Therefore, the lithium metal battery prepared by the present invention has the advantages of good cycle stability and excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the scanning electron microscopy image of the Li5Sn2 / LiBr / PVDF-HFP-Li surface;

[0027] Figure 2 This is the scanning electron microscope image of the cross section of Li5Sn2 / LiBr / PVDF-HFP-Li;

[0028] Figure 3 The cycle morphologies of Li5Sn2 / LiBr / PVDF-HFP-Li at 1, 10, 50, and 100 cycles (ad);

[0029] Figure 4 The cyclic morphology of bare Li at 1, 10, 50, and 100 cycles (ad);

[0030] Figure 5 The symmetrical battery cycle performance diagram of the lithium metal battery with Li5Sn2 / LiBr / PVDF-HFP-Li as the negative electrode after being placed in air for 30 minutes;

[0031] Figure 6This is the full cell rate performance diagram of the lithium metal battery with Li5Sn2 / LiBr / PVDF-HFP-Li as the negative electrode after being placed in air for 30 minutes;

[0032] Figure 7 This is the full battery cycle performance diagram of the lithium metal battery with Li5Sn2 / LiBr / PVDF-HFP-Li as the negative electrode after being placed in air for 30 minutes. DETAILED DESCRIPTION

[0033] The following is a further description of specific embodiments of the present invention. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0034] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0035] Example 1:

[0036] This embodiment provides a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide, and a polymer, and a preparation method thereof comprises the following steps:

[0037] (1) 0.334 g of tin bromide was added to 30 mL of dimethyl sulfoxide solution and stirred with a magnetic stirrer (at 400 rpm) for 6 h to obtain a white mixed solution;

[0038] (2) Immerse a lithium sheet with a diameter of 15.6 mm in the white mixed solution of step (1). After reacting for 20 minutes, tin and lithium bromide are generated on the surface of the lithium sheet. Then, remove the lithium sheet, wipe the lithium sheet twice with dust-free paper, and dry it at room temperature for 24 hours.

[0039] (3) The lithium sheet obtained in step (2) was placed on a constant temperature heating magnetic stirrer at 160° C. and heated for 30 minutes to form an artificial interface layer of lithium tin alloy and lithium bromide on the surface of the lithium sheet.

[0040] (4) 1.1 g of poly(vinylidene fluoride-co-hexafluoropropylene) was added to 20 mL of dimethyl sulfoxide solution and stirred with a magnetic stirrer (at a speed of 400 rpm) for 24 h to obtain a white mixed solution;

[0041] (5) 10 μL of the white mixed solution from step (4) was added dropwise to the lithium sheet from step (3), and the mixture was heated on a constant temperature magnetic stirrer at 50°C for 24 h to form an artificial interface layer of lithium tin alloy, lithium bromide and polymer composite on the surface of the lithium sheet. The resulting lithium sheet was labeled Li5Sn2 / LiBr / PVDF-HFP-Li.

[0042] The morphology of Li5Sn2 / LiBr / PVDF-HFP-Li prepared in Example 1 was characterized. Figure 1 and Figure 2 The surface scanning electron microscopy images and cross-sectional scanning electron microscopy images of Li5Sn2 / LiBr / PVDF-HFP-Li respectively show that Li5Sn2 alloy particles and lithium bromide particles are evenly distributed on the surface of Li5Sn2 / LiBr / PVDF-HFP-Li. In addition, the thickness of the composite artificial interface layer of Li5Sn2 / LiBr / PVDF-HFP-Li is about 9.8μm. At the same time, in order to verify that the Li5Sn2 / LiBr / PVDF-HFP composite interface layer effectively improves the unevenness and fragility of the lithium sheet interface, the Li5Sn2 / LiBr / PVDF-HFP composite interface layer is 1mA / cm 2 Current density and 1mAh / cm 2 Under the conditions of surface capacity, the morphologies of Li5Sn2 / LiBr / PVDF-HFP-Li and bare Li at different cycle numbers were characterized by SEM. Figure 3 ad are the cycle morphologies of Li5Sn2 / LiBr / PVDF-HFP-Li at 1, 10, 50 and 100 cycles, respectively. Figure 4 Figures ad are the cycling morphologies of bare Li at 1, 10, 50, and 100 cycles, respectively. It can be observed that after 1 cycle, the electrode surface presents a uniform and dense deposition morphology without any dendrites or pores. As the number of cycles increases to 10 and 50, SEM observations show that the electrode surface always maintains a flat and smooth feature. Even after 100 deep cycles, the electrode still maintains its initial dense structure without dendrite growth or "dead lithium" accumulation. In contrast, after the first cycle, the bare Li electrode shows obvious unevenness and local protrusions on the surface, indicating uneven lithium deposition. When the number of cycles increases to 10, a typical moss-like lithium deposition morphology has formed on the electrode surface, accompanied by the generation of a large number of micron-sized pores. This morphological deterioration is further aggravated after 50 cycles, manifested as: (1) the appearance of whisker-like lithium dendrites with a length exceeding 20 μm; (2) the formation of a "dead lithium" accumulation layer with uneven thickness. After 100 cycles, the electrode structure is completely destroyed and the entire surface is covered by a loose and porous "dead lithium" layer.

[0043] Comparative Example 1:

[0044] This comparative example provides a lithium sheet having a composite artificial interface layer of lithium-tin alloy and lithium bromide, and a preparation method thereof comprises the following steps:

[0045] (1) 0.334 g of tin bromide was added to 30 mL of dimethyl sulfoxide solution and stirred with a magnetic stirrer (at 400 rpm) for 6 h to obtain a white mixed solution;

[0046] (2) Immerse a lithium sheet with a diameter of 15.6 mm in the white mixed solution of step (1). After reacting for 20 minutes, tin and lithium bromide are generated on the surface of the lithium sheet. Then, remove the lithium sheet, wipe the lithium sheet twice with dust-free paper, and dry it at room temperature for 24 hours.

[0047] (3) The lithium sheet obtained in step (2) was placed on a constant temperature heating magnetic stirrer at 160° C. and heated for 30 min to form an artificial interface layer of lithium tin alloy and lithium bromide on the surface of the lithium sheet. The obtained lithium sheet was labeled as Li5Sn2 / LiBr-Li.

[0048] Comparative Example 2:

[0049] This comparative example provides a lithium sheet having a polymer artificial interface layer, and the preparation method thereof comprises the following steps:

[0050] (1) 1.1 g of poly(vinylidene fluoride-co-hexafluoropropylene) was added to 20 mL of dimethyl sulfoxide solution and stirred with a magnetic stirrer (at 400 rpm) for 24 h to obtain a white mixed solution;

[0051] (2) 10 μL of the white mixed solution from step (1) was added dropwise to a lithium sheet with a diameter of 15.6 mm, and the sheet was heated on a constant temperature magnetic stirrer at 50°C for 24 h to form a polymer artificial interface layer on the surface of the lithium sheet. The resulting lithium sheet was labeled PVDF-HFP-Li.

[0052] Experimental example: Performance characterization of lithium metal batteries with Li5Sn2 / LiBr / PVDF-HFP-Li, Li5Sn2 / LiBr-Li, and PVDF-HFP-Li as negative electrodes after being placed in air for 30 minutes

[0053] Li5Sn2 / LiBr / PVDF-HFP-Li, Li5Sn2 / LiBr-Li and PVDF-HFP-Li were used as negative electrodes for lithium metal battery electrochemical performance tests:

[0054] 1. Characterization of symmetrical battery cycling performance

[0055] (1) Assembly of symmetrical cells: Two pieces of Li5Sn2 / LiBr / PVDF-HFP-Li, Li5Sn2 / LiBr-Li and PVDF-HFP-Li after being placed in air for 30 min were respectively assembled into Li5Sn2 / LiBr / PVDF-HFP-Li||Li5Sn2 / LiBr / PVDF-HFP-Li, Li5Sn2 / LiBr-Li||Li5Sn2 / LiBr-Li and PVDF-HFP-Li||PVDF-HFP-Li symmetrical cells in a glove box filled with argon and with water and oxygen content less than 0.1 ppm. The electrolyte system selected a 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME) (v / v = 1:1) solution containing 2 wt% lithium nitrate (LiNO3) electrolyte additive and 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The separator used a commercial polypropylene porous membrane.

[0056] (2) Electrochemical test: The above symmetrical battery was tested at 1 mA / cm 2 The current density was 1 mAh / cm 2 The repeated deposition / stripping of metallic lithium has a cycling performance such as Figure 5 As shown, the Li5Sn2 / LiBr / PVDF-HFP-Li||Li5Sn2 / LiBr / PVDF-HFP-Li symmetric cell exhibited a stable cycling curve within 1600 hours (at least 1000 cycles) with a hysteresis voltage of only 25mV. The hysteresis voltages of the Li5Sn2 / LiBr-Li||Li5Sn2 / LiBr-Li and PVDF-HFP-Li||PVDF-HFP-Li symmetric cells were both relatively high, demonstrating that the lithium sheet constructed with a lithium-tin alloy, lithium bromide, and polymer composite artificial interface layer has better electrochemical performance.

[0057] 2. Characterization of full battery rate performance

[0058] (1) Assembly of the full cell: Li5Sn2 / LiBr / PVDF-HFP-Li after being placed in air for 30 min was mixed with an active material loading of 3.35 mg / cm 2 The lithium iron phosphate (LFP) cathode was placed in a glove box and assembled into a Li5Sn2 / LiBr / PVDF-HFP-Li||LFP full cell. The electrolyte system selected was a 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME) (v / v = 1:1) solution containing 2wt% lithium nitrate (LiNO3) electrolyte additive and 1mol / L lithium bistrifluoromethanesulfonyl imide (LiTFSI). A polypropylene porous membrane was used as the separator material.

[0059] (2) Electrochemical test: The Li5Sn2 / LiBr / PVDF-HFP-Li||LFP full battery was charged and discharged between 2.4 and 4 V at a rate of 0.1 to 5 C. The rate performance is as follows: Figure 6 As shown, it can be seen that the reversible capacities of the Li5Sn2 / LiF-Li||LFP full battery at 1C, 2C and 5C are as high as 131, 112 and 75 mAh / g, respectively.

[0060] 3. Characterization of full battery cycle performance

[0061] (1) Assembly of the full cell: Li5Sn2 / LiBr / PVDF-HFP-Li after being placed in air for 30 min was mixed with an active material loading of 3.35 g / cm 2 The lithium iron phosphate (LFP) cathode was placed in a glove box and assembled into a Li5Sn2 / LiBr / PVDF-HFP-Li||LFP full battery. The electrolyte system used was a 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME) (v / v = 1:1) solution containing 2wt% lithium nitrate (LiNO3) electrolyte additive and 1mol / L lithium bistrifluoromethanesulfonyl imide (LiTFSI), and a polypropylene porous membrane was used as the separator material.

[0062] (2) Electrochemical test: The Li5Sn2 / LiBr / PVDF-HFP-Li||LFP full battery was charged and discharged between 2.4 and 4 V at a 2C rate. The cycle performance is shown in the following table. Figure 7 As shown, it can be seen that the Li5Sn2 / LiBr / PVDF-HFP-Li||LFP full battery can stably perform 400 cycles at 2C, with a reversible capacity of up to 100mAh / g and a charge and discharge efficiency maintained at above 98%, indicating that the lithium-tin alloy, lithium bromide and polymer composite artificial interface layer can effectively reduce the side reaction between lithium and the electrolyte, and give the lithium sheet hydrophobicity, making the lithium sheet stable in the air, which is conducive to the uniform and stable deposition of lithium metal, inhibiting the growth of lithium dendrites, and making the full battery have excellent cycle performance.

[0063] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations of these embodiments may be made without departing from the principles and spirit of the present invention, and the changes still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium sheet having a composite artificial interface layer of lithium tin alloy, lithium bromide and polymer, characterized in that: The following steps are involved: S1. Add tin bromide to dimethyl sulfoxide solution and dissolve to obtain a white mixed solution; S2, immersing the lithium sheet in the white mixed solution of step S1, and generating tin and lithium bromide on the surface of the lithium sheet after reaction; S3, taking out the lithium sheet, wiping and drying it, and then heating it to form a composite artificial interface layer of lithium-tin alloy and lithium bromide on the surface of the lithium sheet; S4, adding poly(vinylidene fluoride-co-hexafluoropropylene) to the dimethyl sulfoxide solution and dissolving the poly(vinylidene fluoride-co-hexafluoropropylene) to obtain a white mixed solution; S5, dropping the white mixed solution of step S4 onto the lithium sheet of step S3, and forming a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer on the surface of the lithium sheet after heating and drying.

2. The method for preparing a lithium sheet having a composite artificial interface layer of lithium tin alloy, lithium bromide and polymer according to claim 1, characterized in that: In the white mixed solution of step S1, the concentration of tin bromide is 0.3-0.5 g / 20-50 mL.

3. The method for preparing a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer according to claim 1, characterized in that: In step S1, a magnetic stirrer is used to dissolve tin bromide, the stirring speed is 200-1000 rpm, and the stirring time is 3-10 hours.

4. The method for preparing a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer according to claim 1, characterized in that: In step S2, the immersion reaction time is 15-50 minutes.

5. The method for preparing a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer according to claim 1, characterized in that: In step S3, after the lithium sheet is taken out, it is wiped 2-5 times with dust-free paper and dried for 20-30 hours.

6. The method for preparing a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer according to claim 1, characterized in that: In step S3, the heating treatment temperature is 150-180° C. and the time is 20-50 minutes.

7. The method for preparing a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer according to claim 1, characterized in that: In the white mixed solution of step S4, the concentration of poly(vinylidene fluoride-co-hexafluoropropylene) is 1-2 g / 15-40 mL.

8. The method for preparing a lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer according to claim 1, characterized in that: In step S5, the temperature of the heating and drying treatment is 40-70° C. and the time is 20-30 hours.

9. A lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer, prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the lithium sheet having a composite artificial interface layer of lithium-tin alloy, lithium bromide and polymer as claimed in claim 9 as a negative electrode of a lithium metal battery.

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