Three-dimensional structure composite lithium alloy material and preparation method thereof

Abstract

Three-dimensional structure composite lithium alloy material and preparation method thereof, the material structure comprises a lithium alloy layer, a cellulose / lithium alloy composite layer and a surface protection layer; the cellulose / lithium alloy composite layer is arranged above the lithium alloy layer, and the surface protection layer is arranged above the cellulose / lithium alloy composite layer; the preparation method comprises the following steps: S1. preparing a lithium alloy strip by melting and calendering; S2. preparing a lithium alloy strip by melting and calendering; S3. pretreating cellulose nanofibers to obtain modified cellulose nanofibers; S4. homogenizing and dispersing the modified cellulose nanofibers, a binder and a solvent, coating the cellulose nanofibers on the surface of the lithium alloy strip to obtain a cellulose / lithium alloy composite strip semi-product; S5. laminating and calendering to composite the cellulose / lithium alloy composite layer strip semi-product to obtain a three-dimensional structure composite strip; S6. calendering to composite the lithium alloy strip and the cellulose / lithium alloy composite strip to obtain a lithium alloy layer-cellulose / lithium alloy composite layer strip; and S7. coating a surface protection layer on the upper layer of the lithium alloy layer-cellulose / lithium alloy composite layer strip, which has the advantages of preventing lithium ion deposition from being non-uniform to cause lithium dendrite growth, simplifying the process and reducing the equipment requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a three-dimensional structure composite lithium alloy material and a preparation method thereof. BACKGROUND

[0002] In recent years, with the increasing demand for battery energy density in the field of new energy vehicles and other fields, lithium metal negative electrode has attracted attention again due to its high energy density. The theoretical specific capacity of lithium metal is 3860mAh / g, and the electrochemical potential is-3.04V(vs standard hydrogen electrode), which is a very ideal lithium battery negative material. The research and development of lithium metal battery aims to further improve the performance of the battery, especially the energy density. Companies such as SolidEnergy have developed a new type of lithium metal foil anode, which has significantly reduced the size of the battery. Lithium metal batteries have a wide range of applications, including unmanned aerial vehicles, 3C electronic products, electric vehicles, etc.

[0003] Lithium metal negative electrode is prone to dendrite and dead lithium problems during charging and discharging, which affects the safety and stability of the battery. To use metal lithium as the negative material of lithium ion battery, we still face two challenges: safety and cycle life. One of the main problems that plague metal lithium negative electrode is lithium dendrite. During the cycle process, due to the factor of local polarization, lithium dendrites grow on the surface of metal lithium. When the lithium dendrites grow to a certain extent, they may penetrate the separator and cause safety problems. If the lithium dendrites break, "dead lithium" will be formed, causing loss of battery capacity. In addition, the side reaction between lithium metal and electrolyte is also an important and complex technical challenge in lithium metal batteries, which not only affects the cycle life performance of the battery, but also may cause safety hazards.

[0004] To solve the above problems, patent CN 114784259 A discloses a "lithium metal negative material and its preparation method", which is designed by a lithium metal gradient material layer, which can improve the energy density of the battery and reduce the generation of lithium dendrites during lithium deposition, and improve the cycle performance and stability of the battery. However, the preparation process uses immersion and evaporation to prepare the composite layer, which has low controllability of chemical reaction, i.e. the chemical reaction will preferentially occur at the edge of the metal grain boundary, resulting in a non-uniform and non-dense composite layer. In the long-term battery cycle process, the non-dense alloy layer will still cause lithium dendrite growth and dead lithium deposition, causing battery failure. Moreover, the preparation process is complex and requires high equipment.

[0005] Therefore, it is of great significance to develop a three-dimensional structure composite lithium alloy material and a preparation method thereof. SUMMARY

[0006] The present application aims to overcome the deficiencies of the prior art, and provides a three-dimensional structure composite lithium alloy material and a preparation method thereof, which can completely solve the problem of uneven lithium ion deposition of lithium batteries leading to lithium dendrite growth, and can simplify the preparation process and reduce the equipment requirements.

[0007] The present application aims to overcome the deficiencies of the prior art, and provides a three-dimensional structure composite lithium alloy material and a preparation method thereof, which can completely solve the problem of uneven lithium ion deposition of lithium batteries leading to lithium dendrite growth, and can simplify the preparation process and reduce the equipment requirements.

[0008] The present application aims to overcome the deficiencies of the prior art, and provides a three-dimensional structure composite lithium alloy material and a preparation method thereof, which can completely solve the problem of uneven lithium ion deposition of lithium batteries leading to lithium dendrite growth, and can simplify the preparation process and reduce the equipment requirements.

[0009] The present application aims to overcome the deficiencies of the prior art, and provides a three-dimensional structure composite lithium alloy material and a preparation method thereof, which can completely solve the problem of uneven lithium ion deposition of lithium batteries leading to lithium dendrite growth, and can simplify the preparation process and reduce the equipment requirements.

[0010] S1. Adopting a melting-rolling method to prepare a first lithium alloy strip with a thickness of 50-150 microns;

[0011] S2. Adopting a melting-rolling method to prepare a second lithium alloy strip with a thickness of 50-150 microns;

[0012] S3. Pre-treating cellulose nanofibers to obtain modified cellulose nanofibers with a lithium ion conductivity of not less than 1*10 -4 S / cm;

[0013] S4. Homogenizing and dispersing the modified cellulose nanofibers obtained in step S3 with a binder and a solvent, and then coating the cellulose nanofibers on the surface of the second lithium alloy strip obtained in step S2 to preliminarily obtain a cellulose / lithium alloy composite strip semi-product;

[0014] S5. Adopting a laminated rolling method to further composite the cellulose / lithium alloy composite strip semi-product prepared in step S4, so that the cellulose is uniformly distributed in the lithium alloy to form a three-dimensional structure cellulose / lithium alloy composite strip;

[0015] S6. Adopting a rolling method to roll composite the first lithium alloy strip obtained in step S1 and the cellulose / lithium alloy composite strip obtained in step S5 to prepare a first lithium alloy layer-second cellulose / lithium alloy composite layer strip;

[0016] S7. Coating a surface protection layer on the upper layer of the first lithium alloy layer-second cellulose / lithium alloy composite layer strip prepared in step S6.

[0017] Compared with the prior art, the present application has the following advantages or effects:

[0018] Because the third surface protection layer is arranged on the surface of the three-dimensional structure composite lithium alloy material prepared by the components and process of the application, the side reaction between the lithium alloy and the electrolyte, even water and oxygen can be effectively inhibited, the cycle life of the battery is improved, and the storage environment requirement is reduced; meanwhile, because the solid electrolyte powder dispersed in the third protection layer contains the cellulose nanofiber with high lithium ion conductivity uniformly distributed at the second cellulose / lithium alloy composite layer, the lithium ion is helped to be transmitted to the second cellulose / lithium alloy composite layer to start deposition, the lithium ion is further transmitted to the first lithium metal layer, and nucleation and deposition are carried out at the first lithium metal layer; in addition, because the cellulose nanofiber and the lithium alloy form an interlaced layout in the three-dimensional structure composite lithium alloy negative electrode, the mechanical strength of the whole negative electrode system can be effectively toughened and increased, and the integrity of the whole structure is ensured; in addition, because a large number of lithium-philic sites are uniformly distributed in the first lithium alloy layer, the nucleation overpotential of lithium is reduced, the lithium is stably adsorbed on the surface of the alloy and uniformly grows, the diffusion speed of lithium in the lithium alloy such as Li13In3, LiZn, Li9Al4, Li22Sn5 is faster, and the preparation process is simple and the equipment requirement is low. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a three-dimensional structure composite lithium alloy material structure according to the application.

[0020] Figure 2 is a preparation method of the three-dimensional structure composite lithium alloy material structure. Figure 1

[0021] The application will be further described in detail below with reference to the drawings. DETAILED DESCRIPTION

[0022] As shown in the drawings, the three-dimensional structure composite lithium alloy material structure is used to solve the problems of dendrite and dead lithium, and comprises a first lithium alloy layer, a second cellulose / lithium alloy composite layer and a third surface protection layer. Figure 1

[0023] The three-dimensional structure composite lithium alloy material structure of the application further comprises:

[0024] The alloy elements in the first lithium alloy layer include one or more of aluminum Al, zinc Zn, indium In, tin Sn, boron B, silver Ag and the like.

[0025] The alloy element of the second cellulose / lithium alloy composite layer is magnesium Mg, the cellulose is cellulose nanofiber, and the lithium ion conductivity is greater than or equal to 1*10 -4 S / cm.​​

[0026] The third surface protection layer is mainly composed of at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, and polyperfluoroethylene propylene, and contains nanoscale solid electrolyte powder in the protection layer,

[0027] The solid electrolyte powder is lithium lanthanum zirconium oxide and a doped modified powder thereof.

[0028] The thickness of the first lithium alloy is 20-50 μm.

[0029] The thickness of the second cellulose / lithium alloy composite layer is 10-25 μm.

[0030] The thickness of the third surface protection layer is 0.1-5 μm.

[0031] The content of alloying elements in the first lithium alloy is not more than 1.5 at. %.

[0032] The content of alloying elements in the second cellulose / lithium alloy composite layer is in the range of 0.1-10 at. %.

[0033] The cellulose nanofiber has a diameter of 5-50 nm and a length of 0.2-3 μm, and the content of cellulose nanofiber is in the range of 0.1-20 wt. %.

[0034] As shown in Figure 2 The preparation method of the three-dimensional structure composite lithium alloy negative electrode material comprises the following process steps and conditions:

[0035] S1. A first lithium alloy strip with a thickness of 50-150 μm is prepared by a melting-calendering method;

[0036] S2. A second lithium alloy strip with a thickness of 50-150 μm is prepared by a melting-calendering method;

[0037] S3. The cellulose nanofiber is pretreated to obtain modified cellulose nanofiber with a lithium ion conductivity of ≥1×10 -4 S / cm;

[0038] S4. The modified cellulose nanofiber obtained in step S3 is uniformly grinded and dispersed with a binder and a solvent, and then the cellulose nanofiber is coated on the surface of the second lithium alloy strip obtained in step S2 to preliminarily obtain a cellulose / lithium alloy composite strip semi-product;

[0039] S5. The cellulose / lithium alloy composite layer strip semi-product prepared in step S4 is further compounded by a laminated calendering method, so that the cellulose is uniformly distributed in the lithium alloy to form a three-dimensional structure cellulose / lithium alloy composite strip;

[0040] S6. The first lithium alloy strip obtained in step S1 and the cellulose / lithium alloy composite strip obtained in step S5 are subjected to calendering to prepare a first lithium alloy layer-second cellulose / lithium alloy composite layer strip by calendering.

[0041] S7. A surface protection layer is coated on the upper layer of the first lithium alloy layer-second cellulose / lithium alloy composite layer strip prepared in step S6.

[0042] The process flow and conditions of the present application can be further:

[0043] The lithium alloy melting temperature in steps S1 and S2 should be higher than the melting point of the equilibrium phase diagram.

[0044] The lithium alloy in step S1 is cooled at a cooling rate of >200℃ / min or is cooled by using a mold with forced cooling.

[0045] The pretreatment method of the cellulose nanofiber in step S3 includes at least one of ion coordination and functional group grafting.

[0046] The ion coordination in step S3 is achieved by coordinating copper ions Cu 2+ with one-dimensional cellulose nanofiber, changing the crystal structure of cellulose, so that the spacing between polymer chains is expanded into a molecular channel for lithium ion Li + insertion and rapid transmission.

[0047] The functional group grafting in step S3 is achieved by further reacting isocyanate with the hydroxyl group of cellulose nanofiber to obtain small molecule structures such as -CN, -CF3 and -COO groups, while generating urea bonds to enhance lithium ion conduction.

[0048] The binder used in step S4 includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, butadiene rubber, polyacrylonitrile, polyethylene, etc.

[0049] The solvent used in step S4 includes at least one of N-methylpyrrolidone, tetrahydrofuran, ethylene glycol dimethyl ether, dimethyl carbonate, dimethyl sulfoxide, N,N-dimethylformamide, etc.

[0050] The mass ratio of cellulose nanofiber to binder used in step S4 is 50-98:2-50,

[0051] The mass ratio of cellulose nanofiber to binder used in step S4 is 90-98:2-10,

[0052] The coating method in step S4 includes any one of flow coating, doctor blade coating, spraying, etc.

[0053] The step S5 includes rolling and calendering of the cellulose / lithium alloy composite layer material, and the stacking mode is AB / AB, wherein A represents the fiber side and B represents the lithium alloy side.

[0054] The number of times of rolling used in the step S5 is 4-6 times; the final thickness of rolling is 20-100 μm, and the final thickness of rolling is 20-50 μm.

[0055] In the step S6, the calendering makes the first lithium alloy layer and the second cellulose / lithium alloy composite layer more closely combined, and further reduces the thickness.

[0056] In the step S7, the coating mode of the protective layer includes any one of flow coating, doctor blade coating, spraying, gravure coating, microgravure coating, spin coating, extrusion coating, etc.

[0057] Example 1

[0058] Battery-grade lithium metal and high-purity aluminum metal (≥99.99% purity) are weighed and sampled in a molar ratio of 99:1, and are stirred and melted under an argon protective atmosphere, with a melting temperature of 690°C. After uniform stirring, the first lithium-aluminum alloy is obtained by casting and cooling (the cooling mold is pure copper, and the temperature is cooled to below 80°C in 3 minutes). Then, the lithium-aluminum alloy is calendered to a thickness of 100 μm.

[0059] Battery-grade lithium metal and high-purity magnesium metal (≥99.99% purity) are weighed and sampled in a molar ratio of 97:3, and are stirred and melted under an argon protective atmosphere, with a melting temperature of 450°C. After uniform stirring, the lithium-magnesium alloy is obtained by casting and cooling. Then, the lithium-aluminum alloy is calendered to a thickness of 100 μm. The cellulose nanofiber (diameter 50 nm, length 1-3 μm) treated with copper ion (Cu2+) coordination is mixed with polyvinylidene fluoride in a mass ratio of 95:5, and is dissolved in dimethyl carbonate with a solid content of 30%. After uniform homogenization and dispersion, the mixture is coated on the 100 μm-thick lithium-magnesium alloy by doctor blade coating and dried. The cellulose nanofiber film layer has a thickness of about 20 μm. The cellulose / lithium-magnesium alloy composite material semi-product is stacked and rolled 6 times to obtain a second cellulose / lithium-magnesium alloy composite material with a three-dimensional uniform distribution and a thickness of 50 μm.

[0060] The obtained lithium-aluminum alloy and the cellulose / lithium-magnesium alloy composite material are calendered and combined. The oxide layer on the material bonding surface is removed before rolling. The roll gap is gradually reduced during the rolling process until the overall thickness is reduced to 60 μm. Finally, a protective layer of rubidium-tantalum-doped lithium lanthanum zirconium oxide / polyvinylidene fluoride-hexafluoropropylene is coated on the surface of the composite material. The protective layer has a thickness of 3 μm, the particle size of the rubidium-tantalum-doped lithium lanthanum zirconium oxide is about 300 nm, and the proportion is 20 wt%. Finally, a three-dimensional structure composite lithium alloy negative electrode is obtained.

[0061] Example 2

[0062] The same as Example 1, except that the first lithium alloy is battery metal lithium and high purity zinc metal (≥ 99.99% purity) with a molar ratio of 99.5:0.5, the smelting temperature is 500°C, and the cooling time is 2 min to below 80°C during casting.

[0063] Example 3

[0064] The same as Example 1, except that the first lithium alloy is battery metal lithium and high purity indium metal (≥ 99.99% purity) with a molar ratio of 99.5:0.5, the smelting temperature is 450°C, and the cooling time is 1.5 min to below 80°C during casting.

[0065] Example 4

[0066] The same as Example 1, except that the first lithium alloy is battery metal lithium and high purity silver metal (≥ 99.99% purity) with a molar ratio of 99:1, the smelting temperature is 450°C, and the cooling time is 1.5 min to below 80°C during casting.

[0067] Example 5

[0068] The same as Example 1, except that the first lithium alloy is battery metal lithium and high purity zinc metal (≥ 99.99% purity) with a molar ratio of 99.5:0.5, the smelting temperature is 500°C, and the cooling time is 2 min to below 80°C during casting.

[0069] Comparative Example 1

[0070] The same as Example 1, except that during the preparation process, the pretreated cellulose nanofiber is not compounded into the lithium-magnesium alloy, and there is no three-dimensionally distributed cellulose nanofiber in the final composite lithium alloy negative electrode.

[0071] Comparative Example 2

[0072] The same as Example 1, except that a layer of rubidium-doped tantalum-lithium lanthanum zirconium oxide / polyvinylidene fluoride-hexafluoropropylene protective layer is not coated on the surface of the composite material, and there is no surface protective layer structure in the final composite lithium alloy negative electrode.

[0073] Comparative Example 3

[0074] Lithium-aluminum alloy, thickness 60 μm. Battery metal lithium and high purity aluminum metal (≥ 99.99% purity) are weighed and sampled according to a molar ratio of 99:1, and smelting is carried out under an argon protective atmosphere, with a smelting temperature of 690°C. After uniform stirring, the first lithium-aluminum alloy is cast and cooled (the cooling mold is pure copper, and the cooling time is 3 min to below 80°C), and then the lithium-aluminum alloy is calendered to a thickness of 60 μm.

[0075] Comparative Example 4

[0076] Lithium-magnesium alloy, thickness 60 μm. Lithium metal and high-purity magnesium metal (≥ 99.99% purity) were weighed according to a molar ratio of 97:3, stirred and melted under an argon protective atmosphere, the melting temperature was 450°C, after uniform stirring, the lithium-magnesium alloy was cast and cooled, and then the lithium-magnesium alloy was calendered to a thickness of 60 μm.

[0077] Comparative Example 5

[0078] Commercial battery-grade pure lithium metal, thickness 60 μm.

[0079] Test Example

[0080] (1) Cycle capacity retention rate

[0081] The lithium ion batteries prepared in the above examples and comparative examples were tested for cycle capacity retention rate. At room temperature, first activated at a current of 0.1C, then constant current charge and discharge at a current density of 1C, the charge and discharge cut-off voltages were 4.5V and 3V respectively, the positive electrode was a commercial NCM811 positive electrode material, and the electrolyte was a commercial ternary electrolyte. The test results are as follows:

[0082] Test results table

[0083]

[0084] From the test results of the experimental data of the above examples and comparative examples, it can be seen that examples 1-5 all have better capacity retention rate, and the cycle performance of the three-dimensional structure composite lithium alloy prepared by the composition and process of the present application is significantly better than that of the material not using the composition and process of the present application.

[0085] As described above, the present application can be better achieved. The above examples are only the best embodiments of the present application, but the embodiments of the present application are not limited by the above examples, other changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application, all should be equivalent replacement methods, all are included in the protection scope of the present application.

Claims

1. A three-dimensional composite lithium alloy material, characterized in that... It comprises a first lithium alloy layer, a second cellulose / lithium alloy composite layer, and a third surface protective layer; the second cellulose / lithium alloy composite layer is disposed above the first lithium alloy layer, and the third surface protective layer is disposed above the second cellulose / lithium alloy composite layer; the lithium-ion conductivity of the second cellulose is ≥1×10⁻⁶. -4 S / cm; the third surface protective layer contains nanoscale solid electrolyte powder.

2. The composite lithium alloy material according to claim 1, characterized in that... The alloying elements in the first lithium alloy layer include one or more of aluminum (Al), zinc (Zn), indium (In), tin (Sn), boron (B), and silver (Ag).

3. The composite lithium alloy material according to claim 1, characterized in that... The alloying element of the second cellulose / lithium alloy composite layer is magnesium (Mg), and the cellulose is cellulose nanofiber.

4. The composite lithium alloy material according to claim 1, characterized in that... The third surface protective layer is mainly composed of at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, and perfluoroethylene propylene.

5. The composite lithium alloy material according to claim 4, characterized in that... The solid electrolyte powder is lithium lanthanum zirconium oxide and powders that have been doped and modified with it.

6. The composite lithium alloy material according to claim 1 or 2, characterized in that... The thickness of the first lithium alloy layer is 20~50μm.

7. The composite lithium alloy material according to claim 1 or 3, characterized in that: The thickness of the second cellulose / lithium alloy composite layer is 10~25μm.

8. The composite lithium alloy material according to claim 1 or 4, characterized in that... The thickness of the third surface protective layer is 0.1~5μm.

9. The composite lithium alloy material according to claim 1 or 2, characterized in that: The content of alloying elements in the first lithium alloy layer does not exceed 1.5 at.%.

10. The composite lithium alloy material according to claim 1 or 3, characterized in that... The content of alloying elements in the second cellulose / lithium alloy composite layer ranges from 0.1 to 10 at.%.

11. The composite lithium alloy material according to claim 3, characterized in that... The cellulose nanofibers have a diameter of 5-50 nm, a length of 0.2-3 μm, and a cellulose nanofiber content ranging from 0.1-20 wt.%.

12. A method for preparing a three-dimensional composite lithium alloy anode material, characterized in that... The process steps and conditions include the following: S1. First lithium alloy strips with a thickness of 50~150μm were prepared by melting-rolling method; S2. Second lithium alloy strips with a thickness of 50~150μm were prepared by melting-rolling method; S3. Pretreatment of cellulose nanofibers yields lithium-ion conductivity ≥1×10⁻⁶. -4 Modified cellulose nanofibers with a density of S / cm; S4. By homogenizing and dispersing the modified cellulose nanofibers obtained in step S3 with binder and solvent, and then coating the cellulose nanofibers onto the surface of the second lithium alloy strip obtained in step S2, a preliminary cellulose / lithium alloy composite strip semi-finished product is obtained. S5. The cellulose / lithium alloy composite strip semi-finished product prepared in step S4 is further composited by the stack rolling method, so that the cellulose is uniformly distributed in the lithium alloy to form a three-dimensional cellulose / lithium alloy composite strip. S6. Using a rolling method, the first lithium alloy strip obtained in step S1 and the cellulose / lithium alloy composite strip obtained in step S5 are rolled together to prepare a first lithium alloy layer-second cellulose / lithium alloy composite layer strip. S7. A third surface protective layer is coated on the upper second cellulose / lithium alloy composite layer of the first lithium alloy layer-second cellulose / lithium alloy composite layer strip prepared in step S6, and the third surface protective layer contains nanoscale solid electrolyte powder.

13. The method according to claim 12, characterized in that: In steps S1 and S2, the lithium alloy melting temperature should be higher than the melting point of the equilibrium phase diagram.

14. The method according to claim 12, characterized in that: In step S1, the lithium alloy is cooled by a rapid cooling method with a cooling rate >200℃ / min or by a mold with forced cooling.

15. The method according to claim 12, characterized in that: In step S3, the cellulose nanofibers are pretreated using ion coordination.

16. The method according to claim 15, characterized in that: In step S3, ion coordination is achieved by using copper ions (Cu ions) 2+ Coordination with cellulose nanofibers alters the crystal structure of cellulose, increasing the spacing between polymer chains to accommodate lithium ions (Li). + Molecular channels for embedding and rapid transport.

17. The method according to claim 12, characterized in that: The adhesive used in step S4 includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, styrene-butadiene rubber, polyacrylonitrile, and polyethylene.

18. The method according to claim 12, characterized in that: The solvent used in step S4 includes at least one of N-methylpyrrolidone, tetrahydrofuran, ethylene glycol dimethyl ether, dimethyl carbonate, dimethyl sulfoxide, and N,N-dimethylformamide.

19. The method according to claim 12, characterized in that: The mass ratio of cellulose nanofibers to binder used in step S4 is 50~98:2~50.

20. The method according to claim 12, 17, 18, or 19, characterized in that: The coating method in step S4 includes any one of casting coating, blade coating, or spray coating.

21. The method according to claim 12, characterized in that: In step S5, the stacking and calendering includes a cellulose / lithium alloy composite layer material, which is stacked in an AB / AB manner, where A represents the fiber side and B represents the lithium alloy side.

22. The method according to claim 12, characterized in that: The number of times the lamination is performed in step S5 is 4 to 6; the final lamination thickness is 20 to 100 μm.

23. The method according to claim 22, characterized in that: The final thickness of the lamination in step S5 is 20~50μm.

24. The method according to claim 12, characterized in that: In step S6, rolling makes the first lithium alloy layer and the second cellulose / lithium alloy composite layer bond more tightly, while further reducing the thickness.

25. The method according to claim 12, characterized in that: In step S7, the coating method of the third surface protective layer includes any one of casting coating, blade coating, spraying, gravure coating, micro-gravure coating, spin coating, and extrusion coating.

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