Surface protection layer of ultrathin lithium strip as well as preparation method and application of surface protection layer

Abstract

The invention discloses a surface protection layer of an ultrathin lithium strip as well as a preparation method and application of the surface protection layer, and belongs to the technical field of lithium batteries. The surface protection layer is formed after lithium metal reacts with a composite additive, and the composite additive is composed of solid powder and an organic solvent; wherein the solid powder is selected from one or more of dialkyl dithiophosphate or metal fluoride; the organic solvent is selected from any one of dimethyl sulfoxide, formamide, butyrolactam, acetone, 1, 4-dioxane, tetrahydrofuran, trimethyl phosphate, triethyl phosphate and propylene carbonate. The electrochemical performance of the produced lithium strip with the surface protection layer is remarkably improved, large-scale production can be achieved on the premise that existing equipment is not transformed and technological processes are not increased by means of the preparation method, the technical advantages in cost and technology are achieved, and therefore the lithium strip with the surface protection layer has a good application prospect. The surface protection layer of the ultrathin lithium strip and the preparation method of the surface protection layer have good application prospects.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to a surface protective layer for an ultrathin lithium strip, its preparation method, and its application. Background Technology

[0002] Currently, the energy density of lithium-ion batteries using graphite as the anode material is approaching its theoretical limit. Researchers have proposed using lithium metal instead of graphite as the anode material, as lithium metal anodes have a theoretically higher capacity (3860 mAh g⁻¹). -1 It has a lower chemical potential (-3.04 V) and is lighter (0.534 g cm⁻¹). -3 6.94 g mol -1 This can greatly improve the energy density of batteries and meet the needs of power battery development.

[0003] Lithium metal anodes are made of ultra-thin lithium strips, but they still face many challenges in practical applications. Due to the high reactivity of lithium metal, a solid electrolyte interphase (SEI) film spontaneously forms upon contact with the electrolyte. During charge and discharge, lithium metal undergoes volume deformation and lithium dendrite formation, which can cause the fragile SEI film to rupture. The exposed lithium metal continues to react with the electrolyte, consuming it and leading to reduced coulombic efficiency, decreased capacity, and poor cycle stability. Furthermore, the uneven ion transport properties of the SEI film exacerbate lithium dendrite growth, causing the separator to be punctured, resulting in short circuits and safety issues.

[0004] Constructing a surface protective layer at the lithium metal / electrolyte interface is considered an effective way to solve the above problems. This surface protective layer is expected to have the following characteristics: (1) excellent chemical and electrochemical stability, and electronic insulation to prevent continuous electrolyte decomposition and lithium consumption; (2) high mechanical modulus and flexibility to suppress dendrite growth and volume changes in the lithium metal anode during cycling; and (3) high ionic conductivity, enabling Li… + It can achieve uniform deposition, thereby suppressing the growth of lithium dendrites.

[0005] The current mainstream method for constructing a surface protective layer involves a secondary treatment after the lithium anode is produced. Chemical reagents capable of forming a surface protective layer are applied to the lithium anode through methods such as rolling, spraying, or coating. For example: CN118658957A discloses a lithium metal anode with a protective layer. A first protective layer is formed by applying solution A to the surface of lithium metal through various methods such as immersion, spin coating, scraping, and spraying. Then, solution B is applied to the surface of the first protective layer to form a second protective layer.

[0006] CN117638006B discloses a lithium metal fluorinated high-entropy SEI layer, its preparation method and its application. High-entropy fluoride powder is applied to the surface of lithium metal by rolling, and the fluoride reacts with the lithium metal to form a fluorinated high-entropy SEI layer.

[0007] CN113481502B provides a method for surface protection of lithium metal strips, its products and applications, and equipment. The method involves spraying a mixed solution containing organic and inorganic solutes onto the surface of the lithium metal strip using a spraying device, and then drying it in a drying device to form a surface protective layer.

[0008] The above technologies all involve secondary processing of the finished lithium anode or adding additional equipment to the production line to process the lithium anode. These processes are complex and costly, and none of them describe the time required for the formation of the surface protective layer. However, practical experience has shown that the reaction between various reactants, including metal fluorides, and lithium metal is slow. Therefore, developing a simple, low-cost, rapid, and scalable technology to construct a surface protective layer on the lithium anode surface is an urgent problem to be solved.

[0009] In view of this, the present invention is proposed. Summary of the Invention

[0010] The purpose of this invention is to provide a surface protective layer for an ultrathin lithium strip, its preparation method, and its application. This surface protective layer can limit the volume change of the lithium anode, promote uniform lithium ion deposition, and inhibit lithium dendrite growth.

[0011] This invention is implemented as follows: In a first aspect, the present invention provides a surface protective layer for an ultrathin lithium strip, wherein the lithium strip is a pure lithium strip with a lithium content of ≥99% or a lithium alloy strip with a lithium content of ≥50%, and the surface protective layer is a protective layer formed by reacting lithium metal with a composite additive, wherein the composite additive is composed of solid powder and organic solvent. The solid powder is selected from one or more of dialkyl dithiophosphates or metal fluorides; the organic solvent is selected from any one of dimethyl sulfoxide, formamide, butyrolactam, acetone, 1,4-dioxane, tetrahydrofuran, trimethyl phosphate, triethyl phosphate, and propylene carbonate.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned surface protective layer, which includes: adding solid powder to an organic solvent in proportion, mixing thoroughly to obtain a composite additive; adding the composite additive to rolling oil, mixing thoroughly, and then using it as a lubricant to roll an ultra-thin lithium strip to obtain an ultra-thin lithium strip with a protective layer.

[0013] Thirdly, the present invention provides an ultrathin lithium strip comprising the aforementioned lithium metal surface protective layer.

[0014] Fourthly, the present invention provides the application of the above-mentioned ultrathin lithium strip in the preparation of lithium metal battery anodes.

[0015] The present invention has the following beneficial effects: This invention achieves simultaneous rolling and surface protective layer preparation by adding additives to the rolling oil. The surface protective layer produced on ultrathin lithium strips using this method significantly reduces the SEI film impedance, charge transfer impedance, and nucleation overpotential, and substantially increases cycle time. Compared with other known methods, the preparation method of this invention has relatively low cost and significantly improved production efficiency, enabling large-scale production. Therefore, the surface protective layer of ultrathin lithium strips and its preparation method of this invention have promising application prospects. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a comparison diagram of the reaction between the organic solvent-promoting additive and lithium metal in Example 1; Figure 2 Bright-field image of the surface morphology of the lithium band in Example 1; Figure 3 Dark field image of the surface morphology of the lithium band in Example 1; Figure 4 Bright-field image of the surface morphology of the lithium band in Comparative Example 1; Figure 5 Dark-field image of the surface morphology of the lithium band in Comparative Example 1; Figure 6 EIS impedance spectra of symmetrical lithium-ion batteries from Example 1 and Comparative Example 1; Figure 7 The above are the nucleation overpotential curves of the symmetrical cells in Example 1 and Comparative Example 1. Figure 8 The graphs show the symmetrical battery cycle curves of Example 1 and Comparative Example 1. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] Because lithium metal is relatively soft and has strong self-welding ability, it tends to stick to the die during the rolling and thinning process of lithium strip production, causing the lithium strip to not form properly and damaging the die. Therefore, various organic liquids are used in industry as rolling oils to lubricate and prevent sticking. This invention is the first to propose the preparation of a protective layer on the surface of the lithium strip during the rolling process. That is, an organic or inorganic protective layer is formed by reacting the rolling oil with the surface of the lithium strip. The preparation method of this invention can achieve large-scale production without modifying existing equipment or adding process steps, and has technical advantages in terms of cost and process. At the same time, the electrochemical performance of the lithium strip with the protective layer produced is also significantly improved.

[0020] Based on this, the present invention provides a surface protective layer for an ultrathin lithium strip, which is a protective layer formed by the reaction of lithium metal with composite additives in rolling oil.

[0021] In this invention, the composite additive is composed of a solid powder and an organic solvent. The solid powder is selected from one or more of the following: zinc dialkyl dithiophosphate, molybdenum dialkyl dithiophosphate, sodium dialkyl dithiophosphate, antimony dialkyl dithiophosphate, lanthanum dialkyl dithiophosphate, copper dialkyl dithiophosphate, stannous fluoride, zinc fluoride, indium trifluoride, silver fluoride, antimony trifluoride, cobalt trifluoride, manganese trifluoride, vanadium trifluoride, copper fluoride, niobium pentafluoride, cerium fluoride, and barium fluoride. The organic solvent is selected from any one of the following: dimethyl sulfoxide, formamide, butyrolactam, acetone, 1,4-dioxane, tetrahydrofuran, trimethyl phosphate, triethyl phosphate, and propylene carbonate.

[0022] Solid powder is the main substance that reacts with lithium metal. Through the reaction, a protective layer can be formed. The type of protective layer includes any one or more of lithium alloy, lithium fluoride, lithium nitride, and organic thin film.

[0023] The role of the organic solvent in this invention is to dissolve the solid powder. It needs to be able to dissolve the solid powder and be miscible with the rolling oil. In addition, the preferred organic solvent can react with lithium metal to form an SEI film, so it can also participate in the reaction to form a surface protective layer. The reaction between the additive and lithium metal alone is relatively slow at room temperature, but by adding the preferred organic solvent, the reaction between the additive and lithium metal can be significantly accelerated.

[0024] In an optional embodiment, the concentration of the solid powder in the composite additive is 1–100 mmol / L. Specifically, the concentration of the solid powder in the composite additive can be 1 mmol / L, 5 mmol / L, 10 mmol / L, 15 mmol / L, 20 mmol / L, 25 mmol / L, 30 mmol / L, 35 mmol / L, 40 mmol / L, 45 mmol / L, 50 mmol / L, 55 mmol / L, 60 mmol / L, 65 mmol / L, 70 mmol / L, 75 mmol / L, 80 mmol / L, 85 mmol / L, 90 mmol / L, 95 mmol / L, or 100 mmol / L, or any other value between 1 and 100 mmol / L. Preferably, the concentration of the solid powder in the composite additive is 10–50 mmol / L. Within the above concentration range, the prepared composite additive can generate a suitable surface protective layer thickness and results in better production efficiency.

[0025] In optional embodiments, the rolling oil is selected from those with a dynamic viscosity of 0.9~3.5 mPa·s at 20°C, including but not limited to one or more of cyclobutane, cyclopentane, cyclohexane, polydimethylsiloxane, polydiethylsiloxane, butyl carbonate, dimethyl carbonate, butyl stearate, dioctyl carbonate, methyl methyl carbonate, methyl propionate, ethyl acetate, palmitate, butyl stearate, phthalate, isopropyl benzoate, and dodecyl / tetradecyl oleate. Since the dynamic viscosity of the rolling oil affects the rolling thickness of the lithium strip, the rolling oil selected in this invention can roll the lithium strip to ≤50μm, obtaining an ideal ultra-thin lithium strip. This ultra-thin lithium strip is particularly thin and light, and prone to wrinkling, which is difficult to restore after wrinkling. Subsequent secondary processing such as roll forming and spraying after rolling is quite challenging.

[0026] In an optional embodiment, the volume ratio of rolling oil to composite additive is 1 to 20:1. Specifically, the volume ratio can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, or 20:1, or any other value between 1 and 20:1. Preferably, the volume ratio of rolling oil to composite additive is 6 to 12:1. Within the above concentration range, a suitable surface protective layer thickness can be generated, resulting in better production efficiency and rolling effect.

[0027] Correspondingly, the present invention also provides a method for preparing the surface protective layer of the above-mentioned ultrathin lithium strip, which includes: adding solid powder to an organic solvent in proportion, mixing thoroughly to obtain a composite additive; adding the composite additive to rolling oil, mixing thoroughly, and then using it as a lubricant to roll the ultrathin lithium strip to obtain an ultrathin lithium strip with a protective layer.

[0028] The rolling process in the above preparation method uses conventional rolling methods in this field, so it will not be described in detail.

[0029] The ultrathin lithium strip with a surface protective layer obtained by the preparation method of the present invention can be used in the preparation of lithium metal battery anodes. It can not only save costs and achieve large-scale production, but also improve electrochemical performance and has industrial applicability.

[0030] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0031] Example 1 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add stannous fluoride powder to trimethyl phosphate, with a solid powder molar ratio of 20 mmol / L. After stirring until fully dissolved, a liquid additive is obtained.

[0032] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 6:1.

[0033] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0034] Example 2 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add stannous fluoride powder to trimethyl phosphate, with a solid powder molar ratio of 10 mmol / L. After stirring until fully dissolved, a liquid additive is obtained.

[0035] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 6:1.

[0036] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0037] Example 3 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add stannous fluoride powder to trimethyl phosphate, with a solid powder molar ratio of 50 mmol / L. After stirring and dissolving completely, a liquid additive is obtained.

[0038] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 6:1.

[0039] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0040] Example 4 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add zinc fluoride powder to trimethyl phosphate, with a solid powder molar ratio of 20 mmol / L. After stirring and dissolving completely, a liquid additive is obtained.

[0041] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 6:1.

[0042] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0043] Example 5 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add indium trifluoride powder to trimethyl phosphate, with the solid powder accounting for 20 mmol / L. After stirring and dissolving completely, a liquid additive is obtained.

[0044] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 6:1.

[0045] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0046] Example 6 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add zinc dialkyl dithiophosphate powder to trimethyl phosphate, with a solid powder molar ratio of 20 mmol / L. After stirring and dissolving completely, a liquid additive is obtained.

[0047] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 6:1.

[0048] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0049] Example 7 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add stannous fluoride powder to dimethyl sulfoxide, with a solid powder molar ratio of 20 mmol / L. After stirring until fully dissolved, a liquid additive is obtained.

[0050] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 6:1.

[0051] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0052] Example 8 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add stannous fluoride powder to triethyl phosphate, with a solid powder molar ratio of 20 mmol / L. After stirring until fully dissolved, a liquid additive is obtained.

[0053] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 6:1.

[0054] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0055] Example 9 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add stannous fluoride powder to propylene carbonate, with a solid powder molar ratio of 20 mmol / L. After stirring until fully dissolved, a liquid additive is obtained.

[0056] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 6:1.

[0057] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0058] Example 10 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add stannous fluoride powder to trimethyl phosphate, with a solid powder molar ratio of 20 mmol / L. After stirring until fully dissolved, a liquid additive is obtained.

[0059] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 8:1.

[0060] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0061] Example 11 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add stannous fluoride powder to trimethyl phosphate, with a solid powder molar ratio of 20 mmol / L. After stirring until fully dissolved, a liquid additive is obtained.

[0062] (2) Add liquid additives to cyclopentylsiloxane / polydimethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 10:1.

[0063] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0064] Example 12 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add stannous fluoride powder to trimethyl phosphate, with a solid powder molar ratio of 20 mmol / L. After stirring until fully dissolved, a liquid additive is obtained.

[0065] (2) Add liquid additives to cyclobutane / polydiethylsiloxane and stir to mix. The volume ratio of rolling oil to liquid additives is 6:1.

[0066] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0067] Example 13 This embodiment provides a method for preparing a lithium strip with a surface protective layer, including the following specific steps: (1) Add stannous fluoride powder to trimethyl phosphate, with a solid powder molar ratio of 20 mmol / L. After stirring until fully dissolved, a liquid additive is obtained.

[0068] (2) Add liquid additive to dioctyl carbonate and stir to mix. The volume ratio of rolling oil to liquid additive is 6:1.

[0069] (3) Using the above-mentioned rolling oil containing additives as a lubricant, thin lithium strip is rolled on a roller press. The mill exit speed is 5m / min, the rolling force is 18kN, and the interval for intermittently replenishing the rolling oil is 20s.

[0070] Comparative Example 1 This comparative example provides a lithium strip without a surface protective layer. The difference from Example 1 is that it uses an additive-free rolling oil as a lubricant. The specific steps are as follows: Cyclopentasiloxane / polydimethylsiloxane was used as a lubricant to roll thinned lithium strip on a rolling mill. The mill exit speed was 5 m / min, the rolling force was 18 kN, and the interval for intermittent replenishment of rolling oil was 20 s.

[0071] Experimental Example 1 To verify the electrochemical performance of the ultrathin lithium strips with surface protective layers prepared in Examples 1-13 and Comparative Example 1, coin cell symmetrical batteries were assembled using the ultrathin lithium strips of each group as negative electrodes for electrochemical testing, including the following steps: (1) Cut the ultrathin lithium strip with / without artificial SEI film into circular electrodes with a diameter of 16 mm; (2) The above-mentioned circular electrode is moved into an argon glove box and assembled into a button-type symmetrical battery in the order of positive electrode shell, electrode sheet, electrolyte, diaphragm, electrode sheet, gasket, spring sheet and negative electrode shell. (3) After the above coin cell was left to stand for 10 hours, the impedance was tested using an electrochemical workstation. (4) After the impedance test is completed, a cyclic test is performed on a constant current charge-discharge instrument.

[0072] Figure 1 This is a schematic diagram of the reaction between the organic solvent-accelerated additive (solid powder) and lithium metal in Example 1. The lithium metal does not show any obvious changes in trimethyl phosphate, and there is no obvious change when stannous fluoride powder is sprinkled on the lithium metal. On this basis, after adding trimethyl phosphate, a rapid reaction occurs, and the surface of the lithium metal turns black.

[0073] Figure 2-3 The images show the bright-field and dark-field plots of the lithium strip surface morphology from Example 1. Figure 4-5 The images shown are bright-field and dark-field images of the surface morphology of the lithium strip in Comparative Example 1. It can be observed that the surface morphology of the lithium strip in Example 1 and the lithium strip in Comparative Example 1 are significantly different. The lithium strip in Example 1 has a layer of "dark" substance on its surface, which is a surface protective layer formed by the reaction of additives with lithium metal.

[0074] Figure 6 The images show the EIS impedance spectra of the lithium-ion batteries in Example 1 and Comparative Example 1. Compared to the lithium-ion battery in Comparative Example 1, the SEI film impedance and charge transfer impedance of the lithium-ion battery in Example 1 are significantly reduced because the surface protective layer promotes ion migration and charge transfer.

[0075] Figure 7 The graphs show the nucleation overpotential curves of the symmetrical cells in Example 1 and Comparative Example 1. Compared to the lithium strip in Comparative Example 1, the nucleation overpotential of the lithium strip in Example 1 is significantly reduced because the surface protective layer is an excellent conductor of ions.

[0076] Figure 8 The graphs show the symmetrical battery cycle curves of Example 1 and Comparative Example 1. Compared to the lithium band of Comparative Example 1, the stable cycle time of the lithium band of Example 1 is significantly increased because the surface protective layer helps to distribute the charge evenly and suppress material deformation.

[0077] Table 1 summarizes the electrochemical test data of Examples 1-13 and Comparative Example 1.

[0078] Table 1. Electrochemical test data of Examples 1-13 and Comparative Example 1

[0079] According to the test results in Table 1, compared with the absence of a surface protective layer, the ultrathin lithium strips of Examples 1-13 show significant improvements in performance in terms of SEI film impedance, charge transfer impedance, nucleation overpotential, and stable cycle time.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A surface protection layer of an ultrathin lithium ribbon, characterized by, The lithium strip is a pure lithium strip with lithium content ≥ 99% or a lithium alloy strip with lithium content ≥ 50%, and the surface protection layer is a protection layer formed by reaction of lithium metal with a composite additive. The solid powder is selected from one or more of a dialkyldithiophosphate or a metal fluoride; and the organic solvent is selected from any one of dimethyl sulfoxide, formamide, butyrolactam, acetone, 1,4-dioxane, tetrahydrofuran, trimethyl phosphate, triethyl phosphate, propylene carbonate.

2. The surface protection layer according to claim 1, characterized in that, The solid powder is selected from one or more of zinc dialkyldithiophosphate, molybdenum dialkyldithiophosphate, sodium dialkyldithiophosphate, antimony dialkyldithiophosphate, lanthanum dialkyldithiophosphate, copper dialkyldithiophosphate, stannous fluoride, zinc fluoride, indium trifluoride, silver fluoride, antimony trifluoride, cobalt trifluoride, manganese trifluoride, vanadium trifluoride, copper fluoride, niobium pentafluoride, cerium fluoride, barium fluoride.

3. The surface protection layer according to claim 2, characterized in that The concentration of the solid powder in the composite additive is 1-100 mmol / L. Preferably, the concentration of the solid powder in the composite additive is 10-50 mmol / L.

4. The surface protection layer according to claim 1, characterized in that, The composite additive is dissolved in rolling oil, and the dynamic viscosity of the rolling oil at 20°C is 0.9-3.5 mPa·s. Preferably, the rolling oil is selected from one or more of cyclobutylsiloxane, cyclopentylsiloxane, cyclohexylsiloxane, polydimethylsiloxane, polydiethylsiloxane, butylene carbonate, dimethyl carbonate, butyl stearate, dicaprylyl carbonate, methyl ethyl carbonate, methyl propionate, ethyl acetate, palmitate, butyl stearate, phthalate, isopropyl benzoate, and dodecyl / tetradecyl alcohol oleate.

5. The surface protection layer according to claim 4, characterized in that The volume ratio of the rolling oil to the composite additive is 1-20:

1.

6. The surface protection layer according to claim 5, characterized in that The volume ratio of the rolling oil to the composite additive is 6-12:

1.

7. The surface protection layer according to claim 5, characterized in that The thickness of the ultra-thin lithium strip is ≤ 50 μm.

8. The method for producing a surface protective layer according to any one of claims 1 to 7, wherein The method comprises: The solid powder is added to the organic solvent in a proportion, and after sufficient mixing, the composite additive is obtained; the composite additive is added to the rolling oil, and after sufficient mixing, the ultra-thin lithium strip is rolled as a lubricating oil, thereby obtaining an ultra-thin lithium strip with a protection layer.

9. An ultrathin lithium ribbon, characterized by, The surface protection layer comprises the composite additive.

10. Use of the ultra-thin lithium strip of claim 9 in the preparation of a lithium metal battery negative electrode.

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