A method for in-situ constructing an organic / inorganic composite solid electrolyte layer on the surface of lithium metal and a lithium battery made therefrom.

Abstract

This application discloses a method for in-situ construction of an organic / inorganic composite solid electrolyte layer on the surface of lithium metal and a lithium battery made therefrom, belonging to the field of lithium battery materials. It describes the in-situ construction of a novel organic / inorganic composite solid electrolyte layer (SEI) on the surface of lithium metal using PVDF, LiF, and LiNO3. This invention is the first to utilize lithium-metal-stable ether solvents to dissolve polymer PVDF at high temperatures, thereby achieving the construction of a PVDF / LiNO3 / LiF composite film on the lithium metal surface at room temperature. During lithium metal electrode cycling, the LiNO3 within the film is slowly released into ether or ester electrolytes, forming a localized LiNO3 concentration electrolyte structure in the initial stage of cycling, and ultimately forming a PVDF / LiF / Li3N SEI layer with a high concentration of Li3N on the lithium metal surface. Furthermore, the introduction of LiF into the SEI layer significantly improves the uniformity and mechanical strength of the SEI film.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery materials, specifically relating to the preparation of an organic / inorganic composite solid electrolyte layer constructed in situ on the surface of a lithium anode and the lithium battery made therefrom. Background Technology

[0002] Lithium metal, with its high theoretical capacity and lowest redox potential, is considered the holy grail of anode materials. However, the uncontrollable dendrite growth and side reactions during cycling limit the cycle stability and safety of lithium metal anodes.

[0003] Therefore, in recent years, to address the problems arising from the practical application of lithium anodes and to construct stable solid electrolyte layers, various new strategies have been proposed and developed to improve battery safety and lifespan, suppress side reactions, and prevent dendrite growth and dead lithium formation on the lithium metal anode side. Constructing a stable solid electrolyte layer (SEI) on the lithium metal surface, achieving high lithium-ion transport rates and uniformity while enhancing its mechanical strength, is an effective strategy for suppressing dendrite growth and side reactions, and is crucial for improving the cycle stability and safety of lithium metal.

[0004] Existing methods for constructing SEI layers primarily involve in-situ and ex-situ chemical reactions, such as pretreatment of lithium metal surfaces with chemicals and in-situ reactions between electrolyte components and lithium metal. Traditionally, polar solvents such as NMP (N-methylpyrrolidone), DMAc (N,N-dimethylacetamide), and DMF (N,N-dimethylformamide) are often used to dissolve polymers. However, during in-situ construction on lithium metal surfaces, these polar solvents can undergo side reactions with the lithium metal, forming a fragile and uneven SEI layer, increasing interfacial impedance. Furthermore, in ex-situ processes on lithium metal anode surfaces, the interfacial stability of existing SEI layers is compromised by misfitting processes and the introduction of impurities, limiting further improvements in the cycle stability of lithium anodes. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a solid electrolyte layer in situ on the surface of a lithium anode and a lithium battery made therefrom.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for in-situ constructing an organic / inorganic composite solid electrolyte layer on a lithium metal surface, obtained through the following process: (1) Polyvinylidene fluoride (PVDF) is dissolved in dimethyl ethylene glycol (DME). The mixture is heated and stirred at 120 ℃-140 ℃ to dissolve the PVDF. Then, lithium nitrate (LiNO3) and lithium fluoride (LiF) are added to the solution. The mixture is magnetically stirred at 55~65 ℃ for 1~2 h to obtain a DPLL mixture. The concentration of PVDF in the DME is 20~200 mg / ml. -1 ; (2) The DPLL mixture is drop-coated onto the lithium sheet and naturally evaporated to obtain a lithium sheet covered with an organic / inorganic composite solid electrolyte layer.

[0007] Preferably, the concentration of LiNO3 in ethylene glycol dimethyl ether is 0.1~1 mol / L, and the dispersion of LiF in ethylene glycol dimethyl ether is 0.1~1 mol / L.

[0008] Preferably, the stirring speed of the PVDF in the DME is 550 rpm to 750 rpm. The stirring speed of the LiNO3 and LiF in the DME is 500 rpm to 600 rpm.

[0009] The lithium sheet with an organic / inorganic composite solid electrolyte layer was prepared by the above method.

[0010] The lithium symmetric battery fabricated using the lithium sheet covered with the above-mentioned organic / inorganic composite solid electrolyte layer uses the lithium sheet covered with the organic / inorganic composite solid electrolyte layer as the positive and negative electrodes, and uses an ether electrolyte or an ester electrolyte. The ether electrolyte composition is: a mixed solution of ethylene glycol dimethyl ether and 1,3-dioxolane with a volume ratio of 1:1 for 0.5~2 mol / L LiTFSI; the ester electrolyte composition is: a mixed solution of ethylene carbonate, diethyl carbonate and fluoroethylene carbonate with a volume ratio of 0.45:0.45:0.1 for 0.5~2 mol / L lithium hexafluorophosphate.

[0011] A lithium-sulfur battery fabricated using the aforementioned lithium sheet coated with an organic / inorganic composite solid electrolyte layer uses an aluminum foil coated with carbon material, binder, and sulfur as the positive electrode, a lithium sheet coated with an organic / inorganic composite solid electrolyte layer as the negative electrode, and a mixed solution of 0.5~2 mol / L LiTFSI ethylene glycol dimethyl ether and 1,3-dioxolane as the electrolyte, with a volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane of 1:1. The positive electrode is prepared by the following process: porous carbon and sulfur in a mass ratio of 3:7 are ground evenly in a mortar, and then heated at 150~160℃ for 10~15 h under argon protection to obtain sulfur-loaded carbon. The sulfur-loaded carbon, Ketjen black, and binder are uniformly mixed in N-methylpyrrolidone in a mass ratio of 8:1:1, and then coated onto aluminum foil and dried to obtain the desired product. The sulfur loading on the electrode is 1.5~4 mg cm⁻¹. -2 .

[0012] The lithium iron phosphate battery or nickel-cobalt-manganese 811 battery prepared using the lithium sheet covered with the above-mentioned organic / inorganic composite solid electrolyte layer uses an aluminum foil loaded with lithium iron phosphate or nickel-cobalt-manganese 811 as the positive electrode, a lithium sheet covered with an organic / inorganic composite solid electrolyte layer as the negative electrode, and an ether electrolyte or an ester electrolyte. The ether electrolyte composition is: a mixed solution of ethylene glycol dimethyl ether and 1,3-dioxolane in 0.5~2 mol / L LiTFSI, with a volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane of 1:1; the ester electrolyte composition is: a mixed solution of ethylene carbonate, diethyl carbonate and fluoroethylene carbonate in 0.5~2 mol / L lithium hexafluorophosphate, with a volume ratio of ethylene carbonate, diethyl carbonate and fluoroethylene carbonate of 0.45:0.45:0.1.

[0013] Further, aluminum foil loaded with lithium iron phosphate or nickel cobalt manganese 811 is prepared by the following process: lithium iron phosphate material or nickel cobalt manganese 811 material, polyvinylidene fluoride, and Ketjen black are uniformly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1, and then evenly stretched onto aluminum foil using a four-sided spreader and dried to obtain the desired product. The loading mass of lithium iron phosphate on the aluminum foil is controlled at 3 mg / cm³. -2 ~6 mg cm -2 The loading mass of nickel-cobalt-manganese 811 on aluminum foil was controlled at 7.5 mg / cm³. -2 ~8.5 mg cm -2 .

[0014] The lithium pouch battery fabricated using the aforementioned lithium sheet coated with an organic / inorganic composite solid electrolyte layer uses an aluminum foil loaded with lithium iron phosphate as the positive electrode and a copper foil coated with a lithium strip covered with an organic / inorganic composite solid electrolyte layer as the negative electrode. The electrolyte addition amount is 20~30 μL mAh. -1It is packaged with an aluminum-plastic film and uses a mixed solution of 0.5~2 mol / L LiTFSI ethylene glycol dimethyl ether and 1,3-dioxolane as the electrolyte, with a volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane of 1:1.

[0015] The aluminum foil loaded with lithium iron phosphate in lithium-ion pouch batteries is prepared by the following process: lithium iron phosphate material, polyvinylidene fluoride, and Ketjen black are uniformly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1. Then, the mixture is evenly stretched onto aluminum foil using a four-sided milling machine and dried. The mass of lithium iron phosphate loaded on the aluminum foil is controlled at 3 mg / cm³. -2 ~6 mg cm -2 .

[0016] In the above technical solution, the solution preparation is carried out in an anhydrous environment at room temperature.

[0017] Compared with the prior art, the present invention has the following advantages: 1. This invention achieves in-situ construction of an organic / inorganic composite solid electrolyte layer (SEI) on the surface of a lithium anode. For the first time, it utilizes lithium-metal-stable ether solvents to dissolve polymer PVDF at high temperatures, thereby enabling the construction of a PVDF / lithium nitrate / lithium fluoride composite film on the lithium metal surface at room temperature. During lithium metal electrode cycling, the LiNO3 within the film is slowly released into the ether (or ester) electrolyte, forming a localized LiNO3 concentration gradient electrolyte structure in the initial stage of cycling, and ultimately forming a high-concentration Li3N PVDF / LiF / Li3N SEI layer on the lithium metal surface. Furthermore, the introduction of LiF into the SEI layer significantly improves the uniformity and mechanical strength of the SEI film.

[0018] 2. The PVDF solvents used are typically highly polar solvents, such as NMP (N-methylpyrrolidone), DMAc (N,N-dimethylacetamide), and DMF (N,N-dimethylformamide). However, these solvents have low LOMO energy levels and readily undergo violent side reactions with lithium metal. This results in a low ion transport rate for the formation of the SEI layer on the lithium metal surface, significantly reducing the uniformity of lithium metal deposition and stripping, and leading to a significant decrease in cycle performance. Therefore, PVDF solutions dissolved in these highly polar solvents are unsuitable for in-situ formation of PVDF polymers on the lithium metal surface.

[0019] 3. This invention realizes a simple strategy for dissolving PVDF with low-polarity ether solvents to construct an organic / inorganic composite solid electrolyte layer (SEI) on the lithium anode surface in situ. Compared with non-situ construction, it can achieve good adhesion with lithium metal and avoid the introduction of impurities during the film transfer process.

[0020] 4. Compared with polymer solid electrolyte layers, organic / inorganic composite solid electrolyte layers can bring better results. In the process of suppressing the growth of lithium dendrites at the interface, a high concentration of nitrate ions is generated at the interface, which can bring a high N content SEI to the lithium anode, while also making the deposition of lithium ions more uniform and better realizing the stable operation of lithium metal batteries.

[0021] 5. This invention utilizes a simple coating process on the lithium metal surface to in-situ construct an organic-inorganic composite PVDF / LiF / LiNO3 film, which can form a high lithium-ion transport rate and mechanical strength SEI layer on the lithium metal surface. Li-Li symmetric batteries constructed with this film achieve high cycle life. Compared to existing LiNO3-added electrolyte systems, different types of lithium metal full cells constructed with this film exhibit higher cycle life and capacity retention. This organic-inorganic composite SEI layer construction strategy is also expected to improve the cycle stability of other alkali metal-based batteries. Attached Figure Description

[0022] Figure 1 Optical photographs of PVDF in DME before (a) dissolution, after (b) dissolution, and after (c) standing for a period of time after dissolution; Figure 2 Preparation process of PLL lithium sheet for in-situ construction of solid electrolyte layer on lithium anode surface; Figure 3 To compare the effects of different solvents on lithium metal batteries, 100 mg of PVDF, LiNO3, and LiF were added to 2 ml of DMAc, DMSO, and NMP solvents, respectively, to achieve a LiNO3 concentration of 0.4 M and a LiF dispersion of 0.2 M. The solutions were stirred and dissolved at room temperature to prepare DMAc-PLL, DMSO-PLL, and NMP-PLL solutions. 60 μL of each solution was dropped onto a lithium metal surface for observation. Then, 12 mm diameter plates were cut, and 15 μL of a 1 M LiTFSI DOL / DME (volume ratio 1:1) electrolyte was added to both the positive and negative electrodes. Lithium-ion batteries were then assembled from these lithium plates. The effects of DMAc, DMSO, and NMP solvents on (a) the surface impedance of lithium metal and (b) the interfacial impedance after cycling under in-situ conditions were observed. 60 μL of DMAc-PLL solution, DMSO-PLL solution, and NMP-PLL solution were dropped onto the surface of copper foil, dried, peeled off, and placed on the surface of a 12 mm lithium sheet. 15 μL of DOL / DME (volume ratio 1:1) electrolyte with 1M LiTFSI was added to the positive and negative electrodes to assemble a lithium symmetric battery. The effects of DMAc, DMSO, and NMP solvents on (c) the surface impedance of lithium metal and (d) the interfacial impedance after cycling under non-in-situ conditions were observed. Figure 4Surface characterization of in-situ constructed organic / inorganic composite solid electrolyte layers on the lithium anode surface: Similar to the DPLL solution preparation process, 60 μL of DME-PVDF, DME-PVDF-LiNO3, and DME-PVDF-LiF solutions with the same content as the DPLL solution were used to prepare DME-PVDF films and lithium sheets, DME-PVDF-LiNO3 films and lithium sheets, and DME-PVDF-LiF films and lithium sheets. (a) Optical and SEM images of PVDF on the lithium metal surface; (b) Optical and SEM images of PVDF-LiNO3 on the lithium metal surface; (c) Optical and SEM images of PVDF-LiF on the lithium metal surface; (d) Optical and SEM images of PVDF-LiNO3-LiF on the lithium metal surface; (e) Cross-section of PVDF-LiF-LiNO3 (PLL); (f) SEM image of the PLL film after washing away lithium nitrate; (g) XRD patterns of PLL and corresponding PVDF, LiF, and LiNO3; (h) Mechanical test patterns of films with different compositions; (i) TGA pattern of PLL; Figure 5 XPS plot of SEI without cycling on lithium metal electrode: XPS plot of N and F elements on the surface after PLL film is constructed on lithium metal surface; Figure 6 Performance testing of lithium-ion symmetric batteries: (a) Li(PLL) at a current of 0.5 mA cm⁻¹ -2 The capacity is 0.5 mAhcm -2 The cyclic diagram; Li(PLL) and the control group (referred to as Li(LiNO3) in the figure) at a current of 1 mA cm⁻¹ -2 The capacities are (b) 1 mAh cm -2 (c) 5 mAh cm -2 (d) 10 mAh cm -2 (e) Cyclic comparison diagram of PVDF, PVDF-LiNO3, PVDF-LiF and PLL; (f) Cyclic comparison diagram of in-situ film formation and washing away lithium nitrate (Cell 1), non-in-situ film formation and washing away lithium nitrate (Cell 2) and PLL (Cell 3); Figure 7A schematic diagram of the construction of a solid electrolyte layer (SEI) during lithium metal electrode cycling: (a) LiNO3 in the PLL membrane is slowly released in an ether (or ester) electrolyte to form a local LiNO3 concentration gradient electrolyte structure in the early stage of cycling, and eventually forms a PVDF / LiF / Li3N SEI layer with a high concentration of Li3N on the lithium metal surface; (b) Construction of the surface SEI of the lithium metal anode containing LiNO3 in the electrolyte. As LiNO3 is continuously consumed, an uneven and low N content SEI is generated, leading to the formation of lithium dendrites on the surface; Figure 8 For in-situ optical microscopy characterization: for lithium anodes containing PLL and lithium anodes containing 0.46 M lithium nitrate (a, b), at a current of 2 mA cm⁻¹ -2 The deposition effect; (c, d) SEM images of the surface morphology of the lithium anode containing PLL and the lithium anode containing 0.46 M lithium nitrate after 50 cycles; Figure 9 For complete stripping tests during battery cycling: (a) Complete stripping curves of lithium copper batteries assembled with Li (PLL) and Li (LiNO3); (b) and (c) Optical photographs of the lithium anode after stripping of lithium copper batteries assembled with Li (PLL) and Li (LiNO3). Figure 10 For electrochemical characterization: (a) Impedance testing of a symmetric cell containing PLL (hereinafter referred to as Li(PLL)) and a symmetric cell containing 0.46 M lithium nitrate (hereinafter referred to as Li(LiNO3)) before cycling; (b) Impedance testing of a symmetric cell containing PLL (hereinafter referred to as Li(PLL)) and a symmetric cell containing 0.46 M lithium nitrate (hereinafter referred to as Li(LiNO3)) after 50 cycles; (c) Tafel curve testing of Li(PLL) and Li(LiNO3); (d) CV curves of Li(PLL) and Li(LiNO3) at different LiNO3 concentrations; (e) CV cycle testing of a lithium copper battery with Li(PLL) in 1–10 cycles; (f) CV cycle testing of a lithium copper battery with 0.5 M lithium nitrate in 1–10 cycles. Figure 11 For ultraviolet-absorption spectroscopy analysis (UV-Vis): (a) Comparison of UV absorption spectra of DME solutions with different concentrations of lithium nitrate; (b) Comparison of UV absorption spectra of lithium nitrate slow release within PLL membrane over time; Figure 12Characterization of the negative electrode surface after cycling: (a, b) XPS depth etching characterization of N element in Li(PLL) and Li(LiNO3); (c, d) XPS etching content characterization of N element in Li(PLL) and Li(LiNO3); (e, f) N and LiNO3 content in Li(PLL) and Li(LiNO3). - LiF, Li - O 2- Static-time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis of elements; Figure 13 EDS spectra of F, N, and O elements on the surface of Li(PLL) before (a) and after (b) cycling; Figure 14 Electrochemical performance of Li(PLL) and Li(LiNO3) full cells: (a) Li / S cell at a current rate of 0.5 C and (b) Li / S cell with a mass loading of 5 mg cm⁻¹. -2 The Li / / LiFePO4 battery, and (c) and 12 mg cm -2 (d) Cycling at a rate current of 0.5 C with a load of 75 mg in a Li / / LiFePO4 pouch cell at a rate current of 1 C (test voltage range 4.0-2.5 V); (e) Cycling at a rate current of 1 C with a load of 130 mg in a Li / / LiFePO4 pouch cell; (f) Optical photograph of a Li(PLL) Li / / LiFePO4 pouch cell; Figure 15 Electrochemical performance tests of lithium-ion symmetric batteries for ester batteries: (a) Cyclic test of symmetric batteries containing PLLs, Li(PLL) and Li(K); (b, c) Impedance tests of symmetric batteries containing PLLs, Li(PLL) and Li(K), after 50 and 100 cycles. Figure 16 Characterization of the negative electrode surface of ester batteries after cycling: (a, b) XPS depth etching characterization of N element in Li(PLL) and Li(K); (c, d) XPS etching content characterization of N element in Li(PLL) and Li(K); Figure 17 Electrochemical performance of Li(PLL) and Li(K) NMC811 full cells in esters: (a, b) Li(PLL) and Li(K) NMC811 full cells at a loading of 8 mg cm⁻¹ -2 Electrochemical performance at rate currents of 0.5 C and 1 C. Detailed Implementation

[0023] To make the technical objectives, technical solutions, and superior effects of the present invention clearer, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0024] Example 1: Materials sourced from: Diethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), lithium di(trifluoromethane)sulfonylimide (LiTFSI), and lithium hexafluorophosphate (LiPF6) were purchased directly from Suzhou Duoduo Chemical Co., Ltd., China. The solvent water content was less than 20 ppm, and the lithium salt water content was less than 40 ppm. Lithium sheets, lithium strips, copper foil, aluminum foil, lithium iron phosphate, ternary nickel-cobalt-manganese 811 (NCM811), and Ketjen carbon black were purchased from Krohde Chemical Co., Ltd. The lithium sheets were 450 μm thick and 15.6 mm in diameter; the lithium strips were 10 cm wide, 100 cm long, and 50 μm and 100 μm thick, respectively. The PP film is a polypropylene film, model: Cegard2400. The PVDF was purchased from Dongguan Zhanyang Polymer Materials Co., Ltd., with a molecular weight of 900,000.

[0025] The argon gas used in the experiment had a purity of 99.999%. All materials used for battery assembly were stored in a glove box filled with argon gas.

[0026] (1) Preparation of PLL negative electrode: 100 mg PVDF was added to a vial containing 2 ml DME and dissolved by magnetic stirring at 140 °C. Then, LiNO3 and LiF were added to the vial so that the concentration of LiNO3 in DME was 0.4 M and the dispersion of LiF was 0.2 M. The vial was stirred magnetically at 60 °C for 1 h to obtain a uniformly dispersed DPLL solution.

[0027] Inside the glove box, 60 μL of DPLL solution was pipetted and uniformly applied to a lithium metal surface with a diameter of 15.6 mm. After natural evaporation, a lithium metal anode (hereinafter referred to as PLL lithium sheet) with a white organic / inorganic composite film was obtained. In addition, copper foil was cut into 16 mm diameter discs, and 60 μL of DPLL solution was added to prepare copper foil with a white film on the surface (hereinafter referred to as Cu(PLL)).

[0028] DME-PVDF solution: Add 100 mg PVDF to a vial containing 2 ml DME and dissolve by magnetic stirring at 140 ℃; DME-PVDF-LiNO3 solution: Add 100 mg PVDF to a vial containing 2 ml DME, stir magnetically at 140 °C to dissolve, then add LiNO3 to the vial to make the concentration of LiNO3 in DME 0.4 M, and stir magnetically at 60 °C for 1 h. DME-PVDF-LiF solution: Add 100 mg PVDF to a vial containing 2 ml DME, stir magnetically at 140 °C to dissolve, then add LiF to the vial to make the LiF dispersion in DME 0.2 M, and stir magnetically at 60 °C for 1 h. (2) Preparation of the positive electrode: Preparation of the lithium-sulfur positive electrode: Porous carbon and sulfur in a mass ratio of 3:7 were ground evenly in a mortar. The powder was then poured into a crucible and placed in a tube furnace. Under argon protection, it was heated at 155°C for 12 h. Finally, the sulfur-loaded carbon, Ketjen black, and binder (PVDF) were weighed in a mass ratio of 8:1:1 and uniformly mixed in N-methylpyrrolidone. This mixture was then coated onto aluminum foil and placed in an oven to dry at 60°C for 12 h. The resulting product was then ready for use as the battery positive electrode, with a sulfur loading of 1.5 mg / cm³. -2 Preparation of lithium iron phosphate cathode: Lithium iron phosphate, polyvinylidene fluoride, and Ketjen black were uniformly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1. The mixture was then evenly stretched onto aluminum foil using a four-sided electrode preformer. The electrode was heated at 80℃ under vacuum for 10 h. The lithium iron phosphate loading on the aluminum foil was controlled to be 5 ± 0.2 mg / cm³. -2 The cathode preparation process for the pouch cell is as described above, with the lithium iron phosphate loading controlled at 3 ± 0.2 mg cm⁻¹. -2 and 5. mg ± 0.4 mg cm -2 Preparation of the nickel-cobalt-manganese 811 cathode: Nickel-cobalt-manganese 811 material, polyvinylidene fluoride, and Ketjen black were uniformly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1. The mixture was then evenly stretched onto aluminum foil using a four-sided electrode preformer. The electrode was heated at 80℃ under vacuum for 10 h. The loading mass of nickel-cobalt-manganese 811 on the aluminum foil was controlled at 8 ± 0.2 mg / cm². -2 All of the above current collectors are circular sheets with a diameter of 12 mm when assembling coin cells.

[0029] (3) Preparation of electrolytes: Preparation of ether electrolytes: Ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) were mixed in a volume ratio of 1:1, and LiTFSI was added and shaken to dissolve, so that the concentration of LiTFSI was 1 M, which was used as the electrolyte for the experimental group; Ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) were mixed in a volume ratio of 1:1, and LiTFSI and LiNO3 were added and shaken to dissolve, so that the concentration of LiTFSI was 1 M and the concentration of LiNO3 was 0.46 M, which was used as the electrolyte for the blank group; Preparation of ester electrolytes: Ethyl carbonate (EC), diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) were mixed in a volume ratio of 0.45:0.45:0.1, and lithium hexafluorophosphate (LiPF6) was added and shaken to dissolve, so that the concentration of LiPF6 was 1 M; (4) Battery Assembly: Button Cell Assembly: Ether electrolyte batteries were assembled using the experimental group's electrolyte. A 12mm diameter PLL lithium sheet was used as both the positive and negative electrodes, with 15 μL of ether electrolyte added to each electrode to form a Li|Li symmetric battery. A 12mm diameter PLL lithium sheet was used as the positive electrode, and a 16mm diameter Cu covering the PLL was used as the negative electrode, with 15 μL of electrolyte added to each electrode to form a Li|Cu half-cell for testing. A 15.6mm diameter PLL lithium sheet was used as the negative electrode, and lithium iron phosphate was used as the positive electrode, with 20 μL of ether electrolyte added to each electrode to form an LFP full cell for testing. A 15.6mm diameter PLL lithium sheet was used as the negative electrode, and sulfur-loaded carbon paper was used as the positive electrode, with 20 μL of ether electrolyte added to each electrode to form a Li|S full cell for testing. Pouch Cell Assembly: Both positive and negative electrode areas were 4 cm × 6 mm. The cathode is an aluminum foil loaded with lithium iron phosphate, and the anode is a copper foil covering a 100µm lithium band PLL film. The amount of ether electrolyte added is 25 μL mAh. -1 It is encapsulated in an aluminum-plastic film with a thickness of only 1.152 mm.

[0030] Ester-based electrolyte batteries were assembled using ester-based electrolytes. A Li|Li symmetric battery was constructed by adding 20 μL of ester electrolyte to each of the positive and negative electrodes using a 12 mm diameter PLL lithium sheet as the positive and negative electrodes. A full cell was also assembled using a 15.6 mm diameter PLL lithium sheet as the negative electrode and a 12 mm diameter aluminum foil loaded with nickel-cobalt-manganese 811 as the positive electrode, with 20 μL of ester electrolyte added to each electrode. In ether-based batteries, the PLL-based battery is designated Li(PLL), and the battery assembled with bare lithium and 0.46 M LiNO3 ether electrolyte is designated Li(LiNO3). In ester-based batteries, the battery assembled with a PLL as the negative electrode is designated Li(PLL), and the battery assembled with bare lithium is designated Li(K).

[0031] 1. PVDF dissolves in DME First, through Figure 1 The optical photographs show that this application achieved the dissolution of PVDF in DME at high temperature, realizing the dissolution of polymers in low-polarity solvents, which lays the foundation for subsequent experiments.

[0032] 2. Preparation of PLL-lithium wafers like Figure 2 As shown, 100 mg of PVDF was dissolved in 2 ml of DME solution, and LiNO3 (0.4 M) and LiF (0.2 M) were added. The mixture was shaken and stirred to disperse the LiF particles evenly. 60 μL of the solution was dropped onto the surface of a lithium sheet with a diameter of 15.6 mm. After natural evaporation, a PLL lithium sheet was obtained.

[0033] 3. The Influence of Highly Polar Solvents Figure 3 (a) and (b) in the figures represent DMAc-PLL solution, DMSO-PLL solution, and NMP-PLL solution, respectively. 60 μL of each solution was dropped onto the lithium anode surface to observe the effect. Then, lithium sheets with a diameter of 12 mm were cut and 1 M LiTFSI DOL / DME (volume ratio 1:1) electrolyte were added to assemble lithium-ion symmetric batteries. The effects of DMAc, DMSO, and NMP solvents on the surface and interfacial impedance of the lithium metal after cycling under in-situ conditions were observed. At room temperature, PVDF, LiNO3, LiF, DMAc, DMSO, and NMP were used as in-situ solvents to affect the surface and interfacial impedance of the lithium metal. It was observed that the lithium anode surface turned black after cycling, and the impedance before cycling was significantly increased compared to Li(LiNO3). This further indicates that polar solvents react with the lithium anode, and the reactants increase the interfacial impedance. DMAc-PLL solution, DMSO-PLL solution, and NMP-PLL solution were dropped onto the surface of copper foil, dried, peeled off, and placed on the surface of a 12 mm lithium sheet. 1 M LiTFSI DOL / DME (volume ratio 1:1) electrolyte was added to assemble lithium-ion symmetric batteries. Lithium-ion symmetric batteries were assembled using M LiTFSI DOL / DME (volume ratio 1:1) electrolyte. The effects of DMAc, DMSO, and NMP solvents on (c) the lithium metal surface and (d) the interfacial impedance after cycling under non-in-situ conditions were observed. It can be seen that although non-in-situ cycling did not affect the impedance of the lithium anode before cycling, it did affect the stability of the interface after cycling. Black side reaction substances were generated at the interfaces of the three solvents, which also indicates that the residual solvents will accelerate the corrosion of the interface during cycling and affect the stability of the lithium metal battery.

[0034] 4. The effect of PLL lithium sheets on cycle stability in ether-based systems like Figure 4As shown, this application prepared PVDF, PVDF-LiNO3, PVDF-LiF, and PVDF-LiNO3-LiF (referred to as PLL) films using DME as a solvent. The surface of the PVDF film is as follows. Figure 4 Figure a shows a flat and dense structure. The PVDF-LiNO3 membrane, as shown... Figure 4 Figure b shows a porous structure, which may be due to the loose contact between PVDF and LiNO3 within the membrane. To address the issue of the loose structure of the PVDF / LiNO3 membrane, this application attempts to introduce LiF nanoparticles into the PVDF / LiNO3 membrane to improve its uniformity and mechanical strength. First, this application introduces LiF nanoparticles into the PVDF membrane, resulting in a flat and dense PVDF / LiF membrane surface. Compared to the PVDF / LiNO3 composite membrane, the PVDF / LiF / LiNO3 (PLL) membrane exhibits superior performance. Figure 4 The d-composite membrane has a dense structure and contains micropores. This is because the presence of LiF promotes the densification of the PVDF / LiNO3 membrane, which is crucial for improving the mechanical strength of the PLL membrane. The membrane color changes from the transparency of PVDF and PVDF / LiF to the white of PLL due to the uniform distribution of LiNO3 particles within the membrane. Figure 4 As shown in Figure e, a PLL composite film with a thickness of approximately 9 μm was formed in situ on the lithium metal surface using a simple drop-coating method. After further cleaning the PLL film with DME solvent, as shown... Figure 4 As shown in figure f, the PLL film exhibits a uniform porous structure with pore sizes of several hundred nanometers. This indicates that LiNO3 exists in the PLL film as uniform aggregates. Figure 4 As shown in Figure g, the XRD pattern confirms that PVDF, LiNO3, and LiF are dispersed in the PLL film. Figure 4 The indentation elastic modulus (EIT) of the PVDF / LiNO3 membrane shown in figure h was 0.23 GPa. After the addition of LiF, the PLL membrane significantly increased to 1.84 GPa. This confirms the effect of LiF on enhancing the mechanical strength of the membrane. Figure 4 In i, the TGA curve shows that the PLL film has high thermal stability, reaching up to 380℃. To demonstrate the initial formation of substances on the lithium metal surface, such as... Figure 5 As shown, the composition of the initial SEI layer on the lithium metal surface after the removal of the PLL film was detected by X-ray photoelectron spectroscopy (XPS). It was found that the initial SEI layer contained Li3N and LiN. x O y The species are reaction products of lithium metal and LiNO3. Additionally, CF and Li-F were also observed. The presence of stable substances is crucial for the chemical reactions between the lithium anode and the solvent during the early stages of cycling, and is beneficial for the sustainable cycling of the lithium anode.

[0035] The above results indicate that organic / inorganic PLL membranes have a potential protective effect on Li metal cycling. To examine this property, this application assembled a Li / / Li symmetric cell with an ether electrolyte (1 M LiTFSI). To illustrate the effect of solid LiNO3 in the PLL membrane on the stability of Li metal cycling, this application used LiNO3 containing the electrolyte (0.46 M, the same amount of LiNO3) as the reference electrode, which is significantly different from most reports that use bare Li electrodes as the reference electrode. The battery assembled with PLL lithium is denoted as Li(PLL), and the battery assembled with bare lithium and an ether electrolyte of 0.46 M LiNO3 is denoted as Li(LiNO3). Figure 6 As shown, at a current density of 0.5 mA cm⁻¹ -2 And a capacity of 0.5 mAh cm -2 The Li / / Li symmetric cell (Li(PLL)) achieved a cycle life of 8000 h, approximately one year; when the current density and capacity were increased to 1 mA cm⁻¹, the cycle life was further improved. -2 and 1 mAh cm -2 At that time, the cycle life reached 6000 h, far exceeding the 800 h of Li(LiNO3). For example... Figure 6 As shown in c, at a current density of 1 mA cm⁻¹ -2 , with a capacity of 1 mAh cm -2 Under the specified conditions, the Li / / Cu half-cell containing Li (PLL) can stably cycle for 550 cycles with a coulombic efficiency (CE) of 98.33%, while the CE of the Li (LiNO3)-containing battery drops rapidly after 100 cycles. To further demonstrate the advantages of the Li anode protected by the PLL film, this application tested the Li / / Li battery with a capacity of 5 mAh cm⁻¹. -2 and 10 mAh cm -2 The cycle stability and cycle life were 2000 h and 1600 h, respectively, which are significantly improved compared to Li(LiNO3). To demonstrate the positive role of lithium nitrate in anode cycling, such as... Figure 6As shown in Figure f, firstly, the LiNO3 on the PLL-protected lithium electrode was washed away, and then an equal amount of LiNO3 was added to the electrolyte. The prepared Li electrode was then assembled into a Li / / Li symmetric cell, designated Cell 1. Next, a PLL film was prepared on copper foil (the preparation process was the same as described above), and LiNO3 was removed from the PLL using DME solvent. The LiNO3-free PLL film was then applied to the Li electrode, and 0.46 M LiNO3 electrolyte was added to assemble a Li / / Li symmetric cell, designated Cell 2. The lithium symmetric cell assembled with the PLL film was designated Cell 3. Experiments showed that the stable cycling performance of Cell 1 could be extended to 1600 h, significantly better than Cell 2 (1000 h). This confirms the importance of in-situ films for long-term cycling of lithium anodes. However, the cycle life of Cell 1 was much lower than that of Cell 3 (6000 h), indicating that the solid LiNO3 on the Li electrode via PLL is more effective in improving cycle stability compared to LiNO3 dissolved in the electrolyte. Furthermore, the cycle life of Cell 1 (1600 h) is further improved compared to Li(LiNO3), indicating that the PVDF / LiF film is also important for improving the cycle stability of lithium anodes. This further demonstrates the synergistic effect of PVDF, LiF and LiNO3 in constructing advanced SEI layers, which is beneficial to the long-term cycle stability of lithium anodes.

[0036] Therefore, this application analyzes the causes of long cycles in Li(PLL), such as Figure 7 The schematic diagram illustrates the formation of a polymer / inorganic SEI layer with uniform and good ionic conductivity on the lithium metal surface during cycling. During battery cycling, LiNO3 from the PLL film is released into the ether (or ester) electrolyte, initially forming a localized LiNO3 concentration gradient structure. This results in the formation of a PVDF / LiF / Li3N composite SEI layer on the lithium metal surface with uniform ionic conductivity and good mechanical strength. Figure 7 As shown, the formation of the surface SEI of the lithium metal anode containing LiNO3 in the electrolyte results in an uneven and low-N content SEI as LiNO3 is continuously consumed, leading to the formation of lithium dendrites on the surface.

[0037] To further confirm the promoting effect of the SEI layer (solid electrolyte layer) generated by the PLL on lithium metal cycling, this application used in-situ optical microscopy to observe the effect of a current density of 2 mA cm⁻¹. -2 Li deposition process of Li(PLL) and Li(LiNO3) Figure 8 a and 8b. Under these conditions, lithium dendrite growth appeared on the Li(LiNO3) surface after 5 min of deposition. Conversely, no dendrite growth was observed on Li(PLL). Further investigation revealed… Figure 8In samples c and 8d, the surface of the lithium anode after 50 cycles was observed using scanning electron microscopy (SEM). Spherical lithium metal deposits were observed on the Li(LiNO3) surface, while the surface of the PLL-protected lithium sheet was uniform and smooth. Compared to Li(LiNO3), the SEI layer constructed with the PLL film showed better performance in suppressing side reactions and inducing planar deposition of lithium metal. The reduction in the contact area between the lithium metal surface and the electrolyte led to a significant improvement in the cycling stability of Li(PLL). Figure 9 As shown, this application used a 50 μm thick lithium sheet covering a PLL with a theoretical capacity of 10 mAh as the positive electrode and a Cu foil covering the PLL as the negative electrode. An ether-based electrolyte was used to assemble a Li / / Cu battery for complete stripping experiments, further confirming the advantages of PLL protection for the Li electrode. At a cutoff voltage of 1 V, the stripping capacity of Li(LiNO3) was 8.74 mAh, with a capacity of 87.4%. In contrast, the stripping capacity of Li(PLL) reached 9.73 mAh, with a capacity of 97.3%, indicating that the Li(PLL) electrode has fewer side reactions and better cycle stability. Optical photographs demonstrate that the lithium metal stripping of Li(PLL) is more complete than that of Li(LiNO3).

[0038] To confirm that the SEI constructed with a PLL membrane possesses superior electrochemical performance, such as... Figure 10 As shown in ab, this application analyzed the interfacial impedance before and after 50 cycles using EIS (impedance spectroscopy). It can be seen that Li(PLL) has a smaller interfacial impedance compared to Li(LiNO3). Furthermore... Figure 10 In section c, Tafel curves were calculated using linear sweep voltammetry (LSV) to investigate the reaction kinetics of lithium metal deposition and stripping processes. Fitting data from a potential range of -125 mV to -75 mV revealed that the exchange current density of Li(LiNO3) was 0.467 mA, lower than that of Li(PLL) (0.860 mA). This indicates that the SEI layer constructed on the Li(PLL) surface possesses higher ionic conductivity. Figure 10 As shown in d, in the CV test of lithium copper, Li(PLL) exhibits the highest lithium deposition / stripping current value compared to bare lithium in electrolytes containing different concentrations of LiNO3. Furthermore, in Figure 10In sections e and 10f, this application further compared the cyclic CV tests of Li(PLL) and an electrolyte containing 0.5 M lithium nitrate (Li(LiNO3)). As CV cycling progressed, the reaction kinetics of Li(PLL) gradually increased. Conversely, the reaction kinetics of Li(LiNO3) increased and then remained relatively stable. This indicates that the SEI layer generated by the PLL film improves lithium-ion transport during battery cycling, thereby significantly enhancing the kinetics of lithium metal deposition and stripping reactions. In summary, the synergistic effect of PVDF, LiF, and LiNO3 is the reason for constructing a uniform SEI layer to improve the long-term cycling stability of the lithium anode.

[0039] The above results demonstrate the unique performance of PLL membranes in constructing advanced SEI layers. In previous Cell 1, Cell 2, and Cell 3 cycle stability experiments, this application found that the solid LiNO3 on the lithium anode is more important than the dissolution of LiNO3 in the electrolyte. To investigate the mechanism, this application first placed the PLL membrane and 2 mL of DME electrolyte in a glass bottle, and detected the concentration changes of LiNO3 in the diethyl ether electrolyte at different time scales using UV-Vis spectroscopy. To elucidate the sustained-release effect of PLL lithium nitrate in solution, such as... Figure 11 As shown in Figure a, it is demonstrated that the concentration of lithium nitrate in DME is directly proportional to the peak UV absorption of lithium nitrate. Furthermore, the concentration changes of lithium nitrate released from the DME solution at different times were compared, with the supernatant taken after standing for different periods for comparison. Figure 11 As shown in b, the lithium nitrate concentration increases over time, but remains below the electrolyte peak of 0.46 M lithium nitrate. This indicates that some lithium nitrate in the PLL film is released, while some remains internally, enabling it to better participate in the formation of the SEI on the lithium metal surface.

[0040] 5. SEI composition analysis of PLL membrane To elucidate the structural characteristics of the PLL-derived SEI layer, this application characterized the chemical composition of the SEI layer using XPS. The SEI layer was etched with Ar ions in XPS, and the changes in chemical composition in three-dimensional space were analyzed. Figure 12 As shown in a and 12b, the XPS N 1s peaks at 388.73 eV and 403.8 eV correspond to Li3N and LiN, respectively. x O y As the etching depth increases, Li3N and LiN... x O y The content of [Li3N] increased, but only a small amount of Li3N and LiN appeared in the SEI layer of Li(LiNO3). x O = species, and its content is reduced. In Figure 12Further analysis of elemental composition in samples c and 12d revealed that, with increasing etching time, the N content in the SEI layer produced by Li(PLL) exceeded 1.10 mol%, while the N content of Li(LiNO3) was 0.63 mol%. This confirms the presence of Li3N and LiN in the SEI layer produced by the PLL film. x O y The number of species produced by LiNO3 electrolyte is far greater than the number of species produced by LiNO3 electrolyte.

[0041] To further verify the structural characteristics of the SEI layer, static-time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to analyze the N and LiNO3 content in the SEI layer after 50 cycles of Li(PLL) and Li(LiNO3) electrodes. - LiF, Li - The elemental distribution of O was explained using 3D visualization. Figure 12 e and Figure 12 f reveals that the uniformity and N content of the SEI layer in Li(LiNO3) are much smaller than those in the SEI layer of Li(PLL). Similarly, using a 3D visualization of the SEI layer, the LiNO content... - The uniformity and content of Li (PLL) are also higher than those of Li (LiNO3). Previous studies have shown that LiNO3 reacts with lithium metal to form LiNO2 and Li2O, and LiNO2 can further react with lithium metal to form Li3N and Li2O. Three-dimensional visualization confirms that the content of Li2O in the SEI of Li (PLL) is higher than that of Li (LiNO3), which further illustrates that PLL films can achieve a more uniform distribution of N and F elements in the SEI, which is beneficial for uniform lithium metal deposition / stripping behavior. Furthermore, the distribution of Li element in the SEI of Li (PLL) is more uniform than that of Li (LiNO3). This uniform distribution of elements demonstrates the uniform distribution of the SEI in Li (PLL), which is one of the key reasons for its long-term cycling stability. Figure 13 a and Figure 13 The scanning electron microscope (SEM) energy-dispersive X-ray spectroscopy (EDS) images in section b also show the changes in elemental composition of the PLL membrane before and after cycling. It can be seen that the N, F, and O content of the PLL membrane decreases after cycling, confirming the release of LiNO3 from the membrane. Furthermore, the presence of the PVDF / LiF porous structure demonstrates the stability of the PLL membrane during cycling.

[0042] 6. The effect of PLL film on electrode cycling The above results indicate that the PLL-derived in-situ SEI layer, containing uniformly distributed materials with high ionic conductivity, can significantly improve the cycle stability of lithium metal electrodes. To further elucidate this effect, such as... Figure 14As shown, this application assembles various full cells, including Li / / S cells and Li / / LiFePO4 cells. In the Li / / S cells, the Li(LiNO3)-containing cell exhibits a rapid capacity decrease after 200 cycles at 0.5 C, with only 44.9 mAh g⁻¹ remaining after 750 cycles. -1 In comparison, the Li(PLL)-containing battery had a capacity of 445.2 mAh g after 750 cycles. -1 This application further assembles a Li / / LiFePO4 battery with a PLL-protected lithium anode. At a current of 0.5 C and 5 mg cm⁻¹... -2 Under the load, the capacity of the Li(PLL) battery after 1000 cycles is 84.1 mAh g. -1 This is far greater than the capacity of lithium-containing (LiNO3) batteries (12.5 mAh g). -1 At a current of 0.5 C and 12 mg cm⁻¹ -2 Under certain load conditions, the capacity of Li(LiNO3) rapidly decreased after 230 cycles, while the capacity retention of Li(PLL) batteries reached 80.94% after 800 cycles. This is because the SEI derived from PLL provides effective protection for the lithium anode during cycling. To evaluate the practical applications of Li(PLL) electrodes, such as... Figure 14 d. This application assembled a pouch cell with an N / P ratio of 2 and a Li(PLL) loading of 75 mg LiFePO4. After 700 cycles, the remaining capacity was 107 mAh g. -1 .like Figure 14 e. Under harsh conditions of N / P = 1 and LiFePO4 loading of 130 mg, the capacity of the Li(LiNO3)-containing pouch cell rapidly decreased to 74.1 mAh g after activation. -1 Only 6 mAh g was retained after 350 cycles. -1 In comparison, the activated capacity of the pouch cell containing Li(PLL) is 143.2 mAh g. -1 The capacity remains 106.3 mAh g after 350 cycles. -1 This further confirms the enormous practical application potential of Li(PLL) electrodes. To demonstrate the stability of pouch cells, such as... Figure 14 As shown in f, this application uses Li / / LiFePO4 batteries and Li(PLL) to power the LED light board, and it operates successfully.

[0043] 7. Application of PLL in ester electrolytes The above results confirm that the PLL-protected lithium anode can cycle stably in ether electrolytes, making it suitable for low-voltage battery applications. To further illustrate the wide applicability of PLL-protected lithium anodes, this application assembled a Li / / Li symmetric cell using an ester electrolyte. Figure 15 As shown in figure a, at a current density of 1 mA cm⁻¹ -2 The capacity is 1 mAh cm -2 Under the specified conditions, the symmetric cell of Li(PLL) achieved stable cycling for 1200 h, which is three times that of the LiK electrode (400 h), demonstrating the role of PLL in deriving and stabilizing the SEI layer in ester electrolytes. Figure 15 Electrochemical impedance spectroscopy (EIS) at b and 15c showed that the battery with Li(PLL) exhibited a small interfacial impedance from 50 to 100 cycles and a significant decrease compared to Li(LiNO3) and Li(K), indicating high and increased ionic conductivity of the SEI layer. To characterize the distribution of materials with high ionic conductivity, such as... Figure 16 As shown in a and 16b, XPS etching was performed in this application to analyze the surface composition of the cycled lithium anode after 50 cycles in an ester electrolyte. It can be seen that Li3N and LiN are also present on the lithium anode containing the PLL film. x O y The SEI layer of Li(K) contains extremely low nitrogen content because ester electrolytes cannot dissolve lithium nitrate. Figure 16 The N element content curves obtained from XPS argon etching experiments in samples c and 16d further confirm the extensive distribution and high content of N in the SEI of the lithium anode containing the PLL film. Further assembly of a Li / / NCM811 full cell verifies the effectiveness of PLL protection for the lithium anode in high-voltage cathode materials. Figure 17 As shown in figure a, at a rate current of 0.5 C and 8 mg cm⁻¹ -2 Under NCM811 load, the Li(PLL)-containing battery showed 136.9 mAh g⁻¹ after 500 cycles. -1 The capacity of the battery was maintained at 73.3%. In stark contrast, the battery containing Li(K) began to degrade after 240 cycles, and the capacity was only 0.9 mAhg after 400 cycles. -1 .like Figure 17 As shown in b, at a rate current of 1 C, the capacity of the Li(PLL)-containing battery remains 154.5 mAh g after 500 cycles. -1 It boasts a cycle life exceeding 1900 hours with a capacity decay rate of only 0.035% per cycle. In contrast, Li(K) exhibits a capacity decay of only 58.1 mAh g⁻¹ after 500 cycles. -1The above results clearly demonstrate that the PLL-derived organic / inorganic PVDF / LiF / Li3N SEI layer provides advanced protection for the lithium electrode during cycling in high-voltage lithium metal batteries.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for in-situ constructing an organic / inorganic composite solid electrolyte layer on the surface of lithium metal, characterized in that, Obtained through the following process: (1) Polyvinylidene fluoride (PVDF) is dissolved in dimethyl ethylene glycol (DME) and heated with stirring at 120 ℃~140 ℃ to dissolve PVDF. Then, lithium nitrate (LiNO3) and lithium fluoride (LiF) are added to the solution and magnetically stirred at 55~65 ℃ for 1~2 h to obtain a DPLL mixture. The concentration of PVDF in the DME is 20~200 mg / mL. -1 ; (2) The DPLL mixture is drop-coated onto the lithium sheet and naturally evaporated to obtain a lithium sheet covered with an organic / inorganic composite solid electrolyte layer.

2. The method for in-situ constructing an organic / inorganic composite solid electrolyte layer on the surface of lithium metal according to claim 1, characterized in that, The concentration of LiNO3 in ethylene glycol dimethyl ether is 0.1~1 mol / L, and the dispersion of LiF in ethylene glycol dimethyl ether is 0.1~1 mol / L.

3. The lithium sheet covered with an organic / inorganic composite solid electrolyte layer obtained by the method of claim 1 or 2.

4. A lithium symmetric battery fabricated using a lithium sheet covered with an organic / inorganic composite solid electrolyte layer as described in claim 3, characterized in that, The positive and negative electrodes are lithium sheets covered with organic / inorganic composite solid electrolyte layers. The electrolytes are ether-based or ester-based. The ether-based electrolyte is composed of a 0.5~2 mol / L LiTFSI solution of ethylene glycol dimethyl ether and 1,3-dioxolane, with a volume ratio of 1:

1. The ester-based electrolyte is composed of a 0.5~2 mol / L lithium hexafluorophosphate solution of ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate, with a volume ratio of 0.45:0.45:0.

1.

5. A lithium-sulfur battery fabricated using a lithium sheet covered with an organic / inorganic composite solid electrolyte layer as described in claim 3, characterized in that, An aluminum foil coated with carbon material, binder, and sulfur was used as the positive electrode, and a lithium sheet covered with an organic / inorganic composite solid electrolyte layer was used as the negative electrode. A mixed solution of 0.5–2 mol / L LiTFSI in ethylene glycol dimethyl ether and 1,3-dioxolane was used as the electrolyte, with a volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane of 1:

1. The positive electrode was prepared by the following process: porous carbon and sulfur in a mass ratio of 3:7 were ground evenly in a mortar, and then heated at 150–160 °C for 10–15 h under argon protection to obtain sulfur-loaded carbon. The sulfur-loaded carbon, Ketjen black, and binder were uniformly mixed in N-methylpyrrolidone at a mass ratio of 8:1:1, and then coated onto the aluminum foil and dried to obtain the electrode. The sulfur loading on the electrode was 1.5–4 mg cm⁻¹. -2 .

6. A lithium iron phosphate battery or a nickel-cobalt-manganese 811 battery made using a lithium sheet covered with an organic / inorganic composite solid electrolyte layer as described in claim 3, characterized in that, The positive electrode is an aluminum foil loaded with lithium iron phosphate or nickel cobalt manganese 811, and the negative electrode is a lithium sheet covered with an organic / inorganic composite solid electrolyte layer. The electrolyte is an ether electrolyte or an ester electrolyte. The ether electrolyte is composed of a 0.5~2 mol / L LiTFSI solution of ethylene glycol dimethyl ether and 1,3-dioxolane, with a volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane of 1:

1. The ester electrolyte is composed of a 0.5~2 mol / L lithium hexafluorophosphate solution of ethylene carbonate, diethyl carbonate and fluoroethylene carbonate, with a volume ratio of ethylene carbonate, diethyl carbonate and fluoroethylene carbonate of 0.45:0.45:0.

1.

7. The lithium iron phosphate battery or nickel-cobalt-manganese 811 battery made from a lithium sheet covered with an organic / inorganic composite solid electrolyte layer as described in claim 6, characterized in that, Aluminum foil loaded with lithium iron phosphate or nickel cobalt manganese 811 was prepared by the following process: Lithium iron phosphate or nickel cobalt manganese 811 material, polyvinylidene fluoride, and Ketjen black were uniformly mixed in N-methylpyrrolidone at a mass ratio of 8:1:

1. The mixture was then evenly stretched onto aluminum foil using a four-sided spreader and dried. The lithium iron phosphate loading mass on the aluminum foil was controlled to be within 3 mg / cm³. -2 ~6 mg cm -2 The loading mass of nickel-cobalt-manganese 811 on aluminum foil was controlled at 7.5 mg / cm³. -2 ~8.5mg cm -2 .

8. A lithium pouch battery made using the lithium sheet covered with an organic / inorganic composite solid electrolyte layer as described in claim 3, characterized in that, Using aluminum foil loaded with lithium iron phosphate as the positive electrode and copper foil with lithium strips covered with an organic / inorganic composite solid electrolyte layer as the negative electrode, the electrolyte addition amount is 20~30 μL mAh. -1 It is packaged with an aluminum-plastic film and uses a mixed solution of 0.5~2 mol / L LiTFSI ethylene glycol dimethyl ether and 1,3-dioxolane as the electrolyte, with a volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane of 1:

1.

9. The lithium pouch battery made from a lithium sheet covered with an organic / inorganic composite solid electrolyte layer as described in claim 8, characterized in that, The lithium iron phosphate-loaded aluminum foil was prepared by the following process: lithium iron phosphate material, polyvinylidene fluoride, and Ketjen black were uniformly mixed in N-methylpyrrolidone at a mass ratio of 8:1:

1. The mixture was then evenly stretched onto aluminum foil using a four-sided milling machine and dried. The lithium iron phosphate loading mass on the aluminum foil was controlled to be within 3 mg / cm³. -2 ~6 mg cm -2 .

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