High-salt-concentration polymer electrolyte thin film, method for preparing same, and use thereof

Abstract

This invention discloses a high-salt-concentration polymer electrolyte film, its preparation method, and its application. The raw materials for the electrolyte film include a polymer, a plasticizer, cellulose, and a lithium salt. The method involves first mixing the polymer and cellulose, then adding an organic solvent and continuing the reaction under heating conditions to obtain a homogeneous solution. The lithium salt and plasticizer are then mixed to form a low-eutectic solvent. This low-eutectic solvent is added to the homogeneous solution, and the reaction is continued under heating conditions to obtain a reaction solution. The reaction solution is then cast into a tetrafluoroethylene mold and vacuum-dried until the solvent is completely evaporated, yielding the high-salt-concentration polymer electrolyte film. The electrolyte material preparation method of this invention is simple, low-cost, and easy to mass-produce, exhibiting good electrochemical performance when used in lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of polymer solid-state battery technology, specifically to a high-salt-concentration polymer electrolyte thin film, its preparation method, and its application. Background Technology

[0002] Faced with the severe challenges of increasingly depleted fossil fuels and escalating environmental pollution, the transition to a clean and low-carbon energy system has become a general consensus in the international community. Secondary battery technology is not only a core cornerstone for achieving efficient energy utilization, but also represents national energy security and the global competitiveness of high-end manufacturing industries. However, existing commercial lithium-ion batteries are limited by the flammability of flammable organic electrolytes and the capacity limits of graphite anodes, with their energy density approaching the physical maximum of 300 Wh / kg. Furthermore, they are prone to catastrophic thermal runaway under extreme conditions such as puncture and overcharging. Therefore, this presents a historic development opportunity for solid-state batteries (SSBs), which possess intrinsic safety advantages and high energy density.

[0003] Solid-state electrolytes, as a key component of solid-state batteries, not only serve as the core channel for Li+ transport within the battery assembly but also as an electronic insulation and physical separator, physically separating the positive and negative electrodes. Furthermore, their non-flammable and leak-proof properties address the safety hazards of thermal runaway inherent in liquid electrolytes. However, solid-state electrolytes suffer from poor interfacial contact with the positive and negative electrodes, leading to high interfacial impedance and poor cycle stability. Polymer electrolytes, primarily composed of polymers, small-molecule solvents, and lithium salts, possess good flexibility and ductility, enabling good contact with electrode materials. However, their poor ionic conductivity, mechanical strength, and narrow voltage window severely limit their development and practical application.

[0004] Strategies such as using inorganic fillers and adding plasticizers can improve the mechanical strength or ionic conductivity of polymer electrolytes. Increasing the lithium salt concentration can effectively improve the ionic conductivity of polymer electrolytes; however, under high lithium salt concentrations, the mechanical strength of the polymer electrolyte decreases sharply, leading to rapid battery failure. Therefore, developing polymer electrolytes that combine high mechanical strength and high ionic conductivity is crucial for achieving high-performance solid-state battery systems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a high-salt-concentration polymer electrolyte film and its application. The high-salt-concentration polymer electrolyte of this invention has the characteristics of low cost and high production efficiency, while maintaining a certain mechanical strength, so as to solve the problems of poor interfacial contact and poor mechanical strength of polymer electrolytes.

[0006] To achieve the above objectives, the technical solution designed by the present invention is as follows: This invention provides a high-salt-concentration polymer electrolyte membrane, wherein the raw materials of the electrolyte membrane include a polymer, a plasticizer, cellulose, and a lithium salt; wherein, The polymer is any one or more of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polymethyl methacrylate (PMMA). The cellulose is any one or more of cellulose acetate (CA), bacterial cellulose (BC), microcrystalline cellulose (MCC), and carboxymethyl cellulose (CMC). The plasticizer is any one of succinic anionyl nitrile (SN), dimethacrylamide (DMAM), and acrylamide (AM). The lithium salt is any one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LIFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), and lithium fluoride (LiF). The mass ratio of the polymer to the lithium salt is 50:1 to 1:1, and the molar ratio of the ether oxygen (EO) unit of the polymer to the lithium ion in the lithium salt is (nEO∶nLi). + The ratio is 2~25:1; The mass ratio of the polymer to cellulose is 95:5-5:95. The mass ratio of the polymer to the plasticizer is 95:5-5:95.

[0007] Furthermore, the polymer is polyethylene oxide (PEO) or polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). The cellulose is cellulose acetate (CA) or bacterial cellulose (BC). The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl)imide (LIFSI). The mass ratio of the polymer to the lithium salt is 10:1 to 1:1, and the molar ratio (nEO:nLi+) of the ether oxygen (EO) unit of the polymer to the lithium ion in the lithium salt is 6 to 16:1. The mass ratio of the polymer to cellulose is 20:5-5:20. The mass ratio of the polymer to the plasticizer is 2:1 to 1:2.

[0008] Furthermore, the raw materials for the electrolyte membrane include polyethylene oxide (PEO), cellulose acetate (CA), succinic anionyl nitrile (SN), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); wherein, The mass ratio of the polymer to the lithium salt is 15:12, and the molar ratio (nEO∶nLi+) of the polymer to the lithium ions in the lithium salt is 8:1. The mass ratio of the polymer to cellulose is 12:5. The mass ratio of the polymer to the plasticizer is 1:1.

[0009] The present invention also provides a method for preparing the above-mentioned high-salt-concentration polymer electrolyte film, comprising the following steps: 1) Mix the polymer and cellulose by stirring, then add an organic solvent and continue stirring under heating conditions to obtain a homogeneous solution; wherein the organic solvent is any one or more of acetonitrile (ACN), N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP); 2) Mix lithium salt and plasticizer to form a low eutectic solvent; 3) Add a eutectic solvent to the homogeneous solution and stir the reaction under heating conditions to obtain a reaction solution; 4) The reaction solution is cast into a tetrafluoroethylene mold and vacuum dried until the solvent is completely evaporated to obtain a high salt concentration polymer electrolyte film, wherein the thickness of the electrolyte film is 20~120μm and the diameter is 10~20mm.

[0010] Further, in step 1), the organic solvent is acetonitrile (ACN) or N,N-dimethylformamide (DMF).

[0011] Furthermore, the organic solvent is acetonitrile (ACN).

[0012] Furthermore, in step 1), the heating temperature is 60~70℃ and the stirring time is 3~6h; In step 3), the heating temperature is 65~75℃ and the stirring time is 5~8h; In step 4), the vacuum drying temperature is 50~70℃ and the time is 24-72h.

[0013] Furthermore, in step 1), the heating temperature is 65°C and the stirring time is 4 hours; In step 3), the heating temperature is 70°C and the stirring time is 6 hours. In step 4), the vacuum drying temperature is 60°C and the time is 48 hours.

[0014] Furthermore, the electrolyte film has a thickness of 40~80μm and a diameter of 12mm.

[0015] The present invention also provides an application of the above-mentioned high salt concentration polymer electrolyte film in the preparation of lithium batteries.

[0016] The positive electrode material of the aforementioned lithium battery includes conductive agent, active material, binder, and additive; The conductive agent is selected from at least one of Super-P, superconducting carbon black, acetylene black, and Ketjen black, with Super-P being preferred; The active material is one of lithium iron phosphate, lithium nickel oxide and lithium cobalt oxide, preferably lithium iron phosphate; The adhesive is selected from at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR), preferably polyvinylidene fluoride; The additive is at least one of polyethylene oxide and succinic acid; The method for preparing the positive electrode material of the above-mentioned electrolyte thin film includes the following steps: The above-mentioned positive electrode active material is mixed with conductive agent, binder and additive, and N-methylpyrrolidone (NMP) is used as solvent to form a uniform slurry. Aluminum foil is used as current collector, and the slurry is uniformly coated on the aluminum foil. The mixture is then vacuum dried at 100°C for 12 hours to obtain a positive electrode material that matches the solid electrolyte.

[0017] The beneficial effects of this invention are: (1) The higher lithium salt concentration expands the amorphous region inside the polymer, making the polymer chain segment movement more active and the ion transport more efficient.

[0018] (2) The addition of cellulose gives the prepared electrolyte material good mechanical strength, and even in the presence of plasticizer, the polymer can still maintain a high lithium salt concentration.

[0019] (3) High lithium salt concentration makes the electrolyte material more compatible with the electrode material at the interface, greatly reducing the interface impedance.

[0020] The electrolyte material of this invention has a simple preparation method, low cost, and is easy to mass-produce, and exhibits good electrochemical performance when used in lithium batteries. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope (SEM) image of a cross-section of the high-salt-concentration polymer electrolyte film 1 prepared in Example 1; Figure 2 XRD results for preparing high-salt-concentration polymer electrolyte films with different concentration gradients 1-6 (Examples 1-6); Figure 3 The impedance spectra of high-salt-concentration polymer electrolyte films 1-7 (Examples 1-7) are compared under different lithium salt concentrations. Figure 4 Comparison of ionic conductivity of high-salt-concentration polymer electrolyte films 1-7 (Examples 1-7) at different lithium salt concentrations; (Examples 1-7) Figure 5 Symmetrical cells 1-2 prepared for Examples 1-2 were used at 0.1 mA / cm². 2 -0.1mAh / cm 2 The following is a cycle diagram; In the figure, red represents the voltage-time curve of symmetrical battery 1 in Example 1, and black represents the voltage-time curve of symmetrical battery 2 in Example 2. Figure 6 A schematic diagram showing the charge-discharge specific capacity and corresponding coulombic efficiency of the full cell (Li||SPE||LFP cell) fabricated for Example 1 at 0.5 C; In the diagram, the purple and blue spheres represent the charging specific capacity and discharging specific capacity, respectively, while the black hollow sphere represents the coulombic efficiency. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can understand it.

[0023] Example 1 1. Preparation of high-salt-concentration polymer electrolyte film 1 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat and stir at 65℃ for 4h to obtain a homogeneous solution (the solution is transparent and gel-like, denoted as ①).

[0024] 2) Weigh 0.489g LiTFSI (n EO : n Li + =8:1), 0.60g SN (succinate) were mixed to form a low eutectic solvent. 3) The low eutectic solvent is slowly added to the homogeneous solution in ①, and the mixed reaction system is heated and stirred at 70℃ for 6 hours to obtain the reaction solution; 4) Use a pipette to draw up the reaction solution and cast it into a tetrafluoroethylene mold. Place it in a vacuum oven and bake at 60°C for 36 hours until the solvent is completely evaporated to obtain a high-salt-concentration polymer electrolyte film 1.

[0025] 2. Polymer electrolyte ionic conductivity test Using a gold-plated stainless steel pad as a blocking electrode, battery 1 was assembled in the following order: gold-plated steel sheet / high-salt-concentration polymer electrolyte film 1 / gold-plated steel sheet. Impedance testing was performed on an electrochemical workstation according to the formula: The ionic conductivity of the material was calculated.

[0026] Impedance spectra measured from different polymer electrolytes, and ionic conductivity calculated from the impedance spectra.

[0027] 3. Lithium-ion symmetric battery assembly The obtained high-salt-concentration polymer electrolyte film 1 is used as a separator, and lithium sheets are used as positive / negative electrodes. The lithium-lithium symmetric battery 1 is assembled in the order of negative electrode shell-pad-negative electrode-polymer electrolyte-positive electrode-pad-spring sheet-positive electrode shell.

[0028] 4. Lithium-Lithium Symmetric Battery Testing The lithium-ion symmetric battery 1 was tested at 25℃, at 0.1 mA / cm². 2 -0.1mAh / cm 2 A constant current charge-discharge test was then performed.

[0029] 5. Full battery assembly The obtained electrolyte film was used as the separator, the positive electrode material was used as the positive electrode, and the lithium sheet was used as the negative electrode. The symmetrical battery (full cell 1) was assembled in the order of negative electrode shell-pad-negative electrode-polymer electrolyte-positive electrode-pad-spring sheet-positive electrode shell.

[0030] 6. Full Battery Test The full battery 1 was tested at 25℃, and constant current charge-discharge tests were performed at a 0.5C rate. Figure 6 .

[0031] Example 2 1. Preparation of high-salt-concentration polymer electrolyte membrane 2 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4h to obtain a homogeneous solution (the solution is transparent and gel-like, denoted as ①). 2) Weigh 0.652 g LiTFSI (n EO :n Li + =6:1), 0.60g SN (succinate) were mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) Use a pipette to draw up the reaction solution and cast it into a tetrafluoroethylene mold. Place it in a vacuum oven and bake at 60°C for 36 hours until the solvent is completely evaporated to obtain a high-salt-concentration polymer electrolyte film 2.

[0032] 2. The other steps are the same as in Example 1.

[0033] Example 3 1. Preparation of high-salt-concentration polymer electrolyte membrane 3 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4h to obtain a homogeneous solution (the solution is transparent and gel-like, denoted as ①). 2) Weigh 0.978g LiTFSI (n EO :n Li + =4:1), 0.60g SN (succinate) were mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) Use a pipette to draw up the reaction solution and cast it into a tetrafluoroethylene mold. Place it in a vacuum oven and bake at 60°C for 36 hours until the solvent is completely evaporated to obtain a high-salt-concentration polymer electrolyte film 3.

[0034] 2. The other steps are the same as in Example 1.

[0035] Example 4 1. Preparation of high-salt-concentration polymer electrolyte membrane 4 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4h to obtain a homogeneous solution (the solution is transparent and gel-like, denoted as ①). 2) Weigh 0.326g LiTFSI (n EO :n Li + =12:1), 0.60g SN (succinate) were mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) Use a pipette to draw up the reaction solution and cast it into a tetrafluoroethylene mold. Place it in a vacuum oven and bake at 60°C for 36 hours until the solvent is completely evaporated to obtain a high-salt-concentration polymer electrolyte film 4.

[0036] 2. The other steps are the same as in Example 1.

[0037] Example 5 1. Preparation of high-salt-concentration polymer electrolyte membrane 5 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4h to obtain a homogeneous solution (the solution is transparent and gel-like, denoted as ①). 2) Weigh 0.3912g LiTFSI (n EO :n Li + =10:1), 0.60g SN (succinate) were mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) Use a pipette to draw up the reaction solution, pour it into a tetrafluoroethylene mold, place it in a vacuum oven, and bake at 60°C for 36 hours until the solvent is completely evaporated to obtain a high-salt-concentration polymer electrolyte film 5.

[0038] 2. The other steps are the same as in Example 1.

[0039] Example 6 1. Preparation of high-salt-concentration polymer electrolyte membrane 6 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4h to obtain a homogeneous solution (the solution is transparent and gel-like, denoted as ①). 2) Weigh 0.2445g LiTFSI (n EO :n Li + =16:1), 0.60g SN (succinate) were mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) After the reaction is complete, a certain amount of the reaction solution is taken with a pipette and cast into a tetrafluoroethylene mold. The mold is then placed in a vacuum oven and dried at 60°C for 36 hours until the solvent is completely evaporated, thus obtaining a high-salt-concentration polymer electrolyte film 6.

[0040] 2. The other steps are the same as in Example 1.

[0041] Example 7 1. Preparation of high-salt-concentration polymer electrolyte membrane 7 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4h to obtain a homogeneous solution (the solution is transparent and gel-like, denoted as ①). 2) Weigh 0.1956g LiTFSI (n EO :n Li + =20:1), 0.60g SN (succinate) were mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) Use a pipette to draw up the reaction solution, pour it into a tetrafluoroethylene mold, place it in a vacuum oven, and bake at 60°C for 36 hours until the solvent is completely evaporated to obtain a high-salt-concentration polymer electrolyte film 7.

[0042] 2. The other steps are the same as in Example 1.

[0043] Example 8 1. Preparation of high-salt-concentration polymer electrolyte membrane 8 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4h to obtain a homogeneous solution (the solution is transparent and gel-like, denoted as ①). 2) Weigh 0.2794g LiTFSI (n EO :n Li + =14:1), 0.80g SN (succinate) were mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) After the reaction is complete, a certain amount of the reaction solution is taken with a pipette and cast into a tetrafluoroethylene mold. The mold is then placed in a vacuum oven and dried at 60°C for 36 hours until the solvent is completely evaporated, thus obtaining a high-salt-concentration polymer electrolyte film 8.

[0044] 2. The other steps are the same as in Example 1.

[0045] Example 9 1. Preparation of high-salt-concentration polymer electrolyte membrane 9 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4 hours to obtain a homogeneous solution (the solution is transparent and gel-like). 2) Weigh 0.1304g LiTFSI (n EO :n Li + =30:1), 0.80g SN (succinate) were mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) Use a pipette to draw up the reaction solution, pour it into a tetrafluoroethylene mold, place it in a vacuum oven, and bake at 60°C for 36 hours until the solvent is completely evaporated to obtain a high-salt-concentration polymer electrolyte film 9.

[0046] 2. The other steps are the same as in Example 1.

[0047] Example 10 1. Preparation of high-salt-concentration polymer electrolyte film 10 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4 hours to obtain a homogeneous solution (the solution is transparent and gel-like). 2) Weigh 0.3912g LiTFSI (n EO :n Li + =10:1), 0.80g SN (succinate) were mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) Use a pipette to draw up the reaction solution, pour it into a tetrafluoroethylene mold, place it in a vacuum oven, and bake at 60°C for 36 hours until the solvent is completely evaporated to obtain a high-salt-concentration polymer electrolyte film 10.

[0048] 2. The other steps are the same as in Example 1.

[0049] Example 11 1. Preparation of high-salt-concentration polymer electrolyte film 11 1) Weigh 0.60g PEO (polyethylene oxide) and 0.25g CA (cellulose acetate) into an oil bath and start stirring. While stirring, slowly add 15mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4 hours to obtain a homogeneous solution (the solution is transparent and gel-like). 2) Weigh 0.078g LiTFSI (n EO :n Li + =50:1), 0.02g LiF and 0.80g SN (succinate) are mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) Use a pipette to draw up the reaction solution, pour it into a tetrafluoroethylene mold, place it in a vacuum oven, and bake at 60°C for 36 hours until the solvent is completely evaporated to obtain a high-salt-concentration polymer electrolyte film 11.

[0050] 2. The other steps are the same as in Example 1.

[0051] Example 12 1. Preparation of high-salt-concentration polymer electrolyte film 12 1) Weigh 0.60g of PEO (polyethylene oxide) into an oil bath and start stirring. While stirring, slowly add 10mL of acetonitrile. After adding the solvent, start heating and heat at 65℃ for 4 hours to obtain a homogeneous solution (the solution is transparent and gel-like). 2) Weigh 0.1304g LiTFSI (n EO :n Li + =30:1), 0.80g SN (succinate) were mixed to form a low eutectic solvent; 3) Slowly add the eutectic solvent to the homogeneous solution in ①, and continue to heat and stir the mixed reaction system at 70℃ for 6 hours to obtain the reaction solution; 4) Use a pipette to draw up the reaction solution, pour it into a tetrafluoroethylene mold, place it in a vacuum oven, and bake at 60°C for 36 hours until the solvent is completely evaporated to obtain a high-salt-concentration polymer electrolyte film 12.

[0052] 2. The other steps are the same as in Example 1.

[0053] I. Detection of n EO :n Li + Cross-sectional flatness and thickness of high-salt-concentration polymer electrolyte film 1 with a ratio of 8:1 (Example 1) 1. Method Characterizing n using scanning electron microscopy (SEM) EO :nLi + Cross-sectional flatness and thickness of polymer films with a ratio of 8:1 (Example 1) 2. Conclusion from Figure 1 It can be seen that the prepared electrolyte film has a cross-section of 40 μm and the cross-section is flat and dense.

[0054] II. Detection of the crystallinity of high-salt-concentration polymer electrolyte films 1-8 in Examples 1-6 1. Method The crystallinity of the polymer films in Examples 1-6 was characterized using X-ray diffraction (XRD). 2. Conclusion With n EO :n Li + As the proportion increases and the concentration decreases, the crystallinity of the polymer film increases, and the crystallization peaks become more pronounced. III. Electrochemical Impedance Spectroscopy of High Salt Concentration Polymer Electrolyte Films 1-7 in Examples 1-7 1. Method Electrochemical impedance spectroscopy (EIS) was used to detect the electrochemical impedance spectra of polymer films with different concentration ratios by assembling stainless steel sheet-polymer film-stainless steel sheet batteries.

[0055] 2. Conclusion In n EO :n Li + When the concentration is >8, the impedance spectrum decreases as the salt concentration increases, and at n EO :n Li + It reaches its minimum value when the value is 8, and then increases again.

[0056] IV. Calculation of the ionic conductivity of the high-salt-concentration polymer electrolyte films 1-7 in Examples 1-7 1. Method Based on the formula for calculating ionic conductivity and the measured electrochemical impedance spectroscopy, the ionic conductivity of polymer films under different concentration gradients was calculated.

[0057] 2. Conclusion In n EO :n Li + When the concentration of salt is greater than 8, the ionic conductivity increases with increasing salt concentration, and at n EO :n Li + It reaches its maximum at 8, and then decreases.

[0058] V. Testing the Cyclic Stability of High-Salt-Concentration Polymer Electrolyte Films When Matched with Lithium Metal Anodes 1. Method Based on the constant current charge-discharge method, the symmetrical batteries assembled using Examples 1 and 2 were tested at 0.1 mA / cm². -2 ~0.1mAhcm -2 Its cycling capacity was tested under different current densities and deposition amounts.

[0059] 2. Conclusion Example 1 achieves a longer cycle time and a smaller polarization voltage.

[0060] VI. Testing the cycle stability of high-salt-concentration polymer electrolyte films when assembling full cells with lithium iron phosphate cathodes. 1. Method The cycling stability of the LFP full cell assembled in Example 1 at 0.5C was tested using a constant current charge-discharge method.

[0061] 2. Conclusion Example 1 successfully achieved 100 stable cycles with minimal capacity fluctuations.

[0062] All other parts not described in detail are existing technologies. Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A high-salt-concentration polymer electrolyte film, characterized in that: The raw materials for the electrolyte membrane include polymers, plasticizers, cellulose, and lithium salts; wherein, The polymer is any one or more of polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride-hexafluoropropylene, and polymethyl methacrylate. The cellulose is any one or more of cellulose acetate, bacterial cellulose, microcrystalline cellulose and carboxymethyl cellulose; The plasticizer is any one of succinic acid, dimethacrylamide, and acrylamide; The lithium salt is any one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium fluoride. The mass ratio of the polymer to the lithium salt is 50:1 to 1:1, and the molar ratio of the ether oxygen unit of the polymer to the lithium ion in the lithium salt is 2 to 25:

1. The mass ratio of the polymer to cellulose is 95:5-5:95; The mass ratio of the polymer to the plasticizer is 95:5-5:

95.

2. The high-salt-concentration polymer electrolyte film according to claim 1, characterized in that: The polymer is polyethylene oxide or polyvinylidene fluoride-hexafluoropropylene; The cellulose is cellulose acetate or bacterial cellulose; The lithium salt is lithium bis(trifluoromethanesulfonylimide) or lithium bis(fluorosulfonylimide); The mass ratio of the polymer to the lithium salt is 10:1 to 1:1, and the molar ratio of the ether oxygen unit of the polymer to the lithium ion in the lithium salt is 6 to 16:

1. The mass ratio of the polymer to cellulose is 20:5-5:20; The mass ratio of the polymer to the plasticizer is 2:1 to 1:

2.

3. The high-salt-concentration polymer electrolyte film according to claim 1 or 2, characterized in that: The raw materials for the electrolyte film include polyethylene oxide, cellulose acetate, succinic anionyl nitrile, and lithium bis(trifluoromethanesulfonyl)imide; wherein, The mass ratio of the polymer to the lithium salt is 5:4, and the molar ratio of the ether oxygen unit of the polymer to the lithium ion in the lithium salt is 8:

1. The mass ratio of the polymer to cellulose is 12:5; The mass ratio of the polymer to the plasticizer is 1:

1.

4. A method for preparing a high-salt-concentration polymer electrolyte film according to any one of claims 1 to 3, characterized in that: Includes the following steps: 1) Mix the polymer and cellulose by stirring, then add an organic solvent and continue stirring the reaction under heating conditions to obtain a homogeneous solution; wherein the organic solvent is any one or more of acetonitrile, N,N-dimethylformamide and N-methylpyrrolidone; 2) Mix lithium salt and plasticizer to form a low eutectic solvent; 3) Add a eutectic solvent to the homogeneous solution and stir the reaction under heating conditions to obtain a reaction solution; 4) The reaction solution is cast into a tetrafluoroethylene mold and vacuum dried until the solvent is completely evaporated to obtain a high salt concentration polymer electrolyte film, wherein the thickness of the electrolyte film is 20~120μm and the diameter is 10~20mm.

5. The preparation method according to claim 4, characterized in that: In step 1), the organic solvent is acetonitrile or N,N-dimethylformamide.

6. The preparation method according to claim 5, characterized in that: The organic solvent is acetonitrile.

7. The preparation method according to claim 4, characterized in that: In step 1), the heating temperature is 60~70℃ and the stirring time is 3~6h; In step 3), the heating temperature is 65~75℃ and the stirring time is 5~8h; In step 4), the vacuum drying temperature is 50~70℃ and the time is 24-72h.

8. The preparation method according to claim 7, characterized in that: In step 1), the heating temperature is 65℃ and the stirring time is 4h; In step 3), the heating temperature is 70°C and the stirring time is 6 hours; in step 4), the vacuum drying temperature is 60°C and the time is 48 hours.

9. The preparation method according to claim 4, characterized in that: The electrolyte film has a thickness of 40~80μm and a diameter of 12mm.

10. The application of the high salt concentration polymer electrolyte film according to any one of claims 1 to 3 in the preparation of lithium batteries.

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