Preparation method of in-situ gel electrolyte lithium metal battery based on PTFE diaphragm

Abstract

The invention provides a preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm, and belongs to the technical field of lithium batteries. Mixing a polymeric monomer, a lithium salt, a solvent and an initiator to obtain a precursor solution; injecting part of the precursor solution into a battery equipped with a positive electrode and a negative electrode, and carrying out preliminary infiltration; a PTFE diaphragm is added, the remaining precursor solution is added, and secondary infiltration is carried out; and placing in a drying oven, standing, and completing in-situ polymerization to obtain the lithium metal battery based on the PTFE diaphragm and the gel electrolyte. The gel electrolyte can effectively reduce the interface resistance and has a certain repulsive effect on FSI <-> in the electrolyte, so that the FSI <-> can reach an interface in advance to be decomposed to form SEI (solid electrolyte interface) which is mainly controlled by anions and is rich in inorganic components, the interface stability is enhanced, and the growth of lithium dendrites can be effectively inhibited.

Description

Technical Field

[0001] The present application relates to a preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm, belonging to the technical field of lithium batteries. Background Art

[0002] The lithium metal anode is considered the best candidate to replace the graphite anode in high-performance rechargeable batteries due to its theoretical capacity more than 10 times higher than that of the graphite anode (3860 mAh g -1 ), and its extremely low electrode potential (-3.04V vs. standard hydrogen electrode). Most lithium metal batteries use liquid electrolytes (LE), which have advantages such as good interfacial compatibility, high lithium ion transference number, and easy preparation; however, there are also problems such as narrow electrochemical window, leakage, and flammability. Solid-state electrolytes (SPE) have received extensive attention due to their thermal and chemical stability, low density, and good processability, and SPE can effectively inhibit the formation of lithium dendrites, which greatly improves the safety performance of the battery; however, most SPEs have disadvantages such as low ionic conductivity, poor electrochemical stability, and low lithium ion transference number, and most of the current methods for improving the ionic conductivity of SPEs will reduce their mechanical properties. Gel polymer electrolytes (GPE) are semi-solid electrolytes between solid-state electrolytes (SPE) and liquid electrolytes (LE), which are composed of polymers and electrolytes within the polymers. GPE contains tiny pores for the movement of lithium ions, so its conductivity and lithium ion transference number are much higher than those of SPE.

[0003] Traditional methods for manufacturing GPE mainly use the casting method, including steps such as polymer dissolution, solution casting, and solvent evaporation. This method requires the use and volatilization of a large amount of solvents, which increases the manufacturing cost and causes environmental pollution. Summary of the Invention

[0004] In view of this, the present application provides a preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm. This lithium metal battery uses polytetrafluoroethylene (PTFE) as the diaphragm, and the electrolyte used can be polymerized in-situ into a gel state in the lithium battery, which has good interfacial contact with the electrodes and can effectively reduce the interfacial resistance.

[0005] Specifically, the present application is realized through the following scheme: A preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm, the steps are as follows: Step 1, mixing a polymerization monomer, a lithium salt, a solvent, and an initiator to obtain a precursor solution; Step 2, injecting a part of the precursor solution into the battery containing the positive and negative electrodes for preliminary infiltration; Step 3: After adding the PTFE separator, add the remaining precursor solution for secondary infiltration to complete the battery assembly; Step 4: Place the assembled battery in an oven and let it stand still to complete in-situ polymerization, obtaining a lithium metal battery based on a PTFE separator and a gel electrolyte.

[0006] This application uses an in-situ polymerization method to directly form a gel-state electrolyte during the battery assembly process. This method inherits the good interfacial contact characteristics between the liquid electrolyte and the electrode. The electrolyte can be more closely combined with the electrode simultaneously, thereby effectively reducing the interfacial resistance. Moreover, the above method is compatible with the existing lithium-ion battery manufacturing process, which helps to achieve large-scale production; while the negative potential of the PTFE separator has a certain repulsive effect on FSI in the electrolyte, enabling FSI - to decompose in advance and form an SEI rich in inorganic components dominated by anions, thereby enhancing the interfacial stability and effectively inhibiting the growth of lithium dendrites. This application solves the problems of narrow electrochemical window, leakage, flammability, etc. of liquid electrolytes (LE), as well as the disadvantages of low ionic conductivity, poor electrochemical stability, and low lithium ion transference number of solid electrolytes (SPE). -

[0007] Furthermore, as a preference: In Step 1: The polymerization monomer is 2-methoxyethyl acrylate (2-MTA).

[0008] The lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI).

[0009] The initiator is azobisisobutyronitrile (AIBN).

[0010] The solvent is 1,2-dimethoxyethane (DME).

[0011] Adding a polymer monomer to the lithium salt gives a monomer solution, adding a solvent to the lithium salt gives an electrolyte solution, and mixing the monomer solution, the electrolyte solution, and the initiator gives a precursor solution. More preferably: The concentration of the monomer solution is 0.5 - 4 mol / L, preferably 1 - 3 mol / L, and more preferably 2 mol / L.

[0012] The concentration of the electrolyte solution is 2 - 12 mol / L, preferably 4 - 10 mol / L, and more preferably 8 mol / L.

[0013] The volume ratio of the monomer solution to the electrolyte solution added is 4:1 - 1:4, preferably 1:1 - 4, and more preferably 1:2.

[0014] The addition amount of the initiator is 0.2~2 wt% of the mass of the monomer liquid, preferably 1~1.5 wt%, and 1 wt% is more preferable.

[0015] The melting point of the PTFE diaphragm is 327 °C, the pore size is 0.1~0.45 μm, and preferably 0.2~0.4 μm. The diaphragm thickness is appropriately controlled to be 10~100 μm.

[0016] In step two, the temperature of the primary infiltration is controlled at 10~30 °C.

[0017] In step three, the temperature of the secondary infiltration is controlled at 10~30 °C.

[0018] The volume ratio of the precursor solution added in the primary infiltration to the volume of the precursor solution added in the secondary infiltration is 1:1. Infiltrating in two times can make the precursor liquid better infiltrate the positive and negative electrodes.

[0019] In step four, the static temperature (i.e., the oven temperature) is 40~80 °C, and the static time is 4~20 h.

[0020] The lithium metal battery is a Li | electrolyte-PTFE | Li symmetric battery or a Li | electrolyte-PTFE | NCM811 full battery.

[0021] Among them, the preparation method of NCM811 is as follows: PVDF is stirred evenly in an NMP solution to prepare a mixed solution with a mass fraction of 3~8%wt (preferably 4~6wt%); then the active material NCM811 powder, conductive carbon black Super P and the mixed solution (based on the mass of PVDF) are stirred and ground evenly according to a mass ratio of 8:1:1 to obtain an active material slurry; the aluminum foil is fixed and laid flat, the active material slurry is poured on the aluminum foil and scraped, and vacuum dried at 80 °C for 12 h, and then cut to obtain the positive electrode plate NCM811.

[0022] The beneficial effects of the present invention are as follows: Due to the negative potential of the PTFE diaphragm, there is a certain repulsive effect on FSI in the electrolyte, - so that FSI - can reach the interface and decompose in advance, forming an SEI rich in inorganic components dominated by anions, enhancing the interface stability, and effectively inhibiting the growth of lithium dendrites. In addition, since FSI - is anchored near the cathode, reducing the shuttle of FSI - on both sides of the diaphragm, making the Li + transportation smoother, and accelerating the Li +The migration speed, therefore, the use of PTFE greatly reduces the probability of thermal runaway, reduces the infiltration time, increases the liquid absorption rate, and also increases the number of migrating lithium ions, enhances the migration rate of lithium ions, effectively inhibits the growth of lithium dendrites, thereby significantly improving the battery safety performance, kinetic performance, and cycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a schematic diagram of the high-temperature resistance ability of Embodiments 5 and 6 of the present application and Comparative Examples 2 and 3. a - PTFE state at 60°C, b - PTFE state at 100°C, c - PTFE state at 150°C, d - PTFE state at 200°C, e - PE state at 60°C, f - PE state at 100°C, g - PE state at 150°C, h - PE state at 200°C; Figure 2 It is a schematic diagram of the electrolyte contact angle of Embodiments 5 and 6 of the present application and Comparative Examples 2 and 3. a - Contact angle when the liquid droplet is initially dropped onto PTFE, b - Contact angle between PTFE and the liquid droplet after 60 s, c - Contact angle when the liquid droplet is initially dropped onto PE, d - Contact angle between PE and the liquid droplet after 60 s; Figure 3 It is a comparison chart of the cycling performance of lithium / electrolyte / lithium symmetric batteries composed of different separators at a constant current density. Figure 4 It is a comparison chart of the cycling performance of lithium / electrolyte / NCM811 full batteries composed of different separators at a constant current density. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In order to make the technical problems, technical solutions, and beneficial effects to be solved by the present application more clearly understood, the following will further elaborate on the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the technical solutions of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present application.

[0026] In this embodiment, the constant current charge-discharge performance was tested using Land CT2001 from Wuhan Blue Electronic Co., Ltd.

[0027] Example 1

[0028] In this embodiment, the preparation of the precursor solution was carried out. The process is as follows: Step 1, preparation of the polymer monomer solution: Lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in 2-methoxyethyl acrylate (2-MTA) to prepare a polymer monomer solution with a concentration of 2 mol / L.

[0029] Step 2, preparation of the electrolyte solution: Lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in 1,2-dimethoxyethane (DME) to prepare an electrolyte solution with a concentration of 8 mol / L.

[0030] Step 3, preparation of the precursor solution: The polymer monomer solution and the electrolyte solution were mixed at a volume ratio of 1:2, and 1 wt% of the initiator azobisisobutyronitrile (AIBN) based on the mass of the monomer was added. After stirring evenly, the precursor solution was obtained.

[0031] Example 2

[0032] This embodiment has the same settings as Example 1, except that in Step 1, the concentration of the polymer monomer solution was adjusted to 0.5 mol / L, 1 mol / L, 3 mol / L, and 4 mol / L respectively.

[0033] In the polymer monomer solution, when the concentration of LiFSI is too low (such as when the concentration of the monomer solution in this embodiment is 4 mol / L), the solubility of LiFSI in 2-MTA is limited, and thus the actual dissolved concentration may be lower than the nominal value, resulting in a significant decrease in the total lithium salt concentration in the obtained precursor solution; when the concentration of LiFSI in the polymer monomer solution is too high, the solution viscosity becomes too large (such as when the concentration of the monomer solution in this embodiment is 0.5 mol / L), making it difficult to disperse evenly during the preparation of the precursor solution, and finally local crystallization precipitation occurs in the precursor solution. The conductivity after film formation is only 60% of that in Example 1, and the mechanical strength decreases significantly. Therefore, the concentration of the monomer solution is preferably controlled at 1 - 3 mol / L, and 2 mol / L is better.

[0034] Example 3

[0035] This embodiment has the same settings as Example 1, except that in Step 2, the concentration of the electrolyte solution was adjusted to 2 mol / L, 4 mol / L, 6 mol / L, 10 mol / L, and 12 mol / L respectively.

[0036] When the lithium salt concentration in the electrolyte solution is too low, it will cause the migratable Li +The quantity decreases. When the concentration of the electrolyte drops to 2 mol / L, the conductivity of the corresponding precursor solution after film formation drops to 30 - 50% of that in Example 1. If the concentration of the lithium salt in the electrolyte is too high (such as exceeding 10 mol / L), the viscosity of the solution will increase sharply, resulting in poor fluidity of the precursor solution and inability to complete infiltration evenly and sufficiently. Therefore, the concentration of the electrolyte is preferably controlled at 4 - 10 mol / L, and 8 mol / L is more preferable.

[0037] Example 4

[0038] This example is the same as Example 1, except that in Step 3, the volume ratios of the polymer monomer solution to the electrolyte are 1:1, 1:3, 1:4, 2:1, and 4:1 respectively.

[0039] Insufficient proportion of the electrolyte will lead to a decrease in the total lithium salt concentration. When the volume ratio of the polymer monomer solution to the electrolyte drops to 4:1, the conductivity of the corresponding precursor solution after film formation is only 70% of that in Example 1. At the same time, when the monomer ratio is too high (such as 1:1), the hardness of the film formed by the polymerized precursor will be too large, and cracks will appear during the charge and discharge stage of the battery. Therefore, when preparing the precursor solution, the volume ratio of the monomer solution to the electrolyte is preferably controlled at 1:1 - 4, and 1:2 is more preferable.

[0040] Comparative Example 1

[0041] This comparative example is the same as Example 1, except that the polymerization monomer 2-methoxyethyl acrylate (2-MTA) is replaced with ethoxyethyl acrylate (EEA) and methyl methacrylate (MMA) respectively.

[0042] The results show that when other acrylate esters containing ether oxygen groups (such as EEA in this comparative example) or other acrylate monomers (such as MMA in this comparative example) are used as the polymerization monomer, the solubility of LiFSI decreases significantly. Especially for MMA, the lack of ether oxygen groups in its structure results in its inability to promote Li + dissociation through dipole interaction, and the Li + solvation ability is weak, resulting in a decrease in conductivity.

[0043] Example 5

[0044] This example provides a lithium metal battery with an in-situ gel electrolyte based on a PTFE separator: Li |GPE-PTFE| NCM811 full battery. The positive electrode uses LiNi 0.8 Co 0.1 Mn 0.1 O2 (denoted as NCM811), and the electrode loading is 1 mAh / cm -2, with a ratio of 8:1:1. The negative electrode uses a lithium metal sheet with a thickness of 20 μm, and the separator uses a hydrophilic PTFE membrane with a thickness of 50 μm, a pore size of 0.22 μm, and a melting point of 327 °C (purchased from Zhejiang Geltex Environmental Protection Special Materials Technology Co., Ltd.).

[0045] The battery assembly process based on in-situ polymerization is as follows: 1) Primary infiltration: At room temperature (about 25 °C), 75 μL of the precursor liquid prepared by the method of Example 1 was dropped onto the surface of the positive electrode plate for preliminary infiltration.

[0046] 2) Secondary infiltration: At room temperature (about 25 °C), after covering the hydrophilic PTFE membrane, 75 μL of the precursor liquid prepared by the method of Example 1 was dropped onto the PTFE separator again for secondary infiltration.

[0047] 3) In-situ polymerization: The battery assembled in Step Five was placed in an oven at 60 °C and left standing for 12 h to complete in-situ polymerization, obtaining a Li|GPE-PTFE|NCM811 full battery.

[0048] In the above scheme, the preparation method of NCM811 is as follows: PVDF was stirred evenly in an NMP solution to prepare a mixed solution with a mass fraction of 6 wt%. The active material NCM811 powder, conductive carbon black Super P, and binder PVDF were stirred and ground evenly in a mortar according to a mass ratio of 8:1:1. A piece of aluminum foil of appropriate size was taken and fixed and laid flat on a glass plate. Then the obtained active material slurry was poured onto the aluminum foil and scraped with a film applicator, and then placed in a vacuum oven and vacuum dried at 80 °C for 12 h. The dried sample was cut into NCM811 circular positive electrodes with a diameter of 12 mm by a cutting machine, and the active material content in each positive electrode was about 3 mg cm -2 .

[0049] The obtained full battery was subjected to normal cycle testing with a cycle rate of 0.2C for charging / 1C for discharging and a cut-off voltage of 4.4 V. The Li|GPE-PTFE|NCM811 full battery maintained a capacity retention of >90% during 285 cycles at 1C, with an average coulombic efficiency (CE) >99.9%, and at the same time provided >100 mAh g at a high current density of 5C -1 .

[0050] Comparative Example 2

[0051] This comparative example was set up the same as Example 5, except that the separator was polyethylene (PE), a common battery separator for lithium metal batteries, and a Li|GPE-PE|NCM811 full battery was assembled.

[0052] Example 6

[0053] This embodiment provides an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm: a Li|GPE-PTFE|Li symmetric button battery. Two lithium foils with a diameter of 14 mm are used as the positive and negative electrodes of the battery respectively. The diaphragm is a hydrophilic PTFE membrane with a thickness of 50 μm, a pore size of 0.22 μm, and a melting point of 327 °C (purchased from Zhejiang Geertaisi Environmental Protection Special Materials Technology Co., Ltd.).

[0054] The battery assembly process based on in-situ polymerization is as follows: 1) Primary infiltration: At room temperature (about 25 °C), 75 μL of the precursor solution prepared by the method of Example 1 is dropped onto the surface of the positive lithium foil for preliminary infiltration.

[0055] 2) Secondary infiltration: At room temperature (about 25 °C), after covering the hydrophilic PTFE membrane, 75 μL of the precursor solution prepared by the method of Example 1 is dropped onto the PTFE diaphragm again for secondary infiltration.

[0056] 3) In-situ polymerization: The battery assembled in Step 5 is placed in an oven at 60 °C and left standing for 12 h to complete in-situ polymerization, obtaining a Li|GPE-PTFE|Li symmetric button battery.

[0057] The obtained battery is tested. The Li|GPE-PTFE|Li symmetric battery exhibits stable plating / stripping behavior for more than 1600 hours.

[0058] Comparative Example 3

[0059] This comparative example is the same as the setting of Example 6, except that the diaphragm is polyethylene (PE), a common battery diaphragm for lithium metal batteries, and a Li|GPE-PE|Li symmetric battery (2032 type button battery) is assembled.

[0060] The tests of Example 5 and Comparative Example 2, Example 6 and Comparative Example 3 are carried out, and the results are as Figures 1 to 4 shown. The Li|GPE-separator|NCM811 full battery and the Li|GPE-separator|Li symmetric battery perform the same. Specifically: Combined with Figure 1 , polyethylene (PE) has a relatively low melting point (about 120 °C). When the temperature rises to 100 °C, changes occur ( Figure 1 f in), and when the temperature rises to 150 °C, melting occurs ( Figure 1 g in), and when the temperature rises to 200 °C, it completely becomes a yellow droplet shape ( Figure 1 h in), proving that its safety is poor. While the diaphragm in this case uses polytetrafluoroethylene PTFE, which has a melting point as high as 327 °C and still has good stability when the temperature rises to 200 °C ( Figure 1In d), it has good safety.

[0061] Figure 2 From the comparison between c and d, it can be seen that the wettability of PE is poor, and the contact angle of the droplet changes slightly with time; while for hydrophilic polytetrafluoroethylene PTFE, the contact angle at the initial droplet dripping is 35.94° ( Figure 2 in a), it has been completely absorbed by 60 s, and the contact angle is 0° ( Figure 2 in b). It proves that when using hydrophilic polytetrafluoroethylene PTFE as the separator in this case, its absorption capacity for the electrolyte is significantly stronger than that of PE as the separator.

[0062] Figure 3 The long-term cycling performance of Li / electrolyte / Li symmetric cells with different separators at a current density of 0.1 mA cm -2 and a capacity density of 0.2 mAh cm -2 : Among them, the GPE-PTFE system has a voltage fluctuation always stable within ±0.1 V during 1600-hour cycling, showing extremely low polarization and excellent interfacial stability; while the GPE-PE system shows significant voltage drift (exceeding ±0.15 V), indicating an increase in interfacial impedance and lithium dendrite growth. The above experimental results also confirm that: the PTFE separator repels FSI - anions through its negative surface potential, promoting its preferential decomposition at the electrode interface to form an inorganic SEI layer rich in LiF / Li3N, thereby inhibiting lithium dendrites and increasing the Li + transference number to 0.56 (0.42 for the PE system), indicating that the PTFE separator has better ionic conductivity and interfacial compatibility during the lithium metal deposition / stripping process.

[0063] Figure 4 The cycling performance of Li / electrolyte / NCM811 full cells with different separators at a constant current density. This cycling performance graph compares the long-term performance of lithium metal full cells (Li|electrolyte|NCM811) based on polytetrafluoroethylene (GPE-PTFE) and polyethylene (GPE-PE) separators at a cut-off voltage of 4.4 V, a 20-μm lithium negative electrode, and a 1 mAh cm -2 positive electrode loading. The data shows that the GPE-PTFE system still maintains a reversible capacity of >180 mAh g -1 after 450 cycles (the initial efficiency >92%), the capacity retention rate is above 90%, and the Coulomb efficiency is always stable at 99.5% - 99.9%; while the GPE-PE system has a rapid capacity decay to below 120 mAh g -1 after 300 cycles (the retention rate <70%), and the Coulomb efficiency fluctuates significantly (the lowest drops to 97%). This difference is due to the fact that the PTFE separator regulates the anion distribution through the electrostatic repulsion effect to form a high ionic conductivity (0.56 Li+ (transference number), and an inorganic SEI layer with high modulus, effectively suppressing side reactions at the NCM811 cathode interface and lithium dendrite growth. The above experimental results are consistent with the conclusion in the previous text that this application can achieve "capacity retention > 90% after 285 cycles", fully verifying the technical advantages of the PTFE-based gel electrolyte in a high-voltage (> 4.3V), high-loading (1 mAh cm -2 ) system, providing key support for the commercialization of high-energy-density lithium metal batteries.

[0064] Example 7

[0065] This example provides an in-situ gel electrolyte lithium metal battery based on a PTFE separator: Li |GPE-PTFE|Li symmetric battery. Take two lithium foils with a diameter of 14 mm as the positive and negative electrodes of the battery respectively. The separator uses a hydrophilic PTFE membrane with a thickness of 50 μm and a melting point of 327 °C (purchased from Zhejiang Gertais Environmental Protection Special Materials Technology Co., Ltd.), and the pore sizes of the hydrophilic PTFE membrane are 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, and 0.45 μm respectively.

[0066] The battery assembly process based on in-situ polymerization is as follows: 1) Primary infiltration: At room temperature (about 25 °C), 75 μL of the precursor solution prepared by the method of Example 1 was dropped onto the surface of the positive lithium foil for primary infiltration.

[0067] 2) Secondary infiltration: At room temperature (about 25 °C), after covering the hydrophilic PTFE membrane, 75 μL of the precursor solution prepared by the method of Example 1 was dropped onto the PTFE separator again for secondary infiltration.

[0068] 3) In-situ polymerization: The battery assembled in step five was placed in an oven at 60 °C and left standing for 12 h to complete in-situ polymerization, obtaining a Li |GPE-PTFE| Li symmetric button battery.

[0069] Through AC impedance spectroscopy tests, it was found that the ionic conductivity of the separator with a pore size of 0.22 μm (Example 6) reached up to 1.2×10 -3 S / cm (25 °C), while in this example, the 0.10 μm group had blocked ion migration due to too small pore size (8.7×10 - 4 S / cm), and the mechanical strength of the 0.45 μm group decreased and dendrites penetrated. XPS analysis showed that the content of inorganic components (LiF, Li3N) in the SEI of the 0.22 mm separator group reached 78%, significantly higher than other groups.

[0070] The influence of the above pore sizes was consistent in the Li |GPE-PE| NCM811 full battery.

[0071] When using PTFE as the separator, the pore size is preferably controlled within the range of 0.2 - 0.4 μm, and more preferably 0.22 mm.

[0072] Example 8

[0073] This example provides an in-situ gel polymer electrolyte lithium metal battery based on a PTFE separator: a Li|GPE-PTFE|Li symmetric coin cell. Two lithium foils with a diameter of 14 mm are used as the positive and negative electrodes of the battery, respectively. The separator is a hydrophilic PTFE membrane with a thickness of 50 μm, a pore size of 0.22 μm, and a melting point of 327 °C (purchased from Zhejiang Glorious Environmental Materials Technology Co., Ltd.).

[0074] The battery assembly process based on in-situ polymerization is as follows: 1) Primary infiltration: At room temperature (about 25 °C), 75 μL of the precursor solution is dropped onto the surface of the positive lithium foil for primary infiltration.

[0075] 2) Secondary infiltration: At room temperature (about 25 °C), after covering the hydrophilic PTFE membrane, 75 μL of the precursor solution is dropped onto the PTFE separator for secondary infiltration.

[0076] 3) In-situ polymerization: The battery assembled in step five is placed in an oven at 60 °C and left standing for 12 h to complete in-situ polymerization, obtaining a Li|GPE-PTFE|Li symmetric coin cell.

[0077] In the above process, the preparation method of the precursor solution is as follows: Step 1, prepare the polymer monomer solution: Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in 2-methoxyethyl acrylate (2-MTA) to prepare a polymer monomer solution with a concentration of 2 mol / L.

[0078] Step 2, prepare the electrolyte solution: Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in 1,2-dimethoxyethane (DME) to prepare an electrolyte solution with a concentration of 8 mol / L.

[0079] Step 3, prepare the precursor solution: Mix the polymer monomer solution and the electrolyte solution at a volume ratio of 1:2, and add 0.2 wt%, 0.5 wt%, 1.5 wt%, and 2 wt% of the initiator azobisisobutyronitrile (AIBN) based on the mass of the monomer solution, respectively. After stirring evenly, four groups of precursor solutions are obtained.

[0080] Tests show that when the initiator concentration is 1 wt% (Example 6), the in-situ polymerization reaction is the most uniform, and the interfacial impedance of the battery only increases by 15% after 200 cycles at 0.2C; when it is lower than 0.5 wt%, there will be local unpolymerized regions, and when it exceeds 2 wt%, stress cracks will occur due to the too-fast reaction, and the impedance increases by 38% and 45% after cycling, respectively.

[0081] The influence of the initiator dosage described above is consistent in the Li |GPE-PE| NCM811 full cell.

[0082] The initiator dosage is preferably controlled at 1 - 1.5 wt%, and more preferably 1 wt% of the mass of the polymerizable monomer liquid.

[0083] Example 9

[0084] This example provides an in-situ gel electrolyte lithium metal battery based on a PTFE separator: Li |GPE-PTFE| NCM811 full cell. The positive electrode uses LiNi 0.8 Co 0.1 Mn 0.1 O2 (denoted as NCM811) with a positive electrode loading of 1 mAh / cm -2 , in a ratio of 8:1:1. The negative electrode uses a lithium metal sheet with a thickness of 20 μm, and the separator uses a hydrophilic PTFE membrane with a thickness of 50 μm, a pore size of 0.22 μm, and a melting point of 327 °C (purchased from Zhejiang Gertais Environmental Protection Special Materials Technology Co., Ltd.).

[0085] The battery assembly process based on in-situ polymerization is as follows: 1) Primary infiltration: At room temperature (about 25 °C), 75 μL of the precursor liquid prepared by the method of Example 1 was dropped onto the surface of the positive electrode sheet for preliminary infiltration.

[0086] 2) Secondary infiltration: At room temperature (about 25 °C), after covering the hydrophilic PTFE membrane, 75 μL of the precursor liquid prepared by the method of Example 1 was dropped onto the PTFE separator again for secondary infiltration.

[0087] 3) In-situ polymerization: The battery assembled in step five was placed in an oven at 60 °C and left standing for 12 h to complete in-situ polymerization, obtaining the Li |GPE-PTFE| NCM811 full cell.

[0088] Among them, the preparation method of NCM811 is as follows: PVDF was stirred evenly in an NMP solution to prepare mixed solutions with mass fractions of 3 wt%, 4 wt%, 5 wt%, and 8 wt% respectively. The active material NCM811 powder, conductive carbon black Super P, and binder PVDF were mixed in a ratio of 8:1:1 by mass (the amount of NMP needs to be adjusted to achieve the same solid content), and were thoroughly stirred and ground in a mortar. A piece of aluminum foil of appropriate size was taken and fixed and laid flat on a glass plate. Then the obtained active material slurry was poured onto the aluminum foil and scraped with a film applicator, and then placed in a vacuum oven at 80 °C for vacuum drying for 12 h. The dried sample was cut into NCM811 circular positive electrodes with a diameter of 12 mm using a cutting machine.

[0089] Comparing Comparative Example 5 with Example 9 shows that when the mass fraction of the mixed solution is less than 4%, the low-concentration PVDF cannot effectively fix the active material, and the electrode plate expands and cracks after being immersed in the electrolyte. Therefore, it is appropriate to control the mass fraction of the mixed solution at 4-6 wt%.

[0090] In summary, the present invention introduces an in-situ polymerized polytetrafluoroethylene gel electrolyte into a lithium battery. This electrolyte not only has a high affinity for lithium metal but also has an affinity for solvent molecules. Through the electrostatic repulsion characteristics of the polytetrafluoroethylene (PTFE) separator, the distribution behavior of bis(fluorosulfonyl)imide anions (FSI - ) in the electrolyte can be directionally regulated. Specifically, the negative surface potential of PTFE forces FSI - to preferentially accumulate in the electrode-electrolyte interface region, triggering its premature electrochemical decomposition to form a solid electrolyte interface (SEI) layer dominated by inorganic substances (such as LiF, Li3N) with anions in the majority. This high-modulus, high-ion-conducting SEI structure effectively passivates the lithium metal surface, significantly reduces the interfacial polarization, and inhibits the uncontrollable growth of lithium dendrites. At the same time, the localized distribution of FSI - near the cathode can inhibit its transmembrane diffusion, reduce the anion concentration polarization phenomenon, and make the transport path of lithium ions (Li + ) more directional. This synergistic effect not only promotes the efficient desolvation of Li + by reducing the solvation energy but also realizes the uniform deposition of metallic lithium by regulating the distribution of lithium ion flow. Experimental data show that the transference number of Li + in the PTFE-based system is increased to 0.56 (only 0.42 in the PE system), and finally endows the battery with a capacity retention rate of >90% after up to 285 cycles and a reversible capacity of >100 mAh g -1 at a 5C rate, demonstrating excellent rate performance and long-cycle stability.

[0091] The above-described embodiments only represent several feasible implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention patent. The embodiments are not intended to limit the protection scope of the claims of the present invention. For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. Any equivalent implementation or change made without departing from the present invention should be included in the technology of the present invention.

Claims

1. A preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm, characterized in that, The steps are as follows: Step 1: Mix the polymerization monomer, lithium salt, solvent, and initiator to obtain a precursor solution; Step 2: Inject part of the precursor solution into the battery with positive and negative electrodes to conduct preliminary infiltration; Step 3: Add a PTFE separator, and add the remaining precursor solution to conduct secondary infiltration; Step 4: Place it in an oven, let it stand still, complete in-situ polymerization, and obtain a lithium metal battery based on a PTFE separator and a gel electrolyte.

2. The preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 1, characterized in that: The polymerization monomer is 2-methoxyethyl acrylate, the lithium salt is lithium bis(fluorosulfonyl)imide, and the polytetrafluoroethylene is hydrophilic polytetrafluoroethylene.

3. The preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 1, characterized in that: In Step 1, the lithium salt is added to the polymer monomer to obtain a monomer solution, the lithium salt is added to the solvent to obtain an electrolyte solution, and the monomer solution, electrolyte solution, and initiator are mixed to obtain a precursor solution.

4. The preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 3, wherein: The concentration of the monomer solution is 0.5 - 4 mol / L.

5. The preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 3, wherein: The concentration of the electrolyte solution is 2 - 12 mol / L.

6. The preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 3, characterized in that: When mixing to obtain the precursor solution, the volume ratio of the added monomer solution to the electrolyte solution is 4:1 - 1:

4.

7. The preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 3, characterized in that: The addition amount of the initiator is 0.2 - 2 wt% of the mass of the monomer solution.

8. The preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 3, characterized in that: The pore size of the PTFE separator is 0.1 - 0.45 μm.

9. The preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 1, wherein: The battery is a Li | electrolyte-PTFE | Li symmetric battery or a Li | electrolyte-PTFE | NCM811 full battery.

10. The preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 9, characterized in that, The preparation method of NCM811 is as follows: Stir PVDF evenly in an NMP solution to prepare a mixed solution with a mass fraction of 3 - 6%wt; then, the active material NCM811 powder, conductive carbon black Super P, and the mixed solution are fully stirred and ground evenly according to a mass ratio of 8:1:1 to obtain an active material slurry; fix and lay flat the aluminum foil, pour the active material slurry on the aluminum foil and scrape it, dry it in vacuum at 80°C for 12 h, and cut it to obtain the positive electrode sheet NCM811.

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