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

Abstract

The present application provides a preparation method of an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm, which belongs to the technical field of lithium batteries. A polymerization monomer, a lithium salt, a solvent, and an initiator are mixed to obtain a precursor solution; a portion of the precursor solution is injected into the interior of a battery equipped with positive and negative electrodes for preliminary infiltration; a PTFE diaphragm is added, and the remaining precursor solution is added for secondary infiltration; the battery is placed in an oven and allowed to stand to complete in-situ polymerization, thereby obtaining a lithium metal battery based on a PTFE diaphragm and a gel electrolyte. The gel electrolyte of the present invention can effectively reduce the interfacial resistance and has a great influence on the FSI in the electrolyte. ‑ There is a certain repulsive effect, making FSI ‑ It 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.

Description

Technical Field

[0001] The present application relates to a method for preparing 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 has a theoretical capacity (3860 mAh g) that is more than 10 times higher than that of the graphite anode. -1 ) and its extremely low electrode potential (-3.04 V vs. standard hydrogen electrode), it is considered the best candidate to replace graphite anodes in high-performance rechargeable batteries. Most lithium metal batteries use liquid electrolytes (LEs), which offer advantages such as good interfacial compatibility, high lithium ion transference numbers, and ease of preparation. However, they also suffer from issues such as a narrow electrochemical window, leakage, and flammability. Solid-state electrolytes (SPEs) have attracted widespread attention due to their thermal and chemical stability, low density, and good processability. SPEs can effectively inhibit the formation of lithium dendrites, significantly improving battery safety. However, most SPEs suffer from low ionic conductivity, poor electrochemical stability, and low lithium ion transference numbers. Current methods for improving SPE ionic conductivity often degrade mechanical properties. Gel electrolytes (GPEs) are a semi-solid electrolyte between solid electrolytes (SPEs) and liquid electrolytes (LEs). They consist of a polymer and an electrolyte solution enclosed within the polymer. GPEs contain micropores for lithium ion movement, resulting in significantly higher conductivity and lithium ion transference numbers than SPEs.

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

[0004] In view of this, the present application provides a method for preparing an in-situ gel electrolyte lithium metal battery based on PTFE membrane. The lithium metal battery uses polytetrafluoroethylene (PTFE) as a membrane, and the electrolyte used can be in-situ polymerized into a gel state in the lithium battery. It has good interface contact with the electrode and can effectively reduce the interface resistance.

[0005] Specifically, this application is implemented through the following solutions:

[0006] A method for preparing an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm, comprising the following steps:

[0007] Step 1: mixing a polymerization monomer, a lithium salt, a solvent, and an initiator to obtain a precursor solution;

[0008] Step 2: inject part of the precursor solution into the battery containing the positive and negative electrodes for preliminary infiltration;

[0009] Step 3: After adding the PTFE diaphragm, add the remaining precursor solution for secondary infiltration to complete the battery assembly;

[0010] Step 4: Place the assembled battery in an oven and let it stand to complete in-situ polymerization to obtain a lithium metal battery based on PTFE membrane and gel electrolyte.

[0011] This application adopts the in-situ polymerization method to directly form a gel electrolyte during the battery assembly process. This method inherits the good interface contact characteristics of the liquid electrolyte and the electrode. The electrolyte can also be more closely combined with the electrode, thereby effectively reducing the interface resistance. The above method is compatible with the existing lithium-ion battery manufacturing process and is conducive to large-scale production. The negative potential of the PTFE diaphragm has a great influence on the FSI in the electrolyte. - Has a certain repulsive effect, making FSI - It can decompose in advance and form an inorganically rich SEI dominated by anions, thereby enhancing interfacial stability and effectively inhibiting the growth of lithium dendrites. This application solves the problems of liquid electrolytes (LE) such as narrow electrochemical window, leakage, and flammability, as well as the shortcomings of solid-state electrolytes (SPEs) such as low ionic conductivity, poor electrochemical stability, and low lithium ion transference number.

[0012] Furthermore, as a preference:

[0013] In step one:

[0014] The polymerizable monomer is 2-methoxyethyl 2-acrylate (2-MTA).

[0015] The lithium salt is lithium bis(fluorosulfonyl)imide (LIFSI).

[0016] The initiator is azobisisobutyronitrile (AIBN).

[0017] The solvent is dimethyl ether (DME).

[0018] Lithium salt is added to polymer monomer to obtain monomer solution, lithium salt is added to solvent to obtain electrolyte solution, monomer solution, electrolyte solution and initiator are mixed to obtain precursor solution. More preferably:

[0019] The concentration of the monomer solution is 0.5-4 mol / L, preferably 1-3 mol / L, and most preferably 2 mol / L.

[0020] The concentration of the electrolyte is 2-12 mol / L, preferably 4-10 mol / L, and most preferably 8 mol / L.

[0021] The volume ratio of the monomer solution to the electrolyte solution is 4:1 to 1:4, preferably 1:1 to 4, and most preferably 1:2.

[0022] The amount of the initiator added is 0.2-2 wt% of the monomer liquid, preferably 1-1.5 wt%, and most preferably 1 wt%.

[0023] The PTFE membrane has a melting point of 327°C, a pore size of 0.1-0.45 μm, and preferably 0.2-0.4 μm. The membrane thickness is preferably controlled to be 10-100 μm.

[0024] In step 2, the temperature of the initial infiltration is controlled at 10-30°C.

[0025] In step 3, the temperature of the secondary soaking is controlled at 10~30℃.

[0026] The volume ratio of the precursor solution added in the first infiltration to the volume ratio of the precursor solution added in the second infiltration is 1:1. The two infiltrations can make the precursor liquid better infiltrate the positive and negative electrodes.

[0027] In step 4, the standing temperature (i.e., oven temperature) is 40-80°C, and the standing time is 4-20 hours.

[0028] The lithium metal battery is a Li|electrolyte-PTFE|Li symmetric battery or a Li|electrolyte-PTFE|NCM811 full battery.

[0029] Among them, the preparation method of NCM811 is: PVDF is evenly stirred in 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 mixed solution (based on the mass of PVDF) are mixed in a mass ratio of 8:1:1, and are fully stirred and ground to obtain active material slurry; fixed and flat aluminum foil, the active material slurry is poured on the aluminum foil and scraped, vacuum dried at 80°C for 12h, and cut to obtain the positive electrode sheet NCM811.

[0030] The beneficial effects of the present invention are:

[0031] Due to the negative potential of PTFE separator, FSI in electrolyte - There is a certain repulsive effect, making FSI - It 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. - Anchored near the cathode, reducing FSI - Shuttle between the two sides of the diaphragm, so that Li +Transmission is smoother, speeding up Li + Therefore, the use of PTFE greatly reduces the probability of thermal runaway, reduces the wetting time, improves the liquid absorption rate, increases the number of lithium ion migration, improves the migration rate of lithium ions, and effectively inhibits the growth of lithium dendrites, thereby achieving a significant improvement in battery safety, kinetics and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0033] Figure 1 Schematic diagram of high temperature resistance of Examples 5 and 6 of the present application and Comparative Examples 2 and 3.

[0034] a-PTFE state at 60℃, b-PTFE state at 100℃, c-PTFE state at 150℃, d-PTFE state at 200℃, e-PE state at 60℃, f-PE state at 100℃, g-PE state at 150℃, h-PE state at 200℃;

[0035] Figure 2 Schematic diagram of the electrolyte contact angle of Examples 5 and 6 of the present application and Comparative Examples 2 and 3,

[0036] a-PTFE contact angle when the droplet is initially dropped, b-PTFE contact angle with the droplet after 60s, c-PE contact angle when the droplet is initially dropped, d-PE contact angle with the droplet after 60s;

[0037] Figure 3 A comparison chart of the cycling performance of lithium / electrolyte / lithium symmetric batteries composed of different separators at a constant current density;

[0038] Figure 4 A comparison chart of the cycling performance of lithium / electrolyte / NCM811 full batteries composed of different separators at constant current density. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the technical solutions in the embodiments of this application will be further described in detail below in conjunction with the drawings in the embodiments of this application. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit the technical solutions of this application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of this application.

[0040] In this embodiment, the constant current charge and discharge performance is tested using Land CT2001 produced by Wuhan Landian Electronics Co., Ltd.

[0041] Example 1

[0042] This example is about the preparation of precursor liquid. The process is as follows:

[0043] Step 1: preparing a polymer monomer solution: dissolving lithium bis(fluorosulfonyl)imide (LIFSI) in 2-methoxyethyl 2-acrylate (2-MTA) to prepare a polymer monomer solution with a concentration of 2 mol / L.

[0044] Step 2: Prepare an electrolyte: dissolve lithium bis(fluorosulfonyl)imide (LIFSI) in ethylene glycol dimethyl ether (DME) to prepare an electrolyte with a concentration of 8 mol / L.

[0045] Step 3: Prepare a precursor liquid: Mix the polymer monomer liquid and the electrolyte in a volume ratio of 1:2, add 1 wt% of the monomer mass of the initiator azobisisobutyronitrile (AIBN), and stir evenly to obtain a precursor liquid.

[0046] Example 2

[0047] The configuration of this embodiment is the same as that of embodiment 1, except that in step 1, the concentration of the polymer monomer solution is adjusted from 2 mol / L to 0.5 mol / L, 1 mol / L, 3 mol / L, and 4 mol / L, respectively.

[0048] In the polymer monomer solution, if the LiFSI concentration is too low (such as when the monomer solution concentration is 4 mol / L in this example), the solubility of LiFSI in 2-MTA is limited, and the actual solubility concentration may be lower than the nominal value, resulting in a significant decrease in the total lithium salt concentration in the precursor solution obtained after mixing. If the LiFSI concentration in the polymer monomer solution is too high, the solution viscosity will be too high (such as when the monomer solution concentration is 0.5 mol / L in this example), making it difficult to uniformly disperse the precursor solution during preparation. Ultimately, the precursor solution will exhibit localized crystallization, and the conductivity of the film after formation will be only 60% of that in Example 1, and the mechanical strength will be significantly reduced. Therefore, the concentration of the monomer solution is preferably controlled between 1 and 3 mol / L, with 2 mol / L being the best.

[0049] Example 3

[0050] The configuration of this embodiment is the same as that of embodiment 1, except that in step 2, the concentration of the electrolyte is adjusted from 8 mol / L to 2 mol / L, 4 mol / L, 6 mol / L, 10 mol / L, and 12 mol / L, respectively.

[0051] If the lithium salt concentration in the electrolyte is too low, it will cause the mobile Li + When the electrolyte concentration drops to 2 mol / L, the conductivity of the precursor solution after film formation drops to 30-50% of that in Example 1. If the lithium salt concentration in the electrolyte is too high (e.g., exceeding 10 mol / L), the solution viscosity increases sharply, resulting in poor precursor fluidity and inability to achieve uniform and sufficient infiltration. Therefore, the electrolyte concentration is preferably controlled between 4 and 10 mol / L, with 8 mol / L being preferred.

[0052] Example 4

[0053] The configuration of this embodiment is the same as that of embodiment 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.

[0054] An insufficient electrolyte ratio will result in a decrease in the total lithium salt concentration. When the volume ratio of the polymer monomer solution to the electrolyte is reduced to 4:1, the corresponding conductivity of the precursor solution after film formation is only 70% of that in Example 1. At the same time, a high monomer ratio (e.g., 1:1) will result in excessive hardness of the precursor film after polymerization, leading to cracks during the battery's charge and discharge phases. Therefore, when preparing the precursor solution, the volume ratio of the monomer solution to the electrolyte should be controlled between 1:1 and 4, with 1:2 being preferred.

[0055] Comparative Example 1

[0056] The configuration of this comparative example is the same as that of Example 1, except that the polymerization monomer 2-methoxyethyl acrylate (2-MTA) is replaced by ethoxyethyl acrylate (EEA) and methyl methacrylate (MMA), respectively.

[0057] The results show that when the polymerization monomer is other acrylates containing ether groups (such as EEA in this comparative example) or other acrylate monomers (such as MMA in this comparative example), the solubility of LiFSI decreases significantly, especially MMA, which lacks ether groups in its structure, resulting in its inability to promote the diffusion of Li by dipole action. + Dissociation, Li + The solvation ability is weak and the conductivity decreases.

[0058] Example 5

[0059] This embodiment provides an in-situ gel electrolyte lithium metal battery based on PTFE diaphragm: Li | GPE-PTFE | NCM811 full battery, the positive electrode of which is LiNi 0.8 Co 0.1 Mn 0.1 O2 (denoted as NCM811) electrode loading 1mAh / cm -2 , ratio 8:1:1, the negative electrode uses a lithium metal sheet with a thickness of 20μm, and the separator uses a hydrophilic PTFE membrane with a thickness of 50μm, a pore size of 0.22μm, and a melting point of 327℃ (purchased from Zhejiang Geertaisi Environmental Protection Special Materials Technology Co., Ltd.).

[0060] The battery assembly process based on in situ polymerization is as follows:

[0061] 1) Initial infiltration: At room temperature (about 25°C), 75 μL of the precursor solution prepared by the method in Example 1 was added dropwise to the surface of the positive electrode sheet for initial infiltration.

[0062] 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 dripped onto the PTFE membrane again for secondary infiltration.

[0063] 3) In-situ polymerization: The battery assembled in step 5 was placed in a 60°C oven and allowed to stand for 12 h to complete in-situ polymerization and obtain a Li|GPE-PTFE|NCM811 full battery.

[0064] In the above scheme, the preparation method of NCM811 is as follows:

[0065] PVDF was stirred evenly in the 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 mixed and ground evenly in a mortar at a mass ratio of 8:1:1. Take a piece of aluminum foil of appropriate size and fix it flat on a glass plate. Then pour the obtained active material slurry on the aluminum foil and apply it with a film applicator. Then place it in a vacuum oven and vacuum dry it at 80 ° C for 12 hours. The dried sample was cut into NCM811 disc positive electrodes with a diameter of 12 mm using a cutting machine. The active material content in each positive electrode sheet is approximately 3 mg cm -2 .

[0066] The obtained full cell was subjected to normal cycle testing with a cycle rate of charge 0.2C / discharge 1C and a cut-off voltage of 4.4 V. The Li|GPE-PTFE|NCM811 full cell maintained a capacity retention of >90% over 285 cycles at 1C, with an average Coulombic efficiency (CE) of >99.9%, while delivering >100 mAh g at a high current density of 5C. -1.

[0067] Comparative Example 2

[0068] This comparative example has the same configuration as Example 5, except that the separator is polyethylene (PE), a common separator for lithium metal batteries, and the Li|GPE-PE|NCM811 full cell is assembled.

[0069] Example 6

[0070] This example provides an in-situ gel electrolyte lithium metal battery based on a PTFE separator: a Li|GPE-PTFE|Li symmetric button cell. Two lithium sheets 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 Geertaisi Environmental Protection Special Materials Technology Co., Ltd.).

[0071] The battery assembly process based on in situ polymerization is as follows:

[0072] 1) Initial infiltration: At room temperature (about 25°C), 75 μL of the precursor solution prepared by the method in Example 1 was added dropwise to the surface of the positive electrode lithium sheet for initial infiltration.

[0073] 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 dripped onto the PTFE membrane again for secondary infiltration.

[0074] 3) In situ polymerization: The battery assembled in step 5 was placed in a 60°C oven and allowed to stand for 12 h to complete in situ polymerization and obtain a Li|GPE-PTFE|Li symmetric button cell.

[0075] The obtained battery was tested and the Li|GPE-PTFE|Li symmetric battery exhibited stable plating / stripping behavior for more than 1600 hours.

[0076] Comparative Example 3

[0077] This comparative example has the same configuration as Example 6, except that the separator is polyethylene (PE), a common battery separator for lithium metal batteries, and is assembled to form a Li|GPE-PE|Li symmetrical battery (2032 type button cell).

[0078] The results of testing with Example 5 and Comparative Example 2, and Example 6 and Comparative Example 3 are as follows: Figures 1 to 4 As shown, the Li|GPE-separator|NCM811 full cell and the Li|GPE-separator|Li symmetric cell perform the same. Specifically:

[0079] Combine Figure 1, polyethylene (PE) has a low melting point (about 120 ° C), and changes have occurred when the temperature rises to 100 ° C ( Figure 1 f in the figure), melting occurs when the temperature rises to 150°C ( Figure 1 g in the figure), when the temperature rises to 200℃, it completely turns into yellow droplets ( Figure 1 The h in the figure shows that its safety is poor. However, the diaphragm in this case uses polytetrafluoroethylene (PTFE), which has a melting point of 327°C and is still stable even when the temperature rises to 200°C ( Figure 1 d) in the figure has good security.

[0080] Figure 2 The comparison between c and d shows that the wettability of PE is poor, and the contact angle of the droplet changes slightly over time; while the contact angle of hydrophilic polytetrafluoroethylene PTFE when the droplet is initially dropped is 35.94° ( Figure 2 a in the figure), it has been completely absorbed by 60s, and the contact angle is 0° ( Figure 2 b) proves that when hydrophilic polytetrafluoroethylene (PTFE) is used as the diaphragm in this case, its ability to absorb electrolyte is significantly stronger than that of PE as the diaphragm.

[0081] Figure 3 The lithium / electrolyte / lithium symmetric battery with different separators at a current density of 0.1 mA cm -2 , capacity density is 0.2mAh cm -2 The long-term cycle performance under the test conditions: the voltage fluctuation of the GPE-PTFE system remained stable within ±0.1 V during the 1600-hour cycle, showing extremely low polarization and excellent interface stability; while the GPE-PE system showed a significant voltage drift (exceeding ±0.15 V), indicating increased interfacial impedance and lithium dendrite growth. The above experimental results also confirmed that the PTFE membrane repels FSI through its negative surface potential. - anions, which promote their preferential decomposition at the electrode interface to form an inorganic SEI layer rich in LiF / Li3N, thereby inhibiting lithium dendrites and improving Li + The migration number reaches 0.56 (0.42 for the PE system), indicating that the PTFE membrane has better ionic conductivity and interfacial compatibility during the lithium metal deposition / stripping process.

[0082] Figure 4 The cycling performance of lithium / electrolyte / NCM811 full cells with different separators at constant current density is compared. The cycling performance graph compares the cycling performance of lithium metal full cells (Li|electrolyte|NCM811) based on polytetrafluoroethylene (GPE-PTFE) and polyethylene (GPE-PE) separators at a cutoff voltage of 4.4 V, a 20 μm lithium anode, and a 1 mAh cm -2Long-term performance under high cathode loading. Data show that the GPE-PTFE system still maintains >180 mAh g after 450 cycles. -1 The reversible capacity of the GPE-PE system was 120 mAh g after 300 cycles, and the capacity retention rate was over 90%. The coulombic efficiency was always stable at 99.5%~99.9%. -1 Below (retention rate <70%), the coulombic efficiency fluctuates significantly (down to 97%). This difference is due to the fact that the PTFE membrane regulates the anion distribution through the electrostatic repulsion effect, forming a high ion conductivity (0.56 Li + The above experimental results are consistent with the conclusion that the present application can achieve "capacity retention > 90% after 285 cycles", which fully verifies the PTFE-based gel electrolyte under high voltage (> 4.3V) and high loading (1mAh cm -2 ) system provides key support for the commercialization of high energy density lithium metal batteries.

[0083] Example 7

[0084] This embodiment provides an in-situ gel electrolyte lithium metal battery based on a PTFE separator: a Li|GPE-PTFE|Li symmetric battery. Two lithium sheets with a diameter of 14 mm are used as the positive and negative electrodes of the battery, respectively. The separator adopts a hydrophilic PTFE membrane with a thickness of 50 μm and a melting point of 327°C (purchased from Zhejiang Geltais Environmental Protection Special Materials Technology Co., Ltd.). 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.

[0085] The battery assembly process based on in situ polymerization is as follows:

[0086] 1) Initial infiltration: At room temperature (about 25°C), 75 μL of the precursor solution prepared by the method in Example 1 was added dropwise to the surface of the positive electrode lithium sheet for initial infiltration.

[0087] 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 dripped onto the PTFE membrane again for secondary infiltration.

[0088] 3) In situ polymerization: The battery assembled in step 5 was placed in a 60°C oven and allowed to stand for 12 h to complete in situ polymerization and obtain a Li|GPE-PTFE|Li symmetric button cell.

[0089] The AC impedance spectroscopy test showed that the ionic conductivity of the membrane with a pore size of 0.22 μm (Example 6) was as high as 1.2×10-3 S / cm (25°C), while the 0.10 μm group in this embodiment had a small pore size, which resulted in the ion migration being hindered (8.7×10 - 4 S / cm), and the 0.45μm group showed decreased mechanical strength and dendrite penetration. XPS analysis showed that the inorganic component (LiF, Li3N) content in the SEI of the 0.22mm separator group reached 78%, significantly higher than that of the other groups.

[0090] The above-mentioned effects of pore size are consistent in Li|GPE-PE|NCM811 full cells.

[0091] When PTFE is used as the diaphragm, the pore size is preferably controlled within a range of 0.2 to 0.4 μm, and preferably 0.22 mm.

[0092] Example 8

[0093] This example provides an in-situ gel electrolyte lithium metal battery based on a PTFE separator: a Li|GPE-PTFE|Li symmetric button cell. Two lithium sheets 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 Geertaisi Environmental Protection Special Materials Technology Co., Ltd.).

[0094] The battery assembly process based on in situ polymerization is as follows:

[0095] 1) Initial infiltration: At room temperature (about 25°C), add 75 μL of precursor solution to the surface of the positive electrode lithium sheet for initial infiltration.

[0096] 2) Secondary infiltration: At room temperature (approximately 25°C), after covering the hydrophilic PTFE membrane, add 75 μL of precursor liquid to the PTFE membrane for secondary infiltration.

[0097] 3) In situ polymerization: The battery assembled in step 5 was placed in a 60°C oven and allowed to stand for 12 h to complete in situ polymerization and obtain a Li|GPE-PTFE|Li symmetric button cell.

[0098] In the above process, the preparation method of the precursor liquid is as follows:

[0099] Step 1: preparing a polymer monomer solution: dissolving lithium bis(fluorosulfonyl)imide (LIFSI) in 2-methoxyethyl 2-acrylate (2-MTA) to prepare a polymer monomer solution with a concentration of 2 mol / L.

[0100] Step 2: Prepare an electrolyte: dissolve lithium bis(fluorosulfonyl)imide (LIFSI) in ethylene glycol dimethyl ether (DME) to prepare an electrolyte with a concentration of 8 mol / L.

[0101] Step 3: Prepare the precursor liquid: Mix the polymer monomer liquid and the electrolyte in a volume ratio of 1:2, add 0.2wt%, 0.5wt%, 1.5wt% and 2wt% of the initiator azobisisobutyronitrile (AIBN) based on the mass of the monomer liquid, respectively, and stir evenly to obtain four groups of precursor liquids.

[0102] Tests found that when the initiator concentration was 1 wt% (Example 6), the in-situ polymerization reaction was most uniform, and the interfacial impedance only increased by 15% after the battery was cycled 200 times at 0.2C. However, when the initiator concentration was lower than 0.5 wt%, local unpolymerized areas would appear, and when the concentration exceeded 2 wt%, stress cracks would be generated due to the excessively rapid reaction, and the impedance after cycling would increase by 38% and 45%, respectively.

[0103] The above-mentioned effects of initiator dosage are consistent in Li|GPE-PE|NCM811 full cells.

[0104] The amount of initiator is preferably controlled at 1-1.5 wt%, and preferably 1 wt% of the mass of the polymerization monomer liquid.

[0105] Example 9

[0106] This embodiment provides an in-situ gel electrolyte lithium metal battery based on PTFE diaphragm: Li | GPE-PTFE | NCM811 full battery, the positive electrode uses LiNi 0.8 Co 0.1 Mn 0.1 O2 (denoted as NCM811) electrode loading 1mAh / cm -2 , ratio 8:1:1, the negative electrode uses a lithium metal sheet with a thickness of 20μm, and the separator uses a hydrophilic PTFE membrane with a thickness of 50μm, a pore size of 0.22μm, and a melting point of 327℃ (purchased from Zhejiang Geertaisi Environmental Protection Special Materials Technology Co., Ltd.).

[0107] The battery assembly process based on in situ polymerization is as follows:

[0108] 1) Initial infiltration: At room temperature (about 25°C), 75 μL of the precursor solution prepared by the method in Example 1 was added dropwise to the surface of the positive electrode sheet for initial infiltration.

[0109] 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 dripped onto the PTFE membrane again for secondary infiltration.

[0110] 3) In-situ polymerization: The battery assembled in step 5 was placed in a 60°C oven and allowed to stand for 12 h to complete in-situ polymerization and obtain a Li|GPE-PTFE|NCM811 full battery.

[0111] The preparation method of NCM811 is as follows:

[0112] PVDF was mixed 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 and ground thoroughly in a mortar at a mass ratio of 8:1:1 (the NMP dosage needed to be adjusted to achieve the same solid content). A piece of aluminum foil of appropriate size was placed flat on a glass plate. The resulting active material slurry was then poured onto the foil and coated with a doctor blade. The mixture was then dried in a vacuum oven at 80°C for 12 hours. The dried sample was cut into 12 mm diameter NCM811 discs for the positive electrode using a sheet cutter.

[0113] Comparing Example 5 with Example 9, it can be seen that when the mass fraction of the mixed solution is lower than 4%, the low-concentration PVDF cannot effectively fix the active material, and the electrode expands and cracks after being immersed in the electrolyte. Therefore, it is appropriate to control the mass fraction of the mixed solution to 4-6wt%.

[0114] In summary, the present invention introduces an in-situ polymerized polytetrafluoroethylene gel electrolyte into a lithium battery. This electrolyte has a high affinity not only for lithium metal but also for solvent molecules. Through the electrostatic repulsion characteristics of the polytetrafluoroethylene (PTFE) separator, the bis(fluorosulfonyl)imide anion (FSI) in the electrolyte can be directional controlled. - ) distribution behavior. Specifically, the negative surface potential of PTFE forces FSI - It preferentially accumulates in the electrode-electrolyte interface region, triggering its premature electrochemical decomposition, forming a solid electrolyte interface (SEI) layer dominated by anions and inorganic substances (such as LiF, Li3N). This high modulus, high ion conductivity SEI structure effectively passivates the lithium metal surface, significantly reduces the interface polarization, and inhibits the uncontrollable growth of lithium dendrites. At the same time, FSI - The localized distribution near the cathode can inhibit its cross-membrane diffusion and reduce the anion concentration polarization phenomenon, making the lithium ion (Li + ) transport pathways are more directional. This synergistic effect not only promotes the transport of Li by reducing the solvation energy + The efficient desolvation of PTFE-based system can also achieve uniform deposition of metallic lithium by regulating the distribution of lithium ion flow. + The migration number is increased to 0.56 (only 0.42 for the PE system), ultimately giving the battery a capacity retention rate of >90% after 285 cycles and maintaining >100 mAh g at a 5C rate. -1 The reversible capacity shows excellent rate performance and long cycle stability.

[0115] The above-described embodiments merely represent several feasible implementation methods of the present invention. The description thereof is relatively specific and detailed, but it should not be understood as limiting the scope of the invention. The embodiments are not intended to limit the scope of protection in the claims of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention. Any equivalent implementation or modification that does not depart from the scope of the present invention should be included in the technology of the present invention.

Claims

1. A method for preparing an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm, characterized in that: Here are the steps: Step 1: Add lithium salt to polymer monomer to obtain a monomer solution with a concentration of 0.5 to 4 mol / L, add solvent to lithium salt to obtain an electrolyte with a concentration of 2 to 12 mol / L, mix the monomer solution, electrolyte and initiator to obtain a precursor solution, the volume ratio of monomer solution to electrolyte is 4:1 to 1:4, the amount of initiator added is 0.2 to 2 wt% of the mass of the monomer solution, the polymer monomer is 2-methoxyethyl 2-acrylate, and the lithium salt is lithium bis(fluorosulfonyl)imide; Step 2: inject part of the precursor solution into the battery containing the positive and negative electrodes for preliminary infiltration; Step 3: Add a PTFE membrane and add the remaining precursor solution for secondary infiltration. The PTFE membrane is hydrophilic polytetrafluoroethylene with a melting point of 327°C and a pore size of 0.1-0.45 μm. Step 4: Place in an oven and let it stand to complete in-situ polymerization to obtain a lithium metal battery based on PTFE membrane and gel electrolyte.

2. The method for preparing an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 1, characterized in that: The battery was a Li|electrolyte-PTFE|Li symmetric cell or a Li|electrolyte-PTFE|NCM811 full cell.

3. The method for preparing an in-situ gel electrolyte lithium metal battery based on a PTFE diaphragm according to claim 2, characterized in that: The preparation method of NCM811 is as follows: PVDF is stirred evenly in 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 mixed and ground evenly in 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, vacuum dried at 80°C for 12 hours, and cut to obtain the positive electrode sheet NCM811.

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