A porous gel electrolyte membrane based on polyvinylidene fluoride and a method for preparing the same
By combining phase inversion and inorganic nanofillers, a porous gel electrolyte membrane based on PVdF was prepared, which solved the problem of PVdF gelation in alkaline environment, achieved high porosity and stable lithium-ion transport, and improved the safety and performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INST OF METAL RESEARCH - CHINESE ACAD OF SCI
- Filing Date
- 2023-10-10
- Publication Date
- 2026-07-24
AI Technical Summary
Existing PVdF-based gel electrolytes are prone to gelation in alkaline environments, resulting in poor slurry flowability. Furthermore, existing film-forming methods have low porosity, affecting ion transport and lithium interface stability.
Porous gel electrolyte membranes were prepared using a phase inversion method. Inorganic ceramic nanofillers and lithium salt additives were used to form a uniform porous structure, which inhibited the defluorination reaction of PVdF and induced the transformation of PVdF from the α phase to the β phase, thereby improving ionic conductivity and mechanical properties.
A gel electrolyte membrane with abundant pore structure was prepared, which improved lithium-ion transport capacity and interfacial stability, suppressed lithium dendrite formation, and improved the cycle stability and ionic conductivity of the battery.
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Figure CN117374382B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a porous gel electrolyte membrane based on polyvinylidene fluoride and its preparation method, belonging to the field of polymer gel electrolytes. Background Technology
[0002] With the rapid development of electronic technology in recent years, lithium-ion batteries have been increasingly widely used in various portable electronic devices. In existing lithium-ion battery systems, most employ fluid organic liquid electrolytes to facilitate the wetting and storage of lithium ions between the active material and the pores of the separator. However, organic electrolytes are typically volatile and flammable, posing a risk of leakage when used in portable devices and thus creating safety hazards. Polymer gel electrolytes, falling between solid and liquid electrolytes, offer better deformability and lithium-ion transport capabilities compared to pure solid electrolytes. Because they lack fluidity, they eliminate the risk of leakage during use, making them safer and more reliable, and can be used to replace liquid electrolytes and separators in lithium-ion batteries.
[0003] Polyvinylidene fluoride (PVdF)-based gel electrolytes, due to their strong electron-withdrawing functional groups and high dielectric constant, facilitate the dissociation of lithium salts, thus providing a high concentration of charge carriers. Their high thermal stability also makes them more suitable as a matrix for gel electrolytes. However, the interfacial reaction between lithium and fluorine results in low chemical stability of fluorinated polymers towards lithium. Therefore, the interfacial stability of PVdF-based polymer electrolytes towards lithium metal still needs improvement.
[0004] To improve the mechanical strength and ionic conductivity of PVdF-based gel electrolytes, lithium lanthanum zirconium tantalum oxide (Li₂O₃) with high ionic conductivity is typically selected. 6.4 La3Zr 1.4 Ta 0.6 O 12 Inorganic solid electrolytes such as LLZTO are used as fillers. However, PVdF is prone to gelation when used in an alkaline environment, which reduces the fluidity of the slurry. The alkaline substances remaining on the surface of LLZTO will exacerbate the gelation of PVdF and even induce the defluorination of the PVdF skeleton, causing discoloration of the slurry and hindering the preparation of gel electrolytes and the stability of their electrochemical performance.
[0005] Currently, existing methods employ coating to form a coating layer on the surface of LLZTO to prevent its reaction with PVdF, or by adding acidic substances to neutralize alkalinity and inhibit the reaction. However, since the introduced substances are all electrochemically inactive, they increase the amount of inactive materials in the battery, reduce the overall energy density, and may also cause other side reactions. Furthermore, existing film-forming methods mostly rely on thermal evaporation and drying after coating, resulting in low porosity, which is detrimental to ion transport within the gel electrolyte. Summary of the Invention
[0006] To address the shortcomings of existing technologies, the present invention aims to provide a porous gel electrolyte membrane based on polyvinylidene fluoride and its preparation method. This method is simple, environmentally friendly, and easy to scale up industrially. By adjusting the additive components, the mechanical properties, ion transport dynamics, and lithium interface stability of the gel electrolyte can be improved, resulting in a safer porous gel electrolyte membrane.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0008] A porous gel electrolyte membrane based on polyvinylidene fluoride (PVDF) is provided. The porous gel electrolyte membrane includes a gel electrolyte matrix, inorganic ceramic nanofillers, lithium salt electrolyte, and lithium salt additives. A gel electrolyte slurry prepared by the gel electrolyte matrix, lithium salt additives, inorganic ceramic nanofillers, and solvent is used to obtain a uniform porous structure membrane by phase inversion curing. The porous structure membrane is then immersed in a liquid electrolyte containing lithium salt electrolyte to gel and form a porous gel electrolyte membrane.
[0009] The gel electrolyte matrix is composed of one or more of the following fluorinated homopolymers and copolymers: polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), vinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P(VdF-TrFE-CFE)), poly(vinylidene fluoride-trifluorochloroethylene) (P(VdF-CTFE)), and poly(vinylidene fluoride-trifluoroethylene) (P(VdFTrFE)).
[0010] The porous gel electrolyte membrane based on polyvinylidene fluoride utilizes inorganic ceramic nanofillers to enhance its ionic conductivity and mechanical strength. The inorganic ceramic nanofillers are composed of one or a combination of two of the following inorganic nanoparticles: nano-lithium lanthanum zirconium oxide (LLZO) and nano-lithium lanthanum zirconium tantalum oxide (LLZTO).
[0011] The porous gel electrolyte membrane based on polyvinylidene fluoride contains a lithium salt and an organic solvent in its liquid electrolyte: the lithium salt is one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI); the organic solvent is one or more of the following ester solvents: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), or one or more of the following ether solvents: dioxolane (DOL) and dimethyl ethylene glycol (DME), or an ionic liquid.
[0012] The porous gel electrolyte membrane based on polyvinylidene fluoride uses lithium salt additives selected from lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), and lithium bis(oxalateborate) (LiBOB).
[0013] The method for preparing a porous gel electrolyte membrane based on polyvinylidene fluoride employs a phase inversion method to prepare the porous membrane, and the method includes the following steps:
[0014] 1) Mix the gel electrolyte matrix, lithium salt additive and solvent in a mass ratio of 1:(0.1~0.5):(5~9) to form a uniformly dispersed gel solution;
[0015] 2) Add inorganic ceramic nanofiller to gel electrolyte matrix at a mass ratio of 1:(5~20) to form a uniformly dispersed gel electrolyte slurry.
[0016] 3) The prepared gel electrolyte slurry is coated onto the substrate material and then transferred into the phase inversion solution for phase inversion and curing for 10 to 600 minutes. After removal, it is dried to obtain a uniform porous membrane.
[0017] 4) Immerse the porous membrane obtained in step 3) into a liquid electrolyte containing lithium salt electrolyte for gelation for 10 to 150 minutes. Remove the membrane and dry the surface liquid to obtain the porous gel electrolyte membrane based on polyvinylidene fluoride.
[0018] The method for preparing the porous gel electrolyte membrane based on polyvinylidene fluoride uses one of N,N-dimethylformamide (DMF), acetone, and N-methylpyrrolidone (NMP) as the solvent.
[0019] The method for preparing a porous gel electrolyte membrane based on polyvinylidene fluoride includes a method for dispersing the gel solution and the gel electrolyte slurry, which is one or a combination of two or more of the following: magnetic stirring dispersion, mechanical stirring dispersion, ultrasonic dispersion, and high-speed shear dispersion.
[0020] The method for preparing a porous gel electrolyte membrane based on polyvinylidene fluoride uses polyethylene terephthalate (PET) film or glass plate as the substrate material.
[0021] The method for preparing a porous gel electrolyte membrane based on polyvinylidene fluoride uses a phase inversion solution that is one or a combination of two of deionized water and ethanol, wherein ethanol accounts for 0-75% of the total volume of the phase inversion solution.
[0022] The preparation method of the porous gel electrolyte membrane based on polyvinylidene fluoride includes drying by either vacuum drying at 60°C or freeze drying.
[0023] The design concept of this invention is:
[0024] By utilizing lithium salt additives to improve the slurry stability of PVdF-based gel electrolytes, the crystal phase structure of the gel electrolyte membrane is altered, thereby enhancing the lithium interface stability of the gel electrolyte membrane. Furthermore, the ionic conductivity and mechanical properties of the gel electrolyte membrane are further optimized through phase transformation and the addition of inorganic nanoparticles.
[0025] This invention relates to a porous gel electrolyte membrane based on PVdF. A uniform porous structure is obtained through phase transformation curing, enhancing the gel electrolyte membrane's adsorption and storage capacity for electrolyte. Inorganic ceramic nanofillers with high ionic conductivity are used to enhance the ionic conductivity and mechanical strength of the gel electrolyte membrane. Lithium salt added during the preparation process inhibits the defluorination reaction of PVdF, ensuring the stability of the slurry. Furthermore, by inducing a transition from the α-phase to the β-phase in the PVdF matrix, uniform deposition of Li ions is promoted, thereby improving the cycle stability of the battery.
[0026] Compared with the prior art, the porous gel electrolyte membrane based on PVdF prepared according to the method provided by the present invention has the following characteristics and beneficial effects:
[0027] 1. In this invention, a porous gel electrolyte matrix membrane is prepared by phase inversion, which can form a rich pore structure inside, which helps the electrolyte to absorb, wet and rapidly transport lithium ions. Compared with the thermal evaporation drying method, the organic solvent in the membrane is easier to completely remove, the preparation conditions are milder and the organic solvent is easier to recover.
[0028] 2. The addition of lithium salt in the preparation process of this invention can suppress the discoloration caused by the defluorination reaction in the slurry, making the slurry more stable. Excess lithium salt can be removed by dissolving in the phase inversion solution during the phase inversion process after coating.
[0029] 3. The addition of lithium salt in this invention can also induce a phase transition from α phase to β phase in PVdF. The ordered arrangement of polar functional groups in β phase PVdF can make the Li ion flux more uniformly distributed during charging and discharging, thereby improving ionic conductivity and suppressing the formation of lithium dendrites.
[0030] 4. The method for preparing the porous gel electrolyte membrane based on PVdF in this invention is simple, easy to control, green, and environmentally friendly. The prepared porous gel electrolyte membrane can be applied to a variety of electrode materials and battery systems, and is also suitable for flexible wearable electronic devices. Attached Figure Description
[0031] Figure 1 This is a schematic diagram of the method for preparing a porous gel electrolyte membrane precursor (ungelled) based on PVdF according to the present invention.
[0032] Figure 2 This is a scanning electron microscope image of the microstructure of the porous gel electrolyte membrane (ungelled) based on PVdF prepared in Example 1 of the present invention.
[0033] Figure 3 These are comparative photos of the slurry preparations of Example 1 and Comparative Example 1 two weeks after preparation.
[0034] Figure 4 Microstructure and macroscopic images of the porous gel electrolyte membrane prepared in Example 2 of the present invention and the gel electrolyte membrane prepared in Comparative Example 2 (both ungelled).
[0035] Figure 5 This is a comparison of the porosity and liquid absorption rate of the porous gel electrolyte membrane prepared in Example 2 of the present invention with those of Comparative Examples 2 and 3.
[0036] Figure 6 The XRD curves of the PVdF-based porous gel electrolyte membrane (ungelled) prepared in Example 1 of this invention are compared. In the figure, the horizontal axis 2θ represents the diffraction angle (degree), and the vertical axis Intensity represents the relative intensity (au).
[0037] Figure 7 This is a comparison of the infrared spectra of the PVdF-based porous gel electrolyte membrane (ungelled) prepared in Example 1 of this invention. In the figure, the horizontal axis Wavenumber represents the wavenumber (cm²). -1 ).
[0038] Figure 8 This figure shows an impedance comparison of Embodiment 1, Comparative Example 1, and Comparative Example 3 of the present invention in the application of lithium iron phosphate (LFP) electrodes. In the figure, the horizontal axis Re(Z) represents the real part (Ω) of the impedance Z, and the vertical axis -lm(Z) represents the imaginary part (Ω) of the impedance Z.
[0039] Figure 9 This figure compares the lithium-ion transference numbers in the LFP electrode of Example 1(a) and Comparative Example 1(b) of the present invention. In the figure, the horizontal axis Time represents time (s), and the vertical axis Current represents current (mA); in the inset, the horizontal axis Z′ represents the real part of the impedance (Ω), and the vertical axis -Z″ represents the imaginary part of the impedance (Ω). Initial represents the initial state, and Steady represents the stable state.
[0040] Figure 10 This figure compares the charge-discharge rate performance of Example 1 and Comparative Example 3 in the LFP electrode. In the figure, the horizontal axis represents the number of cycles, and the vertical axis represents the specific capacity (mAh g). -1 ).
[0041] Figure 11 This figure compares the cycling performance of Example 1 and Comparative Example 3 at 1C in an LFP electrode. In the figure, the horizontal axis represents the number of cycles, and the vertical axis represents the specific capacity (mAh g). -1 ). Detailed Implementation
[0042] like Figure 1 As shown, in specific implementation, the preparation process of the PVdF-based porous gel electrolyte membrane precursor of this invention is as follows:
[0043] First, lithium salt additives are dissolved in N-methylpyrrolidone (NMP) to form a homogeneous solution. Then, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) is added and stirred until completely dissolved. Finally, inorganic ceramic nanofillers are added to form a uniformly dispersed gel electrolyte slurry. The prepared gel electrolyte slurry is coated onto a substrate material and then transferred to a phase inversion solution (one or a combination of deionized water and ethanol) for phase inversion curing to obtain a uniform porous membrane as a precursor. Further, the porous membrane is immersed in a liquid electrolyte containing lithium salt electrolyte for gelation to form a porous gel electrolyte membrane.
[0044] To further understand the present invention, a detailed and complete description of the invention is provided below with reference to the accompanying drawings and embodiments. These descriptions are merely illustrative of the features and advantages of the invention and are not intended to limit the scope of the claims.
[0045] Example 1
[0046] LiFSI, nano-LLZTO powder, PVDF-HFP, and NMP were mixed in a mass ratio of 0.9:1:9:50. The mixing order was as follows: first, LiFSI was dissolved in NMP to form a homogeneous solution; then, PVDF-HFP was added and stirred until completely dissolved; finally, LLZTO powder was added and stirred and dispersed for 3 hours, followed by ultrasonic dispersion for 1 hour to form a homogeneous grayish-white gel slurry. The prepared slurry was coated onto the surface of a PET substrate and then transferred to a phase inversion solution (H2O / ethanol volume ratio 1:1) for phase inversion curing for 60 minutes. During this process, the gel electrolyte slurry gradually solidified into a porous membrane and detached from the PET substrate. After removing this porous membrane, it was vacuum dried to obtain a white, opaque porous gel electrolyte membrane (ungelled). Figure 2The scanning electron microscope (SEM) images of the microstructure show that it has a very rich porous structure, which is beneficial for electrolyte absorption and wetting, as well as rapid lithium-ion conduction. The prepared precursor membrane was cut and placed in a glove box, then immersed in a liquid electrolyte containing lithium salt for 30 minutes to gel. After removing it and drying the surface liquid, the porous gel electrolyte membrane based on PVdF was obtained.
[0047] The liquid electrolyte containing lithium salt comprises lithium salt and organic solvent: the lithium salt is lithium hexafluorophosphate with a molar concentration of 1M, and the organic solvent is a mixture of ethylene carbonate and diethyl carbonate (volume ratio of 1:1).
[0048] like Figure 3 As shown, a comparison of the slurry prepared in Example 1 and the slurry prepared in Comparative Example 1 after standing for 2 weeks reveals that the slurry in Comparative Example 1 underwent a significant color change, changing from the initial grayish-white to yellow, and the color became darker over time. In contrast, the color of the slurry in Example 1 remained unchanged, indicating that the stability of the slurry was significantly improved.
[0049] Example 2
[0050] To illustrate the advantages of the phase inversion method for membrane fabrication, LLZTO and lithium salt additives were not added during the preparation process of Example 2, and the preparation process was compared with that of the thermal evaporation method in Comparative Example 2. The specific preparation process of Example 2 is as follows:
[0051] PVDF-HFP and NMP were mixed at a mass ratio of 9:50 and stirred until completely dissolved to form a uniform and transparent gel slurry. The prepared slurry was coated onto the surface of a PET substrate and then transferred into a phase inversion solution (H2O / ethanol volume ratio 1:1) for phase inversion and curing for 60 min. Finally, it was removed from the phase inversion solution and vacuum dried to obtain the microstructure and macroscopic images of the porous gel electrolyte membrane (ungelled).
[0052] like Figure 4 As shown, the gel membrane prepared by the phase inversion method is macroscopically white and opaque, and microscopically has a rich porous structure. In contrast, the membrane prepared by the thermal evaporation method in Comparative Example 2 is macroscopically colorless and transparent, and microscopically lacks a porous structure, with only sporadic pores observed on the surface, and is generally more dense.
[0053] pass Figure 5 The comparison of porosity and liquid absorption rate of Example 2, Comparative Example 2 and Comparative Example 3 (commercial PP membrane) shows that the membrane prepared by the phase inversion method has a rich pore structure, which significantly increases its porosity and thus exhibits the best liquid absorption capacity, which is conducive to the adsorption, storage and transport of electrolyte and lithium ions.
[0054] Example 3
[0055] The difference from Example 1 is that LLZTO was not added in Example 3, resulting in a uniform and transparent gel slurry. The prepared gel electrolyte slurry was coated onto a PET substrate, then transferred to a phase inversion solution (H2O / ethanol volume ratio 1:1) for phase inversion curing for 60 min. Finally, it was removed from the phase inversion solution and vacuum dried to obtain a white, opaque, self-supporting porous gel electrolyte membrane.
[0056] pass Figure 6 Comparison of XRD in China and Figure 7 The comparison of mid-infrared spectra shows that the PVdF in Example 3 and Example 1 both have a β-phase structure, while the PVdF in Comparative Example 1 and Example 2, which did not have lithium salt added during preparation, have an α-phase structure. This indicates that the addition of lithium salt can change the phase structure of the PVdF gel matrix. Due to the ordered arrangement of polar functional groups in the β-phase PVdF, the Li ion flux during charging and discharging can be more uniformly distributed, thereby improving ionic conductivity and suppressing the formation of lithium dendrites.
[0057] In Example 2, no inorganic ceramic nanofiller LLZTO and lithium salt additives were added, and the ionic conductivity was 1.168 × 10⁻⁶. - 3 S cm -1 In Example 3, no inorganic ceramic nanofiller LLZTO was added, but the ionic conductivity was increased to 1.431 × 10⁻⁶ due to the use of lithium salt additives during the preparation process. -3 S cm -1 In Example 1, the ionic conductivity was further increased to 1.942 × 10⁻⁶ due to the simultaneous addition of inorganic ceramic nanofiller LLZTO and lithium salt additives during the preparation process. -3 S cm -1 .
[0058] Comparative Example 1
[0059] The difference from Example 1 is that no lithium salt LiFSI was added in Comparative Example 1, only LLZTO was added.
[0060] Example 1 and Comparative Example 1 were assembled into half-cells with an LFP electrode and a Li sheet, respectively, and their electrochemical impedance and lithium-ion transference number were tested. Figure 8 The results show that the impedance of Example 1 is significantly lower than that of Comparative Example 1, indicating that the addition of lithium salt can reduce the interface resistance in the battery and improve the interface charge transfer rate. Figure 9 As shown in the comparison of lithium-ion transference numbers, the lithium-ion transference number of Example 1 is significantly higher than that of Comparative Example 1, indicating that the addition of lithium salt during the preparation process can significantly improve lithium-ion diffusion kinetics.
[0061] Comparative Example 2
[0062] The difference from Example 2 is that after the prepared gel slurry is scraped onto the surface of the glass substrate, it is directly transferred into an oven at 100°C for vacuum drying.
[0063] Comparative Example 3
[0064] Comparative Example 3 in this invention is a commercially available PP diaphragm, Celgard 2400.
[0065] Examples 1 and 3 were assembled into half-cells with LFP electrodes and Li sheets, respectively, and their capacity at different charge / discharge rates and cycle stability at 1C were tested. Figure 10 It can be seen that Example 1 exhibits higher specific capacity at all rates above 0.5C, mainly due to the improved lithium-ion diffusion kinetics in the gel electrolyte membrane, allowing it to exert more capacity at the same charge / discharge rate. Figure 11 It can be seen that the cycle stability of Example 1 at 1C is significantly improved compared with Comparative Example 3. Since the gel electrolyte with high ion mobility number also has a certain lithium dendrite suppression ability, it can effectively improve the cycle stability of the battery.
[0066] The results of the examples show that the porous gel electrolyte membrane based on PVdF prepared in this invention achieves a uniform porous structure through phase inversion, thereby improving the adsorption and storage capacity of the electrolyte. The addition of lithium salt during the preparation process effectively suppresses the defluorination reaction of PVdF and the discoloration of the slurry caused by the addition of LLZTO, making the slurry more stable. Simultaneously, it also causes a transformation of the PVdF matrix from the α-phase to the β-phase, which helps in the uniform deposition of Li ions and the suppression of lithium dendrites, thus significantly improving cycle stability and increasing the ionic conductivity to 1.9 × 10⁻⁶. -3 S cm -1 Therefore, the porous gel electrolyte membrane prepared using the method of this invention can significantly improve the ion transport kinetics and electrochemical stability of lithium-ion batteries, and has great application prospects in portable electronic devices.
Claims
1. A porous gel electrolyte membrane based on polyvinylidene fluoride, characterized in that, The porous gel electrolyte membrane includes a gel electrolyte matrix, inorganic ceramic nanofillers, lithium salt electrolyte and lithium salt additives. A gel electrolyte slurry prepared by the gel electrolyte matrix, lithium salt additives, inorganic ceramic nanofillers and solvent is used to obtain a uniform porous structure membrane by phase inversion curing. The porous structure membrane is immersed in a liquid electrolyte containing lithium salt electrolyte to gel and form a porous gel electrolyte membrane. The gel electrolyte matrix is composed of one or more of the following fluorinated homopolymers and copolymers: polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), vinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P(VdF-TrFE-CFE)), poly(vinylidene fluoride-trifluorochloroethylene) (P(VdF-CTFE)), and poly(vinylidene fluoride-trifluoroethylene) (P(VdFTrFE)). Porous gel electrolyte membranes utilize inorganic ceramic nanofillers to enhance their ionic conductivity and mechanical strength. The inorganic ceramic nanofillers are composed of one or a combination of two of the following inorganic nanoparticles: nano-lithium lanthanum zirconium oxide (LLZO) and nano-lithium lanthanum zirconium tantalum oxide (LLZTO). The lithium salt additive is one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(oxalateborate)borate (LiBOB); The addition of lithium salt during the preparation process suppresses the defluorination reaction of PVdF, ensuring slurry stability. Furthermore, by inducing a transformation from the α-phase to the β-phase in the PVdF matrix, the ordered arrangement of polar functional groups in the β-phase PVdF facilitates uniform Li ion deposition and suppresses lithium dendrite formation, thereby significantly improving cycle stability and increasing ionic conductivity to 1.9 × 10⁻⁶. -3 S cm -1 above.
2. The porous gel electrolyte membrane based on polyvinylidene fluoride according to claim 1, characterized in that, The liquid electrolyte containing lithium salt contains lithium salt and organic solvent: the lithium salt is one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI); the organic solvent is one or more of the following ester solvents: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC), or one or more of the following ether solvents: dioxolane (DOL) and dimethyl ethylene glycol (DME), or an ionic liquid.
3. A method for preparing a porous gel electrolyte membrane based on polyvinylidene fluoride according to any one of claims 1 to 2, characterized in that, Porous membranes are prepared using a phase inversion method, which includes the following steps: 1) Mix the gel electrolyte matrix, lithium salt additive and solvent in a mass ratio of 1:(0.1~0.5):(5~9) to form a uniformly dispersed gel solution; 2) Add inorganic ceramic nanofiller to gel electrolyte matrix at a mass ratio of 1:(5~20) to form a uniformly dispersed gel electrolyte slurry; 3) The prepared gel electrolyte slurry is coated onto the substrate material and then transferred into the phase inversion solution for phase inversion and curing for 10~600 min. After removal, it is dried to obtain a uniform porous membrane. 4) Immerse the porous membrane obtained in step 3) into a liquid electrolyte containing lithium salt electrolyte for gelation for 10-150 min, remove it and dry the surface liquid to obtain the porous gel electrolyte membrane based on polyvinylidene fluoride.
4. The method for preparing a porous gel electrolyte membrane based on polyvinylidene fluoride according to claim 3, characterized in that, The solvent is one of N,N-dimethylformamide (DMF), acetone, and N-methylpyrrolidone (NMP).
5. The method for preparing a porous gel electrolyte membrane based on polyvinylidene fluoride according to claim 3, characterized in that, The dispersion method for gel solutions and gel electrolyte slurries is one or a combination of two or more of the following: magnetic stirring dispersion, mechanical stirring dispersion, ultrasonic dispersion, and high-speed shear dispersion.
6. The method for preparing a porous gel electrolyte membrane based on polyvinylidene fluoride according to claim 3, characterized in that, The substrate material is polyethylene terephthalate (PET) film or glass plate.
7. The method for preparing a porous gel electrolyte membrane based on polyvinylidene fluoride according to claim 3, characterized in that, The phase inversion solution is one or a combination of two of deionized water and ethanol, wherein ethanol accounts for 0-75% of the total volume of the phase inversion solution.
8. The method for preparing a porous gel electrolyte membrane based on polyvinylidene fluoride according to claim 3, characterized in that, The drying method is either vacuum drying at 60℃ or freeze drying.