Pvdf-hfp-@peg-based electrolyte, preparation method thereof and lithium battery

Abstract

The application discloses a kind of PVDF-HFP-@PEG-based electrolyte and its preparation method and lithium battery, belong to electrolyte preparation technical field.It obtains precursor solution by solvent blending of two polymer phases, after continuous stirring uniformly at normal temperature, it is carried out to pour membrane;Then it is sequentially carried out normal temperature drying and high temperature crosslinking under vacuum condition and obtains polymer base film;The target polymer electrolyte is obtained after the obtained base film is soaked in electrolyte for a period of time, finally cut into certain size electrolyte sheet and further assemble lithium metal battery.The application proposes a new crosslinking strategy-"slight crosslinking method", without introducing catalyst or crosslinking agent, amino group polyethylene glycol is combined with PVDF-HFP matrix to form stable structure crosslinked polymer, which can significantly improve the ionic conductivity, mechanical properties and chemical / thermal stability of electrolyte.This method is expected to realize important breakthroughs in fast charging performance, cycle life and safety of corresponding lithium metal battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery polymer electrolyte materials, and mainly relates to a preparation method of a cross-linked polymer electrolyte formed by special bonding between a double-end amino polyethylene glycol (NH2-PEG-NH2) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and application of the cross-linked polymer electrolyte in a metal battery. BACKGROUND

[0002] At present, lithium ion batteries are mainly liquid batteries based on volatile organic electrolytes, and the energy density that can be achieved is only 250 Wh / kg, and there are hidden dangers in safety, which cannot fully meet the urgent needs of people for high-performance energy storage devices. In recent years, polymer-based lithium metal batteries have attracted more and more attention due to their high intrinsic safety, good flexibility and high theoretical energy density.

[0003] As a key component of polymer-based lithium metal batteries, polymer electrolytes have been widely valued by academia and industry. Studies have shown that the stable storage of a small amount of electrolyte in the polymer electrolyte matrix to form a quasi-solid polymer electrolyte is an effective strategy to improve the comprehensive performance of the electrolyte and the battery. As a core component of such electrolytes, the design and preparation of polymer matrix are crucial. The materials currently studied more include polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), etc. Among them, PVDF-HFP has the advantages of high dielectric constant, good mechanical properties, stable electrochemical performance, etc., and has been widely concerned and studied by researchers.

[0004] In order to solve the shortcomings of such polymers, such as high crystallinity, low electrolyte affinity, and poor interface stability with electrodes, a combination of PEG-based polymers with complementary properties is often used to form PVDF-HFP-PEG polymers to improve their comprehensive performance. The main strategies for introducing PEG into PVDF-HFP to form PVDF-HFP-PEG polymers currently include physical blending, physical cross-linking, and chemical cross-linking. Although these cross-linking strategies can combine the advantages of the two to some extent, there are still important challenges. Among them, the simple blending strategy will cause phase separation due to the incomplete solubility of the two phases, and the physical cross-linking strategy will cause poor stability due to the introduction of impurities and weak bonding. The occurrence of these problems will eventually seriously affect the key performance of the corresponding lithium metal battery, such as power density, cycle life and safety.

[0005] To address the above challenges, the present invention proposes a unique cross-linking strategy - "light cross-linking method", which can successfully realize the significant improvement of the key performance of the obtained PVDF-HFP-@PEG-based electrolyte in terms of ionic conductivity, mechanical properties, chemical / thermal stability, etc. without introducing any catalyst or cross-linking agent. SUMMARY

[0006] The present invention addresses the existing scientific and technical problems and first proposes the "light cross-linking method" strategy in the field of lithium metal battery electrolyte, and applies it to construct a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) based light cross-linked polymer (PVDF-HFP-@PEG) film with a specific structure, which realizes the significant improvement of the corresponding electrolyte in mechanical and electrochemical properties. The obtained polymer electrolyte can effectively promote the optimization of the key electrochemical performance of the corresponding lithium metal battery.

[0007] The present invention adopts the following technical solutions:

[0008] A preparation method of a PVDF-HFP-@PEG-based electrolyte, the PVDF-HFP-@PEG polymer film is soaked in an electrolyte under an inert atmosphere and dried to obtain a PVDF-HFP-@PEG-based electrolyte, and the structural general formula of the PVDF-HFP-@PEG polymer film is:

[0009]

[0010] wherein x is a positive integer greater than 0 and less than n, y is a positive integer greater than 0 and less than m, at least one of x and y is greater than or equal to 1, and the values of m and n are determined based on the PVDF-HFP used.

[0011] The preparation method of the PVDF-HFP-@PEG polymer film is:

[0012] The preparation method of the PVDF-HFP-@PEG polymer film is: first, mix PVDF-HFP and NH2-PEG-NH2 in a solvent to mix uniformly, then spread the obtained precursor mixture into a thin liquid layer and vacuum dry at room temperature, and finally, perform cross-linking reaction under vacuum at 130-230 ℃ to obtain the PVDF-HFP-@PEG polymer film. The mass ratio of PVDF-HFP to NH2-PEG-NH2 is 2-6:1. Preferably, the vacuum drying time at room temperature is 12-48 hours, and the cross-linking reaction is 0.5-5 hours.

[0013] ​​The solvent is one of N,N-dimethylformamide (DMF), N-methyl pyrrolidone (NMP), acetonitrile (CH3CN), N,N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), hexamethylphosphoramide (HMPA).

[0014] The electrolyte comprises a metal salt and an organic solvent, the metal salt comprises but is not limited to one of lithium salt, sodium salt, zinc salt. Among them, the lithium salt is one or more of lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis (oxalate) borate (LiBOB), lithium difluoro (oxalate) borate (LiDFOB), lithium bis (difluorosulfonyl) imide (LiFSI), the concentration of lithium salt in the electrolyte is 0.5-3 mol / L; the sodium salt is one or more of sodium hexafluorophosphate (NaPF6), sodium triflate (NaOTF), sodium bis (fluorosulfonyl) imide (NaFSI), sodium bis (trifluoromethylsulfonyl) imide (NaTFSI), sodium tetrafluoroborate (NaBF4), sodium bis (oxalate) borate (NaBOB), sodium difluoro (oxalate) borate (NaDFOB), sodium perchlorate (NaClO4), the concentration of sodium salt in the electrolyte is 0.5-3 mol / L; the zinc salt is one or more of zinc sulfate (ZnSO4), zinc triflate (ZnOTF), the concentration of zinc salt in the electrolyte is 0.5-3 mol / L. The organic solvent is one or more of 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME), hydrofluoroether (TTE), ethylene carbonate (EC), vinyl carbonate (VC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC) and diethyl carbonate (DEC).

[0015] The preparation method of the PVDF-HFP-@PEG-based electrolyte, the application of the polymer electrolyte in a battery, and the assembly of the lithium battery by placing the polymer electrolyte between the positive electrode and the negative electrode.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] (1) The present application can prepare a PVDF-HFP-@PEG-based polymer electrolyte with elastomer characteristics, which has strong mechanical properties, can adapt to the volume change in the long-term lithium plating and stripping process, can maintain good interface contact between the electrolyte and the electrode for a long time, thereby reducing the interface impedance and inhibiting the growth of lithium dendrites.

[0018] (2) The present application can prepare a PVDF-HFP-@PEG-based polymer electrolyte with ultrahigh dielectric constant, which can significantly strengthen the dissociation of lithium salt and improve the free Li+ The concentration of lithium-ion batteries increases the capacity of the corresponding lithium batteries and reduces the number of dead lithium-ion cells during long-term charge-discharge cycles, thus ensuring coulombic efficiency and optimizing the long-term stable cycle performance of the batteries.

[0019] (2) The present invention can prepare PVDF-HFP-@PEG-based polymer electrolyte with a special configuration. The PEG "bridge" chain present in the polymer electrolyte expands the interchain spacing of the original PVDF-HFP matrix and introduces a large number of oxygen sites on the PEG chain, providing more abundant, more diversified and more efficient lithium ion migration pathways.

[0020] (3) The present invention can prepare PVDF-HFP-@PEG-based polymer electrolyte with a special configuration. The polymer electrolyte has good mechanical properties, thermal stability and electrolyte retention capacity. No matter whether it is subjected to external force or high temperature environment, it can maintain its own structural and shape stability and effectively retain electrolyte components, which can significantly improve the safety of the corresponding lithium battery operation.

[0021] (4) The polymer electrolyte prepared by this invention has a uniformly distributed composition, a stable internal structure, and excellent lithium-ion dissociation and transport capabilities. The lithium metal battery assembled with it exhibits excellent electrochemical performance in high current tolerance and fast charging performance tests.

[0022] (5) The polymer electrolyte raw materials involved in this invention have good cost competitiveness, and the preparation process is simple and easy to operate, which is conducive to industrial production and expansion. Attached Figure Description

[0023] Figure 1 This is a graph showing the high-rate, long-cycle performance of a lithium metal battery assembled with the PVDF-HFP-@PEG-based electrolyte prepared in Example 1.

[0024] Figure 2 This is a comparison chart of the long-cycle performance of lithium metal batteries assembled from the PVDF-HFP-@PEG-based electrolyte prepared in Example 1 and the PVDF-HFP-based electrolyte prepared in Comparative Example 1.

[0025] Figure 3 The images show planar SEM images of the PVDF-HFP-@PEG polymer membrane prepared in Example 1, the PVDF-HFP polymer membrane prepared in Comparative Example 1, and the PVDF-HFP+PEG polymer membrane prepared in Comparative Example 2.

[0026] Figure 4is the thermal stability test comparison chart of PVDF-HFP-@PEG polymer film prepared in Example 1, PVDF-HFP polymer film prepared in Comparative Example 1, and PVDF-HFP+PEG polymer film prepared in Comparative Example 2, respectively.

[0027] Figure 5 is the Fourier transform infrared test (FT-IR) comparison chart of PVDF-HFP-@PEG polymer film prepared in Example 1, PVDF-HFP polymer film prepared in Comparative Example 1, and PVDF-HFP+PEG polymer film prepared in Comparative Example 2, respectively.

[0028] Figure 6 is the stress-strain curve comparison chart of PVDF-HFP-@PEG polymer film prepared in Example 1, PVDF-HFP polymer film prepared in Comparative Example 1, and PVDF-HFP+PEG polymer film prepared in Comparative Example 2, respectively.

[0029] Figure 7 is the thermogravimetric analysis (TGA) test comparison chart of PVDF-HFP-@PEG-based electrolyte prepared in Example 1, PVDF-HFP-based electrolyte prepared in Comparative Example 1, and PVDF-HFP+PEG-based electrolyte prepared in Comparative Example 2, respectively.

[0030] Figure 8 is the high-rate long cycle performance chart of lithium metal battery assembled by PVDF-HFP-@PEG-based electrolyte prepared in Example 2.

[0031] Figure 9 is the high-rate long cycle performance chart of lithium metal battery assembled by PVDF-HFP-@PEG-based electrolyte prepared in Example 3. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the present application will be described clearly and completely below in combination with the embodiments.

[0033] Example 1

[0034] (1) Preparation of PVDF-HFP-@PEG polymer membrane: 300 mg of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP, purchased from Aladdin, CAS No. 9011-17-0) and 100 mg of double-amine polyethylene glycol (NH2-PEG-NH2) were mixed in a glove box, and then a N,N-dimethylformamide solution (DMF) was added for dissolution to obtain a precursor solution. Then, the obtained precursor solution was continuously stirred at room temperature for 12 hours to form a uniform solution. Finally, the uniformly stirred precursor solution was poured into a glass dish with a diameter of 8 cm, dried under vacuum at room temperature for 12 hours, and then further crosslinked under vacuum at 200 °C for 2 hours to obtain a PVDF-HFP-@PEG polymer membrane.

[0035] (2) Preparation of PVDF-HFP-@PEG-based electrolyte: First, an electrolyte (2M LiTFSI / DOL+DME, volume ratio of solvent 3:1) was prepared. Then, the prepared PVDF-HFP-@PEG polymer membrane was soaked in the electrolyte for 48 hours, and then further dried and cut to obtain the target PVDF-HFP-@PEG-based electrolyte.

[0036] (3) Preparation of battery positive electrode: LiFePO4 (LFP), conductive carbon black, and polyvinylidene fluoride (PVDF) were ground uniformly in a mass ratio of 8:1:1, and then a proper amount of DMF was added and stirred uniformly to obtain a slurry, which was uniformly coated on an aluminum foil. Then, the coated electrode was transferred to an oven for vacuum drying for 24 hours, cut into a 10 mm diameter disc, and stored in a glove box for standby.

[0037] (4) Assembly of lithium metal battery: The cut LFP positive electrode and electrolyte were placed in a glove box, and then a CR2032 button cell was assembled in the order of positive electrode shell, positive electrode, electrolyte, negative electrode, gasket, spring, and negative electrode shell.

[0038] The charge-discharge performance of the above assembled button cell was tested at room temperature using a Land CT3002A battery test system.

[0039] The polymer electrolyte was used to assemble a lithium metal battery and perform electrochemical performance tests. The corresponding high-rate and long-cycle battery performance data are shown in Table 1. Figure 1 As can be seen from the table, the Li|PVDF-HFP-@PEG|LiFePO4 lithium metal battery has a capacity retention rate of 92% and a coulombic efficiency of 99.9% after 12000 cycles at a rate of 30C, with excellent performance.

[0040] Comparative Example 1

[0041] (1) Preparation of PVDF-HFP polymer film: 300 mg of PVDF-HFP was weighed in a glove box, and then DMF was added for dissolution to obtain a precursor solution. Then, the obtained precursor solution was continuously stirred at room temperature for 12 hours to form a uniform solution. Finally, the uniformly stirred precursor solution was poured into a glass dish with a diameter of 8 cm, and after vacuum drying at room temperature for 24 hours, a PVDF-HFP film was obtained.

[0042] (2) Preparation of PVDF-HFP-based electrolyte: First, an electrolyte (2M LiTFSI / DOL+DME, volume ratio of solvent 3:1) was prepared. Then, the prepared PVDF-HFP polymer film was soaked in the electrolyte for 48 hours, and then further dried and cut to obtain the target polymer PVDF-HFP-based electrolyte.

[0043] (3) Preparation of battery positive electrode: LFP, conductive carbon black, and polyvinylidene fluoride (PVDF) were uniformly ground in a mass ratio of 8:1:1, and then an appropriate amount of DMF was added and stirred uniformly to obtain a slurry, which was uniformly coated on an aluminum foil. Then, the coated electrode was transferred to an oven for vacuum drying for 24 hours, cut into a 10 mm diameter disc, and stored in a glove box for standby.

[0044] (4) Assembly of lithium metal battery: The cut LFP positive electrode and electrolyte were placed in a glove box, and then a CR2032 button cell was assembled in the order of positive electrode shell, positive electrode, electrolyte, negative electrode, gasket, spring, and negative electrode shell.

[0045] The charge-discharge performance of the above assembled button cell was tested at room temperature using a Land CT3002A battery test system.

[0046] The polymer electrolyte prepared was used to assemble a lithium metal battery and perform electrochemical performance testing. The long cycle battery performance data corresponding to Example 1 and Comparative Example 1 are shown in Table 1. Figure 2 As can be seen from the table, the lithium metal battery corresponding to Example 1 has a capacity retention rate of 98% and a coulombic efficiency of 99.9% after 3000 cycles under 1C operating conditions, which is significantly better than the short cycle life of 277 cycles, a capacity retention rate of 53.8% of the lithium metal battery of Comparative Example 1, and the battery cycle stability is significantly improved.

[0047] Comparative Example 2

[0048] (1) Preparation of PVDF-HFP+PEG polymer membrane: 300 mg and 100 mg of PVDF-HFP and NH2-PEG-NH2 were weighed and mixed in a glove box, and then DMF was added to dissolve them to obtain a precursor solution. Then, the obtained precursor solution was stirred continuously at room temperature for 12 hours to form a homogeneous solution. Finally, the homogeneous precursor solution was poured into a glass dish with a diameter of 8 cm and dried under vacuum at room temperature for 24 hours to obtain the PVDF-HFP+PEG polymer membrane.

[0049] The polymer film of the sample was imaged using a scanning electron microscope (SEM). Figure 3 As can be seen from the surface SEM image, the PVDF-HFP-@PEG polymer membrane prepared in Example 1 has formed a uniform and tightly connected porous structure that is completely different from the PVDF-HFP polymer membrane prepared in Comparative Example 1 and the PVDF-HFP+PEG polymer membrane prepared in Comparative Example 2. Although the polymer membrane in Example 2 increases the porosity of the membrane, obvious phase separation phenomenon also appears.

[0050] Depend on Figure 4 The thermal stability test of the polymer film shows that, compared with Example 1, the PVDF-HFP polymer film prepared in Example 1 began to curl significantly at 125°C and began to melt at 175°C. The PVDF-HFP+PEG polymer film prepared in Example 2 curled at 175°C and partially charred at 275°C. In contrast, the PVDF-HFP-@PEG polymer film prepared in Example 1 began to melt at a temperature as high as 325°C, and only showed obvious melting at 375°C. Moreover, the overall shape of the film did not change from beginning to end. This intuitively shows that the thermal stability of the polymer film was greatly improved before and after modification.

[0051] Fourier transform infrared (FT-IR) testing was performed, and the results are as follows: Figure 5 As shown. By comparing the FT-IR results of Example 1 and Comparative Example 2, the reduction in the CF2 symmetric stretching vibration peak (1072 cm⁻¹) is observed. −1 1171 cm −1 ) and 1670 cm −1 The appearance of the peak (the characteristic peak of the imine bond C=N) confirms the formation of the cross-linked structure of the PVDF-HFP-@PEG polymer film prepared in Example 1, proving the feasibility of the "slight cross-linking method" practice.

[0052] The polymer film was subjected to mechanical tensile testing using an INSTRON 5967 universal testing machine. Figure 6It can be seen that the stress-strain curves of the PVDF-HFP polymer film prepared in Comparative Example 1 and the PVDF-HFP+PEG polymer film prepared in Comparative Example 2 show obvious "Luders bands", indicating that they have strong plasticity, and the contribution of plastic strain to the overall strain is large during the entire stretching process. However, the "Luders band" in the stress-strain curve of the PVDF-HFP-@PEG polymer film prepared in Example 1 disappears, and the main strain form is also converted to elastic deformation, indicating that the plasticity of the material is greatly reduced, achieving the purpose of reducing the crystallinity. Although the addition of NH2-PEG-NH2 plasticizer to the PVDF-HFP matrix reduces the mechanical properties of the polymer film, Example 1 still maintains an excellent polymer film tensile modulus of 14.2 MPa, showing excellent durability during lithium battery operation, achieving a synergistic improvement in physical and electrochemical properties.

[0053] (2) Preparation of PVDF-HFP+PEG-based electrolyte: First, prepare the electrolyte (2M LiTFSI / DOL+DME, volume ratio of solvent is 3:1). Then, the prepared PVDF-HFP+PEG polymer film is soaked in the electrolyte for 48 hours, and then further dried and cut to obtain the target PVDF-HFP+PEG-based electrolyte.

[0054] Thermogravimetric analysis (TGA) test: below 300°C is mainly the decomposition of lithium salt and electrolyte solvent, as shown in FIG. 6, when reaching high temperature of 300°C, the PVDF-HFP-@PEG-based electrolyte prepared in Example 1 can still maintain an ultra-high mass retention rate of 94.3%, and has excellent liquid retention capacity. Figure 7

[0055] Example 2

[0056] (1) Preparation of PVDF-HFP-@PEG polymer film: 500 mg of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and 100 mg of double-end amino polyethylene glycol (NH2-PEG-NH2) are weighed in a glove box, then N,N-dimethylformamide solution (DMF) is added for dissolution to obtain a precursor solution. Then, the obtained precursor solution is continuously stirred at room temperature for 12 hours to form a uniform solution. Finally, the uniformly stirred precursor solution is poured into a glass dish with a diameter of 8 cm, dried under vacuum at room temperature for 12 hours, and then further cross-linked under vacuum at a high temperature of 200°C for 2 hours to obtain a PVDF-HFP-@PEG polymer film.

[0057] ​(2) Preparation of PVDF-HFP-@PEG-based electrolyte: First, prepare the electrolyte (1M LiPF6 / EC+FEC, the volume ratio of the solvent is 3:1). Then, immerse the prepared PVDF-HFP-@PEG polymer film in the electrolyte for 48 hours, and then further dry and cut to obtain the target PVDF-HFP-@PEG-based electrolyte.

[0058] (3) Preparation of battery cathode: same as Example 1.

[0059] (4) Assembly of lithium metal battery: same as Example 1.

[0060] The charge-discharge performance of the above assembled button cell was tested at room temperature by using Land CT3002A battery test system.

[0061] The lithium metal battery was assembled using the prepared electrolyte and the electrochemical performance test was carried out. The corresponding high rate and long cycle battery performance data are shown in Table 1. Figure 8 As can be seen from the table, the capacity retention rate of the lithium metal battery assembled by the electrolyte prepared in Example 2 is 74% and the coulombic efficiency is 99.9% after 9000 cycles under the condition of 20C operation, which has excellent performance.

[0062] Example 3

[0063] (1) Preparation of PVDF-HFP-@PEG polymer film: 200 mg of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and 100 mg of double-amine polyethylene glycol (NH2-PEG-NH2) were mixed in a glove box, and then N,N-dimethylformamide solution (DMF) was added for dissolution to obtain a precursor solution. Then, the obtained precursor solution was continuously stirred at room temperature for 12 hours to form a uniform solution. Finally, the uniformly stirred precursor solution was poured into a glass dish with a diameter of 8 cm, dried under vacuum at room temperature for 12 hours, and then further crosslinked under vacuum at 180°C for 1 hour to obtain a PVDF-HFP-@PEG polymer film.

[0064] (2) Preparation of PVDF-HFP-@PEG-based electrolyte: First, prepare the electrolyte (1M LiFSI / DME+TTE, the volume ratio of the solvent is 5:1). Then, immerse the prepared PVDF-HFP-@PEG polymer film in the electrolyte for 48 hours, and then further dry and cut to obtain the target PVDF-HFP-@PEG-based electrolyte.

[0065] (3) Preparation of battery cathode: same as Example 1.

[0066] (4) Assembly of lithium metal battery: same as Example 1.

[0067] The charge-discharge performance of the above assembled button cell was tested at room temperature by using Land CT3002A battery test system.

[0068] The lithium metal battery was assembled by using the prepared electrolyte and the electrochemical performance test was carried out. The corresponding high load, long cycle battery performance data are shown in Figure 9 As can be seen from the figure, the lithium metal battery assembled by the electrolyte prepared in Example 3 has a capacity retention rate of 93.2% and a coulombic efficiency of 99.9% after 130 cycles under the operating condition of a higher positive electrode load. -1 The capacity retention rate is 93.2% and the coulombic efficiency is 99.9% after 130 cycles under the operating condition of a higher positive electrode load.

Claims

1. A method for preparing a PVDF-HFP-@PEG-based electrolyte, characterized in that, A PVDF-HFP-@PEG polymer membrane was immersed in an electrolyte under an inert atmosphere and then dried to obtain a PVDF-HFP-@PEG-based electrolyte. The general structural formula of the PVDF-HFP-@PEG polymer membrane is as follows: ， Where x is a positive integer greater than 0 and less than n, y is a positive integer greater than 0 and less than m, at least one of x and y is greater than or equal to 1, and the values ​​of m and n are determined based on the PVDF-HFP used; The preparation method of the PVDF-HFP-@PEG polymer film is as follows: ； First, PVDF-HFP and NH2-PEG-NH2 are added to a solvent and mixed evenly. Then, the resulting precursor mixture is spread into a thin liquid layer and dried under vacuum at room temperature. Finally, a crosslinking reaction is carried out under vacuum conditions of 130~230 ℃ to obtain a PVDF-HFP-@PEG polymer film. The mass ratio of PVDF-HFP to NH2-PEG-NH2 is 2~6:

1.

2. The preparation method of the PVDF-HFP-@PEG-based electrolyte according to claim 1, characterized in that, Vacuum drying at room temperature takes 12 to 48 hours, and cross-linking reaction takes 0.5 to 5 hours.

3. The method for preparing PVDF-HFP-@PEG-based electrolyte according to claim 2, characterized in that, The solvent is one of N,N-dimethylformamide, N-methylpyrrolidone, acetonitrile, N,N-dimethylacetamide, dimethyl sulfoxide, and hexamethylphosphoric triamine.

4. The preparation method of the PVDF-HFP-@PEG-based electrolyte according to claim 3, characterized in that, The electrolyte comprises a metal salt and an organic solvent, wherein the metal salt is one of lithium salt, sodium salt, or zinc salt.

5. The method for preparing the PVDF-HFP-@PEG-based electrolyte according to claim 4, characterized in that, The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate, lithium bis(oxalate-borate), lithium difluorooxalate-borate, and lithium bis(difluorosulfonyl)imide, with a lithium salt concentration of 0.5-3 mol / L in the electrolyte; the sodium salt is one or more of sodium hexafluorophosphate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium tetrafluoroborate, sodium bis(oxalate-borate), sodium difluorooxalate-borate, and sodium perchlorate, with a sodium salt concentration of 0.5-3 mol / L in the electrolyte; the zinc salt is one or more of zinc sulfate and zinc trifluoromethanesulfonate, with a zinc salt concentration of 0.5-3 mol / L in the electrolyte; and the organic solvent is one or more of 1,3-dioxolane, ethylene glycol dimethyl ether, hydrofluoroether, ethylene carbonate, ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and diethyl carbonate.

6. The PVDF-HFP-@PEG-based electrolyte prepared by the preparation method according to any one of claims 1-5.

7. A lithium battery comprising a positive electrode, a negative electrode, and the PVDF-HFP-@PEG-based electrolyte of claim 6, wherein the PVDF-HFP-@PEG-based electrolyte is placed between the positive electrode and the negative electrode, and the battery is assembled.

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