A gel electrolyte, its preparation method and use

Abstract

The application provides a preparation method of a gel electrolyte, comprising the following steps: preparation of a mixed solution: poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) copolymer, ionic liquid N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide and lithium salt are added into a solvent, mixed and uniformly stirred to obtain a mixed solution; preparation of an electrolyte film: the mixed solution in the foregoing step is placed in a glass culture dish, and is treated by volatilization at high temperature, so that the gel electrolyte is obtained. The gel electrolyte has high room temperature ionic conductivity and lithium ion transference number, and a lithium metal battery prepared based on the gel electrolyte has good battery cycle performance and stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery technology, specifically relating to a gel electrolyte, its preparation method, and its application. Background Technology

[0002] Solid-state electrolytes can be used to replace flammable liquid electrolytes to improve the safety of lithium metal batteries. Compared with ceramic solid-state electrolytes, polymer solid-state electrolytes exhibit good processability and flexibility, but show extremely low ionic conductivity at room temperature. Introducing ceramic fillers to prepare composite solid-state electrolytes can improve ionic conductivity. However, fillers can impair the flexibility of solid-state electrolytes and are prone to agglomeration at high concentrations, leading to uneven ion transport and subsequently initiating the growth of lithium dendrites.

[0003] To balance the high ionic conductivity and flexibility of solid-state electrolytes, another approach is to introduce ionic liquids into the prepared electrolyte to form a gel electrolyte. However, Li + Transport in the polymer phase of the gel electrolyte is significantly lower than that in the ionic liquid and the polymer-ionic liquid interface, which leads to Li + Uneven transport can induce lithium dendrite growth. Therefore, despite their high ionic conductivity, lithium metal batteries based on gel electrolytes struggle to achieve stable cycling beyond 800 cycles. + The reason for the low transport efficiency in the polymer phase is because of Li + Transport along the polymer chain is via Li + Coordination and decoordination occur with polar groups in the molecular chain. Furthermore, a large number of organic cations in ionic liquids also coordinate with polar groups in the polymer chain, thereby occupying Li... + The transmission sites reduce Li + Transport efficiency in the gel electrolyte polymer phase. Meanwhile, Li + It can also complex with anions in ionic liquids to form ionic clusters, reducing the free Li. + The quantity will further reduce Li + The transmission efficiency is affected. Adding carbonate solvents with high dielectric constants can promote the dissociation of these ion clusters, but the solvents are flammable and explosive, which is not conducive to the preparation of high-safety lithium metal batteries (LMBs). Summary of the Invention

[0004] The purpose of this invention is to provide a gel electrolyte, its preparation method, and its application. In the preparation process, poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) is innovatively used as raw material to obtain a gel electrolyte with high room temperature ionic conductivity and lithium ion transference number. Moreover, the lithium metal battery prepared based on the gel electrolyte has good battery cycle performance and stability.

[0005] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0006] In the first aspect, the present application provides a preparation method of a gel electrolyte, comprising the following steps:

[0007] (1) Preparation of a mixed solution: poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) copolymer, ionic liquid N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide salt (Pyr 13 TFSI) and lithium salt are added into a solvent, and mixed and stirred uniformly to obtain a mixed solution;

[0008] (2) Preparation of an electrolyte film: the mixed solution in step (1) is placed in a glass culture dish, and is treated by evaporation at high temperature to obtain the gel electrolyte.

[0009] Preferably, in the above step (1), the weight average relative molecular mass of the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) copolymer is 580,000 g / mol, the molar content of trifluoroethylene in the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) copolymer is 6.7-26.2%, and the molar content of trifluorochloroethylene is 8.8-25.3%.

[0010] Preferably, the molar content of trifluoroethylene in the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) copolymer is 13.6-26.2%, and the molar content of trifluorochloroethylene is 8.8-18.4%.

[0011] Preferably, the molar content of trifluoroethylene in the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) copolymer is 23.1-26.2%, and the molar content of trifluorochloroethylene is 8.8-8.9%.

[0012] Preferably, the molar content of trifluoroethylene in the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) copolymer is 26.2%, and the molar content of trifluorochloroethylene is 8.8%.

[0013] Preferably, in the above step (1), the lithium salt is lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) and / or lithium bis (fluorosulfonyl) imide (LiFSI).

[0014] Preferably, in the above step (1), the purity of the lithium salt is greater than 99.9%.

[0015] Preferably, in the above step (1), the mass ratio of the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) copolymer, ionic liquid N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide salt and lithium salt is 4:3-4:3-4.

[0016] Preferably, in step (1) above, the solvent is any one of N,N-dimethylformamide, N-methylpyrrolidone, and tetrahydrofuran.

[0017] Preferably, in step (2) above, the evaporation process includes blower drying and vacuum drying in sequence, wherein the temperature and time of blower drying are 50-60℃ and 24-28h, respectively, and the temperature and time of vacuum drying are 50-60℃ and 0.5-1h, respectively.

[0018] Secondly, the present invention also provides a gel electrolyte prepared according to the above method.

[0019] Thirdly, the present invention also provides an application of the gel electrolyte in a lithium metal battery.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. This invention uses poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) [P(VDF-TrFE-CTFE, abbreviated as PTC] as the polymer matrix, and reacts it with the ionic liquid N-propyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imine salt (Pyr 13 A novel gel electrolyte was prepared using a complex of TFSI (phosphorus voltammetric acid) and Pyr. Compared to conventional PVDF, PTC and Pyr... 13 Pyr in TFSI 13 + The binding energy is weak, which reduces the Li + The transition site was Pyr 13 + The possibility of occupancy. Simultaneously, PTC itself has a high dielectric constant, which is beneficial for promoting the dissociation of lithium ions from anion clusters. The combined effect of these two factors makes Li... + The transport efficiency in the polymer phase is significantly improved, ensuring that the electrolyte has a more uniform Li content. + Transport channels. The prepared gel electrolyte exhibits high room temperature ionic conductivity, and the corresponding solid-state lithium metal battery demonstrates an ultra-long cycle life.

[0022] 2. The poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) selected in this invention has suitable polarity and high dielectric constant, which reduces the possibility of Li+ jumping sites being occupied, facilitates the dissociation of lithium ions and anion clusters, and improves the cycling stability of the gel electrolyte, thus preparing a high-performance gel electrolyte.

[0023] 3. The poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) used in this invention has a weight-average relative molecular mass of 580,000 g / mol, of which the molar content of trifluoroethylene is 26.2% and the molar content of trifluorochloroethylene is 8.8%. It has suitable polarity and high dielectric constant, which reduces the possibility of Li+ jumping sites being occupied (the polymer substrate with the most suitable polarity and high dielectric constant has a weaker adsorption energy with the ionic liquid cation, thus becoming the occupied site of lithium ions). This is conducive to the dissociation of lithium ions from anion clusters, thereby improving the room temperature ionic conductivity and lithium ion transference number. Moreover, the lithium metal battery based on the gel electrolyte prepared in this invention shows good flame retardant properties and ultra-stable cycle performance.

[0024] 4. In this invention, the mass ratio of poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene), ionic liquid N-propyl-N-methylpyrrolidone bis(trifluoromethanesulfonyl)imide, and lithium salt is 4:4:3, ensuring high ionic conductivity. Although the high dielectric constant of poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) can promote salt dissociation, the appropriate proportion of ionic liquid can also greatly affect ionic conductivity. If the ionic liquid content is too low, the interfacial contact performance deteriorates, affecting the construction of efficient ion transport channels; if the ionic liquid content is too high, it will increase the electrolyte viscosity, which will also affect the efficient transport of lithium ions. This invention rationally utilizes the mass ratio of poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) and ionic liquid to maintain a high level of ionic conductivity.

[0025] 5. In this invention, the excess solvent in the mixed solution can be removed by blowing air and the water in the mixed solution (water in the air) can be further removed by vacuum drying, so as to avoid the presence of water in the gel electrolyte, which would affect the application of lithium-ion batteries and further enhance its stability in the application of lithium metal batteries.

[0026] 5. The present invention obtains a gel electrolyte by dissolving poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene), the ionic liquid N-propyl-N-methylpyrrolidone bis(trifluoromethanesulfonyl)imide and lithium salt in a solvent and then drying them. This method is simple to operate, low in cost, and suitable for large-scale production. Attached Figure Description

[0027] To make the technical problems solved by this invention, the technical means adopted, and the technical effects achieved clearer, specific embodiments of this invention will be described in detail below with reference to the accompanying drawings. However, it should be noted that the drawings described below are merely drawings of exemplary embodiments of this invention. Those skilled in the art can obtain drawings of other embodiments based on these drawings without any creative effort.

[0028] Figure 1Cycling performance plots for Li / Li symmetric cells of Example 1 and Comparative Example 2 at 25°C and 0.1 mA / cm2current density. 2 Cycling performance plots for Li / Li symmetric cells of Example 1 and Comparative Example 2 at 25°C and 0.1 mA / cm2current density.

[0029] Figure 2 Cycling performance plots for LFP (lithium iron phosphate) / Li cells of Example 1 and Comparative Example 2 at 25°C and 1 C rate. DETAILED DESCRIPTION

[0030] Exemplary embodiments of the present application will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments can be embodied as many different forms. Although the exemplary embodiments are disclosed in the drawings and the specification, the present application is not limited to the embodiments set forth and can be implemented in various forms. There can be many alterations and changes in the exemplary embodiments and these should be construed as examples that do not limit the present application. Accordingly, the scope of the application should be construed that it encompasses a substitute of each and every published patent publication and non-patent publication referred to herein or known by those skilled in the art.

[0031] In the introduction of the specific embodiments, the detailed description of the structure, performance, effect or other features is to make the embodiments fully understood by those skilled in the art. However, it does not exclude that those skilled in the art can implement the present application without the above-mentioned structure, performance, effect or other features in specific cases.

[0032] The steps in the present application are arranged with reference numerals, but are not used to limit the sequence of the steps, unless the sequence of the steps is explicitly described or the execution of a certain step needs other steps as a basis, otherwise the relative sequence of the steps can be adjusted. It can be understood that the term "and / or" used herein relates to and covers any and all possible combinations of one or more of the associated listed items.

[0033] Unless otherwise specified, the chemicals and materials in the present application are purchased through market channels.

[0034] Example 1

[0035] A method for preparing an ionogel solid-state poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) electrolyte, comprising the following steps:

[0036] (1) Preparation of mixed solution: poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) with 26.2% of molar content of trifluoroethylene and 8.8% of molar content of trifluorochloroethylene, ionic liquid N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide and lithium bis (trifluoromethanesulfonyl) imide are mixed in a mass ratio of 4:4:3, and then added into N,N-dimethylformamide solvent, stirred at room temperature for 8 hours to form a uniform solution, and the weight average relative molecular mass of the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) is 580,000 g / mol;

[0037] (2) Preparation of electrolyte film: the mixed solution uniformly mixed in (1) is poured into a glass culture dish, placed in a blast oven at 55°C for 24 h, and then placed in a vacuum oven at 55°C for 40 min, and then the shaped film is peeled off from the glass culture dish to obtain a poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) / N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide / lithium bis (fluorosulfonyl) imide gel electrolyte.

[0038] Example 2

[0039] A preparation method of an ionic gel solid-state poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) electrolyte, comprising the following steps:

[0040] (1) Preparation of mixed solution: poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) with 26.2% of molar content of trifluoroethylene and 8.8% of molar content of trifluorochloroethylene, ionic liquid N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide and lithium bis (trifluoromethanesulfonyl) imide are mixed in a mass ratio of 4:4:3, and then added into N,N-dimethylformamide solvent, stirred at room temperature for 8 hours to form a uniform solution, and the weight average relative molecular mass of the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) is 580,000 g / mol;

[0041] (2) Preparation of electrolyte film: the mixed solution uniformly mixed in (1) is poured into a glass culture dish, placed in a blast oven at 55°C for 24 h, and then placed in a vacuum oven at 55°C for 40 min, and then the shaped film is peeled off from the glass culture dish to obtain a poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) / N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide / lithium bis (fluorosulfonyl) imide gel electrolyte.

[0042] Example 2 and Example 1 are different in that the lithium salt selected in the embodiment is lithium bis (trifluoromethanesulfonyl) imide.

[0043] Example 3

[0044] A method for preparing an ion gel solid-state poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) electrolyte, comprising the following steps:

[0045] (1) Preparation of a mixed solution: poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) with a molar content of 23.1% of trifluoroethylene and 8.9% of chlorotrifluoroethylene, an ionic liquid N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide and lithium bis(fluorosulfonyl) imide are mixed in a mass ratio of 4:4:3, and then added into N,N-dimethylformamide solvent, stirred at room temperature for 8 hours to form a uniform solution, and the weight average relative molecular mass of the poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) is 580,000 g / mol;

[0046] (2) Preparation of an electrolyte film: the mixed solution uniformly mixed in (1) is poured into a glass culture dish, placed in a blast oven at 55°C for 24 hours, and then placed in a vacuum oven at 55°C for 40 minutes, and then the shaped film is peeled off from the glass culture dish to obtain a poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) / N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide / lithium bis(fluorosulfonyl) imide gel electrolyte.

[0047] The difference between Example 3 and Example 1 is that the poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) used in this example has a molar content of 23.1% of trifluoroethylene and 8.9% of chlorotrifluoroethylene.

[0048] Example 4

[0049] A method for preparing an ion gel solid-state poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) electrolyte, comprising the following steps:

[0050] (1) Preparation of a mixed solution: poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) with a molar content of 23.1% of trifluoroethylene and 8.9% of chlorotrifluoroethylene, an ionic liquid N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide and lithium bis(fluorosulfonyl) imide are mixed in a mass ratio of 4:4:3, and then added into N,N-dimethylformamide solvent, stirred at room temperature for 8 hours to form a uniform solution, and the weight average relative molecular mass of the poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) is 580,000 g / mol;

[0051] (2) Preparation of electrolyte membrane: Pour the mixed solution uniformly mixed in (1) into a glass culture dish, place it in a blast oven at 55°C for 24h, then place it in a vacuum oven at 55°C for 40min, then take the shaped membrane from the glass culture dish to obtain a poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) / N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide / bisfluorosulfonylimide lithium gel electrolyte.

[0052] The difference between Example 4 and Example 1 is that the poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) used in this example has a molar content of 13.6% of trifluoroethylene and a molar content of 18.4% of trifluorochloroethylene.

[0053] Example 5

[0054] A preparation method of an ionic gel solid-state poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) electrolyte, comprising the following steps:

[0055] (1) Preparation of mixed solution: After mixing poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) with a molar content of 6.7% of trifluoroethylene and a molar content of 25.3% of trifluorochloroethylene, ionic liquid N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide and bisfluorosulfonylimide lithium in a mass ratio of 4:4:3, add N,N-dimethylformamide solvent, stir for 8 hours at room temperature to form a uniform solution, and the weight average relative molecular mass of the poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) is 580,000 g / mol;

[0056] (2) Preparation of electrolyte membrane: Pour the mixed solution uniformly mixed in (1) into a glass culture dish, place it in a blast oven at 55°C for 24h, then place it in a vacuum oven at 55°C for 40min, then take the shaped membrane from the glass culture dish to obtain a poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) / N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide / bisfluorosulfonylimide lithium gel electrolyte.

[0057] The difference between Example 5 and Example 1 is that the poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) used in this example has a molar content of 6.7% of trifluoroethylene and a molar content of 25.3% of trifluorochloroethylene.

[0058] Comparative Example 1

[0059] A preparation method of an ionic gel solid-state poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) electrolyte, comprising the following steps:

[0060] (1) Preparation of mixed solution: poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) with 26.2% of molar content of trifluoroethylene and 8.8% of molar content of trifluorochloroethylene, ionic liquid N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide and lithium bis (fluorosulfonyl) imide were mixed in a mass ratio of 4:3:3, and then added into N,N-dimethylformamide solvent to form a uniform solution after stirring at room temperature for 8 hours, and the weight average relative molecular mass of the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) was 580,000 g / mol;

[0061] (2) Preparation of electrolyte film: the mixed solution uniformly mixed in (1) was poured into a glass culture dish, placed in a blast oven at 55°C for 24 h, and then placed in a vacuum oven at 55°C for 40 min, and then the shaped film was peeled off from the glass culture dish to obtain a poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) / N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide / lithium bis (trifluoromethylsulfonyl) imide gel electrolyte.

[0062] The difference between Comparative Example 1 and Example 1 is that the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) used in the present comparative example, ionic liquid N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide and lithium bis (fluorosulfonyl) imide were mixed in a mass ratio of 1:1:1

[0063] Comparative Example 2

[0064] A preparation method of an ionic gel solid-state polyvinylidene fluoride electrolyte, comprising the following steps:

[0065] (1) Preparation of mixed solution: poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) with 26.2% of molar content of trifluoroethylene and 8.8% of molar content of trifluorochloroethylene, ionic liquid N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide and lithium bis (fluorosulfonyl) imide were mixed in a mass ratio of 4:3:3, and then added into N,N-dimethylformamide solvent to form a uniform solution after stirring at room temperature for 8 hours, and the weight average relative molecular mass of the poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) was 580,000 g / mol;

[0066] (2) Preparation of electrolyte film: the mixed solution uniformly mixed in (1) was poured into a glass culture dish, placed in a blast oven at 55°C for 24 h, and then placed in a vacuum oven at 55°C for 40 min, and then the shaped film was peeled off from the glass culture dish to obtain a poly (vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) / N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide / lithium bis (trifluoromethylsulfonyl) imide gel electrolyte.

[0067] The difference between Comparative Example 2 and Example 1 is that the polymer matrix used in the present comparative example is polyvinylidene fluoride.

[0068] Comparative Example 3

[0069] A method for preparing an ion gel solid-state poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) electrolyte, comprising the following steps:

[0070] (1) Preparation of a mixed solution: poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) with a molar content of 26.2% of trifluoroethylene and 8.8% of chlorotrifluoroethylene, ionic liquid N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide and lithium bisfluorosulfonylimide are mixed in a mass ratio of 4:5:3, and then added into N,N-dimethylformamide solvent, stirred at room temperature for 8 hours to form a uniform solution, and the weight average relative molecular mass of the poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) is 580,000 g / mol;

[0071] (2) Preparation of an electrolyte film: the mixed solution uniformly mixed in (1) is poured into a glass culture dish, placed in a blast oven at 55°C for 24 hours, and then placed in a vacuum oven at 55°C for 40 minutes, and then the shaped film is peeled off from the glass culture dish to obtain a poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) / N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide / lithium bis(trifluoromethylsulfonyl) imide gel electrolyte.

[0072] The difference between Comparative Example 3 and Example 1 is that the poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) used in the present comparative example, ionic liquid N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide and lithium bisfluorosulfonylimide are mixed in a mass ratio of 4:3:4

[0073] Comparative Example 4

[0074] A method for preparing an ion gel solid-state poly(vinylidene fluoride) electrolyte, comprising the following steps:

[0075] (1) Preparation of a mixed solution: poly(vinylidene fluoride), ionic liquid N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide and lithium bis(trifluoromethylsulfonyl) imide are mixed in a mass ratio of 4:4:3, and then added into N,N-dimethylformamide solvent, stirred at room temperature for 8 hours to form a uniform solution.

[0076] (2) Preparation of an electrolyte film: the mixed solution uniformly mixed in (1) is poured into a glass culture dish, placed in a blast oven at 55°C for 24 hours, and then placed in a vacuum oven at 55°C for 40 minutes, and then the shaped film is peeled off from the glass culture dish to obtain a poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) / N-propyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide / lithium bis(trifluoromethylsulfonyl) imide gel electrolyte.

[0077] The difference between Comparative Example 4 and Example 1 is that the polymer matrix used in the present comparative example is polyvinylidene fluoride, and the lithium salt used is lithium bis-trifluoromethanesulfonimide.

[0078] The products prepared in Examples 1-5 and Comparative Examples 1-4 of the present application were tested for ionic conductivity, activation energy, lithium ion transference number and battery cycle performance, and the testing methods are as follows:

[0079] (1) Ionic conductivity test: the gel electrolyte was assembled into a steel sheet-electrolyte-steel sheet (SS / Iono-SPEs / SS) battery in an argon-filled glove box, and the AC impedance was tested using an electrochemical workstation, and the ionic conductivity was calculated using the following formula 1.

[0080]

[0081] Wherein L is the thickness of the electrolyte film, R is the EIS impedance of the SS / Iono-SPEs / SS battery, and S is the area of the steel sheet.

[0082] (2) Activation energy calculation: after obtaining the ionic conductivity at different temperatures, it was plotted into a data graph, which was fitted and combined with formula 2 to calculate the activation energy of lithium ion transference.

[0083]

[0084] Wherein σ0 is the pre-exponential factor, E a is the activation energy.

[0085] (3) Ion transference number calculation: after the electrolyte was assembled into a lithium metal-electrolyte-lithium metal (Li / Iono-SPEs / Li) battery, EIS test was carried out at room temperature, wherein the frequency was 7MHz-1Hz and the amplitude was 10mV, the impedance R0 at this time was recorded, then a polarization voltage of 10mV was continuously applied, the initial response current I0 was recorded, when the steady-state current (I s ) was reached, the voltage was stopped, and EIS test was carried out again and the impedance R s at this time was recorded. The calculation formula is shown in formula 3:

[0086]

[0087] Wherein I0 is the initial response current, R0 is the initial impedance, I s is the steady-state current, and R s is the impedance when the steady-state current is reached.

[0088] (4) Battery cycle performance test: the above electrolyte was assembled into a LFP / lithium metal full battery, which was tested at 25℃ and 1C rate.

[0089] The results of the performance tests of the products in Examples 1-5 and Comparative Examples 1-4 are shown in Table 1.

[0090] Table 1

[0091]

[0092] Result analysis:

[0093] (1) Under the same preparation conditions, compared with Comparative Example 2, Examples 1-5 have higher ionic conductivity, lower activation energy and better battery cycle performance because the strong polar poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) is selected as the matrix to prepare the gel electrolyte. This shows that the poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) with appropriate polarity and high dielectric constant exhibits weaker adsorption energy with Pyr 13 + , reduces the possibility of Li + jumping sites being occupied, and is conducive to the dissociation of lithium ions and anion clusters, promoting the transmission of Li + in the polymer phase, thereby greatly improving the ionic conductivity of the electrolyte and improving the cycle stability of the battery.

[0094] (2) Compared with Comparative Example 1 and Comparative Example 3, Example 1 has higher ionic conductivity, lower activation energy and better battery cycle performance, indicating that the poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) and the ionic liquid need to be controlled at a specific ratio. If the content of the ionic liquid is too low, the interface contact performance will be poor, the flame retardancy will be poor, and the construction of the efficient transport channel of ions will be affected. If the content of the ionic liquid is too high, the viscosity of the electrolyte will increase, which will also affect the efficient transport of lithium ions. Therefore, when the ratio of poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) and ionic liquid is 1:1, the highest ionic conductivity will be achieved.

[0095] (3) In Examples 1 and 3-5, the ionic conductivity decreases with the decrease of the content of trifluoroethylene monomer. This is because, with the increase of the content of trifluoroethylene monomer, the polarity of the polymer increases, and it no longer has the most appropriate local polarity, thereby the adsorption of the ionic liquid cation will be stronger, reducing the occupied sites of lithium ions, and making the ionic conductivity and the like decrease.

[0096] (4) In order to further test the ability of the prepared gel electrolyte to inhibit the growth of lithium dendrites, the lithium-lithium symmetric battery of Example 1 is assembled for testing. The experimental results are shown in Table 2. The lithium-lithium symmetric battery containing the gel electrolyte of Example 1 has a current density of 0.1 mA / cm Figure 1 at room temperature, and the growth of lithium dendrites is inhibited. 2At the same test conditions, the lithium-lithium battery containing the gel electrolyte in Comparative Example 2 could cycle stably for 1500 hours with a relatively low polarization voltage of 50mV. However, under the same test conditions, the lithium-lithium battery containing the gel electrolyte in Comparative Example 2 only cycled for 150 hours before short-circuiting, and its polarization voltage was much higher (60mV). This indicates that the ion-gel solid poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) electrolyte has a good ability to suppress lithium dendrites because its system contains more free lithium ions, providing more opportunities for the uniform deposition of lithium ions on the lithium anode.

[0097] (5) To illustrate the compatibility between the prepared gel electrolyte and the LFP cathode, this application assembled the above Example 1 into an LFP-lithium full cell for long-cycle performance testing. For example... Figure 2 As shown, the LFP-lithium full cell containing the gel electrolyte of Example 1 can stably cycle for more than 1600 cycles at room temperature and 1C rate, and retains 91.5% of its capacity after 1000 cycles; while the LFP-lithium full cell containing the gel electrolyte of Comparative Example 2 exhibits drastic capacity decay at room temperature and 1C rate, with a capacity retention of only 7.9% after 1000 cycles. This indicates that the ion-gel solid poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) electrolyte can be better matched with the LFP cathode, which is helpful for the preparation of high energy density lithium metal batteries.

[0098] In summary, this invention utilizes the suitable polarization intensity and high dielectric constant of poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) to enhance the ionic conductivity of the gel electrolyte by leveraging its ability to promote the dissociation of lithium salts while simultaneously exhibiting weak coordination with ionic liquid cations. This results in the preparation of a high-performance gel electrolyte with high room-temperature ionic conductivity and lithium-ion transference number. Furthermore, lithium metal batteries constructed using the gel electrolyte prepared in this invention exhibit high discharge specific capacity and good cycle stability, showing promising development prospects.

[0099] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0100] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0101] In the above embodiments, the endpoints of the ranges of disclosure and any values that are recited are not to be understood as being limited to the exact range or value. It is understood that the disclosure is also container to values approximately ranging from the stated value. For numerical ranges having endpoints, each endpoint is disclosed with the other endpoint, and each endpoint is disclosed with the endpoints of any other numerical range. For numerical ranges having endpoints, each endpoint is disclosed with the other endpoint, and each endpoint is disclosed with the endpoints of any other numerical range.

[0102] In the above embodiments, the description of each embodiment is focused on, and the part not described in detail in a certain embodiment can refer to the relevant description of other embodiments.

[0103] The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

[0104] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as limiting the patent application scope. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. A method for producing a gel electrolyte, characterized by, The method comprises the following steps: (1) Preparation of mixed solution: poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) copolymer, ionic liquid N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide salt and lithium salt are added into a solvent, mixed and stirred uniformly to obtain a mixed solution; (2) Preparation of electrolyte membrane: the mixed solution in step (1) is placed in a glass culture dish and treated by evaporation at high temperature to obtain the gel electrolyte.

2. The method of claim 1, wherein the gel electrolyte is prepared by mixing the polymer, the electrolyte, and the solvent. In step (1), the weight average relative molecular mass of the poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) copolymer is 580,000 g / mol, the molar content of trifluoroethylene in the poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) copolymer is 6.7-26.2%, and the molar content of chlorotrifluoroethylene is 8.8-25.3%.

3. The method of claim 2, wherein the gel electrolyte is prepared by mixing the polymer solution and the electrolyte solution. The molar content of trifluoroethylene in the poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) copolymer is 26.2%, and the molar content of chlorotrifluoroethylene is 8.8%.

4. The method of claim 1, wherein the gel electrolyte is prepared by adding the electrolyte solution to the polymer solution. In step (1), the lithium salt is lithium bis (trifluoromethylsulfonyl) imide and / or lithium bis (fluorosulfonyl) imide.

5. The method of claim 1, wherein the gel electrolyte is prepared by mixing the polymer, the electrolyte solution, and the inorganic filler. In step (1), the purity of the lithium salt is greater than 99.9%.

6. The method of claim 1, wherein the gel electrolyte is prepared by mixing the polymer, the electrolyte, and the solvent. In step (1), the mass ratio of the poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) copolymer, ionic liquid N-propyl-N-methyl pyrrolidinium bis (trifluoromethylsulfonyl) imide salt and lithium salt is 4:3-4:3-4.

7. The method of claim 1, wherein the gel electrolyte is prepared by mixing the polymer, the electrolyte solution, and the inorganic particles. In step (1), the solvent is any one of N,N-dimethylformamide, N-methyl pyrrolidone and tetrahydrofuran.

8. The method of claim 1, wherein the gel electrolyte is prepared by the steps of: In step (2), the evaporation treatment comprises air evaporation and vacuum evaporation in sequence, wherein the temperature and time of air evaporation are 50-60°C and 24-28h respectively, and the temperature and time of vacuum evaporation are 50-60°C and 0.5-1h respectively.

9. A gel electrolyte prepared by the method according to any one of claims 1-8.

10. Use of the gel electrolyte according to claim 9 in a lithium metal battery.

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