Polyion liquid / polyvinylidene fluoride-hexafluoropropene-based solid electrolyte with microscopic liquid phase and preparation method and application of polyion liquid / polyvinylidene fluoride-hexafluoropropene-based solid electrolyte

Abstract

The invention discloses a polyion liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase and a preparation method and application thereof, and the preparation method comprises the following steps: adding a lithium salt into N-methyl-2-pyrrolidone, and stirring until the lithium salt is completely dissolved; then adding imidazolyl polyion liquid to prepare a solution A; adding polyvinylidene fluoride-hexafluoropropylene into N-methyl-2-pyrrolidone to prepare a solution, adding the solution into the solution A, continuously stirring until the solution is fully dissolved to obtain a precursor solution of the solid electrolyte, casting the precursor solution onto a polytetrafluoroethylene mold, and carrying out vacuum drying to obtain the solid electrolyte. And the polyvinylidene fluoride-hexafluoropropylene polymer-based solid electrolyte added with the imidazolyl polyion liquid is prepared by adding the imidazolyl polyion liquid into the polyvinylidene fluoride-hexafluoropropylene polymer-based solid electrolyte. The polymer-based solid electrolyte with a microscopic liquid phase is obtained through an electrolyte preparation process which is mild in condition, simple to operate and easy for large-scale production, and the solid electrolyte has good conductivity and mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state lithium batteries and relates to a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase and a preparation method and application thereof. Background Art

[0002] Driven by the growing demand for high energy density, long cycle life and safety equipment, lithium metal batteries have become popular due to the use of ten times higher theoretical capacity (3861 mA h g) than traditional graphite anodes. -1 ) and extremely low electrochemical potential (-3.04 V. SHE) of lithium metal anodes are regarded as the holy grail of battery technology. However, the capacity decay caused by uneven lithium deposition and lithium dendrite growth, as well as the safety hazards caused by the use of volatile and flammable organic liquid electrolytes, have severely limited the practical application of lithium metal batteries. In order to accelerate the development of the next generation of lithium-ion power batteries, the proposed power battery monomer energy density has reached 300 Wh kg in the medium term. -1 , reaching 400 Wh kg in the long term -1 The actual capacity of graphite is close to its theoretical limit, so the application of lithium metal negative electrode is very advantageous. The use of solid electrolytes will be the most effective way for lithium metal batteries to achieve high energy density and high safety. Among them, polymer-based solid electrolytes are compatible with large-scale manufacturing processes due to their excellent flexibility, good contact with the electrode interface to ensure low interface resistance between the electrode and the electrolyte, as well as low cost and high stability. They can potentially combine the advantages of low interface impedance of liquid electrolytes and high mechanical strength of inorganic solid electrolytes, and are expected to lead lithium metal batteries to break through. Among them, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP)-based solid electrolytes have a high dielectric constant ( ɛ =8.4) is conducive to the dissolution of lithium salts, excellent heat resistance (85 ℃), electrochemical stability (>4.0 V), and good mechanical properties, making PVDF-HFP studied by many scholars. However, in practical applications, the slow ion transport inside the PVDF-HFP-based solid electrolyte membrane and at the interface with the positive and negative electrodes and the low ion conductivity limit its application. In addition, the porous morphology of the PVDF-HFP membrane after drying limits its mechanical properties. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention provides a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase and a preparation method and application thereof, thereby solving the technical problems in the prior art that lithium ion batteries based on polyvinylidene fluoride-hexafluoropropylene solid electrolytes have low ionic conductivity and poor mechanical properties.

[0004] The present invention is achieved through the following technical solutions: A method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase comprises the following steps: S1: adding lithium salt to N-methyl-2-pyrrolidone and stirring until completely dissolved; then adding imidazole-based polyionic liquid to prepare solution A; S2: Add polyvinylidene fluoride-hexafluoropropylene to N-methyl-2-pyrrolidone to prepare a solution, add it to the solution A, continue stirring until it is completely dissolved, to obtain a solid electrolyte precursor solution, shape the solid electrolyte precursor solution and vacuum dry it to obtain the polyionic liquid / polyvinylidene fluoride-hexafluoropropylene based solid electrolyte with a microscopic liquid phase.

[0005] Preferably, the anion of the imidazolyl polyionic liquid includes bromide ion, bis(trifluoromethanesulfonyl)imide ion, chloride ion or iodide ion.

[0006] Preferably, the purity of the lithium salt and N-methyl-2-pyrrolidone is greater than 99%.

[0007] Preferably, the mass ratio of the polyvinylidene fluoride-hexafluoropropylene to the lithium salt is 1:(0.5~1.5).

[0008] Preferably, the mass ratio of the polyvinylidene fluoride-co-hexafluoropropylene to the imidazole-based polyionic liquid is (3-6):1.

[0009] Preferably, the vacuum drying temperature is 80-100° C. and the time is 12-24 h.

[0010] Preferably, the vacuum degree of the vacuum drying is 0.1~10 KPa.

[0011] A polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase is prepared by the above method.

[0012] Preferably, the thickness of the polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase is 200-260 μm.

[0013] The application of the above-mentioned polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase in a lithium ion battery, wherein the conductivity of the lithium ion battery is 10 -4 S cm -1 Magnitude.

[0014] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention provides a method for preparing a poly(ionic liquid) / poly(vinylidene fluoride - hexafluoropropylene) solid electrolyte with a microscopic liquid phase. In terms of improving the conductivity, the imidazolium-based poly(ionic liquid) added in the present invention forms nano-scale liquid microdomains in the poly(vinylidene fluoride - hexafluoropropylene) matrix. These microdomains form a continuous ion transport network through π-π stacking of imidazole rings and ion-dipole interactions. The presence of the liquid phase effectively reduces the activation energy for lithium ion migration, significantly improving the ionic conductivity. At the same time, the high polarity of the imidazole group promotes the dissociation of lithium salts, increasing the concentration of free Li⁺ and forming a "cation-dominated" transport mechanism, which improves the lithium ion transference number and enhances the system conductivity. In terms of improving the mechanical properties, the long-chain structure of the poly(ionic liquid) and poly(vinylidene fluoride - hexafluoropropylene) form an interpenetrating network through hydrogen bonds and van der Waals forces, improving the mechanical properties of the material. Therefore, by introducing the imidazolium-based poly(ionic liquid), the present invention effectively improves the conductivity and mechanical properties of the poly(vinylidene fluoride - hexafluoropropylene)-based solid electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0016] Figure 1 It is a schematic flow chart of a method for preparing a poly(ionic liquid) / poly(vinylidene fluoride - hexafluoropropylene) solid electrolyte with a microscopic liquid phase in the present invention; Figure 2 It is a critical current density diagram of a lithium symmetric battery assembled with a poly(vinylidene fluoride - hexafluoropropylene)-based electrolyte added with an imidazolium-based poly(ionic liquid) prepared in Example 1 of the present invention and a pure poly(vinylidene fluoride - hexafluoropropylene) matrix respectively and placed in a battery test system; Figure 3 It is a cycle performance diagram obtained by long-term cycling test of a lithium symmetric battery assembled with a poly(ionic liquid) / poly(vinylidene fluoride - hexafluoropropylene) solid electrolyte with a microscopic liquid phase prepared in Example 1 of the present invention; Figure 4 It is a cyclic voltammogram of a poly(ionic liquid) / poly(vinylidene fluoride - hexafluoropropylene) solid electrolyte with a microscopic liquid phase prepared in Example 2 of the present invention as a lithium ion battery electrolyte; Figure 5 It is a constant current charge-discharge curve of a poly(ionic liquid) / poly(vinylidene fluoride - hexafluoropropylene) solid electrolyte with a microscopic liquid phase prepared in Example 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0018] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0019] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0020] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0021] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0022] like Figure 1 As shown, the present invention provides a method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase, which specifically comprises the following steps: S1: Add N-methyl-2-pyrrolidone (NMP) measured at a specific ratio into a 10 mL serum bottle, add a certain amount of lithium salt (lithium bis(trifluoromethanesulfonyl imide, C 2 F 6 LiNO 4 S 2 , LiTFSI) and then stirred on a magnetic stirrer for 30 min. The purity (w / w%) of LiTFSI and NMP were both ≥99%; S2: adding imidazolyl polyionic liquids (PILs) containing different anions in a specific ratio into the serum bottle containing lithium salt.

[0023] The anions of the imidazolyl polyionic liquid include bromide ions, bis(trifluoromethanesulfonyl)imide ions (TFSI - ), chloride ions or iodide ions.

[0024] S3: Add a certain amount of polymer matrix PVDF-HFP dissolved in NMP to the serum bottle containing PILs and lithium salts, and place it on a magnetic stirrer for stirring for 12 hours. The content of the polymer matrix PVDF-HFP added is 0.3~0.6g; specifically, the quantitative relationship between the polymer matrix PVDF-HFP and the NMP and LiTFSI added in step S1 is: the mass ratio of PVDF-HFP to NMP is 1:1.027, and the mass ratio of PVDF-HFP to LiTFSI is 1:(0.5~1.5); the quantitative relationship between the polymer matrix PVDF-HFP and the PILs added in step S2 is: the mass ratio of PVDF-HFP to PILs is (3~6):1; stir on a magnetic stirrer for 12 hours; S4: Pour the above-mentioned uniformly stirred precursor solution onto a polytetrafluoroethylene mold for shaping, and place it in a vacuum drying oven for drying. After drying, package and store the electrolyte membrane to obtain a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte (PVDF-HFP / LiTFSI / PILs) with a microscopic liquid phase. The drying temperature in the vacuum drying oven is 80~100℃, the drying time is 12~24 h, and the vacuum degree is 0.1~10 Kpa. The longer the drying time here, the less residual solvent NMP and the like in the electrolyte membrane.

[0025] The thickness of the electrolyte obtained by the method of the present invention is 200~260μm, and the ionic conductivity of the polymer-based solid electrolyte is affected by the thickness of the membrane. For the same electrolyte, the thinner the thickness, the higher the ionic conductivity. In addition, due to the presence of a microscopic liquid phase after adding a polyionic liquid, the ionic conductivity of the electrolyte membrane is significantly increased, but its mechanical properties are hardly reduced, so that the electrolyte membrane has both high ionic conductivity and strong mechanical properties, solving the problem that improving the ionic conductivity of polyvinylidene fluoride co-hexafluoropropylene solid electrolytes in the prior art will reduce mechanical properties, the two are incompatible, and it is impossible to have multi-dimensional integrated solid electrolyte performance and cannot be used in practice. The polymer-based electrolyte obtained by the method of the present invention has good electrical conductivity and mechanical properties, shows considerable comprehensive performance, and can achieve high ionic conductivity, optimal mechanical properties and good safety.

[0026] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0027] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0028] Example 1 A method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase comprises the following steps: Step 1: Add 0.3 mL of N-methyl-2-pyrrolidone (NMP) to a 10 mL serum bottle and add 0.15 g of lithium salt (lithium bis(trifluoromethanesulfonyl)imide, C 2 F 6 LiNO 4 S 2 , LiTFSI) and then stirred on a magnetic stirrer for 30 min. The purity (w / w%) of LiTFSI and NMP were both ≥99%; Step 2: Add 0.05 g of imidazolyl polyionic liquids (PILs) with bromide anions into the serum bottle containing lithium salt.

[0029] Step 3: Add 0.3 g of the polymer matrix PVDF-HFP dissolved in NMP to the serum bottle containing PILs and lithium salts, place it on a magnetic stirrer and stir for 12 hours to obtain a precursor solution; specifically, the mass ratio of PVDF-HFP to NMP in step S1 is 1:1.027, the mass ratio to LiTFSI is 1:0.5, and the mass ratio of PVDF-HFP to PILs is 6:1.

[0030] Step 4: Cast the above-mentioned precursor solution that has been stirred evenly onto a polytetrafluoroethylene mold, place it in a vacuum drying oven and dry it to obtain an electrolyte membrane, and encapsulate the electrolyte membrane to obtain a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte PVDF-HFP / LiTFSI / PILs with a microscopic liquid phase. The drying temperature in the vacuum drying oven is 90°C, the drying time is 16 h, and the thickness of the obtained electrolyte is 220 μm. The polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte PVDF-HFP / LiTFSI / PILs with a microscopic liquid phase prepared in this embodiment was assembled into a lithium-lithium symmetrical battery in a glove box, and the critical current density test was performed as follows: Figure 2 As shown, it has a smaller polarization voltage than that of pure polyvinylidene fluoride-hexafluoropropylene electrolyte membrane.

[0031] The cycle performance of the polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase prepared in this embodiment after being assembled into a lithium-lithium symmetrical battery is as follows: Figure 3 As shown in the figure, it can be seen that the electrolyte membrane still maintains a low polarization voltage after 1500 h of circulation, while the control group, the polyvinylidene fluoride-hexafluoropropylene electrolyte membrane without adding polyionic liquid has almost no performance after about 1000 h of circulation. Example 2 A method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase comprises the following steps: Step 1: Add 0.45 mL of N-methyl-2-pyrrolidone (NMP) to a 10 mL serum bottle and add 0.5625 g of lithium salt (lithium bis(trifluoromethanesulfonyl)imide, C 2 F 6 LiNO 4 S 2 , LiTFSI) and then stirred on a magnetic stirrer for 30 min. The purity (w / w%) of LiTFSI and NMP were both ≥99%; S2: Add 0.1 g of imidazolyl polyionic liquid (PILs) whose anion is bromide ion into the serum bottle containing lithium salt.

[0032] S3: Add 0.45 g of the polymer matrix PVDF-HFP dissolved in NMP to the above-mentioned serum bottle containing PILs and lithium salt, place it on a magnetic stirrer and stir for 12 hours to obtain a precursor solution; specifically, the mass ratio of PVDF-HFP to NMP in step S1 is 1:1.027, and the mass ratio to LiTFSI is 1:1.25; the mass ratio of PVDF-HFP to PILs is 4.5:1.

[0033] S4: Cast the above-mentioned uniformly stirred precursor solution on a polytetrafluoroethylene mold, place it in a vacuum drying oven for drying, obtain an electrolyte membrane, and encapsulate it to obtain a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte PVDF-HFP / LiTFSI / PILs with a microscopic liquid phase. The drying temperature in the vacuum drying oven is 100°C, the drying time is 12 h, and the thickness of the electrolyte is approximately 200μm.

[0034] The polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase prepared in this example and having bromide ions as the added anions was assembled into a full battery with a lithium metal negative electrode and a lithium iron phosphate positive electrode in a glove box for voltammetric testing. Figure 4 As shown, after three cycles of CV curve observation, the curve has almost no deviation, indicating that after the first charge and discharge, almost no side reaction occurs at the interface, and the electrolyte membrane has good stability.

[0035] Example 3 A method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase comprises the following steps: Step 1: Add 0.6 mL of N-methyl-2-pyrrolidone (NMP) to a 10 mL serum bottle and add 0.9 g of lithium salt (lithium bis(trifluoromethanesulfonyl)imide, C 2 F 6 LiNO 4 S 2 , LiTFSI) and then stirred on a magnetic stirrer for 30 min. The purity (w / w%) of LiTFSI and NMP were both ≥99%; S2: Add 0.2 g of imidazolyl polyionic liquid (PILs) with bromide anion into the serum bottle containing lithium salt.

[0036] S3: 0.6 g of polymer matrix PVDF-HFP dissolved in NMP was added to the serum bottle containing PILs and lithium salts, and stirred on a magnetic stirrer for 12 h. Specifically, the mass ratio of PVDF-HFP to NMP in step S1 was 1:1.027, and the mass ratio of PVDF-HFP to LiTFSI was 1:1.5; the mass ratio of PVDF-HFP to PILs was 3:1.

[0037] S4: The above-mentioned precursor solution is poured onto a polytetrafluoroethylene mold, placed in a vacuum drying oven for drying, and then an electrolyte membrane is obtained, which is then packaged to obtain a polymer-based electrolyte PVDF-HFP / LiTFSI / PILs with an imidazole-based polyionic liquid having bromide ions as an anion. The drying temperature in the vacuum drying oven is 80°C, the drying time is 18 h, and the thickness of the electrolyte is approximately 240 μm.

[0038] The polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase prepared in this embodiment was assembled in a glove box and then subjected to constant current charge and discharge test and cycle performance test. The constant current charge and discharge curve is shown in Figure 5 As shown in the figure, it can be seen that the 5 charge and discharge curves almost completely overlap, indicating that its electrochemical performance is stable, it has high ionic conductivity, and it is well compatible with the positive electrode material lithium iron phosphate without side reactions.

[0039] Example 4 The difference between this embodiment and embodiment 1 is: The amount of NMP added in step S1 is 0.45 mL, and the amount of lithium salt added (lithium bis(trifluoromethanesulfonyl imide, C 2 F 6 LiNO 4 S 2 , LiTFSI) is 0.5625 g; In step S2, 0.15 g of imidazole-based polyionic liquids (PILs) whose anions are bistrifluoromethanesulfonyl imide ions (TFSI) are added; In step S3, 0.45 g of the polymer matrix PVDF-HFP dissolved in NMP was added to the serum bottle containing PILs and lithium salts, and the solution was placed on a magnetic stirrer and stirred for 12 h; In step S4, the uniformly stirred precursor solution is cast on a polytetrafluoroethylene mold, placed in a vacuum drying oven for drying, and an electrolyte membrane is obtained, and the electrolyte membrane is packaged to obtain a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene solid electrolyte with a microscopic liquid phase to which an imidazole-based polyionic liquid with TFSI anion is added. The drying temperature in the vacuum drying oven is 100° C., the drying time is 24 hours, and the thickness of the electrolyte is approximately 260 μm.

[0040] When a lithium-ion battery is assembled using the polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase prepared in this embodiment, the reversible lithium storage capacity of the lithium-ion battery is 130 mAh / g when the current density is 50 mA / g.

[0041] Example 5 The difference between this embodiment and embodiment 1 is: The amount of NMP added in step S1 is 0.3 mL, and the amount of lithium salt (lithium bis(trifluoromethanesulfonyl imide, C 2 F 6 LiNO 4 S 2 , LiTFSI) is 0.45 g; In step S2, 0.1 g of imidazole-based polyionic liquid (PILs) whose anions are chloride ions is added; In step S3, 0.3 g of the polymer matrix PVDF-HFP dissolved in NMP was added to the serum bottle containing PILs and lithium salt, and placed on a magnetic stirrer for stirring for 12 h; In step S4, the uniformly stirred precursor solution is cast on a polytetrafluoroethylene mold, placed in a vacuum drying oven for drying, and an electrolyte membrane is obtained, which is packaged to obtain a polymer-based electrolyte PVDF-HFP / LiTFSI / PILs with an imidazole-based polyionic liquid with chloride ions as an anion. The drying temperature in the vacuum drying oven is 90°C, the drying time is 12 hours, and the thickness of the electrolyte is approximately 240 μm.

[0042] When a lithium-ion battery is assembled using the polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase prepared in this embodiment, the reversible lithium storage capacity of the lithium-ion battery is 160 mAh / g when the current density is 50 mA / g.

[0043] Example 6 The difference between this embodiment and embodiment 1 is: The amount of NMP added in step S1 is 0.45 mL, and the amount of lithium salt added (lithium bis(trifluoromethanesulfonyl imide, C 2 F 6 LiNO 4 S 2 , LiTFSI) is 0.5625 g; In step S2, 0.15 g of imidazole-based polyionic liquid (PILs) whose anions are iodide ions is added; In step S3, 0.45 g of the polymer matrix PVDF-HFP dissolved in NMP was added to the serum bottle containing PILs and lithium salts, and the solution was placed on a magnetic stirrer and stirred for 12 h; In step S4, the uniformly stirred precursor solution is cast on a polytetrafluoroethylene mold, placed in a vacuum drying oven for drying, and an electrolyte membrane is obtained, and the electrolyte is packaged to obtain a polymer-based electrolyte PVDF-HFP / LiTFSI / PILs with an imidazole-based polyionic liquid whose anions are iodide ions. The drying temperature in the vacuum drying oven is 80°C, the drying time is 16 hours, and the thickness of the electrolyte is approximately 200 μm.

[0044] After a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase prepared by this embodiment is assembled into a lithium ion battery, the reversible lithium storage capacity of the lithium ion battery is 170 mAh / g when the current density is 50 mA / g.

[0045] Example 7 The difference between this embodiment and embodiment 6 is: In step S2, 0.15 g of imidazole-based polyionic liquid (PILs) whose anion is bromide ion is added; In step S3, 0.45 g of the polymer matrix PVDF-HFP dissolved in NMP was added to the serum bottle containing PILs and lithium salts, and the solution was placed on a magnetic stirrer and stirred for 12 h; In step S4, the uniformly stirred precursor solution is cast on a polytetrafluoroethylene mold, placed in a vacuum drying oven for drying, and an electrolyte membrane is obtained, which is packaged to obtain a polymer-based electrolyte PVDF-HFP / LiTFSI / PILs with an imidazole-based polyionic liquid whose anions are bromide ions. The drying temperature in the vacuum drying oven is 100°C, the drying time is 12 hours, and the thickness of the electrolyte is approximately 220 μm.

[0046] When a lithium-ion battery is assembled using the polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase prepared in this embodiment, the reversible lithium storage capacity of the lithium-ion battery is 150 mAh / g when the current density is 50 mA / g.

[0047] Example 8 The difference between this embodiment and embodiment 6 is: In step S2, 0.2 g of imidazole-based polyionic liquid (PILs) whose anion is bromide ion is added; In step S3, 0.45 g of the polymer matrix PVDF-HFP dissolved in NMP was added to the serum bottle containing PILs and lithium salts, and the solution was placed on a magnetic stirrer and stirred for 12 h; In step S4, the uniformly stirred precursor solution is cast on a polytetrafluoroethylene mold, placed in a vacuum drying oven for drying, and an electrolyte membrane is obtained, which is packaged to obtain a polymer-based electrolyte PVDF-HFP / LiTFSI / PILs with an imidazole-based polyionic liquid whose anions are bromide ions. The drying temperature in the vacuum drying oven is 90°C, the drying time is 24h, and the thickness of the electrolyte is approximately 240μm.

[0048] When a lithium-ion battery is assembled using the polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase prepared in this embodiment, the reversible lithium storage capacity of the lithium-ion battery is 135 mAh / g when the current density is 50 mA / g.

[0049] Example 9 The difference between this embodiment and embodiment 6 is: In step S2, 0.1 g of imidazole-based polyionic liquids (PILs) with TFSI as anion was added; In step S4, the uniformly stirred precursor solution is cast on a polytetrafluoroethylene mold, placed in a vacuum drying oven for drying, and an electrolyte membrane is obtained, and the electrolyte is packaged to obtain a preparation method of a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte with a microscopic liquid phase. The drying temperature in the vacuum drying oven is 80°C, the drying time is 12 hours, and the thickness of the electrolyte is approximately 220 μm.

[0050] When a lithium-ion battery is assembled using the polymer-based electrolyte added with imidazole-based polyionic liquid prepared in this embodiment, the reversible lithium storage capacity of the lithium-ion battery is 160 mAh / g when the current density is 50 mA / g.

[0051] Example 10 The difference between this embodiment and embodiment 6 is: In step S2, 0.2 g of imidazole-based polyionic liquids (PILs) with TFSI as anion was added; In step S4, the uniformly stirred precursor solution is cast on a polytetrafluoroethylene mold, placed in a vacuum drying oven for drying, and an electrolyte membrane is obtained, which is then packaged to obtain a polymer-based electrolyte PVDF-HFP / LiTFSI / PILs with an imidazole-based polyionic liquid with TFSI as an anion. The drying temperature in the vacuum drying oven is 100°C, the drying time is 18 h, and the thickness of the electrolyte is approximately 200 μm.

[0052] When a lithium ion battery is assembled using the microscopic liquid phase polyionic liquid / polyvinylidene fluoride-hexafluoropropylene based solid electrolyte prepared in this embodiment, the reversible lithium storage capacity of the lithium ion battery is 165 mAh / g when the current density is 50 mA / g.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase, characterized in that: The following steps are involved: S1: adding lithium salt to N-methyl-2-pyrrolidone and stirring until completely dissolved; then adding imidazole-based polyionic liquid to prepare solution A; S2: Add polyvinylidene fluoride-hexafluoropropylene to N-methyl-2-pyrrolidone to prepare a solution, add it to the solution A, continue stirring until it is completely dissolved, to obtain a solid electrolyte precursor solution, shape the solid electrolyte precursor solution and vacuum dry it to obtain the polyionic liquid / polyvinylidene fluoride-hexafluoropropylene based solid electrolyte with a microscopic liquid phase.

2. The method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase according to claim 1, characterized in that: The anion of the imidazolyl polyionic liquid includes a bromide ion, a bis(trifluoromethanesulfonyl)imide ion, a chloride ion or an iodide ion.

3. The method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase according to claim 1, characterized in that: The purity of the lithium salt and N-methyl-2-pyrrolidone is greater than 99%.

4. The method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase according to claim 1, characterized in that: The mass ratio of the polyvinylidene fluoride-hexafluoropropylene to the lithium salt is 1:(0.5-1.5).

5. The method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase according to claim 1, characterized in that: The mass ratio of the polyvinylidene fluoride co-hexafluoropropylene to the imidazole-based polyionic liquid is (3-6):

1.

6. The method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase according to claim 1, characterized in that: The vacuum drying temperature is 80-100°C and the time is 12-24 h.

7. The method for preparing a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase according to claim 1, characterized in that: The vacuum degree of the vacuum drying is 0.1~10 KPa.

8. A polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase, characterized in that: Prepared by the method according to any one of claims 1 to 7.

9. The polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase according to claim 8, characterized in that: The thickness of the polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase is 200-260 μm.

10. Use of a polyionic liquid / polyvinylidene fluoride-hexafluoropropylene-based solid electrolyte having a microscopic liquid phase according to any one of claims 8 to 9 in a lithium ion battery, characterized in that: The conductivity of the lithium-ion battery is 10 -4 S cm -1 Magnitude.

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