Vinylimidazole polyionic liquid-based solid-state polymer electrolyte membrane for lithium battery and preparation method thereof

Abstract

The application belongs to the field of polymer electrolyte, and particularly relates to a vinyl imidazole polyionic liquid-based solid-state polymer electrolyte membrane for lithium battery and a preparation method thereof. Vinyl imidazole is reacted with a sulfonic acid lactone at room temperature to obtain a vinyl imidazole zwitterionic liquid; the zwitterionic liquid is mixed with lithium bis(trifluoromethanesulfonyl)imide in methanol to obtain an ionic liquid containing a lithium source, and after vacuum drying, the ionic liquid is ultraviolet light initiated with methoxy polyethylene glycol acrylate in a proportion to obtain the vinyl imidazole polyionic liquid-based solid-state polymer electrolyte membrane. The application realizes lithium ion migration number of 0.78 of the polymer electrolyte membrane and ionic conductivity of 0.11*10 ‑4 S·cm ‑1 at room temperature by virtue of the unique advantages of the zwitterionic liquid and the existence of ether oxygen structure.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer electrolyte, and relates to a solid-state electrolyte film, in particular to a vinyl imidazole polyionic liquid-based solid-state polymer electrolyte film for lithium batteries and a preparation method thereof. BACKGROUND

[0002] With the continuous development of society, the demand for energy is becoming larger and larger. As a traditional energy, fossil energy is non-renewable and causes environmental hazards after use, so people must seek new energy. At present, new energy mainly includes solar energy, wind energy, tidal energy, etc. Although the above-mentioned energy can replace non-renewable fossil energy, these energy sources have the characteristics of intermittency and locality, so it is necessary to find suitable energy storage devices to store these energy sources to ensure continuous use of energy.

[0003] Among many energy storage devices, electrochemical cells can convert chemical energy and electrical energy to achieve energy storage and output. Among the batteries, lithium ion batteries in rechargeable secondary batteries are widely used in energy storage devices due to their high energy density, high power density, long cycle life, no memory effect, and other advantages. Lithium ion batteries mainly consist of four parts: positive electrode, negative electrode, electrolyte, and separator. As one of the four cores of the battery, the electrolyte has a crucial influence on the performance of the battery. For traditional electrolytes, organic ester organic solvents are mainly used, which have good performance, but they have the risk of flammability and leakage, which may even cause safety problems such as positive and negative short circuit and battery explosion. Therefore, it is necessary to find a more suitable electrolyte to replace the traditional liquid electrolyte.

[0004] Compared with traditional electrolytes, polymer electrolytes obtained by polymerization not only can act as electrolytes, but also can act as separators to separate the positive and negative electrodes. This effectively improves the safety problems caused by organic electrolytes acting as electrolytes. However, for traditional polymer electrolytes, the low room temperature conductivity and low lithium ion transference number limit their application and development. Therefore, how to improve the ionic conductivity and lithium ion transference number of polymer electrolytes is an urgent problem to be solved. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a vinyl imidazole polyionic liquid-based solid-state polymer electrolyte film.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a vinyl imidazole polyionic liquid-based polymer electrolyte film, the structure general formula of which is as follows:

[0007]

[0008] In the formula, X and Y represent the mass ratio of two structures, the ratio ranges from 3:1 to 1:3, and n = 8.

[0009] Another object of the present application is to provide a preparation method of the above-mentioned vinyl imidazole-based polyionic liquid, the main steps of which are as follows:

[0010] (1) Dissolve the vinyl imidazole and the sulfolane in organic solvents respectively, mix them uniformly, then slowly drop the sulfolane solution into the solution of the vinyl imidazole, react at room temperature for 24 hours, and then obtain the vinyl zwitterionic liquid by suction filtration, and dry it at room temperature under vacuum for 24 hours.

[0011] In the formula, the sulfolane is 1,3-propane sulfolane or 1,4-butane sulfolane; the molar ratio of the vinyl imidazole to the sulfolane is 1:1; and the organic solvent is acetone.

[0012] (2) Dissolve the product of step (1) and lithium bis-trifluoromethanesulfonimide in an organic solvent in a certain proportion, stir at room temperature for 24 hours, spin dry the organic solvent, and further dry it at room temperature under vacuum for 24 hours to obtain the ionic liquid containing a lithium source with a certain viscosity at room temperature.

[0013] In the formula, the organic solvent is anhydrous methanol; and the molar ratio of the vinyl zwitterionic liquid to lithium bis-trifluoromethanesulfonimide is 1:1.

[0014] (3) Mix the ionic liquid obtained in step (2) with methoxy polyethylene glycol acrylate, a crosslinking agent and a photoinitiator in a certain proportion, mix them uniformly, then drop them onto a cleaned glass plate, and irradiate the glass plate under a UV lamp for 20 minutes to obtain the corresponding solid-state polymer electrolyte membrane.

[0015] In the formula, the mass ratio of the ionic liquid to the methoxy polyethylene glycol acrylate ranges from 2:1 to 1:2.

[0016] The crosslinking agent is polyethylene glycol diacrylate, and its amount is 5% of the mass of the ionic liquid and the methoxy polyethylene glycol acrylate; the photoinitiator is benzoin ethyl ether, and its amount is 0.5% of the mass of the ionic liquid and the methoxy polyethylene glycol acrylate.

[0017] Beneficial effects: the application is based on a vinyl imidazole polyionic liquid, by adopting a specific structure design, lithium ions in lithium bis-trifluoromethanesulfonimide are separated from TFSI, and are combined with sulfonate ions and imidazole cations respectively, and the dissociation energy of sulfonate and lithium ions is low, which is beneficial to the conduction of lithium ions. The ether oxygen groups in the comonomer methoxy polyethylene glycol acrylate and the crosslinking agent PEGDA can be coordinated with lithium ions, which can further promote the migration of lithium ions, and thus improve the ionic conductivity. At the same time, the structure of the zwitterion gives it the characteristics of only orientation without movement in the electric field. Compared with the introduction of traditional ionic liquid, the zwitterion can maximize the migration of lithium ions, so that the vinyl imidazole polyionic liquid-based solid-state polymer electrolyte realizes the double guarantee of conductivity and migration number. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Data graph of lithium ion migration number for example 3.

[0019] Figure 2 Cycle test graph of LiFePO4 / SPE / Li battery assembled for example 3 at 0.1C.

[0020] Figure 3 Cycle test graph of Li / SPE / Li battery assembled for example 3 at 0.1mA / cm 2 DETAILED DESCRIPTION

[0021] The application will be further described below in conjunction with examples, but is not limited thereto.

[0022] Example 1

[0023] The application is based on a polymer electrolyte film of a vinyl imidazole polyionic liquid, and its structure general formula is as follows:

[0024]

[0025] In the formula, X and Y represent the mass ratio of two structures, the ratio range is 3:1-1:3, and n=8.

[0026] Through a specific structure design, a zwitterionic liquid is obtained, and a higher lithium ion migration number is achieved. The introduction of methoxy polyethylene glycol acrylate enriches the ether oxygen structure, promotes the conduction of lithium ions in the system, and overcomes the problems of low lithium ion migration number and low room temperature conductivity in traditional solid-state electrolytes.

[0027] Example 1

[0028] The embodiment provides a polymer electrolyte film based on a vinyl imidazole polyionic liquid and a preparation method thereof, and the specific steps are as follows: ​

[0029] (1) 4.7 g (0.05 mol) of vinyl imidazole and 6.1 g (0.05 mol) of 1,3-propane sultone were dissolved in 40 mL of acetone, respectively, and after mixing, the 1,3-propane sultone solution was added dropwise into the vinyl imidazole solution, and the reaction was carried out at room temperature for 24 h. After filtration and vacuum drying at room temperature for 24 h, a vinyl zwitterionic liquid was obtained.

[0030] (2) 0.33 g of the product of step (1) and 0.44 g of lithium bistrifluoromethanesulfonimide were dissolved in 3 mL of anhydrous methanol, respectively, and after mixing, the latter was added dropwise into the former solution, and the mixture was stirred at room temperature for 24 h. After vacuum rotary evaporation of the organic solvent at room temperature, further vacuum drying at room temperature for 24 h was carried out, and a lithium source-containing ionic liquid having a certain viscosity at room temperature was obtained.

[0031] (3) 0.6 g of the ionic liquid obtained in step (2) was mixed with 0.3 g of methoxy polyethylene glycol acrylate, 0.045 g of polyethylene glycol diacrylate and 0.0045 g of benzoin ethyl ether, and after mixing, the mixture was added dropwise onto a cleaned glass plate, and the glass plate was irradiated under a UV lamp for 20 min, to obtain a corresponding solid-state polymer electrolyte film.

[0032] The polymer electrolyte film was subjected to conductivity and lithium ion transference number determination, and the lithium ion transference number was measured to be 0.83, and the conductivity at room temperature was measured to be 0.10 x 10 -5 S·cm -1 , and the tensile strength was 1.57 MPa. At the same time, in order to test the application of the polymer electrolyte film in a full solid-state lithium battery, the polymer electrolyte film was assembled with a positive electrode (lithium iron phosphate electrode sheet) and a negative electrode (metal lithium sheet) into a button cell, and the charge-discharge cycle performance test was carried out at room temperature: the initial discharge specific capacity of the battery was measured to be 70 mAh·g -1 at 0.1C rate, gradually stabilized at 99 mAh·g -1 , and the final capacity retention rate was 98.6%.

[0033] Example 2

[0034] The present example provides a vinyl imidazole-based polyionic liquid-based polymer electrolyte film and a preparation method thereof, which is basically the same as that of Example 1, except that the 1,3-propane sultone in step (1) is 1,4-butane sultone. The lithium ion transference number of the polymer electrolyte film was measured to be 0.79, and the conductivity at room temperature was measured to be 0.13 x 10 -5 S·cm -1, and the tensile strength was 1.46 MPa. To test the application of the polymer electrolyte membrane in the all-solid-state battery, the LiFePO4 / SPE / Li battery was assembled and the charge-discharge cycle performance was tested at room temperature. The initial discharge specific capacity of the battery was 80 mAh-g -1 at 0.1C rate, and gradually stabilized at 100 mAh-g -1 , and the final capacity retention was 97.0%.

[0035] Example 3

[0036] This example provides a polymer electrolyte membrane based on vinyl imidazole polyionic liquid and a preparation method thereof, which is basically the same as that of Example 1, except that the mass of the ionic liquid in step (3) is 0.45 g, and the mass of the methoxy polyethylene glycol acrylate is 0.45 g. The lithium ion transference number of the polymer electrolyte membrane was 0.78, the conductivity at room temperature was 0.11 x 10 -4 S-cm -1 , and the tensile strength was 0.24 MPa. To test the application of the polymer electrolyte membrane in the all-solid-state battery, the LiFePO4 / SPE / Li battery was assembled and the charge-discharge cycle performance was tested at room temperature. The initial discharge specific capacity of the battery was 103 mAh-g -1 at 0.1C rate, and gradually stabilized at 122 mAh-g -1 , and the final capacity retention was 96.3%.

[0037] Example 4

[0038] This example provides a polymer electrolyte membrane based on vinyl imidazole polyionic liquid and a preparation method thereof, which is basically the same as that of Example 1, except that the mass of the ionic liquid in step (3) is 0.3 g, and the mass of the methoxy polyethylene glycol acrylate is 0.6 g. The lithium ion transference number of the polymer electrolyte membrane was 0.67, the conductivity at room temperature was 0.2 x 10 -4 S-cm -1 , and the tensile strength was 0.11 MPa. To test the application of the polymer electrolyte membrane in the all-solid-state battery, the LiFePO4 / SPE / Li battery was assembled and the charge-discharge cycle was tested at room temperature. The initial discharge specific capacity of the battery was 109 mAh-g -1 at 0.1C rate, and gradually stabilized at 113 mAh-g -1 , and the final capacity retention was 99%.

[0039] The reason for this phenomenon is that with the increase of the content of methoxyl polyethylene glycol acrylate in the electrolyte system, more and more ether oxygen structures in the structure promote the conduction of lithium ions in the system, thereby improving the ionic conductivity of the system. The increase of the transference number with the increase of the content of the zwitterion also proves the contribution of the zwitterion to the migration of lithium ions in the system.

[0040] Comparative Example 1

[0041] This example provides a preparation method of a polymer electrolyte film, which is basically the same as that of Example 2, except that the methoxyl polyethylene glycol acrylate in step (3) is replaced by acrylonitrile, and the LiFePO4 / SPE / Li battery is assembled and tested for charge-discharge cycling at room temperature. The first discharge specific capacity of the battery is measured to be 28 mAh·g -1 at 0.1C rate. The capacity retention rate is 32%.

[0042] The reason for this phenomenon is that acrylonitrile does not contain ether oxygen bonds as methoxyl polyethylene glycol acrylate does, and has very limited effect on the migration of lithium ions.

[0043] Comparative Example 2

[0044] This example provides a preparation method of a polymer electrolyte film, which is basically the same as that of Example 2, except that the zwitterionic liquid in step (3) is replaced by methyl methacrylate, and the LiFePO4 / SPE / Li battery is assembled and tested for charge-discharge cycling at room temperature. The first discharge specific capacity of the battery is measured to be 60 mAh·g -1 at 0.1C rate. Stable at 70 mAh·g -1 , the capacity retention rate is 28.5%.

[0045] The reason for this phenomenon is that the number of ether oxygen in methyl methacrylate cannot be compared with that of methoxyl polyethylene glycol acrylate, and the electrochemical performance is poorer. However, compared with Comparative Example 1, the electrochemical performance is improved.

[0046] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A vinyl imidazole polyionic liquid based solid state polymer electrolyte membrane, characterized by: The structural general formula of the solid-state polymer electrolyte film is as follows: In the formula, X and Y represent the mass ratio of two structures, the ratio ranges from 3:1 to 1:3, and n=8.

2. A method for preparing a vinyl imidazole poly ionic liquid based solid state polymer electrolyte membrane, characterized by: The preparation method comprises the following steps: (1) Dissolve the vinyl imidazole and the sulfolane in organic solvents respectively, mix them uniformly, then drop the sulfolane solution into the vinyl imidazole solution by using a constant-pressure separating funnel, react at room temperature for 24 hours, perform suction filtration to obtain a vinyl zwitterionic liquid, and perform vacuum drying at room temperature for 24 hours; (2) Dissolve the product of step (1) and lithium bis-trifluoromethanesulfonimide in an organic solvent according to a proportion, stir at room temperature for 24 hours, spin dry the organic solvent, and further perform vacuum drying at room temperature for 24 hours to obtain an ionic liquid containing a lithium source; (3) Mix the ionic liquid obtained in step (2) with methoxy polyethylene glycol acrylate, a crosslinking agent and a photoinitiator according to a proportion, mix them uniformly, then drop them onto a cleaned glass plate, and irradiate the glass plate under a UV lamp for 20 minutes to obtain a solid-state polymer electrolyte film.

3. The method for preparing the vinylimidazolium polyionic liquid-based solid polymer electrolyte membrane according to claim 2, characterized in that: In step (1), the sulfolane is 1,3-propane sulfolane or 1,4-butane sulfolane, and the organic solvent is acetone; the molar ratio of the vinyl imidazole to the sulfolane is 1:

1.

4. The method for preparing a vinylimidazolium polyionic liquid-based solid polymer electrolyte membrane according to claim 2, characterized in that: In step (2), the organic solvent is anhydrous methanol; and the molar ratio of the vinyl zwitterionic liquid to lithium bis-trifluoromethanesulfonimide is 1:

1.

5. The method for preparing a vinylimidazolium polyionic liquid-based solid polymer electrolyte membrane according to claim 2, characterized in that: In step (3), the mass ratio of the ionic liquid to the methoxy polyethylene glycol acrylate is 2:1-1:

2.

6. The method for preparing a vinylimidazolium polyionic liquid-based solid polymer electrolyte membrane according to claim 2, characterized in that: In step (3), the crosslinking agent is polyethylene glycol diacrylate, and the amount of the crosslinking agent is 5% of the mass of the ionic liquid and the methoxy polyethylene glycol acrylate.

7. The method for preparing a vinylimidazolium polyionic liquid-based solid polymer electrolyte membrane according to claim 2, characterized in that: In step (3), the photoinitiator is benzpinacol, and the amount of the photoinitiator is 0.5% of the mass of the ionic liquid and the methoxy polyethylene glycol acrylate.

8. Use of the vinyl imidazole polyionic liquid based solid state polymer electrolyte membrane according to claim 1, characterized by: The solid-state polymer electrolyte film is used for lithium battery electrolyte films.

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