Gel polymer electrolyte membrane and preparation method therefor, and secondary battery

Abstract

The present invention relates to a gel polymer electrolyte membrane and a preparation method therefor, and a secondary battery. The gel polymer electrolyte membrane comprises an ionic liquid and a polyionic liquid obtained by polymerizing the ionic liquid. Further provided is a gel polymer electrolyte membrane having both a high ionic conductivity and high mechanical properties.

Description

Gel polymer electrolyte membrane, preparation method thereof, and secondary battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on January 18, 2024, with application number 2024100749324. The entire contents of the above application are incorporated by reference into this application.

[0002] Technical Field

[0003] The present application relates to the technical field of electrolyte materials, and in particular to a gel polymer electrolyte membrane, a preparation method thereof, and a secondary battery.

[0004] Background Art

[0005] Gel polymer electrolytes function as both conductors and separators, with ionic conductivity primarily occurring in liquid plasticizers. Conventional gel polymer electrolytes are typically plasticized with liquid electrolytes, which improves their ionic conductivity and mechanical properties. However, the introduction of liquid electrolytes inevitably introduces safety risks, and similar risks exist as with pure liquid electrolytes, such as leakage, flammability, and even explosion. While gel polymer electrolytes maintain their overall performance, their safety performance falls short of meeting operational requirements.

[0006] Compared to solid electrolytes, which have disadvantages such as low interfacial compatibility and high impedance, gel polymer electrolytes are clearly the best alternative type at present. Gel polymer electrolytes combine the advantages of high safety of solid polymer electrolytes and high ionic conductivity of liquid electrolytes to a certain extent, and are considered to be the most suitable electrolyte system for practical applications. In addition, gel polymer electrolytes have advantages such as designability, processability and lightweight. At the same time, their flexibility enables them to form a conformal interface with battery electrodes, making them a good research direction for electrolytes.

[0007] Technical issues

[0008] In this field, there is an urgent need to develop a gel polymer electrolyte to improve the above-mentioned deficiencies.

[0009] The present application provides a gel polymer electrolyte membrane, a preparation method thereof, and a secondary battery. The present application provides a gel polymer electrolyte membrane having both high ionic conductivity and mechanical properties.

[0010] Technical Solutions

[0011] In a first aspect, the present application provides a gel polymer electrolyte membrane, which includes an ionic liquid and a polyionic liquid obtained by polymerizing the ionic liquid.

[0012] In a second aspect, the present application provides a method for preparing the gel polymer electrolyte membrane according to the first aspect, the method comprising the following steps:

[0013] The polyionic liquid, solvent and ionic liquid are mixed to obtain a mixed solution; the mixed solution is cast into a film to obtain the gel polymer electrolyte membrane.

[0014] In a third aspect, the present application provides a secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte comprises the gel polymer electrolyte membrane according to the first aspect.

[0015] Beneficial effects

[0016] Compared with the related art, this application has the following beneficial effects:

[0017] The present application provides a gel polymer electrolyte membrane, which replaces the liquid electrolyte disclosed in the prior art with an ionic liquid, and at the same time plasticizes with the polyionic liquid electrolyte, so that the gel polymer electrolyte membrane has both high ionic conductivity and mechanical properties. Different from traditional liquid electrolytes, ionic liquids are composed of anions and cations, and have a melting point below 100°C. Therefore, ionic liquids have excellent ionic conductivity and high safety that liquid electrolytes do not have, and are regarded as an effective substitute for electrolytes. In addition, considering that the traditional polymer matrix has insufficient compatibility with ionic liquids and it is difficult to fully exert all their characteristics, the present application uses a polymerizable ionic liquid as a polymer substrate, relying on the natural compatibility between the two, and thus being able to maximize the advantages.

[0018] Still other aspects will become apparent upon reading and understanding the detailed description.

[0019] Modes for Carrying Out the Invention

[0020] This application adopts ionic liquid to replace the liquid electrolyte disclosed in the prior art, and at the same time, it plasticizes with the polyionic liquid electrolyte, so that the gel polymer electrolyte membrane has both high ionic conductivity and mechanical properties. Different from traditional liquid electrolytes, ionic liquids are composed of anions and cations, and the melting point is lower than 100 ° C. Therefore, ionic liquids have excellent ionic conductivity and high safety that liquid electrolytes do not have, and are regarded as an effective substitute for electrolytes. In addition, considering that the traditional polymer matrix has insufficient compatibility with ionic liquids and it is difficult to fully exert all their characteristics, this application uses polymerizable ionic liquids as the polymer substrate, relying on the natural compatibility between the two, and thus being able to maximize the advantages.

[0021] Optionally, the mass ratio of the ionic liquid to the polyionic liquid is 1:(1-4), optionally 1:2, for example, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, 1:3.2, 1:3.5, 1:3.8, 1:4, etc.

[0022] In the present application, the plasticizing effect of the ionic liquid is optimized by regulating the mass ratio of the ionic liquid to the polyionic liquid. A too low mass ratio will result in the system being unable to achieve sufficient ionic conductivity, and conversely, the mechanical properties of the system will deteriorate.

[0023] In the present application, by selecting specific types of ionic liquids and polyionic liquids, the two can be better combined with each other to achieve dual guarantees of ionic conductivity and mechanical properties.

[0024] Optionally, the reaction temperature is 55-65°C, for example, 55°C, 58°C, 60°C, 62°C, 65°C, etc.; the reaction time is 18-24h, for example, 18h, 20h, 22h, 24h, etc.

[0025] Optionally, the preparation method of the ionic liquid includes stirring methylimidazole, a halogen-substituted propane compound and an N-methylpyrrolidone solvent, and removing the N-methylpyrrolidone solvent to obtain a precursor material; mixing the precursor material, a lithium salt and water, and removing the water to obtain the ionic liquid.

[0026] Optionally, the halogen-substituted propane compound includes a bromopropane compound and / or an iodopropane compound.

[0027] Optionally, the mixing process includes ultrasonically stirring the polyionic liquid and the solvent for 18-24 hours, for example, 18 hours, 20 hours, 22 hours, 24 hours, etc.; then adding the ionic liquid and continuing stirring for 4-8 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc.; to obtain a mixed solution.

[0028] Optionally, the casting film forming process includes casting the mixed solution on the surface of the substrate and vacuum drying to obtain the gel polymer electrolyte membrane.

[0029] Optionally, the vacuum drying temperature is 55-65°C, for example, 55°C, 58°C, 60°C, 62°C, 65°C, etc.; the time is 18-24h, for example, 18h, 20h, 22h, 24h, etc.

[0030] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0031] Example 1

[0032] This embodiment provides a gel polymer electrolyte membrane comprising a 1-propyl-3-methyl-imidazolium trifluoromethanesulfonyl imide ionic liquid and a polyionic liquid obtained by polymerizing the 1-propyl-3-methyl-imidazolium trifluoromethanesulfonyl imide ionic liquid. The mass ratio of the 1-propyl-3-methyl-imidazolium trifluoromethanesulfonyl imide ionic liquid to the polyionic liquid is 1:2.

[0033] This embodiment also provides a method for preparing the above-mentioned gel polymer electrolyte membrane, which comprises the following steps:

[0034] Methylimidazole, a bromopropane compound, and an N-methylpyrrolidone solvent are stirred at room temperature, and after precipitation occurs, the solvent is removed by rotary evaporation to obtain a precursor material; the precursor material, a lithium salt of bis(fluorosulfonyl)imide, and deionized water are mixed and stirred at room temperature for 24 hours, and water is removed by rotary evaporation. Anhydrous magnesium sulfate is then added and filtered to further remove water, and the mixture is dried in a vacuum drying oven at 60° C. and then stored to obtain a 1-propyl-3-methyl-imidazole trifluoromethanesulfonyl imide ionic liquid;

[0035] The 1-propyl-3-methyl-imidazolium trifluoromethanesulfonyl imide ionic liquid and azobisisobutyronitrile were subjected to solution polymerization, heated at 60° C. for 24 h, and the reaction product was washed with acetone to obtain a polyionic liquid;

[0036] The polyionic liquid and N,N-dimethylformamide solvent were ultrasonically stirred for 24 hours, and then the ionic liquid was added and stirred for 8 hours to obtain a mixed solution; the mixed solution was poured onto the surface of a polytetrafluoroethylene plate and vacuum dried at 60° C. for 24 hours to obtain the gel polymer electrolyte membrane.

[0037] Example 2

[0038] The difference between this embodiment and embodiment 1 is that 1-propyl-3-methyl-imidazole trifluoromethanesulfonyl imide is replaced by 1-methylimidazole trifluoromethanesulfonyl imide, and the rest is the same as embodiment 1.

[0039] Example 3

[0040] The difference between this embodiment and embodiment 1 is that 1-propyl-3-methyl-imidazole trifluoromethanesulfonyl imide is replaced by 1-propyl-3-methyl-imidazole bis(trifluoromethanesulfonyl)imide, and the rest is the same as embodiment 1.

[0041] Example 4

[0042] The difference between this embodiment and embodiment 1 is that the mass ratio of 1-propyl-3-methyl-imidazole trifluoromethanesulfonyl imide ionic liquid to polyionic liquid is 1:4, and the other aspects are the same as those in embodiment 1.

[0043] Example 5

[0044] The difference between this embodiment and embodiment 1 is that the mass ratio of 1-propyl-3-methyl-imidazole trifluoromethanesulfonyl imide ionic liquid to polyionic liquid is 1:1, and the other aspects are the same as those in embodiment 1.

[0045] Example 6

[0046] The difference between this embodiment and embodiment 1 is that the mass ratio of 1-propyl-3-methyl-imidazole trifluoromethanesulfonyl imide ionic liquid to polyionic liquid is 1:1.5, and the other aspects are the same as those in embodiment 1.

[0047] Example 7

[0048] The difference between this embodiment and embodiment 1 is that the mass ratio of 1-propyl-3-methyl-imidazole trifluoromethanesulfonyl imide ionic liquid to polyionic liquid is 1:3, and the other aspects are the same as those in embodiment 1.

[0049] Comparative Example 1

[0050] The difference between this comparative example and Example 1 is that the polyionic liquid is replaced by polyvinylidene fluoride of the same content, and the other contents are the same as those in Example 1.

[0051] Comparative Example 2

[0052] The difference between this comparative example and Example 1 is that the ionic liquid is replaced by an equal amount of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide lithium, and the polyionic liquid is replaced by poly(1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide lithium). Other contents are the same as in Example 1.

[0053] Test conditions

[0054] The gel polymer electrolyte membranes provided by Examples 1 to 7 and Comparative Examples 1 to 2 were tested using the following test methods:

[0055] (1) Tensile strength: The electrolyte membrane was cut into 2 × 5 cm strips and the tensile strength was tested using a tensile testing machine.

[0056] (2) Ionic conductivity: The electrolyte membrane was cut into 20 mm diameter discs using a punching machine. A button cell was prepared by assembling stainless steel / electrolyte membrane / stainless steel. AC impedance testing was performed using a CHI-660 electrochemical workstation, and the specific conductivity value was obtained using the conductivity formula.

[0057] The test results are shown in Table 1:

[0058] Table 1

[0059]

[0060] As shown in Table 1, the ionic conductivity of the gel polymer electrolyte membranes prepared in Examples 2, 1, and 3 gradually increased with the introduction of different types of ionic liquids, but the mechanical properties of the gel polymer electrolyte membranes gradually decreased. As shown in Examples 1-7, the best overall performance of the gel polymer electrolyte membrane was achieved in Example 1 by adjusting the ratio of ionic liquid to polyionic liquid to 1:2 and the types of both liquids.

[0061] It can be seen from Examples 1 and 4-7 that the more ionic liquid is added, the better. In order to achieve a better balance, by adjusting the ratio of ionic liquid to polyionic liquid to 1:2, the prepared gel polymer electrolyte membrane not only meets certain mechanical properties but also maintains a high ionic conductivity at room temperature.

[0062] Comparative Example 1 shows that although the target of greater tensile strength is achieved by replacing the type of polyionic liquid, the ionic conductivity of the gel polymer electrolyte membrane is greatly reduced.

[0063] Comparative Example 2 shows that replacing the types of ionic liquids and polyionic liquids results in poor compatibility between other types of ionic liquids and polyionic liquids, and also fails to achieve high ionic conductivity.

Claims

1. A gel polymer electrolyte membrane comprising an ionic liquid and a polyionic liquid obtained by polymerizing the ionic liquid.

2. The gel polymer electrolyte membrane according to claim 1, wherein The mass ratio of the ionic liquid to the polyionic liquid is 1:(1-4), and can be optionally 1:

2.

3. The gel polymer electrolyte membrane according to claim 1 or 2, wherein: The ionic liquid includes 1-propyl-3-methyl-imidazole trifluoromethanesulfonimide.

4. The gel polymer electrolyte membrane according to any one of claims 1 to 3, wherein: The polyionic liquid is obtained by free radical polymerization of 1-propyl-3-methyl-imidazole trifluoromethanesulfonyl imide.

5. A method for preparing a gel polymer electrolyte membrane according to any one of claims 1 to 4, comprising the following steps: The polyionic liquid, the solvent and the ionic liquid are mixed to obtain a mixed solution; the mixed solution is cast into a film to obtain the gel polymer electrolyte membrane.

6. The method according to claim 5, wherein: The preparation method of the polyionic liquid comprises reacting an ionic liquid, an initiator and an organic solvent to obtain the polyionic liquid.

7. The method according to claim 6, wherein: The initiator includes azobisisobutyronitrile.

8. The method according to claim 6 or 7, wherein: The reaction temperature is 55-65°C and the reaction time is 18-24h.

9. The method according to any one of claims 5 to 8, wherein: The preparation method of the ionic liquid comprises the following steps: stirring methylimidazole, a halogen-substituted propane compound and an N-methylpyrrolidone solvent, removing the N-methylpyrrolidone solvent to obtain a precursor material; and mixing the precursor material, a lithium salt and water, removing the water to obtain the ionic liquid.

10. The method according to claim 9, wherein: The halogen-substituted propane compound includes a bromopropane compound and / or an iodopropane compound; Optionally, the stirring temperature is room temperature.

11. The method according to claim 9 or 10, wherein: The lithium salt includes bis(fluorosulfonyl)imide lithium salt; Optionally, the mixing is performed at room temperature.

12. The method according to any one of claims 5 to 11, wherein: The solvent includes N,N-dimethylformamide.

13. The method according to any one of claims 5 to 12, wherein: The mixing process includes ultrasonically stirring the polyionic liquid and the solvent for 18-24 hours, and then adding the ionic liquid and continuing to stir for 4-8 hours to obtain a mixed solution.

14. The method according to any one of claims 5 to 13, wherein: The casting film forming process comprises casting the mixed solution on the surface of the substrate and vacuum drying to obtain the gel polymer electrolyte membrane; Optionally, the vacuum drying is carried out at a temperature of 55-65° C. and for a time of 18-24 hours.

15. A secondary battery, wherein: The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and the electrolyte includes the gel polymer electrolyte membrane according to any one of claims 1 to 4.

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