A poss-based zwitterionic polymer electrolyte membrane and a method of making the same

Abstract

The application discloses a POSS-based zwitterionic polymer electrolyte film and a preparation method thereof, and relates to the technical field of solid electrolytes. First, a zwitterionic monomer is prepared, and the zwitterionic monomer and nano POSS material are introduced into the preparation of a polymer electrolyte film, so that a polymer electrolyte film with high ionic conductivity is obtained, and the problems of poor safety of a commercial liquid electrolyte and low ionic conductivity of a traditional polymer electrolyte are solved.

Description

Technical Field

[0001] This invention relates to the field of solid electrolytes, specifically to a POSS-based zwitterionic polymer electrolyte membrane and its preparation method. Background Technology

[0002] With the widespread adoption of 5G communication technology and the ever-growing demand for electric vehicles, high-energy-density lithium metal batteries have become a research hotspot in recent years. However, the traditional liquid electrolyte in lithium metal batteries uses flammable and volatile organic solvents, posing safety hazards such as electrolyte leakage, combustion, and uncontrolled lithium dendrite growth leading to short circuits, severely hindering the commercial application of lithium metal batteries. Solving these safety issues is imperative for the development of next-generation lithium metal batteries.

[0003] All-solid-state polymer electrolytes contain no volatile organic solvents, exhibit excellent stability and good contact with electrodes, which fundamentally eliminates many safety hazards. However, all-solid-state polymer electrolytes still suffer from low conductivity (room temperature ionic conductivity only reaches approximately 1 × 10⁻⁶). -5 S cm -2 The current method for addressing conductivity issues cannot meet the application requirements of electrolytes. A common approach to solving this problem is to convert all-solid-state electrolytes into gel polymer electrolytes. However, this inevitably introduces the electrolyte back into the electrolyte system, and safety risks remain. Therefore, there is an urgent need to develop a new all-solid-state polymer electrolyte with high ionic conductivity to pave the way for next-generation lithium metal batteries. Summary of the Invention

[0004] To address the problems of existing technologies, the present invention aims to overcome the shortcomings of existing technologies and provide a POSS-based zwitterionic polymer electrolyte membrane and its preparation method. By chemically crosslinking, POSS and zwitterions are introduced into the polymer electrolyte membrane with polyethylene glycol diacrylate as the backbone, thereby improving the ionic conductivity of the solid polymer electrolyte membrane and solving the problems of poor safety of commercial liquid electrolytes and low ionic conductivity of traditional polymer electrolytes.

[0005] One objective of this invention is to provide a technical solution for a method of preparing zwitterionic monomers, specifically as follows:

[0006] A method for preparing a zwitterionic monomer includes the following steps:

[0007] S11: Trifluoromethanesulfonamide, 3-chloropropanesulfonyl chloride, and lithium hydroxide are dissolved in anhydrous acetonitrile and reacted at 0°C. After the reaction is complete, the reactants are filtered, recrystallized, and vacuum dried to obtain a white solid powder.

[0008] S12. Dissolve the white solid powder and 1-vinylimidazole in N,N-dimethylformamide and reflux at 120°C. After the reaction is complete, add anhydrous acetonitrile, then filter, collect the filtrate, concentrate the filtrate, and precipitate with ethyl acetate to obtain the initial solid product. After washing and vacuum drying, obtain the zwitterionic monomer.

[0009] The second objective of this invention is to provide a technical solution for a zwitterionic monomer, specifically as follows:

[0010] An amphoteric monomer is prepared using the above-described method for preparing amphoteric monomers.

[0011] The structural formula of the zwitterionic monomer is:

[0012]

[0013] The third objective of this invention is to provide a technical solution for a POSS-based zwitterionic polymer electrolyte membrane formulation, specifically as follows:

[0014] A POSS-based zwitterionic polymer electrolyte membrane formulation comprises the following components:

[0015]

[0016] Preferably, the crosslinking agent is one or more of pentaerythritol tetraacrylate, pentaerythritol triacrylate, or pentaerythritol tetra-3-mercaptopropionate.

[0017] Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium dioxaborate.

[0018] Preferably, the initiator is one or more of azobisisobutyronitrile, 2-hydroxy-2-methyl-1-phenyl-1-propanone, or α,α-dimethoxy-α-phenylacetophenone.

[0019] The fourth objective of this invention is to provide a technical solution for preparing a POSS-based zwitterionic polymer electrolyte membrane using the above-mentioned POSS-based zwitterionic polymer electrolyte membrane formulation, specifically as follows:

[0020] A method for preparing a POSS-based zwitterionic polymer electrolyte membrane includes the following steps:

[0021] S21. Prepare a solution containing poly(vinylidene fluoride-hexafluoropropylene) and POSS, and stir it at 70-80°C until it is completely dissolved to form a uniform and transparent organic solution.

[0022] S22. Add polyethylene glycol diacrylate, crosslinking agent, zwitterionic monomer, lithium salt and initiator to the organic solution, and then stir evenly at 70°C to obtain the precursor solution.

[0023] S23. The precursor solution is coated on a glass plate and photoinitiated to obtain an initial POSS electrolyte membrane.

[0024] S24. The initial POSS electrolyte membrane is dried at 70-80°C to obtain the POSS-based zwitterionic polymer electrolyte membrane.

[0025] Preferably, in step S21, the POSS monomer is nano-sized heptaisobutylmethacryloxypropyl cage-type polysilsesquioxane.

[0026] Preferably, in step S21, the solvent of the organic solution is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylacetamide (NMA), or isopropanol.

[0027] The fifth objective of this invention is to provide a technical solution for a POSS-based zwitterionic polymer electrolyte membrane, specifically as follows:

[0028] A POSS-based zwitterionic polymer electrolyte membrane is prepared by the above-mentioned preparation method of a POSS-based zwitterionic polymer electrolyte membrane, wherein the POSS-based zwitterionic polymer electrolyte membrane has a 3D cross-linked network.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] The present invention provides a formulation and preparation method for a POSS-based zwitterionic polymer electrolyte membrane. First, by introducing POSS groups, a 3D cross-linked network is generated inside the polymer electrolyte membrane, which not only improves the mechanical properties and enhances the safety of the polymer electrolyte membrane, but also, while disrupting the internal regularity of the polymer electrolyte, provides more lithium-ion jumping points in conjunction with the EO segments in polyethylene glycol diacrylate, thereby improving ionic conductivity. Second, the organic-inorganic hybrid nanomaterial POSS, with its internal Si-O-Si structure, promotes lithium-ion conduction and improves the effective migration rate of lithium ions in the electrolyte system.

[0031] On the other hand, the present invention also provides a method for preparing a zwitterionic monomer and introducing the zwitterionic monomer into a polymer electrolyte membrane. Due to the strong electronegativity of fluorine atoms in zwitterions, the electron density is higher around fluorine atoms, forming a negative charge, while the electron density around sulfur atoms is lower, forming a positive charge. This charge asymmetry results in a difference in the distribution of positive and negative charges, which gives zwitterions a large dipole moment, thereby promoting the dissociation of lithium salt in the electrolyte system, releasing more mobile free ions, improving ion migration efficiency, and thus promoting ion conduction. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the synthesis principle of zwitterionic monomers in this invention.

[0033] Figure 2 The impedance spectra of the electrolyte membrane prepared in Example 2 of this invention at 25°C and 75°C are shown. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] To facilitate understanding, the abbreviations or names mentioned below will be explained first:

[0036] DMF: N,N-dimethylformamide;

[0037] POSS: cage-type polysilsesquioxane;

[0038] MAPOSS: Heptaisobutylmethacryloyloxypropyl cage-type polysilsesquioxane.

[0039] This specific embodiment provides an example of a method for preparing a zwitterionic monomer, and also provides an example of a method for preparing a POSS-based zwitterionic polymer electrolyte membrane using the zwitterionic monomer.

[0040] First, we introduce an example of a method for preparing zwitterionic monomers.

[0041] Example 1

[0042] A method for preparing a zwitterionic monomer includes the following steps:

[0043] S11: Trifluoromethanesulfonamide, 3-chloropropanesulfonyl chloride, and lithium hydroxide are dissolved in anhydrous acetonitrile at a molar ratio of 1:1:0.2 (the amount of solvent is preferably sufficient to completely dissolve the solute; in this example, the solute-solvent ratio is 0.5 g / ml). The reaction is carried out at 0°C. After the reaction is completed, the reactants are filtered, recrystallized, and vacuum dried to obtain a white solid powder.

[0044] S12. Dissolve the white solid powder and 1-vinylimidazole in N,N-dimethylformamide at a molar ratio of 1:1 and reflux at 120°C. After the reaction is complete, add anhydrous acetonitrile to completely precipitate the inorganic salt (in this example, the mass ratio of white solid powder to anhydrous acetonitrile is 3:50). Then filter, collect the filtrate and concentrate it by rotary evaporation. Add ethyl acetate to the concentrated filtrate to precipitate and obtain the initial solid product. After washing and vacuum drying, obtain the zwitterionic monomer.

[0045] In this embodiment, in step S1, the reaction at 0°C is carried out using an ice bath for 24 hours to ensure a complete reaction.

[0046] In step S12, the reaction is refluxed at 120°C for 48 hours to ensure a complete reaction.

[0047] In step S12, the initial solid product is washed three times with ethanol and then vacuum dried at 80°C.

[0048] Specifically, the synthetic route of the zwitterionic monomer in this embodiment is as follows: Figure 1 As shown.

[0049] The structural formula of the prepared zwitterionic monomer is:

[0050]

[0051] It is a molecule that is locally charged but generally neutral, with cation and anion groups covalently linked.

[0052] Example 2

[0053] A method for preparing a zwitterionic monomer, the steps of which are basically the same as those in Example 1 above, with the difference being:

[0054] In step S11, the molar ratio of trifluoromethanesulfonamide, 3-chloropropanesulfonyl chloride, and lithium hydroxide is 1:1:0.3.

[0055] In step S12, the reflux temperature is 110℃ and the vacuum drying temperature is 60℃.

[0056] Example 3

[0057] A method for preparing a zwitterionic monomer, the steps of which are basically the same as those in Example 1 above, with the difference being:

[0058] In step S11, the molar ratio of trifluoromethanesulfonamide, 3-chloropropanesulfonyl chloride, and lithium hydroxide is 1:1:0.5.

[0059] In step S12, the reflux temperature is 115℃ and the vacuum drying temperature is 70℃.

[0060] The following is an example of a method for preparing a POSS-based zwitterionic polymer electrolyte membrane.

[0061] A method for preparing a POSS-based zwitterionic polymer electrolyte membrane includes the following steps:

[0062] S21. Prepare an organic solution by adding poly(vinylidene fluoride-hexafluoropropylene) to DMF and dissolving it completely (solute-to-solvent ratio of 1 g / ml), and adding POSS monomer to isopropanol and dissolving it completely (solute-to-solvent ratio of 0.4 g / ml). Mix the two solutions and stir at 70°C until they are completely dissolved to form a uniform and transparent solution.

[0063] S22. Add polyethylene glycol diacrylate, pentaerythritol tetraacrylate, zwitterionic monomer, lithium bis(fluorosulfonyl)imide, and 2-hydroxy-2-methyl-1-phenyl-1-propanone to the solution described in S21, and then stir evenly at 70°C to obtain the precursor solution.

[0064] S23. The precursor solution is coated onto a glass plate using a glass plate pressing method, and photoinitiated for 20 minutes to obtain the initial POSS electrolyte membrane.

[0065] S24. Peel the initial POSS electrolyte membrane off the glass plate and dry it in an oven at 75°C to obtain a POSS-based zwitterionic polymer electrolyte membrane.

[0066] It should be noted that in step S21, the solvent of the organic solution can be replaced with one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylacetamide (NMA), or isopropanol;

[0067] Pentaerythritol tetraacrylate may be replaced by one or more of pentaerythritol tetraacrylate, pentaerythritol triacrylate or pentaerythritol tetra-3-mercaptopropionate;

[0068] Lithium bis(fluorosulfonyl)imide can be replaced by one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide or lithium dioxolaneborate.

[0069] 2-Hydroxy-2-methyl-1-phenyl-1-propanone may be replaced by one or more of azobisisobutyronitrile, 2-hydroxy-2-methyl-1-phenyl-1-propanone or α,α-dimethoxy-α-phenylacetophenone;

[0070] In step S22, it is best to control the temperature during stirring within the range of 70-80℃.

[0071] In step S24, it is best to control the drying temperature within the range of 70 to 80°C.

[0072] Furthermore, the structural formula of the zwitterionic monomer is:

[0073]

[0074] Furthermore, the POSS monomer used is a nanoscale MAPOSS monomer, with the following structural formula:

[0075]

[0076] Where R = isobutyl

[0077] Furthermore, the average molecular weight of poly(vinylidene fluoride-hexafluoropropylene) is 400,000; the average molecular weight of polyethylene glycol diacrylate is 200–5,000.

[0078] The prepared POSS-based zwitterionic polymer electrolyte membrane has a 3D cross-linked network.

[0079] The following are several examples of the preparation method of the above-mentioned POSS-based zwitterionic polymer electrolyte membrane, wherein the amount of DMF is 10 mL (mass concentration of 1 to 2 parts per mL), the amount of isopropanol is 10 mL (mass concentration of 0.2 to 0.8 parts per mL), and other formulations are shown in Table 1.

[0080] Table 1 Formulations of the four embodiments

[0081]

[0082] In the comparative example, 10 parts of poly(vinylidene fluoride-hexafluoropropylene), 53 parts of polyethylene glycol diacrylate, 2 parts of pentaerythritol tetraacrylate, 35 parts of lithium bis(fluorosulfonyl)imide, and 1 part of 2-hydroxy-2-methyl-1-phenyl-1-propanone were added to DMF and completely dissolved (solute-to-solvent ratio of 0.5 g / ml). The solution was stirred at 70°C until completely dissolved to form a homogeneous and transparent comparative precursor solution. The comparative precursor solution did not contain POSS or zwitterions.

[0083] The precursor solution was subjected to photoinitiation for 20 minutes using a glass plate pressing method to obtain an initial electrolyte membrane free of POSS and zwitterions.

[0084] The initial electrolyte membrane, free of POSS and zwitterions, was peeled off from the glass plate and dried in an oven at 75°C to obtain a polymer electrolyte membrane free of POSS and zwitterions.

[0085] The electrolyte membranes prepared in Examples 4 to 7 and the comparative example were respectively used to assemble 2016 type button batteries with two stainless steel sheets, and tested in a frequency range of 1.0 × 10⁻⁶. 6 Ionic conductivity was measured at Hz to 0.1 Hz, 25 °C, and 75 °C, respectively.

[0086] The impedance spectrum of the electrolyte membrane prepared in Example 5 is as follows: Figure 2 As shown, the polymer electrolyte membrane containing POSS and zwitterions exhibits low impedance. The volume resistance R (Ω) of the electrolyte is taken as the value of Z' (Ω) when -Z" (Ω) has a minimum, and the ionic conductivity of the electrolyte is calculated using σ = L / (R × S). Here, L is the polymer electrolyte membrane thickness of 150 μm, and S is the area of ​​the stainless steel electrode sheet of 2.06 cm². 2 Its ionic conductivity at 25℃ was calculated to be 7.71 × 10⁻⁶. -4 S cm -1 The ionic conductivity at 75℃ is 1.48 × 10⁻⁶. -3 S cm -1 .

[0087] The test results for each embodiment and comparative example are shown in Table 2.

[0088] Table 2. Ionic conductivity test results of electrolyte membrane-assembled batteries in Examples 4 to 7 and Comparative Examples.

[0089]

[0090] It can be seen that, compared with the comparative examples, the ionic conductivity of Examples 4 to 7 is significantly improved.

[0091] In summary, in Examples 4 to 7, the zwitterions act as "ion dissociation agents," promoting lithium-ion conduction in the polymer electrolyte membrane and serving as additives to increase the transport of target ions in the electrolyte system.

[0092] The selected POSS is an organic-inorganic hybrid nanomaterial, which is a molecule with a highly ordered cage structure composed of Si-O-Si bonds. In this invention, a larger volume POSS is introduced to inhibit the crystallization of the polymer backbone. Moreover, its internal inorganic silicon-oxygen structure promotes lithium-ion conduction and increases the heat resistance, flame retardancy and electrochemical stability of the polymer electrolyte membrane.

[0093] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended embodiments and their equivalents.

Claims

1. A POSS-based zwitterionic polymer electrolyte membrane formulation, characterized in that, It contains the following components: The structural formula of the zwitterionic monomer is as follows: 。 2. The electrolyte membrane formulation according to claim 1, characterized in that, The crosslinking agent is one or more of pentaerythritol tetraacrylate, pentaerythritol triacrylate, or pentaerythritol tetra-3-mercaptopropionate.

3. The electrolyte membrane formulation according to claim 1, characterized in that, The lithium salt is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, or lithium dioxaborate.

4. The electrolyte membrane formulation according to claim 1, characterized in that, The initiator is one or more of azobisisobutyronitrile, 2-hydroxy-2-methyl-1-phenyl-1-propanone, or α,α-dimethoxy-α-phenylacetophenone.

5. The electrolyte membrane formulation according to claim 1, characterized in that, The preparation method of the zwitterionic monomer includes the following steps: S11: Trifluoromethanesulfonamide, 3-chloropropanesulfonyl chloride, and lithium hydroxide are dissolved in anhydrous acetonitrile and reacted at 0°C. After the reaction is complete, the reactants are filtered, recrystallized, and vacuum dried to obtain a white solid powder. S12. Dissolve the white solid powder and 1-vinylimidazole in N,N-dimethylformamide and reflux at 120°C. After the reaction is complete, add anhydrous acetonitrile, then filter, collect the filtrate, concentrate the filtrate, and precipitate with ethyl acetate to obtain the initial solid product. After washing and vacuum drying, obtain the zwitterionic monomer.

6. A method for preparing a POSS-based zwitterionic polymer electrolyte membrane, characterized in that, It is prepared using the electrolyte membrane formulation according to any one of claims 1 to 5, and includes the following steps: S21. Prepare a solution containing poly(vinylidene fluoride-hexafluoropropylene) and POSS, and stir it at 70~80℃ until it is completely dissolved to form a uniform and transparent organic solution. S22. Add polyethylene glycol diacrylate, crosslinking agent, zwitterionic monomer, lithium salt and initiator to the organic solution, and then stir evenly at 70°C to obtain the precursor solution. S23. The precursor solution is coated on a glass plate and photoinitiated to obtain an initial POSS electrolyte membrane. S24. The initial POSS electrolyte membrane is dried at 70-80°C to obtain the POSS-based zwitterionic polymer electrolyte membrane.

7. The preparation method according to claim 6, characterized in that, In step S21, the POSS monomer is nano-sized heptaisobutylmethacryloxypropyl cage-type polysilsesquioxane.

8. The preparation method according to claim 6, characterized in that, The solvent of the organic solution is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylacetamide (NMA), or isopropanol.

9. A POSS-based zwitterionic polymer electrolyte membrane, prepared by any one of the preparation methods described in claims 6 to 8, wherein the POSS-based zwitterionic polymer electrolyte membrane has a 3D cross-linked network.

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