Polyamide semi-solid electrolyte with high lithium salt content as well as preparation method and application of polyamide semi-solid electrolyte

Abstract

The invention discloses a polyamide semi-solid electrolyte with high lithium salt content. The semi-solid electrolyte comprises a film and an electrolyte, the film is obtained by blending polyamide and lithium salt; the polyamide is obtained by polymerizing a fluorine-containing diamine monomer, a diamine monomer 1 and diacyl halide; the diamine monomer 1 is a fluorine-containing diamine monomer; and the diamine monomer 2 is at least one of a diamine monomer containing carboxyl and a diamine monomer containing sulfonic acid group. The invention also discloses a preparation method of the polyamide semi-solid electrolyte with high lithium salt content. The invention also discloses an application of the polyamide semi-solid electrolyte with high lithium salt content in a lithium battery. The semi-solid electrolyte disclosed by the invention has good lithium ion solvation-desolvation capability, can improve the content of lithium salt in a thin film and the ionic conductivity, improves the cycle performance of a battery, and has good mechanical property and high temperature resistance.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a polyamide semi-solid electrolyte with high lithium salt content, its preparation method, and its application. Background Technology

[0002] Semi-solid polymer electrolytes, also known as gel polymer electrolytes, can solve safety issues such as leakage, flammability, and toxicity associated with liquid electrolytes, and can also improve the low ionic conductivity of solid polymer electrolytes. Semi-solid polymer electrolytes consist of a polymer matrix, an electrolyte salt, and a liquid solvent as a plasticizer. The polymer matrix primarily provides mechanical strength, maintains high-temperature stability, and keeps the electrolyte in a quasi-solid state, thereby minimizing the safety risks caused by leakage of liquid components.

[0003] Existing polymer matrices can be aliphatic polymers, polyimides, etc., but aliphatic polymers have insufficient mechanical properties, low glass transition temperatures, and poor temperature resistance. While polyimides have good mechanical properties and high temperature resistance, polyimide films have poor solvation-desolvation lithium-ion capabilities, and the content of lithium salts added to the films cannot be too high, which limits their applications. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a polyamide semi-solid electrolyte with high lithium salt content, its preparation method and application. The semi-solid electrolyte of the present invention has good solvation-desolvation lithium ion capability, which can improve the lithium salt content and ion conductivity in the film, improve the battery cycle performance, and has good mechanical properties and high temperature resistance.

[0005] This invention proposes a polyamide semi-solid electrolyte with high lithium salt content, the semi-solid electrolyte comprising: a thin film and an electrolyte; the thin film is obtained by blending polyamide and lithium salt; the polyamide is obtained by polymerization of a fluorinated diamine monomer, diamine monomer 1, and a diacyl halide;

[0006] Diamine monomer 1 is a fluorinated diamine monomer; diamine monomer 2 is at least one of a carboxyl-containing diamine monomer and a sulfonic acid-containing diamine monomer.

[0007] Preferably, the lithium salt content in the film is 75-85 wt%.

[0008] Preferably, the lithium salt is at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, or lithium bis(fluorosulfonyl)imide.

[0009] Preferably, the weight ratio of the film to the electrolyte is 1:2-4.

[0010] Preferably, the solute in the electrolyte is at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, or lithium bis(fluorosulfonyl)imide.

[0011] Preferably, the solvent of the electrolyte is at least one of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate.

[0012] Preferably, the diamine monomer 1 comprises at least one of: 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, 4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid, 4,4'-diamino-2,2'-biphenyl disulfonic acid, and 4,4'-diamino-3,3'-biphenyl disulfonic acid.

[0013] Preferably, the fluorinated diamine monomer is at least one of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 4,4'-diaminooctafluorobiphenyl.

[0014] Preferably, the diacyl halide is 2,2'-bipyridine-4,4'-dicarboxyl chloride.

[0015] Preferably, the molar ratio of fluorinated diamine monomer, diamine monomer 1, and diacyl halide is 0.75-0.8:0.2-0.25:1.

[0016] The weight-average molecular weight of the above-mentioned polyamides is 10,000-600,000.

[0017] The present invention also proposes a method for preparing the above-mentioned polyamide semi-solid electrolyte with high lithium salt content, comprising the following steps: taking a fluorinated diamine monomer, diamine monomer 1, and diacyl halide and carrying out a polymerization reaction in an organic solvent, adding reagent 1 to remove HCl, and obtaining a polyamide solution; then adding lithium salt to the polyamide solution and mixing well to prepare a film; then soaking or wetting the film with electrolyte to obtain a polyamide semi-solid electrolyte with high lithium salt content.

[0018] The reaction is carried out in an inert gas atmosphere; the polymerization reaction is carried out at room temperature.

[0019] Preferably, the organic solvent is N,N-dimethylacetamide.

[0020] Preferably, reagent 1 is proline.

[0021] Preferably, the solid content of the polyamide solution is 8-12 wt%.

[0022] The present invention also proposes the application of the above-mentioned polyamide semi-solid electrolyte in lithium batteries.

[0023] This invention selects suitable fluorinated diamine monomers, including diamine monomer 1, to introduce biphenyl, pyridine structures, and fluorine elements into polyamide. The synergistic effect of pyridine and fluorine elements enables the polyamide film to possess excellent solvation-desolvation lithium-ion capabilities, thereby increasing the lithium salt content and ionic conductivity of the film. Diamine monomer 1 also incorporates carboxyl or sulfonic acid groups, which can further promote lithium-ion migration and improve ionic conductivity. The synergistic effect of biphenyl, pyridine structures, and fluorine elements can improve the high-temperature resistance and mechanical properties of the film, and maintain the stability of the film volume after absorbing electrolyte, thus improving the cycle stability of the battery.

[0024] Furthermore, by adjusting the amount of fluorinated monomers and controlling the fluorine content, the polyamide film can have a good absorption and retention rate of electrolyte, thereby further improving the ion conductivity and battery cycle performance. It can also avoid the problem of reduced mechanical properties of the film after absorbing electrolyte due to excessive fluorine content, and the stability of mechanical properties can further improve the cycle performance of the battery. Detailed Implementation

[0025] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0026] Example 1

[0027] A polyamide semi-solid electrolyte with high lithium salt content, the semi-solid electrolyte comprising: a thin film and an electrolyte; the thin film is obtained by blending polyamide with lithium hexafluorophosphate;

[0028] The polyamide is obtained by polymerization of 4,4'-diaminooctafluorobiphenyl, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, and 2,2'-bipyridine-4,4'-dicarboxylic acid chloride in a molar ratio of 0.75:0.25:1.

[0029] The preparation method of the above-mentioned high lithium salt content polyamide semi-solid electrolyte includes the following steps: 4,4'-diaminobiphenyl and N,N-dimethylacetamide are added to a three-necked round-bottom flask equipped with a mechanical stirrer and nitrogen inlet and outlet, and stirred to dissolve. Then, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid is added and stirred to dissolve. Nitrogen gas is introduced to purge air. Then, 2,2'-bipyridine-4,4'-dicarboxylic acid chloride is added. The viscosity of the solution increases until a gel is formed. Then, proline is added and stirred to break the gel, forming a viscous and homogeneous solution. The solution is stirred at room temperature for 4 hours. The solid content is adjusted to 8 wt% with N,N-dimethylacetamide to obtain a polyamide solution. Then, lithium hexafluorophosphate is added and mixed. The solution is cast into a film and dried to obtain a film with a thickness of 80 μm. The lithium hexafluorophosphate content in the film is 80 wt%.

[0030] Then, the film was cut into circular pieces with a diameter of 20 mm, and the film was soaked in the electrolyte for 2 hours. Then, the film was taken out and the residual electrolyte on the surface of the film was wiped dry to obtain a polyamide semi-solid electrolyte with high lithium salt content. The electrolyte was a 1 mol / L lithium hexafluorophosphate solution, and the solvent was an equal volume of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate. The weight ratio of the film to the electrolyte was 1:3.1.

[0031] Example 2

[0032] A polyamide semi-solid electrolyte with high lithium salt content, the semi-solid electrolyte comprising: a thin film and an electrolyte; the thin film is obtained by blending polyamide with lithium bis(fluorosulfonyl)imide;

[0033] The polyamide is obtained by polymerization of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-biphenyl disulfonic acid, and 2,2'-bipyridine-4,4'-dicarboxylic acid chloride in a molar ratio of 0.8:0.2:1.

[0034] The preparation method of the above-mentioned high lithium salt content polyamide semi-solid electrolyte includes the following steps: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and N,N-dimethylacetamide are added to a three-necked round-bottom flask equipped with a mechanical stirrer and nitrogen inlet and outlet, and stirred to dissolve. Then, 4,4'-diamino-2,2'-biphenyl disulfonic acid is added and stirred to dissolve. Nitrogen gas is introduced to purge air. Then, 2,2'-bipyridine-4,4'-dicarboxyl chloride is added. The viscosity of the solution increases until a gel is formed. Then, proline is added and stirred to break the gel, forming a viscous and homogeneous solution. The solution is stirred at room temperature for 4 hours. The solid content is adjusted to 12 wt% with N,N-dimethylacetamide to obtain a polyamide solution. Then, lithium bis(fluorosulfonyl)imide is added and mixed. The solution is cast into a film and dried to obtain a film with a thickness of 80 μm. The content of lithium bis(fluorosulfonyl)imide in the film is 75 wt%.

[0035] Then, the film was cut into circular pieces with a diameter of 20 mm, and the film was soaked in the electrolyte for 2 hours. Then, the film was taken out and the residual electrolyte on the surface of the film was wiped dry to obtain a polyamide semi-solid electrolyte with high lithium salt content. The electrolyte was a 1 mol / L lithium bis(fluorosulfonyl)imide solution, and the solvent was an equal volume of methyl ethyl carbonate, dimethyl carbonate and diethyl carbonate. The weight ratio of the film to the electrolyte was 1:3.3.

[0036] Example 3

[0037] A polyamide semi-solid electrolyte with high lithium salt content, the semi-solid electrolyte comprising: a thin film and an electrolyte; the thin film is obtained by blending polyamide with lithium bis(trifluoromethanesulfonyl)imide;

[0038] The polyamide is obtained by polymerization of 4,4'-diaminooctafluorobiphenyl, 4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid, and 2,2'-bipyridine-4,4'-dicarboxylic acid chloride in a molar ratio of 0.77:0.23:1.

[0039] The preparation method of the above-mentioned high lithium salt content polyamide semi-solid electrolyte includes the following steps: 4,4'-diaminooctafluorobiphenyl and N,N-dimethylacetamide are added to a three-necked round-bottom flask equipped with a mechanical stirrer and nitrogen inlet and outlet, and stirred to dissolve. Then, 4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid is added and stirred to dissolve. Nitrogen gas is introduced to purge air. Then, 2,2'-bipyridine-4,4'-dicarboxyl chloride is added. The viscosity of the solution increases until a gel is formed. Then, proline is added and stirred to break the gel, forming a viscous and homogeneous solution. The solution is stirred at room temperature for 4 hours. The solid content is adjusted to 10 wt% with N,N-dimethylacetamide to obtain a polyamide solution. Then, lithium bis(trifluoromethanesulfonyl)imide is added and mixed. The solution is cast into a film and dried to obtain a film with a thickness of 80 μm. The content of lithium bis(trifluoromethanesulfonyl)imide in the film is 85 wt%.

[0040] Then, the film was cut into circular pieces with a diameter of 20 mm, and the film was soaked in the electrolyte for 2 hours. Then, the film was taken out and the residual electrolyte on the surface of the film was wiped dry to obtain a polyamide semi-solid electrolyte with high lithium salt content. The electrolyte was a 1 mol / L bis(trifluoromethanesulfonyl)imide lithium solution, and the solvent was an equal volume of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate. The weight ratio of the film to the electrolyte was 1:3.2.

[0041] Comparative Example 1

[0042] A method for preparing a polyamide semi-solid electrolyte with high lithium salt content includes the following steps:

[0043] Replace “2,2'-bipyridine-4,4'-dicarboxylic acid chloride” with “terephthaloyl chloride”, otherwise the same as in Example 3.

[0044] Comparative Example 2

[0045] A method for preparing a polyamide semi-solid electrolyte with high lithium salt content includes the following steps:

[0046] Replace “4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid” with “4,4'-diaminooctafluorobiphenyl”, otherwise the same as in Example 3.

[0047] Comparative Example 3

[0048] A method for preparing a polyamide semi-solid electrolyte with high lithium salt content includes the following steps:

[0049] Replace “4,4'-diaminooctafluorobiphenyl” with “4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid”, otherwise the same as in Example 3.

[0050] The performance of the semi-solid electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 was tested, and the results are shown in Table 1.

[0051] Thermal stability was tested in an N2 atmosphere using thermogravimetric analysis in the range of 80-600℃.

[0052] The method for detecting ionic conductivity is as follows: a semi-solid electrolyte is sandwiched between two stainless steel electrodes (SS) to assemble an SS||ISM||SS ion-barrier battery, its intrinsic resistance R is measured, and the ionic conductivity is calculated according to the formula σ=d / (A*R), where σ is the ionic conductivity, d is the film thickness, and A is the effective area.

[0053] LFP||ISM||Li half-cells were prepared using a semi-solid electrolyte, and their cycle performance was tested.

[0054] Table 1 Test Results

[0055]

[0056]

[0057] As can be seen from Table 1, the polyamide semi-solid electrolyte prepared by this invention maintains good mechanical properties and high temperature resistance while maintaining a high lithium salt content; and the prepared lithium battery has high ionic conductivity and good cycle stability.

[0058] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A polyamide semi-solid electrolyte with high lithium salt content, characterized in that, The semi-solid electrolyte comprises: a thin film and an electrolyte solution; the thin film is obtained by blending polyamide with lithium salt; the polyamide is obtained by polymerization of fluorine-containing diamine monomer, diamine monomer 1 and diacyl halide; The diamine monomer 1 is a fluorine-containing diamine monomer; the diamine monomer 2 is at least one of a carboxyl-containing diamine monomer and a sulfonic acid group-containing diamine monomer.

2. The high lithium salt content polyamide semi-solid electrolyte of claim 1, wherein, The content of lithium salt in the thin film is 75-85wt%; preferably, the lithium salt is at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluorosulfonyl)imide.

3. The high lithium salt content polyamide semi-solid electrolyte according to claim 1 or 2, characterized in that, The weight ratio of the thin film to the electrolyte solution is 1:2-4; preferably, the solute of the electrolyte solution is at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluorosulfonyl)imide; preferably, the solvent of the electrolyte solution is at least one of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate or diethyl carbonate.

4. The high-lithium content polyamide semi-solid electrolyte according to any one of claims 1-3, characterized in that, The diamine monomer 1 comprises at least one of 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, 4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid, 4,4'-diamino-2,2'-biphenyldisulfonic acid and 4,4'-diamino-3,3'-biphenyldisulfonic acid.

5. The high-lithium content polyamide semi-solid electrolyte according to any one of claims 1-4, characterized in that, The fluorine-containing diamine monomer is at least one of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 4,4'-diamino octafluorobiphenyl.

6. The high-lithium content polyamide semi-solid electrolyte according to any one of claims 1-5, characterized in that, The diacyl halide is 2,2'-bipyridine-4,4'-dicarboxylic chloride.

7. The high-lithium content polyamide semi-solid electrolyte according to any one of claims 1-6, characterized in that, The molar ratio of the fluorine-containing diamine monomer, the diamine monomer 1 and the diacyl halide is 0.75-0.8:0.2-0.25:

1.

8. A method for producing a high lithium salt content polyamide semi-solid electrolyte according to any one of claims 1 to 7, characterized by, The method comprises the following steps: polymerizing the fluorine-containing diamine monomer, the diamine monomer 1 and the diacyl halide in an organic solvent, adding reagent 1 to remove HCl to obtain a polyamide solution; then adding lithium salt to the polyamide solution and mixing to prepare a thin film; then soaking or wetting the thin film with an electrolyte solution to obtain a high-lithium-salt-content polyamide semi-solid electrolyte.

9. The method of claim 8, wherein the high lithium salt content polyamide semi-solid electrolyte is prepared by the steps of: a) dissolving a lithium salt in a solvent; b) adding a polyamide to the solution of step a); and c) removing the solvent from the solution of step b) to form the high lithium salt content polyamide semi-solid electrolyte. The organic solvent is N,N-dimethylacetamide; preferably, the reagent 1 is proline; preferably, the solid content of the polyamide solution is 8-12wt%.

10. Use of the high-lithium-salt-content polyamide semi-solid electrolyte according to any one of claims 1-7 in a lithium battery.

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