Flame-retardant solid polymer electrolyte as well as preparation method and application thereof and gel polymer electrolyte of flame-retardant solid polymer electrolyte

Abstract

The invention relates to the technical field of battery electrolytes, in particular to a flame-retardant solid polymer electrolyte and a preparation method and application thereof and a gel polymer electrolyte.The preparation method comprises the steps that a lithium salt, a polymer monomer, a cross-linking agent, an initiator, an additive and an organic solvent are mixed, heated and stirred to be uniform, and a precursor is obtained; and introducing a catalyst into the precursor to polymerize and cure the precursor to obtain the solid polymer electrolyte. The solid polymer electrolyte prepared by the invention has extremely strong flame retardant property; a unique cross-linked structure enhances the mechanical strength, and destroys the regularity of a polyether chain segment, so that the polyether chain segment is in an amorphous state, and therefore, the polyether chain segment has high ionic conductivity; due to the introduction of bicyclic carbonate, the oxidation stability is enhanced, high stability is shown on a high-voltage positive electrode, and the lithium ion transference number of the electrolyte is also increased to a certain extent; and finally, the assembled battery shows excellent cycling stability and rate capability.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrolytes, and particularly relates to a flame-retardant solid polymer electrolyte, a preparation method and an application thereof, and a gel polymer electrolyte. Background Art

[0002] As a representative of a new generation of battery technologies, lithium metal batteries are regarded as energy storage batteries with great development potential due to their significant advantages such as high theoretical specific capacity and low electrode potential. However, currently, liquid lithium-ion batteries are still widely used in the market. Due to the safety hazards existing when lithium metal contacts with liquid electrolytes, accidents such as combustion and even explosion are likely to occur, which greatly restricts the commercialization process and wide application of lithium metal batteries, and belongs to a major problem existing in the application of current lithium metal batteries.

[0003] In order to overcome the above problems, efforts have been made to find safer and more efficient electrolyte materials. As an ideal choice to replace liquid electrolytes, solid polymer electrolytes are the best solutions to solve the problems of combustion and explosion and improve the energy density of lithium batteries. Poly(ethylene oxide) (PEO), as one of the most commonly used solid polymer electrolytes at present, occupies an important position in the field of solid electrolytes due to its good solvation ability for lithium salts, excellent ionic conductivity and thermal properties at high temperatures, and overall excellent electrochemical properties. However, a significant defect of PEO-based electrolytes is that they do not have flame-retardant properties, and there is still little research on the application of flame-retardant polymer solid electrolytes in lithium metal batteries. Therefore, improving the flame-retardant performance of polymer solid electrolytes is of great significance for the development of high-safety lithium batteries.

[0004] In view of this, the research on flame-retardant polymer solid electrolytes is particularly important. Polyphosphoester, as a biodegradable polymer material with a phosphoester bond as the main chain, has been widely used in the biomedical field due to its unique structure, rich physical and chemical properties, and good biocompatibility. Particularly importantly, polyphosphoester has attracted much attention due to the high flame retardancy of phosphorus elements. During the combustion process, polyphosphoester can quickly form a dense isolation layer to effectively isolate the surrounding oxygen, thus achieving a significant flame-retardant effect. This property makes solid electrolytes based on polyphosphoester have significant advantages in improving the safety of lithium batteries and helps to significantly reduce the risk of thermal runaway of the battery under extreme conditions.

[0005] In addition, polyphosphoester also exhibits excellent electrochemical stability and mechanical properties, and has good compatibility with electrode materials, which helps to reduce interfacial side reactions and further improve the cycle stability of the battery. However, the ionic conductivity of polyphosphoester is relatively low, especially only 10 -6 S cm -1, this value is much lower than the actual usage requirements of lithium batteries. Therefore, how to improve the ionic conductivity of polyphosphate while maintaining its flame retardancy has become a key issue that urgently needs to be solved.

[0006] On the other hand, although polyethers (such as PEO) have high dielectric constants and lithium salt solubilities, the polyether segments have good regularity and are extremely easy to crystallize. The ionic conductivity of polymers mainly depends on the segmental motion in the amorphous region, and the regular segments in the crystalline region hardly contribute to the ionic conductivity. Therefore, the ionic conductivity of polyether electrolytes is very low at room temperature. Although the ionic conductivity increases at high temperatures, the significant reduction in mechanical strength limits its application in high-temperature environments. Therefore, how to improve its crystallinity, increase ionic conductivity and mechanical strength while maintaining the excellent properties of polyether materials is also an important challenge in the field of solid electrolytes. Summary of the Invention

[0007] To solve the deficiencies of the existing technology, the present invention provides a flame-retardant solid polymer electrolyte, its preparation method and application, and its gel polymer electrolyte, which can improve the flame retardancy, increase the ionic conductivity and mechanical strength while maintaining the excellent properties of the polymer solid electrolyte. The solid polymer electrolyte prepared by combining polyether and polyphosphate through a cross-linked structure can make up for each other's advantages and disadvantages, and improve the flame retardancy and electrochemical stability of the polyether electrolyte. The introduction of the polycarbonate cross-linked structure can improve the mechanical strength of the polymer solid electrolyte, disrupt the regularity of the polyether segments, reduce the room-temperature crystallinity, increase the ionic conductivity, and achieve better electrochemical performance; in addition, the introduction of polyphosphate and polycarbonate also endows the solid electrolyte with biodegradability.

[0008] To achieve the above object, the technical solution of the present invention is: a preparation method of a flame-retardant solid polymer electrolyte, comprising the following steps:

[0009] (1) Mix a lithium salt, a polymer monomer, a cross-linking agent, an initiator, an additive and an organic solvent, and heat and stir evenly to obtain a precursor;

[0010] (2) Then introduce a catalyst into the precursor to polymerize and solidify the precursor to obtain a solid polymer electrolyte;

[0011] The structural general formula of the polymer monomer is formula (Ⅰ), and the structural general formula of the cross-linking agent is formula (Ⅱ). The structural formulas of formula (Ⅰ) and formula (Ⅱ) are as follows:

[0012]

[0013] Among them, R1 is selected from one of hydrogen, halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, and substituted or unsubstituted heteroatom-containing groups;

[0014] R2 is selected from -O-, -CH2OCH2-, -CH2OC(=O)OCH2-, -(CH2) x -, -CH2OC(=O)(CH2) y C(=O)OCH2-, -CH2OC(=O)O(CH2) z OC(=O)OCH2-, -CH2OC(=O)CH2(CH2OCH2) m CH2C(=O)OCH2-, CH2OC(=O)OCH2(CH2OCH2)nCH2OC(=O)OCH2-, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, or a substituted or unsubstituted heteroatom-containing group;

[0015] Wherein, when being substituted, the substituent is selected from halogen; the heteroatom is selected from at least one of B, N, O, Si, and P; x, y, and z are all integers greater than or equal to 1, and m and n are both integers greater than or equal to 0; the number of carbon atoms in the alkyl group is less than or equal to 20; the number of carbon atoms in the alkenyl group is less than or equal to 20; the number of carbon atoms in the alkynyl group is less than or equal to 20; the number of carbon atoms in the heteroatom-containing group is less than or equal to 20.

[0016] Furthermore, the molar ratio of the polymer monomer, crosslinking agent, initiator, and catalyst is 50 - 500:5:4.5:0.9, the mass of the lithium salt accounts for 0.1 - 50.0 wt% of the total mass of the solid polymer electrolyte, the mass of the additive accounts for 0 - 80.0 wt% of the total mass of the solid polymer electrolyte, and the mass of the organic solvent accounts for 0 - 80.0 wt% of the total mass of the solid polymer electrolyte.

[0017] Furthermore, the structural general formula of the initiator is formula (III), and the structural formula of formula (III) is as follows:

[0018]

[0019] R3 is selected from -(CH2) a -, -(CH2OCH2) b -, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, or a substituted or unsubstituted heteroatom-containing group;

[0020] Among them, when being substituted, the substituent is selected from halogens; the heteroatom is selected from at least one of B, N, O, Si, P, and S; both a and b are integers greater than or equal to 1; the number of carbon atoms in the alkyl group is less than or equal to 20; the number of carbon atoms in the alkenyl group is less than or equal to 20; the number of carbon atoms in the alkynyl group is less than or equal to 20; the number of carbon atoms in the heteroatom-containing group is less than or equal to 20.

[0021] Furthermore, the lithium salt is selected from one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium oxalato(phosphate), lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(difluoromethanesulfonyl)imide salt, and lithium bis(trifluoromethylsulfonyl)imide.

[0022] Furthermore, the organic solvent is selected from one or more of diethyl ether, benzene, toluene, xylene, chloroform, carbon disulfide, acetonitrile, acetone, N,N-dimethylpyrrolidone, N,N-dimethylformamide, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethylene sulfite, allyl methyl carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, ethyl propionate, propyl propionate, ethyl acetate, n-butyl acetate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, tetrahydropyran, dioxolane, dimethyl sulfoxide, and dimethyl sulfone.

[0023] Furthermore, the additive is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid, polyacrylonitrile, poly(methyl methacrylate carbonate), polyethylene oxide, polyethylene, polypropylene, polyamide, polyimide, polyvinyl alcohol, polyvinyl butyral, polysiloxane, polytetrafluoroethylene, inorganic filler oxide solid electrolyte, sulfide solid electrolyte, silicon monoxide, silicon dioxide, titanium oxide, zirconium oxide, aluminum oxide, boehmite, montmorillonite, plastic crystal, and tetraethylene glycol dimethyl ether.

[0024] Furthermore, the catalyst is selected from one or more of 1,8-diazabicyclo[5,4,0]undec-7-ene, dimethylaminopyridine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, and thiourea.

[0025] A flame-retardant solid polymer electrolyte prepared by the preparation method of the flame-retardant solid polymer electrolyte described above.

[0026] An application of the flame-retardant solid polymer electrolyte described above in a lithium battery, the lithium battery includes a positive electrode, a negative electrode, and a separator, and further includes the flame-retardant solid polymer electrolyte disposed between the positive electrode and the negative electrode.

[0027] A flame-retardant gel polymer electrolyte, comprising the above-mentioned solid polymer electrolyte and a lithium-ion battery electrolyte; the lithium-ion battery electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive;

[0028] The lithium salt is at least one of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium oxalato(phosphate), lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(difluoromethanesulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and the content of the lithium salt accounts for 0.1 to 25.0 wt% of the total mass of the lithium-ion battery electrolyte;

[0029] The non-aqueous organic solvent is at least one of ethylene carbonate, propylene carbonate, butylene carbonate, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, n-butyl acetate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, tetrahydropyran, dioxolane, dimethyl sulfoxide, dimethyl sulfone, acetone, N,N-dimethylformamide, and the content of the non-aqueous organic solvent accounts for 20.0 to 70.0 wt% of the total mass of the lithium-ion battery electrolyte;

[0030] The additive is at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, ethylene sulfate, methylene methanedisulfonate, propylene sultone, citraconic anhydride, succinonitrile, adiponitrile, ethylene glycol diether, and hexane trinitrile, and the content of the additive accounts for 0.1 to 20.0 wt% of the total mass of the lithium-ion battery electrolyte.

[0031] The beneficial effects achieved by the present invention are as follows:

[0032] The solid polymer electrolyte prepared by the present invention can be in-situ cured and is in close contact with the electrode interface, ensuring efficient ion transport between the solid polymer electrolyte and the electrode, reducing the interfacial resistance, and thus improving the overall performance of the battery.

[0033] The unique cross-linked structure design in the solid polymer electrolyte prepared by the present invention not only greatly enhances the mechanical strength of the electrolyte, enabling it to maintain the structural stability and integrity under various use conditions, but also effectively destroys the regularity of the polyether chain segments, making it amorphous. This amorphous structure is conducive to the rapid migration of ions, endowing the electrolyte with high ionic conductivity and further promoting the high-efficiency operation of the battery.

[0034] The introduction of the polyphosphate ester in the present invention enhances the high-temperature flame retardancy of the solid polymer electrolyte, enabling it to remain stable in high-temperature environments and not prone to safety hazards such as fires. At the same time, the addition of the polyphosphate ester also further improves the mechanical strength of the electrolyte to a certain extent, making the battery assembled with the electrolyte of the present invention exhibit excellent cycle stability and rate performance, and capable of meeting the stringent requirements of modern battery technologies such as high energy density, long life, and fast charging and discharging.

[0035] The present invention can achieve the regulation of the matrix structure of the solid polymer electrolyte to change its properties, and can flexibly adjust the composition and structure of the electrolyte according to different application scenarios and requirements to adapt to various different situations.

[0036] The electrolyte of the present invention introduces a bio-friendly phosphate ester into the main chain, which is structurally stable in the battery. After being exposed to the environment, it can undergo a degradation reaction, decomposing the electrolyte into small molecules and oligomers, avoiding environmental damage, and also being of great significance in promoting green energy and sustainable development. Brief Description of the Drawings

[0037] Figure 1 Schematic diagram of the mechanism of the flame-retardant solid electrolyte;

[0038] Figure 2 is the solid polymer electrolyte membrane prepared by casting;

[0039] Figure 3 is the infrared spectrum of the solid polymer electrolyte prepared in Example 5;

[0040] Figure 4 is the graph of the ionic conductivity-temperature relationship of the solid polymer electrolyte;

[0041] Figure 5 is the linear sweep voltammogram of the steel sheet / solid electrolyte / lithium sheet battery in Example 5;

[0042] Figure 6 is the graph of the lithium ion transference number of the lithium / solid electrolyte / lithium battery in Example 5;

[0043] Figure 7 is the 0.2C cycle graph of the lithium nickel cobalt manganese oxide 622 / solid electrolyte / lithium battery in Example 5 at 60 °C;

[0044] Figure 8 is the 0.2C cycle graph of the lithium iron phosphate / solid electrolyte / lithium battery in Example 5 at 60 °C;

[0045] Figure 9 is the 0.5C cycle graph of the lithium iron phosphate / solid electrolyte / lithium battery in Example 7 at 60 °C;

[0046] Figure 10 It is the 0.2C cycle diagram of the lithium iron phosphate / solid-state electrolyte / lithium battery in Example 7 at 25°C;

[0047] Figure 11 It is the flame retardancy performance test diagram of Example 5. Specific implementation manners

[0048] In order to better understand the purpose, structure and function of the present invention, the following further describes in detail a flame-retardant solid polymer electrolyte, its preparation method and application thereof and a gel polymer electrolyte of the present invention with reference to the accompanying drawings.

[0049] The following examples are only used to illustrate the present invention, but the present invention is not limited to these examples. All equivalent changes and modifications made within the scope of the present invention shall fall within the scope covered by the present invention. All raw materials involved in the specification are purchased from the market, and the sources, purities and models of some reagents and instruments are shown in Table 1 and Table 2.

[0050] Table 1 Reagent sources and purities

[0051]

[0052] Table 2 Instruments and equipment

[0053]

[0054] Method for fabricating the positive electrode sheet: Superconductive carbon black (100 mg) and positive electrode active material (800 mg) are mixed and ground for 20 minutes to form a powder. Then, a solution of polyvinylidene fluoride in N-methylpyrrolidone with a concentration of 2.5 wt% (4000 mg) is added to the above mixed powder, and a heating magnetic stirrer is used at 200 revolutions / min for stirring for 12 h to obtain a positive electrode paste. The above paste is scraped onto an aluminum foil with a thickness of 16 microns using a 200-micron doctor blade, transferred to a forced-air drying oven at 60°C for drying for 10 hours, and then transferred to a vacuum drying oven at 120°C for vacuum drying for 10 hours; after pressing by a molding press, it is cut into circular pieces with a diameter of 14 mm for use. The positive electrode active material is lithium iron phosphate or nickel cobalt manganese lithium 622 (NCM622).

[0055] The structures of polymer monomer 1, polymer monomer 2, crosslinking agent compound 3 and initiator compound 4 used in the following examples are as shown in Formula a, Formula b, Formula c and Formula d respectively. Among them, n in Formula d is 21-23.

[0056]

[0057]

[0058] Example 1:

[0059] In an argon glove box (moisture < 0.01 ppm, oxygen < 0.01 ppm), weigh and add polymer monomer 1 (103 mg, 0.5 mmol) and crosslinking agent compound 3 (15 mg, 0.05 mmol) into a sample bottle, then add initiator compound 4 (45 mg, 0.045 mmol) and lithium bis(trifluoromethanesulfonyl)imide (70 mg). Add a magnetic stir bar and stir at 60 °C for 12 hours to obtain a precursor. Then, add catalyst DBU (1.36 mg, 0.009 mmol) dropwise and stir to obtain a liquid electrolyte. After standing and curing, 0.239 g of a solid polymer electrolyte is obtained.

[0060] Battery assembly: Take 100 μL of the above liquid electrolyte and coat it on the electrode sheets respectively. Let it stand for half an hour until the electrolyte is pre-cured. Assemble a CR 2032 type coin cell in the order of "negative electrode case - lithium sheet - electrolyte membrane - positive electrode sheet - gasket - spring piece - positive electrode case". Let it stand at room temperature for 24 h until it is completely cured, and the battery assembly is completed. According to the test content, the electrode sheets are selected from steel sheets, lithium iron phosphate positive electrode sheets, lithium cobalt oxide positive electrode sheets, NCM622 positive electrode sheets, and lithium sheets.

[0061] Example 2:

[0062] In an argon glove box (moisture < 0.01 ppm, oxygen < 0.01 ppm), weigh and add polymer monomer 1 (206 mg, 1 mmol) and crosslinking agent compound 3 (15 mg, 0.05 mmol) into a sample bottle, then add initiator compound 4 (45 mg, 0.045 mmol) and lithium bis(trifluoromethanesulfonyl)imide (117 mg). Add a magnetic stir bar and stir at 60 °C for 12 hours to obtain a precursor. Then, add catalyst DBU (1.36 mg, 0.009 mmol) dropwise and stir to obtain a liquid electrolyte. After standing and curing, 0.392 g of a solid polymer electrolyte is obtained.

[0063] Battery assembly: Take 100 μL of the above liquid electrolyte and coat it on the electrode sheets respectively. Let it stand for half an hour until the electrolyte is pre-cured. Assemble a CR 2032 type coin cell in the order of "negative electrode case - lithium sheet - electrolyte membrane - positive electrode sheet - gasket - spring piece - positive electrode case". Let it stand at room temperature for 24 h until it is completely cured, and the battery assembly is completed. According to the test content, the electrode sheets are selected from steel sheets, lithium iron phosphate positive electrode sheets, lithium cobalt oxide positive electrode sheets, NCM622 positive electrode sheets, and lithium sheets.

[0064] Example 3:

[0065] In an argon glove box (with moisture < 0.01 ppm and oxygen < 0.01 ppm), weigh and add polymer monomer 1 (412 mg, 2 mmol) and crosslinking agent compound 3 (15 mg, 0.05 mmol) into a sample bottle. Then add initiator compound 4 (45 mg, 0.045 mmol) and lithium bis(trifluoromethanesulfonyl)imide (209 mg). Add a magnetic stir bar and stir at 60 °C for 12 hours to obtain a precursor. Then add dropwise catalyst DBU (1.36 mg, 0.009 mmol) and stir to obtain a liquid electrolyte. After standing and curing, 0.698 g of a solid polymer electrolyte is obtained.

[0066] Battery assembly: Take 100 μL of the above liquid electrolyte and coat it on a steel sheet respectively. Let it stand for half an hour until the electrolyte is pre-cured. Assemble a CR 2032 coin cell in the order of "negative electrode case - steel sheet - electrolyte film - steel sheet - shrapnel - positive electrode case". Let it stand at room temperature for 24 h until it is completely cured, and the battery assembly is completed.

[0067] Example 4:

[0068] In an argon glove box (with moisture < 0.01 ppm and oxygen < 0.01 ppm), weigh and add polymer monomer 1 (1.03 g, 5 mmol) and crosslinking agent compound 3 (15 mg, 0.05 mmol) into a sample bottle. Then add initiator compound 4 (45 mg, 0.045 mmol) and lithium bis(trifluoromethanesulfonyl)imide (484 mg). Add a magnetic stir bar and stir at 60 °C for 12 hours to obtain a precursor. Then add dropwise catalyst DBU (1.36 mg, 0.009 mmol) and stir to obtain a liquid electrolyte. After standing and curing, 1.614 g of a solid polymer electrolyte is obtained.

[0069] Battery assembly: Take 100 μL of the above liquid electrolyte and coat it on a steel sheet respectively. Let it stand for half an hour until the electrolyte is pre-cured. Assemble a CR 2032 coin cell in the order of "negative electrode case - steel sheet - electrolyte film - steel sheet - shrapnel - positive electrode case". Let it stand at room temperature for 24 h until it is completely cured, and the battery assembly is completed.

[0070] Example 5:

[0071] In an argon glove box (with moisture < 0.01 ppm and oxygen < 0.01 ppm), weigh and add polymer monomer 1 (206 mg, 1 mmol), additive (tetraethylene glycol dimethyl ether) (21 mg), and crosslinking agent compound 3 (15 mg, 0.05 mmol) into a sample bottle. Then add initiator compound 4 (45 mg, 0.045 mmol) and lithium bis(trifluoromethanesulfonyl)imide (126 mg). Add a magnetic stir bar and stir at 60 °C for 12 hours to obtain a precursor. Then add catalyst DBU (1.36 mg, 0.009 mmol) dropwise and stir to obtain a liquid electrolyte. After standing and curing, 0.42 g of a solid polymer electrolyte is obtained.

[0072] Battery assembly: Take 100 μL of the above liquid electrolyte and coat it on a steel sheet respectively. Let it stand for half an hour until the electrolyte is pre-cured. Assemble a CR 2032 coin cell in the order of "negative electrode case - steel sheet - electrolyte film - steel sheet - shrapnel - positive electrode case". Let it stand at room temperature for 24 h to complete curing, and the battery assembly is completed.

[0073] Example 6:

[0074] In an argon glove box (with moisture < 0.01 ppm and oxygen < 0.01 ppm), weigh and add polymer monomer 1 (412 mg, 2 mmol), additive (tetraethylene glycol dimethyl ether) (42 mg), and crosslinking agent compound 3 (15 mg, 0.05 mmol) into a sample bottle. Then add initiator compound 4 (45 mg, 0.045 mmol) and lithium bis(trifluoromethanesulfonyl)imide (250 mg). Add a magnetic stir bar and stir at 60 °C for 12 hours to obtain a precursor. Then add catalyst DBU (1.36 mg, 0.009 mmol) dropwise and stir to obtain a liquid electrolyte. After standing and curing, 0.833 g of a solid polymer electrolyte is obtained.

[0075] Battery assembly: Take 100 μL of the above liquid electrolyte and coat it on a steel sheet respectively. Let it stand for half an hour until the electrolyte is pre-cured. Assemble a CR 2032 coin cell in the order of "negative electrode case - steel sheet - electrolyte film - steel sheet - shrapnel - positive electrode case". Let it stand at room temperature for 24 h to complete curing, and the battery assembly is completed.

[0076] Example 7:

[0077] In an argon glove box (with moisture < 0.01 ppm and oxygen < 0.01 ppm), 103 mg (1 mmol) of polymer monomer 1 and 15 mg (0.05 mmol) of crosslinking agent compound 3 were weighed and added to a sample bottle. Then, 45 mg (0.045 mmol) of initiator compound 4 and 126 mg of lithium bis(trifluoromethanesulfonyl)imide were added. A magnetic stir bar was added and the mixture was stirred at 60 °C for 12 hours to obtain a precursor. Subsequently, 1.36 mg (0.009 mmol) of catalyst DBU was added dropwise and stirred to obtain a liquid electrolyte. After standing and curing, 0.42 g of a solid polymer electrolyte was obtained.

[0078] Battery assembly: 100 μL of the liquid electrolyte was separately coated in a polytetrafluoroethylene mold and allowed to stand for half an hour for pre-curing of the electrolyte. Subsequently, in the order of "negative electrode case - steel sheet - electrolyte membrane - steel sheet - spring piece - positive electrode case", 60 μL of electrolyte solution (1 mol / L LiPF6 in EC:DMC = 1:1 Vol%) was added, and a CR 2032 type coin cell was assembled. It was allowed to stand at room temperature for 24 h for complete curing, and the battery assembly was completed.

[0079] Example 8:

[0080] In an argon glove box (with moisture < 0.01 ppm and oxygen < 0.01 ppm), 138 mg (1 mmol) of polymer monomer 2, 13 mg of additive (tetraethylene glycol dimethyl ether), and 15 mg (0.05 mmol) of crosslinking agent compound 3 were weighed and added to a sample bottle. Then, 45 mg (0.045 mmol) of initiator compound 4 and 91 mg of lithium bis(trifluoromethanesulfonyl)imide were added. A magnetic stir bar was added and the mixture was stirred at 60 °C for 12 hours to obtain a precursor. Subsequently, 1.36 mg (0.009 mmol) of catalyst DBU was added dropwise and stirred to obtain a liquid electrolyte. After standing and curing, 0.256 g of a solid polymer electrolyte was obtained.

[0081] Battery assembly: 100 μL of the above liquid electrolyte was separately coated on a steel sheet and allowed to stand for half an hour for pre-curing of the electrolyte. In the order of "negative electrode case - steel sheet - electrolyte membrane - steel sheet - spring piece - positive electrode case", a CR 2032 type coin cell was assembled. It was allowed to stand at room temperature for 24 h for complete curing, and the battery assembly was completed.

[0082] The compositions of each component in Examples 1 - 8 are shown in Table 3.

[0083] Table 3 Composition components of the solid polymer electrolyte

[0084]

[0085]

[0086] Performance testing

[0087] Preparation of solid polymer electrolyte membrane: The liquid electrolyte prepared in Example 5 was poured onto a polytetrafluoroethylene mold and allowed to stand and solidify to obtain a solid polymer electrolyte membrane. The structure is as Figure 2 shown. This solid polymer electrolyte membrane has a certain flexibility, can be applied to flexible batteries and has a certain mechanical strength. The structure of the solid polymer electrolyte prepared in Example 5 was characterized by Fourier transform infrared spectroscopy, as Figure 3 shown. The results show that the initiator initiates a polymerization reaction under the action of a catalyst to generate a cross-linked polyphosphate-polyethylene glycol electrolyte. Among them, the interaction between the lithium salt and the ether bond is observed at 1100 cm -1 to broaden the ether bond peak shape.

[0088] The electrochemical performance was all obtained by testing with an electrochemical workstation.

[0089] Figure 4 is a graph of the ionic conductivity-temperature relationship of the solid polymer electrolyte. The polymer electrolytes in this system all have excellent ionic conductivity. Among them, the ionic conductivity of the solid polymer electrolyte in Example 5 is the highest, and the ionic conductivity is 1.19×10 -3 S cm -1 at 80 °C; the ionic conductivity is 3.7×10 -4 S cm -1 at 30 °C. The ionic conductivities of each electrolyte at different temperatures are shown in Table 4.

[0090] Example 7 is based on the solid polymer electrolyte and 60 μL of electrolyte solution (1 mol / L LiPF6 in EC:DMC = 1:1 Vol%) is added to form a gel polymer electrolyte. From the ionic conductivity of the gel polymer electrolyte, it can be seen that the polymer electrolytes in this system all have excellent ionic conductivity. The ionic conductivity is 8.9×10 -4 S cm -1 at 80 °C; the ionic conductivity is 3.8×10 -4 S cm -1 at 30 °C. The addition of the electrolyte solution greatly increases the surface contact ability between the electrolyte and the electrode and improves the battery cycling ability. The ionic conductivities of the electrolyte at different temperatures are shown in Example 7 in Table 4.

[0091] Table 4 Ionic conductivities of solid polymer electrolytes at different temperatures

[0092]

[0093] Figure 5Linear sweep voltammetry curve of the steel sheet / solid electrolyte / lithium battery of Example 5; it can be seen from the figure that the electrolyte decomposition voltage is as high as 5.3 V, and it can remain stable and non-decomposed under the high-voltage conditions of the battery with lithium nickel cobalt manganese oxide 622 as the positive electrode.

[0094] Figure 6 For the lithium ion transference number diagram of the lithium / solid electrolyte / lithium battery of Example 5, the lithium ion transference number is shown as 0.6.

[0095] The charge and discharge performance of the battery is tested by a battery cycling system.

[0096] Figure 7 Cycling diagram at 0.2C of the lithium nickel cobalt manganese oxide 622 / solid electrolyte / lithium battery of Example 5 at 60 °C; Figure 8 Cycling diagram at 0.2C of the lithium iron phosphate / solid electrolyte / lithium battery of Example 5 at 60 °C.

[0097] Figure 7 and Figure 8 It shows that the solid polymer electrolyte prepared in Example 5 has good cycling performance in practical applications. When the positive electrode is lithium iron phosphate, the capacity hardly decays after 50 cycles at 0.2C and 60 degrees Celsius; even for the lithium nickel cobalt manganese oxide 622 positive electrode with a voltage as high as 4.3V, the flux retention rate is as high as 80% after 40 cycles under the same conditions. Therefore, the battery containing the solid polymer electrolyte prepared in Example 5 not only has good compatibility with the lithium iron phosphate positive electrode, but also can still show excellent cycling stability for the high-voltage positive electrode.

[0098] Figure 9 Cycling diagram at 0.5C of the lithium iron phosphate / solid electrolyte / lithium battery of Example 7 at 60 °C; Figure 10 Cycling diagram at 0.2C of the lithium iron phosphate / solid electrolyte / lithium battery of Example 7 at 25 °C. When the positive electrode is lithium iron phosphate, the capacity hardly decays after 100 cycles at 0.5C and 60 degrees Celsius. Even at 25 degrees Celsius, for the lithium iron phosphate positive electrode battery at 0.2C, after 50 cycles, the capacity also does not decay.

[0099] Figure 11 Flame retardancy test of Example 5. In the test, the electrolyte continued in the flame for 2 s, still showing no sign of combustion, and immediately self-extinguished after leaving the flame.

[0100] It is understood that the present invention is described by way of some embodiments, and those skilled in the art will be aware that various changes or equivalent replacements can be made to these features and embodiments without departing from the spirit and scope of the present invention. Additionally, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A preparation method of a flame-retardant solid polymer electrolyte, characterized in that, It includes the following steps: (1) Mix a lithium salt, a polymer monomer, a crosslinking agent, an initiator, an additive, and an organic solvent, and heat and stir evenly to obtain a precursor; (2) Then introduce a catalyst into the precursor to polymerize and solidify the precursor to obtain a solid polymer electrolyte; The structural general formula of the polymer monomer is formula (Ⅰ), and the structural general formula of the crosslinking agent is formula (Ⅱ). The structural formulas of formula (Ⅰ) and formula (Ⅱ) are as follows: Wherein, R1 is selected from one of hydrogen, halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, and substituted or unsubstituted heteroatom-containing group; R2 is selected from -O-, -CH2OCH2-, -CH2OC(=O)OCH2-, -(CH2) x -, -CH2OC(=O)(CH2) y C(=O)OCH2-, -CH2OC(=O)O(CH2) z OC(=O)OCH2-, -CH2OC(=O)CH2(CH2OCH2) m CH2C(=O)OCH2-, CH2OC(=O)OCH2(CH2OCH2)nCH2OC(=O)OCH2-, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, or a substituted or unsubstituted heteroatom-containing group; Wherein, when being substituted, the substituent is selected from halogen; the heteroatom is selected from at least one of B, N, O, Si, P, and S; x, y, and z are all integers greater than or equal to 1, and m and n are both integers greater than or equal to 0; the number of carbon atoms in the alkyl is less than or equal to 20; the number of carbon atoms in the alkenyl is less than or equal to 20; the number of carbon atoms in the alkynyl is less than or equal to 20; the number of carbon atoms in the heteroatom-containing group is less than or equal to 20.

2. The preparation method of a flame-retardant solid polymer electrolyte according to claim 1, characterized in that, The molar ratio of the polymer monomer, the crosslinking agent, the initiator, and the catalyst is 50-500:5:4.5:0.

9. The mass of the lithium salt accounts for 0.1-50.0 wt% of the total mass of the solid polymer electrolyte, the mass of the additive accounts for 0-80.0 wt% of the total mass of the solid polymer electrolyte, and the mass of the organic solvent accounts for 0-80.0 wt% of the total mass of the solid polymer electrolyte.

3. The preparation method of a flame-retardant solid polymer electrolyte according to claim 1, wherein The structural general formula of the initiator is formula (Ⅲ). The structural formula of formula (Ⅲ) is as follows: The R3 is selected from -(CH2) a -, -(CH2OCH2) b -, one of substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, and substituted or unsubstituted heteroatom-containing group; Wherein, when being substituted, the substituent is selected from halogen; the heteroatom is selected from at least one of B, N, O, Si, P, and S; a and b are both integers greater than or equal to 1; the number of carbon atoms in the alkyl is less than or equal to 20; the number of carbon atoms in the alkenyl is less than or equal to 20; the number of carbon atoms in the alkynyl is less than or equal to 20; the number of carbon atoms in the heteroatom-containing group is less than or equal to 20.

4. The preparation method of a flame-retardant solid polymer electrolyte according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium oxalato(phosphate), lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(difluoromethylsulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

5. The preparation method of a flame-retardant solid polymer electrolyte according to claim 1, characterized in that, The organic solvent is selected from one or more of diethyl ether, benzene, toluene, xylene, chloroform, carbon disulfide, acetonitrile, acetone, N,N-dimethylpyrrolidone, N,N-dimethylformamide, ethylene carbonate, propylene carbonate, butylene carbonate, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethylene sulfite, allyl methyl carbonate, ethylene ethylene carbonate, fluorinated ethylene carbonate, ethyl propionate, propyl propionate, ethyl acetate, n-butyl acetate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, tetrahydropyran, dioxolane, dimethyl sulfoxide, and dimethyl sulfone.

6. The preparation method of a flame-retardant solid polymer electrolyte according to claim 1, wherein, The additive is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid, polyacrylonitrile, poly(methyl methacrylate carbonate), polyethylene oxide, polyethylene, polypropylene, polyamide, polyimide, polyvinyl alcohol, polyvinyl butyral, polysiloxane, polytetrafluoroethylene, inorganic filler oxide solid electrolyte, sulfide solid electrolyte, silicon monoxide, silicon dioxide, titanium oxide, zirconium oxide, aluminum oxide, boehmite, montmorillonite, plastic crystal, tetraethylene glycol dimethyl ether.

7. The preparation method of a flame-retardant solid polymer electrolyte according to claim 1, characterized in that, The catalyst is selected from one or more of 1,8-diazabicyclo[5,4,0]undec-7-ene, dimethylaminopyridine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, thiourea.

8. A flame-retardant solid polymer electrolyte prepared by the preparation method of the flame-retardant solid polymer electrolyte according to any one of claims 1 to 7.

9. Use of the flame-retardant solid polymer electrolyte according to claim 8 in a lithium battery, characterized in that, The lithium battery includes a positive electrode, a negative electrode and a separator, and further includes the flame-retardant solid polymer electrolyte according to claim 8 disposed between the positive electrode and the negative electrode.

10. A flame-retardant gel polymer electrolyte, characterized in that, It includes the solid polymer electrolyte according to claim 8 and a lithium-ion battery electrolyte; the lithium-ion battery electrolyte includes a lithium salt, a non-aqueous organic solvent and an additive; The lithium salt is at least one of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium oxalato phosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(difluoromethanesulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide, and the content of the lithium salt accounts for 0.1 to 25.0 wt% of the total mass of the lithium-ion battery electrolyte; The non-aqueous organic solvent is at least one of ethylene carbonate, propylene carbonate, butylene carbonate, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, γ-butyrolactone, ethylene glycol dimethyl ether, tetrahydrofuran, tetrahydropyran, dioxolane, dimethyl sulfoxide, dimethyl sulfone, acetone, N,N-dimethylformamide, and the content of the non-aqueous organic solvent accounts for 20.0 to 70.0 wt% of the total mass of the lithium-ion battery electrolyte; The additive is at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, ethylene sulfate, methylene methanedisulfonate, propylene sultone, citraconic anhydride, succinonitrile, adiponitrile, ethylene glycol diether and hexane trinitrile, and the content of the additive accounts for 0.1 to 20.0 wt% of the total mass of the lithium-ion battery electrolyte.

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