Flame-retardant high-ionic-conductivity gel electrolyte, preparation method thereof and semi-solid lithium battery

Abstract

The invention provides a flame-retardant and high-ionic-conductivity gel electrolyte, a preparation method thereof and a semi-solid-state lithium battery, belongs to the field of semi-solid-state polymer electrolytes, and can solve a series of safety problems of leakage / electrolyte volatilization, fire breakout, explosion and the like when a liquid electrolyte is adopted by a lithium ion battery, and an all-solid-state electrolyte technology is not mature yet. The defects of low ionic conductivity, relatively large interface impedance and the like are caused. A precursor solution of the flame-retardant high-ionic-conductivity gel electrolyte comprises 35 to 90 wt% of an organic solvent, 5 to 40 wt% of a lithium salt, 0.1 to 20 wt% of an additive, 3 to 30 wt% of a polymeric monomer, 0.1 to 5 wt% of a cross-linking agent, 0.01 to 1 wt% of an initiator and 1 to 20 wt% of a reactive flame retardant, and the reactive flame retardant is an unsaturated phosphorus compound. The preparation method can be applied to preparation of the semi-solid lithium battery, and has high ionic conductivity and relatively good electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of semi-solid polymer electrolytes, and in particular relates to a flame-retardant, high-ionic conductivity gel electrolyte and a preparation method thereof, and a semi-solid lithium battery. Background Art

[0002] Currently, lithium-ion batteries are widely used in power applications such as portable electronic devices, electric vehicles, and large-scale energy storage stations. With the rapid increase in market demand for high-energy-density batteries, higher safety requirements are also being placed on lithium-ion batteries. As a key component of lithium-ion batteries, the performance of electrolytes directly affects their energy density, power density, and safety. Electrolytes include liquid electrolytes, solid electrolytes, and semi-solid electrolytes. Currently, most liquid electrolytes use volatile and flammable carbonate solvents, which can easily cause a series of safety issues such as electrolyte leakage, fire, and even explosion. At the same time, when using a high-nickel cathode + silicon-based anode system, the energy density of liquid lithium batteries at 350Wh / kg may be close to the limit, and no further breakthroughs can be achieved. Therefore, traditional liquid electrolytes are unlikely to meet the needs of lithium-ion batteries for further development towards safety and high energy density. Solid-state electrolytes have a theoretical energy density of 500-900Wh / kg and have the greatest potential to fundamentally resolve lithium-ion safety issues. However, all-solid-state electrolyte technology is not yet mature and has disadvantages such as low ionic conductivity, high cost, and high solid-solid interface resistance. Semi-solid electrolytes are between liquid electrolytes and all-solid-state electrolytes. The manufacturing process of semi-solid batteries is similar to that of liquid batteries, balancing performance and cost. They are considered a transitional solution to all-solid-state batteries. However, existing semi-solid electrolytes often have shortcomings such as low conductivity, poor flame retardancy, and potential safety issues after integration. Summary of the Invention

[0003] The present invention addresses the technical problems that the liquid electrolyte used in the above-mentioned lithium-ion batteries has a series of safety issues such as leakage / electrolyte volatilization, fire, and explosion, and the all-solid-state electrolyte technology is still immature, resulting in disadvantages such as low ionic conductivity and large interfacial impedance. A gel electrolyte with high ionic conductivity and good electrochemical properties is proposed.

[0004] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a flame-retardant, high-ionic conductivity gel electrolyte, wherein the precursor solution includes 35-90wt% of an organic solvent, 5-40wt% of a lithium salt, 0.1-20wt% of an additive, 3-30wt% of a polymer monomer, 0.1-5wt% of a cross-linking agent, 0.01-1wt% of an initiator, and 1-20wt% of a reactive flame retardant, wherein the reactive flame retardant is an unsaturated phosphorus compound.

[0005] In one embodiment, the precursor solution includes 60-80 wt% of organic solvent, 10-30 wt% of lithium salt, 0.1-5 wt% of additive, 5-15 wt% of polymerizable monomer, 0.1-1 wt% of cross-linking agent, 0.01-0.1 wt% of initiator, and 5-10 wt% of reactive flame retardant.It is understood that, according to actual conditions, those skilled in the art can adjust the weight percentage of each component within the above range, for example, the organic solvent can also be 60wt%, 65wt%, 70wt%, 75wt%, 80wt% or any point value within the above range, the lithium salt can also be 10wt%, 15wt%, 20wt%, 25wt%, 30wt% or any point value within the above range, and the additive can also be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%. t%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt %, 2.9wt%, 3.0wt%, 3.1wt%, 3.2wt%, 3.3wt%, 3.4wt%, 3.5wt%, 3.6wt%, 3.7wt%, 3.8wt%, 3.9wt%, 4.0wt%, 4.1wt%, 4.2wt%, 4.3wt%, 4.4wt% %, 4.5wt%, 4.6wt%, 4.7wt%, 4.8wt%, 4.9wt%, 5.0wt% or any value within the above range, the polymerization monomer can also be 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt% or any value within the above range, the cross-linking agent can also be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt% or any value within the above range, the initiator The amount of the reactive flame retardant can also be 0.01wt%, 0.02wt%, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt% or any value within the above range; the reactive flame retardant can also be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt% or any value within the above range.

[0006] In one embodiment, the unsaturated phosphorus compound includes any one or more of phosphazene compounds, bispirocyclic phosphorus compounds, phosphorus compounds containing a benzene ring structure, and phosphate compounds.

[0007] In one embodiment, the unsaturated phosphorus compound includes any one or more of the following compounds of Formula I to Formula VIII:

[0008]

[0009]

[0010] Formula VIII, wherein R1 and R2 are each independently selected from methyl, methylenebenzene, phenyl ether, halogen, ester group, allyl group (H2C=CH-CH2-) or cyano-substituted allyl group.

[0011] In one embodiment, the polymerizable monomer includes any one or more of methyl acrylate, methyl methacrylate, butyl acrylate, vinyl ethylene carbonate, polyethylene glycol methyl ether methacrylate, polydimethylsiloxane acrylate, acrylonitrile, methyl cyanoacrylate, isocyanoethyl methacrylate, 2,2,2-trifluoroethyl acrylate, trifluoroethyl methacrylate, pentafluorophenyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, octafluoropentyl acrylate, dodecafluoroheptyl acrylate, and perfluorobutyl acrylate.

[0012] In one embodiment, the additive includes any one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, propylene sulfate, methylene methanedisulfonate, tris(trimethylsilyl)phosphate, or tris(trimethylsilyl)borate.

[0013] In one embodiment, the crosslinking agent is at least one of a siloxane compound and an acrylate compound.

[0014] Another aspect of the present invention provides a method for preparing a flame-retardant, high ionic conductivity gel electrolyte, comprising the following steps:

[0015] uniformly mixing an organic solvent, a lithium salt, and an additive to prepare an organic electrolyte;

[0016] Adding a polymerizable monomer, a cross-linking agent, and a flame retardant to an organic electrolyte solution and stirring the mixture, adding an initiator, and mixing the mixture uniformly to obtain a gel electrolyte precursor solution;

[0017] At 40°C to 60°C, the gel electrolyte precursor solution is dropped onto the separator and in-situ polymerized for 2h to 48h to obtain a flame-retardant, high ionic conductivity gel electrolyte.

[0018] Another aspect of the present invention provides a semi-solid lithium battery comprising the flame-retardant, high ionic conductivity gel electrolyte.

[0019] The present invention also provides a method for preparing a semi-solid lithium battery, comprising the following steps: assembling a lithium-ion battery in the order of a positive electrode shell, a positive electrode, a diaphragm to which a gel electrolyte precursor solution is dropwise added, a negative electrode, a steel sheet, a shrapnel, and a negative electrode shell; packaging the battery according to a set pressure, allowing it to stand for 4 to 24 hours, and performing in-situ polymerization at 40 to 60° C. for 2 to 48 hours to obtain a semi-solid lithium-ion battery.

[0020] Compared with the prior art, the advantages and positive effects of the present invention are:

[0021] (1) The gel polymer electrolyte of the present invention has high ionic conductivity, high mechanical strength and good flame retardancy, and can effectively improve the electrochemical performance and safety performance of semi-solid lithium-ion batteries. By combining a multifunctional phosphorus compound with other cross-linking agents, the mechanical strength and ionic conductivity are balanced by regulating the cross-linking density.

[0022] (2) The gel electrolyte of the present invention uses unsaturated phosphorus compounds as flame retardants. At high temperatures, the flame retardancy of the electrolyte is improved through a dual gas phase / condensed phase flame retardant mechanism. On the one hand, the unsaturated phosphorus compounds decompose at high temperatures to generate polyphosphoric acid, which promotes the carbonization of the polymer matrix through dehydration to form a dense, continuous phosphorus-containing coke layer, effectively isolating oxygen and heat, thereby inhibiting the continued progress of the combustion chain reaction; on the other hand, the compound releases phosphorus-containing free radicals, which combine with the active free radicals (H·, OH·) in the combustion chain reaction to generate inert substances such as H2O and CO2, interrupting the combustion reaction; in addition, the unsaturated phosphorus compounds are both flame retardants and polymerizable cross-linking agents, and are embedded in the polymer network through covalent bonds, avoiding the flame retardant migration problem caused by traditional physical addition. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1 is a charge and discharge curve diagram of a Li / AG battery corresponding to Example 2 of the present invention;

[0024] Figure 2 This is a charge and discharge curve diagram of the Li / NCM811 battery corresponding to Example 2 of the present invention. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0026] The embodiments of the present invention provide a flame-retardant, high-ionic conductivity gel electrolyte and a preparation method thereof. The gel polymer electrolyte has high ionic conductivity, high mechanical strength and good flame retardancy, and can effectively improve the electrochemical performance and safety performance of semi-solid lithium-ion batteries. By compounding a multifunctional phosphorus compound with other cross-linking agents, the mechanical strength and ionic conductivity are balanced by regulating the cross-linking density.

[0027] The present invention discloses a flame-retardant, high-ionic conductivity gel electrolyte. The precursor solution comprises 35-90 wt% of an organic solvent, 5-40 wt% of a lithium salt, 0.1-20 wt% of an additive, 3-30 wt% of a polymerizable monomer, 0.1-5 wt% of a cross-linking agent, 0.01-1 wt% of an initiator, and 1-20 wt% of a reactive flame retardant. The reactive flame retardant is an unsaturated phosphorus compound. Unsaturated phosphorus compounds are used as flame retardants. At high temperatures, the flame retardancy of the electrolyte is improved through a dual gas phase / condensed phase flame retardancy mechanism. On the one hand, the unsaturated phosphorus compounds decompose at high temperatures to generate polyphosphoric acid, which promotes the carbonization of the polymer matrix through dehydration to form a dense, continuous phosphorus-containing coke layer, effectively isolating oxygen and heat, thereby inhibiting the continued progress of the combustion chain reaction. On the other hand, the compounds release phosphorus-containing free radicals, which combine with active free radicals (H·, OH·) in the combustion chain reaction to generate inert substances such as H2O and CO2, interrupting the combustion reaction. In addition, the unsaturated phosphorus compounds are both flame retardants and polymerizable crosslinkers, and are embedded in the polymer network through covalent bonds, avoiding the flame retardant migration problem caused by traditional physical addition. At the same time, the multifunctional phosphorus compounds are compounded with other crosslinkers to balance mechanical strength and ionic conductivity by regulating the crosslinking density. The gel polymer electrolyte of the present invention has high ionic conductivity, high mechanical strength and good flame retardancy, and can effectively improve the electrochemical performance and safety performance of semi-solid lithium ion batteries.

[0028] In one embodiment, a precursor solution of a flame-retardant, high ionic conductivity gel electrolyte includes 60-80 wt% of an organic solvent, 10-30 wt% of a lithium salt, 0.1-5 wt% of an additive, 5-15 wt% of a polymerizable monomer, 0.1-1 wt% of a cross-linking agent, 0.01-0.1 wt% of an initiator, and 5-10 wt% of a reactive flame retardant.

[0029] The unsaturated phosphorus compounds in the flame-retardant, high ionic conductivity gel electrolyte of the present invention include any one or more of phosphazene compounds, bispirocyclic phosphorus compounds, phosphorus compounds containing benzene ring structures, and phosphate compounds. Flame retardants with different structures have different effects, among which the flame retardant effect of phosphazene compounds is significantly higher than that of bispirocyclic compounds, but both are better than flame retardants with benzene ring structures; the main reason is that the phosphazene structure is a phosphorus-nitrogen flame retardant formed after nitrogen is added to the phosphorus compound. Since the nitrogen compound releases a variety of non-flammable gases after heating, these non-combustible gases can effectively block the supply of oxygen, achieving the purpose of flame retardant synergy and synergy. The bispirocyclic structure contains a large amount of carbon, so it has a strong carbon-forming ability, which is conducive to the performance of its flame retardant properties. The phosphorus compound with a benzene ring structure is mainly gas-phase flame retardant, with medium flame retardant efficiency, but the introduction of the benzene ring makes it compatible with a variety of polymers.

[0030] In one embodiment, the unsaturated phosphorus compound includes any one or more of the following compounds of Formula I to Formula VIII:

[0031]

[0032]

[0033] Formula VIII, wherein R1 and R2 are each independently selected from methyl, methylenebenzene, phenyl ether, halogen, ester group, allyl group (H2C=CH-CH2-) or cyano-substituted allyl group.

[0034] The organic solvent in the flame-retardant, high ionic conductivity gel electrolyte of the present invention includes any one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, methyl propyl carbonate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl butyrate, butyl acetate, propyl acetate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, and 1,3-dioxolane.

[0035] The lithium salt in the flame-retardant, high ionic conductivity gel electrolyte of the present invention includes any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethylsulfonyl imide), and lithium trifluoromethanesulfonate.

[0036] The additives in the flame-retardant, high ionic conductivity gel electrolyte of the present invention include any one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, propylene sulfate, methylene methanedisulfonate, tris(trimethylsilyl)phosphate or tris(trimethylsilyl)borate.

[0037] The polymerizable monomers in the flame-retardant, high-ionic conductivity gel electrolyte of the present invention include any one or more of methyl acrylate, methyl methacrylate, butyl acrylate, vinyl ethylene carbonate, polyethylene glycol methyl ether methacrylate, polydimethylsiloxane acrylate, acrylonitrile, methyl cyanoacrylate, isocyanoethyl methacrylate, 2,2,2-trifluoroethyl acrylate, trifluoroethyl methacrylate, pentafluorophenyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, octafluoropentyl acrylate, dodecafluoroheptyl acrylate, and perfluorobutyl acrylate.

[0038] The crosslinking agent in the flame-retardant, high-ionic conductivity gel electrolyte of the present invention is a siloxane or acrylate compound. In one embodiment, the crosslinking agent includes any one or more of octavinylsilsesquioxane, tetrakis(dimethylvinylsiloxy)silane, methyltri(isopropyleneoxy)silane, 1,1,3,3-tetramethoxy-1,3-divinyldisiloxane, (acryloxymethyl)dimethylmethoxysilane, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, and pentaerythritol tetraethylene glycol ester.

[0039] The initiator in the flame-retardant, high ionic conductivity gel electrolyte of the present invention comprises any one or more of 2,4-dichlorobenzoyl peroxide, azobisisobutyronitrile, dimethyl azobisisobutyrate, benzoyl peroxide, ammonium persulfate, and stannous isooctanoate.

[0040] The method for preparing the flame-retardant, high ionic conductivity gel electrolyte of the present invention specifically comprises the following steps:

[0041] uniformly mixing an organic solvent, a lithium salt, and an additive to prepare an organic electrolyte;

[0042] Adding a polymerizable monomer, a cross-linking agent, and a flame retardant to an organic electrolyte solution and stirring the mixture, adding an initiator, and mixing the mixture uniformly to obtain a gel electrolyte precursor solution;

[0043] At 40°C to 60°C, the electrolyte precursor solution is dropped onto the separator and in-situ polymerized for 2h to 48h to obtain a flame-retardant, high ionic conductivity gel electrolyte.

[0044] The present invention also provides a semi-solid lithium battery comprising a flame-retardant, high ionic conductivity gel electrolyte, the preparation method of which comprises the following steps:

[0045] The lithium-ion battery is assembled in the order of positive electrode shell, positive electrode, diaphragm with electrolyte precursor solution added, negative electrode, steel sheet, shrapnel and negative electrode shell, the battery is packaged according to the set pressure, left to stand for 4 to 24 hours, and in situ polymerized for 2 to 48 hours at 40 to 60°C to obtain a semi-solid lithium-ion battery.

[0046] In order to more clearly and in detail introduce the flame-retardant, high ionic conductivity gel electrolyte and its preparation method, and the semi-solid lithium battery provided by the embodiments of the present invention, they will be described below in conjunction with specific embodiments.

[0047] Example 1

[0048] The method for preparing the semi-solid-state battery of this embodiment includes the following steps:

[0049] Weigh 2.77 g of ethyl methyl carbonate (EMC) and 1.19 g of ethylene carbonate (EC) as solvents, add 0.93 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) to the above mixed solvents, and stir until completely dissolved;

[0050] 0.052 g of lithium difluorooxalatoborate (LiODFB) and 0.05 g of fluoroethylene carbonate (FEC) were added to the above solution and stirred until fully dissolved to obtain a basic electrolyte.

[0051] Add 0.50 g of acrylonitrile, 0.025 g of tetrakis(dimethylvinylsiloxy)silane and 0.025 g of the compound of formula I to the above-mentioned basic electrolyte, stir and mix well to obtain a transparent and uniform precursor solution;

[0052] Add 0.001 g of dimethyl azobisisobutyrate to the precursor solution and stir until it is completely dissolved to obtain a polymerization precursor solution which is then stored at low temperature.

[0053] Place the negative electrode shell flat on an insulating table, place the metal lithium sheet in the center of the negative electrode shell, drip 100ul of electrolyte, then place the diaphragm flat on the upper layer of the lithium sheet, use a pipette to take 100ul of electrolyte and drip it onto the surface of the diaphragm, use insulating tweezers to place the test positive electrode sheet, gasket, spring sheet and positive electrode shell on the upper layer of the diaphragm in sequence to complete the battery assembly. The active material side of the test electrode sheet should be close to the diaphragm;

[0054] The button battery was placed at room temperature for 2 hours and then placed in a 50°C forced air oven for 10 hours to achieve in-situ curing of the polymer electrolyte precursor, thereby preparing a semi-solid-state battery containing a gel polymer electrolyte.

[0055] Example 2

[0056] The difference between this embodiment and embodiment 1 is that the polymerization monomer "0.50g acrylonitrile" in embodiment 1 is changed to "0.1g vinyl ethylene carbonate (VEC), 0.4g methyl methacrylate (MMA)", and other raw materials and steps remain unchanged.

[0057] The charge and discharge curves of the Li / AG battery corresponding to Example 2 are as follows: Figure 1 As shown, the charge and discharge curves of the Li / NCM811 battery corresponding to Example 2 are as follows Figure 2 As shown, it can be seen that Example 2 has good compatibility with both NCM811 positive electrode material and graphite negative electrode material, indicating that the solid electrolyte has good compatibility with positive and negative electrode materials.

[0058] Example 3

[0059] The difference between this embodiment and embodiment 2 is that the flame retardant "0.025g of compound 1" in embodiment 2 is changed to "0.025g of compound of formula III", and other raw materials and steps remain unchanged, wherein R1 is allyl and R2 is cyanoallyl.

[0060] Example 4

[0061] The difference between this embodiment and embodiment 2 is that the flame retardant "0.025g of compound 1" in embodiment 2 is changed to "0.025g of compound of formula IV", and the other raw materials and steps remain unchanged, wherein R1 is a formate group and R2 is an acetate group.

[0062] Example 5

[0063] The difference between this embodiment and embodiment 2 is that the flame retardant "0.025 g of compound 1" in embodiment 2 is changed to "0.25 g of compound of formula V", and other raw materials and steps remain unchanged, wherein R1 is methylenebenzene.

[0064] Example 6

[0065] The difference between this embodiment and embodiment 2 is that the flame retardant "0.025 g of compound 1" in embodiment 2 is changed to "0.25 g of compound of formula VII", and other raw materials and steps remain unchanged.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is that the crosslinking agent "0.025g tetrakis(dimethylvinylsiloxy)silane" in Example 1 is changed to "0.025g (acryloxymethyl)dimethylmethoxysilane", no flame retardant compound is added, and other raw materials and steps remain unchanged.

[0068] Comparative Example 2

[0069] This comparative example differs from Example 2 in that no flame retardant compound is added, and other raw materials and steps remain unchanged.

[0070] Comparative Example 3

[0071] The difference between this comparative example and comparative example 1 is that the "0.025 g tetrakis(dimethylvinylsiloxy)silane" in comparative example 1 is changed to "0.025 g polyethylene glycol dimethacrylate (PEGDMA, n=9)", and other raw materials and steps remain unchanged.

[0072] Performance Testing

[0073] The semi-solid state batteries prepared in Examples 1-6 and Comparative Examples 1-3 were tested for ionic conductivity, oxidation potential, ion migration number, and oxygen limiting index with reference to the group standard T / SPSTS 020-2021. The test results are shown in Table 1.

[0074] Table 1 Performance test table of semi-solid batteries prepared in Examples 1-6 and Comparative Examples 1-3

[0075] electrolytes <![CDATA[Ionic conductivity / mS cm -1 > Oxidation potential / V Ion mobility Limited oxygen index Example 1 0.60 ＞4.5 0.71 31.8 Example 2 0.70 ＞4.5 0.73 31.3 Example 3 0.65 ＞4.5 0.72 30.7 Example 4 0.63 ＞4.5 0.73 30.1 Example 5 0.62 ＞4.5 0.74 29.5 Example 6 0.62 ＞4.5 0.71 28.8 Comparative Example 1 0.55 ＞4.5 0.70 23.6 Comparative Example 2 0.59 ＞4.5 0.70 22.5 Comparative Example 3 0.54 ＞4.5 0.68 22.1

[0076] From the above, it can be seen that by comparing Example 2 with Example 1 and Comparative Example 1, it can be seen that monomers with strong polarity or cross-linking agents with high functionality can effectively improve the ionic conductivity of the polymer electrolyte; by comparing Examples 1 to 6 with Comparative Example 2, it can be verified that all phosphorus-based compounds are flame retardant, but the flame retardants with different structures have different effects, among which the phosphazene compound (Formula I compound) has a significantly higher flame retardant effect than the double spiro ring structure compound (Formula III compound), and both are superior to the benzene ring structure flame retardant (Formula IV compound); the main reason is that the phosphazene structure is a phosphorus-nitrogen flame retardant formed by adding nitrogen to the phosphorus-based compound. Since the nitrogen compound releases a variety of non-flammable gases after heating, these non-combustible gases can effectively block the oxygen supply, thereby achieving the purpose of flame retardant synergy and synergy; the double spiro ring structure contains a large amount of carbon, and therefore has a strong charring ability, which is conducive to the performance of its flame retardant properties; while the phosphorus-based compound with a benzene ring structure is mainly gas-phase flame retardant, with a moderate flame retardant efficiency, but the introduction of the benzene ring makes it compatible with a variety of polymers. At the same time, the comparison between Examples 2 and 3 shows that the siloxane polymer has a higher oxygen limitation index than the acrylic polymer. This is because the Si-O bond dissociation energy of siloxane is much higher than that of CO or CC bond, so it has higher thermal stability.

[0077] The above-described embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations, modifications, evolutions, and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A flame retardant, high ionic conductivity gel electrolyte, characterized in that: The precursor solution includes 35-90 wt% of organic solvent, 5-40 wt% of lithium salt, 0.1-20 wt% of additive, 3-30 wt% of polymer monomer, 0.1-5 wt% of cross-linking agent, 0.01-1 wt% of initiator, and 1-20 wt% of reactive flame retardant, wherein the reactive flame retardant is an unsaturated phosphorus compound.

2. The flame-retardant, high ionic conductivity gel electrolyte according to claim 1, characterized in that: The precursor solution includes 60-80 wt% of organic solvent, 10-30 wt% of lithium salt, 0.1-5 wt% of additive, 5-15 wt% of polymer monomer, 0.1-1 wt% of cross-linking agent, 0.01-0.1 wt% of initiator and 5-10 wt% of reactive flame retardant.

3. The flame-retardant, high ionic conductivity gel electrolyte according to claim 1, characterized in that: The unsaturated phosphorus compounds include any one or more of phosphazene compounds, bispirocyclic phosphorus compounds, phosphorus compounds containing a benzene ring structure, and phosphate compounds.

4. The flame-retardant, high ionic conductivity gel electrolyte according to claim 1, characterized in that: The unsaturated phosphorus compounds include any one or more of the following compounds of formula I to formula VIII: Formula I, Formula II Formula III, Formula IV Formula V, Formula VI, Formula VII, Formula VIII, wherein R1 and R2 are each independently selected from methyl, methylenebenzene, phenyl ether, halogen, ester group, allyl group (H2C=CH-CH2-) or cyano-substituted allyl group.

5. The flame-retardant, high ionic conductivity gel electrolyte according to claim 1, characterized in that: The polymerization monomer includes any one or more of methyl acrylate, methyl methacrylate, butyl acrylate, vinyl ethylene carbonate, polyethylene glycol methyl ether methacrylate, polydimethylsiloxane acrylate, acrylonitrile, methyl cyanoacrylate, isocyanoethyl methacrylate, 2,2,2-trifluoroethyl acrylate, trifluoroethyl methacrylate, pentafluorophenyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, octafluoropentyl acrylate, dodecafluoroheptyl acrylate, and perfluorobutyl acrylate.

6. The flame-retardant, high ionic conductivity gel electrolyte according to claim 1, characterized in that: The additives include any one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, propylene sulfate, methylene methanedisulfonate, tris(trimethylsilyl)phosphate or tris(trimethylsilyl)borate.

7. The flame-retardant, high ionic conductivity gel electrolyte according to claim 1, characterized in that: The crosslinking agent is at least one of a siloxane compound and an acrylate compound.

8. A method for preparing a flame-retardant, high ionic conductivity gel electrolyte, characterized in that: The following steps are involved: uniformly mixing an organic solvent, a lithium salt, and an additive to prepare an organic electrolyte; Adding a polymerizable monomer, a cross-linking agent, and a flame retardant to an organic electrolyte solution and stirring the mixture, adding an initiator, and mixing the mixture uniformly to obtain a gel electrolyte precursor solution; At 40°C to 60°C, the gel electrolyte precursor solution is dropped onto the separator and in-situ polymerized for 2h to 48h to obtain a flame-retardant, high ionic conductivity gel electrolyte.

9. A semi-solid lithium battery, characterized in that: The invention comprises the flame-retardant, high ion conductivity gel electrolyte according to any one of claims 1 to 7.

10. The method for preparing a semi-solid lithium battery according to claim 9, characterized in that: The method comprises the following steps: assembling a lithium-ion battery in the order of a positive electrode shell, a positive electrode, a diaphragm with a gel electrolyte precursor solution dropped therein, a negative electrode, a steel sheet, a shrapnel, and a negative electrode shell; packaging the battery according to a set pressure, standing the battery for 4 to 24 hours, and performing in-situ polymerization at 40 to 60° C. for 2 to 48 hours to obtain a semi-solid lithium-ion battery.

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