A fluorinated cyclotriphosphazene compound, a flame-retardant electrolyte, and an alkali metal-based battery

Abstract

This invention relates to the field of alkali metal-based battery technology, and particularly to a fluorinated cyclic triphosphazene compound, a flame-retardant electrolyte, and an alkali metal-based battery. The fluorinated cyclic triphosphazene compound provided by this invention has the general structural formula shown in Formula I: Formula I; R1~R6 are each independently selected from -F or ; and one or two of R1~R6 are ; R7 is selected from substituted or unsubstituted alkylene groups, substituted or unsubstituted chain ether groups, substituted or unsubstituted cyclic ether groups; substitution means that at least one hydrogen in the group is independently replaced by a halogen, cyano, olefinic, or alkyne group. This invention applies a fluorinated cyclic triphosphazene compound containing a specific difluoromethyl terminal group to a flame-retardant electrolyte. Utilizing the unique hydrogen bonding and supramolecular halogen bonding interactions between the molecules of this compound, a stable phosphazene supramolecular network is formed inside the electrolyte, thus simultaneously ensuring battery safety, high-voltage stability, and high-temperature adaptability.

Description

Technical Field

[0001] This invention relates to the field of alkali metal-based battery technology, and more particularly to a fluorinated cyclic triphosphazene compound, a flame-retardant electrolyte, and an alkali metal-based battery. Background Technology

[0002] Lithium-ion batteries have distinguished themselves among various battery systems due to their high energy density, long effective lifespan, and environmental friendliness, successfully occupying fields such as consumer electronics, new energy vehicles, and energy storage, becoming an indispensable component in people's lives and industrial production. However, conventional lithium-ion batteries primarily use flammable organic electrolytes based on carbonates, making them prone to combustion and even explosion under conditions of abuse such as high-temperature exposure, partial short circuits, and mechanical impact. In recent years, there have been numerous incidents of spontaneous combustion and fires involving electric vehicles and mobile phones, seriously threatening people's lives and property. The low safety caused by flammable organic electrolytes has become a bottleneck factor restricting the further development of lithium-ion batteries.

[0003] Furthermore, as the applications of lithium-ion batteries become increasingly widespread, the required energy density and effective operating temperature range are also widening. However, conventional carbonate electrolytes, when reaching 4.3V (vs. Li / Li),... + At voltages of 600V and above, and under extreme temperature conditions such as high temperatures, solvent molecules in the electrolyte tend to volatilize. Simultaneously, severe oxidative decomposition side reactions occur on the surface of the cathode material, resulting in significant gas release, transition metal dissolution, and cathode material breakage. These adverse effects severely reduce battery stability and safety, causing capacity decay, shortened lifespan, and even fire or explosion. Therefore, developing a flame-retardant or even non-flammable lithium-ion battery electrolyte that exhibits high voltage and high temperature adaptability while simultaneously achieving high energy density and high safety has significant scientific and practical value.

[0004] Current publicly reported electrolyte research primarily focuses on adding flame-retardant additives to enhance electrolyte flame retardancy and improve battery safety. Patent CN115832428A discloses a flame-retardant lithium-ion battery electrolyte using bromoether 1,2-bis(2-bromoethoxy)ethane as a flame-retardant additive, reducing the risk of high-temperature flammability. However, this flame-retardant additive does not positively impact battery cycle performance, and excessive addition can significantly reduce battery energy density. Patent CN120574256A discloses a flame-retardant film-forming additive for lithium-ion battery electrolytes containing aluminum tripolyphosphate salts. It utilizes polyphosphate groups and borate ester groups synthesized through esterification to achieve good interfacial film formation and flame-retardant effects, improving high-voltage cycle stability and reducing electrolyte flammability. However, this flame-retardant additive is limited by the low solubility of polyvalent metal salts in the electrolyte, resulting in limited improvement in cycle stability and safety. Therefore, there is an urgent need to develop a new electrolyte system that combines excellent flame retardancy, high voltage stability, and high temperature adaptability to promote the practical development of high-safety, high-performance alkali metal batteries. Summary of the Invention

[0005] This invention provides a fluorinated triphosphazene compound, a flame-retardant electrolyte, and an alkali metal-based battery to address the serious safety hazards caused by the flammability of conventional electrolytes in the prior art, as well as their poor stability under high voltage and high temperature conditions, which leads to poor battery cycle performance. This invention aims to improve the battery's stable cycle performance and safe use under high voltage and high temperature conditions.

[0006] This invention provides a fluorinated cyclic triphosphazene compound having the general structural formula shown in Formula I: Formula I; Among them, R1 to R6 are each independently selected from -F or And one or two of R1 to R6 are R7 is selected from substituted or unsubstituted alkylene groups, substituted or unsubstituted chain ether groups, and substituted or unsubstituted cyclic ether groups; the substitution means that at least one hydrogen in the group is independently replaced by a halogen, cyano, olefinic or alkyne group.

[0007] Compared to existing phosphazene compounds, most of which cannot directly dissolve lithium salts and can only be used as small additives in electrolytes, the compound of Formula I provided by this invention can not only be used as an additive but also has lithium salt dissolving ability, making it suitable as a solvent. The compound of Formula I of this invention can form a phosphazene supramolecular network within the electrolyte through hydrogen bonding and supramolecular halogen bonding interactions between the unique locally polarized H and F atoms in the terminal difluoromethyl group and the triphosphazene ring. This significantly improves the overall stability of the electrolyte under extreme environments such as high temperature and high pressure. Simultaneously, the non-covalent weak interactions of the supramolecular network create a highly dynamic and stable environment for the electrolyte, achieving excellent ion transport performance. Electrolytes using the compound of Formula I as an additive or solvent exhibit complete non-flammability, high temperature stability, good ionic conductivity, high oxidation stability, and high reduction stability. Furthermore, the compound of Formula I can form a stable fluorine-rich passivation layer on the positive and negative electrode surfaces, significantly improving the high-pressure and high-temperature cycle stability of the electrolyte. This achieves a balance of excellent safety, stability, and adaptability to various operating conditions in lithium batteries, making it highly valuable for practical applications.

[0008] In this invention, one or two of R1 to R6 are If R1~R6 If there are more than two, the compound shown in Formula I will have excessive viscosity and poor flowability, which may prevent the formation of a flame-retardant electrolyte with good flowability, thus affecting the overall performance of the flame-retardant electrolyte.

[0009] Furthermore, The terminal group must be a difluoromethyl group. If it is methyl, trifluoromethyl or monofluoromethyl, it will directly lose the ability to form hydrogen bonds and supramolecular halogen bonds between molecules and within molecules, which will significantly reduce the improvement of electrolyte stability.

[0010] In the fluorocyclic triphosphazene compound according to the present invention, R7 is selected from substituted or unsubstituted C1-C10 alkylene groups, substituted or unsubstituted chain ether groups having 2-10 carbon atoms, and substituted or unsubstituted cyclic ether groups having 2-10 carbon atoms. Preferably, R7 is selected from substituted or unsubstituted C1-C6 alkylene groups, substituted or unsubstituted chain ether groups having 2-6 carbon atoms, and substituted or unsubstituted cyclic ether groups having 2-6 carbon atoms.

[0011] In the fluorocyclic triphosphazene compound according to the present invention, R7 is selected from substituted or unsubstituted chain ether groups having 2-10 carbon atoms and 1-5 oxygen atoms, or substituted or unsubstituted cyclic ether groups having 2-10 carbon atoms and 1-5 oxygen atoms. Preferably, R7 is selected from substituted or unsubstituted chain ether groups having 2-6 carbon atoms and 1-4 oxygen atoms, or substituted or unsubstituted cyclic ether groups having 2-6 carbon atoms and 1-4 oxygen atoms.

[0012] According to the fluorinated triphosphazene compound of the present invention, the compound represented by Formula I is selected from one or more of Formulas I-1 to I-10:

[0013] The compound represented by Formula I provided by this invention can be prepared using synthetic methods known in the art. For example, when the compound represented by Formula I is I-1, its preparation method may include the following steps: The first step involves dissolving difluoroethanol and hexafluorocyclotriphosphazene in diethyl ether. After the sample is completely mixed, potassium carbonate is added, and the mixture is then sealed and stirred at room temperature for 18-30 hours. After the reaction is complete, the resulting mixture is filtered, and the solvent is removed from the filtrate under vacuum to obtain the crude product. The second step involves subjecting the crude product to vacuum distillation to obtain the pure target product.

[0014] For example, when the compound represented by Formula I is I-6, its preparation method may include the following steps: The first step involves dissolving difluoromethyl diethylene glycol methyl ether and hexafluorocyclotriphosphazene in diethyl ether. After the sample is completely mixed, potassium carbonate is added, and the mixture is then sealed and stirred at room temperature for 18-30 hours. After the reaction is complete, the resulting mixture is filtered, and the solvent is removed from the filtrate under vacuum to obtain the crude product. The second step involves vacuum distillation of the crude product to obtain the pure target product.

[0015] In this invention, the compounds shown in Formulas I-2 to I-4 and the compounds shown in Formulas I-7 to I-10 can all be prepared using methods similar to those used for the compounds shown in Formulas I-1 and I-6.

[0016] According to a second aspect of the present invention, the present invention also provides a flame-retardant electrolyte containing not less than 0.1% by volume of the aforementioned fluorocyclic triphosphazene compound. For example, the content can be 0.1%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 99%, etc., and other values ​​within the above ranges are also possible and are not limited herein.

[0017] The flame-retardant electrolyte according to the present invention includes a solvent, a lithium salt electrolyte, and optionally additives; the solvent and / or additives use the fluorinated triphosphazene compound.

[0018] According to the flame-retardant electrolyte of the present invention, the fluorinated triphosphazene compound is used as a component of the solvent, and the volume of the fluorinated triphosphazene compound accounts for 5%-100% of the total volume of the solvent, preferably 50-100%. The fluorinated triphosphazene compound used as the solvent component can be I-5, I-6, I-7, I-8, I-9, or I-10.

[0019] According to the flame-retardant electrolyte of the present invention, the solvent further includes one or more of the following: ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, diethyl ether, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methyl nonafluorobutyl ether, and bis(2,2,2-trifluoroethyl) ether.

[0020] Preferably, the solvent further includes 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether or 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

[0021] In the above scheme, by further adding the specified solvent, there are other solvents as well. These solvents, when used in combination with the compound shown in Formula I, work synergistically to better improve the overall performance of the electrolyte, such as safety, cycleability, conductivity, and stability.

[0022] In some specific embodiments, when the fluorinated triphosphazene compound is a component of the solvent, the solvent further includes 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether or 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether. In some specific embodiments, when the fluorinated triphosphazene compound is the main solvent, the solvent further includes 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, with the amount added being 0%-50% of the electrolyte volume percentage. In some specific embodiments, when the fluorinated triphosphazene compound is used as a co-solvent, the amount of other organic solvents used is 50%-100% of the electrolyte volume percentage.

[0023] The flame-retardant electrolyte according to the present invention includes an additive, a solvent, and a lithium salt electrolyte, wherein the fluorinated cyclotriphosphazene compound is used as an additive component; the amount of the fluorinated cyclotriphosphazene compound is 0.1-5% (preferably 0.5-5%) of the volume of the solvent; the fluorinated cyclotriphosphazene compound used as an additive component can be I-1, I-2, I-3, or I-4.

[0024] Preferably, the solvent includes one or more of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, diethyl ether, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0025] According to the flame-retardant electrolyte of the present invention, the lithium salt electrolyte includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium difluorooxalateborate, lithium tetrafluoroborate, lithium bis(oxalateborate), and lithium perchlorate.

[0026] In the above scheme, the lithium salt electrolyte provides lithium ions and transports lithium ions between the positive and negative electrodes, which has a decisive influence on the physical and chemical properties of the electrolyte. By selecting a suitable type of lithium salt electrolyte, a better synergistic effect can be formed with the solvent, thereby improving the overall performance of the electrolyte, such as safety, cycle performance, conductivity, and stability.

[0027] Preferably, the concentration of the lithium salt electrolyte is 0.01~5 mol / L.

[0028] Optionally, the concentration of the lithium salt electrolyte can be 0.01 mol / L, 0.025 mol / L, 0.05 mol / L, 0.075 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, or 5 mol / L, or other values ​​within the above range. It is not limited here, but preferably 0.5~2 mol / L.

[0029] The flame-retardant electrolyte according to the present invention comprises a lithium salt electrolyte and a solvent. The concentration of the lithium salt electrolyte is 0.5~2 mol / L. The lithium salt electrolyte is one or both of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethyl)sulfonyl)imide. The solvent comprises compounds of formula I-6 and other solvents. The other solvents are one or both of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether or 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether. The compounds of formula I-6 account for 50~100% of the total volume of the solvent.

[0030] The flame-retardant electrolyte according to the present invention comprises a lithium salt electrolyte, an additive, and a solvent. The concentration of the lithium salt electrolyte is 0.5~2 mol / L. The lithium salt electrolyte is one or both of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethyl)sulfonyl)imide. The additive is a compound represented by Formula I. The solvent is one or more of dimethyl carbonate, propylene carbonate, or triethylene glycol dimethyl ether. The amount of additive is 1-5% of the solvent volume.

[0031] According to a third aspect of the present invention, the present invention also provides an alkali metal-based battery comprising the flame-retardant electrolyte described above.

[0032] The flame-retardant electrolyte of the present invention can be used alone as an electrolyte in alkali metal-based batteries, or it can be used as part of a solid-liquid composite electrolyte or a quasi-solid gel electrolyte in alkali metal-based batteries.

[0033] The alkali metal-based battery described in this invention can be a liquid alkali metal-based battery or a solid alkali metal-based battery. Correspondingly, the electrolyte is a non-aqueous liquid electrolyte or a polymer solid electrolyte.

[0034] The alkali metal-based battery of the present invention is not limited in shape and can be cylindrical, aluminum-cased, plastic-cased, or pouch-cased.

[0035] The alkali metal-based battery described in this invention can be an alkali metal battery or an alkali metal ion battery. The alkali metal can be lithium, sodium, or potassium.

[0036] Furthermore, the alkali metal-based battery also includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode and the negative electrode are placed in the flame-retardant electrolyte, and the separator is placed between the positive electrode and the negative electrode.

[0037] Preferably, the positive electrode comprises one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese, lithium manganese iron phosphate, or ternary positive electrode materials, more preferably ternary positive electrode materials, such as LiNi. x Co y Mn 1-x-y O2, where 0 < x < 1, 0 < y < 1, and x + y < 1.

[0038] Preferably, the negative electrode is a lithium metal negative electrode, a graphite negative electrode, a silicon negative electrode, a hard carbon negative electrode, or an organic negative electrode; preferably, the separator is a polypropylene film or a polyethylene film.

[0039] The flame-retardant electrolyte provided by this invention introduces a phosphazene compound containing a specific difluoromethyl terminal group into the electrolyte. By utilizing the unique hydrogen bond and supramolecular halogen bond interactions between the molecules of this compound, a stable phosphazene supramolecular network is formed inside the electrolyte. This allows the battery to simultaneously achieve safety, high-voltage stability, and high-temperature adaptability, providing an important technical solution for the development of high-safety, high-performance alkali metal-based batteries. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 The figures show the experimental results of the high-temperature hot box for Comparative Example 2 and Example 2 of the present invention.

[0042] Figure 2 The graph shows the cycle performance of the NCM811 / Li batteries prepared by Comparative Example 2 and Example 2 at 60°C and 4.5 V cutoff voltage. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] Unless otherwise specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0045] The organic solvents, lithium salt electrolytes, and additives used in the embodiments and comparative examples of this invention are all battery grade. The fluorinated triphosphazene compounds prepared in this invention undergo multi-step purification and strict drying.

[0046] In the following examples, the electrolyte was prepared in a glove box filled with 99.999% pure argon gas, with a moisture content of less than 0.1 ppm and a temperature of room temperature.

[0047] The compounds of formulas I-1 to I-10 used in the following examples and comparative examples were synthesized using the following methods: The preparation method of the compound of formula I-1 may include the following steps: Step 1: Dissolve 82g of difluoroethanol and 248g of hexafluorocyclotriphosphazene in 1500ml of diethyl ether. After the sample is completely mixed, add 420g of potassium carbonate, then seal and stir at room temperature for 30h. After the reaction is complete, filter the resulting mixture, and remove the solvent from the filtrate under vacuum to obtain the crude product. Step 2: Distill the crude product under reduced pressure to obtain the target product (yield 35%). MS: [M+H] + m / z = 311.95.

[0048] The preparation method of the compound of formula I-2 may include the following steps: similar to the preparation method of the compound of formula I-1, except that difluoroethanol is replaced with an equimolar amount of difluoropropanol. MS: [M+H] + m / z = 325.96.

[0049] The preparation method of compounds of formula I-3 may include the following steps: similar to the preparation method of compounds of formula I-1, except that difluoroethanol is replaced with an equimolar amount of 2,2,3,3-tetrafluoropropanol. MS: [M+H] + m / z = 361.94.

[0050] The preparation method of compounds of formula I-4 may include the following steps: similar to the preparation method of compounds of formula I-1, except that difluoroethanol is replaced with an equimolar amount of 2,2,3,3,4,4,5,5,6,6-decafluorohexanol. MS: [M+H] + m / z = 511.93.

[0051] The preparation method of compounds of formula I-5 may include the following steps: similar to the preparation method of compounds of formula I-1, except that difluoroethanol is replaced with an equimolar amount of 2-(difluoromethoxy)ethanol. MS: [M+H + m / z = 341.96.

[0052] The preparation method of compounds of formula I-6 may include the following steps: similar to the preparation method of compounds of formula I-1, except that difluoroethanol is replaced with an equimolar amount of 2-(2-(difluoromethoxy)ethoxy)ethanol. MS: [M+H + m / z = 385.98.

[0053] The preparation method of compounds of formula I-7 may include the following steps: similar to the preparation method of compounds of formula I-1, except that difluoroethanol is replaced with an equimolar amount of 5-(difluoromethyl)tetrahydrofuran-3-ol. MS: [M+H] + m / z = 367.97.

[0054] The preparation method of compounds of formula I-8 may include the following steps: similar to the preparation method of compounds of formula I-1, except that difluoroethanol is replaced with twice the molar amount of 2-(difluoromethoxy)ethanol. MS: [M+H] + m / z = 462.01.

[0055] The preparation method of compounds of formula I-9 may include the following steps: similar to the preparation method of compounds of formula I-1, except that difluoroethanol is replaced with an equimolar amount of 2-(2-(2-(2,2-difluoroethoxy)ethoxy)ethoxy)ethanol-1-ol. MS: [M+H] + m / z = 444.02.

[0056] The preparation method of compounds of formula I-10 may include the following steps: similar to the preparation method of compounds of formula I-1, except that difluoroethanol is replaced with an equimolar amount of 14,14-difluoro-3,6,9,12-tetraoxatetradecane-1-ol. MS: [M+H] + m / z = 488.0504.

[0057] Example 1 This embodiment provides a flame-retardant electrolyte, using the compound of Formula I-1 above as an additive, comprising 187g of lithium difluorosulfonylimide, 1000mL of dimethyl carbonate and 50mL of the compound of Formula I-1 above.

[0058] The preparation method is as follows: In a glove box filled with argon, take 187g of lithium difluorosulfonylimide, 1000mL of dimethyl carbonate and 50mL of the above-mentioned compound I-1, stir and let stand to obtain the product.

[0059] Example 2 This embodiment provides a flame-retardant electrolyte that uses the compounds of formula I-6 above as the main solvent, including 187g of lithium difluorosulfonylimide and 1000mL of the compounds of formula I-6 above.

[0060] The preparation method is as follows: In a glove box filled with argon, take 187g of lithium difluorosulfonylimide and 1000mL of the above-mentioned compound I-6, stir and let stand to obtain the product.

[0061] Example 3 This embodiment provides a flame-retardant electrolyte that uses the compounds of formula I-6 above as co-solvents, including 287g of lithium bis(trifluoromethanesulfonylimide), 500mL of the compounds of formula I-6 above, and 500mL of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0062] The preparation method is as follows: In a glove box filled with argon, take 287g of lithium bis(trifluoromethanesulfonyl)imide, 500mL of the above-mentioned compound I-6 and 500mL of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, stir and let stand to obtain the product.

[0063] Example 4 This embodiment provides a flame-retardant electrolyte, which uses the compounds of Formula I-4 above as additives, including 187g of lithium difluorosulfonylimide, 1000mL of propylene carbonate and 50mL of the compounds of Formula I-4 above.

[0064] The preparation method is as follows: In a glove box filled with argon, take 187g of lithium difluorosulfonylimide, 1000mL of propylene carbonate and 50mL of the above-mentioned compound I-4, stir and let stand to obtain the product.

[0065] Example 5 This embodiment provides a flame-retardant electrolyte that uses compounds of formula I-7 as co-solvents, including 187g of lithium bis(fluorosulfonyl)imide, 600mL of compounds of formula I-7, and 400mL of diethyl carbonate.

[0066] The preparation method is as follows: In a glove box filled with argon, take 187g of lithium difluorosulfonylimide, 600mL of the above-mentioned compound I-7, and 400mL of diethyl carbonate, stir and let stand to obtain the product.

[0067] Example 6 This embodiment provides a flame-retardant electrolyte, which uses compounds of formula I-8 as additives, including 187g of lithium difluorosulfonylimide, 1000mL of triethylene glycol dimethyl ether and 50mL of compounds of formula I-8.

[0068] The preparation method is as follows: In a glove box filled with argon, take 187g of lithium difluorosulfonylimide, 1000mL of triethylene glycol dimethyl ether and 50mL of the above-mentioned compound I-8, stir and let stand to obtain the product.

[0069] Example 7 This embodiment provides a flame-retardant electrolyte, which differs from Embodiment 2 in that it uses a compound of Formula I-5 instead of a compound of Formula I-6.

[0070] Example 8 This embodiment provides a flame-retardant electrolyte for lithium batteries, which differs from Embodiment 1 in that a compound of Formula I-6 is used instead of a compound of Formula I-1.

[0071] Example 9 This embodiment provides a flame-retardant electrolyte, which differs from Example 8 in that the amount of compound of formula I-6 used is 5 mL.

[0072] Example 10 This embodiment provides a flame-retardant electrolyte, which differs from Example 8 in that the amount of compound of formula I-6 used is 10 mL.

[0073] Example 11 This embodiment provides a flame-retardant electrolyte, which differs from Embodiment 2 in that it uses a compound of Formula I-9 instead of a compound of Formula I-6.

[0074] Example 12 This embodiment provides a flame-retardant electrolyte, which differs from Embodiment 2 in that a compound of Formula I-10 is used instead of a compound of Formula I-6.

[0075] Comparative Example 1 This comparative example provides an electrolyte comprising 187g of lithium bis(fluorosulfonyl)imide and 1000mL of dimethyl carbonate.

[0076] The preparation method is as follows: In a glove box filled with argon, take 187g of lithium difluorosulfonylimide and 1000mL of dimethyl carbonate, stir and let stand to obtain the product.

[0077] Comparative Example 2 This comparative example provides an electrolyte comprising 187g of lithium difluorosulfonylimide, 500mL of ethylene glycol dimethyl ether, and 500mL of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0078] The preparation method is as follows: In a glove box filled with argon, take 187g of lithium difluorosulfonylimide, 500mL of ethylene glycol dimethyl ether, and 500mL of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, stir and let stand to obtain the product.

[0079] Comparative Example 3 This comparative example provides an electrolyte comprising 187g of lithium bis(fluorosulfonyl)imide and 1000mL of ethylene glycol dimethyl ether.

[0080] The preparation method is as follows: In a glove box filled with argon, take 187g of lithium difluorosulfonylimide and 1000mL of ethylene glycol dimethyl ether, stir and let stand to obtain the product.

[0081] Comparative Example 4 This comparative example provides a flame-retardant electrolyte, which differs from Example 2 in that it uses a compound represented by Formula II instead of I-6. The preparation method of the compound represented by Formula II is similar to that of the compound represented by Formula I-1. Its preparation method is the same as in Example 2.

[0082] Formula II.

[0083] Comparative Example 5 This comparative example provides a flame-retardant electrolyte, which differs from Example 2 in that it uses a compound represented by Formula III instead of I-6. The preparation method of the compound represented by Formula III is similar to that of the compound represented by Formula I-1. Its formulation method is the same as in Example 2.

[0084] Formula III.

[0085] Comparative Example 6 This comparative example provides a flame-retardant electrolyte, which differs from Example 2 in that it uses a compound represented by Formula IV instead of I-6. The preparation method of the compound represented by Formula IV is similar to that of the compound represented by Formula I-1. Its formulation method is the same as in Example 2.

[0086] Formula IV.

[0087] Comparative Example 7 This comparative example provides a flame-retardant electrolyte, which differs from Example 2 in that a compound represented by Formula V is used instead of I-6. The preparation method of the compound represented by Formula V is similar to that of the compound represented by Formula I-1. Its formulation method is the same as in Example 2.

[0088] , formula V.

[0089] Performance testing The electrolytes prepared in the above embodiments and comparative examples were subjected to flame retardancy tests, as follows: The igniter flame was brought close to each of the 100 μL electrolytes, held for 3 seconds, and then removed. The self-extinguishing time of the flame was measured. The experiment was repeated 3 times for each electrolyte, and the average value was calculated. The test results are shown in Table 1.

[0090] Table 1 Comparison of self-extinguishing time between the examples and comparative examples Self-extinguishing time (s / g) Example 1 0 Example 2 0 Example 3 0 Example 4 0 Example 5 0 Example 6 0 Example 7 0 Example 8 0 Example 9 0 Example 10 0 Example 11 0 Example 12 0 Comparative Example 1 85 Comparative Example 2 50 Comparative Example 3 115 Comparative Example 4 0 Comparative Example 5 0 Comparative Example 6 0 Comparative Example 7 0 The liquid electrolytes prepared in the above embodiments and comparative examples were assembled into batteries and then subjected to high-temperature hot box experiments, as follows: With LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811) was used as the positive electrode, lithium foil as the negative electrode, and aluminum foil as the positive current collector. A Celgard 2325 separator was used. The pouch cells were assembled in a glove box, and after electrolyte injection, they were allowed to stand for 24 hours before testing. After charging to 4.3 V at 1 / 5C at room temperature, the cells were transferred to a heating chamber and heated to 150°C in 30 minutes, then held at 150°C for 60 minutes. Changes in battery voltage and surface temperature were recorded.

[0091] Table 2 Comparison of short-circuit times in high-temperature hot box experiments of the embodiments and comparative examples. High temperature short circuit time Example 1 90 minutes without short circuit Example 2 90 minutes without short circuit Example 3 90 minutes without short circuit Example 4 90 minutes without short circuit Example 5 90 minutes without short circuit Example 6 90 minutes without short circuit Example 7 90 minutes without short circuit Example 8 90 minutes without short circuit Example 9 90 minutes without short circuit Example 10 90 minutes without short circuit Example 11 90 minutes without short circuit Example 12 90 minutes without short circuit Comparative Example 1 45 minutes Comparative Example 2 56 minutes Comparative Example 3 30 minutes Comparative Example 4 70 minutes Comparative Example 5 80 minutes Comparative Example 6 74 minutes Comparative Example 7 82 minutes Figure 1 The graph shows the experimental results of the high-temperature hot box for Comparative Example 2 and Example 2. Figure 1 As can be seen from Tables 1 and 2, the fluorinated triphosphazene compound used in this invention exhibits excellent non-flammability and high-temperature stability, effectively achieving non-flammability of the liquid electrolyte while reducing high-temperature decomposition of the electrolyte. Compared with comparative batteries that do not use or use phosphazenes with other structures, it exhibits higher safety.

[0092] The electrolytes prepared in the above embodiments and comparative examples were assembled into batteries and then subjected to high-temperature and high-pressure cycling performance tests, as follows: With LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) was used as the positive electrode, lithium foil as the negative electrode, and aluminum foil as the positive current collector. A Celgard 2325 separator was used. Button half-cells were assembled in a glove box and tested after 24 hours of rest. The batteries were activated by three charge-discharge cycles at a constant temperature of 60°C, with a rate of 1 / 10C between 3.0 V and 4.3 V. Charge-discharge cycles were then performed at a rate of 1 / 3C at high cutoff voltages of 4.5 V and 4.6 V. The test results are shown in Table 3.

[0093] Table 3 shows the cycling results of the NCM811 / Li full cells assembled in the examples and comparative examples at 60°C and cutoff voltages of 4.5V and 4.6V.

[0094] Figure 2 The graph shows the cycle performance of the NCM811 / Li batteries prepared by Comparative Example 2 and Example 2 at 60°C and 4.5 V cutoff voltage.

[0095] From Table 3 and Figure 2As can be seen, under high temperature and high voltage conditions, the capacity and cycle stability of the liquid electrolyte prepared in this embodiment are significantly better than those of the comparative example, indicating that the fluorinated cyclotriphosphazene compound provided by this invention can significantly improve the cycle stability of the battery and obtain excellent high voltage resistance and high temperature stability.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A fluorinated cyclic triphosphazene compound, characterized in that, It has the general formula shown in Equation I: Equation I; Among them, R1 to R6 are each independently selected from -F or And one or two of R1 to R6 are ; R7 is selected from substituted or unsubstituted alkylene groups, substituted or unsubstituted chain ether groups, and substituted or unsubstituted cyclic ether groups; the substitution means that at least one hydrogen in the group is independently replaced by a halogen, cyano, olefinic or alkyne group.

2. The fluorinated cyclic triphosphazene compound according to claim 1, characterized in that, R7 is selected from substituted or unsubstituted C1-C10 alkylene groups, substituted or unsubstituted chain ether groups with 2-10 carbon atoms, and substituted or unsubstituted cyclic ether groups with 2-10 carbon atoms. Preferably, R7 is selected from substituted or unsubstituted chain ether groups with 2-10 carbon atoms and 1-5 oxygen atoms, or substituted or unsubstituted cyclic ether groups with 2-10 carbon atoms and 1-5 oxygen atoms.

3. The fluorinated cyclic triphosphazene compound according to claim 1 or 2, characterized in that, The compound represented by Formula I is selected from one or more of Formulas I-1 to I-10:

4. A flame-retardant electrolyte, characterized in that, It contains at least 0.1% by volume the fluorocyclic triphosphazene compound as described in any one of claims 1-3.

5. The flame-retardant electrolyte according to claim 4, characterized in that, It includes a solvent, a lithium salt electrolyte, and optionally additives; the solvent and / or additives use the fluorinated triphosphazene compound.

6. The flame-retardant electrolyte according to claim 5, characterized in that, The fluorinated triphosphazene compound is used as a component of the solvent, and the volume of the fluorinated triphosphazene compound accounts for 5%-100% of the total volume of the solvent, preferably 50-100%.

7. The flame-retardant electrolyte according to claim 6, characterized in that, The solvent also includes one or more of the following: ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, diethyl ether, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methyl nonafluorobutyl ether, and bis(2,2,2-trifluoroethyl) ether; Preferably, the solvent further includes 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether or 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

8. The flame-retardant electrolyte according to claim 5, characterized in that, The mixture includes additives, solvents, and a lithium salt electrolyte, wherein the fluorinated cyclic triphosphazene compound is a component of the additives; the volume of the fluorinated cyclic triphosphazene compound is 0.1-5% of the volume of the solvent. Preferably, the solvent includes one or more of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, diethyl ether, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

9. The flame-retardant electrolyte according to any one of claims 5-8, characterized in that, The lithium salt electrolyte includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium difluorooxalateborate, lithium tetrafluoroborate, lithium bis(oxalateborate), and lithium perchlorate. Preferably, the concentration of the lithium salt electrolyte is 0.01~5 mol / L.

10. An alkali metal-based battery, characterized in that, Includes the flame-retardant electrolyte according to any one of claims 4-9.

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