Lithium ion battery electrolyte based on dual-function synergistic effect and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion battery electrolyte, and provides lithium ion battery electrolyte based on a dual-function synergistic effect and a preparation method thereof. The preparation method comprises the following steps: carrying out an alkylation reaction on N-methylpyrrolidine, carrying out a reaction on bis (trifluoromethylsulfonyl) lithium imide, introducing a flexible side chain to improve the ion migration ability at a low temperature, introducing a piperidinol oxide to embed a free radical capture group to inhibit the decomposition of the electrolyte under a high-voltage condition, and introducing a fluorine-boron functional group to improve the oxidation resistance of the electrolyte; secondly, carrying out silane substitution by taking hexachlorocyclotriphosphazene as a core, introducing a boric acid ester group, and reacting a boric acid ester substitute with methyl trifluoromethanesulfonate to enhance the thermal stability; according to the electrolyte, excellent performance in a wide temperature range is realized through low-temperature performance optimization of the flexible chain segment, high-voltage stability improvement of the free radical capture group, an ion migration enhancement function of the fluorine-boron structure and interface stability optimization of the functionalized cyclotriphosphazene.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery electrolytes, and relates to a lithium-ion battery electrolyte based on the synergistic effect of dual functions and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are one of the most widely used energy storage technologies at present. Their widespread use in fields such as electronic devices, electric vehicles, and energy storage power grids has promoted the progress of modern energy technologies. With its high energy density, long cycle life, low self-discharge rate, and relatively mature manufacturing process, lithium-ion batteries have become an indispensable core technology in the process of modern energy transformation. Although lithium-ion batteries have made significant progress in performance and application scope, with the diversification of application scenarios and the increasing demand for use in extreme environments, the problem of performance stability in a wide temperature range has gradually become the main technical bottleneck restricting its further development. In practical applications, the electrochemical performance of lithium-ion batteries largely depends on the properties and stability of their electrolytes. As one of the core functional components of lithium-ion batteries, the main role of the electrolyte is to provide a migration channel for lithium ions between the positive and negative electrodes to ensure the normal progress of the electrochemical reaction. At the same time, through the interfacial reaction with the electrode material, a solid electrolyte interface and a cathode electrolyte interface are formed, thereby protecting the electrode material and improving the cycle stability of the battery. Traditional electrolytes usually consist of lithium salts and organic carbonate solvents. Although they perform excellently under normal temperature conditions, their performance under extreme temperature conditions is significantly insufficient.

[0003] In a low-temperature environment, the solvent viscosity of the electrolyte will increase significantly, resulting in a decrease in the dissociation degree of the lithium salt, and thus a sharp drop in the ionic conductivity of the electrolyte. In addition, low-temperature conditions will also exacerbate the kinetic barrier of lithium-ion deposition on the negative electrode surface, leading to an increase in internal resistance, a rapid decay of battery capacity, and safety problems. In a high-temperature environment, the stability of the electrolyte also faces challenges. The electrolyte system with lithium hexafluorophosphate as the main lithium salt is prone to decomposition reactions under high-temperature conditions, generating corrosive by-products. These by-products will not only accelerate the decomposition of the solvent but also damage the SEI and CEI films on the electrode surface, resulting in a shortened cycle life of the battery and even a risk of thermal runaway. Therefore, the applicability of traditional lithium-ion battery electrolytes in a wide temperature range is poor and cannot meet the requirements for the efficient operation of batteries in extreme environments. In order to meet the performance requirements of lithium-ion batteries under extreme temperature conditions, developing an electrolyte that can work stably in a wide temperature range has become a key problem and an important direction in current battery technology research. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a lithium-ion battery electrolyte based on the synergistic effect of dual functions and its preparation method. By introducing fluoroboron-modified ionic liquid and functionalized cyclotriphosphazene, the stability and ionic conductivity of the electrolyte in a wide temperature range are realized. First, using N-methylpyrrolidine as the starting material, through alkylation reaction, introducing flexible chain segments, free radical capture groups and fluoroboron functional groups, a fluoroboron-modified ionic liquid with high thermal stability and low-temperature conductivity is prepared. At the same time, using hexachlorocyclotriphosphazene as the core, through a series of substitution reactions, siloxy groups, boric acid esters and trifluoromethanesulfonic acid groups are introduced to prepare functionalized cyclotriphosphazene, which is used to improve the interfacial stability and ionic migration ability of the electrolyte, so as to meet the needs of actual production.

[0005] To achieve this purpose, the present invention adopts the following technical solutions:

[0006] In the first aspect, the present invention provides a preparation method of a lithium-ion battery electrolyte based on the synergistic effect of dual functions, and the preparation method includes:

[0007] S1. Mix N-methylpyrrolidine with the first portion of anhydrous acetonitrile, add 1-bromobutane under a nitrogen atmosphere, raise the temperature to the first temperature and reflux for reaction. After the reaction is completed, rotary evaporation is carried out to obtain a pre-product. Disperse the pre-product in deionized water, then add lithium bis(trifluoromethanesulfonyl)imide and stir at room temperature. After extraction and rotary evaporation, an ionic liquid is obtained. Disperse the ionic liquid, polyethylene glycol and potassium carbonate in the second portion of anhydrous acetonitrile, and under a nitrogen atmosphere, raise the temperature to the first temperature for reaction. After rotary evaporation, an ionic liquid grafted with a flexible side chain is obtained. Disperse the ionic liquid grafted with a flexible side chain and piperidine N-oxide in the first portion of anhydrous dichloromethane, add triethylamine under an ice-water bath condition and stir. After rotary evaporation, an ionic liquid embedded with a free radical capture group is obtained. Disperse the ionic liquid embedded with a free radical capture group and sodium tetrafluoroborate in the second portion of anhydrous dichloromethane, add boron trifluoride ether complex and stir at room temperature. After rotary evaporation, a fluoroboron-modified ionic liquid is obtained;

[0008] S2. Under a nitrogen atmosphere, disperse hexachlorocyclotriphosphazene, pyridine and trimethylsilanol in the first portion of anhydrous tetrahydrofuran, raise the temperature to the second temperature and stir for reaction. After the reaction is completed, filter and rotary evaporate to obtain a silane substitute. Under an ice-water bath condition, disperse the silane substitute, trimethyl borate, anhydrous methanol and triethylamine in anhydrous dichloromethane and stir at room temperature. Filter and rotary evaporate to obtain a boric acid ester substitute. Under a nitrogen atmosphere and an ice-water bath condition, disperse the boric acid ester substitute, methyl trifluoromethanesulfonate and potassium carbonate in the second portion of anhydrous tetrahydrofuran and stir at room temperature for reaction. After the reaction is completed, filter and rotary evaporate to obtain functionalized cyclotriphosphazene;

[0009] S3. Add a lithium salt, a fluoroboron-modified ionic liquid and functionalized cyclotriphosphazene to an organic solvent, and mix evenly to obtain a lithium-ion battery electrolyte based on the synergistic effect of dual functions.

[0010] N - methylpyrrolidine is a cyclic secondary amine that contains a five - membered nitrogen - containing heterocycle in its structure. The nitrogen atom has a lone pair of electrons, showing strong nucleophilicity. This nucleophilicity enables N - methylpyrrolidine to rapidly undergo a nucleophilic substitution reaction when reacting with primary alkyl halides (such as 1 - bromobutane), forming a compound with a quaternary ammonium structure. As a primary alkyl halide, the bromine atom of 1 - bromobutane makes the adjacent carbon atom carry a partial positive charge through the inductive effect, and this positive charge enhances its reactivity as an electrophilic reagent. In anhydrous acetonitrile, a polar aprotic solvent, the nitrogen atom of N - methylpyrrolidine attacks the carbon - bromine bond of 1 - bromobutane with its lone pair of electrons, and the bromine atom leaves as a leaving group, thus forming a quaternary ammonium salt. The generated quaternary ammonium salt is an ionic compound with strong ionic properties. The molecular skeleton of the quaternary ammonium salt has relatively high stability, and its quaternary ammonium cation structure can improve the thermal stability and electrochemical stability of the compound, laying the foundation for the subsequent functional modification of ionic liquids.

[0011] After the quaternary ammonium salt is generated in the above - mentioned reaction, the next step is to replace the bromide ion with the bis(trifluoromethylsulfonyl)imide anion through an anion - exchange reaction. This process is achieved by dispersing the quaternary ammonium salt in water and adding lithium bis(trifluoromethylsulfonyl)imide as the anion - exchange reagent. The bis(trifluoromethylsulfonyl)imide anion is a weakly coordinating anion with a complex structure and a relatively large volume. It is formed by bridging two trifluoromethylsulfonyl groups through a nitrogen atom. This structure results in a highly dispersed charge distribution and a low coordination ability of the bis(trifluoromethylsulfonyl)imide anion, thereby reducing the intensity of its interaction with cations. Due to the strong coordination ability of the bromide ion, the bis(trifluoromethylsulfonyl)imide anion will preferentially bind to the cationic skeleton during the exchange process, generating an ionic liquid with the bis(trifluoromethylsulfonyl)imide anion. The introduction of the bis(trifluoromethylsulfonyl)imide anion has an impact on the properties of the ionic liquid. First, due to the large volume and dispersed charge distribution of the bis(trifluoromethylsulfonyl)imide anion, the force between it and the cation is weak, resulting in a significant reduction in the cohesive force of the ionic liquid, thus lowering the melting point and glass transition temperature of the ionic liquid. This is crucial for the low - temperature performance of the electrolyte. The reduced glass transition temperature ensures that the ionic liquid still has good fluidity in a low - temperature environment, avoiding problems such as excessive viscosity or crystallization at low temperatures. Second, the bis(trifluoromethylsulfonyl)imide anion itself has extremely high thermal stability and antioxidant properties, which significantly improves the chemical stability of the ionic liquid under high - temperature conditions, thereby broadening the high - temperature working window of the electrolyte. In addition, the weak coordination of the bis(trifluoromethylsulfonyl)imide anion is beneficial to the dissolution and dissociation of lithium salts, improving the ionic mobility and conductivity of the electrolyte.

[0012] To further improve the physicochemical properties of ionic liquids, polyethylene glycol was introduced as a flexible side chain in the experiment. Specifically, in the presence of a base (potassium carbonate), the terminal hydroxyl group of polyethylene glycol undergoes a chemical reaction with the active site on the ionic liquid cation backbone, connecting the flexible side chain to the ionic liquid. The terminal hydroxyl group of polyethylene glycol is first deprotonated under the action of potassium carbonate to generate an alkoxide anion with high nucleophilicity. This alkoxide anion can attack the active site in the ionic liquid cation backbone, thereby generating a modified ionic liquid with a flexible polyethylene glycol chain. In this process, the flexible polyethylene glycol chain weakens the stacking interaction between ionic liquid molecules, further reducing the cohesive energy between molecules, and thus significantly lowering the glass transition temperature, which is crucial for the design of low-temperature electrolytes because a lower glass transition temperature means that the electrolyte can still maintain sufficient fluidity and ion migration ability in extremely low-temperature environments. On the other hand, the polyethylene glycol chain itself has a certain ability to dissolve lithium salts, and its polar segments can coordinate with lithium ions in the lithium salts, thereby enhancing the solubility of the ionic liquid in lithium salts and further improving the ion migration rate and overall conductivity of the electrolyte. After the introduction of the flexible side chain, to improve the antioxidant performance and chemical stability of the ionic liquid, the present invention completed the functional modification of the radical capture group by introducing piperidine N-oxide. Piperidine N-oxide is a radical scavenger that can be embedded into the ionic liquid molecule in the form of a chemical bond, enhancing its ability to capture radicals. Triethylamine acts as a base and may activate the functional groups in the ionic liquid, enabling it to undergo a chemical reaction with piperidine N-oxide. The piperidine N-oxide molecule binds to the ionic liquid cation backbone through a chemical bond to form a functionalized ionic liquid with a radical capture group. The introduction of piperidine N-oxide is of great significance for the high-temperature stability of the electrolyte. Under high-temperature conditions, the electrolyte may generate oxidation radicals due to oxidation, and these radicals will trigger a series of side reactions, leading to the decomposition and performance degradation of the electrolyte. The piperidine N-oxide radical capture group can quickly react with these radicals, capture and neutralize them, thereby inhibiting the chain reaction initiated by oxidation radicals and improving the antioxidant and chemical stability of the electrolyte.

[0013] Finally, through the reaction of sodium tetrafluoroborate, boron trifluoride ether complex with the ionic liquid, tetrafluoroborate was introduced. Tetrafluoroborate is a weakly coordinating anion with stable chemical properties, excellent antioxidant and thermal stability. Through anion exchange, tetrafluoroborate replaced some of the original anions in the ionic liquid, further enhancing the thermal stability and electrochemical stability window of the ionic liquid. Specifically, tetrafluoroborate can effectively inhibit the decomposition reaction of the electrolyte under high voltage conditions, which is of great significance for the long-term stable operation of lithium-ion batteries in a high-voltage environment. In addition, the low coordination ability of tetrafluoroborate can also reduce the formation of ion pairs in the ionic liquid, increase the transference number of lithium ions, and thus further optimize the ionic conductivity of the electrolyte. In summary, the introduction of bis(trifluoromethylsulfonyl)imide anion and the modification of flexible polyethylene glycol side chains reduce the glass transition temperature, enabling the electrolyte to maintain good fluidity and ion migration ability under low temperature conditions; at the same time, the introduction of fluoroboron modification and radical scavenging groups enhances the antioxidant and thermal stability of the ionic liquid, giving it a longer service life at high temperatures. In addition, the synergistic effect of polyethylene glycol chains and large-volume weakly coordinating anions improves the solubility of lithium salts and ion mobility, further enhancing the conductivity of the electrolyte.

[0014] Hexachlorocyclotriphosphazene is a symmetric cyclic compound. Its molecular structure consists of three phosphorus atoms and three nitrogen atoms arranged alternately, forming a six-membered cyclic skeleton. Each phosphorus atom is connected to a chlorine atom by a single bond. The particularity of this molecular structure endows hexachlorocyclotriphosphazene with relatively high chemical reactivity. Especially the P-Cl bonds on its phosphorus atoms, due to the strong electron-withdrawing effect of chlorine atoms and the action of the empty orbitals of phosphorus atoms, make these bonds have relatively high electrophilicity and are easily attacked by nucleophiles. Therefore, hexachlorocyclotriphosphazene is often used as an ideal multifunctional molecular skeleton and different functional groups can be introduced through functionalization modification. First, hexachlorocyclotriphosphazene undergoes a nucleophilic substitution reaction with trimethylsilanol in an anhydrous tetrahydrofuran solvent. The hydroxyl group in trimethylsilanol shows strong nucleophilicity due to the lone pair of electrons on the oxygen atom. During the reaction, the hydroxyl group of trimethylsilanol interacts with the solvent or base through hydrogen bonding and is further activated, thus enhancing the nucleophilicity of the oxygen atom. Subsequently, the oxygen atom in the hydroxyl group attacks the empty orbital of the phosphorus atom in the hexachlorocyclotriphosphazene molecule, and at the same time the chloride ion on the phosphorus breaks and leaves as a leaving group, generating a silane-substituted cyclotriphosphazene derivative with a P-O-Si(CH₃)₃ bond. In this reaction, some P-Cl bonds are converted into P-O-Si(CH₃)₃ bonds with higher chemical stability, and the introduction of the trimethylsilyl group changes the physical and chemical properties of cyclotriphosphazene. The silane-substituted cyclotriphosphazene shows improvements in many aspects. First, the trimethylsilyl group is a relatively large flexible group. Its introduction significantly reduces the stacking tendency between molecules through steric hindrance effects, thereby reducing the glass transition temperature of the material and improving its flow performance under low-temperature conditions, which is particularly important for the application of lithium-ion battery electrolytes in low-temperature environments; secondly, the silane substitution significantly reduces the number of highly reactive P-Cl bonds in the cyclotriphosphazene molecule, reducing the possibility of side reactions occurring at high temperatures, thereby further improving the thermal stability of the material. In addition, the trimethylsilyl group has relatively high chemical inertness and is not easily involved in further chemical reactions. Therefore, the chemical stability of cyclotriphosphazene after silane substitution is also greatly improved.

[0015] On the basis of silane substitution, the functionalized cyclotriphosphazene is further reacted with trimethyl borate in anhydrous dichloromethane to undergo an intermolecular esterification reaction. This reaction generates a functionalized cyclotriphosphazene with borate groups by further converting some of the trimethylsilylphosphate bonds into phosphoxyboron bonds. The ester group in the trimethyl borate molecule forms a coordination bond with the phosphorus atom in the cyclotriphosphazene through the lone pair electrons on the oxygen atom, while the trimethylsilyl group is displaced as a leaving group. Through this chemical modification, borate groups are introduced into the molecule, endowing the cyclotriphosphazene with new functional properties. The introduction of borate groups improves the electrolyte performance of cyclotriphosphazene. On the one hand, the boron atom has an unsaturated coordination ability and can form a weak coordination interaction with lithium ions, thus significantly improving the solubility and distribution of lithium salts in the electrolyte. This property is of great significance for increasing the ionic conductivity of the electrolyte. On the other hand, the introduction of phosphoxyboron bonds further improves the thermal stability and chemical inertness of the molecule, enabling it to maintain the integrity of the molecular structure under high-temperature conditions and reducing possible degradation reactions. In addition, the flexible and polar properties of the borate groups can further reduce the intermolecular packing effect, thereby optimizing the physical properties of the material.

[0016] Subsequently, the borate-functionalized cyclotriphosphazene is reacted with methyl trifluoromethanesulfonate and potassium carbonate to further introduce trifluoromethanesulfonic acid groups, completing the multi-functionalization modification of cyclotriphosphazene. In this reaction, potassium carbonate acts as a base to activate methyl trifluoromethanesulfonate, and the oxygen atom in the trifluoromethanesulfonic acid group undergoes a nucleophilic attack on the phosphorus atom in the cyclotriphosphazene. The trifluoromethanesulfonic acid group is a strong electron-withdrawing group, and its introduction significantly reduces the electron cloud density of the cyclotriphosphazene molecule, thereby improving the antioxidant performance of the molecule and enabling it to inhibit the decomposition of the electrolyte under high-voltage conditions. In addition, due to the high polarity and flexibility of the trifluoromethanesulfonic acid group, its introduction further reduces the intermolecular packing effect, lowers the glass transition temperature, and improves the performance of the electrolyte under low-temperature conditions. Through the multi-step functionalization modification of hexachlorocyclotriphosphazene, first, silane substitution and borate modification significantly improve the thermal stability of cyclotriphosphazene, enabling it to maintain the integrity of the molecular structure under high-temperature conditions; second, the introduction of borate groups significantly improves the solubility and distribution of lithium salts through weak coordination with lithium ions, thereby increasing the ionic conductivity of the electrolyte; the introduction of trifluoromethanesulfonic acid groups enhances the antioxidant performance of cyclotriphosphazene, reduces the decomposition risk under high-voltage conditions, and broadens the electrochemical stability window of the electrolyte; finally, the flexible structures of silane substitution and trifluoromethanesulfonic acid groups lower the glass transition temperature of the molecule, enabling the electrolyte to still have good fluidity and ionic migration ability at low temperatures.

[0017] In the present invention, the electrolyte is designed by combining functionalized cyclotriphosphazene with fluoroborate-modified ionic liquid and their co-action with lithium salt, achieving a dual-functional synergistic effect. Through multi-step chemical modification (silyl substitution, borate ester modification, and introduction of trifluoromethylsulfonic acid group), the highly reactive P-Cl bonds in the molecule of functionalized cyclotriphosphazene are transformed into stable P-O-Si and P-O-B bonds, improving the thermal stability and antioxidant properties of cyclotriphosphazene, enabling it to maintain the integrity of the molecular structure in high-temperature and strongly oxidizing environments. The fluoroborate and trifluoromethylsulfonyl groups in the fluoroborate-modified ionic liquid have strong electron-withdrawing characteristics, further reducing the electron cloud density of the molecular system and enhancing the antioxidant properties of the electrolyte. The thermal stability of the fluoroborate-modified ionic liquid itself and the stability of functionalized cyclotriphosphazene act synergistically to enable the electrolyte to remain stable under high-temperature conditions. At low temperatures, the viscosity of the electrolyte often increases, and the intermolecular packing effect is significant, resulting in a decrease in the migration ability of lithium ions. Functionalized cyclotriphosphazene reduces the glass transition temperature of the molecule by introducing trimethylsilyl groups. The trimethylsilyl group is a group with relatively high flexibility, with a large volume and a low intermolecular interaction strength, which can effectively disrupt the close packing between cyclotriphosphazene molecules, increase the degree of freedom of the molecules, optimize the fluidity of the electrolyte, and enable it to still have a high molecular motion ability under low-temperature conditions. The large-volume anions in the fluoroborate-modified ionic liquid further reduce the interaction between ions, reduce the cohesive force of the electrolyte, and synergistically with the flexible effect of the trimethylsilyl groups in functionalized cyclotriphosphazene, improve the fluidity of the electrolyte at low temperatures.

[0018] In terms of ion transport, the borate groups on the functionalized cyclotriphosphazene provide active sites with weak coordination to lithium ions. The Lewis acid nature of boron atoms can form weak interactions with lithium ions, enhancing the solubility and uniform distribution of lithium salts in the electrolyte, promoting the dissociation of lithium ions and reducing the aggregation effect of lithium ions in the solvent, thus improving the ionic conductivity of the electrolyte. On the other hand, the tetrafluoroborate and trifluoromethylsulfonylimide groups in the fluoroborate-modified ionic liquid are large-volume anions with low coordination ability, which can reduce the interaction between lithium ions and anions, further promoting the migration of lithium ions. Acting in synergy with the weak lithium ion coordination provided by the borate groups in the functionalized cyclotriphosphazene, the ion transport performance is enhanced. During the preparation of the fluoroborate-modified ionic liquid, piperidine alcohol oxide is introduced into the molecular structure to form a functional group with free radical capture ability. Piperidine alcohol oxide can effectively capture the free radicals generated during the operation of lithium-ion batteries in the electrolyte, thereby inhibiting the further damage of these highly reactive intermediates to the electrode material and the electrolyte. The trifluoromethanesulfonic acid group in the functionalized cyclotriphosphazene has a strong electron-withdrawing effect, which can reduce the electron cloud density of the molecule, further enhancing the passivation effect of the electrolyte on free radicals and simultaneously inhibiting the chain reaction induced by free radicals. The synergistic effect with piperidine alcohol oxide significantly improves the antioxidant performance and free radical capture ability of the electrolyte, protecting the electrolyte and the electrode surface and extending the cycle life of the battery.

[0019] As a preferred technical solution of the present invention, in S1, the mass-volume ratio of N-methylpyrrolidine to the first portion of anhydrous acetonitrile is 1 g:10 mL.

[0020] In some alternative examples, the mass ratio of N-methylpyrrolidine to 1-bromobutane is 1:1.7.

[0021] In some alternative examples, the first temperature is 80 - 90 °C, for example, it can be 80.0 °C, 81.0 °C, 82.0 °C, 83.0 °C, 84.0 °C, 85.0 °C, 86.0 °C, 87.0 °C, 88.0 °C, 89.0 °C or 90.0 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0022] In some alternative examples, the reflux reaction time at the first temperature is 10 - 12 h, for example, it can be 10.0 h, 10.2 h, 10.4 h, 10.6 h, 10.8 h, 11.0 h, 11.2 h, 11.4 h, 11.6 h, 11.8 h or 12.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0023] In some alternative examples, the mass-volume ratio of the pre-product to deionized water is 1 g:10 mL.

[0024] In some alternative examples, the mass ratio of the pre-product to lithium bis(trifluoromethanesulfonyl)imide is 2:3.

[0025] In some alternative examples, the time for stirring at room temperature is 6 - 8 h, for example, it can be 6.0 h, 6.2 h, 6.4 h, 6.6 h, 6.8 h, 7.0 h, 7.2 h, 7.4 h, 7.6 h, 7.8 h or 8.0 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0026] In some alternative examples, the mass ratio of the ionic liquid, polyethylene glycol to potassium carbonate is 20:15:3.

[0027] In some alternative examples, the mass-to-volume ratio of the ionic liquid to the second portion of anhydrous acetonitrile is 1 g:10 mL.

[0028] In some alternative examples, the reaction time at the first temperature is 10 - 12 h, for example, it can be 10.0 h, 10.2 h, 10.4 h, 10.6 h, 10.8 h, 11.0 h, 11.2 h, 11.4 h, 11.6 h, 11.8 h or 12.0 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0029] In some alternative examples, the mass ratio of the ionic liquid grafted with a flexible side chain to piperidine N-oxide is 4:1.

[0030] In some alternative examples, the mass-to-volume ratio of the ionic liquid grafted with a flexible side chain to the first portion of anhydrous dichloromethane is 1 g:10 mL.

[0031] In some alternative examples, the mass ratio of the ionic liquid grafted with a flexible side chain to triethylamine is 20:1.

[0032] In some alternative examples, the time for adding triethylamine and stirring is 3 - 4 h, for example, it can be 3.0 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h or 4.0 h, but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0033] In some alternative examples, the mass ratio of the ionic liquid embedded with a radical trapping group to sodium tetrafluoroborate is 10:1.

[0034] In some alternative examples, the mass-to-volume ratio of the ionic liquid embedded with a radical trapping group to the second portion of anhydrous dichloromethane is 1 g:10 mL.

[0035] In some alternative examples, the time for adding boron trifluoride ether complex and stirring at room temperature is 5 - 6 h. For example, it can be 5.0 h, 5.1 h, 5.2 h, 5.3 h, 5.4 h, 5.5 h, 5.6 h, 5.7 h, 5.8 h, 5.9 h or 6.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] As a preferred technical solution of the present invention, in S2, the mass ratio of hexachlorocyclotriphosphazene, pyridine to trimethylsilanol is 15:16:12.

[0037] In some alternative examples, the mass - to - volume ratio of hexachlorocyclotriphosphazene to the first portion of anhydrous tetrahydrofuran is 1 g:20 mL.

[0038] In some alternative examples, the second temperature is 50 - 60 °C. For example, it can be 50.0 °C, 51.0 °C, 52.0 °C, 53.0 °C, 54.0 °C, 55.0 °C, 56.0 °C, 57.0 °C, 58.0 °C, 59.0 °C or 60.0 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] In some alternative examples, the reaction time for stirring at the second temperature is 10 - 12 h. For example, it can be 10.0 h, 10.2 h, 10.4 h, 10.6 h, 10.8 h, 11.0 h, 11.2 h, 11.4 h, 11.6 h, 11.8 h or 12.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0040] In some alternative examples, the mass ratio of the silane substituent, trimethyl borate, anhydrous methanol to triethylamine is 9:4:10:5.

[0041] In some alternative examples, the mass - to - volume ratio of the silane substituent to anhydrous dichloromethane is 9 g:100 mL.

[0042] In some alternative examples, the time for stirring at room temperature after dispersing in anhydrous dichloromethane is 10 - 12 h. For example, it can be 10.0 h, 10.2 h, 10.4 h, 10.6 h, 10.8 h, 11.0 h, 11.2 h, 11.4 h, 11.6 h, 11.8 h or 12.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0043] In some alternative examples, the mass - to - volume ratio of the borate substituent, methyl trifluoromethanesulfonate to potassium carbonate is 5 g:5 mL:4 g.

[0044] In some alternative embodiments, the mass-volume ratio of the borate substituent to the second portion of anhydrous tetrahydrofuran is 1 g:40 mL.

[0045] In some alternative embodiments, the time for the stirring reaction at room temperature is 10 - 12 h. For example, it can be 10.0 h, 10.2 h, 10.4 h, 10.6 h, 10.8 h, 11.0 h, 11.2 h, 11.4 h, 11.6 h, 11.8 h or 12.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0046] As a preferred technical solution of the present invention, in S3, the lithium salt is one or two of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate.

[0047] In some alternative embodiments, the organic solvent is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate, with a mass ratio of 3:5:3.

[0048] In some alternative embodiments, the concentration of the lithium salt is 1 mol / L.

[0049] In some alternative embodiments, the mass ratio of the lithium salt, fluoroborate-modified ionic liquid, and functionalized cyclotriphosphazene is 10:0.3:0.4.

[0050] In some alternative embodiments, when the lithium salt is lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate, the mass ratio of lithium bis(trifluoromethanesulfonyl)imide to lithium bis(oxalato)borate is 1:1.

[0051] In a second aspect, the present invention provides a lithium-ion battery electrolyte based on the synergistic effect of bifunction prepared by the preparation method described in the first aspect.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Through silane substitution, borate modification, and the introduction of trifluoromethylsulfonic acid groups, the functionalized cyclotriphosphazene improves the thermal stability and chemical inertness of the molecule, inhibits the decomposition reaction at high temperatures, and the fluoroborate anion and trifluoromethylsulfonyl anion in the fluoroborate-modified ionic liquid further enhance the antioxidant performance and high-temperature stability of the electrolyte. The synergistic effect of the two enables the electrolyte to maintain stability under high-temperature conditions.

[0053] (2) The trimethylsilyl group in the functionalized cyclotriphosphazene reduces the glass transition temperature, enhances the molecular flexibility and low-temperature fluidity of the electrolyte, and the large-volume anion in the fluoroborate-modified ionic liquid reduces the interaction between ions and optimizes the solvation structure. This synergistic effect improves the ion migration ability and electrolyte fluidity under low-temperature conditions.

[0054] (3) The borate groups of the functionalized cyclotriphosphazene promote the dissociation of lithium salts and reduce the strong interaction between lithium ions and anions through weak coordination with lithium ions. The large-sized anions in the fluoroboron-modified ionic liquid further reduce the formation probability of ion pairs, improve the ionic conductivity of the electrolyte. Meanwhile, by introducing piperidine alcohol oxide, the radical capture ability is enhanced, effectively passivating the radicals generated during the operation of the battery, and synergistically acting with the antioxidant performance of the functionalized cyclotriphosphazene to reduce the degradation of the electrolyte and electrode materials. Description of the Drawings

[0055] Figure 1 This is a flow chart of the preparation method of the lithium-ion battery electrolyte based on the dual-functional synergistic effect of the present invention. Detailed Embodiments

[0056] The technical solutions of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific specific implementation manners of the present invention for explaining the concept of the present invention; these explanations are all explanatory and exemplary, and should not be construed as limiting the implementation manner of the present invention and the protection scope of the present invention. Except for the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of the present application, and these technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments recorded herein.

[0057] The chemical reagents used in the embodiments and comparative examples of the present invention are all commercially available products and have not been further purified.

[0058] Example 1

[0059] This example provides a lithium-ion battery electrolyte based on the dual-functional synergistic effect. Referring to Figure 1 , its preparation method specifically includes the following steps:

[0060] S1. Mix 10 g of N-methylpyrrolidine with 100 mL of anhydrous acetonitrile. Under a nitrogen atmosphere, add 17 g of 1-bromobutane, and heat the mixture to 88 °C for reflux reaction for 10.4 h. After the reaction, rotary evaporation is performed to obtain a pre-product. Disperse 20 g of the pre-product in 200 mL of deionized water, then add 30 g of lithium bis(trifluoromethanesulfonyl)imide and stir at room temperature for 7.1 h. After extraction and rotary evaporation, an ionic liquid is obtained. Disperse 20 g of the ionic liquid, 15 g of polyethylene glycol, and 3 g of potassium carbonate in 200 mL of anhydrous acetonitrile. Under a nitrogen atmosphere, heat the mixture to 89 °C and react for 11.7 h. After rotary evaporation, an ionic liquid grafted with a flexible side chain is obtained. Disperse 20 g of the ionic liquid grafted with a flexible side chain and 5 g of piperidine N-oxide in 200 mL of anhydrous dichloromethane. Under an ice-water bath condition, add 1 g of triethylamine and stir for 3.8 h. Rotary evaporation is performed to obtain an ionic liquid embedded with a radical capture group. Disperse 20 g of the ionic liquid embedded with a radical capture group and 2 g of sodium tetrafluoroborate in 200 mL of anhydrous dichloromethane, add 1 mL of boron trifluoride ether complex, and stir at room temperature for 5.2 h. Rotary evaporation is performed to obtain a fluoroborate-modified ionic liquid;

[0061] S2. Under a nitrogen atmosphere, disperse 15 g of hexachlorocyclotriphosphazene, 16 g of pyridine, and 12 g of trimethylsilanol in 300 mL of anhydrous tetrahydrofuran, heat the mixture to 55 °C and stir for reaction for 11.4 h. After the reaction, filtration and rotary evaporation are performed to obtain a silane-substituted product. Under an ice-water bath condition, disperse 18 g of the silane-substituted product, 8 g of trimethyl borate, 20 g of anhydrous methanol, and 10 g of triethylamine in 200 mL of anhydrous dichloromethane and stir at room temperature for 10.3 h. Filtration and rotary evaporation are performed to obtain a borate-substituted product. Under a nitrogen atmosphere and an ice-water bath condition, disperse 5 g of the borate-substituted product, 5 mL of methyl trifluoromethanesulfonate, and 4 g of potassium carbonate in 200 mL of anhydrous tetrahydrofuran and stir at room temperature for reaction for 10.1 h. After the reaction is completed, filtration and rotary evaporation are performed to obtain a functionalized cyclotriphosphazene;

[0062] S3. Add a lithium salt, a fluoroborate-modified ionic liquid, and a functionalized cyclotriphosphazene with a mass ratio of 10:0.3:0.4 to an organic solvent. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate, and the organic solvent is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate with a mass ratio of 3:5:3. Mix them evenly to obtain a lithium-ion battery electrolyte based on the dual-functional synergistic effect with a lithium salt concentration of 1 mol / L.

[0063] Example 2

[0064] This example provides a lithium-ion battery electrolyte based on the dual-functional synergistic effect, and its preparation method specifically includes the following steps:

[0065] S1. Mix 10 g of N-methylpyrrolidine with 100 mL of anhydrous acetonitrile. Under a nitrogen atmosphere, add 17 g of 1-bromobutane, and heat the mixture to 82 °C for reflux reaction for 11.8 h. After the reaction is completed, rotary evaporation is carried out to obtain a pre-product. Disperse 20 g of the pre-product in 200 mL of deionized water, then add 30 g of lithium bis(trifluoromethanesulfonyl)imide and stir at room temperature for 7.8 h. After extraction and rotary evaporation, an ionic liquid is obtained. Disperse 20 g of the ionic liquid, 15 g of polyethylene glycol, and 3 g of potassium carbonate in 200 mL of anhydrous acetonitrile. Under a nitrogen atmosphere, heat the mixture to 81 °C for reaction for 10.2 h. After rotary evaporation, an ionic liquid grafted with a flexible side chain is obtained. Disperse 20 g of the ionic liquid grafted with a flexible side chain and 5 g of piperidine N-oxide in 200 mL of anhydrous dichloromethane. Under an ice-water bath condition, add 1 g of triethylamine and stir for 3.3 h. After rotary evaporation, an ionic liquid embedded with a radical trapping group is obtained. Disperse 20 g of the ionic liquid embedded with a radical trapping group and 2 g of sodium tetrafluoroborate in 200 mL of anhydrous dichloromethane. Add 1 mL of boron trifluoride ether complex and stir at room temperature for 5.9 h. After rotary evaporation, a fluoroborate-modified ionic liquid is obtained;

[0066] S2. Under a nitrogen atmosphere, disperse 15 g of hexachlorocyclotriphosphazene, 16 g of pyridine, and 12 g of trimethylsilanol in 300 mL of anhydrous tetrahydrofuran. Heat the mixture to 51 °C and stir for reaction for 11.7 h. After the reaction is completed, filter and rotary evaporate to obtain a silane-substituted product. Under an ice-water bath condition, disperse 18 g of the silane-substituted product, 8 g of trimethyl borate, 20 g of anhydrous methanol, and 10 g of triethylamine in 200 mL of anhydrous dichloromethane and stir at room temperature for 11.8 h. Filter and rotary evaporate to obtain a borate-substituted product. Under a nitrogen atmosphere and an ice-water bath condition, disperse 5 g of the borate-substituted product, 5 mL of methyl trifluoromethanesulfonate, and 4 g of potassium carbonate in 200 mL of anhydrous tetrahydrofuran and stir at room temperature for reaction for 11.5 h. After the reaction is completed, filter and rotary evaporate to obtain a functionalized cyclotriphosphazene;

[0067] S3. Add a lithium salt, a fluoroborate-modified ionic liquid, and a functionalized cyclotriphosphazene with a mass ratio of 10:0.3:0.4 to an organic solvent. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate, and the organic solvent is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate with a mass ratio of 3:5:3. Mix them evenly to obtain a lithium-ion battery electrolyte based on dual-functional synergistic effect with a lithium salt concentration of 1 mol / L.

[0068] Example 3

[0069] This example provides a lithium-ion battery electrolyte based on dual-functional synergistic effect, and its preparation method specifically includes the following steps:

[0070] S1. Mix 10 g of N-methylpyrrolidine with 100 mL of anhydrous acetonitrile. Under a nitrogen atmosphere, add 17 g of 1-bromobutane, and heat the mixture to 85 °C for reflux reaction for 11.2 h. After the reaction, rotary evaporation is carried out to obtain a pre-product. Disperse 20 g of the pre-product in 200 mL of deionized water, then add 30 g of lithium bis(trifluoromethanesulfonyl)imide and stir at room temperature for 6.2 h. After extraction and rotary evaporation, an ionic liquid is obtained. Disperse 20 g of the ionic liquid, 15 g of polyethylene glycol, and 3 g of potassium carbonate in 200 mL of anhydrous acetonitrile. Under a nitrogen atmosphere, heat the mixture to 83 °C and react for 11.5 h. After rotary evaporation, an ionic liquid grafted with a flexible side chain is obtained. Disperse 20 g of the ionic liquid grafted with a flexible side chain and 5 g of piperidine N-oxide in 200 mL of anhydrous dichloromethane. Under an ice-water bath condition, add 1 g of triethylamine and stir for 3.1 h. After rotary evaporation, an ionic liquid embedded with a radical trapping group is obtained. Disperse 20 g of the ionic liquid embedded with a radical trapping group and 2 g of sodium tetrafluoroborate in 200 mL of anhydrous dichloromethane. Add 1 mL of boron trifluoride ether complex and stir at room temperature for 5.5 h. After rotary evaporation, a fluoroborate-modified ionic liquid is obtained;

[0071] S2. Under a nitrogen atmosphere, disperse 15 g of hexachlorocyclotriphosphazene, 16 g of pyridine, and 12 g of trimethylsilanol in 300 mL of anhydrous tetrahydrofuran, and heat the mixture to 59 °C and stir for reaction for 10.2 h. After the reaction, filter and rotary evaporate to obtain a silane-substituted product. Under an ice-water bath condition, disperse 18 g of the silane-substituted product, 8 g of trimethyl borate, 20 g of anhydrous methanol, and 10 g of triethylamine in 200 mL of anhydrous dichloromethane and stir at room temperature for 11.3 h. Filter and rotary evaporate to obtain a borate-substituted product. Under a nitrogen atmosphere and an ice-water bath condition, disperse 5 g of the borate-substituted product, 5 mL of methyl trifluoromethanesulfonate, and 4 g of potassium carbonate in 200 mL of anhydrous tetrahydrofuran and stir at room temperature for reaction for 11.2 h. After the reaction is completed, filter and rotary evaporate to obtain a functionalized cyclotriphosphazene;

[0072] S3. Add a lithium salt, a fluoroborate-modified ionic liquid, and a functionalized cyclotriphosphazene with a mass ratio of 10:0.3:0.4 to an organic solvent. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate, and the organic solvent is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate with a mass ratio of 3:5:3. Mix them evenly to obtain a lithium-ion battery electrolyte based on bifunctional synergistic effects with a lithium salt concentration of 1 mol / L.

[0073] Example 4

[0074] This example provides a lithium-ion battery electrolyte based on bifunctional synergistic effects, and its preparation method specifically includes the following steps:

[0075] S1. Mix 10 g of N-methylpyrrolidine with 100 mL of anhydrous acetonitrile. Under a nitrogen atmosphere, add 17 g of 1-bromobutane, and heat the mixture to 80 °C for reflux reaction for 10.7 h. After the reaction, perform rotary evaporation to obtain a pre-product. Disperse 20 g of the pre-product in 200 mL of deionized water, then add 30 g of lithium bis(trifluoromethanesulfonyl)imide and stir at room temperature for 6.7 h. After extraction and rotary evaporation, obtain an ionic liquid. Disperse 20 g of the ionic liquid, 15 g of polyethylene glycol, and 3 g of potassium carbonate in 200 mL of anhydrous acetonitrile. Under a nitrogen atmosphere, heat the mixture to 85 °C for reaction for 10.5 h. After rotary evaporation, obtain an ionic liquid grafted with a flexible side chain. Disperse 20 g of the ionic liquid grafted with a flexible side chain and 5 g of piperidine N-oxide in 200 mL of anhydrous dichloromethane. Under an ice-water bath condition, add 1 g of triethylamine and stir for 3.7 h. After rotary evaporation, obtain an ionic liquid embedded with a radical capture group. Disperse 20 g of the ionic liquid embedded with a radical capture group and 2 g of sodium tetrafluoroborate in 200 mL of anhydrous dichloromethane. Add 1 mL of boron trifluoride ether complex and stir at room temperature for 5.7 h. After rotary evaporation, obtain a fluoroborate-modified ionic liquid;

[0076] S2. Under a nitrogen atmosphere, disperse 15 g of hexachlorocyclotriphosphazene, 16 g of pyridine, and 12 g of trimethylsilanol in 300 mL of anhydrous tetrahydrofuran. Heat the mixture to 53 °C and stir for reaction for 10.8 h. After the reaction, filter and perform rotary evaporation to obtain a silane-substituted product. Under an ice-water bath condition, disperse 18 g of the silane-substituted product, 8 g of trimethyl borate, 20 g of anhydrous methanol, and 10 g of triethylamine in 200 mL of anhydrous dichloromethane and stir at room temperature for 10.6 h. Filter and perform rotary evaporation to obtain a borate-substituted product. Under a nitrogen atmosphere and an ice-water bath condition, disperse 5 g of the borate-substituted product, 5 mL of methyl trifluoromethanesulfonate, and 4 g of potassium carbonate in 200 mL of anhydrous tetrahydrofuran and stir at room temperature for reaction for 10.6 h. After the reaction is completed, filter and perform rotary evaporation to obtain a functionalized cyclotriphosphazene;

[0077] S3. Add a lithium salt, a fluoroborate-modified ionic liquid, and a functionalized cyclotriphosphazene with a mass ratio of 10:0.3:0.4 to an organic solvent. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate, and the organic solvent is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate with a mass ratio of 3:5:3. Mix them evenly to obtain a lithium-ion battery electrolyte based on the dual-functional synergistic effect with a lithium salt concentration of 1 mol / L.

[0078] Comparative Example 1

[0079] This comparative example provides a lithium-ion battery electrolyte based on the dual-functional synergistic effect. The difference from Example 1 is that the mass of sodium tetrafluoroborate in S1 is adjusted to 0.1 g, which is 1.9 g less than that in Example 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0080] Comparative Example 2

[0081] This comparative example provides a lithium-ion battery electrolyte based on the synergistic effect of dual functions. The difference from Example 1 is that in S1, the mass of sodium tetrafluoroborate is adjusted to 4 g, an increase of 2 g compared to Example 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0082] Comparative Example 3

[0083] This comparative example provides a lithium-ion battery electrolyte based on the synergistic effect of dual functions. The difference from Example 1 is that in S2, the volume of methyl trifluoromethanesulfonate is adjusted to 1 mL, a decrease of 4 mL compared to Example 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0084] Comparative Example 4

[0085] This comparative example provides a lithium-ion battery electrolyte based on the synergistic effect of dual functions. The difference from Example 1 is that in S2, the volume of methyl trifluoromethanesulfonate is adjusted to 10 mL, an increase of 5 mL compared to Example 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0086] Inject the lithium-ion battery electrolyte based on the synergistic effect of dual functions prepared in the present invention into an unencapsulated battery. The positive electrode material is lithium nickel cobalt manganese oxide, and the negative electrode material is graphite. Cycle performance test: The lithium-ion battery is charged at a constant current and voltage of 0.5C to 4.2V with a cut-off current of 0.05C, and then discharged at a constant current of 0.5C to 3.0V. The capacity retention rate is calculated after 200 charge / discharge cycles. 60°C storage capacity retention rate: The lithium-ion battery is cycled at a constant current of 0.5C (4.2 - 3.0V) 5 times at room temperature, and the initial capacity before battery storage is recorded. Then the battery is charged at a constant current and voltage to 4.2V in a fully charged state and placed in an environment of 60°C for 7 days. After storage, the battery is taken out and cooled to room temperature, and the retained capacity of the battery is measured by discharging it at 0.5C to 3.0V. The test results are shown in Table 1.

[0087] Table 1 Test Results of Lithium-Ion Battery Electrolytes Based on the Synergistic Effect of Dual Functions in Examples 1 - 4 and Comparative Examples 1 - 4

[0088]

[0089] As can be seen from Table 1, compared with Example 1, the 25°C cycle capacity retention rate, 50°C cycle capacity retention rate, and 60°C storage capacity retention rate of Comparative Example 1 are all lower than those of Example 1; the 25°C cycle capacity retention rate, 50°C cycle capacity retention rate, and 60°C storage capacity retention rate of Comparative Example 2 are all lower than those of Example 1. This is because in Comparative Example 1, the amount of sodium tetrafluoroborate is insufficient, and the concentration of tetrafluoroborate ions is insufficient, which will lead to an incomplete structure of the fluoroborate-modified ionic liquid, may affect the uniformity and stability of the ionic liquid, and at the same time reduce its solubility of lithium salts. In addition, the lack of tetrafluoroborate at high temperatures may not effectively inhibit side reactions at high temperatures, resulting in an unstable interface layer, thereby reducing the high-temperature cycle capacity retention rate. In Comparative Example 2, the amount of sodium tetrafluoroborate is excessive. The excessive tetrafluoroborate ions will increase the viscosity of the ionic liquid, reduce the ionic conductivity, and increase the migration resistance of lithium ions. At high temperatures, the excessive tetrafluoroborate ions may react with the electrode interface to generate an unstable interface layer, resulting in capacity decay.

[0090] As can be seen from Table 1, compared with Example 1, the 25°C cycle capacity retention rate, 50°C cycle capacity retention rate, and 60°C storage capacity retention rate of Comparative Example 3 are all lower than those of Example 1; the 25°C cycle capacity retention rate, 50°C cycle capacity retention rate, and 60°C storage capacity retention rate of Comparative Example 4 are all lower than those of Example 1. This is because in Comparative Example 3, the amount of methyl trifluoromethanesulfonate is insufficient, which may lead to incomplete introduction of trifluoromethanesulfonic acid groups on the functionalized cyclotriphosphazene. Some phosphazene molecules may still retain unmodified borate groups or other nucleophilic sites, resulting in insufficient antioxidant performance and free radical capture ability of cyclotriphosphazene, thus affecting the electrochemical stability and interface stability of the electrolyte. At high temperatures, the incompletely modified cyclotriphosphazene may not effectively capture free radicals, resulting in capacity decay. In Comparative Example 4, the amount of methyl trifluoromethanesulfonate is excessive. The unremoved excessive methyl trifluoromethanesulfonate may trigger side reactions with lithium salts or other components, reducing the capacity retention rate.

[0091] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. Preparation method of electrolyte for lithium-ion battery based on bifunctional synergistic effect, characterized in that, The preparation method includes: S1. Mix N-methylpyrrolidine with the first portion of anhydrous acetonitrile, add 1-bromobutane, and react to obtain a pre-product. Disperse the pre-product in deionized water, add lithium bis(trifluoromethanesulfonyl)imide to obtain an ionic liquid. Disperse the ionic liquid, polyethylene glycol, and potassium carbonate in the second portion of anhydrous acetonitrile and react to obtain an ionic liquid grafted with a flexible side chain. Disperse the ionic liquid grafted with a flexible side chain and piperidine alcohol oxide in the first portion of anhydrous dichloromethane, add triethylamine to obtain an ionic liquid embedded with a radical capture group. Disperse the ionic liquid embedded with a radical capture group and sodium tetrafluoroborate in the second portion of anhydrous dichloromethane, add boron trifluoride ether complex to obtain a fluoroborate-modified ionic liquid; S2. Disperse hexachlorocyclotriphosphazene, pyridine, and trimethylsilanol in the first portion of anhydrous tetrahydrofuran and react to obtain a silane-substituted product. Disperse the silane-substituted product, trimethyl borate, anhydrous methanol, and triethylamine in anhydrous dichloromethane to obtain a borate-substituted product. Disperse the borate-substituted product, methyl trifluoromethanesulfonate, and potassium carbonate in the second portion of anhydrous tetrahydrofuran and react to obtain a functionalized cyclotriphosphazene; S3. Add a lithium salt, the fluoroborate-modified ionic liquid, and the functionalized cyclotriphosphazene to an organic solvent, and mix evenly to obtain a lithium-ion battery electrolyte based on the synergistic effect of dual functions.

2. The preparation method of the lithium-ion battery electrolyte based on the synergistic effect of dual functions according to claim 1, wherein In S1, The mass ratio of the N-methylpyrrolidine to the 1-bromobutane is 1:1.7; The mass ratio of the pre-product to the lithium bis(trifluoromethanesulfonyl)imide is 2:

3.

3. The preparation method of the lithium-ion battery electrolyte based on the synergistic effect of bifunction as claimed in claim 1, wherein, In S1, The mass ratio of the ionic liquid, polyethylene glycol, and potassium carbonate is 20:15:

3.

4. The preparation method of the lithium-ion battery electrolyte based on the synergistic effect of dual functions according to claim 1, characterized in that In S1, The mass ratio of the ionic liquid grafted with a flexible side chain to the piperidine alcohol oxide is 4:1; The mass ratio of the ionic liquid embedded with a radical capture group to the sodium tetrafluoroborate is 10:

1.

5. The preparation method of the lithium-ion battery electrolyte based on the synergistic effect of bifunction according to claim 1, characterized in that, In S2, The mass ratio of the hexachlorocyclotriphosphazene, pyridine, and trimethylsilanol is 15:16:12; The mass ratio of the silane-substituted product, trimethyl borate, anhydrous methanol, and triethylamine is 9:4:10:

5.

6. The preparation method of the lithium-ion battery electrolyte based on the synergistic effect of bifunction according to claim 1, wherein, In S2, The mass-volume ratio of the borate-substituted product, methyl trifluoromethanesulfonate, and potassium carbonate is 5g:5mL:4g.

7. The preparation method of the lithium-ion battery electrolyte based on the synergistic effect of bifunction as claimed in claim 1, wherein, In S3, The lithium salt is one or two of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate; The organic solvent is a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate, and the mass ratio is 3:5:

3.

8. The preparation method of the lithium-ion battery electrolyte based on the synergistic effect of bifunction according to claim 1, characterized in that, In S3, The mass ratio of the lithium salt, the fluoroborate-modified ionic liquid, and the functionalized cyclotriphosphazene is 10:0.3:0.

4.

9. According to the preparation method of the lithium-ion battery electrolyte based on the synergistic effect of dual functions as claimed in claim 7, wherein When the lithium salt is lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate, the mass ratio of lithium bis(trifluoromethanesulfonyl)imide to lithium bis(oxalato)borate is 1:

1.

10. A lithium-ion battery electrolyte based on the synergistic effect of dual functions obtained by the preparation method according to any one of claims 1-9.

Images