Low-moisture propylene carbonate-based lithium ion energy storage electrolyte and preparation process thereof

Abstract

The application discloses low-moisture propylene carbonate-based lithium ion energy storage electrolyte and a preparation process thereof, and belongs to the technical field of electrolyte preparation, and is used for solving the technical problem that the cycle performance of lithium ion batteries needs to be further improved due to the incompatibility of propylene carbonate-based electrolyte with a graphite negative electrode and the side reactions caused by moisture in the system in the prior art, and specifically comprises the following components in parts by weight: 60-80 parts of propylene carbonate, 2-5 parts of alkenyl-terminated fluoropolyether, 10-15 parts of lithium salt, 3-6 parts of boron-containing amine ester flame-retardant water-removing agent and 1-5 parts of functional additive. The boron-containing amine ester flame-retardant water-removing agent is prepared, cooperates with the alkenyl-terminated fluoropolyether, removes trace moisture in the electrolyte, blocks the hydrolysis reaction of lithium hexafluorophosphate, avoids the generation of hydrofluoric acid, simultaneously optimizes the electrochemical compatibility of the electrolyte with the negative electrode, and significantly improves the cycle life and interface safety of the battery.

Description

Technical Field

[0001] This invention relates to the field of electrolyte preparation technology, specifically to a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte and its preparation process. Background Technology

[0002] With the increasing application of lithium-ion energy storage batteries in grid peak shaving, new energy grid connection and large-scale energy storage systems, the requirements for safety and cycle stability of electrolytes, as key ion transport media in battery systems, are constantly increasing. Propylene carbonate (PC) has received widespread attention and is gradually being applied in high-voltage energy storage electrolyte systems due to its high dielectric constant, excellent low-temperature fluidity and wide electrochemical stability window. In recent years, PC-based electrolytes have made some progress in improving lithium salt solubility, improving low-temperature rate performance and expanding wide-temperature applicability, but there is still a need for further improvement in long cycle life, high-voltage stability and interface safety.

[0003] Currently, PC-based lithium-ion energy storage electrolytes typically use lithium hexafluorophosphate as the main lithium salt, and combine it with fluorocarbonates, borate esters, and sulfonyl lactones as film-forming components for performance regulation. Common modification methods include using highly stable lithium salts or compound additives to improve high-voltage cycling performance. However, these methods mostly rely on physical compounding or single-functional additives to achieve local optimization, which makes it difficult to solve problems such as lithium salt hydrolysis caused by trace moisture residue in the electrolyte system, by-product hydrofluoric acid generation, and continuous interface degradation, thus restricting the further application of PC-based electrolytes in high-voltage, long-life energy storage scenarios.

[0004] Meanwhile, trace amounts of moisture impurities are unavoidable in the preparation and use of PC-based electrolyte systems. This moisture can easily induce the hydrolysis of lithium hexafluorophosphate and generate corrosive hydrofluoric acid, which accelerates the destruction of the positive and negative electrode interface film, causes metal dissolution and increased polarization, leading to a decrease in cycle life and an increase in safety hazards. Furthermore, PC molecules have the risk of solvation co-intercalation on the graphite negative electrode surface, which can easily cause the negative electrode structure to peel off and the interface to become unstable. In addition, propylene carbonate itself is a flammable organic carbonate solvent, which can easily amplify the risk of combustion and spread under high energy density and high voltage conditions.

[0005] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte and its preparation process, in order to solve the technical problem in the prior art that the incompatibility between the propylene carbonate-based electrolyte and the graphite anode and the side reactions caused by moisture in the system lead to the need for further improvement in the cycle performance of lithium-ion batteries.

[0007] The objective of this invention can be achieved through the following technical solution: a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte, comprising the following components by weight: 60-80 parts propylene carbonate, 2-5 parts alkenyl-terminated fluorinated polyether, 10-15 parts lithium salt, 3-6 parts boron-containing urethane flame retardant and dehydrating agent, and 1-5 parts functional additives. The preparation method of the alkenyl-terminated fluorinated polyether is as follows: fluorinated polyether diol, dibutyltin dilaurate and ethyl acetate are placed in a reaction vessel under nitrogen atmosphere and stirred. Propylene 3-isocyanate is added, the reaction vessel is heated to 70-80℃, and the reaction is maintained for 2-4 hours. The alkenyl-terminated fluorinated polyether is then obtained after post-treatment.

[0008] Furthermore, the ratio of the fluorinated polyether diol, dibutyltin dilaurate, ethyl acetate and propylene 3-isocyanate is 8-10g:0.2-0.4g:50-70mL:2-4g. The post-processing steps include: after the reaction is completed, heating the reaction vessel to 80-90℃, removing low-boiling substances under reduced pressure to obtain alkenyl-terminated fluorinated polyether.

[0009] The reaction formula for preparing alkenyl-terminated fluorinated polyethers is as follows:

[0010] Furthermore, the fluorinated polyether diol is prepared by the following steps: A1. Place 2,2,2-trifluoroethanol, potassium hydroxide aqueous solution and tetrabutylammonium bromide in a reaction vessel and stir. Heat the reaction vessel to 70-80℃, add 3-(chloromethyl)-3-ethyloxetane, keep the reaction at the temperature for 10-12h, and then process to obtain a fluorine-containing oxetane monomer. A2. Place 1,4-butanediol, dichloromethane, and boron trifluoride tetrahydrofuran in a reaction vessel under nitrogen atmosphere protection, stir at room temperature for 0.5-1h, cool the reaction vessel to 0-5℃ in an ice bath, add fluorine-containing heterocyclic monomers, keep the reaction at this temperature for 2-4h, and then perform post-treatment to obtain fluorine-containing polyether diol.

[0011] The reaction formula for the preparation of fluorinated polyether diols is as follows:

[0012] Furthermore, the mass spectrometry data of the fluorine-containing heterocyclic monomers are: m / z: 198.06 (100.0%), 199.06 (8.9%).

[0013] Further, in step A1, the ratio of 2,2,2-trifluoroethanol, potassium hydroxide aqueous solution, tetrabutylammonium bromide, and 3-(chloromethyl)-3-ethyloxecyclobutane is 4-6 g:4-6 mL:0.3-0.5 g:6-8 g, and the concentration of potassium hydroxide aqueous solution is 40-50 wt%. The post-treatment steps include: after the reaction is completed, the reaction system is cooled to room temperature, filtered, the filtrate is added to a separatory funnel and allowed to stand for separation, the organic phase is washed with deionized water 1-3 times, transferred to a rotary evaporator at a temperature of 40-50℃, and rotary evaporated under reduced pressure for 1-2 h to obtain a fluorine-containing oxecyclobutane monomer.

[0014] Further, in step A2, the ratio of 1,4-butanediol, dichloromethane, boron trifluoride tetrahydrofuran, and fluorinated oxyheterocyclic monomer is 5-7g:40-60mL:1-2g:100-120g. The post-processing steps include: after the reaction is completed, adding deionized water to quench the reaction, allowing it to stand and separate the liquids, placing the organic phase in a 1000DA polyvinylidene fluoride dialysis bag, and placing a 500DA polyvinylidene fluoride dialysis bag outside the 1000DA polyvinylidene fluoride dialysis bag. The polyvinylidene fluoride dialysis bag is immersed in dichloromethane for dialysis for 20-25 hours, during which the dichloromethane is replaced every 2 hours. After dialysis is completed, the organic matter present in the 500DA dialysis bag is transferred to a rotary evaporator with a water bath temperature of 50-60℃, and the low-boiling substances are removed by vacuum evaporation to obtain fluorinated polyether diol.

[0015] Furthermore, the boron-containing urethane flame retardant and dehydrating agent is prepared by the following steps: B1. Place 1,4-phenyldiboronic acid, magnesium sulfate and tetrahydrofuran in a reaction vessel and stir. Add 1,2,4-butanetriol and stir at room temperature for 20-24 hours. Post-treatment yields phenylboronic acid ester polyol. B2 involves placing phenylboronic acid ester polyol and toluene in a nitrogen-protected reactor and stirring. The reactor is heated to 70-80°C and stirred for 10-20 minutes. Isophorone diisocyanate is then added, and the reaction is maintained at this temperature for 4-6 hours. Post-treatment yields a boron-containing urethane flame retardant and dehydrating agent.

[0016] The preparation reaction formula for boron-containing urethane flame retardant and dehydrating agent is as follows:

[0017] Furthermore, the mass spectrometry data of the phenylboronic acid ester polyols are as follows: m / z: 306.17 (100.0%), 305.18 (49.7%), 307.18 (16.7%), 306.18 (7.8%), 304.18 (6.2%), 308.18 (2.4%).

[0018] Further, in step B1, the ratio of 1,4-phenyldiboronic acid, magnesium sulfate, tetrahydrofuran, and 1,2,4-butanetriol is 4-6g:8-10g:50-70mL:6-8g. The post-processing step includes: after the reaction is completed, filtration is performed, the filtrate is transferred to a rotary evaporator at a temperature of 80-90℃, and vacuum distillation is performed until no liquid is collected to obtain phenylboronic acid ester polyol.

[0019] Further, in step B2, the ratio of the phenylboronic acid ester polyol to toluene is 8-10g:90-110mL, and the molar amount of isophorone diisocyanate is 0.55 times the total molar amount of the hydroxyl groups in the phenylboronic acid ester polyol. The post-treatment step includes: after the reaction is completed, heating the reaction vessel to 80-90℃, depressurizing it to below -0.095MPa, and performing vacuum distillation until no liquid is distilled off, to obtain a boron-containing urethane flame retardant and dehydrating agent.

[0020] The present invention also proposes a preparation process for a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte, comprising the following steps: S1. In a glove box protected by an argon atmosphere, propylene carbonate, alkenyl-terminated fluorinated polyether and boron-containing urethane flame retardant and dehydrating agent are placed in a reaction vessel and stirred at room temperature for 0.5-1 h to obtain a homogeneous solution. S2. In a glove box protected by argon atmosphere, place the homogeneous solution in the reactor and stir. Cool the reactor to 15-25℃ in an ice bath, slowly add lithium salt, restore the reactor to room temperature, stir for 1-2 hours, add functional additives, stir at room temperature for 15-30 minutes, filter, and obtain a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte.

[0021] Further, in step S2, the lithium salt is one or more of lithium hexafluorophosphate, lithium difluorosulfonylimide, and lithium tetrafluoroborate; the functional additive is composed of a film-forming co-solvent, a lithium salt additive, and a high-temperature stabilizer in a mass ratio of 30-50:5-15:5-15; the film-forming co-solvent is one or more of fluoroethylene carbonate, vinylene carbonate, and ethylene ethylene carbonate; the lithium salt additive is one or two of lithium difluorooxalate borate and lithium dioxalate borate; and the high-temperature stabilizer is one or more of 1,3-propane sulpholactone, vinyl sulfate, and 1,3-propene sulpholactone.

[0022] The present invention has the following beneficial effects: 1. This invention introduces a boron-containing urethane flame-retardant dehydrating agent, utilizing the highly active isocyanate groups retained at the ends of its molecular chains as chemical capture sites. In the initial stage of electrolyte preparation, this agent undergoes an irreversible chemical reaction with trace amounts of water in the solvent system, creating a strictly anhydrous pretreatment environment. The remaining active isocyanate groups serve as dynamic chemical capture sites, continuously capturing and neutralizing water generated by side reactions during subsequent battery cycles and storage. This fundamentally blocks the reaction pathway of lithium hexafluorophosphate hydrolysis to generate corrosive hydrofluoric acid, effectively preventing acidic impurities from eroding the cathode material lattice and damaging the electrolyte interface film. Simultaneously, the rigid five-membered ring boronate structure in the dehydrating agent skeleton endows the system with excellent thermal stability and flame-retardant properties. This synergistic mechanism of chemical dehydration, acid production inhibition, and skeleton flame retardancy significantly improves the long-cycle reliability of the energy storage battery.

[0023] 2. This invention also utilizes the active unsaturated double bonds at the ends of the alkenyl-terminated fluorinated polyether molecular chains to preferentially undergo in-situ electrochemical polymerization on the negative electrode surface during the first charging process of the battery, prior to the solvent molecules of propylene carbonate. Together with the reduction decomposition products of the film-forming additives, a dense electrolyte interface film is constructed. This interface film acts as a selective physical barrier, ensuring rapid lithium-ion insertion and extraction while effectively blocking the channels for the co-intercalation of solvated propylene carbonate molecules between graphite layers. This completely eliminates the hidden dangers of graphite layer peeling and negative electrode structure collapse caused by solvent co-intercalation. While retaining the high dielectric constant and wide temperature range of propylene carbonate, the compatibility between propylene carbonate molecules and the graphite negative electrode is improved.

[0024] 3. This invention also significantly improves the high-voltage performance of the system through the strong electron-withdrawing effect of the fluorinated side chain and the synergistic effect of the boron-containing backbone. The trifluoroethoxy side chain introduced into the molecular structure utilizes the low surface energy of fluorine to improve the wetting ability of high-viscosity propylene carbonate on the microporous electrode and reduce the interfacial impedance. At the same time, the high oxidation decomposition potential of the fluorinated group and the char-forming and flame-retardant properties of the boron-containing urethane complement each other, effectively suppressing the risk of oxidative decomposition and thermal runaway of the electrolyte under high voltage. In addition, the flexible backbone of the fluorinated polyether increases the lithium-ion transference number and endows the interfacial film with mechanical toughness to adapt to the volume expansion of the negative electrode, thereby improving the structural integrity and safety of the high-energy-density lithium-ion energy storage battery under extreme conditions. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1 This embodiment provides a preparation process for a boron-containing urethane flame retardant and dehydrating agent, including the following steps: Step I: Preparation of phenylboronic acid ester polyol Weigh 40g of 1,4-phenyldiboronic acid, 80g of magnesium sulfate and 500mL of tetrahydrofuran and place them in a reaction vessel and stir. Add 60g of 1,2,4-butanetriol and stir at room temperature for 20h. After the reaction is complete, filter the solution and transfer the filtrate to a rotary evaporator at 80℃. Distill under reduced pressure until no liquid is collected to obtain phenylboronic acid ester polyol.

[0027] Step II: Preparation of boron-containing urethane flame retardant and dehydrating agent Weigh 80g of phenylboronic acid ester polyol and 900mL of toluene and place them in a reaction vessel under nitrogen atmosphere and stir. Heat the reaction vessel to 70℃ and stir for 10min. Add isophorone diisocyanate at 0.55 times the total molar amount of hydroxyl groups of phenylboronic acid ester polyol and keep the reaction at this temperature for 4h. After the reaction is complete, heat the reaction vessel to 80℃ and reduce the pressure to below -0.095MPa. Perform vacuum distillation until no liquid is distilled off to obtain boron-containing urethane flame retardant and dehydrating agent.

[0028] Magnesium sulfate is used as a desiccant to induce the condensation of 1,4-phenylenediboric acid with the hydroxyl groups in 1,2,4-butanetriol, generating a phenylboronic acid polyol with a stable five-membered ring structure. The active hydroxyl groups in the phenylboronic acid polyol launch a nucleophilic attack on the isocyanate groups of isophorone diisocyanate to form urethane bonds. By controlling the excess of isophorone diisocyanate, the product end groups retain highly active isocyanate groups, thus obtaining an isocyanate-terminated boron urethane flame retardant and desiccant.

[0029] By utilizing magnesium sulfate for deep dehydration to drive esterification equilibrium, a highly stable five-membered ring borate ester framework is constructed, providing a robust flame-retardant barrier and hydrolysis-resistant foundation for the electrolyte. Through excessive isocyanate end-capping, the electrolyte material is endowed with highly active isocyanate groups as chemical capture sites, which can continuously and dynamically remove trace amounts of water and hydrofluoric acid from the system, significantly improving the high-voltage stability and battery cycle safety of propylene carbonate-based electrolytes.

[0030] Example 2 This embodiment provides a preparation process for a boron-containing urethane flame retardant and dehydrating agent, including the following steps: Step I: Preparation of phenylboronic acid ester polyol Weigh out 50g of 1,4-phenyldiboronic acid, 90g of magnesium sulfate and 600mL of tetrahydrofuran and place them in a reaction vessel and stir. Add 70g of 1,2,4-butanetriol and stir at room temperature for 22h. After the reaction is complete, filter the mixture and transfer the filtrate to a rotary evaporator at 85℃. Distill under reduced pressure until no liquid is collected to obtain phenylboronic acid ester polyol.

[0031] Step II: Preparation of boron-containing urethane flame retardant and dehydrating agent Weigh 90g of phenylboronic acid ester polyol and 1000mL of toluene and place them in a reaction vessel under nitrogen atmosphere and stir. Heat the reaction vessel to 75℃ and stir for 15min. Add isophorone diisocyanate at 0.55 times the total molar amount of hydroxyl groups of phenylboronic acid ester polyol and keep the reaction at this temperature for 5h. After the reaction is complete, heat the reaction vessel to 85℃ and reduce the pressure to below -0.095MPa. Perform vacuum distillation until no liquid distills out to obtain boron-containing urethane flame retardant and dehydrating agent.

[0032] Example 3 This embodiment provides a preparation process for a boron-containing urethane flame retardant and dehydrating agent, including the following steps: Step I: Preparation of phenylboronic acid ester polyol Weigh 60g of 1,4-phenyldiboronic acid, 100g of magnesium sulfate and 700mL of tetrahydrofuran and place them in a reaction vessel and stir. Add 80g of 1,2,4-butanetriol and stir at room temperature for 24h. After the reaction is complete, filter the solution and transfer the filtrate to a rotary evaporator at 90℃. Distill under reduced pressure until no liquid is collected to obtain phenylboronic acid ester polyol.

[0033] Step II: Preparation of boron-containing urethane flame retardant and dehydrating agent Weigh 100g of phenylboronic acid ester polyol and 1100mL of toluene and place them in a reaction vessel under nitrogen atmosphere and stir. Heat the reaction vessel to 80℃ and stir for 20min. Add isophorone diisocyanate at 0.55 times the total molar amount of hydroxyl groups of phenylboronic acid ester polyol and keep the reaction at this temperature for 6h. After the reaction is complete, heat the reaction vessel to 90℃ and reduce the pressure to below -0.095MPa. Perform vacuum distillation until no liquid is distilled off to obtain boron-containing urethane flame retardant and dehydrating agent.

[0034] Example 4 This embodiment provides a preparation process for alkenyl-terminated fluorinated polyethers, including the following steps: Step ①: Preparation of fluorine-containing oxyheterocyclic monomers Weigh 40g of 2,2,2-trifluoroethanol, 40mL of 40wt% potassium hydroxide aqueous solution and 3g of tetrabutylammonium bromide and place them in a reaction vessel and stir. Heat the reaction vessel to 70℃, add 60g of 3-(chloromethyl)-3-ethyloxetane, and keep the reaction at this temperature for 10h. After the reaction is complete, wait for the reaction system to cool to room temperature, filter, add the filtrate to a separatory funnel and let it stand to separate the liquids. Wash the organic phase once with deionized water and transfer it to a rotary evaporator at 40℃. Rotary evaporate under reduced pressure for 1h to obtain a fluorine-containing oxetine monomer.

[0035] Step ②: Preparation of fluorinated polyether diol Weigh 50g of 1,4-butanediol, 400mL of dichloromethane, and 10g of boron trifluoride tetrahydrofuran into a reaction vessel under a nitrogen atmosphere. Stir at room temperature for 0.5h, then cool the reaction vessel to 0℃ in an ice bath. Add 1000g of a fluorinated heterocyclic monomer and maintain the temperature for 2h. After the reaction is complete, quench with deionized water, allow to stand and separate the liquids. Place the organic phase in a 1000DA polyvinylidene fluoride dialysis bag, and place a 500DA polyvinylidene fluoride dialysis bag over the 1000DA polyvinylidene fluoride dialysis bag. Immerse the polyvinylidene fluoride dialysis bag in dichloromethane for dialysis for 20-25h, changing the dichloromethane every 2h. After dialysis, transfer the organic matter in the 500DA dialysis bag to a rotary evaporator with a water bath temperature of 50-60℃. Remove low-boiling substances by vacuum evaporation to obtain fluorinated polyether diol.

[0036] Step ③: Preparation of alkenyl-terminated fluorinated polyether Weigh out 80g of fluorinated polyether diol, 2g of dibutyltin dilaurate and 500mL of ethyl acetate and place them in a reaction vessel under nitrogen atmosphere and stir. Add 20g of propylene 3-isocyanate, heat the reaction vessel to 70℃ and keep it at that temperature for 2h. After the reaction is complete, heat the reaction vessel to 80℃ and remove low-boiling substances under reduced pressure to obtain alkenyl-terminated fluorinated polyether.

[0037] With the assistance of the phase-transfer catalyst tetrabutylammonium bromide, 2,2,2-trifluoroethanol underwent nucleophilic substitution of the chlorine atom in the side chain of 3-(chloromethyl)-3-ethyloxetane via Williamson ether synthesis to synthesize a fluorinated oxetine monomer. Using 1,4-butanediol as a bifunctional initiator and boron trifluoride as a Lewis acid catalyst, the fluorinated monomer underwent cationic ring-opening polymerization. By controlling the molar ratio of 1,4-butanediol to the fluorinated oxetine monomer, the degree of polymerization was kept at a low level, and a low molecular weight fluorinated polyether diol oligomer with hydroxyl groups at both ends was synthesized. Further utilizing the nucleophilic addition characteristics of the terminal hydroxyl groups of the polyether to the isocyanate groups in propylene isocyanate, urethane bonds were formed under organotin catalysis, introducing the unsaturated double bond of the olefin to the molecular chain end, and preparing an alkenyl-terminated fluorinated polyether.

[0038] The introduction of trifluoroethoxy fluorinated side chains enhances the high-voltage resistance and flame retardant properties of the electrolyte material. The low surface energy of fluorine improves the wettability of the electrolyte to the electrode. The further constructed fluorinated polyether flexible backbone ensures both efficient lithium-ion transport channels and electrochemical stability. The olefin unsaturated double bonds introduced at the end groups end up with the ability to polymerize in situ at the electrode interface to form a dense electrolyte interface film, effectively suppressing the solvation co-intercalation damage of propylene carbonate molecules to the negative electrode material, and ensuring the structural integrity and safety of the energy storage battery during long-cycle processes.

[0039] Example 5 This embodiment provides a preparation process for alkenyl-terminated fluorinated polyethers, including the following steps: Step ①: Preparation of fluorine-containing oxyheterocyclic monomers Weigh 50g of 2,2,2-trifluoroethanol, 50mL of 45wt% potassium hydroxide aqueous solution, and 4g of tetrabutylammonium bromide and place them in a reaction vessel and stir. Heat the reaction vessel to 75℃, add 70g of 3-(chloromethyl)-3-ethyloxetane, and keep the reaction at this temperature for 11h. After the reaction is complete, wait for the reaction system to cool to room temperature, filter, add the filtrate to a separatory funnel and let it stand to separate the liquids. Wash the organic phase twice with deionized water and transfer it to a rotary evaporator at 45℃. Evaporate under reduced pressure for 1.5h to obtain a fluorine-containing oxetine monomer.

[0040] Step ②: Preparation of fluorinated polyether diol Weigh 60g of 1,4-butanediol, 500mL of dichloromethane, and 15g of boron trifluoride tetrahydrofuran into a reaction vessel under a nitrogen atmosphere. Stir at room temperature for 1 hour, then cool the reaction vessel to 3°C in an ice bath. Add 1100g of a fluorinated heterocyclic monomer and maintain the temperature for 3 hours. After the reaction is complete, quench with deionized water, allow to stand, and separate the liquids. Place the organic phase in a 1000DA polyvinylidene fluoride (PVDF) dialysis bag, and place a 500DA PVDF dialysis bag over the 1000DA PVDF dialysis bag. Immerse the PVDF dialysis bag in dichloromethane for dialysis for 20-25 hours, changing the dichloromethane every 2 hours. After dialysis, transfer the organic matter in the 500DA dialysis bag to a rotary evaporator with a water bath temperature of 50-60°C. Remove low-boiling-point substances by vacuum evaporation to obtain fluorinated polyether diol.

[0041] Step ③: Preparation of alkenyl-terminated fluorinated polyether Weigh out 90g of fluorinated polyether diol, 3g of dibutyltin dilaurate and 600mL of ethyl acetate and place them in a reaction vessel under nitrogen atmosphere protection and stir. Add 30g of propylene 3-isocyanate, heat the reaction vessel to 75℃ and keep it at this temperature for 3h. After the reaction is complete, heat the reaction vessel to 85℃ and remove low-boiling substances under reduced pressure to obtain alkenyl-terminated fluorinated polyether.

[0042] Example 6 This embodiment provides a preparation process for alkenyl-terminated fluorinated polyethers, including the following steps: Step ①: Preparation of fluorine-containing oxyheterocyclic monomers Weigh 60g of 2,2,2-trifluoroethanol, 60mL of 50wt% potassium hydroxide aqueous solution, and 5g of tetrabutylammonium bromide and place them in a reaction vessel and stir. Heat the reaction vessel to 80℃, add 80g of 3-(chloromethyl)-3-ethyloxetane, and keep the reaction at this temperature for 12h. After the reaction is complete, wait for the reaction system to cool to room temperature, filter, add the filtrate to a separatory funnel and let it stand to separate the liquids. Wash the organic phase three times with deionized water and transfer it to a rotary evaporator at 50℃. Evaporate under reduced pressure for 2h to obtain a fluorine-containing oxetine monomer.

[0043] Step ②: Preparation of fluorinated polyether diol Weigh 70g of 1,4-butanediol, 600mL of dichloromethane, and 20g of boron trifluoride tetrahydrofuran into a reaction vessel under a nitrogen atmosphere. Stir at room temperature for 1h, then heat the reaction vessel to 5℃ in an ice bath. Add 1200g of a fluorinated heterocyclic monomer and maintain the temperature for 4h. After the reaction is complete, quench with deionized water, allow to stand, and separate the organic phase into a 1000DA polyvinylidene fluoride dialysis bag. Place a 500DA polyvinylidene fluoride dialysis bag over the 1000DA polyvinylidene fluoride dialysis bag. Immerse the polyvinylidene fluoride dialysis bag in dichloromethane for dialysis for 20-25h, changing the dichloromethane every 2h. After dialysis, transfer the organic matter in the 500DA dialysis bag to a rotary evaporator with a water bath temperature of 50-60℃. Remove low-boiling substances by vacuum evaporation to obtain fluorinated polyether diol.

[0044] Step ③: Preparation of alkenyl-terminated fluorinated polyether Weigh out 100g of fluorinated polyether diol, 4g of dibutyltin dilaurate and 700mL of ethyl acetate and place them in a reaction vessel under nitrogen atmosphere and stir. Add 40g of propylene 3-isocyanate, heat the reaction vessel to 80℃ and keep it at that temperature for 4h. After the reaction is complete, heat the reaction vessel to 90℃ and remove low-boiling substances under reduced pressure to obtain alkenyl-terminated fluorinated polyether.

[0045] Example 7 This embodiment provides a preparation process for a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte, including the following steps: Step (1): Preparation of homogeneous solution Weigh out the following amounts by weight: In an argon-atmospheric glove box, place 60 parts of propylene carbonate, 2 parts of the alkenyl-terminated fluorinated polyether prepared in Example 4, and 3 parts of the boron-containing urethane flame retardant and dehydrating agent prepared in Example 1 into a reaction vessel and stir at room temperature for 0.5 h to obtain a homogeneous solution. Step 2: Prepare a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte. Fluoroethylene carbonate, lithium difluorooxalate borate and 1,3-propane sulcolone were mixed evenly in a mass ratio of 30:5:5 to obtain a functional additive for later use. Weigh out the following parts by weight: In a glove box protected by an argon atmosphere, place all the homogeneous solution prepared in step (1) into a reaction vessel and stir. Cool the reaction vessel to 15°C using an ice bath. Slowly add 10 parts of lithium hexafluorophosphate. Allow the reaction vessel to return to room temperature and stir for 1 hour. Add 1 part of functional additive and stir at room temperature for 15 minutes. Filter the reaction solution through a 1 μm polytetrafluoroethylene filter membrane to obtain a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte.

[0046] The highly active isocyanate groups retained in the boron-containing urethane additive are used as chemical traps to undergo irreversible chemical reactions with trace amounts of water in the system, achieving deep dehydration of the solvent. The high dielectric constant of propylene carbonate promotes the dissociation and solvation of the lithium hexafluorophosphate lattice. The anhydrous environment established in the previous steps blocks the decomposition pathway of hydrofluoric acid produced by lithium salt hydrolysis. The electrolyte system is then physically compounded with multi-component additives to form a thermodynamically stable electrolyte system.

[0047] By utilizing the chemical capture mechanism of boron-containing urethane flame retardant dehydrating agent to pre-remove trace amounts of moisture from the solvent matrix, a strictly anhydrous pretreatment environment is constructed, eliminating the interference of moisture on subsequent lithium salt dissolution from the source. This effectively inhibits the hydrolysis reaction of lithium hexafluorophosphate, blocks the formation pathway of corrosive hydrofluoric acid, and ensures the chemical stability of the electrolyte components. Utilizing the active double bonds at the ends of the alkenyl-terminated fluorinated polyether molecular chains, it preferentially undergoes in-situ polymerization on the negative electrode surface during the first charge of the battery, prior to propylene carbonate. Together with the reduction decomposition products of the film-forming additives, it constructs a dense electrolyte interface film. This electrolyte interface film acts as a physical barrier, allowing lithium-ion intercalation and deintercalation while blocking the channels for solvated propylene carbonate molecules to co-intercalate between graphite layers. This avoids graphite layer peeling and negative electrode structure collapse caused by propylene carbonate co-intercalation. While retaining the advantages of propylene carbonate's high dielectric constant and wide temperature range, electrochemical compatibility with the graphite negative electrode is achieved, significantly improving the cycle life and interface safety of the energy storage system.

[0048] Example 8 This embodiment provides a preparation process for a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte, including the following steps: Step (1): Preparation of homogeneous solution Weigh out the following amounts by weight: In an argon-atmosphere protected glove box, place 70 parts of propylene carbonate, 3.5 parts of the alkenyl-terminated fluorinated polyether prepared in Example 5, and 4.5 parts of the boron-containing urethane flame retardant and dehydrating agent prepared in Example 2 into a reaction vessel and stir at room temperature for 1 hour to obtain a homogeneous solution. Step 2: Prepare a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte. Fluoroethylene carbonate, lithium difluorooxalate borate and 1,3-propane sulpholol were mixed evenly in a mass ratio of 40:10:10 to obtain a functional additive for later use. Weigh out the following parts by weight: In a glove box protected by an argon atmosphere, place all the homogeneous solution prepared in step (1) into a reaction vessel and stir. Cool the reaction vessel to 20°C using an ice bath. Slowly add 12.5 parts of lithium hexafluorophosphate. Allow the reaction vessel to return to room temperature and stir for 1.5 hours. Add 3 parts of functional additives and stir at room temperature for 23 minutes. Filter the reaction solution through a 2 μm polytetrafluoroethylene filter membrane to obtain a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte.

[0049] Example 9 This embodiment provides a preparation process for a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte, including the following steps: Step (1): Preparation of homogeneous solution Weigh out the following amounts by weight: In a glove box protected by an argon atmosphere, place 80 parts of propylene carbonate, 5 parts of the alkenyl-terminated fluorinated polyether prepared in Example 6, and 6 parts of the boron-containing urethane flame retardant and dehydrating agent prepared in Example 3 into a reaction vessel, and stir at room temperature for 1 hour to obtain a homogeneous solution. Step 2: Prepare a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte. Fluoroethylene carbonate, lithium difluorooxalate borate and 1,3-propane sulpholol were mixed evenly in a mass ratio of 50:15:15 to obtain a functional additive for later use. Weigh out the following parts by weight: In a glove box protected by an argon atmosphere, place all the homogeneous solution prepared in step (1) into a reaction vessel and stir. Cool the reaction vessel to 25°C using an ice bath. Slowly add 15 parts of lithium hexafluorophosphate. Allow the reaction vessel to return to room temperature and stir for 2 hours. Add 5 parts of functional additives and stir at room temperature for 30 minutes. Filter the reaction solution through a 2μm polytetrafluoroethylene filter membrane to obtain a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte.

[0050] Comparative Example 1 The difference between this comparative example and Example 9 is that the boron-containing urethane flame retardant and dehydrating agent was omitted in step (1) when preparing the homogeneous solution.

[0051] Comparative Example 2 The difference between this comparative example and Example 9 is that, in step (1) when preparing the homogeneous solution, an equal amount of boron-containing urethane flame retardant and dehydrating agent is replaced with phenylboronic acid ester polyol.

[0052] Comparative Example 3 The difference between this comparative example and Example 9 is that the use of alkenyl-terminated fluorinated polyether was omitted in step (1) when preparing the homogeneous solution.

[0053] Performance testing: The water content and free acid (HF) of the lithium-ion energy storage electrolytes prepared in Examples 7-9 and Comparative Examples 1-3 were tested in accordance with the standard SJ / T 11723-2018 "Electrolytes for Lithium-ion Batteries". The lithium-ion energy storage electrolytes prepared in Examples 7-9 and Comparative Examples 1-3 were loaded into the sample cup of a closed-cup flash point apparatus. The temperature was increased at a specified rate. The vapor space above the sample cup was ignited with an igniter at certain temperature intervals. When the vapor was first ignited and a blue flame appeared (lasting ≥2 seconds), the corresponding temperature was the closed-cup flash point of the electrolyte. Battery assembly: The entire process is carried out in an argon-atmospheric glove box. Battery-grade lithium iron phosphate, conductive acetylene black, and polyvinylidene fluoride are mixed at amounts of 85wt%, 6wt%, and 9wt%, respectively, and formulated into a slurry with a solid content of 50% using N-methylpyrrolidone, based on an areal density of 10 mg / cm³. 2 The positive electrode sheet is prepared by coating the aluminum foil surface with a coating agent and vacuum drying at 70°C for 5 hours. Graphite, conductive acetylene black, and polyvinylidene fluoride are mixed at 90 wt%, 5 wt%, and 5 wt% respectively, and then formulated with N-methylpyrrolidone to prepare a slurry with a solid content of 50%, based on an areal density of 3 mg / cm³. 2 The graphite negative electrode sheet was prepared by scraping and coating on the surface of copper foil and vacuum drying at 70°C for 5 hours. Celgard 2400 was used as the separator, and the low-moisture propylene carbonate-based lithium-ion energy storage electrolyte prepared in Examples 7-9 and Comparative Examples 1-3 was used as the electrolyte. The electrolyte volume was 50 μL. The cells were assembled into CR2025 button cells and tested after standing for 12 hours. The battery samples assembled in Examples 7-9 and Comparative Examples 1-3 were subjected to constant current and constant voltage charging and constant current discharging tests using the LAND-CT2001A battery testing system. The test temperature was 25°C, the voltage range was 2.0-3.65V, the rate was 1C, and the room temperature cycle capacity retention rate was tested. The battery samples assembled in Examples 7-9 and Comparative Examples 1-3 were subjected to constant current and constant voltage charging and constant current discharging tests using the LAND-CT2001A battery testing system. The test temperature was 25°C, the voltage range was 2.0-3.75V, the rate was 1C, and high voltage cycle stability was tested. Specific data are shown in Table 1.

[0054] Table 1 - Performance Test Data for Each Sample

[0055] Data Analysis: A comparative analysis of the data in the above table revealed that the water content of the propylene carbonate-based lithium-ion energy storage electrolyte prepared in this invention is 5 mg·Kg. -1 The free acid content is 2 mg / kg. -1 With a flash point of 105℃, the battery assembled using propylene carbonate-based lithium-ion energy storage electrolyte retains 88% of its capacity after 500 cycles at room temperature and 80% of its capacity after 300 cycles under high voltage. All these data are superior to the comparative example.

[0056] The invention utilizes magnesium sulfate to drive the reaction of 1,4-phenylenediboric acid with 1,2,4-butanetriol to synthesize phenylboronic acid ester polyol, which is then reacted with isophorone diisocyanate to prepare a boron-containing urethane flame retardant and dehydrating agent. Fluorinated polyether is synthesized by reacting fluorooxyheterocyclic monomers with fluorinated polyether diols, and finally, alkenyl-terminated fluorinated polyether is introduced. By removing trace amounts of moisture, the hydrolysis reaction of lithium hexafluorophosphate is blocked, preventing the formation of hydrofluoric acid. At the same time, the electrochemical compatibility between the electrolyte and the negative electrode is optimized, significantly improving the cycle life and interface safety of the battery.

[0057] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A low-moisture propylene carbonate-based lithium-ion energy storage electrolyte, characterized in that, It includes the following components by weight: 60-80 parts propylene carbonate, 2-5 parts alkenyl-terminated fluorinated polyether, 10-15 parts lithium salt, 3-6 parts boron-containing urethane flame retardant and dehydrating agent, and 1-5 parts functional additives. The preparation method of the alkenyl-terminated fluorinated polyether is as follows: fluorinated polyether diol, dibutyltin dilaurate and ethyl acetate are placed in a reaction vessel under nitrogen atmosphere and stirred. Propylene 3-isocyanate is added, the reaction vessel is heated to 70-80℃, and the reaction is maintained for 2-4 hours. The alkenyl-terminated fluorinated polyether is then obtained after post-treatment.

2. The low-moisture propylene carbonate-based lithium-ion energy storage electrolyte according to claim 1, characterized in that, The ratio of the amount of fluorinated polyether diol, dibutyltin dilaurate, ethyl acetate and propylene 3-isocyanate is 8-10g:0.2-0.4g:50-70mL:2-4g.

3. The low-moisture propylene carbonate-based lithium-ion energy storage electrolyte according to claim 1, characterized in that, The fluorinated polyether diol is prepared by the following steps: A1. Place 2,2,2-trifluoroethanol, potassium hydroxide aqueous solution and tetrabutylammonium bromide in a reaction vessel and stir. Heat the reaction vessel to 70-80℃, add 3-(chloromethyl)-3-ethyloxetane, keep the reaction at the temperature for 10-12h, and then process to obtain a fluorine-containing oxetane monomer. A2. Place 1,4-butanediol, dichloromethane, and boron trifluoride tetrahydrofuran in a reaction vessel under nitrogen atmosphere protection, stir at room temperature for 0.5-1h, cool the reaction vessel to 0-5℃ in an ice bath, add fluorine-containing heterocyclic monomers, keep the reaction at this temperature for 2-4h, and then perform post-treatment to obtain fluorine-containing polyether diol.

4. The low-moisture propylene carbonate-based lithium-ion energy storage electrolyte according to claim 3, characterized in that, In step A1, the ratio of 2,2,2-trifluoroethanol, potassium hydroxide aqueous solution, tetrabutylammonium bromide, and 3-(chloromethyl)-3-ethyloxetane is 4-6 g:4-6 mL:0.3-0.5 g:6-8 g, and the concentration of potassium hydroxide aqueous solution is 40-50 wt%; in step A2, the ratio of 1,4-butanediol, dichloromethane, boron trifluoride tetrahydrofuran, and fluorine-containing oxetine monomer is 5-7 g:40-60 mL:1-2 g:100-120 g.

5. The low-moisture propylene carbonate-based lithium-ion energy storage electrolyte according to claim 1, characterized in that, The boron-containing urethane flame retardant and dehydrating agent is prepared by the following steps: B1. Place 1,4-phenyldiboronic acid, magnesium sulfate and tetrahydrofuran in a reaction vessel and stir. Add 1,2,4-butanetriol and stir at room temperature for 20-24 hours. Post-treatment yields phenylboronic acid ester polyol. B2 involves placing phenylboronic acid ester polyol and toluene in a nitrogen-protected reactor and stirring. The reactor is heated to 70-80°C and stirred for 10-20 minutes. Isophorone diisocyanate is then added, and the reaction is maintained at this temperature for 4-6 hours. Post-treatment yields a boron-containing urethane flame retardant and dehydrating agent.

6. The low-moisture propylene carbonate-based lithium-ion energy storage electrolyte according to claim 5, characterized in that, In step B1, the ratio of 1,4-phenylenediboronic acid, magnesium sulfate, tetrahydrofuran, and 1,2,4-butanetriol is 4-6g:8-10g:50-70mL:6-8g; in step B2, the ratio of phenylboronic acid ester polyol to toluene is 8-10g:90-110mL, and the molar amount of isophorone diisocyanate is 0.55 times the total molar amount of hydroxyl groups in the phenylboronic acid ester polyol.

7. A preparation process for the low-moisture propylene carbonate-based lithium-ion energy storage electrolyte as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. In a glove box protected by an argon atmosphere, propylene carbonate, alkenyl-terminated fluorinated polyether and boron-containing urethane flame retardant and dehydrating agent are placed in a reaction vessel and stirred at room temperature for 0.5-1 h to obtain a homogeneous solution. S2. In a glove box protected by argon atmosphere, place the homogeneous solution in the reactor and stir. Cool the reactor to 15-25℃ in an ice bath, slowly add lithium salt, restore the reactor to room temperature, stir for 1-2 hours, add functional additives, stir at room temperature for 15-30 minutes, filter, and obtain a low-moisture propylene carbonate-based lithium-ion energy storage electrolyte.

8. The preparation process of the low-moisture propylene carbonate-based lithium-ion energy storage electrolyte according to claim 7, characterized in that, In step S2, the lithium salt is one or more of lithium hexafluorophosphate, lithium difluorosulfonylimide, and lithium tetrafluoroborate, and the functional additive is composed of film-forming co-solvent, lithium salt additive, and high-temperature stabilizer in a mass ratio of 30-50:5-15:5-15.

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