An acetonitrile-based electrolyte compatible with high and low temperature performance and its preparation method

Abstract

This invention relates to the field of lithium battery technology, and more particularly to an acetonitrile-based electrolyte compatible with both high and low temperature performance and its preparation method. The electrolyte of this application incorporates a main salt II and an additive II. The novel main salt II has a smaller dipole moment and incorporates sulfite groups, which enhances lithium-ion mobility and forms a low-impedance SEI film. Additive II includes silane groups linked to vinyl groups and silicon elements. The vinyl groups linked to the silicon elements improve the adhesion of vinyl groups to the negative electrode interface, thereby enhancing film stability and high-temperature resistance. The combined use of main salt II and additive II not only retains the performance advantages of acetonitrile electrolytes at low temperatures but also significantly improves high-temperature performance, enhancing the high-temperature cycling and high-temperature storage performance of lithium-ion batteries. The combination of these two components improves the lithium-ion migration rate and the desolvation capability of the SEI film, ensuring the low-temperature performance of the acetonitrile electrolyte and addressing the problem of existing methods failing to balance high and low temperatures.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to an acetonitrile-based electrolyte compatible with high and low temperature performance and its preparation method. Background Technology

[0002] Lithium-ion batteries, as the core of the new energy industry, are widely used not only in electric vehicles and chemical energy storage systems, but also in the starting and energy recovery of gasoline vehicles. As a starting power source for gasoline vehicles, lithium-ion batteries need to maintain excellent performance within a wide temperature range of -40℃ to 60℃. However, lithium-ion batteries face different technical challenges at different temperatures: at -40℃, the electrolyte viscosity increases, making lithium-ion migration more difficult and slowing down the charge transfer rate, resulting in insufficient battery power; at 60℃, the interfacial film is prone to dissolution and decomposition, leading to shortened cycle and storage life.

[0003] From an electrolyte design perspective, the main approach to improving low-temperature power is to reduce solution viscosity and interfacial film density; while the key to improving high-temperature lifespan lies in reducing the electrolyte's dissolution and decomposition of the interfacial film and improving its density. Existing technologies typically optimize additives, solvents, and main salts to balance high and low temperature performance. However, due to the large amounts of solvents and main salts added, the compatibility of the electrolyte with other materials is significantly affected. Therefore, existing technologies generally focus primarily on adjusting additives and developing novel additives.

[0004] Patent CN112310480B discloses a type of multifunctional sulfite additive that can improve low-temperature performance. This additive contains sulfite groups, fluorinated alkyl groups, ether bonds, and allyl groups. The fluorinated alkyl groups increase the reduction potential of the additive, making it a good film-forming additive; the allyl groups help improve the stability of the positive and negative electrode interfaces; the introduction of ether bonds improves the flexibility of the electrode interface film, which is beneficial to improving the interfacial stability of the electrode materials; and the sulfite groups improve the ionic conductivity of the SEI film, reducing the battery impedance at low temperatures, thereby improving low-temperature performance. This additive not only significantly improves the low-temperature cycle performance of lithium-ion batteries but also does not affect the battery's room-temperature and high-temperature performance.

[0005] Patent CN119340475A reports an electrolyte that exhibits excellent performance at both high and low temperatures and under high voltage. The patent primarily describes three additives: the first additive is a pyrosulfate-boron trifluoride composite lithium salt, the second additive is a cyclic sulfonate compound, and the third additive is lithium oxalate salt. This electrolyte, used in lithium-ion secondary batteries, can reduce battery impedance at voltages ≥4.3V, while simultaneously suppressing gas generation during high-temperature storage, thus improving both high-temperature and low-temperature performance.

[0006] Common methods in existing technologies to achieve superior high and low temperature performance in electrolytes include: reducing the amount of high-resistivity additives (usually VC), increasing the amount of low-viscosity solvents (such as EP or DMC), and increasing the amount of high-ion-mobility salts (such as LiFSI). Through these three adjustments, lithium-ion batteries can be charged and discharged normally at -30°C, but cannot operate at -40°C or even -50°C. Existing technologies struggle to address the problem of deteriorating high-temperature performance after low-temperature performance optimization. Even if technological optimization enables lithium-ion batteries to operate normally at low temperatures, it often comes at the cost of sacrificing some high-temperature performance.

[0007] The fundamental reason for the incompatibility between high and low temperature performance lies in the film-forming mechanism of the film-forming additives. When the film density is high, the electrolyte has difficulty entering the negative electrode surface, reducing side reactions that consume lithium ions. This manifests as reduced capacity loss, improved capacity retention, and excellent high-temperature performance in the battery cell. However, increased film density hinders the diffusion of lithium ions on the SEI film, thereby increasing the battery's DCR. At low temperatures, the electrolyte viscosity increases significantly, further exacerbating the SEI film's hindering effect on lithium ion migration and making the battery's DCR deteriorate even more severely. Summary of the Invention

[0008] To address the compatibility issues of electrolytes at high and low temperatures, this invention modifies the existing technical approach by changing the solvent from carbonates and carboxylic esters to acetonitrile, redesigning high and low temperature compatibility additives, and developing a main salt with higher conductivity. This application provides an acetonitrile-based electrolyte with compatible high and low temperature performance and its preparation method.

[0009] In a first aspect, this application provides an acetonitrile-based electrolyte compatible with high and low temperature performance, comprising a solvent, additives, and a main salt;

[0010] The main salt includes main salt I; the additive includes additive I.

[0011] The main salt I is a phosphorus-based main salt and / or a sulfur-based main salt; the additive I includes any one or a combination of several of the following: carbon-based additives, sulfur-based additives, phosphorus-based additives, boron-based additives, nitrogen-based additives, and silicon-based additives.

[0012] The main salt further includes main salt II and / or the additive further includes additive II;

[0013] The structure of the main salt I is as shown in Formula 1;

[0014]

[0015] Formula 1;

[0016] In Equation 1, [F] nThis indicates that it contains n fluorine atoms, where n is the maximum fluorine content of R1;

[0017] In Formula 1, R1, R2, and R3 are single elements, with R1 selected from any one of aluminum, titanium, silicon, phosphorus, arsenic, antimony, selenium, tellurium, and boron; and R2 and R3 selected from any one of carbon, oxygen, nitrogen, and sulfur.

[0018] The structure of additive II is as shown in Formula 2;

[0019]

[0020] Formula 2;

[0021] In Formula 2, R1 is selected from any one of halogen, alkyl, alkenyl, alkynyl, carbonate, phosphate, sulfonate, sulfate, borate, siloxy, sulfite, phenyl, cyano, pyridyl, and pyrrole.

[0022] Optionally, the main salt II includes any one or a combination of lithium hexafluorophosphate, lithium bis(trifluorosulfonyl)imide, lithium bis(oxalate-borate), lithium tetrafluoroborate, lithium di(fluorooxalate-borate), lithium di(fluorophosphate), lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium hexafluoroarsenate.

[0023] Preferably, the main salt II is lithium hexafluorophosphate and / or lithium difluorosulfonylimide.

[0024] Preferably, the acetonitrile-based electrolyte contains 8%-25% by mass of the main salt, 20%-65% by mass of additive I, and 30%-90% by mass of solvent.

[0025] Formula 2 includes silane groups that link vinyl groups. The vinyl groups are attached to silicon, which enhances the adhesion of the vinyl groups to the negative electrode interface and improves film stability. The combination of vinyl groups and silicon can also improve the thermal stability of the organic chain and enhance the high-temperature resistance of the interfacial film.

[0026] Furthermore, in Formula 1, R1 is selected from phosphorus and antimony; R2 and R3 in Formula 1 are oxygen; the structure of main salt I is as shown in T1 or T2, and the structure is as follows:

[0027]

[0028] T1 T2.

[0029] Compared to elements like titanium, silicon, and aluminum, phosphorus and antimony possess moderate metallic and nonmetallic properties. They can form fluorides with fluoride ions through covalent bonds. Their nonmetallic nature ensures that the negative charge on the fluorine element is evenly distributed in the anionic groups, reducing the dipole moment. This significantly lowers the lattice energy for lithium ions, resulting in higher dissociation capabilities and thus higher conductivity in their lithium salts.

[0030] Additive I comprises any combination of several of the following: ethylene carbonate (EC), propylene carbonate (PC), acetonitrile (AN), ethyl propionate (EP), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propyl acetate (PA), propyl propionate (PP), ethyl acetate (EA), vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene ethylene carbonate (VEC), ethylene sulfate (DTD), 1,3-propanesulfonyl lactone (PS), methanesulfonate (MMDS), lithium difluorodioxolane phosphate (LiDFOP), lithium difluorophosphate (LiPF2O2), lithium difluorooxolane borate (LiDFOB), lithium dioxolane borate (LiBOB), tris(trimethylsilane) phosphate (TMSP), tris(trimethylsilane) borate ester (TMSB), lithium hexafluorophosphate (LiPF6), lithium difluorosulfonyl imide (LiFSI), and lithium bis(trifluoromethylsulfonyl imide) (LiTFSI).

[0031] Preferably, the additive I is selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), methylene methane sulfonate (MMDS), 1,3-propane sulfonate lactone (PS), vinyl sulfate (DTD), tris(trimethyl)silyl phosphate (TMSP), lithium tetrafluorooxalate phosphate (LiDFOP), lithium difluorooxalate borate (LiDFOB), and lithium difluorophosphate (LiDFP).

[0032] More preferably, the additive I is selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3-propanesulfonate lactone (PS).

[0033] Furthermore, in Formula 2, R1 is selected from fluorine, with a structure as shown in T3; R1 is selected from sulfite group, with a structure as shown in T4;

[0034]

[0035] T3 T4.

[0036] Furthermore, the solvent includes any one or a combination of several of the following: carbonate solvents, carboxylic acid ester solvents, and nitrile solvents.

[0037] Furthermore, the solvent includes any one or a combination of several of the following: dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, vinylite, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, methyl propionate, propyl formate, fluorobenzene, xylene, toluene, fluoroethylene carbonate, fluoromethyl ethyl carbonate, fluorodimethyl carbonate, fluorodiethyl carbonate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, trimethyl phosphite, triethyl phosphite, tripropyl phosphite, tetrahydrofuran, acetonitrile, sulfolane, dimethyl sulfoxide, and 1,2-dimethoxyethane.

[0038] Preferably, the solvent is selected from ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), acetonitrile (AN), ethyl methyl carbonate (EMC), ethyl propionate (EP), and propyl acetate (PA).

[0039] More preferably, the solvent is selected from ethylene carbonate (EC), propylene carbonate (PC), acetonitrile (AN), and ethyl propionate (EP).

[0040] Furthermore, in the acetonitrile-based electrolyte, the mass percentage of main salt I is 5%-15%, and the mass percentage of main salt II is 3%-10%.

[0041] The mass percentage of additive I is 20%-60%, and the mass percentage of additive II is 0.5%-1.5%.

[0042] Solvent 30%-90%.

[0043] Preferably, additive I comprises vinylene carbonate at a mass percentage of 0.3%-5%, fluorocarbonate at a mass percentage of 0.3%-5%, and 1,3-propanesulfonate lactone at a mass percentage of 0.3%-3%.

[0044] The solvents include ethylene carbonate (5%-15% by mass), propylene carbonate (5%-15% by mass), ethyl propionate (20%-40% by mass), and acetonitrile (20%-40% by mass).

[0045] Secondly, this application provides a method for preparing an acetonitrile-based electrolyte compatible with high and low temperature performance, wherein the main salt II is prepared by reacting fluorosulfonic acid with lithium hexafluorophosphate and lithium hexafluoroantimonyate, respectively; the synthesis steps are as follows:

[0046] .

[0047] Furthermore, the synthesis methods for T1 and T2 are as follows:

[0048] ;

[0049] .

[0050] Preferably, the molar ratio of fluorosulfonic acid to lithium hexafluorophosphate is 1-2:1; the molar ratio of fluorosulfonic acid to lithium hexafluoroantimony oxide is 1-2:1.

[0051] Furthermore, the synthesis steps of compound 2 are as follows:

[0052] ;

[0053] Furthermore, the preparation of T1 and T2 includes the following preparation process:

[0054] 1) Using vinyl sulfite as a raw material, chlorovinyl sulfite is prepared by chlorination reaction, and then coupled with dimethylvinylchlorosilane by Grignard reaction to introduce vinyl and silane groups, thus obtaining (vinyldimethylsilyl)vinyl sulfite intermediate;

[0055] 2) After the above intermediate is chlorinated again, it is dechlorinated and fluorinated using hydrofluoric acid to finally obtain product T3;

[0056] 3) The product T3 was converted into a Grignard reagent and then coupled with the vinyl chloride sulfite prepared in step 1) to generate crude T4; it was then purified by recrystallization in a mixed solvent of ethyl acetate and petroleum ether to finally obtain a high-purity T4 sample.

[0057]

[0058] .

[0059] Thirdly, this application provides a lithium-ion battery comprising the acetonitrile-based electrolyte or the acetonitrile-based electrolyte obtained by the preparation method described above.

[0060] Beneficial effects: 1. This application introduces main salt II and additive II. Main salt II has a smaller dipole moment, and the introduction of sulfite groups can enhance lithium-ion mobility and form an SEI film with lower impedance. Additive II includes silane groups linked to vinyl groups and silicon elements. The vinyl groups are linked to silicon elements, which helps to improve the adhesion of vinyl groups to the negative electrode interface, and improves the film density, stability and high temperature resistance.

[0061] The combined use of main salt II and additive II not only retains the performance advantages of acetonitrile electrolyte at low temperatures, but also significantly improves high-temperature performance, enhances lithium-ion migration rate and SEI film desolvation capability, thereby reducing acetonitrile damage to the SEI film and solving the problems of high-temperature performance deviation of acetonitrile and incompatibility between acetonitrile and the negative electrode interface. The combination of the two ensures the low-temperature performance of acetonitrile electrolyte, improves the problem of existing methods not being able to balance high and low temperatures, enhances the SEI film's resistance to acetonitrile dissolution, and thus improves the battery's impedance, thermal stability and cycle performance. Detailed Implementation

[0062] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0063] Preparation Example 1, Preparation method of T1:

[0064] Instruments or equipment used: PTFE three-necked flask, PTFE condenser, PTFE tubing, PTFE beaker, PTFE constant pressure funnel, Teflon temperature sensor, oil bath, PTFE stopper, -60℃ to -40℃ dew point room, fume hood, and iron stand. The synthesis apparatus was constructed in the fume hood of the -60℃ dew point room.

[0065] Preparation process: Take 121.6 g of lithium hexafluorophosphate and pour it into a polytetrafluoroethylene (PTFE) three-necked flask. Take 200 g of fluorosulfonic acid and pour it into a PTFE constant-pressure funnel. Insert the PTFE constant-pressure funnel into the three-necked flask, and simultaneously insert a Teflon temperature sensor and a PTFE condenser into the three-necked flask. Connect the PTFE condenser to a tap water outlet using a PTFE tube, with the end connected to a water outlet pipe. Fix the entire reaction apparatus on an iron stand and place the three-necked flask in an oil bath. Control the reaction temperature at 60℃ and the dropping rate of fluorosulfonic acid at approximately 10 seconds per drop. Introduce the hydrofluoric acid produced in the reaction into a sodium hydroxide solution to neutralize the hydrofluoric acid. After the reaction is complete, dissolve the product and reaction residue in dimethyl carbonate to form a saturated solution and let it stand for 24 hours. Filter out the liquid to obtain solution T1. Then place the solution in a freezer at -50℃ and let it stand for 24 hours. Filter out the liquid to obtain solution T1.

[0066]

[0067] Preparation Example 2, Preparation method of T2:

[0068] Instruments or equipment used: PTFE three-necked flask, PTFE condenser, PTFE tubing, PTFE beaker, PTFE constant pressure funnel, Teflon temperature sensor, oil bath, PTFE stopper, -60℃ to -40℃ dew point room, fume hood, and iron stand. The synthesis apparatus was constructed in the fume hood of the -60℃ dew point room.

[0069] Preparation process: Take 24.3 g of lithium hexafluoroantimonyate and pour it into a polytetrafluoroethylene (PTFE) three-necked flask. Take 200 g of fluorosulfonic acid and pour it into a PTFE constant-pressure funnel. Insert the PTFE constant-pressure funnel into the three-necked flask, and simultaneously insert a Teflon temperature sensor and a PTFE condenser into the three-necked flask. Connect the PTFE condenser to a tap water outlet using a PTFE tube, with the end connected to a water outlet pipe. Fix the entire reaction apparatus on an iron stand and place the three-necked flask in an oil bath. Control the reaction temperature at 60℃ and the dropping rate of fluorosulfonic acid at approximately 10 seconds per drop. Introduce the hydrofluoric acid produced in the reaction into a sodium hydroxide solution to neutralize the hydrofluoric acid. After the reaction is complete, dissolve the product and reaction residue in dimethyl carbonate to form a saturated solution. Then place the solution in a -50℃ freezer and let it stand for 24 hours. Filter off the liquid to obtain T2.

[0070]

[0071] Preparation Example 3, Preparation method of T3:

[0072] Raw materials: vinyl sulfite, chlorine, anhydrous tetrahydrofuran, magnesium shavings, dimethylvinylchlorosilane, hydrofluoric acid, petroleum ether, ethyl acetate, iodine.

[0073] Synthesis equipment: iron stand, three-necked flask, oil bath, thermometer, spherical condenser, chlorine flow meter, Buchner funnel, activated carbon, anhydrous magnesium sulfate, molecular sieve, freezer.

[0074] The specific synthesis steps for T3 are as follows:

[0075] 1) Add 100 g of vinyl sulfite and 200 g of ethyl acetate to a three-necked flask, then install a spherical condenser and a thermometer. Place the three-necked flask in an oil bath and slowly heat it. When the temperature reaches 60°C, slowly inject chlorine gas into the three-necked flask, controlling the gas flow rate at 0.1 g / min, for a duration of 25 hours, to obtain crude vinyl sulfite chloride.

[0076] 2) Magnesium sulfate and calcium carbonate were added to the product to remove hydrogen chloride and water, resulting in 165 grams of sulfite chloride.

[0077] 3) The purified vinyl chloride sulfite was added to anhydrous tetrahydrofuran, along with 2 g of iodine and 20 g of magnesium shavings. The reaction temperature was raised to 50°C, and the reaction solution was stirred continuously for 2 hours to obtain the Grignard reagent.

[0078] 4) Dimethylvinylchlorosilane was added dropwise to Grignard reagent at a rate of 0.5 g / min for 4.7 hours. After the reaction was complete, the mixture was filtered through a Buchner funnel to remove magnesium chloride, yielding (vinyldimethylsilyl)vinyl sulfite.

[0079] 5) Add (vinyl dimethylsilyl) vinyl sulfite and ethyl acetate back into a three-necked flask, and slowly inject chlorine gas into the three-necked flask, controlling the gas flow rate at 0.1 g / min for 15 hours, to obtain chlorinated (vinyl dimethylsilyl) vinyl sulfite.

[0080] 6) Chloro(vinyldimethylsilyl)vinyl sulfite was added to liquid hydrofluoric acid, and the reaction temperature was controlled at 0°C. Gas was initially produced, and the mixture was slowly stirred for 4 hours. When no further gas was produced, stirring was stopped. The temperature was raised to 40°C, and the hydrogen fluoride was evaporated to dryness. 82 g of T3 was obtained.

[0081] ;

[0082] .

[0083] Preparation Example 4, Preparation method of T4:

[0084] The chloro(vinyldimethylsilyl) sulfite ester obtained in Preparation Example 3 was added to 12 g of magnesium shavings and 1.5 g of iodine. The reaction temperature was raised to 50 °C, and the reaction solution was stirred continuously for 2 hours to obtain the Grignard reagent.

[0085] Vinyl chlorosulfite was added dropwise to Grignard reagent at a rate of 0.2 g / min. The addition was carried out while stirring, and stopped after 7 hours, with stirring continued for another 3 hours. 120 g of crude T4 was obtained. The crude T4 was then added to a mixture of ethyl acetate and petroleum ether (ethyl acetate to graphite ether mass ratio 4:6), and stirred continuously until the T4 was completely dissolved. The mixture was then placed in a -20°C freezer for 24 hours to allow the T4 compound to precipitate again. This purification process was repeated several times to obtain approximately 64 g of purified T4 sample.

[0086] ;

[0087] .

[0088] Example 1: A lithium-ion battery, comprising the following preparation process:

[0089] Preparation of acetonitrile-based electrolyte compatible with high and low temperature performance: The moisture content in the glove box and the solvent were controlled to be below 10 ppm. 12 g of ethylene carbonate, 12 g of propylene carbonate, 35 g of acetonitrile, and 24 g of ethyl propionate were accurately weighed using a percentile balance and poured into an aluminum bottle. After thorough mixing, the bottle was placed in a 0°C incubator and frozen for 1 hour. Then, 9 g of lithium hexafluorophosphate and 5 g of T1 lithium salt (Preparation Example 1) were added while stirring. Finally, 1.2 g of vitamin C, 0.8 g of PS, and 1 g of FEC were added and stirred until homogeneous, yielding an acetonitrile-based electrolyte compatible with high and low temperature performance.

[0090] Preparation of lithium-ion batteries: The electrolyte was injected into lithium-ion dry batteries for start-stop power supplies, and then immersed in an environment of 25°C for 48 hours. After the electrolyte fully immersed the battery, pre-charge formation and capacity grading were carried out. The pre-charge step was to charge at a constant current of 0.01C to 10% SOC, and then to charge at a constant current of 0.02C to 30% SOC. After pre-charge, the batteries were aged at 45°C for 48 hours, followed by vacuum degassing. After aging, the batteries were charged at a constant current and constant voltage of 0.01C to 3.65V, allowed to rest for 10 minutes, then vacuum sealed, and then discharged to 2.5V to determine the initial charge-discharge efficiency. Next, aging continued at 45°C for 24 hours. After aging, capacity grading was performed by charging at a constant current and constant voltage of 0.1C to 3.65V and discharging at a constant current of 0.1C to 2.5V, finally yielding the finished lithium-ion battery.

[0091] Examples 2-8 and Comparative Example 1 are lithium-ion batteries that differ from Example 1 in that they use different electrolyte formulations, as detailed in Table 1.

[0092] Table 1 lists the electrolyte formulations used in Examples 1-8 and Comparative Example 1.

[0093]

[0094] Performance testing:

[0095] The electrolytes and lithium-ion batteries of the examples and comparative examples were tested and their performance differences were compared using the following methods:

[0096] (1) Cyclic test of lithium-ion battery at 45°C

[0097] The embodiments and comparative examples in this patent underwent a 45°C cycle test according to the following steps: A pre-capacitated lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for at least one hour to ensure the internal temperature of the battery was close to 45°C. Then, it was charged at a constant current and constant voltage of 1C, with a cutoff voltage of 3.65V and a cutoff current of 0.05C. Next, it was discharged at a constant current of 1C to 2.5V. The battery was cycled according to the above steps, and the discharge capacity retention rate after 1000 cycles was recorded. The discharge capacity retention rate after 1000 cycles was calculated by dividing the discharge capacity after the first cycle by the discharge capacity of the first cycle. Specific test data are shown in Table 2.

[0098] (2) Lithium-ion battery -40℃ discharge capacity retention test

[0099] The batteries in this patent embodiment and comparative example were tested for discharge capacity retention at -40°C according to the following steps: The batteries were placed in a constant temperature chamber at 25°C and left to stand for 6 hours before charging and discharging. First, they were charged at a constant current and constant voltage of 0.1C to 3.65V, and then discharged at a constant current of 0.1C to 2.5V, thus achieving the battery's initial capacity. Then, at 25°C, they were first charged at a constant current and constant voltage of 0.1C to 3.65V, and then placed in a freezer at -40°C. After standing for 6 hours, the batteries were discharged at 0.1C to 2.5V, yielding the discharge capacity at -40°C. The discharge capacity at -40°C was divided by the discharge capacity at 25°C to obtain the discharge capacity retention rate at -40°C. Specific test results are shown in Table 3.

[0100] (3) Lithium-ion battery storage test at 60°C

[0101] The high-temperature storage performance test steps for the battery in this patent embodiment and comparative example are as follows: The battery with its capacity set is discharged to 2.5V at a constant current of 1C, left to stand for 5 minutes, and then charged to 3.65V at a constant current and constant voltage of 1C, with a cutoff current of 0.05C. The battery is then placed in a 60℃ constant temperature chamber and stored for 30 days and 60 days respectively. After the specified storage date, the battery is removed. The battery with its volume measured is connected to a test cabinet and discharged to 2.5V at a constant current of 1C, then charged at a constant current and constant voltage of 1C. This 1C constant current discharge process is repeated 3 times. The final discharge capacity recovery rate of the battery is obtained, and the relevant test results are shown in Table 4.

[0102] Table 2, Cyclic Performance List

[0103]

[0104] Table 2 shows the capacity retention rates of different batteries after 1000 cycles at 45°C. Comparing the data from the examples and comparative examples, it can be seen that adding the new main salt can slightly improve the cycle performance of the battery, while the new additives can significantly improve the cycle performance of the cell. The amount of reagents T1, T2, T3, and T4 added has a certain impact on the capacity retention rate of lithium-ion batteries during high-temperature cycling, and the capacity retention rate increases significantly with the addition of reagents. The new additives improve the high-temperature cycling performance more than the new main salt. Among the new additives, T4 has the highest capacity retention rate. The combined use of the new main salt and the new additives is more effective, mainly because both can improve the film formation on the negative electrode. Considering all factors, T4 is the best high-temperature additive, and the combination of T2 and T4 is the optimal solution. When the addition amounts of T2 and T4 are 5% and 0.8%, respectively, the high-temperature cycling performance of the cell is optimal.

[0105] Table 3, Capacity Retention List

[0106]

[0107] Table 3 lists the discharge capacity retention rates of the examples and comparative examples at -40°C. The new lithium salt significantly improves low-temperature performance, with T2 showing a greater improvement than T1. The new additive slightly deteriorates low-temperature performance, with T4 showing a greater deterioration than T3. The combined use of the new lithium salt and the new additive helps to reduce the degree of deterioration of low-temperature performance caused by the new additive, ensuring that its low-temperature performance is not worse than that of the comparative example. Overall, T2 exhibits the best low-temperature performance.

[0108] Table 4, High Temperature Performance List

[0109]

[0110] Table 4 lists the high-temperature storage data for the examples and comparative examples. The effects of conventional electrolytes and electrolytes with added new main salts and additives on the capacity recovery rate of lithium-ion batteries during high-temperature storage were compared. Table 3 shows that both the new main salt and the new additives can improve the high-temperature storage performance of lithium-ion batteries, with the new additives showing a more significant improvement. The order of improvement in storage performance is: T4 > T3, T3 significantly > T2, and T2 > T1. Combining the new main salt and the new additives can further improve storage performance. The optimal combination is the combined use of T2 and T4. The antimony element in T2 readily forms complexes with sulfite groups, enhancing the synergistic film-forming effect of T2 and T4, improving the structure of the SEI film, and enhancing its thermal stability, resulting in a significant improvement in high-temperature storage performance.

[0111] Based on data from 45℃ cycling, -40℃ low-temperature discharge, and high-temperature storage, it was determined that the combination of T2+T4 can significantly improve high-temperature storage and high-temperature cycling without deteriorating the discharge capacity retention rate at -40℃.

[0112] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. An acetonitrile-based electrolyte compatible with both high and low temperature performance, characterized in that, Includes solvents, additives, and main salts; The main salt includes main salt I; the additive includes additive I. The main salt I is a phosphorus-based main salt and / or a sulfur-based main salt; the additive I includes any one or a combination of several of the following: carbon-based additives, sulfur-based additives, phosphorus-based additives, boron-based additives, nitrogen-based additives, and silicon-based additives. The main salt further includes main salt II and / or the additive further includes additive II; The structure of the main salt I is as shown in Formula 1; Formula 1; In Equation 1, [F] n This indicates that it contains n fluorine atoms, where n is the maximum fluorine content of R1; In Formula 1, R1, R2, and R3 are single elements, with R1 selected from any one of aluminum, titanium, silicon, phosphorus, arsenic, antimony, selenium, tellurium, and boron; and R2 and R3 selected from any one of carbon, oxygen, nitrogen, and sulfur. The structure of additive II is as shown in Formula 2; Formula 2; In Formula 2, R1 is selected from any one of halogen, alkyl, alkenyl, alkynyl, carbonate, phosphate, sulfonate, sulfate, borate, siloxy, sulfite, phenyl, cyano, pyridyl, and pyrrole.

2. The acetonitrile-based electrolyte with compatible high and low temperature performance according to claim 1, characterized in that, In Formula 1, R1 is selected from phosphorus and antimony; R2 and R3 in Formula 1 are oxygen; the structure of main salt I is as shown in T1 or T2, and the structure is as follows: T1; T2.

3. An acetonitrile-based electrolyte with compatible high and low temperature performance according to claim 1 or 2, characterized in that, In Formula 2, R1 is selected from fluorine, with a structure as shown in T3; R1 is selected from sulfite group, with a structure as shown in T4; T3; T4.

4. The acetonitrile-based electrolyte with compatible high and low temperature performance according to claim 1, characterized in that, The solvent includes any one or a combination of several of the following: carbonate solvents, carboxylic acid ester solvents, and nitrile solvents.

5. An acetonitrile-based electrolyte with compatible high and low temperature performance according to any one of claims 1, 2, and 4, characterized in that, The main salt I has a mass percentage content of 5%-15%, and the main salt II has a mass percentage content of 3%-10%. The mass percentage of additive I is 20%-60%, and the mass percentage of additive II is 0.5%-1.5%. Solvent 30%-90%, The mass percentage of acetonitrile is 20%-40%.

6. A method for preparing an acetonitrile-based electrolyte with compatible high and low temperature performance according to any one of claims 1-5, characterized in that, The main salt II was prepared by reacting fluorosulfonic acid with lithium hexafluorophosphate and lithium hexafluoroantimonate, respectively; the synthesis steps are shown below: 。 7. The method for preparing an acetonitrile-based electrolyte compatible with high and low temperature performance according to claim 6, characterized in that, The synthesis methods for T1 and T2 are as follows: ； 。 8. A method for preparing an acetonitrile-based electrolyte compatible with high and low temperature performance according to claim 6 or 7, characterized in that, The synthetic steps of compound 2 are shown below: 。 9. The method for preparing an acetonitrile-based electrolyte compatible with high and low temperature performance according to claim 8, characterized in that, The preparation of T1 and T2 includes the following preparation process: 1) Using vinyl sulfite as a raw material, chlorovinyl sulfite is prepared by chlorination reaction, and then coupled with dimethylvinylchlorosilane by Grignard reaction to introduce vinyl and silane groups, thus obtaining (vinyldimethylsilyl)vinyl sulfite intermediate; 2) After the above intermediate is chlorinated again, it is dechlorinated and fluorinated using hydrofluoric acid to finally obtain product T3; 3) The product T3 was converted into a Grignard reagent and then coupled with the vinyl chloride sulfite prepared in step 1) to generate crude T4; it was then purified by recrystallization in a mixed solvent of ethyl acetate and petroleum ether to finally obtain a high-purity T4 sample. ； 。 10. A lithium-ion battery, characterized in that, It comprises an acetonitrile-based electrolyte as described in any one of claims 1-5 or an acetonitrile-based electrolyte obtained by the preparation method as described in any one of claims 6-9.

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