Inducing additive and preparation method thereof, electrolyte and alkali metal ion battery

Abstract

The invention discloses an induction additive and a preparation method thereof, an electrolyte and an alkali metal ion battery. The preparation method of the induction additive comprises the following steps: reacting 2-dimethylaminoethyl acetate with an organic halide in the presence of a first solvent to generate a corresponding quaternary ammonium salt; and reacting the quaternary ammonium salt with the bis (sulfonyl) imine salt under the condition of a second solvent to obtain the induction additive. According to the induction additive provided by the invention, after an electrolyte is added, the low-impedance lithium salt type additive can be promoted to preferentially form a film in a formation stage, the consumption of a high-impedance film forming component is inhibited, and the initial SEI film impedance is reduced; meanwhile, more high-temperature stable additives are reserved for later periods of circulation and storage, so that the long-term circulation and storage performance and the service life of the battery are remarkably improved, and the low-temperature performance is considered.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrolyte preparation of alkali metal ion batteries, and particularly relates to an induced additive, a preparation method thereof, an electrolyte and an alkali metal ion battery. BACKGROUND

[0002] In the lithium iron phosphate system considering low-temperature performance and cycle life, an aluminum shell battery cell is adopted, and an A+B electrolyte solution scheme combining one-time injection and secondary injection is implemented. However, this scheme has the problems of large low-temperature impedance and insufficient ionic conductivity; meanwhile, during high-temperature storage or cycle, the direct current resistance (DCR) of the battery significantly increases, resulting in that it is difficult to meet the low-temperature performance requirement at the end of life (EOL). In addition, the applicability of this electrolyte system in battery cells of other packaging forms such as soft package and cylinder is also limited.

[0003] Generally, in order to improve high-temperature performance, a high proportion of high-temperature film-forming additives is added to improve film-forming stability. However, such additives are often preferentially decomposed at the formation stage, forming a high-impedance solid electrolyte interface (SEI) film, which instead deteriorates the low-temperature performance of the battery, thereby limiting its actual application.

[0004] In summary, it is of great significance to develop a new electrolyte for improving the poor low-temperature performance of the battery, inhibiting the increase of direct current resistance (DCR) at high temperature, and relieving the performance decay at the later stage of storage. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide an induced additive, a preparation method thereof, an electrolyte and an alkali metal ion battery, aiming to solve the problems of poor low-temperature performance, increase of direct current resistance and performance decay after storage of the existing battery.

[0006] The purpose of the present application is achieved by the following technical solutions: An induced additive is an ionic liquid composed of an unsaturated quaternary ammonium type cation with an alkyl or ether group in the side chain and a weakly coordinated fluorine-containing sulfonimide anion, and the corresponding chemical structure general formula is as follows:

[0007] wherein R is an alkyl or ether-substituted alkyl with a total number of carbon atoms less than 10, and Y is a bis-fluorosulfonimide anion or a bis-trifluoromethanesulfonimide anion.

[0008] Preferably, R is selected from one of the following groups: -C4H9, -CH3OCH2CH2, -CH3(CH2)6, -CH3(OCH2CH2)2, -CH3(OCH2CH2)3.

[0009] In this invention, the anion of the inducing additive can preferentially react with Li in the liquid phase. + The combination can promote the dissociation of lithium salts, increase the degree of dissociation, thereby increasing the lithium ion transference number and making the electrolyte have higher conductivity. On the other hand, it can inhibit the decomposition of organic molecules (such as vinylene carbonate), thereby improving the low-temperature charge and discharge performance and meeting the requirements of high power.

[0010] Regarding the choice of the group R (R being an alkyl or ether-substituted alkyl group): the electron-donating property of the alkyl group can enhance the N in the cation of the saturated quaternary ammonium ionic liquid. + The stability of the ether group; the high degree of rotational freedom of the ether group can significantly reduce the viscosity of the ionic liquid; in addition, the ether group reacts with Li + Its excellent coordination ability can significantly improve the solubility of lithium salts in this ionic liquid.

[0011] In this invention, the specific combinations of substituents and anions of the R group in the general chemical structural formula of the inducing additive and their corresponding specific compounds are shown in Table 1.

[0012] Table 1. Combinations of R groups and anions in general formulas and corresponding compounds

[0013] The preparation method of the above-mentioned inducing additive includes the following steps: Under the first solvent conditions, 2-dimethylaminoethyl acetate (compound 1) was reacted with an organic halide to generate the corresponding quaternary ammonium salt (compound 2). Wherein, the general chemical formula of the organohalide is RX, where R is an alkyl or ether-substituted alkyl group with a total number of carbon atoms of less than 10, and X is Br or I; Under the second solvent conditions, the above quaternary ammonium salt and bis(sulfonyl)imide salt were reacted to obtain the inducing additive (compound 3). The general chemical formula of the bis(sulfonyl)imide salt is MY, where M is Li. + or K + Y is the difluorosulfonamide anion (FSI) - ) or bis(trifluoromethanesulfonyl)imine anion (TFSI) - ).

[0014] The synthetic route for the aforementioned inducing additives is as follows:

[0015] Preferably, the molar ratio of 2-dimethylaminoethyl acetate to the organohalide is 1:1 to 1.1.

[0016] Preferably, the reaction time of the 2-dimethylaminoethyl acetate and the organohalide is 0.5 to 2 hours.

[0017] Preferably, the first solvent is acetone, dichloromethane, ethyl acetate, and N,N-dimethylformamide. The molar ratio of the quaternary ammonium salt to the bis(sulfonyl)imide salt is 1:1 to 1.1.

[0018] Preferably, the reaction time of the quaternary ammonium salt and the bis(sulfonyl)imide salt is 2-3 hours.

[0019] Preferably, the second solvent is at least one of dichloromethane, acetonitrile, and ethyl acetate.

[0020] An electrolyte comprising the aforementioned inducing additive.

[0021] Preferably, the electrolyte is composed of the following components by mass percentage: 70-80% organic solvent, 13-22% lithium salt, 0.3-3% inducing additive and 2-5% functional additive.

[0022] Preferably, the organic solvent is at least one of a carboxylic acid ester and a carbonate.

[0023] Preferably, the carboxylic acid ester is methyl acetate (MA), ethyl acetate (EA), ethyl fluoroacetate, ethyl propionate (EP), propyl propionate (PP), or ethyl butyrate (EB); and the carbonate is ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or ethylene carbonate (EC).

[0024] Preferably, the lithium salt is a mixture of LiPF6 and sulfonylimide lithium salt in a mass ratio of 1:1 to 2.

[0025] Preferably, the sulfonylimide lithium salt is lithium bis(fluorosulfonylimide) (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0026] Preferably, the functional additive is at least one selected from lithium difluorooxalate borate (LiDFOB), lithium difluorooxalate phosphate (LiDFOP), lithium difluoroborate (LiBOB), lithium difluorophosphate (LiDFP), tris(trimethylsilane) phosphate (TMSP), tris(trimethylsilane) borate ester (TMSB), vinyl sulfite (DTD), ethylene sulfite (ES), methanedisulfonate methylene (MMDS), 1,3-propanesulfonate lactone (PS), vinylene carbonate (VC), and tripropynyl phosphate (TPP).

[0027] The electrolyte design concept of this invention is to introduce inductive additives to promote the dissociation of lithium salts, increase the degree of lithium salt dissociation, thereby increasing the lithium-ion transference number and giving the electrolyte higher conductivity. At the same time, the additives can inhibit the decomposition of high-resistivity film-forming additives (such as VC, TPP, etc.) and promote the decomposition of low-resistivity film-forming additives, ensuring the formation of thin and dense SEI and CEI films during the formation process, thereby improving low-temperature charge-discharge performance. In addition, it can also reduce the consumption of high-temperature additives during the formation stage, so that they can still effectively play a role in improving performance in the later stages of cycling and storage.

[0028] An alkali metal ion battery comprising the above-mentioned electrolyte.

[0029] Preferably, the alkali metal ion battery is a lithium-ion battery or a sodium-ion battery.

[0030] Compared with the prior art, the beneficial effects of the present invention include: This invention introduces inducing additives to promote the preferential participation of low-resistance lithium salt additives in the film-forming reaction during the formation stage, while suppressing the consumption of high-resistance film-forming additives, thereby reducing the impedance of the initial SEI film. At the same time, more high-temperature stable additives are retained to the later stages of cycling and storage, effectively improving the long-term cycling and storage performance of the battery, and significantly extending the battery life while taking into account low-temperature performance. Attached Figure Description

[0031] Figure 1 The ¹H NMR spectrum of [C4NEA]FSI described in Example 1. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Example 1 A method for preparing an inducing additive, comprising the following specific steps: (1) In a 50 mL three-necked flask, add 9.0 g of 2-dimethylaminoethyl acetate and 20 mL of acetone, and add 9.7 g of n-bromobutane dropwise under ice bath conditions. Stir for 0.5 h, remove the ice bath and stir at room temperature for 12 h. Evaporate the acetone and excess n-bromobutane to obtain a light yellow solid. Recrystallize from ethyl acetate to obtain a white solid. Dry under vacuum at room temperature for 24 h to obtain the product. N,N -dimethyl - N -n-Butyl- N -(2-methylacetoxy)ethyl quaternary ammonium bromide, abbreviated as [C4NEA]Br, with a yield of 70%.

[0034] (2) Dissolve 4.0 g of [C4NEA]Br and 4.2 g of potassium bis(fluorosulfonyl)imide (KFSI) in an appropriate amount of deionized water, mix and stir at room temperature for 2 h, then add 20 mL of dichloromethane, wash with deionized water until no bromide ions are detected by 5% AgNO3 solution, remove dichloromethane by evaporation, and dry under vacuum for 12 h to obtain 5.0 g of colorless liquid, which is the product [C4NEA]FSI, with a yield of 85%.

[0035] The ¹H NMR spectrum of the [C4NEA]FSI is attached. Figure 1 As shown.

[0036] 1 H NMR (399.76 MHz; DMSO- d 6; TMS; ppm): delta = 0.94 (t, 3H), 1.30 (m,2H), 1.66 (m, 2H), 1.92 (s, 3H), 3.31 (s, 2 × 3H), 3.36 (t, 2H), 3.70 (t,2H), 4.53 (t, 2H). An electrolyte is composed of the following components in weight percentage: 79% organic solvent, 18% lithium salt, 0.5% inducing additive and 2.5% functional additive; The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 2:3:3. The lithium salt is a mixture of LiPF6 and LiFSI in a mass ratio of 1:2; The functional additive is a mixture of VC and LiPO2F2 in a mass ratio of 4:1.

[0037] The preparation steps of the above electrolyte are as follows: Anhydrous ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 2:3:3. Measured amounts of LiPF6, LiFSI, VC, and LiPO2F2 are added, followed by the prepared [C4NEA]FSI. The mixture is stirred until the solid is completely dissolved to obtain the electrolyte. In the electrolyte, the molar concentration of lithium salt is 1.2 mol / L, and the mass fraction of [C4NEA]FSI is 0.5%.

[0038] The specific steps for assembling lithium-ion batteries using the above electrolyte are as follows: (1) Preparation of positive electrode sheet Weigh out 96% lithium iron phosphate (LFP), 1.8% polyvinylidene fluoride (PVDF), and 2.2% conductive agent (carbon nanotubes (CNT) to conductive carbon black (SP) mass ratio of 1.5:1) according to the solid component mass percentage. Disperse the above materials in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry with a solid content of 61% (i.e., NMP accounts for 39% of the total slurry mass). Subsequently, coat the slurry on both sides onto an aluminum foil current collector, and after drying, rolling, die-cutting, and stamping, obtain the positive electrode sheet with a coating surface density of 73 g / m². 2 .

[0039] (2) Preparation of negative electrode sheet 95% artificial graphite, 2% conductive agent (vapor-grown carbon fiber and SP, mass ratio 1:1), 2% SBR, and 1% binder (CMC) were added to analytical grade deionized water and thoroughly homogenized in a mixing tank to form a uniform negative electrode slurry. The slurry was then coated on both sides onto a copper foil current collector, and after drying, rolling, slitting, die-cutting, and stamping, the negative electrode sheet was obtained with a coating surface density of 36 g / m². 2 .

[0040] (3) Cell assembly The positive electrode, separator (12+2 coated or ceramic), and negative electrode are stacked using a lamination process. After pre-welding the tabs and welding the top cover, the assembly is completed. After being placed into the casing, it is vacuum baked at 75°C. After the moisture content (positive electrode ≤200ppm, negative electrode + separator ≤150ppm) is tested and qualified, the liquid injection process is carried out. After being fully soaked, it undergoes high-temperature formation at 45°C, high-temperature aging, secondary extraction, and capacity testing to finally obtain the lithium-ion battery cell.

[0041] Example 2 Example 2 provides a method for preparing an inducing additive with the chemical formula [C3ONEA]FSI. The preparation method is consistent with the preparation principle of [C4NEA]FSI in Example 1, except that n-butane bromide is replaced with CH3OCH2CH2Br, followed by FSI. - Anion exchange was used. The prepared [C3ONEA]FSI was a colorless liquid with a yield of 85%.

[0042] An electrolyte is composed of the following components by mass percentage: 78.5% organic solvent, 18% lithium salt, 0.5% inducing additive and 3.0% functional additive; The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 2:3:3. The lithium salt is a mixture of LiPF6 and LiFSI in a mass ratio of 1:2; The functional additive is a mixture of VC and LiPO2F2 in a mass ratio of 5:1.

[0043] The preparation steps of the above electrolyte are as follows: Anhydrous ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 2:3:3. Measured amounts of LiPF6, LiFSI, VC, and LiPO2F2 are added, followed by the prepared [C3ONEA]FSI. The mixture is stirred until the solid is completely dissolved to obtain the electrolyte. In the electrolyte, the molar concentration of lithium salt is 1.2 mol / L, and the mass fraction of [C3ONEA]FSI is 0.5%.

[0044] The assembly of lithium-ion batteries using the above-mentioned electrolyte follows the same steps as in Example 1.

[0045] Example 3 Example 3 provides a method for preparing an inducing additive with the chemical formula [C7O3NEA]FSI. The preparation method is consistent with the preparation principle of [C4NEA]FSI in Example 1, except that n-bromobutane is replaced with CH3(OCH2CH2)Br, followed by FSI. - Anion exchange was used to prepare [C7O3NEA]FSI, which was a colorless liquid with a yield of 85%.

[0046] An electrolyte is composed of the following components by mass percentage: 78.5% organic solvent, 18% lithium salt, 0.5% inducing additive and 3.0% functional additive; The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 2:3:3. The lithium salt is a mixture of LiPF6 and LiFSI in a mass ratio of 1:2; The functional additive is a mixture of VC and LiPO2F2 in a mass ratio of 5:1.

[0047] The preparation steps of the above electrolyte are as follows: Anhydrous ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 2:3:3. Measured amounts of LiPF6, LiFSI, VC, and LiPO2F2 are added, followed by the prepared [C7O3NEA]FSI. The mixture is stirred until the solid is completely dissolved to obtain the electrolyte. In the electrolyte, the molar concentration of lithium salt is 1.2 mol / L, and the mass fraction of [C7O3NEA]FSI is 0.5%.

[0048] The assembly of lithium-ion batteries using the above-mentioned electrolyte follows the same steps as in Example 1.

[0049] Example 4 Example 4 provides a method for preparing an inducing additive with the chemical formula [C4NEA]TFSI. The preparation method is consistent with the preparation principle of [C4NEA]FSI in Example 1, except that potassium bis(fluorosulfonyl)imide is replaced with lithium bis(trifluoromethyl)sulfonylimide, followed by anion exchange. The prepared [C4NEA]TFSI is a colorless liquid with a yield of 785%.

[0050] An electrolyte is composed of the following components by mass percentage: 78.5% organic solvent, 18% lithium salt, 0.5% inducing additive and 3.0% functional additive; The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 2:3:3. The lithium salt is a mixture of LiPF6 and LiFSI in a mass ratio of 1:2; The functional additive is a mixture of VC and LiPO2F2 in a mass ratio of 5:1.

[0051] The preparation steps of the above electrolyte are as follows: Anhydrous ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 2:3:3. Measured amounts of LiPF6, LiFSI, VC, and LiPO2F2 are added, followed by the prepared [C4NEA]TFSI. The mixture is stirred until the solid is completely dissolved to obtain the electrolyte. In the electrolyte, the molar concentration of lithium salt is 1.2 mol / L, and the mass fraction of [C4NEA]TFSI is 0.5%.

[0052] The assembly of lithium-ion batteries using the above-mentioned electrolyte follows the same steps as in Example 1.

[0053] Example 5 Example 5 provides a method for preparing an inducing additive with the chemical formula [C3ONEA]TFSI. The preparation method is consistent with the preparation principle of [C4NEA]FSI in Example 1, except that it is obtained by an ion exchange reaction between [C3ONEA]Br and lithium bis(trifluoromethyl)sulfonylimide. The prepared [C3ONEA]TFSI is a colorless liquid with a yield of 75%.

[0054] An electrolyte is composed of the following components by mass percentage: 78.5% organic solvent, 18% lithium salt, 0.5% inducing additive and 3.0% functional additive; The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 2:3:3. The lithium salt is a mixture of LiPF6 and LiFSI in a mass ratio of 1:2; The functional additive is a mixture of VC and LiPO2F2 in a mass ratio of 5:1.

[0055] The preparation steps of the above electrolyte are as follows: Anhydrous ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 2:3:3. Measured amounts of LiPF6, LiFSI, VC, and LiPO2F2 are added, followed by the prepared [C3ONEA]TFSI. The mixture is stirred until the solid is completely dissolved to obtain the electrolyte. In the electrolyte, the molar concentration of lithium salt is 1.2 mol / L, and the mass fraction of [C3ONEA]TFSI is 0.5%.

[0056] The assembly of lithium-ion batteries using the above-mentioned electrolyte follows the same steps as in Example 1.

[0057] Example 6 Example 6 provides a method for preparing an inducing additive with the chemical formula [C7O3NEA]TFSI. The preparation method is consistent with the preparation principle of [C4NEA]FSI in Example 1, except that it is obtained by an ion exchange reaction between [C7O3NEA]Br and lithium bis(trifluoromethyl)sulfonylimide. The prepared [C7O3NEA]TFSI is a colorless liquid with a yield of 85%.

[0058] An electrolyte is composed of the following components by mass percentage: 78.5% organic solvent, 18% lithium salt, 0.5% inducing additive and 3.0% functional additive; The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 2:3:3. The lithium salt is a mixture of LiPF6 and LiFSI in a mass ratio of 1:2; The functional additive is a mixture of VC and LiPO2F2 in a mass ratio of 5:1.

[0059] The preparation steps of the above electrolyte are as follows: Anhydrous ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 2:3:3. Measured amounts of LiPF6, LiFSI, VC, and LiPO2F2 are added, followed by the prepared [C7O3NEA]TFSI. The mixture is stirred until the solid is completely dissolved to obtain the electrolyte. In the electrolyte, the molar concentration of lithium salt is 1.2 mol / L, and the mass fraction of [C7O3NEA]TFSI is 0.5%.

[0060] The assembly of lithium-ion batteries using the above-mentioned electrolyte follows the same steps as in Example 1.

[0061] Example 7 Example 7 provides a method for preparing an inducing additive with the chemical formula [C7O3NEA]TFSI. The preparation method is consistent with the preparation principle of [C4NEA]FSI in Example 1, except that it is obtained by an ion exchange reaction between [C7O3NEA]Br and lithium bis(trifluoromethyl)sulfonylimide. The prepared [C7O3NEA]TFSI is a colorless liquid with a yield of 70%.

[0062] An electrolyte is composed of the following components in weight percentage: 77.5% organic solvent, 18% lithium salt, 1% inducing additive and 3.5% functional additive; The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 2:3:3. The lithium salt is a mixture of LiPF6 and LiFSI in a mass ratio of 1:2; The functional additive is a mixture of VC, LiPO2F2 and LiDFOP in a mass ratio of 5:1:1.

[0063] The preparation steps of the above electrolyte are as follows: Anhydrous ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 2:3:3. Measured amounts of LiPF6, LiFSI, VC, LiPO2F2, and LiDFOP are added, followed by the prepared [C7O3NEA]TFSI. The mixture is stirred until the solid is completely dissolved to obtain the electrolyte. In the electrolyte, the molar concentration of lithium salt is 1.2 mol / L, and the mass fraction of [C7O3NEA]TFSI is 1%.

[0064] The assembly of lithium-ion batteries using the above-mentioned electrolyte follows the same steps as in Example 1.

[0065] Comparative Example 1 Comparative Example 1 provides an electrolyte composed of the following components by mass percentage: 80% organic solvent, 18% lithium salt, and 2% additives; The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a mass ratio of 2:3:3. The lithium salt is a mixture of LiPF6 and LiFSI in a mass ratio of 1:2; The additive is vitamin C.

[0066] The preparation steps of the above electrolyte are as follows: Anhydrous ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 2:3:3, and metered LiPF6, LiFSI, and VC are added. The mixture is stirred until the solid is completely dissolved to obtain the electrolyte. In the electrolyte, the molar concentration of lithium salt is 1.2 mol / L, and the mass fraction of VC is 2%.

[0067] The assembly of lithium-ion batteries using the above-mentioned electrolyte follows the same steps as in Example 1.

[0068] The cells prepared according to Examples 1-7 and Comparative Example 1 were tested for room temperature discharge DC internal resistance (DCR), cycle life, and storage performance. The specific methods are as follows: 1. Room temperature capacity and DCR test (a) At room temperature, discharge at a constant current of 1C to 2.5V, then charge at a constant current of 1C to 3.65V, and switch to constant voltage charging until the current drops to 0.05C; then discharge at a constant current of 1C to 2.5V. Repeat the above charge and discharge process 3 times to complete the constant capacity.

[0069] (b) Adjust the cell to 50% state of charge (SOC) according to the calibrated result, let it stand at room temperature for 3 hours, and then perform a 5C, 10s pulse charge and discharge to test its DC internal resistance (DCR).

[0070] 2. High-temperature storage test (a) At room temperature, charge the cell to 95% SOC (capacity cutoff) with a 1 / 3C current. (b) Store the cell in a 60°C environment for 3 months, remove it and let it stand at room temperature for 6 hours, and test its room temperature discharge capacity and 5C, 10 s discharge DCR.

[0071] 3. Cyclic life test (a) The battery cell was left to stand for 3 hours at the set test temperature (25°C or 45°C); (b) At the same temperature, charge at a constant current of 1C to 3.65V, then switch to constant voltage charging until the current drops to 0.05C, stop charging, and let stand for 5 minutes; (c) At the same temperature, discharge at a constant current of 1C to 2.5 V and let stand for 5 min.

[0072] Repeat steps (b) to (c) until the cell's capacity retention drops to 80% of its initial capacity (i.e., SOH = 80%), and record the number of cycles at this point. The test results are shown in Table 2.

[0073] Table 2 Electrochemical Performance of the Battery

[0074] As shown in Table 2 above, the data shows that compared with Comparative Example 1, when 0.5% [C4NEA]FSI or 0.5% [C4NEA]TFSI is added, the DCR does not change significantly, but the high-temperature performance is slightly improved; when 0.5% [C3ONEA]FSI or 0.5% [C3ONEA]TFSI is added, the DCR decreases by 7%, the cycling performance is improved by 300-550 cycles, and the anionic TFSI... - FSI - The thermal stability is higher; when 0.5% [C7O3NEA]FSI or 0.5% [C7O3NEA]TFSI is added, the DCR is further reduced, and the high-temperature performance is significantly improved. This indicates that the added inducing additives, whose side chains contain hydrocarbon alkyl groups, have electron-donating properties that enable the N-type cations of the saturated quaternary ammonium ionic liquid to... + Enhanced ionic stability can improve reactivity and promote lithium salt dissolution; additionally, inducers with ether groups in their side chains can significantly reduce the viscosity of ionic liquids due to the high rotational freedom of the ether groups, and the ether groups react with Li... + Excellent coordination properties significantly improve its solubility for lithium salts, thereby increasing the system's conductivity, reducing DCR, and enhancing high-temperature performance. Furthermore, comparisons between Examples 2 and 3, or Examples 5 and 6, show that within a certain range, the more carbon atoms in the ether group, the more pronounced the effect. A comparison between Examples 6 and 7 demonstrates that this inducing additive can promote the film formation of more lithium salt-type additives, reduce film resistance, and improve subsequent high-temperature performance.

[0075] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An inducing additive, characterized in that, It is an ionic liquid composed of an unsaturated quaternary ammonium cation with alkyl or ether groups in the side chain and a weakly coordinated fluorosulfonylimide anion, and its corresponding general chemical formula is as follows: Wherein, R is an alkyl or ether-substituted alkyl group with a total number of carbon atoms less than 10, and Y is a bis(fluorosulfonyl)imide anion or a bis(trifluoromethanesulfonyl)imide anion.

2. The inducing additive according to claim 1, characterized in that, The R is selected from one of the following groups: -C4H9, -CH3OCH2CH2, -CH3(CH2)6, -CH3(OCH2CH2)2, -CH3(OCH2CH2)3.

3. The method for preparing the inducing additive according to any one of claims 1 to 2, characterized in that, Includes the following steps: Under the first solvent conditions, 2-dimethylaminoethyl acetate and an organic halide are reacted to generate the corresponding quaternary ammonium salt; Wherein, the general chemical formula of the organohalide is RX, where R is an alkyl or ether-substituted alkyl group with a total number of carbon atoms of less than 10, and X is Br or I; Under the second solvent conditions, the above quaternary ammonium salt and bis(sulfonyl)imide salt are reacted to obtain the inducing additive; The general chemical formula of the bis(sulfonyl)imide salt is MY, where M is Li. + or K + Y is FSI - or TFSI - .

4. The method for preparing the inducing additive according to claim 3, characterized in that, The molar ratio of 2-dimethylaminoethyl acetate to the organic halide is 1:1 to 1.1; The reaction time of the 2-dimethylaminoethyl acetate and the organohalide is 0.5~2h.

5. The method for preparing the inducing additive according to claim 3, characterized in that, The molar ratio of the quaternary ammonium salt to the bis(sulfonyl)imide salt is 1:1 to 1.1; and / or The reaction time of the quaternary ammonium salt and the bis(sulfonyl)imide salt is 2-3 hours.

6. The method for preparing the inducing additive according to claim 3, characterized in that, The first solvent is at least one or two of acetone, dichloromethane, ethyl acetate and N,N-dimethylformamide; The second solvent is at least one of dichloromethane, acetonitrile, and ethyl acetate.

7. An electrolyte, characterized in that, Includes the inducing additive as described in any one of claims 1 to 2.

8. The electrolyte according to claim 7, characterized in that, It consists of the following components by mass percentage: 70-80% organic solvent, 13-22% lithium salt, 0.3-3% inducing additives and 2-5% functional additives.

9. The electrolyte according to claim 8, characterized in that, The organic solvent is at least one of a carboxylic acid ester and a carbonate; and / or The lithium salt is a mixture of LiPF6 and sulfonylimide lithium salt in a mass ratio of 1:1 to 2; and / or The sulfonylimide lithium salt is lithium bis(fluorosulfonylimide) or lithium bis(trifluoromethanesulfonyl)imide; and / or The functional additive is at least one of lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium difluoroborate, lithium difluorophosphate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, vinyl sulfite, ethylene sulfite, methane disulfonate, 1,3-propane sulfonate lactone, vinylene carbonate, and triargyl phosphate.

10. An alkali metal ion battery, characterized in that, It includes the electrolyte according to any one of claims 7 to 9.

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