A fast-charging lithium ion battery electrolyte and application thereof

Abstract

The application provides a fast-charging lithium ion battery electrolyte and application thereof. The fast-charging electrolyte comprises a solvent, a lithium salt, a film-forming additive and a multifunctional additive. The multifunctional additive is a crown ether and a derivative thereof. The fast-charging electrolyte has high ion conductivity and has the beneficial effect of enabling the lithium ion battery to maintain good cycle life at 6C high rate.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to a fast-charging lithium-ion battery electrolyte and its application. Background Technology

[0002] Since their invention, lithium-ion batteries have played a vital role in people's daily lives, with an increasing number of electrical devices requiring their power. Currently, new energy vehicles are developing rapidly due to national subsidies and environmental advantages, but they also face many challenges, such as range anxiety, fast charging, and safety issues. Regarding ultra-fast charging, the electrolyte plays a crucial role. The electrolyte's ability to rapidly conduct lithium ions, its low desolvation energy barrier, and the speed of interfacial transfer all significantly impact the battery's fast-charging capability.

[0003] To improve the fast-charging capability of the electrolyte, patent CN 117374404 A uses a composite solvent of linear carbonate and cyclic carbonate to increase lithium-ion transport number and conductivity, and reduce electrolyte viscosity. Simultaneously, the addition of trimethyl(methylsulfonylmethyl)silane further assists in the formation of a thin and stable SEI film, which exhibits low impedance, high stability, and high ion conductivity. Patent application CN113851725A discloses a fast-charging electrolyte for lithium-ion batteries, with a solvent of MF:EC:EMC:DMC = 1:3:2:4, an electrolyte of LiPF6:LiClO4 = 2:1, a total electrolyte content of 2 mol / L, and an anode film-forming additive of allyloxytrimethylsilane (AMSL). The formed SEI can passivate the material interface, reduce lithium-ion migration resistance, and improve the battery's 5C fast-charging performance and cycle life.

[0004] Regarding electrolytes, methods to improve fast-charging performance include, but are not limited to, using low-viscosity solvents, solvents with weak solvation capabilities, and film-forming additives that help form thin SEI films. However, commonly used solvents may not simultaneously meet the first two requirements. Patent CN111293356 A discloses a crown ether electrolyte additive; research shows that the inner diameter of 12-crown-4 is approximately 120-150 μm, while Li... + Its diameter is 120 μm, and it is capable of interacting with Li + The formation of stable complexes can significantly improve the high-rate performance and cycle performance of batteries, but the performance is singular, only improving conductivity and not improving the SEI film.

[0005] Although the above solutions have improved battery performance to some extent through the targeted selection and combination of additives, there are still several problems such as low electrolyte conductivity and high interfacial impedance. Therefore, the development of high-efficiency lithium iron phosphate electrolytes and batteries remains a key technical challenge that the industry urgently needs to address. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in the related art. Therefore, one object of this invention is to provide a fast-charging electrolyte that has high ionic conductivity and the beneficial effect of enabling lithium-ion batteries to maintain good cycle life even at a high rate of 6C.

[0007] In one aspect, the present invention provides a fast-charging electrolyte. According to an embodiment of the present invention, the fast-charging electrolyte comprises a solvent, a lithium salt, a film-forming additive, and a multifunctional additive, wherein the multifunctional additive is a crown ether and its derivatives. This fast-charging electrolyte has a high ionic conductivity and the beneficial effect of enabling lithium-ion batteries to maintain good cycle life at a high rate of 6C.

[0008] According to embodiments of the present invention, the fast-charging electrolyte may further include at least one of the following additional technical features:

[0009] According to embodiments of the present invention, the crown ether and its derivatives include one or more selected from 4-vinylbenzo-18-crown ether-6, 2-(allyloxymethyl)-18-crown-6-ether, eicosfluoro-15-crown-5-ether, benzo-15-crown ether-5, benzo-18-crown-6-ether, dibenzo-21-crown-7, and dibenzo-24-crown ether-8.

[0010] According to embodiments of the present invention, the solvent comprises two or more selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, ethyl acetate, methyl acetate, propyl acetate, methyl propionate, propyl propionate, ethyl propionate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dimethyl sulfoxide, sulfolane, and dimethyl sulfone.

[0011] According to an embodiment of the present invention, the solvent is ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0012] According to an embodiment of the present invention, the mass ratio of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate is 2.5:2:5.5.

[0013] According to embodiments of the present invention, the lithium salt includes at least one selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate.

[0014] According to an embodiment of the present invention, the lithium salt is lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide.

[0015] According to an embodiment of the present invention, the mass fraction of the lithium hexafluorophosphate is 8.5%.

[0016] According to an embodiment of the present invention, the mass fraction of the lithium difluorosulfonylimide is 5.5%.

[0017] According to embodiments of the present invention, the film-forming additive is selected from one or more of vinyl sulfite, vinyl sulfate, 1,3-propanesulfonate lactone, tris(trimethylsilane) phosphate, lithium difluorooxalate borate, fluoroethylene carbonate, vinylene carbonate, lithium difluorobis(oxalate) phosphate, lithium tetrafluorooxalate phosphate, and lithium difluorophosphate (LiPO2F2).

[0018] According to an embodiment of the present invention, the film-forming additive is vinylene carbonate, vinyl sulfate and tris(trimethylsilyl)phosphate.

[0019] According to an embodiment of the present invention, the ratio of the amount of vinylene carbonate, the amount of vinyl sulfate and the amount of tris(trimethylsilyl)phosphate is 10:5:1.

[0020] According to an embodiment of the present invention, the weight ratio of the crown ether and its derivatives to the total weight of the fast-charging electrolyte is 0.05% to 0.5%.

[0021] According to an embodiment of the present invention, the weight ratio of the solvent to the total weight of the fast-charging electrolyte is 70% to 88%.

[0022] According to an embodiment of the present invention, the weight ratio of the solvent to the total weight of the fast-charging electrolyte is 72% to 85%.

[0023] According to an embodiment of the present invention, the weight ratio of the lithium salt to the total weight of the fast-charging electrolyte is 10% to 20%.

[0024] According to an embodiment of the present invention, the weight ratio of the lithium salt to the total weight of the fast-charging electrolyte is 11% to 16%.

[0025] According to an embodiment of the present invention, the weight ratio of the film-forming additive to the total weight of the fast-charging electrolyte is 0.2% to 5%.

[0026] In another aspect of the invention, a method for preparing the aforementioned fast-charging electrolyte is provided. According to an embodiment of the invention, the method includes:

[0027] The fast-charging electrolyte is obtained by dissolving lithium salt, film-forming additives and multifunctional additives in a solvent.

[0028] According to embodiments of the present invention, the method may further include the following additional technical features:

[0029] According to an embodiment of the present invention, the lithium salt, film-forming additive, and multifunctional additive are dissolved in the solvent in sequence.

[0030] In another aspect, the present invention also provides a battery. According to an embodiment of the invention, the battery comprises the fast-charging electrolyte described above or the fast-charging electrolyte prepared according to the method described above.

[0031] According to embodiments of the present invention, the battery may further include at least one of the following additional technical features:

[0032] According to an embodiment of the present invention, the battery is a lithium-ion battery.

[0033] According to an embodiment of the present invention, the battery further includes a positive electrode, a negative electrode, and a separator.

[0034] According to embodiments of the present invention, the present invention has at least one of the following technical effects:

[0035] (1) A mixed system of P salt and F salt is adopted, wherein lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide in F salt have large anionic groups and are easy to dissociate, so that the electrolyte system has high ionic conductivity.

[0036] (2) A multifunctional crown ether derivative additive is used, which has multiple -O-CH2-CH2- segments in its structure, forming a large cyclic cavity. At the same time, the lone pair electrons of the O atoms on the ring are oriented towards the center of the ring, and Li + The formation of crown ether coordination compounds through dipole-ion interactions enhances the Li + The electron transfer number increases, improving the conductivity and solubility of lithium ions in the solution;

[0037] (3) Multifunctional crown ether derivative additives compete with EC. + The effect of this makes EC and Li + The reduced force facilitates desolvation at the interface, which in turn improves fast charging performance.

[0038] (4) At the same time, the structure of the crown ether derivative additive is also a compound with functional groups such as double bond, fluorine bond, benzene ring, etc., which forms a stable and thin SEI film at the negative electrode interface, which is easy for lithium ions to conduct.

[0039] (5) The lithium-ion battery electrolyte of the present invention has the beneficial effect of enabling lithium-ion batteries to maintain good cycle life at a high rate of 6C. Detailed Implementation

[0040] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0041] I. Electrolyte Preparation

[0042] Example 1

[0043] In an argon-filled glove box (moisture <10 ppm, oxygen <10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 2.5:2:5.5. Then, 8.5% lithium hexafluorophosphate (LiPF6) and 5.5% lithium difluorosulfonylimide (LiFSI) were slowly added to the mixed solvent and stirred until completely dissolved. 2% vinylene carbonate (VC), 1% vinyl sulfate (DTD), 0.2% tris(trimethylsilyl)phosphate (TMSP), and 0.05% 4-vinylbenzo-18-crown ether-6 were added to obtain the electrolyte for this experiment.

[0044] Example 2

[0045] This embodiment provides a lithium-ion battery electrolyte. The similarities with that in Example 1 will not be repeated. The difference between this embodiment and Example 1 is that the amount of 4-vinylbenzo-18-crown ether-6 is different. Based on the total mass of the lithium-ion battery electrolyte, the mass percentage of 4-vinylbenzo-18-crown ether-6 in this embodiment is 0.1%.

[0046] Example 3

[0047] This embodiment provides a lithium-ion battery electrolyte. The similarities with that in Example 1 will not be repeated. The difference between this embodiment and Example 1 is that the amount of 4-vinylbenzo-18-crown ether-6 is different. Based on the total mass of the lithium-ion battery electrolyte, the mass percentage of 4-vinylbenzo-18-crown ether-6 in this embodiment is 0.5%.

[0048] Example 4

[0049] This embodiment provides a lithium-ion battery electrolyte. The similarities with that in Embodiment 1 will not be repeated. The difference between this embodiment and Embodiment 1 is that eicosofo-15-crown-5-ether is used as an electrolyte additive. Based on the total mass of the lithium-ion battery electrolyte, the mass percentage of eicosofo-15-crown-5-ether in this embodiment is 0.05%.

[0050] Example 5

[0051] This embodiment provides a lithium-ion battery electrolyte. The similarities with that in Embodiment 1 will not be repeated. The difference between this embodiment and Embodiment 1 is that eicosofo-15-crown-5-ether is used as an electrolyte additive. Based on the total mass of the lithium-ion battery electrolyte, the mass percentage of eicosofo-15-crown-5-ether in this embodiment is 0.5%.

[0052] Example 6

[0053] This embodiment provides a lithium-ion battery electrolyte. The similarities with that in Embodiment 1 will not be repeated. The difference between this embodiment and Embodiment 1 is that benzo-15-crown ether-5 is used as an electrolyte additive. Based on the total mass of the lithium-ion battery electrolyte, the mass percentage of benzo-15-crown ether-5 in this embodiment is 0.05%.

[0054] Example 7

[0055] This embodiment provides a lithium-ion battery electrolyte. The similarities with that in Embodiment 1 will not be repeated. The difference between this embodiment and Embodiment 1 is that benzo-15-crown ether-5 is used as an electrolyte additive. Based on the total mass of the lithium-ion battery electrolyte, the mass percentage of benzo-15-crown ether-5 in this embodiment is 0.1%.

[0056] Example 8

[0057] This embodiment provides a lithium-ion battery electrolyte. The similarities with that in Embodiment 1 will not be repeated. The difference between this embodiment and Embodiment 1 is that benzo-15-crown ether-5 is used as an electrolyte additive. Based on the total mass of the lithium-ion battery electrolyte, the mass percentage of benzo-15-crown ether-5 in this embodiment is 0.5%.

[0058] Comparative Example 1

[0059] In an argon-filled glove box (moisture <10ppm, oxygen <10ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 2.5:2:5.5. Then, 8.5% lithium hexafluorophosphate (LiPF6) and 5.5% lithium difluorosulfonyl imide (LiFSI) by mass were slowly added to the mixed solvent and stirred until completely dissolved.

[0060] Comparative Example 2

[0061] In an argon-filled glove box (moisture <10ppm, oxygen <10ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 2.5:2:5.5. Then, 8.5% lithium hexafluorophosphate (LiPF6) and 5.5% lithium difluorosulfonylimide (LiFSI) were slowly added to the mixed solvent and stirred until completely dissolved. Finally, 0.5% 4-vinylbenzo-18-crown ether-6 was added.

[0062] Comparative Example 3

[0063] In an argon-filled glove box (moisture <10ppm, oxygen <10ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 2.5:2:5.5. Then, 8.5% lithium hexafluorophosphate (LiPF6) and 5.5% lithium difluorosulfonyl imide (LiFSI) were slowly added to the mixed solvent and stirred until completely dissolved. Finally, 2% ethylene carbonate (VC) was added.

[0064] Comparative Example 4

[0065] In an argon-filled glove box (moisture <10ppm, oxygen <10ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 2.5:2:5.5. Then, 8.5% lithium hexafluorophosphate (LiPF6) and 5.5% lithium difluorosulfonyl imide (LiFSI) by mass were slowly added to the mixed solvent and stirred until completely dissolved. 2% vinylene carbonate (VC) and 1% vinyl sulfate (DTD) were then added.

[0066] Comparative Example 5

[0067] In an argon-filled glove box (moisture <10ppm, oxygen <10ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 2.5:2:5.5. Then, 8.5% lithium hexafluorophosphate (LiPF6) and 5.5% lithium difluorosulfonyl imide (LiFSI) by mass were slowly added to the mixed solvent and stirred until completely dissolved. 2% vinylene carbonate (VC), 1% vinyl sulfate (DTD), and 0.2% tris(trimethylsilyl)phosphate (TMSP) were then added.

[0068] Comparative Example 6

[0069] In an argon-filled glove box (moisture <10ppm, oxygen <10ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 2.5:2:5.5. Then, 8.5% lithium hexafluorophosphate (LiPF6) and 5.5% lithium difluorosulfonyl imide (LiFSI) by mass fraction were slowly added to the mixed solvent and stirred until completely dissolved. 2% vinylene carbonate (VC), 1% vinyl sulfate (DTD), 0.2% tris(trimethylsilyl) phosphate (TMSP), and 1% eicosfluoro-15-crown-5-ether were added.

[0070] Comparative Example 7

[0071] In an argon-filled glove box (moisture <10ppm, oxygen <10ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 2.5:2:5.5. Then, 8.5% lithium hexafluorophosphate (LiPF6) and 5.5% lithium difluorosulfonyl imide (LiFSI) were slowly added to the mixed solvent and stirred until completely dissolved. 2% vinylene carbonate (VC), 1% vinyl sulfate (DTD), 0.2% tris(trimethylsilyl) phosphate (TMSP), and 1% benzo-15-crown ether-5 were added.

[0072] The preparation of lithium-ion batteries using the electrolytes of the examples and comparative examples specifically includes the following steps:

[0073] Preparation of the positive electrode: The positive electrode material (LFP), conductive agent (Super P), carbon nanotubes (CNT), and polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) in a mass ratio of 97.5%:0.5%:0.5%:1.5%, and mixed evenly to form a slurry. The slurry is then coated onto an aluminum foil current collector. The surface density of the positive electrode on one side is 18 mg / cm². 2 Cold-pressed to 2.42 g / m 3 After punching, the positive electrode sheet is obtained.

[0074] Preparation of the negative electrode sheet: Graphite, conductive agent (Super P), single-walled carbon nanotubes (SWCNTs), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber latex (SBR) were added to deionized water in a mass ratio of 96.2%:0.94%:0.06%:2%:0.8%, and thoroughly mixed. The slurry was then coated onto a copper foil current collector. The negative electrode surface density was determined according to an N / P ratio of 1.15, and cold-pressed to 1.55 g / m³. 3 After punching, the negative electrode sheet is formed.

[0075] Cell preparation: The separator, negative electrode, and positive electrode are stacked in a "Z" shape to obtain a bare cell to be injected with electrolyte. The cell is then packaged in aluminum-plastic film to obtain a cell to be injected with electrolyte. After baking, the electrolyte in the example or comparative example is injected at an addition rate of 3.5 g / Ah to obtain a sodium lithium-ion battery with a nominal capacity of 2Ah to be tested.

[0076] The electrolytes prepared in Examples 1-8 and Comparative Examples 1-7 were subjected to conductivity, DCR, 6C fast charging capability, interface lithium plating, and 6C fast charging cycle tests. The specific test conditions are as follows:

[0077] Electrolyte conductivity test: In a glove box filled with argon gas (moisture <10ppm, oxygen <10ppm), the prepared electrolyte was tested using a conductivity meter to measure its conductivity.

[0078] DCR test: Charge the battery to 3.65V with constant current and constant voltage, let it stand for 6 hours, and then test the battery's DC internal resistance.

[0079] Fast charging capability test: The battery was charged and discharged at 2.0 to 3.65V under the conditions of room temperature 25±2℃ and relative humidity 45%~75%. The test procedure was as follows: first, the battery was calibrated to the rated capacity three times at 1C and recorded as C0; then, it was charged to 3.65V at 1C constant current and constant voltage and allowed to stand for 10 minutes; then, it was discharged to 2.0V at 1C constant current and allowed to stand for 10 minutes; finally, it was charged to 3.65V at 6C constant current and constant voltage and recorded as the charging capacity C1.

[0080] 6C fast charging SOC = C1 / C0 * 100%

[0081] 6C interface lithium plating test: The battery cell was charged to 80% SOC at a charging current of 6C in a 45℃ constant temperature chamber. Then the battery was disassembled in a glove box to observe the lithium plating state of the negative electrode.

[0082] 6C rate fast charging cycle test: In a 25℃ constant temperature chamber, the lithium-ion battery is charged at a constant current of 0.2C to a voltage of 3.65V, and discharged at a constant current of 0.2C to a voltage of 2.0V. The discharge capacity of the lithium-ion battery is tested and recorded as C2. After charging at a constant current and constant voltage of 6C to 3.65V, resting for 10 minutes, discharging at a constant current of 1C to 2.0V, and resting for 10 minutes, the discharge capacity of the lithium-ion battery is recorded as C3 after repeating the charge and discharge cycle 500 times.

[0083] Capacity retention rate at 25℃ and 500 cycles = C3 / C2 × 100%;

[0084] The test data for the examples and comparative examples are shown in Table 1.

[0085] Table 1

[0086]

[0087]

[0088] The results show that:

[0089] Conductivity comparison: Compared with Comparative Examples 1, 3, 4, and 5, Examples 1-8 and Comparative Examples 2, 6, and 7 show a significant improvement in conductivity. The fundamental reason for this is the addition of crown ether derivative additives to the electrolyte, which enhances the migration rate of lithium ions.

[0090] The DCR in Comparative Example 1 was lower than that in Examples 1-8 and Comparative Examples 2-7. This was mainly because Comparative Example 1's formulation lacked other film-forming additives, resulting in a thinner SEI film and a lower DCR. However, its fast-charging and cycling performance were poor, and severe interfacial lithium plating was observed. Examples 1-3, compared to Comparative Example 5, added different amounts of 4-vinylbenzo-18-crown ether, showing significantly better performance. This was mainly because the additive improved conductivity, lowered the interfacial desolvation barrier, and contained vinyl groups, resulting in a thinner SEI layer at the interface. Examples 4-5 used eicosfluoro-15-crown-5-ether as an additive, significantly improving fast-charging performance. However, the DCR was slightly lower than in Examples 1-3 because the molecule contained F, resulting in a lower impedance for the LiF-based SEI at the interface compared to the Li2CO3 generated at the vinyl interface. Comparative Example 6 increased the eicosfluoro-15-crown-5-ether content, significantly improving conductivity, but the excessive LiF layer formation led to excessive interfacial impedance and significant lithium plating. In Examples 6-8, benzo-15-crown ether-5 was selected as an additive, and its performance was significantly improved compared to Comparative Example 5. This is because the conjugated structure of the benzene ring enhances the interaction between the electrochemical electrons (ECs) and Li+ through π orbitals, thereby improving the desolvation ability. Simultaneously, the π-π stacking of the benzene ring in the additive preferentially adsorbs at the negative electrode interface, thus inducing the formation of an SEI film at the negative electrode interface. In Comparative Example 7, the content of benzo-15-crown ether-5 was increased. Although the conductivity improved, the electropolymerization of the benzene ring led to a thicker SEI film, increased DCR, and a decrease in performance.

[0091] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A fast-charging electrolyte, characterized in that, The fast-charging electrolyte includes a solvent, a lithium salt, a film-forming additive, and a multifunctional additive, wherein the multifunctional additive is a derivative of a crown ether. The derivatives of the crown ether include one or more of eicosfluoro-15-crown-5-ether, benzo-15-crown-5, benzo-18-crown-6-ether, dibenzo-21-crown-7, and dibenzo-24-crown-8; The solvent is ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate; The mass ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 2.5:2:5.5; Based on the total weight of the fast-charging electrolyte, the weight percentage of the crown ether derivative is 0.05% to 0.5%. Based on the total weight of the fast-charging electrolyte, the solvent accounts for 70% to 88% by weight. Based on the total weight of the fast-charging electrolyte, the weight ratio of the lithium salt is 10% to 20%.

2. The fast-charging electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate.

3. The fast-charging electrolyte according to claim 1, characterized in that, The lithium salt is lithium hexafluorophosphate and / or lithium difluorosulfonylimide.

4. The fast-charging electrolyte according to claim 3, characterized in that, The mass fraction of the lithium hexafluorophosphate is 8.5%.

5. The fast-charging electrolyte according to claim 3, characterized in that, The mass fraction of the lithium difluorosulfonylimide is 5.5%.

6. The fast-charging electrolyte according to claim 1, characterized in that, The film-forming additive is selected from one or more of the following: vinyl sulfite, vinyl sulfate, 1,3-propanesulfonate lactone, tris(trimethylsilane) phosphate, lithium difluorooxalate borate, fluoroethylene carbonate, vinylene carbonate, lithium difluorobis(oxalate) phosphate, lithium tetrafluorooxalate phosphate, and lithium difluorophosphate.

7. The fast-charging electrolyte according to claim 1, characterized in that, The film-forming additives are vinylene carbonate, vinyl sulfate, and tris(trimethylsilyl)phosphate.

8. The fast-charging electrolyte according to claim 1, characterized in that, Based on the total weight of the fast-charging electrolyte, the solvent accounts for 72% to 85% of the total weight.

9. The fast-charging electrolyte according to claim 1, characterized in that, Based on the total weight of the fast-charging electrolyte, the weight ratio of the lithium salt is 11% to 16%.

10. The fast-charging electrolyte according to claim 1, characterized in that, Based on the total weight of the fast-charging electrolyte, the weight ratio of the film-forming additive is 0.2% to 5%.

11. A method for preparing the fast-charging electrolyte according to any one of claims 1-10, characterized in that, include: The fast-charging electrolyte is obtained by dissolving lithium salt, film-forming additives and multifunctional additives in a solvent.

12. The method according to claim 11, characterized in that, The lithium salt, film-forming additive, and multifunctional additive are dissolved in the solvent in sequence.

13. A battery, characterized in that, Includes the fast-charging electrolyte as described in any one of claims 1-10 or the fast-charging electrolyte prepared by the method described in any one of claims 11-12.

14. The battery according to claim 13, characterized in that, The battery is a lithium-ion battery; The battery includes a positive electrode, a negative electrode, and a separator.

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