Electrolyte and functional additive for improving low-temperature performance of batteries

Abstract

The present invention relates to electrolytes for improving the low-temperature performance of batteries and functional additives thereof, and lithium-ion batteries comprising said electrolytes.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to electrolytes and their functional additives, as well as lithium-ion batteries containing said electrolytes. Background Technology

[0002] Since their commercialization, lithium-ion batteries have been widely used in the field of power batteries due to their advantages such as high energy density, high power density, long cycle life, and environmental friendliness. However, the performance of lithium batteries is significantly affected by temperature, especially at low temperatures, where their low-temperature discharge and cycle performance deteriorate significantly, greatly limiting their application in low-temperature environments. Therefore, improving the performance of lithium batteries at low temperatures has become an important research direction in the field of battery manufacturing technology.

[0003] While existing technologies have improved the low-temperature performance of lithium batteries to some extent, several problems and drawbacks remain. First, current solutions often require comprehensive modifications to all components of the battery, increasing both manufacturing costs and complexity. Second, while improving low-temperature performance, existing solutions may negatively impact other performance aspects, such as battery capacity and cycle life. Finally, the effectiveness of existing solutions in improving low-temperature performance is limited, especially at extreme temperatures, where battery performance still falls short of practical application requirements.

[0004] As a crucial component of lithium-ion batteries, the electrolyte has a significant impact on their performance. Adding small amounts of functional additives to the electrolyte to form a stable protective film on the electrode surface is the most economical and effective strategy for improving electrode stability and achieving high-stability, high-energy-density lithium-ion batteries. Currently, various functional additives have been reported to regulate the protective film on the surface of the positive or negative electrode, protecting the electrode while preventing redox decomposition of the electrolyte. However, successful reports of electrolytes and their functional additives that can effectively improve the low-temperature performance of batteries are still rare. Summary of the Invention

[0005] In view of the technical problem that lithium batteries still suffer from significant performance degradation at low temperatures, the present invention aims to provide an electrolyte and its functional additives that can significantly improve the low-temperature performance of batteries.

[0006] To achieve the above and other related objectives, a first aspect of the present invention provides an electrolyte comprising a lithium salt, an organic solvent, a first functional additive, and a second functional additive.

[0007] The first functional additive is selected from vinylene carbonate (VC), ethylene ethylene carbonate (VEC), vinyl sulfate (DTD), 1,3-propanesulfonate lactone (PS), 1,4-butanesulfonate lactone (MMDS), 1,3-propenylsulfonate lactone (PST), tris(trimethylsilane)borate (TMSP), tris(trimethylsilane)phosphite (TMSPi), biphenyl (BP), fluorobenzene (FB), acetonitrile (SN), butyronitrile (AND), and mixtures thereof;

[0008] The second functional additive is a functional additive with the structure shown in formula (I):

[0009]

[0010] R1 is selected from C 0-5 Alkylene; n1 is an integer selected from 1 to 8; and n2 is an integer selected from 0 to 5.

[0011] A second aspect of the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and the electrolyte described in the first aspect of the present invention.

[0012] A third aspect of the present invention provides compounds with the structure shown in formula (I):

[0013]

[0014] R1 is selected from C 0-5 Alkylene; n1 is selected from integers from 1 to 8; and n2 is selected from integers from 0 to 5. The compound can be used as a functional additive in electrolytes to improve the low-temperature performance of batteries.

[0015] A fourth aspect of the invention provides the use of the compounds described in the third aspect of the invention for improving the low-temperature performance of batteries.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] The compounds provided in this invention, when used as functional additives in electrolytes, can induce lithium salt decomposition and thus exhibit good lithium conductivity, effectively reducing the impedance of the negative electrode SEI film. Multiple siloxane modules in the specific structure shown in formula (I) of this invention contribute to more uniform film formation; the cyclic sulfonate module forms a uniform and stable SEI film on the negative electrode, effectively reducing storage gas generation and resulting in good ion conduction performance. Through the synergistic effect of the cyclic sulfonate module and the siloxane module in the aforementioned framework structure, a uniform, stable, low-impedance negative electrode protective film with excellent lithium conductivity and thermal stability can be formed on the negative electrode surface. This protective film effectively protects and isolates the negative electrode from the electrolyte contact, preventing side reactions while allowing lithium ions to pass freely, effectively reducing lithium ion migration resistance and enabling the battery to have excellent low-temperature discharge capability.

[0018] Furthermore, the electrolyte formulation and manufacturing process of this invention are simple and low-cost, which is beneficial for large-scale production. This contrasts sharply with the complex electrolyte formulations and manufacturing processes, which are costly in the prior art. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] Furthermore, the "range" disclosed herein is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0021] A first aspect of the present invention provides an electrolyte comprising a lithium salt, an organic solvent, a first functional additive, and a second functional additive.

[0022] The second functional additive is a functional additive with the structure shown in formula (I):

[0023]

[0024] R1 is selected from C 0-5 Alkylene; n1 is an integer selected from 1 to 8; and n2 is an integer selected from 0 to 5.

[0025] For those selected from C 0-5 For R1 of alkylene groups, C 0-5 The alkylene group can be selected from, for example, the C0 alkylene group, -CH2- (C1 alkylene or methylene), -CH2CH2- (C2 alkylene or ethylene), -CH2CH2CH2- (C3 alkylene or propylene), -CH2CH2CH2CH2- (C4 alkylene or butylene), and -CH2CH2CH2CH2CH2- (C5 alkylene or pentylene).

[0026] In one implementation, R1 is preferably selected from C. 1-3 Alkylene, such as C 2-3 Alkylene.

[0027] For n1, which is an integer selected from 1 to 8, n1 can be 1, 2, 3, 4, 5, 6, 7, or 8.

[0028] In one implementation, n1 is preferably selected from an integer from 1 to 4.

[0029] For n2, which is an integer selected from 0 to 5, n2 can be 0, 1, 2, 3, 4, or 5. It should be noted that when n2 is 0, the -CH2- module does not exist, and the corresponding cyclic sulfonate module is a five-membered ring. In one embodiment, n2 is preferably selected from an integer between 0 and 3.

[0030] In one embodiment, the ratio of n1 to n2 is preferably from about 1:1 to 4:1, for example about 1:1, about 2:1, about 3:1 or about 4:1.

[0031] In one embodiment, the second functional additive is selected from:

[0032]

[0033] and / or

[0034]

[0035] In one embodiment, the content of the second functional additive is 0.01-6 wt%, based on the total weight of the electrolyte. For example, the content of the second functional additive may be 0.1-6 wt%, 0.5-6 wt%, 1-6 wt%, 2-5 wt%, 2-4 wt%, 3-4 wt%, 3 wt%, or 4 wt%. Preferably, the content of the second functional additive is 2-4 wt%, based on the total weight of the electrolyte.

[0036] Without being limited to a specific theory, this invention has found that the content of 2-4 wt% (preferably 3-4 wt%) of a second functional additive can further improve the low-temperature performance of the battery.

[0037] In one embodiment, the first functional additive is selected from vinylene carbonate (VC), ethylene ethylene carbonate (VEC), vinyl sulfate (DTD), 1,3-propanesulfonate lactone (PS), 1,4-butanesulfonate lactone (MMDS), 1,3-propenylsulfonate lactone (PST), tris(trimethylsilane)borate (TMSP), tris(trimethylsilane) phosphite (TMSPi), biphenyl (BP), fluorobenzene (FB), acetonitrile (SN), butyronitrile (AND), and mixtures thereof. Preferably, the first functional additive is selected from vinylene carbonate (VC), acetonitrile (SN), and / or 1,4-butanesulfonate lactone (MMDS).

[0038] In one embodiment, the content of the first functional additive is 0.01-6 wt%, based on the total weight of the electrolyte. For example, the content of the first functional additive may be 0.1-6 wt%, 0.5-6 wt%, 1-6 wt%, 2-5 wt%, 2-4 wt%, 2.5-3.5 wt%, or 3 wt%. Preferably, the content of the first functional additive is 1-2 wt%, based on the total weight of the electrolyte.

[0039] In one embodiment, the lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), lithium bis(fluorosulfonylimide) (LiFSI), and mixtures thereof. Preferably, the lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonylimide) (LiFSI), and mixtures thereof.

[0040] In one embodiment, the lithium salt content is 5-15 wt%, based on the total weight of the electrolyte. For example, the lithium salt content may be 6-15 wt%, 7-15 wt%, 8-15 wt%, 9-15 wt%, 10-15 wt%, 6-14 wt%, 6-13 wt%, 6-12 wt%, 6-11 wt%, 6-10 wt%, 8-12 wt%, 9-11 wt%, or 10 wt%. Preferably, the lithium salt content is 8-12 wt%, based on the total weight of the electrolyte.

[0041] In one embodiment, the organic solvent is selected from ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl methyl carbonate (EMC), methyl formate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), butyl propionate (BP), ethyl butyrate (EB), trimethyl phosphate (TMP), triethyl phosphate (TEP), triphenyl phosphate (TBP), ether solvents, and mixtures thereof. Preferably, the organic solvent is selected from ethylene carbonate (EC), fluoroethylene carbonate (FEC), methyl methyl carbonate (EMC), and / or dimethyl carbonate (DMC).

[0042] In one embodiment, the content of the organic solvent is 70-90 wt%, based on the total weight of the electrolyte. For example, the content of the organic solvent may be 72-88 wt%, 74-86 wt%, 76-84 wt%, 78-82 wt%, or 80%. Preferably, the content of the organic solvent is 76-84 wt%, based on the total weight of the electrolyte.

[0043] In one embodiment, the sum of the contents of lithium salt, organic solvent, first functional additive, and second functional additive is 100%, based on the total weight of the electrolyte. That is, the electrolyte does not contain any other components.

[0044] In one embodiment, the sum of the contents of lithium salt, organic solvent, first functional additive, and second functional additive is less than 100%, based on the total weight of the electrolyte. That is, the electrolyte may also contain one or more other components to achieve corresponding additional functions.

[0045] By using the amount and / or type of lithium salt, organic solvent and first functional additive described in this invention, the second functional additive provided by this invention can be better combined to further ensure that the electrolyte has the excellent effects described in this invention.

[0046] In one embodiment, the electrolyte is obtained by adding lithium salt to an organic solvent, stirring to dissolve it, then adding a first functional additive and a second functional additive, and mixing thoroughly.

[0047] In one embodiment, the electrolyte is prepared under an argon atmosphere, for example in an argon-filled glove box (generally controlling the oxygen content to ≤5ppm and the water content to ≤10ppm).

[0048] A second aspect of the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and the electrolyte described in the present invention.

[0049] In one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The positive electrode active material layer includes a positive electrode active material, and may further include a conductive agent and a binder. The positive electrode active material may be selected from one or more combinations of lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium iron manganese phosphate. Preferably, the positive electrode active material is selected from lithium nickel cobalt manganese oxide, wherein 0.5 ≤ molar fraction of nickel < 1. Those skilled in the art can select conductive agents and binders suitable for lithium-ion batteries. The conductive agent may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The adhesive may include, for example, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0050] In one embodiment, the positive electrode can be prepared by dispersing the above-mentioned components for preparing the positive electrode, such as positive electrode material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and obtaining the positive electrode after drying, cold pressing and other processes.

[0051] In one embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The negative electrode active material layer includes a negative electrode active material, and may further include a plasticizer, a conductive agent, and a binder. The negative electrode active material may be selected from one or more combinations of silicon-carbon, silicon-oxygen, natural graphite, artificial graphite, lithium titanate, amorphous carbon, and lithium metal. Those skilled in the art may select plasticizers, conductive agents, and binders suitable for lithium-ion batteries. The conductive agent may be selected, for example, from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), and sodium carboxymethyl cellulose (CMC-Na).

[0052] In one embodiment, the negative electrode can be prepared by dispersing the components used to prepare the negative electrode, such as negative electrode material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode after drying, cold pressing and other processes.

[0053] In one embodiment, the separator can also be made of materials commonly used in the art that have good stability and a porous structure. For example, polyethylene, polypropylene, polyvinylidene fluoride, and polyethylene terephthalate can be used.

[0054] The present invention also relates to a battery module comprising the lithium-ion battery; and a battery pack comprising one or more of the battery modules.

[0055] A third aspect of the present invention provides compounds with the structure shown in formula (I):

[0056]

[0057] R1 is selected from C 0-5 Alkylene; n1 is an integer selected from 1 to 8; and n2 is an integer selected from 0 to 5.

[0058] In one embodiment, the compound is used as a functional additive in an electrolyte to improve the low-temperature performance of a battery.

[0059] A fourth aspect of the invention provides the use of the compounds described herein for improving the low-temperature performance of batteries.

[0060] In one embodiment, the compound is used as a functional additive in the electrolyte in the above-described uses.

[0061] In one implementation, improving battery low-temperature performance means increasing cycle life under low-temperature cycling and / or improving capacity retention under low-temperature discharge.

[0062] A fifth aspect of the present invention provides a method for preparing a compound with the structure shown in formula (I), comprising the following steps:

[0063] Step 1: Dissolve trimethylsilyl chloride (5-10 mmol) and trimethyl borate (5-10 mmol) in a solvent, and slowly add triethylamine (6-12 mmol) to carry out the reaction;

[0064] Step 2: Filter to remove triethylamine hydrochloride, remove solvent by vacuum distillation to obtain intermediate tris(trimethylsilane)borate ester (TMSP);

[0065] Step 3: TMSP (5 mmol) and cyclic sulfonate (5 mmol) were heated in a solvent to react, and the mixture was purified by column chromatography to obtain a compound with the structure shown in formula (I).

[0066] In one embodiment, the solvent in step 1 is dry tetrahydrofuran (THF); the addition of triethylamine is carried out under argon protection at 0°C, and / or the reaction time is 24–48 hours.

[0067] In one embodiment, the solvent in step 3 is toluene; the heating temperature is 80°C; and / or the reaction time is 12 hours.

[0068] The beneficial effects of the present invention are further illustrated below with reference to embodiments. To make the inventive objective, technical solution, and beneficial technical effects of the present invention clearer, the present invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of the present invention are merely for explaining the present invention and are not intended to limit the present invention, and the embodiments of the present invention are not limited to the embodiments given in the specification. Unless otherwise specified, specific experimental or operating conditions in the embodiments are prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0069] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / electrical appliances mentioned in this invention does not preclude the existence of other devices / appliances before or after the combined devices / appliances, or the insertion of other devices / appliances between these explicitly mentioned devices / appliances, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0070] Unless otherwise specified, all reagents, materials and instruments used in the following embodiments are commercially available.

[0071] Example

[0072] Examples 1-21 and Comparative Example 1

[0073] Electrolyte preparation: In an argon-filled glove box (oxygen content ≤ 5 ppm, water content ≤ 10 ppm), ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly according to the corresponding volume ratios (see Table 1) and stirred continuously. The non-aqueous solvent accounted for 80% of the total mass of the electrolyte. Subsequently, lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonylimide) (LiFSI) were added to the mixed solution and stirred thoroughly to dissolve them, so that their contents were 10% and 5% of the total mass of the electrolyte, respectively. After the mixed solution returned to room temperature, the first functional additive of the corresponding type and content and the second functional additive of the corresponding structure were added in sequence and stirred thoroughly to obtain the electrolytes of Examples 1-9 and Comparative Examples 1-4.

[0074] Table 1

[0075]

[0076]

[0077] Battery fabrication steps: An appropriate amount of the prepared electrolyte is injected into a 4.0 Ah pouch cell and vacuum-sealed. The positive electrode of the pouch cell is NCM, and the negative electrode is artificial graphite and silicon-oxygen anode. The battery is then manufactured through processes such as resting, formation, aging, and capacity testing.

[0078] Performance testing experiment

[0079] 1) Capacity retention at -20℃ and 0.2C: The battery under test was first cycled at 25℃ for 3 weeks at 1C / 1C, and then at 0.2C / 0.2C for 3 weeks to achieve a constant capacity. The battery was then placed in a -10℃ environment for 3 hours. After reaching the target temperature, it was discharged at 0.2C0 to the cutoff voltage, where C0 is the average capacity after the three cycles. The capacity retention was calculated based on the discharge capacity at this temperature.

[0080] 2) -10℃, 1C cycle performance test: The formed battery was placed in a -20℃ environment and charged and discharged at a constant current of 1C / 0.33C until the cutoff voltage for low-temperature cycling. The capacity retention rate was calculated each week, and the current cycle number was recorded when the capacity retention rate was below 80%.

[0081] The test results are shown in Table 2 below.

[0082] Table 2

[0083]

[0084] The results above show that, compared to Comparative Example 1, the solution of this invention significantly improves the low-temperature cycle life and low-temperature discharge capacity retention of the battery, thereby achieving a significant improvement in the battery's low-temperature performance. Furthermore, the content of the second functional additive at 2-4 wt% (preferably 3-4 wt%) can further improve the battery's low-temperature performance. Moreover, when the second functional additive is a compound of structural formula 3, it achieves superior overall low-temperature battery performance compared to compounds of structural formulas 1 and 2.

[0085] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An electrolyte comprising a lithium salt, an organic solvent, a first functional additive, and a second functional additive; The first functional additive is selected from vinylene carbonate (VC), ethylene ethylene carbonate (VEC), vinyl sulfate (DTD), 1,3-propanesulfonate lactone (PS), 1,4-butanesulfonate lactone (MMDS), 1,3-propenylsulfonate lactone (PST), tris(trimethylsilane)borate (TMSP), tris(trimethylsilane)phosphite (TMSPi), biphenyl (BP), fluorobenzene (FB), acetonitrile (SN), butyronitrile (AND), and mixtures thereof; The second functional additive is a functional additive with the structure shown in formula (I): Where R1 is selected from C 0-5 Alkylene; n1 is an integer selected from 1 to 8; and n2 is an integer selected from 0 to 5.

2. The electrolyte according to claim 1, wherein R1 is selected from C 1-3 Alkylene; n1 is an integer selected from 1 to 4; and / or n2 is an integer selected from 0 to 3.

3. The electrolyte according to claim 1 or 2, wherein the ratio of n1 to n2 is about 1:1 to 4:

1.

4. The electrolyte according to any one of claims 1 to 3, wherein the second functional additive is selected from: and / or 5. The electrolyte according to any one of claims 1-4, wherein the content of the second functional additive is 0.01-6 wt%, based on the total weight of the electrolyte.

6. The electrolyte according to any one of claims 1-5, wherein the content of the second functional additive is 2-4 wt%, based on the total weight of the electrolyte.

7. The electrolyte according to any one of claims 1-6, wherein the lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), lithium bis(fluorosulfonylimide) (LiFSI), and mixtures thereof.

8. The electrolyte according to any one of claims 1-7, wherein the lithium salt content is 5-15 wt%, based on the total weight of the electrolyte.

9. The electrolyte according to claim 8, wherein the lithium salt content is 8-12 wt%, based on the total weight of the electrolyte.

10. The electrolyte according to any one of claims 1-9, wherein the organic solvent is selected from ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl methyl carbonate (EMC), methyl formate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), butyl propionate (BP), ethyl butyrate (EB), trimethyl phosphate (TMP), triethyl phosphate (TEP), triphenyl phosphate (TBP), ether solvents, and mixtures thereof.

11. The electrolyte according to any one of claims 1-10, wherein the content of said organic solvent is 70-90 wt%, based on the total weight of the electrolyte.

12. The electrolyte according to any one of claims 1-11, wherein the content of the first functional additive is 0.01-6 wt%, based on the total weight of the electrolyte.

13. The electrolyte according to claim 12, wherein the content of the first functional additive is 1-2 wt%, based on the total weight of the electrolyte.

14. A lithium-ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte according to any one of claims 1-13.

15. The lithium-ion battery according to claim 14, wherein the negative electrode comprises a negative electrode active material selected from one or more combinations of silicon-carbon, silicon-oxygen, natural graphite, artificial graphite, lithium titanate, amorphous carbon, and lithium metal; and / or, The positive electrode includes a positive electrode active material, which is selected from one or more combinations of lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium iron manganese phosphate.

16. Compounds with the structure shown in formula (I): Where R1 is selected from C 0-5 Alkylene; n1 is an integer selected from 1 to 8; and n2 is an integer selected from 0 to 5.

17. The compound according to claim 16, used as a functional additive in an electrolyte for improving the low-temperature performance of a battery.

18. Use of the compound of claim 16 for improving the low-temperature performance of a battery.

19. The use as claimed in claim 18, wherein improving the low-temperature performance of the battery means increasing cycle life under low-temperature cycling and / or improving capacity retention under low-temperature discharge.

20. A method for preparing the compound of claim 16, comprising the following steps: Step 1: Dissolve trimethylsilyl chloride and trimethyl borate in a solvent, and slowly add triethylamine to carry out the reaction; Step 2: Filter to remove triethylamine hydrochloride, remove solvent by vacuum distillation to obtain intermediate tris(trimethylsilane)borate ester (TMSP); Step 3: TMSP and cyclic sulfonate were heated in a solvent to react, and the compound was obtained after purification by column chromatography.

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