A lithium ion battery electrolyte and a lithium ion battery comprising the same

Abstract

The present application relates to a lithium ion battery electrolyte, comprising an organic solvent, a lithium salt and an additive, wherein the additive comprises an acid anhydride compound and a substituted or unsubstituted o-dihydroxybenzene sulfite, and optionally a cyano or cyanoalkoxy-substituted alkane. The present application also relates to a lithium ion battery comprising the electrolyte. The present application can make the lithium ion battery have good storage performance and cycle performance at high temperature, good low-temperature discharge performance at low temperature, and reduce the risk of lithium precipitation during low-temperature cycle.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a lithium ion battery electrolyte and a lithium ion battery comprising the same. BACKGROUND

[0002] Due to the limited resources and environmental pollution of fossil energy, developing new clean energy has become the consensus of all. Since the development of lithium ion batteries, due to its high energy density, long cycle life, wide working range, and small pollution, it has been widely used in consumer digital products. In recent years, with the further improvement of carbon emission requirements, lithium ion batteries are also widely used in the field of electric vehicles. Whether it is consumer digital products or electric vehicles, the application scenarios and environments are various, and better requirements are put forward for lithium ion batteries, which need to adapt to different scenarios and require good high temperature performance and low temperature performance at the same time.

[0003] As one of the key materials of lithium ion batteries, electrolyte has a crucial influence on the high temperature performance and low temperature performance of lithium ion batteries. Generally speaking, it is very difficult to simultaneously consider the high temperature performance and low temperature performance of lithium ion batteries. This is because generally by using a solvent system with lower viscosity to reduce the viscosity of the electrolyte at low temperature, the conductivity is improved to improve the low temperature performance. However, the solvent system at this time is often poor in oxidation resistance and is prone to gas production at high temperature, which has the risk of gas swelling. And by forming a film on the positive electrode to protect the positive electrode and improve the high temperature performance, the impedance is often large, and the polarization is large under low temperature conditions, resulting in poor low temperature performance. Therefore, it is urgent to develop a lithium ion battery with good storage performance and cycle performance at high temperature, and good low temperature discharge performance at low temperature. SUMMARY

[0004] The purpose of the present application is to provide an electrolyte and a lithium ion battery comprising the same, which makes the lithium ion battery have good storage performance and cycle performance at high temperature, and good low temperature discharge performance at low temperature and reduces the risk of lithium precipitation during low temperature cycle after the electrolyte is applied to the lithium ion battery.

[0005] In order to achieve the above purpose, the first aspect of the present application provides a lithium ion battery electrolyte, comprising an organic solvent, a lithium salt and an additive, wherein the additive comprises a first additive and a second additive.

[0006] Further, the first additive is selected from one or more of the compounds represented by formula (I) or formula (II) or formula (III):

[0007] Formula (I): Formula (II): Formula (III):

[0008] R3-R8are each independently H, halogen, hydroxyl, cyano, sulfonyl, fluorosulfonyl, sulfonic acid, fluorosulfonic acid, saturated or unsaturated alkyl of 1-10 carbon atoms, saturated or unsaturated haloalkyl of 1-10 carbon atoms, alkoxy of 1-10 carbon atoms, or fluoroalkoxy of 1-10 carbon atoms, and R1-R2are each independently saturated or unsaturated alkyl of 1-10 carbon atoms, saturated or unsaturated haloalkyl of 1-10 carbon atoms, alkoxy of 1-10 carbon atoms, or fluoroalkoxy of 1-10 carbon atoms;

[0009] The second additive is selected from a compound represented by formula (IV):

[0010] Formula (IV):

[0011] R9-R 12 are each independently H, halogen, hydroxyl, cyano, sulfonyl, fluorosulfonyl, sulfonic acid, fluorosulfonic acid, saturated or unsaturated alkyl of 1-10 carbon atoms, saturated or unsaturated haloalkyl of 1-10 carbon atoms, alkoxy of 1-10 carbon atoms, or fluoroalkoxy of 1-10 carbon atoms.

[0012] Further, the concentration of the first additive in the electrolyte is 0.05wt%-2wt%, preferably 0.3wt%-1wt%; and the concentration of the second additive in the electrolyte is 0.1wt%-3wt%, preferably 0.3wt%-1wt%.

[0013] Further, the weight ratio of the first additive to the second additive is (0.1-3):1, preferably (0.5-2):1.

[0014] Further, the organic solvent is selected from carbonates and / or carboxylic acid esters, the carbonates are selected from one or more of the following solvents which are substituted or unsubstituted: vinyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate; and the carboxylic acid esters are selected from one or more of the following solvents which are substituted or unsubstituted: ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl n-butyrate, n-propyl n-butyrate, propyl isobutyrate, n-pentyl n-butyrate, n-pentyl isobutyrate, n-butyl n-butyrate, isobutyl isobutyrate, n-pentyl n-pentanoate, butyrolactone.

[0015] Further, the concentration of the lithium salt in the electrolyte is 0.5-2mol / L, preferably 0.8-1.2mol / L.

[0016] Furthermore, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluorosulfonyl, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0017] Furthermore, the additive also contains a third additive, which is a cyano or cyanoalkoxy-substituted alkane selected from one or more of acetonitrile, propionitrile, butyronitrile, succinic anhydride, glutaritrile, adiponitrile, heptanitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2-bis(2-cyanoethoxy)propane, 1,2-bis(3-cyanopropoxy)ethane, 1,3,6-hexanetrionitrile, 1,2,3-propanetrionitrile, 1,3,5-pentanetrionitrile, 3,3-bis(cyanomethyl)glutaritrile, 3,3-bis(cyanomethyl)adiponitrile, and 1,2,3-tris(2-cyanoethoxy)propane.

[0018] Furthermore, the concentration of the third additive in the electrolyte is 0.01-10 wt%, preferably 1-5 wt%, and more preferably 1-3 wt%.

[0019] Furthermore, the weight ratio of the third additive to the second additive is (1-30):1, preferably (5-15):1.

[0020] A second aspect of this application provides a lithium-ion battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, wherein the electrolyte is the aforementioned electrolyte.

[0021] Furthermore, the positive electrode material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, and ternary materials; the negative electrode material includes at least one of soft carbon, hard carbon, carbon fiber, graphitized carbon microspheres, artificial graphite, natural graphite, silicon, silicon carbide, and silicon-carbon composite materials.

[0022] Through the above technical solutions, this application enables lithium-ion batteries to have better storage and cycle performance at high temperatures, better low-temperature discharge performance at low temperatures, and reduces the risk of lithium plating during low-temperature cycling.

[0023] Other features and advantages of this application will be described in detail in the following detailed description section. Detailed Implementation

[0024] The specific embodiments of this application are described in detail below. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0025] This application provides an electrolyte comprising an organic solvent, a lithium salt, and additives, wherein the additives include a first additive and a second additive.

[0026] In particular, the first additive is selected from one or more of the compounds of formula (I) or formula (II) or formula (III):

[0027] Formula (I): Formula (II): Formula (III):

[0028] Formula (I) - Formula (III): R3-R8 are each independently H, halogen, hydroxyl, cyano, sulfonyl, fluorosulfonyl, sulfonic acid, fluorosulfonic acid, saturated or unsaturated alkyl of 1-10 carbon atoms, saturated or unsaturated halogenated alkyl of 1-10 carbon atoms, alkoxy of 1-10 carbon atoms, or fluoroalkoxy of 1-10 carbon atoms, R1-R2 are each independently saturated or unsaturated alkyl of 1-10 carbon atoms, saturated or unsaturated halogenated alkyl of 1-10 carbon atoms, alkoxy of 1-10 carbon atoms, or fluoroalkoxy of 1-10 carbon atoms;

[0029] The second additive is selected from the compound of formula (IV):

[0030] Formula (IV):

[0031] Formula (IV): R9-R 12 are each independently H, halogen, hydroxyl, cyano, sulfonyl, fluorosulfonyl, sulfonic acid, fluorosulfonic acid, saturated or unsaturated alkyl of 1-10 carbon atoms, saturated or unsaturated halogenated alkyl of 1-10 carbon atoms, alkoxy of 1-10 carbon atoms, or fluoroalkoxy of 1-10 carbon atoms.

[0032] The first additive can form a film on the negative electrode, and the film has good thermal stability, but has large impedance, resulting in low-temperature discharge performance and easy lithium precipitation of the battery during low-temperature cycling; the second additive is a cyclic sulfite compound, which is an aromatic derivative of ethylene sulfite, and can be reduced to form alkylated lithium sulfate (ROSO2Li) and lithium sulfite (Li2SO3) in the negative electrode, introducing S element into the SEI film, improving the ionic conductivity of the SEI film, and reducing the direct current resistance of the battery. However, the SEI film formed by the second additive has poor high-temperature stability and is easy to break during high-temperature storage. In addition, the unsaturated bond in the unsaturated sulfite compound can passivate the positive electrode surface, inhibit the dissolution of transition metal ions in the positive electrode, and prevent the electrolyte from being oxidized and decomposed by directly contacting the positive electrode active material, thereby improving the stability of the lithium ion battery under high-temperature conditions; when the first additive and the second additive are used together, the first additive and the second additive participate in the formation of the SEI film at the negative electrode interface, and the second additive passivates the positive electrode interface. The introduction of the second additive can improve the low-temperature discharge and lithium precipitation problems of the first additive, and the film formed by the first additive can further improve the high-temperature performance. The introduction of the first additive can improve the stability of the SEI film of the negative electrode, prevent the SEI film of the negative electrode from breaking during high-temperature storage, and further improve the high-temperature performance of the second additive.

[0033] The content of the first additive and the second additive can be varied in a large range, the concentration of the first additive in the electrolyte can be 0.05wt%-2wt%, preferably 0.3wt%-1wt%, and the concentration of the second additive in the electrolyte can be 0.1wt%-3wt%, preferably 0.3wt%-1wt%. In the preferred case where the concentration of the first additive in the electrolyte is 0.3wt%-1wt% and the concentration of the second additive in the electrolyte is 0.3wt%-1wt%, better improvement effects can be achieved, for example, the electrical properties can be more optimized, such as the low-temperature discharge degradation is significantly reduced.

[0034] Preferably, the weight ratio of the first additive to the second additive is (0.1-3):1, preferably (0.5-2):1. In this preferred case, the first additive and the second additive can better complement each other, thereby making the lithium ion battery have better storage performance and cycle performance at high temperature and low temperature, respectively.

[0035] Preferably, the first additive is selected from one or more of the following compounds 1-1 to 1-13, and the second additive is selected from one or more of the following compounds 2-1 to 2-5:

[0036]

[0037]

[0038] In a preferred embodiment of the present application, the first additive is selected from at least one of succinic anhydride, maleic anhydride and citraconic anhydride, and the second additive is selected from catechol cyclic sulfite.

[0039] Optionally, the organic solvent is selected from carbonates and / or carboxylic acid esters, the carbonates being selected from one or more of substituted or unsubstituted solvents of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate; and the carboxylic acid esters being selected from one or more of substituted or unsubstituted solvents of ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl n-butyrate, n-propyl n-butyrate, propyl isobutyrate, n-pentyl n-butyrate, n-pentyl isobutyrate, n-butyl n-butyrate, isobutyl isobutyrate, n-pentyl n-pentanoate, butyrolactone.

[0040] In an embodiment of the present application, when the organic solvent comprises two different organic solvents, the two different organic solvents can be mixed in a mass ratio of 1:1, 2:8, 3:7, 4:6, 8:2, 7:3, 6:4, etc. When the organic solvent is a mixture of two or more solvents, the ratio of the solvents is not particularly limited and can be appropriately selected according to actual needs, as long as the technical solution of the present application can be achieved.

[0041] The concentration of the lithium salt in the electrolyte is not particularly limited and can be appropriately selected according to actual needs, as long as the technical solution of the present application can be achieved. Optionally, the concentration of the lithium salt in the electrolyte is 0.5-2 mol / L, preferably 0.8-1.2 mol / L.

[0042] In an embodiment of the present application, the lithium salt is selected from one or more of inorganic lithium salts and organic lithium salts. Specifically, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluorosulfonate, lithium bisfluorosulfonimide or lithium bis(trifluoromethylsulfonyl)imide.

[0043] According to a preferred embodiment of the present application, the additive further comprises a third additive, the third additive being a cyano or cyano alkoxy substituted alkane, the cyano or cyano alkoxy substituted alkane being selected from one or more of acetonitrile, propionitrile, butyronitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2-bis(2-cyanoethoxy)propane, 1,2-bis(3-cyanopropoxy)ethane, 1,3,6-hexanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 3,3-bis(cyanomethyl)glutaronitrile, 3,3-bis(cyanomethyl)adiponitrile and 1,2,3-tris(2-cyanoethoxy)propane.

[0044] In the preferred case, the cyano group in the third additive is an electron-rich structure, which can complex with transition metal ions on the surface of the positive electrode material. Meanwhile, the third additive can also bind with HF, reducing the corrosion of HF on the surface of the positive electrode material. Thus, the third additive can effectively improve the stability of the positive electrode interface and the high-temperature performance of the lithium ion battery. The sulfite compound and the nitrile compound synergistically act to ensure that the negative electrode SEI film has a low impedance and the stability of the positive electrode interface is ensured, so that the lithium ion battery has good high-temperature and low-temperature performance. In the case where the first additive, the second additive and the third additive coexist, balanced high-temperature performance and low-temperature performance can be achieved.

[0045] Optionally, the concentration of the third additive in the electrolyte is 0.01-10wt%, preferably 1-5wt%, and more preferably 1-3wt%.

[0046] Optionally, the weight ratio of the third additive to the second additive is (1-30):1, preferably (5-15):1.

[0047] Another aspect of the present application provides a lithium ion battery, comprising a positive electrode material, a negative electrode material and the electrolyte as above.

[0048] In an embodiment of the present application, the positive electrode material is selected from at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium iron phosphate, a ternary material and the like.

[0049] In an embodiment of the present application, the negative electrode material is selected from at least one of soft carbon, hard carbon, carbon fiber, graphitized carbon microspheres, artificial graphite, natural graphite, silicon, silicon carbide, silicon-carbon composite material and the like.

[0050] The present application will be further described below by way of comparative examples and examples, but the present application is not limited in any way by this.

[0051] Comparative Example 1

[0052] Preparation of electrolyte: lithium hexafluorophosphate (LiPF6) with a concentration of 13.5wt% is used as the lithium salt, and a mixture of ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) is used as the organic solvent, which is mixed according to the mass percentage of EC:EMC:DEC=30:30:40.

[0053] Preparation of positive electrode sheet: positive electrode active material LiCoO2, conductive agent CNT and binder polyvinylidene fluoride (PVDF) are mixed according to the mass ratio of 97.6:0.8:1.6 with N-methyl pyrrolidone (NMP) to prepare positive electrode slurry, which is coated on a current collector aluminum foil, dried at 85℃, then cold-pressed, followed by edge cutting, sheet cutting and strip dividing, and then dried at 85℃ under vacuum for 4h, and the tab is welded to prepare a positive electrode sheet.

[0054] Preparation of negative electrode sheet: the negative electrode active material graphite, conductive agent Super-P, thickening agent CMC, binder SBR were mixed with deionized water in a mass ratio of 96.6:1.0:1.2:1.2 to prepare a negative electrode slurry, which was coated on a current collector copper foil and dried at 85°C, then cold-pressed, followed by edge cutting, sheet cutting, and striping, and then dried at 110°C under vacuum for 4h, and the tab was welded to prepare a negative electrode sheet.

[0055] Preparation of lithium ion battery: using PE porous polymer film as a separator film; the prepared positive electrode sheet, separator film, and negative electrode sheet were stacked in order with the separator film between the positive and negative electrode sheets, and then wound to obtain a bare cell; the bare cell was placed in an outer package, and the prepared electrolyte (the prepared electrolyte had a water content of less than 20ppm and an acidity of less than 30ppm) was injected into the dried bare cell, and then packaged, stood, formed (0.02C constant current charging to 3.4V, and then 0.1C constant current charging to 3.9V), shaped, and capacity tested to complete the preparation of a soft-pack lithium ion battery (the thickness of the soft-pack lithium ion battery was 4.3mm, the width was 6.3mm, and the length was 8.3mm).

[0056] Comparative Examples 2-9

[0057] Comparative Examples 2-9 were used to illustrate the electrolyte, battery, and preparation method thereof disclosed in the present application, including the operation steps of Comparative Example 1, and the difference was that the electrolyte additives shown in Table I Comparative Examples 2-9 were used.

[0058] Examples 1-18

[0059] Examples 1-18 were used to illustrate the electrolyte, battery, and preparation method thereof disclosed in the present application, including the operation steps of Comparative Example 1, and the difference was that the electrolyte additives shown in Table I Examples 1-18 were used.

[0060] Table I Electrolyte additives and amounts of Comparative Examples 1-9 and Examples 1-18

[0061]

[0062]

[0063] Performance test

[0064] The lithium ion batteries prepared from Comparative Examples 1-9 and Examples 1-18 were subjected to performance tests.

[0065] Low temperature discharge performance: after formation, the lithium ion battery was charged at room temperature to 4.43V with 0.7C constant current and constant voltage, and then cut off at 0.025C, and then discharged at 0.2C constant current to 3.0V, and so on for two cycles, and the second discharge capacity was recorded as the initial capacity at room temperature. The lithium ion battery was charged at room temperature to 4.43V with 0.7C constant current and constant voltage, and then cut off at 0.025C. Then the battery was placed in a -20°C constant temperature box for constant temperature for 4h, and then discharged at 0.25C constant current to 3.0V. The capacity retention rate of the lithium ion battery (-20°C discharge capacity / room temperature initial capacity*100%) and the discharge platform (discharge platform voltage=discharge energy / discharge capacity) were tested.

[0066] 85°C storage performance: after formation, the lithium ion battery was charged at room temperature to 4.43V with 0.7C constant current and constant voltage, and then cut off at 0.025C, and then discharged at 0.2C constant current to 3.0V, and so on for two cycles, and the second discharge capacity was recorded as the initial capacity at room temperature. The lithium ion battery was charged at room temperature to 4.43V with 0.7C constant current and constant voltage, and then cut off at 0.025C, and the full charge thickness was recorded (tested using constant force PPG). The fully charged lithium ion battery was placed in an 85°C constant temperature box for 6h, and the thickness expansion rate after 6h storage ((thickness after 6h storage-initial full charge thickness) / initial full charge thickness*100%) was recorded.

[0067] High temperature cycle performance: after formation, the lithium ion battery was placed in a 45°C constant temperature box for constant temperature for 2h, and then charged to 4.20V with 1.3C constant current and constant voltage, and then cut off at 0.7C. Then 0.7C constant current and constant voltage to 4.43V, cut off at 0.025C. Standby for 5min, discharge at 0.7C constant current to 3.0V. This is one cycle. After 600 cycles, the capacity retention rate of the lithium ion battery was recorded.

[0068] 5°C cycle interface disassembly performance: after formation, the lithium ion battery was placed in a 5°C constant temperature box for constant temperature for 2h, and then charged to 4.43V with 0.5 constant current and constant voltage, and then cut off at 0.025C. Standby for 5min, discharge at 0.5C constant current to 3.0V. This is one cycle. After 100 cycles, the full charge state disassembly was observed for lithium precipitation on the negative electrode interface, and according to the lithium precipitation situation, it was divided into three levels from serious to no: serious, slight, and none.

[0069] The test results are shown in Table II.

[0070] Table II

[0071]

[0072] From Table II, it can be seen that the first additive with an addition content of 0.3 wt% can improve the gassing during 85°C storage and improve the high-temperature cycle retention rate, but deteriorate the low-temperature discharge. This is because the first additive mainly forms a SEI film on the negative electrode, and the SEI film has good thermal stability but large impedance, which deteriorates the negative electrode interface during low-temperature cycling. In addition, it can be seen that the second additive has certain improvement effect on the 85°C storage, high-temperature cycle and low-temperature discharge of the battery. This is because the second additive forms a film on both the positive electrode interface and the negative electrode interface. The CEI film formed on the positive electrode interface can isolate the electrolyte from the positive active material, and has a more significant improvement effect on high-temperature storage. The SEI film formed on the negative electrode interface has small impedance and has certain improvement effect on low-temperature discharge. When the first additive and the second additive are used together, the negative electrode is formed by the two additives, the impedance of the SEI film is reduced, but the thermal stability is still good, and the positive electrode film of the second additive further protects the electrolyte from being oxidized and decomposed, thereby improving the high-temperature resistance of the system. Therefore, the synergistic effect of the first additive and the second additive makes the lithium ion battery have more excellent and more balanced high-temperature performance and low-temperature performance. Further, the introduction of the third additive can further improve the high-temperature cycle retention rate and reduce the thickness expansion rate during 85°C storage. This is because the nitrile additive can complex with transition metal ions on the positive electrode interface to stabilize the positive electrode interface. Moreover, the nitrile additive combines with HF to eliminate free HF, thereby protecting the positive electrode interface from being corroded by HF. The introduction of a small amount of nitrile additive has no significant deterioration effect on the low-temperature performance. Therefore, when the concentration of the first additive in the electrolyte is 0.3 wt% to 1 wt%, and the concentration of the second additive in the electrolyte is 0.3 wt% to 1 wt%, the lithium ion battery can have better high-temperature performance and low-temperature performance; further, when the concentration of the first additive in the electrolyte is 0.3 wt% to 1 wt%, the concentration of the second additive in the electrolyte is 0.3 wt% to 1 wt%, and the concentration of the third additive in the electrolyte is 1 wt% to 3 wt%, the lithium ion battery can have further better high-temperature performance and low-temperature performance.

[0073] Since the first additives 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12 have similar effects, for the sake of simplicity, 1-1, 1-9, 1-10 and 1-11 are randomly taken for implementation and illustration.

[0074] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details in the above-described embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solution of the present application, and these simple modifications all belong to the protection scope of the present application.

[0075] It should be further noted that the various technical features described in the above specific embodiments can be combined in any suitable manner, and the application is not limited to the combinations explicitly described. In order to avoid unnecessary repetition, the various possible combinations are not described separately in the application.

[0076] Furthermore, the various different embodiments of the application can also be combined with each other in any suitable manner, as long as it does not deviate from the idea of the application, it should also be considered as disclosed in the application.

Claims

1. A lithium-ion battery electrolyte, comprising an organic solvent, a lithium salt, and additives, characterized in that, The additive comprises a first additive and a second additive, wherein the first additive is selected from one or more compounds of formula (I), formula (II), or formula (III): Formula (I): Equation (II): Equation (III): In formulas (I) to (III): R3-R8 are each independently H, halogen, hydroxyl, cyano, sulfonyl, fluorosulfonyl, sulfonic acid, fluorosulfonic acid, 1-10 carbon atoms of saturated or unsaturated alkyl, 1-10 carbon atoms of saturated or unsaturated haloalkyl, 1-10 carbon atoms of alkoxy or 1-10 carbon atoms of fluoroalkoxy; R1-R2 are each independently 1-10 carbon atoms of saturated or unsaturated alkyl, 1-10 carbon atoms of saturated or unsaturated haloalkyl, 1-10 carbon atoms of alkoxy or 1-10 carbon atoms of fluoroalkoxy. The second additive is selected from the compound shown in formula (IV): Formula (IV): In formula (IV): R9-R 12 Each of the following can be independently H, halogen, hydroxyl, cyano, sulfonyl, fluorosulfonyl, sulfonic acid, fluorosulfonic acid, 1-10 carbon atoms of saturated or unsaturated alkyl, 1-10 carbon atoms of saturated or unsaturated haloalkyl, 1-10 carbon atoms of alkoxy or 1-10 carbon atoms of fluoroalkoxy.

2. The lithium-ion battery electrolyte according to claim 1, wherein, The concentration of the first additive in the electrolyte is 0.05wt%-2wt%; the concentration of the second additive in the electrolyte is 0.1wt%-3wt%.

3. The lithium-ion battery electrolyte according to claim 2, wherein, The concentration of the first additive in the electrolyte is 0.3wt%-1wt%; the concentration of the second additive in the electrolyte is 0.3wt%-1wt%.

4. The lithium-ion battery electrolyte according to claim 3, wherein, The weight ratio of the first additive to the second additive is (0.1-3):

1.

5. The lithium-ion battery electrolyte according to claim 4, wherein, The weight ratio of the first additive to the second additive is (0.5-2):

1.

6. The lithium-ion battery electrolyte according to any one of claims 1-5, wherein, The first additive is selected from one or more of compounds 1-1 to 1-13: The second additive is selected from one or more of compounds 2-1 to 2-5:

7. The lithium-ion battery electrolyte according to any one of claims 1-5, wherein, The organic solvent is selected from carbonates and / or carboxylic esters, wherein the carbonate is selected from one or more of the following solvents, substituted or unsubstituted: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate; and the carboxylic ester is selected from one or more of the following solvents, substituted or unsubstituted: ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl n-butyrate, n-propyl n-butyrate, isopropyl butyrate, n-pentyl n-butyrate, isopentyl n-butyrate, n-butyl n-butyrate, isobutyl n-butyrate, n-pentyl n-valerate, and butyrolactone.

8. The lithium-ion battery electrolyte according to any one of claims 1-5, wherein, The concentration of the lithium salt in the electrolyte is 0.5-2 mol / L.

9. The lithium-ion battery electrolyte according to claim 8, wherein, The concentration of the lithium salt in the electrolyte is 0.8-1.2 mol / L.

10. The lithium-ion battery electrolyte according to any one of claims 1-5, wherein, The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluorosulfonyl, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

11. The lithium-ion battery electrolyte according to any one of claims 1-5, wherein, The additive further comprises a third additive, which is a cyano or cyanoalkoxy-substituted alkane selected from one or more of acetonitrile, propionitrile, butyronitrile, succinic anhydride, glutaritrile, adiponitrile, heptanitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2-bis(2-cyanoethoxy)propane, 1,2-bis(3-cyanopropoxy)ethane, 1,3,6-hexanetrionitrile, 1,2,3-propanetrionitrile, 1,3,5-pentanetrionitrile, 3,3-bis(cyanomethyl)glutaritrile, 3,3-bis(cyanomethyl)adiponitrile, and 1,2,3-tris(2-cyanoethoxy)propane.

12. The lithium-ion battery electrolyte according to claim 11, wherein, The concentration of the third additive in the electrolyte is 0.01-10 wt%.

13. The lithium-ion battery electrolyte according to claim 12, wherein, The concentration of the third additive in the electrolyte is 1-5 wt%.

14. The lithium-ion battery electrolyte according to claim 13, wherein, The concentration of the third additive in the electrolyte is 1-3 wt%.

15. The lithium-ion battery electrolyte according to any one of claims 12-14, wherein, The weight ratio of the third additive to the second additive is (1-30):

1.

16. The lithium-ion battery electrolyte according to claim 15, wherein, The weight ratio of the third additive to the second additive is (5-15):

1.

17. A lithium-ion battery, characterized in that, The electrolyte in the lithium-ion battery is the electrolyte according to any one of claims 1-16.

Images