Electrolyte and Lithium-ion Battery

Abstract

The present invention provides an electrolyte. The electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive. The additive includes a first additive, and the first additive includes a compound represented by Formula 1, wherein at least one of R1 and R2 is a fluorine atom or a fluorine-substituted hydrocarbon group having 1 to 6 carbon atoms, and the number of fluorine atoms in the compound is 1 to 3. In the present invention, the electrolyte is applied to a lithium-ion battery, improving the normal and high-temperature cycle life and high-temperature storage performance of the battery.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and particularly to an electrolyte and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in daily life, work and production, but people's requirements for them are getting higher and higher, such as higher energy density. Developing lithium-ion batteries with high energy density can increase the voltage of the cathode material or use high-nickel ternary cathode materials, etc., but existing solutions will have an adverse impact on the electrolyte. For example, too high nickel content will reduce the stability of the cathode material, and trivalent unstable nickel ions will cause the electrolyte to oxidize and decompose at the cathode; while increasing the battery charging voltage will make the electrolyte more likely to oxidize and decompose, which will cause a series of problems such as battery swelling and increased interfacial impedance. In view of this, it is necessary to develop an electrolyte formulation that can improve the battery capacity and kinetic performance, while having a long cycle life, good rate performance and high-temperature storage performance.

[0003] There are mainly two problems with existing commercial carbonate-based electrolytes at high voltages: 1) The electrolyte is easily oxidized and decomposed on the surface of the cathode of high-voltage lithium-ion batteries, increasing the internal resistance of the lithium-ion battery; 2) Transition metals on the lithium-ion cathode are easily dissolved and reduced at high voltages, resulting in an increase in the impedance of the lithium-ion battery and deterioration of battery performance. The commonly used methods to improve the high-voltage performance of electrolytes are: (1) Increase the electrolyte concentration. Increasing the concentration of carbonate-based electrolytes can improve the oxidation resistance of the electrolyte. In high-concentration electrolytes, the lithium salt concentration is high, and the antioxidant properties of solvent molecules are enhanced at high voltages. Therefore, high-concentration electrolytes have enhanced stability and flame retardancy compared to traditional electrolytes, and both battery performance and safety are improved. (2) Add specific additives. Adding additives is one of the ways to solve the chemical properties of many materials, and the same method can also be used for high-voltage electrolytes. High-voltage electrolyte additives can form a cathode protective film on the cathode surface to reduce the contact between the cathode and the electrolyte and inhibit the oxidation reaction of the electrolyte. Currently, most high-voltage electrolyte additives are organic additives, mainly vinylene carbonate and new organic additives, etc. The main mechanism is that the organic matter preferentially polymerizes or decomposes during charge and discharge to form an electrode protective film.

[0004] The high-voltage working environment of the battery will be the norm, and with the advent of ultra-high voltage and ultra-fast charging and energy replenishment technologies, the requirements for the working performance of the battery in a high-voltage environment will be an important development direction, and high-voltage electrolytes will be a popular research field. However, currently, due to technical problems, cost problems and other issues to be solved, it is still necessary to increase the research and development efforts. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a high-voltage-resistant electrolyte with long cycle life, high rate performance, and high-temperature storage performance, and a lithium-ion battery containing the same. The electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive. The additive includes a first additive, and the first additive includes a compound represented by Formula 1,

[0006] wherein at least one of R1 and R2 is a fluorine atom or a fluorine-substituted hydrocarbon group containing 1 to 6 carbon atoms, and the number of fluorine atoms in the compound is 1 to 3.

[0007] The second purpose of the present invention is to provide a lithium-ion battery. The lithium-ion battery includes the electrolyte as described in the first purpose, and the lithium-ion battery further includes a positive electrode and a negative electrode.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0009] In the present invention, when the electrolyte is applied to a lithium-ion battery, the normal and high-temperature cycle life and high-temperature storage performance of the battery are improved. The normal-temperature cycle life of the battery can reach more than 950 times, the high-temperature cycle life can reach more than 790 times, the impedance growth rate during 60-day high-temperature storage can be as low as below 16%, and the gas generation rate during 60-day high-temperature storage can be as low as below 10%. Detailed Embodiments

[0010] The present invention provides an electrolyte. The electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive. The additive includes a first additive, and the first additive includes a compound represented by Formula 1,

[0011]

[0012] wherein at least one of R1 and R2 is a fluorine atom or a fluorine-substituted hydrocarbon group containing 1 to 6 carbon atoms, and the number of fluorine atoms in the compound is 1 to 3.

[0013] Wherein, the carbon atoms can be 1, 2, 3, 4, 5, or 6, etc., the fluorine atoms can be 1, 2, or 3, etc., the degree of unsaturation can be 0 to 4, 0, 1, 2, 3, or 4, etc., but not limited to the listed values. Other unlisted values within the above numerical ranges are equally applicable.

[0014] In the compound shown in Formula 1 of the present invention, the presence of fluorine - substituted groups is conducive to the formation of a passivation film rich in inorganic components such as LiF, which can effectively reduce the internal resistance of the battery. The trimethylsilyl group and trimethoxysilyl group in the molecular structure can also form a stable positive - electrode passivation film and can eliminate trace amounts of HF in the electrolyte, thereby improving the stability of the positive - electrode material and the electrolyte at high temperatures and suppressing gas generation to enhance the high - temperature cycle and storage performance of the battery. Thus, it solves the problems of reduced high - temperature storage performance, accelerated high - temperature cycle life, and serious gas generation in lithium - ion batteries at high voltages in the electrolyte.

[0015] As a preferred technical solution of the present invention, the compound includes any one or a combination of at least two of the compounds shown in Formula 2 to Formula 7. Typical but non - limiting examples of the combination include the combination of Formula 2 and Formula 3, the combination of Formula 3 and Formula 4, the combination of Formula 4 and Formula 5, the combination of Formula 5 and Formula 6, or the combination of Formula 6 and Formula 7, etc.

[0016]

[0017] Preferably, the compound includes a combination of at least two of the compounds shown in Formula 2 to Formula 7. As a preferred technical solution of the present invention, based on the mass of the electrolyte being 100%, the mass fraction of the compound in the electrolyte is 0.1% to 10%. The mass fraction can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably it is 0.1% to 5%.

[0018] If the content of the compound in the present invention is too low, the addition of the additive has an insignificant improvement effect on suppressing gas generation. If the content is too high, the addition of the additive will form a relatively thick passivation film, resulting in an increase in the internal impedance of the battery and a decrease in the battery capacity. When the mass of the additive accounts for 0.1% to 10% of the mass of the electrolyte, the battery can obtain better high - temperature performance and at the same time has a higher capacity utilization.

[0019] As a preferred technical solution of the present invention, the additive further includes a second additive.

[0020] Preferably, the second additive includes cyclic carbonates, cyclic sulfonic acid lactones, cyclic sulfuric esters, and lithium - containing additives.

[0021] Preferably, the cyclic carbonate includes any one or a combination of at least two of vinylene carbonate, fluoroethylene carbonate, or ethylene vinylene carbonate. Typical but non - limiting examples of the combination include the combination of vinylene carbonate and fluoroethylene carbonate, the combination of fluoroethylene carbonate and ethylene vinylene carbonate, or the combination of vinylene carbonate and ethylene vinylene carbonate, etc.

[0022] Preferably, the cyclic sultone includes 1,3 - propane sultone and / or 1,3 - propene sultone.

[0023] Preferably, the cyclic sulfate includes vinylene sulfate.

[0024] Preferably, the lithium - containing additive includes any one or a combination of at least two of lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium tetrafluoroborate, or lithium difluorooxalate phosphate. Typical but non - limiting examples of the combination include: the combination of lithium difluorophosphate and lithium difluorooxalate borate, the combination of lithium difluorooxalate borate and lithium bis(oxalato)borate, the combination of lithium bis(oxalato)borate and lithium tetrafluoroborate, or the combination of lithium tetrafluoroborate and lithium difluorooxalate phosphate, etc.

[0025] As a preferred technical solution of the present invention, based on the mass of the electrolyte being 100%, the mass fraction of the second additive in the electrolyte is 0.5% to 20%. The mass fraction can be 0.5%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, or 20%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. Preferably, it is 0.5% to 5%.

[0026] As a preferred technical solution of the present invention, the non - aqueous organic solvent includes any one or a combination of at least two of vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, or diethyl carbonate. Typical but non - limiting examples of the combination include: the combination of vinylene carbonate and dimethyl carbonate, the combination of dimethyl carbonate and ethyl methyl carbonate, the combination of ethyl methyl carbonate and propylene carbonate, or the combination of propylene carbonate and diethyl carbonate, etc.

[0027] As a preferred technical solution of the present invention, the lithium salt includes any one or a combination of at least two of LiFSI, LiTFSI, LiPF6, LiBF4, LiClO4, or LiAsF6. Typical but non - limiting examples of the combination include: the combination of LiFSI and LiTFSI, the combination of LiTFSI and LiPF6, the combination of LiPF6 and LiBF4, the combination of LiBF4 and LiClO4, or the combination of LiClO4 and LiAsF6, etc.

[0028] Preferably, the concentration of the lithium salt in the electrolyte is 0.5 M to 2 M. The concentration can be 0.5 M, 0.8 M, 1.0 M, 1.2 M, 1.4 M, 1.6 M, 1.8 M, or 2 M, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0029] Preferably, based on the mass of the electrolyte being 100%, the mass fraction of the lithium salt in the electrolyte is 12% to 15%. The mass fraction can be 12%, 12.5%, 13%, 13.5%, 14%, 14.5% or 15%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0030] The present invention provides a lithium-ion battery, which includes a positive electrode, a negative electrode, and an electrolyte as described in one of the purposes.

[0031] As a preferred technical solution of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material.

[0032] Preferably, the positive electrode active material includes any one or a combination of at least two of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide. Among them, typical but non-limiting examples of the combination are: a combination of lithium cobalt oxide and lithium nickel oxide, a combination of lithium manganese oxide and lithium nickel manganese oxide, a combination of lithium nickel manganese oxide and lithium nickel cobalt manganese oxide, or a combination of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, etc.

[0033] As a preferred technical solution of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material.

[0034] Preferably, the negative electrode active material includes any one or a combination of at least two of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbide, or lithium titanate. Among them, typical but non-limiting examples of the combination are: a combination of soft carbon and hard carbon, a combination of hard carbon and artificial graphite, a combination of artificial graphite and natural graphite, a combination of natural graphite and silicon, a combination of silicon and silicon oxide, a combination of silicon oxide and silicon carbide, or a combination of silicon carbide and lithium titanate, etc.

[0035] The numerical range described in the present invention not only includes the above-listed point values but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0036] The technical solution of the present invention will be further described below through specific embodiments.

[0037] Example 1

[0038] This example provides a lithium-ion battery electrolyte:

[0039] The lithium-ion battery electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive.

[0040] Non-aqueous organic solvents: ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate; based on the mass of the electrolyte being 100%, the mass fraction of ethylene carbonate in the electrolyte is 13%, the mass fraction of ethyl methyl carbonate in the electrolyte is 45%, and the mass fraction of diethyl carbonate in the electrolyte is 24%.

[0041] Lithium salt: lithium hexafluorophosphate; based on the mass of the electrolyte being 100%, the mass fraction of lithium hexafluorophosphate in the electrolyte is 13.5%.

[0042] Additive: the compound shown in Formula 2 Lithium difluorophosphate, vinylene carbonate, 1,3 - propanesultone, and ethylene sulfate; based on the mass of the electrolyte being 100%, the mass fraction of the compound shown in Formula 2 in the electrolyte is 1%, the mass fraction of lithium difluorophosphate in the electrolyte is 0.5%, the mass fraction of vinylene carbonate in the electrolyte is 2%, the mass fraction of 1,3 - propanesultone in the electrolyte is 0.2%, and the mass fraction of ethylene sulfate in the electrolyte is 0.8%.

[0043] Example 2

[0044] This example provides a lithium-ion battery electrolyte:

[0045] The lithium-ion battery electrolyte includes non-aqueous organic solvents, a lithium salt, and an additive.

[0046] Non-aqueous organic solvents: vinylene carbonate, propylene carbonate, and diethyl carbonate; based on the mass of the electrolyte being 100%, the mass fraction of vinylene carbonate in the electrolyte is 10%, the mass fraction of propylene carbonate in the electrolyte is 45%, and the mass fraction of diethyl carbonate in the electrolyte is 29.4%.

[0047] Lithium salt: LiFSI; based on the mass of the electrolyte being 100%, the mass fraction of LiFSI in the electrolyte is 12%.

[0048] Additive: the compound shown in Formula 2 Lithium difluorooxalate borate, fluorinated vinylene carbonate, 1,3 - propane sultone, and ethylene sulfate; based on the mass of the electrolyte being 100%, the mass fraction of the compound shown in Formula 2 in the electrolyte is 0.1%, the mass fraction of lithium difluorooxalate borate in the electrolyte is 0.5%, the mass fraction of fluorinated vinylene carbonate in the electrolyte is 2%, the mass fraction of 1,3 - propane sultone in the electrolyte is 0.2%, and the mass fraction of ethylene sulfate in the electrolyte is 0.8%.

[0049] Example 3

[0050] This example provides a lithium-ion battery electrolyte:

[0051] The lithium-ion battery electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive.

[0052] Non-aqueous organic solvent: ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate; based on 100% of the mass of the electrolyte, the mass fraction of ethylene carbonate in the electrolyte is 13%, the mass fraction of ethyl methyl carbonate is 39.5%, and the mass fraction of diethyl carbonate is 24%.

[0053] Lithium salt: LiClO4; based on 100% of the mass of the electrolyte, the mass fraction of LiClO4 in the electrolyte is 15%.

[0054] Additive: the compound shown in Formula 2 Lithium tetrafluoroborate, vinylene carbonate, 1,3 - propanesultone, and ethylene sulfate; based on 100% of the mass of the electrolyte, the mass fraction of the compound shown in Formula 2 in the electrolyte is 5%, the mass fraction of lithium tetrafluoroborate is 0.5%, the mass fraction of vinylene carbonate is 2%, the mass fraction of 1,3 - propanesultone is 0.2%, and the mass fraction of ethylene sulfate is 0.8%.

[0055] Example 4

[0056] In this example, except that the compound shown in Formula 2 in the additive is replaced with the compound shown in Formula 3 the other conditions are the same as those in Example 1.

[0057] Example 5

[0058] In this example, except that the compound shown in Formula 2 in the additive is replaced with the compound shown in Formula 4 the other conditions are the same as those in Example 1.

[0059] Example 6

[0060] In this example, except that the compound shown in Formula 2 in the additive is replaced with the compound shown in Formula 5 the other conditions are the same as those in Example 1.

[0061] Example 7

[0062] In this example, except that the compound shown in Formula 2 in the additive Replace with the compound shown in Formula 6 Except for this, other conditions are the same as those in Example 1.

[0063] Example 8

[0064] In this example, except for replacing the compound shown in Formula 2 in the additive with the compound shown in Formula 7 Except for this, other conditions are the same as those in Example 1.

[0065] Example 9

[0066] In this example, except for replacing the mass fraction of the compound shown in Formula 2 in the electrolyte with 1% by 10% and replacing the mass fraction of ethyl methyl carbonate in the electrolyte with 45% by 36%, other conditions are the same as those in Example 1.

[0067] Example 10

[0068] In this example, except for not adding lithium difluorophosphate and replacing the mass fraction of lithium hexafluorophosphate in the electrolyte with 13.5% by 14%, other conditions are the same as those in Example 1.

[0069] Example 11

[0070] In this example, except for not adding vinylene carbonate and replacing the mass fraction of ethyl methyl carbonate in the electrolyte with 45% by 47%, other conditions are the same as those in Example 1.

[0071] Example 12

[0072] In this example, except for not adding 1,3 - propylene sulfonic acid lactone and replacing the mass fraction of ethyl methyl carbonate in the electrolyte with 45% by 45.2%, other conditions are the same as those in Example 1.

[0073] Example 13

[0074] In this example, except for not adding ethylene sulfate and replacing the mass fraction of ethyl methyl carbonate in the electrolyte with 45% by 45.8%, other conditions are the same as those in Example 1.

[0075] Example 14

[0076] In this example, except for not adding lithium difluorophosphate, vinylene carbonate, 1,3 - propylene sulfonic acid lactone and ethylene sulfate and replacing the mass fraction of ethyl methyl carbonate in the electrolyte with 45% by 49.5%, other conditions are the same as those in Example 1.

[0077] Example 15

[0078] In this embodiment, in addition to adding a compound represented by formula 5 with a mass fraction of 1% of the electrolyte, That is, the compounds represented by Formula 2 and Formula 5 were added to the electrolyte at the same time, and the mass fraction of ethyl methyl carbonate in the electrolyte was replaced from 45% to 44%, and other conditions were the same as those in Example 1.

[0079] Example 16

[0080] In this embodiment, in addition to adding a compound represented by formula 7 with a mass fraction of 1% of the electrolyte, That is, the compounds represented by Formula 2 and Formula 7 were added to the electrolyte at the same time, and the mass fraction of ethyl methyl carbonate in the electrolyte was replaced from 45% to 44%, while other conditions were the same as those in Example 1.

[0081] Comparative Example 1

[0082] In this comparative example, except that the compound shown in Formula 2 is not added and the mass fraction of ethyl methyl carbonate in the electrolyte is replaced by 46% from 45%, other conditions are the same as those in Example 1.

[0083] Comparative Example 2

[0084] In this comparative example, the compound shown in Formula 2 is replaced by a compound shown in Formula 8 which does not contain a fluorine substituent. Except for this, other conditions are the same as those in Example 1.

[0085] Comparative Example 3

[0086] In this comparative example, the compound shown in Formula 2 is replaced by a compound shown in Formula 9 which does not contain a trimethylsilyl group. Except for this, other conditions are the same as those in Example 1.

[0087] Comparative Example 4

[0088] In this comparative example, the compound shown in Formula 2 is replaced by a compound shown in Formula 10 which does not contain a trimethylsilyl group. Except for this, other conditions are the same as those in Example 1.

[0089] The electrolytes in Examples 1 to 16 and Comparative Examples 1 to 4 were assembled into lithium-ion batteries, and the assembly method was as follows:

[0090] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (LNCM), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were mixed thoroughly in N-methylpyrrolidone solvent system at a mass ratio of 95:3:2, and then coated on aluminum foil, dried, and cold pressed to obtain a positive electrode sheet with a compaction density of 3.5g / cm 3 .

[0091] The graphite as the negative electrode active material, acetylene black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethyl cellulose (CMC) as the thickener were fully stirred and mixed evenly in a deionized water solvent system according to a mass ratio of 96:2:1:1, and then coated on a Cu foil, dried, and cold-pressed to obtain a negative electrode sheet with a compaction density of 1.65 g / cm 3 .

[0092] A polyethylene (PE) film with a thickness of 9 μm was used as the base film, and a 3-μm nano-aluminum oxide coating was coated on the base film to obtain a separator.

[0093] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in sequence, with the separator placed in the middle of the positive electrode sheet and the negative electrode sheet to play an isolation role, and the stacked sheets were used to obtain a bare battery cell.

[0094] The bare battery cell was placed in an aluminum-plastic film, baked at 80 °C to remove water, then injected with the corresponding electrolyte and sealed. After that, through processes such as standing, hot and cold pressing, formation, clamping, and grading, a finished soft-packaged lithium-ion secondary battery was obtained.

[0095] The lithium-ion batteries in Examples 1-16 and Comparative Examples 1-4 were tested for their performance of normal temperature cycling, high temperature cycling, and high temperature storage. The test methods are as follows:

[0096] (1) Normal temperature cycle life test

[0097] The fully charged battery after grading was discharged to 2.8 V at 1C at 25 °C, and the initial discharge capacity was recorded as DC(1-R). Then it was charged at 1C constant current and constant voltage to 4.2 V at 25 °C, with a cut-off current of 0.05C, allowed to stand for 5 min, and then discharged to 2.8 V at 1C, and the discharge capacity DC(2-R) was recorded. This cycle was repeated until DC(N-R) < 80% DC(1-R). The number of discharge cycles N was recorded, and N was the normal temperature cycle life.

[0098] (2) High temperature cycle life test

[0099] The fully charged battery after grading was placed in an incubator at 45 °C and discharged to 2.8 V at 1C. The initial discharge capacity was recorded as DC(1-H). Then it was charged at 1C constant current and constant voltage to 4.2 V, with a cut-off current of 0.05C, allowed to stand for 5 min, and then discharged to 2.8 V at 1C, and the discharge capacity DC(2-H) was recorded. This cycle was repeated until DC(N-H) < 80% DC(1-H). The number of discharge cycles N was recorded, and N was the high temperature cycle life.

[0100] (3) Gas generation and DCR growth during high temperature storage

[0101] After the battery in the fully charged state after normal temperature formation is left standing for 30 min, it is discharged at 4C for 30 s until it reaches 2.8V, and the initial fully charged state discharge DCR(0-S) is recorded. At the same time, the initial cell volume Vol(0-S) is measured. Then it is placed in an incubator at 60°C for storage for N days. After taking out the battery, it is charged at a constant current and constant voltage of 1C to 4.2V at room temperature with a cut-off current of 0.05C. After standing for 30 min, it is discharged at 4C for 30 s, and the fully charged state discharge DCR(N-S) after N days of storage is recorded. The DCR growth rate = 100% * [DCR(N-S) - DCR(0-S)] / DCR(0-S). At the same time, the cell volume Vol(N-S) is measured. The storage gas generation rate = 100% * [Vol(N-S) - Vol(0-S)] / Vol(0-S).

[0102] Perform normal temperature cycling, high temperature cycling and high temperature storage performance tests on the lithium-ion batteries in Examples 1 to 16 and Comparative Examples 1 to 4 of the present invention. The test results are shown in the following table.

[0103] Table 1

[0104]

[0105]

[0106] From Table 1, it can be obtained that the non-aqueous electrolytes containing different contents of the first additive compound in Examples 1 to 3 can improve the normal temperature and high temperature cycling performance of lithium-ion batteries.

[0107] Table 2

[0108]

[0109] From Table 2, it can be obtained that the application of different first additives in Formula 2 to Formula 8 of the present invention in the electrolyte can improve the normal temperature and high temperature performance of lithium-ion batteries to varying degrees.

[0110] Table 3

[0111]

[0112] From Table 3, it can be obtained that too much content of the first additive leads to a decline in the normal and high temperature cycling performance and storage performance of the battery.

[0113] Table 4

[0114]

[0115] From the comparison between Example 1 and Examples 10 to 14 in Table 4, it can be seen that when the first additive is used in combination with other additives, additives containing substitution groups such as F or N are beneficial to the formation of a passivation film rich in inorganic components such as LiF and Li3N, which can effectively reduce the internal resistance of the battery; the trimethylsilyl and trimethoxysilyl groups in the molecular structure of the first additive can also form a stable positive electrode passivation film and eliminate trace amounts of HF in the electrolyte, thereby improving the stability of the positive electrode material and the electrolyte at high temperatures and inhibiting gas generation to enhance the high-temperature cycle and storage performance of the battery. When the cyclic carbonate additive is missing, the cycle performance will deteriorate to a certain extent but the storage DCR growth can be slightly improved, and there is no obvious effect on gas generation; when the cyclic sultone additive is missing, the cycle performance deteriorates significantly but the storage performance is not significantly affected; when the cyclic sulfate additive is missing, the cycle performance will deteriorate to a certain extent but the storage gas generation and DCR growth can be significantly improved; when the lithium-containing additive is missing, both the cycle performance and the storage performance deteriorate significantly.

[0116] Table 5

[0117]

[0118]

[0119] From Table 5, it can be obtained that: by comparing Example 1, Example 6 and Example 15 or comparing Example 1, Example 8 and Example 16, it can be seen that the combined use of two first additives can more effectively improve the high-temperature cycle performance and storage performance of lithium-ion batteries. After the combination, the content of active groups such as fluorine or trimethylsilyl in the first additive will increase or complement each other, and the effect is better than that of using only the first additive.

[0120] Table 6

[0121]

[0122] From Table 6, it can be obtained that by comparing Example 1 and Comparative Example 1, it can be seen that when the electrolyte without the first additive is applied to a lithium-ion battery, the normal and high-temperature cycle performance and storage performance of the battery both deteriorate. By comparing Example 1 and Comparative Examples 2 to 3, it can be seen that when the additive does not contain a fluorine substituent, trimethylsilyl or trimethoxysilyl, the normal and high-temperature cycle performance and storage performance of the battery both decline. The main reason is considered to be that since there is no first additive or related active group in the comparative example, it is difficult to form a passivation film rich in inorganic components such as LiF to effectively reduce the internal resistance of the battery. At the same time, there are no trimethylsilyl and trimethoxysilyl groups to form a stable positive electrode passivation film and eliminate trace amounts of HF in the electrolyte, so the cycle and storage performances all deteriorate.

[0123] The specific embodiments described above further elaborate on the objective, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive. The additive includes a first additive, and the first additive includes a compound represented by Formula 1. Wherein, at least one of R1 and R2 is a fluorine atom or a fluorine-substituted hydrocarbon group having 1 to 6 carbon atoms, and the number of fluorine atoms in the compound is 1 to 3.

2. The electrolyte according to claim 1, wherein The compound includes any one or a combination of at least two of the compounds represented by Formula 2 to Formula 7.

3. The electrolyte according to claim 1, characterized in that, The mass fraction of the compound in the electrolyte is 0.1% to 10%.

4. The electrolyte according to any one of claims 1-3, characterized in that The additive further includes a second additive. The second additive includes a cyclic carbonate, a cyclic sultone, a cyclic sulfate, and a lithium-containing additive. The cyclic carbonate includes any one or a combination of at least two of vinylene carbonate, fluoroethylene carbonate, or ethylene vinylene carbonate. The cyclic sultone includes 1,3-propane sultone and / or 1,3-propene sultone. The cyclic sulfate includes ethylene sulfate. The lithium-containing additive includes any one or a combination of at least two of lithium difluorophosphate, lithium difluorooxalate borate, dilithium oxalate borate, lithium tetrafluoroborate, or lithium difluorooxalate phosphate.

5. The electrolyte according to claim 4, wherein The mass fraction of the second additive in the electrolyte is 0.5% to 20%.

6. The electrolyte according to any one of claims 1-3, characterized in that, The non-aqueous organic solvent includes any one or a combination of at least two of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, or diethyl carbonate.

7. The electrolyte according to any one of claims 1-3, characterized in that, The lithium salt includes any one or a combination of at least two of LiFSI, LiTFSI, LiPF6, LiBF4, LiClO4, or LiAsF6. The concentration of the lithium salt in the electrolyte is 0.5 M to 2 M, and the mass fraction of the lithium salt in the electrolyte is 12% to 15%.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, and the electrolyte according to any one of claims 1-7.

9. The lithium ion battery according to claim 8, wherein, The positive electrode includes a positive electrode current collector and a positive electrode active material. The positive electrode active material includes any one or a combination of at least two of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

10. The lithium-ion battery according to claim 8, characterized in that, The negative electrode includes a negative electrode current collector and a negative electrode active material. The negative electrode active material includes any one or a combination of at least two of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbide, or lithium titanate.

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