Nonaqueous electrolyte and lithium battery

Abstract

In order to solve the problem of the poor high- and low-temperature performance of a lithium battery, a non-aqueous electrolyte and a lithium battery are provided. The non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the organic solvent comprises one or more of compounds as represented by formula 1, [Formula 1]; and the additive comprises one or more compounds as represented by formula 2, [Formula 2]. By means of the combined use of the compound as represented by formula 1 and the compound as represented by formula 2, a high-voltage lithium-ion battery not only has good electrochemical performance at room temperature and high temperatures, but also has low-temperature and rate performance.

Description

A non-aqueous electrolyte and a lithium battery Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a non-aqueous electrolyte and a lithium battery. Background Technology

[0002] Lithium-ion batteries, with their high specific energy and power density, long cycle life, and environmental friendliness, have been widely used in consumer electronics, electric vehicles, and energy storage. However, as a power source for new energy vehicles, lithium-ion batteries still face several challenges in practical applications. For example, when batteries are exposed to high temperatures, the instability of the electrode / electrolyte interface increases, leading to severe capacity decay. Intense electrode / electrolyte interface reactions and the increasing instability of the solid-electrolyte interphase (SEI) layer result in rapid electrolyte consumption, transition metal dissolution, and a surge in interfacial impedance. High-temperature operation is known to cause rapid battery degradation. At low temperatures, the increased viscosity of the electrolyte leads to decreased electrolyte conductivity, increased electrolyte / electrode interface film impedance and charge transfer impedance, and a reduced migration rate of lithium ions in the active material. This results in intensified electrode polarization at low temperatures, a significant decrease in energy density, and a corresponding impact on cycle life, severely limiting the large-scale use of lithium-ion batteries.

[0003] To mitigate the impact of high and low temperatures on battery performance, researchers and engineers have implemented a series of measures. For example, during battery design and manufacturing, materials resistant to both high and low temperatures are selected, and the battery structure is optimized to improve thermal stability and low-temperature performance. Furthermore, electronic devices and vehicles are equipped with corresponding thermal management systems, such as heat sinks and heating devices, to maintain battery operation within a suitable temperature range. Another example is optimizing the electrolyte formulation to improve the battery's high and low temperature performance. Optimizing the electrolyte formulation is the most direct method to improve battery performance at both high and low temperatures; however, existing electrolyte systems are typically carbonate and carboxylic acid ester systems, which cannot simultaneously address both high and low temperature performance and also limit the battery's ability to charge and discharge rapidly. Summary of the Invention

[0004] The purpose of this invention is to provide a non-aqueous electrolyte and lithium battery with better high and low temperature performance and rate performance.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A first aspect of the present invention provides a non-aqueous electrolyte comprising a lithium salt, an organic solvent, and an additive, wherein the organic solvent comprises one or more compounds represented by Formula 1.

[0007] Formula 1: R1 is alkyl, alkoxy, fluoroalkyl, fluoroalkoxy, alkenyl, fluoroalkenyl, amino, tertiary amine, fluorotertiary amine or -R2SO2R3, wherein R2 is alkyl or fluoroalkyl, and R3 is fluorine, hydrogen, alkyl or fluoroalkyl.

[0008] The additive includes one or more compounds represented by Formula 2.

[0009] Formula 2: R4, R5, and R6 are each independently an alkyl group or an alkyl group substituted with at least one cyano group, wherein at least one of R4, R5, and R6 is an alkyl group substituted with at least one cyano group.

[0010] Furthermore, the number of carbon atoms in R4, R5, and R6 are each an integer between 1 and 6, and even further, an integer between 1 and 3.

[0011] Furthermore, R4, R5, and R6 are independently -CH3, -CH2CH3, -CH2CN, or -CH2CH2CN, respectively.

[0012] In some embodiments, the compounds represented by Formula 2 include diethyl cyanomethyl phosphate (CAS No.: 50586-62-4), bis(cyanomethyl) phosphate (CAS No.: 433979-72-7), and tris(2-cyanoethoxy) phosphate (CAS No.: 875826-91-8).

[0013] Further, the compound represented by Formula 2 accounts for 0.01 to 2% of the total mass of the non-aqueous electrolyte, more specifically 0.1 to 2%, and even more specifically 0.5 to 2%, for example 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, and 2%.

[0014] Further, R1 is an alkyl group with 1 to 4 carbon atoms, a fluoroalkyl group with 1 to 4 carbon atoms, a tertiary amine group with 2 to 6 carbon atoms, or -R2SO2R3, wherein R2 is an alkyl group with 1 to 4 carbon atoms, and R3 is fluorine.

[0015] Furthermore, R1 is -CH3, -CH2CH3, -CH2CH2CH3, -CH2CH2SO2F, -CH2CH2CH2SO2F, -N(CH3)2, -N(CH2CH3)2 or -N(CH3)CH2CH3.

[0016] In some embodiments, the compound represented by Formula 1 includes one or more of ethylsulfonyl fluoride (CAS No.: 754-03-0), propylsulfonyl fluoride (CAS No.: 762-69-6), ethylenedisulfonyl fluoride (CAS No.: 143761-83-5), propylenedisulfonyl fluoride (CAS No.: 110073-91-1), N,N-diethylaminosulfonyl fluoride (CAS No.: 382-97-8), N,N-dimethylaminosulfonyl fluoride (CAS No.: 354-44-9), and N-ethyl-N-methylaminosulfonyl fluoride (CAS No.: 1458771-72-6).

[0017] Furthermore, the compound represented by Formula 1 accounts for 10-50% of the total mass of the organic solvent, more particularly 15-40%, and even more particularly 20-30%.

[0018] Furthermore, the additive also includes additive A other than the compound represented by Formula 2.

[0019] Further, the additive A is selected from one or more of the following: vinylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, 1,3-propane sulpholactone, 1,3-(1-propene) sulpholactone, methane disulfonate, vinyl sulfate, vinyl disulfate, pentaerythritol bicyclic sulfate, tris(trimethylsilane)borate, tris(trimethylsilane) phosphate, methyl cis-butene dianhydride, succinic anhydride, biphenyl, cyclohexylbenzene, trioctyl phosphate, succinic acrylonitrile, adiponitrile, 1,3,6-hexanetrionitrile, 1,2-di(2-cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,2,3-tris(2-cyanoethoxy)propane, decanonitrile, 1,2,3,4,5-penta(dicyanoethoxy)pentane, and lithium difluorophosphate.

[0020] Furthermore, the additive A in the non-aqueous electrolyte has a mass content of 0.1-30%, more specifically 1-15%, and even more specifically 2-10%.

[0021] In some embodiments, the additive further includes fluoroethylene carbonate, succinate, 1,3,6-hexanetrionitrile, and ethylene sulfate.

[0022] Further, the fluoroethylene carbonate accounts for 2-6% of the total mass of the non-aqueous electrolyte, the succinic acid accounts for 1-3% of the total mass of the non-aqueous electrolyte, the 1,3,6-hexanetrionitrile accounts for 2-4% of the total mass of the non-aqueous electrolyte, and the ethylene sulfate accounts for 0.1-1% of the total mass of the non-aqueous electrolyte.

[0023] Furthermore, the additives also include one or more of the following: vinylene carbonate, ethylene ethylene carbonate, 1,3-propane sulpholactone, 1,3-(1-propene) sulpholactone, methane disulfonate, vinyl disulfate, pentaerythritol bicyclic sulfate, tris(trimethylsilane)borate, tris(trimethylsilane) phosphate, methyl cis-butene dianhydride, succinic anhydride, biphenyl, cyclohexylbenzene, trioctyl phosphate, adiponitrile, 1,2-di(2-cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,2,3-tris(2-cyanoethoxy)propane, decanonitrile, 1,2,3,4,5-penta(dicyanoethoxy)pentane, and lithium difluorophosphate.

[0024] In some embodiments, the additive also includes fluoroethylene carbonate, lithium difluorophosphate, and ethylene sulfate.

[0025] Further, the fluoroethylene carbonate accounts for 0.5-2% of the total mass of the non-aqueous electrolyte, the lithium difluorophosphate accounts for 0.5-2% of the total mass of the non-aqueous electrolyte, and the ethylene sulfate accounts for 0.1-1% of the total mass of the non-aqueous electrolyte.

[0026] Furthermore, the additives also include one or more of the following: vinylene carbonate, ethylene ethylene carbonate, 1,3-propane sulpholactone, 1,3-(1-propene) sulpholactone, methane disulfonate, vinyl disulfate, pentaerythritol bicyclic sulfate, tris(trimethylsilane)borate, tris(trimethylsilane) phosphate, methyl cis-butene dianhydride, succinic anhydride, biphenyl, cyclohexylbenzene, trioctyl phosphate, succinic acrylonitrile, adiponitrile, 1,3,6-hexanetrionitrile, 1,2-di(2-cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,2,3-tris(2-cyanoethoxy)propane, decanonitrile, and 1,2,3,4,5-penta(dicyanoethoxy)pentane.

[0027] Furthermore, the organic solvent also includes cyclic esters and chain esters.

[0028] Furthermore, the cyclic ester is selected from one or more of γ-butyrolactone, ethylene carbonate, and propylene carbonate.

[0029] Furthermore, the chain ester is selected from one or more of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl propionate, ethyl propionate, propyl propionate, methyl acetate, ethyl acetate, propyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl fluoropropionate, propyl fluoropropionate, ethyl fluoropropionate, and ethyl fluoropropionate.

[0030] In some embodiments, the organic solvent further includes diethyl carbonate, ethylene carbonate, propylene carbonate, and ethyl propionate.

[0031] Further, the volume ratio of diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl propionate and the compound represented by Formula 1 is 1:(1-3):(0.5-2):(2-4):(2-4), and even more specifically 1:(1.5-2.5):(0.8-1.5):(2.5-3.5):(2.5-3.5).

[0032] In some embodiments, the organic solvent further includes ethylene carbonate and ethyl methyl carbonate.

[0033] Furthermore, the volume ratio of the ethylene carbonate, ethyl methyl carbonate and the compound represented by Formula 1 is 1:(1-2):(0.5-1.5), and even more specifically, 1:(1-1.5):(0.8-1.2).

[0034] Further, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), anhydrous lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium difluorodioxophosphate (LiPF2(C2O4)2), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (LiSO3CF3), lithium difluorodioxophosphate (LiPO8C4F2), and lithium difluorosulfonylimide (LiN(SO2F)2).

[0035] Furthermore, the concentration of the lithium salt in the non-aqueous electrolyte is 0.8–3 mol / L, more specifically 0.8–2 mol / L, and even more specifically 1–1.5 mol / L.

[0036] The present invention also provides a lithium battery comprising the non-aqueous electrolyte as described above.

[0037] Furthermore, the positive electrode material of the lithium battery is lithium cobalt oxide or ternary positive electrode material.

[0038] Furthermore, the negative electrode material of the lithium battery is graphite.

[0039] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0040] This invention combines the compound represented by Formula 1 with the compound represented by Formula 2, enabling lithium-ion batteries to not only have excellent electrochemical performance at room temperature and high temperature, but also to take into account low temperature and rate performance. Detailed Implementation

[0041] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0042] Unless otherwise specified, the reagents, instruments, etc. used in the following examples and comparative examples are all commercially available products commonly used in the art, or can be prepared by conventional preparation methods in the art.

[0043] Example 1

[0044] In an argon-filled glove box (H2O content <10ppm), DEC (diethyl carbonate), EC (ethylene carbonate), PC (propylene carbonate), EP (ethyl propionate), and ethyl sulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 4 wt% fluoroethylene carbonate, 0.1 wt% diethyl cyanomethyl phosphate, 2 wt% succinate, 3 wt% 1,3,6-hexanetrionitrile, and 0.5 wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0045] Example 2

[0046] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and ethylsulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 0.5wt% diethyl cyanomethyl phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0047] Example 3

[0048] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and ethylsulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1wt% diethyl cyanomethyl phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0049] Example 4

[0050] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and ethylsulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% diethyl cyanomethyl phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0051] Example 5

[0052] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and ethylsulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 2wt% diethyl cyanomethyl phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0053] Example 6

[0054] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and ethylsulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% bis(cyanomethyl) phosphate, 2wt% succinic acid, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% ethylene sulfate were added to the electrolyte to prepare the electrolyte solution.

[0055] Example 7

[0056] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and ethylsulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% tris(2-cyanoethoxy) phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0057] Example 8

[0058] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and propylsulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% bis(cyanomethyl) phosphate, 2wt% succinic acid, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% ethylene sulfate were added to the electrolyte to prepare the electrolyte solution.

[0059] Example 9

[0060] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and ethylene disulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% bis(cyanomethyl) phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0061] Example 10

[0062] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and propylene disulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% bis(cyanomethyl) phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0063] Example 11

[0064] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and N,N-diethylaminosulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% bis(cyanomethyl) phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0065] Example 12

[0066] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and N,N-dimethylaminosulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% bis(cyanomethyl) phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0067] Example 13

[0068] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and N-ethyl-N-methylaminosulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% bis(cyanomethyl) phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0069] Example 14

[0070] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and ethylsulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:1:5. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% diethyl cyanomethyl phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0071] Example 15

[0072] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and ethylsulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:5:1. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% diethyl cyanomethyl phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0073] Comparative Example 1

[0074] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP (propyl propionate) were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 4 wt% fluoroethylene carbonate, 2 wt% succinate, 3 wt% 1,3,6-hexanetrionitrile, and 0.5 wt% ethylene sulfate were added to the electrolyte to prepare the electrolyte solution.

[0075] Comparative Example 2

[0076] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and N-ethyl-N-methylaminosulfonyl fluoride were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% ethylene sulfate were added to the electrolyte to prepare the electrolyte solution.

[0077] Comparative Example 3

[0078] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1.5wt% bis(cyanomethyl) phosphate, 2wt% succinate, 3wt% 1,3,6-hexanetrionitrile, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0079] The electrolytes prepared in Examples 1 to 15 and Comparative Examples 1 to 3 were tested for the following performance in a 4.55V lithium cobalt oxide graphite battery:

[0080] The capacity retention rate after being placed at 85℃ for 4 hours is calculated as follows: under constant current / constant voltage (CC / CV) conditions at 25℃, the capacity is charged at 1C to 4.55V and then placed in an oven at 85℃ for 4 hours; the capacity after being placed is discharged at 1C to 3.0V and then discharged at 1C to 3.0V under the same conditions before being placed.

[0081] The battery swelling rate after being placed at 85℃ for 4 hours is calculated by dividing the difference between the battery thickness after placement and the battery thickness before placement by the battery thickness before placement.

[0082] Capacity retention after 200 cycles at 45℃ is calculated by charging the battery at 1C to 4.55V and then discharging it at 1C to 3.0V under constant current / constant voltage (CC / CV) conditions at 45℃ for 200 cycles. The battery capacity after 200 cycles and the capacity after the first cycle of charge / discharge are measured separately. The capacity retention after 200 cycles at 45℃ is equal to the battery capacity after 200 cycles divided by the battery capacity after the first cycle of charge / discharge.

[0083] DCR of 50% SCO and 2C10s.

[0084] The -25℃ low-temperature discharge test involves charging the battery to 4.55V at 1C under constant current / constant voltage (CC / CV) conditions at 25℃, followed by discharging at 1C at -25℃. The -25℃ discharge efficiency is calculated by dividing the -25℃ discharge capacity by the 25℃ charging capacity.

[0085] The relevant experimental data are shown in Table 1.

[0086] Table 1

[0087] As shown in Table 1, the embodiments of the present invention significantly improve the high-temperature storage capacity retention rate and cycle retention rate of the battery by adding sulfonyl fluoride solvents and cyano-containing phosphate additives to the electrolyte system, reduce the high-temperature swelling of the battery, and improve the low-temperature discharge efficiency and internal resistance of the battery, so that the battery has both better high and low temperature performance and rate performance.

[0088] Referring further to Examples 1 to 5, as the amount of cyano-containing phosphate ester additive in the electrolyte increases, the capacity retention rate of the battery after being left to stand at 85°C for 4 hours and the capacity retention rate after 200 cycles at 45°C show a trend of first increasing and then decreasing. The swelling rate of the battery after being left to stand at 85°C for 4 hours shows a trend of first decreasing and then increasing. The discharge efficiency of the battery at -25°C shows a decreasing trend, while the DCR of the battery shows an increasing trend. Therefore, in summary, the amount of cyano-containing phosphate ester additive added should not be too large or too small, preferably 0.1% to 2% of the total mass of the electrolyte, and most preferably 1.5%.

[0089] Referring to Examples 4, 6 and 7, different cyano-containing phosphate additives also have a certain impact on battery performance. Among them, tris(2-cyanoethoxy) phosphate has the best effect on improving battery performance.

[0090] Referring to Examples 6 and 8 to 13, different sulfonyl fluoride solvents also affect battery performance. Among them, N,N-dimethylaminosulfonyl fluoride, N,N-diethylaminosulfonyl fluoride and N-ethyl-N-methylaminosulfonyl fluoride have the best effect on improving battery performance.

[0091] Referring to Examples 1, 14, and 15, both excessively high and low proportions of sulfonyl fluoride solvents will adversely affect battery performance. When the proportion of sulfonyl fluoride solvents is too high (exceeding 50% of the total volume of organic solvents), the battery's low-temperature performance deteriorates, and its high-temperature performance does not show significant improvement; when the proportion of sulfonyl fluoride solvents is too low (below 10% of the total volume of organic solvents), the battery's high-temperature performance deteriorates, and its internal resistance increases.

[0092] Referring to the comparative examples, adding only sulfonyl fluoride solvents to the electrolyte without adding cyano-containing phosphate ester additives (Comparative Example 2) can improve the battery's low-temperature discharge efficiency, reduce the battery's internal resistance, and improve the battery's high-temperature performance, but the improvement in high-temperature performance is limited. Conversely, adding only cyano-containing phosphate ester additives to the electrolyte without adding sulfonyl fluoride solvents (Comparative Example 3) does not help improve low-temperature discharge efficiency and may even increase the battery's internal resistance, with limited improvement in high-temperature performance.

[0093] Example 16

[0094] In an argon-filled glove box (H2O content <10ppm), EC, EMC (ethyl methyl carbonate), and ethyl sulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 1 wt% fluoroethylene carbonate, 0.1 wt% diethyl cyanomethyl phosphate, 1 wt% lithium difluorophosphate, and 0.5 wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0095] Example 17

[0096] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and ethyl sulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 0.5wt% diethyl cyanomethyl phosphate, 1wt% lithium difluorophosphate, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0097] Example 18

[0098] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and ethyl sulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1wt% diethyl cyanomethyl phosphate, 1wt% lithium difluorophosphate, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0099] Example 19

[0100] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and ethyl sulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1.5wt% diethyl cyanomethyl phosphate, 1wt% lithium difluorophosphate, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0101] Example 20

[0102] In an argon-filled glove box (H2O content <10ppm), EC, EMC and ethyl sulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 2wt% diethyl cyanomethyl phosphate, 1wt% lithium difluorophosphate, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0103] Example 21

[0104] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and ethyl sulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1.5wt% bis(cyanomethyl) phosphate, 1wt% lithium difluorophosphate, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0105] Example 22

[0106] In an argon-filled glove box (H2O content <10ppm), EC, EMC and ethyl sulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1.5wt% tris(2-cyanoethoxy) phosphate, 1wt% lithium difluorophosphate, and 0.5wt% ethylene sulfate were added to the electrolyte to prepare the electrolyte solution.

[0107] Example 23

[0108] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and propylsulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1.5wt% tris(2-cyanoethoxy) phosphate, 1wt% lithium difluorophosphate, and 0.5wt% ethylene sulfate were added to the electrolyte to prepare the electrolyte solution.

[0109] Example 24

[0110] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and ethylene disulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1.5wt% tris(2-cyanoethoxy) phosphate, 1wt% lithium difluorophosphate, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0111] Example 25

[0112] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and propylene disulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1.5wt% tris(2-cyanoethoxy) phosphate, 1wt% lithium difluorophosphate, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0113] Example 26

[0114] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and N,N-diethylaminosulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1.5wt% tris(2-cyanoethoxy) phosphate, 1wt% lithium difluorophosphate, and 0.5wt% ethylene sulfate were added to the electrolyte to prepare the electrolyte solution.

[0115] Example 27

[0116] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and N,N-dimethylaminosulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1.5wt% tris(2-cyanoethoxy) phosphate, 1wt% lithium difluorophosphate, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0117] Example 28

[0118] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and N-ethyl-N-methylaminosulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1.5wt% tris(2-cyanoethoxy) phosphate, 1wt% lithium difluorophosphate, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0119] Comparative Example 4

[0120] In an argon-filled glove box (H2O content <10ppm), EC and EMC were mixed uniformly at a volume ratio of 3:7. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1wt% lithium difluorophosphate, and 0.5wt% ethylene sulfate were added to the electrolyte to prepare the electrolyte solution.

[0121] Comparative Example 5

[0122] In an argon-filled glove box (H2O content <10ppm), EC, EMC, and N-ethyl-N-methylaminosulfonyl fluoride were mixed uniformly in a volume ratio of 3:4:3. 1.2mol / L LiPF6 was added to the mixed solution, and then 1wt% fluoroethylene carbonate, 1wt% lithium difluorophosphate, and 0.5wt% ethylene sulfate were added to the electrolyte to prepare the electrolyte solution.

[0123] Comparative Example 6

[0124] In an argon-filled glove box (H2O content <10ppm), EC and EMC were mixed uniformly at a volume ratio of 3:7. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 1wt% tris(2-cyanoethoxy) phosphate, 1wt% lithium difluorophosphate, and 0.5wt% vinyl sulfate were added to the electrolyte to prepare the electrolyte solution.

[0125] The electrolytes prepared in Examples 16 to 28 and Comparative Examples 4 to 6 were tested for the following performance in a 4.4V ternary graphite battery:

[0126] The capacity retention rate after 60 days of high-temperature storage at 60℃ is calculated as follows: under constant current / constant voltage (CC / CV) conditions at 25℃, the capacity is charged to 4.4V at 1C and then stored in an oven at 60℃ for 60 days; the capacity after storage is divided by the capacity after being discharged to 3.0V at 1C under the same conditions before storage.

[0127] The battery swelling rate after being stored at 60℃ for 60 days is calculated by dividing the difference between the battery thickness after storage and the battery thickness before storage by the battery thickness before storage.

[0128] The capacity retention rate after 500 cycles at 45℃ is calculated by charging the battery at 1C to 4.4V and then discharging it at 1C to 3.0V under constant current / constant voltage (CC / CV) conditions at 45℃ for 500 cycles. The battery capacity after 500 cycles and the capacity after the first cycle are measured separately. The capacity retention rate after 500 cycles at 45℃ is equal to the battery capacity after 500 cycles divided by the battery capacity after the first cycle.

[0129] DCR of 50% SCO and 2C10s.

[0130] The -20℃ low-temperature discharge test involves charging the battery to 4.4V at 1C under constant current / constant voltage (CC / CV) conditions at 25℃, followed by discharging at 1C at -20℃. The discharge efficiency at -20℃ is calculated by dividing the discharge capacity at -20℃ by the charging capacity at 20℃.

[0131] The relevant experimental data are shown in Table 2.

[0132] Table 2

[0133] As shown in Table 2, for ternary graphite batteries, adding sulfonyl fluoride solvents and cyano-containing phosphate ester additives to the electrolyte system also achieves similar effects.

[0134] In summary, the electrolyte system of this invention can improve the high-temperature performance of the battery, while also taking into account the low-temperature and rate performance of the battery.

[0135] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be included within the scope of protection of the invention.

Claims

1. A non-aqueous electrolyte, comprising a lithium salt, an organic solvent, and additives, characterized in that: The organic solvent includes one or more compounds represented by Formula 1. Formula 1: R1 is alkyl, alkoxy, fluoroalkyl, fluoroalkoxy, alkenyl, fluoroalkenyl, amino, tertiary amine, fluorotertiary amine or -R2SO2R3, wherein R2 is alkyl or fluoroalkyl, and R3 is fluorine, hydrogen, alkyl or fluoroalkyl. The additive includes one or more compounds represented by Formula 2. Formula 2: R4, R5, and R6 are each independently an alkyl group or an alkyl group substituted with at least one cyano group, wherein at least one of R4, R5, and R6 is an alkyl group substituted with at least one cyano group.

2. The non-aqueous electrolyte according to claim 1, characterized in that: The number of carbon atoms in R4, R5, and R6 are each an integer between 1 and 6.

3. The non-aqueous electrolyte according to claim 2, characterized in that: The number of carbon atoms in R4, R5, and R6 are each an integer between 1 and 3.

4. The non-aqueous electrolyte according to claim 2, characterized in that: R4, R5, and R6 are independently -CH3, -CH2CH3, -CH2CN, or -CH2CH2CN, respectively.

5. The non-aqueous electrolyte according to claim 4, characterized in that: The compounds represented by Formula 2 include diethyl cyanomethyl phosphate, bis(cyanomethyl) phosphate, and tris(2-cyanoethoxy) phosphate.

6. The non-aqueous electrolyte according to claim 1, characterized in that: The compound represented by Formula 2 accounts for 0.01 to 2% of the total mass of the non-aqueous electrolyte.

7. The non-aqueous electrolyte according to claim 1, characterized in that: R1 is an alkyl group with 1 to 4 carbon atoms, a fluoroalkyl group with 1 to 4 carbon atoms, a tertiary amine group with 2 to 6 carbon atoms, or -R2SO2R3, wherein R2 is an alkyl group with 1 to 4 carbon atoms, and R3 is fluorine.

8. The non-aqueous electrolyte according to claim 7, characterized in that: The R1 is -CH3, -CH2CH3, -CH2CH2CH3, -CH2CH2SO2F, -CH2CH2CH2SO2F, -N(CH3)2, -N(CH2CH3)2 or -N(CH3)CH2CH3.

9. The non-aqueous electrolyte according to claim 1, characterized in that: The compounds represented by Formula 1 include ethylsulfonyl fluoride, propylsulfonyl fluoride, ethylenedisulfonyl fluoride, propylenedisulfonyl fluoride, N,N-diethylaminosulfonyl fluoride, N,N-dimethylaminosulfonyl fluoride, and N-ethyl-N-methylaminosulfonyl fluoride.

10. The non-aqueous electrolyte according to claim 1, characterized in that: The compound represented by Formula 1 accounts for 10-50% of the total mass of the organic solvent.

11. The non-aqueous electrolyte according to claim 1, characterized in that: The additive also includes additive A other than the compound represented by formula 2. Additive A is selected from one or more of the following: vinylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, 1,3-propane sulpholactone, 1,3-(1-propene) sulpholactone, methanedisulfonate, vinyl sulfate, vinyl disulfate, pentaerythritol bicyclic sulfate, tris(trimethylsilane)borate, tris(trimethylsilane) phosphate, methyl cis-butene dianhydride, succinic anhydride, biphenyl, cyclohexylbenzene, trioctyl phosphate, succinic acrylonitrile, adiponitrile, 1,3,6-hexanetrionitrile, 1,2-di(2-cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,2,3-tris(2-cyanoethoxy)propane, decanonitrile, 1,2,3,4,5-penta(dicyanoethoxy)pentane, and lithium difluorophosphate; and / or, the mass content of additive A in the non-aqueous electrolyte is 0.1% to 30%.

12. The non-aqueous electrolyte according to claim 1, characterized in that: The organic solvent further includes cyclic esters and chain esters, wherein the cyclic esters are selected from one or more of γ-butyrolactone, ethylene carbonate, and propylene carbonate; and the chain esters are selected from one or more of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl propionate, ethyl propionate, propyl propionate, methyl acetate, ethyl acetate, propyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl fluoropropionate, propyl fluoropropionate, ethyl fluoropropionate, and ethyl fluoropropionate; and / or, The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, anhydrous lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorodioxoyl phosphate, lithium difluorophosphate, lithium trifluoromethanesulfonate, lithium difluorodioxoyl phosphate, and lithium difluorosulfonyl imide; and / or, The concentration of the lithium salt in the non-aqueous electrolyte is 0.8–3 mol / L.

13. The non-aqueous electrolyte according to claim 1, characterized in that: The additives also include fluoroethylene carbonate, succinate, 1,3,6-hexanetrionitrile, and vinyl sulfate; the fluoroethylene carbonate accounts for 2-6% of the total mass of the non-aqueous electrolyte, the succinate accounts for 1-3% of the total mass of the non-aqueous electrolyte, the 1,3,6-hexanetrionitrile accounts for 2-4% of the total mass of the non-aqueous electrolyte, and the vinyl sulfate accounts for 0.1-1% of the total mass of the non-aqueous electrolyte; The organic solvent further includes diethyl carbonate, ethylene carbonate, propylene carbonate and ethyl propionate; the volume ratio of diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl propionate and the compound represented by Formula 1 is 1:(1-3):(0.5-2):(2-4):(2-4).

14. The non-aqueous electrolyte according to claim 1, characterized in that: The additives also include fluoroethylene carbonate, lithium difluorophosphate, and vinyl sulfate; the fluoroethylene carbonate accounts for 0.5-2% of the total mass of the non-aqueous electrolyte, the lithium difluorophosphate accounts for 0.5-2% of the total mass of the non-aqueous electrolyte, and the vinyl sulfate accounts for 0.1-1% of the total mass of the non-aqueous electrolyte. The organic solvent further includes ethylene carbonate and ethyl methyl carbonate; the volume ratio of ethylene carbonate, ethyl methyl carbonate and the compound represented by Formula 1 is 1:(1-2):(0.5-1.5).

15. A lithium battery, characterized in that: Includes the non-aqueous electrolyte according to any one of claims 1 to 14.

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