An electrolyte and a lithium-ion battery containing the electrolyte

Abstract

This invention provides an electrolyte and a lithium-ion battery containing the same. The electrolyte comprises an organic solvent, a lithium salt, and additives, including lithium difluorooxalate borate, propargyl phosphate, and 3-fluoro-1,3-propanesulfonate lactone. The use of lithium difluorooxalate borate, propargyl phosphate, and 3-fluoro-1,3-propanesulfonate lactone as additives enhances the stability of the SEI film on both the positive and negative electrode surfaces, thereby reducing capacity loss at high temperatures.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and specifically to an electrolyte and a lithium-ion battery containing the electrolyte. Background Technology

[0002] With the development of a green, low-carbon, and circular economy, hybrid electric vehicles (HEVs) have become a key focus of automotive research and development due to their energy-saving and low-emission characteristics, and have already been commercialized. The electric power system used in HEVs includes a highly efficient and powerful electric motor, generator, and power-type battery. Lead-acid batteries, currently the mainstream power-type battery, have low energy density, short cycle life, and significant environmental pollution, contradicting the theme of green and low-carbon development. High-power lithium iron phosphate (LFP) batteries not only possess excellent high-current continuous discharge and pulse discharge capabilities, but also feature high specific energy, long cycle life, good safety performance, low cost, and environmental friendliness, and will be widely used in hybrid electric vehicles, aerospace, and military fields in the future. Currently, high-power LFP batteries have significantly improved low-temperature discharge capabilities through the development and application of positive and negative electrode materials, but their operating life is short and performance degrades rapidly at high temperatures.

[0003] The main ways to improve the high-temperature working life of lithium iron phosphate batteries are: (1) Improve the positive electrode / electrolyte interface reaction: suppress the oxidation reaction of the electrolyte on the positive electrode surface by adding electrolyte additives BP (biphenyl) / OTP (ortho-terphenyl); (2) Improve the negative electrode / electrolyte interface reaction: add electrolyte additive VC (ethylene carbonate) to form a low impedance and high thermal stability SEI film on the negative electrode surface; (3) Improve the separator / electrolyte interface reaction: improve the thermal stability of the separator and reduce the shrinkage rate of the separator at high temperature by modifying the separator; (4) Remove impurities in the electrolyte: add a small amount of ethanolamine / hexamethylsilazane to the electrolyte to inhibit the decomposition of lithium salt and improve the stability of the electrolyte.

[0004] CN104269577A discloses an electrolyte and a high-voltage lithium-ion battery, including additives such as fluoroethylene carbonate, dinitrile compounds, 2-methylmaleic anhydride, lithium bis(oxalato)borate, and 1-3-propanesulfonic acid lactone, which can enable the battery to have good cycle performance and storage performance.

[0005] CN111048831A discloses an electrolyte for secondary batteries and a lithium secondary battery containing the electrolyte. The electrolyte includes a difluorophosphite polycyclic compound and compounds such as sulfonyl lactone, which are used to improve the high-rate charge-discharge performance and lifespan performance of the electrolyte under high-temperature storage.

[0006] The aforementioned patents all improve the cycle performance and high-temperature operating life of the electrolyte. However, CN104269577A and CN111048831A require further improvement in the stability of the battery SEI film, and the battery's low-temperature performance is relatively poor.

[0007] Therefore, how to prepare an electrolyte with excellent high and low temperature cycling performance and storage performance is an important research direction in this field. Summary of the Invention

[0008] The purpose of this invention is to provide an electrolyte and a lithium-ion battery containing the electrolyte.

[0009] To achieve this objective, the present invention employs the following technical solution:

[0010] One objective of this invention is to provide an electrolyte comprising an organic solvent, a lithium salt, and additives, wherein the additives include lithium difluorooxalate borate, triargyl phosphate, and 3-fluoro-1,3-propanesulfonate lactone.

[0011] The present invention selects lithium difluorooxalate borate, propyltriethynyl phosphate and 3-fluoro-1,3-propanesulfonate lactone as additives, which can enhance the stability of the SEI film on the positive electrode surface and the SEI film on the negative electrode surface, thereby reducing the capacity loss of the battery at high temperature.

[0012] As a preferred embodiment of the present invention, the mass ratio of lithium difluorooxalate borate, propargyl phosphate, and 3-fluoro-1,3-propanesulfonate lactone is (0.2-0.5):(0.8-1.0):(0.3-0.6). The mass ratio can be 0.2:0.8:0.3, 0.2:0.8:0.3, 0.2:0.8:0.3, 0.2:0.8:0.3, 0.5:0.8:0.3, 0.5:1.0:0.3, 0.5:1.0:0.6, or 0.5:0.8:0.5, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0013] Preferably, the additive further includes any one or a combination of at least two of vinylene carbonate, ethylene carbonate, and fluoroethylene carbonate, wherein typical but non-limiting examples of the combination include: a combination of vinylene carbonate and ethylene carbonate, a combination of ethylene carbonate and fluoroethylene carbonate, or a combination of vinylene carbonate and fluoroethylene carbonate.

[0014] Preferably, the mass ratio of vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, propargyl phosphate, and 3-fluoro-1,3-propanesulfonate lactone is (0.5–1.5):(0.2–0.5):(0.3–0.6):(0.2–0.5):(0.8–1.0):(0.3–0.6), wherein the mass ratio can be 0.5:0.2:0.3:0.2:0.8:0.3, 1.5:0.2:0.3:0.2:0.8: 0.3, 1.5:0.5:0.3:0.2:0.8:0.3, 1.5:0.5:0.6:0.2:0.8:0.3, 1.5:0.5:0.6:0.5:0.8:0.3, 1.5:0.5:0.6:0.5:1.0:0.3, 1.5:0.5:0.6:0.5:1.0:0.6, or 1:0.3:0.5:0.5:0.8:0.5, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0015] As a preferred embodiment of the present invention, the organic solvent includes ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl formate.

[0016] Preferably, the mass ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl formate is (5-7):1:(5-7):(5-7):1, wherein the mass ratio can be any one or a combination of at least two of the following: 5:1:5:5:1, 5:1:5:7:1, 5:1:7:7:1, 6:1:5:5:1, 6:1:5:7:1, 6:1:7:7:1, 7:1:5:5:1, 7:1:5:7:1, or 7:1:7:7:1.

[0017] This invention selects ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl formate as organic solvents for the electrolyte, which reduces the oxidation reaction between the electrolyte solvent and the positive electrode. The co-solvent is not easily vaporized at high temperatures, thereby improving the high-temperature performance of the battery and reducing cell expansion at high temperatures.

[0018] As a preferred embodiment of the present invention, the lithium salt includes lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate.

[0019] This invention selects lithium hexafluorophosphate, which has good electrochemical stability, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate, which have strong thermal stability, as solutes. The mixed lithium salt has better stability at high temperatures, thereby improving the ionic conductivity of the electrolyte and its electrochemical performance at both high and low temperatures.

[0020] Preferably, the mass ratio of lithium hexafluorophosphate, lithium difluorosulfonylimide, and lithium tetrafluoroborate is (7.5–8.5):(1.5–2.5):(0.5–1.5), wherein the mass ratio can be 7.5:1.5:0.5, 7.5:1.5:1.5, 8:1.5:0.5, 8:1.5:1.5, 8.5:1.5:0.5, 8.5:1.5:1.5, or 8.5:1.5:1.5. Any one or a combination of at least two of the following: 7.5:1:0.5, 7.5:1:1.5, 8:1:0.5, 8:1:1.5, 8.5:1:0.5, 8.5:1:1.5, 7.5:2.5:0.5, 7.5:2.5:1.5, 8:2.5:0.5, 8:2.5:1.5, 8.5:2.5:0.5, or 8.5:2.5:1.5.

[0021] Preferably, the concentration of the lithium salt in the electrolyte is 1 to 2 mol / L, wherein the concentration can be 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, or 2 mol / L, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 1.2 to 1.5 mol / L.

[0022] As a preferred embodiment of the present invention, the organic solvent accounts for 75-89% of the electrolyte by mass fraction. The mass fraction can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, or 89%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the lithium salt accounts for 10-20% of the mass fraction of the electrolyte, wherein the mass fraction can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0024] Preferably, the additive accounts for 1.0% to 5.0% of the mass fraction of the electrolyte, wherein the mass fraction can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0025] A second objective of the present invention is to provide a lithium-ion battery comprising the electrolyte as described in one objective.

[0026] The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the electrolyte.

[0027] As a preferred technical solution of the present invention, the positive electrode sheet includes a small-particle-size cation-doped carbon-coated lithium iron phosphate positive electrode material and a positive electrode current collector.

[0028] Preferably, the positive current collector comprises aluminum foil or carbon-coated aluminum foil.

[0029] In this invention, the D50 of the small-particle-size cation-doped carbon-coated lithium iron phosphate cathode material is 3–6 μm.

[0030] As a preferred embodiment of the present invention, the positive electrode material includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0031] Preferably, the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is (90-96):(2-5):(2-5), wherein the mass ratio can be 90:5:5, 91:4:5, 91:5:4, 92:5:3, 92:4:4, 92:3:5, 93:5:2, 93:4:3, 93:3:4, 93:2:5, 94:3:4, 94:4:3, 95:2:3, 95:3:2, or 96:2:2, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0032] As a preferred technical solution of the present invention, the negative electrode sheet includes a small-particle-size pre-lithiated porous carbon-coated negative electrode material and a negative electrode current collector.

[0033] Preferably, the negative electrode current collector comprises copper foil.

[0034] In this invention, the D50 of the small-particle-size pre-lithiated porous carbon-coated anode material is 3–6 μm.

[0035] As a preferred embodiment of the present invention, the negative electrode material includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0036] Preferably, the negative electrode active material includes any one or a combination of at least two of artificial graphite, natural graphite, silicon oxide, silicon carbon, soft carbon, hard carbon, or lithium titanate. Typical but non-limiting examples of such combinations include: combinations of artificial graphite and natural graphite, combinations of natural graphite and silicon oxide, combinations of silicon oxide and silicon carbon, combinations of silicon carbon and soft carbon, combinations of soft carbon and hard carbon, or combinations of hard carbon and lithium titanate.

[0037] Preferably, the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder is (90-96):(2-7):(2-7), wherein the mass ratio can be 90:3:7, 91:3:6, 92:3:5, 93:3:4, 94:3:3, 95:3:2, 92:4:4, 93:4:3, 94:4:2, 96:2:2, or 91:7:2, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0038] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The battery prepared with the electrolyte of this invention has excellent high and low temperature discharge performance. The capacity retention rate can reach more than 84.85% at -30℃ & 5C, the self-discharge can reach less than 9.73% at 60℃ & 30D, and the irreversible capacity loss can reach less than 7.44% at 60℃ & 30D. Attached Figure Description

[0041] Figure 1 The present invention presents the -30℃ / 5C discharge curves of Examples 1, 4-5 and Comparative Examples 1-4.

[0042] Figure 2 The present invention uses the 45℃ & 3C / 3C cycle curves from Examples 1, 4-5 and Comparative Examples 1-4. Detailed Implementation

[0043] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0044] Example 1

[0045] This embodiment provides an electrolyte for improving the high-temperature performance of high-power lithium iron phosphate batteries:

[0046] With the electrolyte mass fraction as 100%, the components in the electrolyte are expressed as mass fractions:

[0047] Lithium salts: lithium hexafluorophosphate 13.51%, lithium bis(fluorosulfonyl)imide 3.33%, lithium tetrafluoroborate 1.65%;

[0048] Organic solvents: ethylene carbonate 23.37%, propylene carbonate 3.90%, dimethyl carbonate 23.37%, ethyl methyl carbonate 23.37%, methyl formate 3.90%;

[0049] Additives: 1.0% vinylene carbonate, 0.3% ethylene ethylene carbonate, 0.5% fluoroethylene carbonate, 0.5% lithium difluorooxalate borate, 0.8% propyltriethynyl phosphate, and 0.5% 3-fluoro-1,3-propanesulfonate lactone.

[0050] Example 2

[0051] This embodiment provides an electrolyte for improving the high-temperature performance of high-power lithium iron phosphate batteries:

[0052] With the electrolyte mass fraction as 100%, the components in the electrolyte are expressed as mass fractions:

[0053] Lithium salts: 15% lithium hexafluorophosphate, 3% lithium difluorosulfonylimide, 2% lithium tetrafluoroborate;

[0054] Organic solvents: ethylene carbonate 22.06%, propylene carbonate 4.41%, dimethyl carbonate 22.06%, ethyl methyl carbonate 22.06%, methyl formate 4.41%;

[0055] Additives: 0.86% vinylene carbonate, 0.85% ethylene ethylene carbonate, 0.52% fluoroethylene carbonate, 0.85% lithium difluorooxalate borate, 1.38% propyltriethynyl phosphate, and 0.54% 3-fluoro-1,3-propanesulfonate lactone.

[0056] Example 3

[0057] This embodiment provides an electrolyte for improving the high-temperature performance of high-power lithium iron phosphate batteries:

[0058] With the electrolyte mass fraction as 100%, the components in the electrolyte are expressed as mass fractions:

[0059] Lithium salts: 8% lithium hexafluorophosphate, 1.5% lithium difluorosulfonylimide, and 0.5% lithium tetrafluoroborate;

[0060] Organic solvents: ethylene carbonate 27.02%, propylene carbonate 3.97%, dimethyl carbonate 27.02%, ethyl methyl carbonate 27.02%, methyl formate 3.97%;

[0061] Additives: 0.39% vinylene carbonate, 0.053% ethylene ethylene carbonate, 0.157% fluoroethylene carbonate, 0.053% lithium difluorooxalate borate, 0.26% propargyl phosphate, and 0.087% 3-fluoro-1,3-propanesulfonate lactone.

[0062] Example 4

[0063] This embodiment provides an electrolyte for improving the high-temperature performance of high-power lithium iron phosphate batteries:

[0064] With the electrolyte mass fraction as 100%, the components in the electrolyte are expressed as mass fractions:

[0065] Lithium salts: lithium hexafluorophosphate 10.80%, lithium difluorosulfonyl imide 4.98%, lithium tetrafluoroborate 2.48%;

[0066] Organic solvents: ethylene carbonate 23.44%, propylene carbonate 3.91%, dimethyl carbonate 23.44%, ethyl methyl carbonate 23.44%, methyl formate 3.91%;

[0067] Additives: 0.8% vinylene carbonate, 0.5% ethylene ethylene carbonate, 0.3% fluoroethylene carbonate, 0.8% lithium difluorooxalate borate, 0.7% propyltriethynyl phosphate, and 0.5% 3-fluoro-1,3-propanesulfonate lactone.

[0068] Example 5

[0069] This embodiment provides an electrolyte for improving the high-temperature performance of high-power lithium iron phosphate batteries:

[0070] With the electrolyte mass fraction as 100%, the components in the electrolyte are expressed as mass fractions:

[0071] Lithium salts: lithium hexafluorophosphate 16.21%, lithium difluorosulfonyl imide 1.66%, lithium tetrafluoroborate 0.84%;

[0072] Organic solvents: ethylene carbonate 23.31%, propylene carbonate 3.88%, dimethyl carbonate 23.31%, ethyl methyl carbonate 23.31%, methyl formate 3.88%;

[0073] Additives: 1.2% vinylene carbonate, 0.5% ethylene ethylene carbonate, 0.8% fluoroethylene carbonate, 0.5% lithium difluorooxalate borate, 0.3% propyltriethynyl phosphate, and 0.3% 3-fluoro-1,3-propanesulfonate lactone.

[0074] Example 6

[0075] In this embodiment, all conditions are the same as in Example 1, except that 1.0% ethylene carbonate is not added and 0.3% ethylene carbonate is replaced with 1.3% ethylene carbonate.

[0076] Example 7

[0077] In this embodiment, all conditions are the same as in Example 1, except that 0.3% ethylene carbonate is not added and 1.0% ethylene carbonate is replaced with 1.3% ethylene carbonate.

[0078] Example 8

[0079] In this embodiment, all conditions are the same as in Example 1, except that 0.5% fluoroethylene carbonate is not added and 1.0% vinylene carbonate is replaced with 1.5% vinylene carbonate.

[0080] Example 9

[0081] In this embodiment, all conditions are the same as in Example 1, except that 1.0% of vinylene carbonate, 0.3% of ethylene carbonate, and 0.5% of fluoroethylene carbonate are not added, and 0.5% of lithium difluorooxalate borate, 0.8% of triargyl phosphate, and 0.5% of 3-fluoro-1,3-propanesulfonate lactone are replaced with 1.0% of lithium difluorooxalate borate, 1.6% of triargyl phosphate, and 1.0% of 3-fluoro-1,3-propanesulfonate lactone.

[0082] Comparative Example 1

[0083] This comparative example provides an electrolyte:

[0084] With the electrolyte mass fraction as 100%, the components in the electrolyte are expressed as mass fractions:

[0085] Lithium salts: lithium hexafluorophosphate 13.51%, lithium bis(fluorosulfonyl)imide 3.33%, lithium tetrafluoroborate 1.65%;

[0086] Organic solvents: ethylene carbonate 23.37%, propylene carbonate 3.90%, dimethyl carbonate 23.37%, ethyl methyl carbonate 23.37%, methyl formate 3.90%;

[0087] Additives: 1.0% vinylene carbonate, 0.5% ethylene ethylene carbonate, 0.5% fluoroethylene carbonate, 0.8% lithium difluorooxalate borate, and 0.8% triargyl phosphate.

[0088] Comparative Example 2

[0089] This comparative example provides an electrolyte:

[0090] With the electrolyte mass fraction as 100%, the components in the electrolyte are expressed as mass fractions:

[0091] Lithium salts: lithium hexafluorophosphate 13.51%, lithium bis(fluorosulfonyl)imide 3.33%, lithium tetrafluoroborate 1.65%;

[0092] Organic solvents: ethylene carbonate 23.37%, propylene carbonate 3.90%, dimethyl carbonate 23.37%, ethyl methyl carbonate 23.37%, methyl formate 3.90%;

[0093] Additives: 1.0% vinylene carbonate, 0.5% ethylene ethylene carbonate, 0.5% fluoroethylene carbonate, 0.8% lithium difluorooxalate borate, and 0.8% 3-fluoro-1,3-propanesulfonate lactone.

[0094] Comparative Example 3

[0095] This comparative example provides an electrolyte:

[0096] With the electrolyte mass fraction as 100%, the components in the electrolyte are expressed as mass fractions:

[0097] Lithium salts: lithium hexafluorophosphate 13.51%, lithium bis(fluorosulfonyl)imide 3.33%, lithium tetrafluoroborate 1.65%;

[0098] Organic solvents: ethylene carbonate 23.37%, propylene carbonate 3.90%, dimethyl carbonate 23.37%, ethyl methyl carbonate 23.37%, methyl formate 3.90%;

[0099] Additives: 1.0% vinylene carbonate, 0.5% ethylene ethylene carbonate, 0.5% fluoroethylene carbonate, 0.8% propyltriethoxylate, and 0.8% 3-fluoro-1,3-propanesulfonate lactone.

[0100] Comparative Example 4

[0101] This comparative example provides an electrolyte:

[0102] With the electrolyte mass fraction as 100%, the components in the electrolyte are expressed as mass fractions:

[0103] Lithium salts: lithium hexafluorophosphate 13.51%, lithium bis(fluorosulfonyl)imide 3.33%, lithium tetrafluoroborate 1.65%;

[0104] Organic solvents: ethylene carbonate 23.37%, propylene carbonate 3.90%, dimethyl carbonate 23.37%, ethyl methyl carbonate 23.37%, methyl formate 3.90%;

[0105] Additives: 1.8% vinylene carbonate, 0.8% ethylene ethylene carbonate, and 1.0% fluoroethylene carbonate.

[0106] Comparative Example 5

[0107] The conditions in this comparative example are the same as in Example 1, except that 3-fluoro-1,3-propanesulfonate lactone is replaced with 1,3-propenylsulfonate lactone.

[0108] The electrolytes from Examples 1-9 and Comparative Examples 1-5 were used to prepare soft-pack lithium-ion batteries using a pouch stacking process. Lithium iron phosphate positive electrode sheets, graphite negative electrode sheets, and PE+OBS separators were stacked, assembled, and baked until the moisture content was within acceptable limits. The electrolytes from Examples 1-9 and Comparative Examples 1-5 were then injected. After hot-pressing formation, high-temperature settling, and encapsulation, the batteries were capacity-graded and then settling at room temperature to obtain the finished batteries. The above lithium iron phosphate batteries were subjected to low-temperature discharge tests, high-temperature storage tests, and cycle tests. The test results are shown in Table 1.

[0109] The low-temperature discharge test was conducted as follows: Examples 1-9 and Comparative Examples 1-5 were calibrated at 25°C using a 1C cycle to obtain capacity C1. The SOC was adjusted to 100%, and the batteries were then placed at -30°C for 8 hours before being discharged at 5C to obtain discharge capacity C2. The test was then completed, and the capacity retention rate was calculated as C2 / C1. The test results are shown in Table 1 and... Figure 1 ( Figure 1 (Test diagrams corresponding to Examples 1, 4-5, and Comparative Examples 1-4).

[0110] The high-temperature cycling test was conducted as follows: Examples 1-9 and Comparative Examples 1-5 were calibrated at 25°C using a 1C cycle with a capacity of C1. The SOC was adjusted to 100%. After the batteries were placed at 60°C for 30 days, they were discharged at 25°C using a 1C cycle to obtain the discharge capacity C3. After 10 cycles, the discharge capacity of the last three cycles was taken as C4, and the test was terminated. Self-discharge = 1 - C3 / C1, irreversible capacity loss = 1 - C4 / C1. The test results are shown in Table 1.

[0111] The high-temperature cycling test was conducted as follows: Examples 1, 4-5, and Comparative Examples 1-4 were calibrated at 25°C using a 1C cycle, followed by a 4-hour rest at 45°C. Then, they were charged and discharged at 3C / 3C, with a charge / discharge voltage range of 2.5V to 3.7V. The test was then completed, and the results are shown below. Figure 2 .

[0112] Table 1

[0113]

[0114]

[0115] The results above show that, compared with Comparative Examples 1-5, the batteries in Examples 1-3 exhibit better capacity retention at -30℃ and 5C discharge, all exceeding 82%, demonstrating superior low-temperature discharge performance. Furthermore, the self-discharge and irreversible capacity loss of Examples 1-3 after being charged to 100% SOC and stored at 60℃ for 30 days are lower than those in Comparative Examples 1-5, indicating good high-temperature storage performance. Example 1 achieves over 3000 cycles at 45℃ & 3C / 3C to EOL (80% capacity retention), demonstrating excellent high-temperature, high-rate cycling performance.

[0116] Compared with Examples 1-3, Examples 4-5 have adjusted the content of each component, which is outside the scope of this invention, and all electrochemical performances of the battery have decreased.

[0117] Compared with Examples 6-9, the performance of Example 1 is higher than that of Examples 6-9, indicating that the addition of lithium salt, additives and organic solvents within the preferred range has better performance. Furthermore, the battery performance is optimal when six additives are present together: vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, triargyl phosphate, and 3-fluoro-1,3-propanesulfonate lactone.

[0118] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An electrolyte, characterized by, The electrolyte comprises an organic solvent, a lithium salt, and additives, the additives including vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, triargyl phosphate, and 3-fluoro-1,3-propanesulfonate lactone. The mass ratio of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, lithium difluorooxalate borate, triargyl phosphate, and 3-fluoro-1,3-propanesulfonate lactone is (0.5~1.5):(0.2~0.5):(0.3~0.6):(0.2~0.5):(0.8~1.0):(0.3~0.6). The additive accounts for 1.0 to 5.0% of the mass fraction of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, The organic solvents include ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl formate.

3. The electrolyte according to claim 2, characterized in that, The mass ratio of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate and methyl formate is (5~7):1:(5~7):(5~7):

1.

4. The electrolyte according to claim 1, characterized in that, The lithium salts include lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate.

5. The electrolyte according to claim 4, characterized in that, The mass ratio of lithium hexafluorophosphate, lithium difluorosulfonyl imide, and lithium tetrafluoroborate is (7.5~8.5):(1.5~2.5):(0.5~1.5).

6. The electrolyte according to claim 1, characterized in that, The concentration of the lithium salt in the electrolyte is 1~2 mol / L.

7. The electrolyte according to claim 1, characterized in that, The concentration of the lithium salt in the electrolyte is 1.2~1.5 mol / L.

8. The electrolyte according to claim 1, characterized in that, The organic solvent accounts for 75-89% of the electrolyte by mass fraction.

9. The electrolyte according to claim 1, characterized in that, The lithium salt accounts for 10-20% of the electrolyte by mass fraction.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte as described in any one of claims 1-9; The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and the electrolyte.

11. The lithium-ion battery according to claim 10, characterized in that, The positive electrode includes a small-particle-size cation-doped carbon-coated lithium iron phosphate positive electrode material and a positive electrode current collector.

12. The lithium-ion battery according to claim 11, characterized in that, The positive current collector includes aluminum foil or carbon-coated aluminum foil.

13. The lithium-ion battery according to claim 11, characterized in that, The positive electrode material includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

14. The lithium-ion battery according to claim 13, characterized in that, The mass ratio of the positive electrode active material, the positive electrode conductive agent and the positive electrode binder is (90~96):(2~5):(2~5).

15. The lithium-ion battery according to claim 10, characterized in that, The negative electrode sheet includes a small-particle-size pre-lithiated porous carbon-coated negative electrode material and a negative electrode current collector.

16. The lithium-ion battery according to claim 15, characterized in that, The negative electrode current collector includes copper foil.

17. The lithium-ion battery according to claim 15, characterized in that, The negative electrode material includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

18. The lithium-ion battery according to claim 17, characterized in that, The negative electrode active material includes any one or a combination of at least two of the following: artificial graphite, natural graphite, silicon oxide, silicon carbon, soft carbon, hard carbon, or lithium titanate.

19. The lithium-ion battery according to claim 17, characterized in that, The mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder is (90~96):(2~7):(2~7).

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