Electrolyte solution and battery

Abstract

Electrolyte solution comprising a first lithium salt, a second lithium salt and a first additive, wherein the first lithium salt comprises at least lithium bis(fluorosulfonyl)imide and the second lithium salt is selected from the group consisting of lithium difluoro(oxalato)borate, lithium difluorobis(oxalato)phosphate and a combination thereof; and the first additive is methylenemethanedisulfonate.

Description

[0001] The present application claims priority over Chinese patent application No. 202310932718.3, filed with the Chinese Patent Office on July 27, 2023, entitled “ELECTROLYTIC SOLUTION AND BATTERY”, which is incorporated in full by reference into this document. TECHNICAL AREA

[0002] The present application relates to an electrolyte solution and a battery and concerns the technical field of batteries. BACKGROUND

[0003] With the wide range of applications for batteries in new energy vehicles, electronic devices, and other fields, improving battery performance has also received considerable attention. As one of the key components of batteries, electrolyte solutions play a crucial role in battery performance. Electrolyte solutions primarily consist of organic solvents and lithium salts dissolved in organic solvents. Lithium hexafluorophosphate (LiPF6) is currently the most widely used lithium salt for electrolyte solutions due to its high conductivity and safety. However, lithium bis(fluorosulfonyl)imide (LiFSI) offers advantages over LiPF6 in terms of solubility, ionic conductivity, and temperature stability. Nevertheless, FSI -LiFSI anions are susceptible to degradation during manufacturing and purification, leading to impurities. Furthermore, removing these impurities is difficult and expensive. In addition, trace amounts of impurities corrode the current collector at high voltage, limiting its use in batteries.

[0004] Adding additives such as lithium difluoro(oxalato)borate (LiODFB) and lithium difluorobis(oxalato)phosphate (LiODFP) to the electrolyte solution helps prevent current collector corrosion by LiFSI, form a low-impedance solid electrolyte interphase (SEI) film, and improve cycle stability and high-temperature storage performance of the battery. However, the oxidation resistance of these additives is insufficient at high potential, which affects the battery's cycle life and high-temperature storage performance at high voltage. SUMMARY

[0005] The present application provides an electrolyte solution to improve the cycle performance and high-temperature storage performance of a battery at high voltage.

[0006] The present application also provides a battery containing the electrolyte solution.

[0007] A first aspect of the present application provides an electrolyte solution comprising a first lithium salt, a second lithium salt, and a first additive, wherein the first lithium salt comprises at least lithium bis(fluorosulfonyl)imide, the second lithium salt is selected from the group consisting of lithium difluoro(oxalato)borate, lithium difluorobis(oxalato)phosphate, and a combination thereof; and The first additive is methylenemethanedisulfonate.

[0008] In one possible embodiment, the molarity of the first lithium salt in the electrolyte solution is in the range of 0.3 mol / l to 2 mol / l.

[0009] In one possible embodiment, the first lithium salt further comprises lithium hexafluorophosphate.

[0010] In one possible embodiment, the molar ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is (0.2-1): 1.

[0011] In one possible embodiment, the mass of the second lithium salt is in the range of 0.1% to 3% of the total mass of the electrolyte solution.

[0012] In one possible embodiment, the second lithium salt comprises lithium difluoro(oxalato)borate and lithium difluorobis(oxalato)phosphate.

[0013] In one possible embodiment, the mass ratio of lithium difluorobis(oxalato)phosphate to lithium difluoro(oxalato)borate is 1:(0.2-4).

[0014] In one possible embodiment, the mass of the first additive is in the range of 0.1% to 10% of the total mass of the electrolyte solution.

[0015] In one possible embodiment, the electrolyte solution further comprises a second additive selected from at least one of vinylene carbonate, vinylethylene carbonate, ethylene sulfate, propylene carbonate, fluoroethylene carbonate, 1,3-propanesultone, prop-1-ene-1,3-sultone, 1,4-butanesultone, succinic anhydride, maleic anhydride, 2-methylmaleic anhydride, methylprop-2-ynyl carbonate, tetravinylsilane, triallyl isocyanurate, hexamethylene diisocyanate, o-phenanthroline, 1,4-phenylene diisocyanate, toluene-2,4-diisocyanate, N-phenylbis(trifluoromethanesulfonimide), 4,4'-Bi-1,3,2-dioxathiolane-2,2,2'2'-tetraoxide, phenylmethanesulfonate, 2,4,8,10-tetraoxa-3,9-dithiaspiro[5.5]undecane-3,3,9,9-tetraoxide, hydroquinone bisfluorosulfate, triallyl phosphate, tripropargyl phosphate, 2,4-butanesultone, 2-isocyanatoethyl methacrylate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris[ethenyl(dimethyl)silyl]phosphate, 4,4'-Bi-1,3-dioxolane-2,2'-dione, propyldiprop-2-ynyl phosphate, ethyldiprop-2-ynyl phosphate, (2-allylphenoxy)trimethylsilane, tetramethylmethylene diphosphonate or 2-fluoropyridine.

[0016] In one possible embodiment, the mass of the second additive is in the range of 0.1% to 5% of the total mass of the electrolyte solution.

[0017] A second aspect of the present application provides a battery that includes any of the electrolyte solutions as described above.

[0018] The electrolyte solution provided by the present application comprises the first lithium salt and the second lithium salt, and further includes the first additive of methylenemethanedisulfonate (NINMS). The second lithium salt helps to improve the cycle stability and high-temperature storage performance of the battery and, in combination with the first additive, improves the oxidation resistance of the second lithium salt at high voltage and further modifies the composition and structure of the SEI film, thereby reducing the impedance of the SEI film, improving the stability of the SEI film and improving the cycle performance and high-temperature storage performance of the battery. DETAILED DESCRIPTION

[0019] To clarify the purpose, technical solution, and advantages of the present application, the technical solution in the embodiments of the present application is described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, but not the entirety of them. Based on the embodiments in the present application, all other embodiments that the person skilled in the art can implement without creative effort are within the scope of protection of the present application.

[0020] Electrolyte solutions mainly contain organic solvents and lithium salts dissolved in organic solvents. LiFSI has advantages in terms of solubility, ionic conductivity, temperature stability, etc. However, FSI -LiFSI anions are susceptible to degradation during manufacturing and purification, leading to impurities. Furthermore, removing these impurities is difficult and costly. Trace amounts of impurities also corrode the current collector at high voltage, limiting its use in batteries. Adding additives such as LiODFB and LiODFP to the electrolyte solution is beneficial in preventing current collector corrosion by LiFSI; however, these additives have insufficient oxidation resistance at high potential, impacting the battery's cycle life and high-temperature storage performance at high voltage.

[0021] To solve the aforementioned technical problem, the first aspect of the present application provides an electrolyte solution comprising a first lithium salt of lithium bis(fluorosulfonyl)imide and a second lithium salt with an inhibitory effect, and further comprising a first additive of MMDS. The second lithium salt helps to improve the cycle stability and high-temperature storage performance of the battery and, in combination with the first additive, improves the oxidation resistance of the second lithium salt at high voltage and further modifies the composition and structure of the SEI film, thereby reducing the impedance of the SEI film, improving the stability of the SEI film and improving the cycle performance and high-temperature storage performance of the battery.

[0022] In a specific embodiment, the molarity of the first lithium salt in the electrolyte solution is in the range of 0.3 mol / l to 2 mol / l, i.e., each liter of the electrolyte solution contains 0.3–2 mol of the first lithium salt. In particular, the molarity of the first lithium salt in the electrolyte solution can be selected from the group consisting of 0.3 mol / l, 0.5 mol / l, 1.0 mol / l, 1.3 mol / l, 1.5 mol / l, 1.8 mol / l, 2.0 mol / l, and any ranges in between.

[0023] Furthermore, the molarity of the first lithium salt in the electrolyte solution ranges from 0.3 mol / l to 1.5 mol / l. Additionally, the molarity of the first lithium salt in the electrolyte solution ranges from 0.3 mol / l to 1.2 mol / l.

[0024] In a specific embodiment, the first lithium salt further comprises LiPF6. As a lithium salt commonly used in the industry, mixing LiPF6 with LiFSI is helpful to improve the overall performance of a battery and reduce production costs.

[0025] If the first lithium salt contains LiPF6 and LiFSI, the molar ratio of LiPF6 to LiFSI is 1:(0.2-1). Furthermore, the molar ratio of LiPF6 to LiFSI is 1:0.5. An insufficient amount of LiFSI negatively impacts the battery's cycle life and high-temperature storage performance, while an excessive amount of LiFSI has a limited effect on improving battery performance and increases battery production costs.

[0026] In a specific embodiment, the second lithium salt is selected from the group consisting of LiODFB, LiODFP, and a combination thereof, and the mass of the second lithium salt is in the range of 0.1% to 3% of the total mass of the electrolyte solution, i.e., each gram of the electrolyte solution contains 0.1 g to 3 g of the second lithium salt. In particular, the mass of the second lithium salt can be selected from the group consisting of 0.1%, 0.5%, 1.0%, 1.1%, 1.5%, 2.0%, 2.1%, 2.5%, 3.0%, and any ranges in between.

[0027] Furthermore, the mass of the second lithium salt is in the range of 0.2% to 2% of the total mass of the electrolyte solution. In addition, the mass of the second lithium salt is in the range of 0.2% to 1.5% of the total mass of the electrolyte solution.

[0028] Furthermore, the second lithium salt contains both LiODFB and LiODFP, and the synergistic effect of LiODFP and LiODFB is helpful in further improving the high-temperature storage performance and cycle performance of the battery.

[0029] Furthermore, if the second lithium salt contains LiODFB and LiODFP, the mass ratio of LiODFP to LiODFB is 1:(0.2-4). Additionally, the mass ratio of LiODFP to LiODFB is 1:(0.5-2). Furthermore, the mass ratio of LiODFP to LiODFB is 1:1.

[0030] In a specific embodiment, the mass of the first additive is in the range of 0.1% to 10% of the total mass of the electrolyte solution; that is, each gram of the electrolyte solution contains 0.1%–10% of MMDS. In particular, the mass of the first additive can be selected from the group consisting of 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, and any ranges in between.

[0031] Furthermore, the mass of the first additive is in the range of 0.1% to 5% of the total mass of the electrolyte solution. Furthermore, the mass of the first additive is in the range of 0.1% to 3% of the total mass of the electrolyte solution. In addition, the mass of the first additive is in the range of 0.1% to 2% of the total mass of the electrolyte solution.

[0032] Furthermore, according to conventional technical means, a second additive can be added to the electrolyte solution to optimize the overall performance of the battery. In a specific embodiment, the second additive is selected from at least one of vinylene carbonate, vinylethylene carbonate, ethylene sulfate, propylene carbonate, fluoroethylene carbonate, 1,3-propanesultone, prop-1-ene-1,3-sultone, 1,4-butanesultone, succinic anhydride, maleic anhydride, 2-methylmaleic anhydride, methylprop-2-ynyl carbonate, tetravinylsilane, triallyl isocyanurate, hexamethylene diisocyanate, o-phenanthroline, 1,4-phenylene diisocyanate, toluene-2,4-diisocyanate, N-phenylbis(trifluoromethanesulfonimide), 4,4'-Bi-1,3,2-dioxathiolane-2,2,2'2'-tetraoxide, phenylmethanesulfonate, 2,4,8,10-tetraoxa-3,9-dithiaspiro[5.5]undecane-3,3,9,9-tetraoxide, hydroquinone bisfluorosulfate, triallyl phosphate, tripropargyl phosphate, 2,4-butanesultone, 2-isocyanatoethyl methacrylate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris[ethenyl(dimethyl)silyl]phosphate, 4,4'-Bi-1,3-dioxolane-2,2'-dione, propyldiprop-2-ynyl phosphate, ethyldiprop-2-ynyl phosphate, (2-allylphenoxy)trimethylsilane, tetramethylmethylene diphosphonate or 2-fluoropyridine.

[0033] Furthermore, the mass of the second additive lies in the range of 0.1% to 5% of the total mass of the electrolyte solution; that is, each gram of the electrolyte solution contains 0.1%–5% of the second additive. Specifically, the mass of the second additive can be selected from the group consisting of 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, and any ranges in between.

[0034] Furthermore, the mass of the second additive is in the range of 0.1% to 3% of the total mass of the electrolyte solution. In addition, the mass of the second additive is in the range of 0.1% to 2% of the total mass of the electrolyte solution.

[0035] The organic solvent provided in the present application is a material conventionally available in the art, and its composition and content can be selected by a person skilled in the art according to the requirements. In one specific embodiment, the organic solvent comprises one or two cyclic organic solvents and one chain-like organic solvent. The cyclic organic solvent is selected from at least one of propylene carbonate, ethylene carbonate, or butylene carbonate, and the chain-like organic solvent is selected from at least dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl formate, ethyl formate, methyl acetate, and ethyl acetate.

[0036] The second aspect of the present application provides a battery that incorporates any of the electrolyte solutions as described above.

[0037] Based on the electrolyte solution provided in the first aspect of the present application, the battery provided by the present application exhibits good high-temperature storage performance and cycle performance.

[0038] In a specific embodiment, the battery includes, in addition to the electrolyte solution provided in the first aspect of the present application, a positive electrode plate, a negative electrode plate and a separator, specifically: The positive electrode plate includes a positive current collector and a layer of active material for positive electrodes arranged on the surface of the positive current collector. The layer of active material for positive electrodes includes an active material for positive electrodes, a conductive agent, or a binder. The positive current collector generally consists of an aluminum foil, and the active material for positive electrodes is selected from at least one of the transition metal oxides of lithium, for example, LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4 or Li2Mn 1-x O4, is M selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B or F, 0≤a<0.2 and 0≤x<1.

[0039] The negative electrode plate includes a negative current collector and a layer of active material for negative electrodes arranged on the surface of the negative current collector; the layer of active material for negative electrodes includes an active material for negative electrodes, a conductive agent, and a binder; the negative current collector is generally a copper foil; and the active material for negative electrodes is selected from at least one of carbon-containing materials, silicon-carbon materials, alloy materials, or lithium-containing metal composite oxides.

[0040] The selection of the conductive material and the binder in the active material layer for positive electrodes and the active material layer for negative electrodes may involve conventional materials used in engineering.

[0041] The separator is a known technical separator suitable for use in batteries. It is stable with the electrolyte solution used and can specifically comprise at least one of polyolefin, aromatic polyamide, polytetrafluoroethylene, or polyethersulfone. Furthermore, the separator comprises at least one of polyethylene or polypropylene. Additionally, the separator can be obtained by means of multiple stacked layers of material. For example, the separator comprises a polypropylene layer, a polyethylene layer, and another polypropylene layer stacked on top of each other.

[0042] The electrolyte solution provided by the present application is described in detail with specific examples as follows: Example 1

[0043] The electrolyte solution provided by this example comprises an organic solvent, a first lithium salt, a second lithium salt, a first additive, and a second additive, where the organic solvent contains ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:7. The first lithium salt contains 1 mol / L LiPF6 and 0.2 mol / L LiFSI. The second lithium salt contains 0.5% LiODFP and 0.5% LiODFB. The first additive is MMDS, which constitutes 0.5% of the total mass of the electrolyte solution. The second additive is vinylene carbonate, which also constitutes 0.5% of the total mass of the electrolyte solution.

[0044] The manufacturing process of the electrolyte solution provided by this example involves the following: EC and EMC were mixed in a mass ratio of 3:7, and the second lithium salt, the first additive, and the second additive were added in the molar concentration and mass fraction of each component after mixing, and the mixture was blended uniformly to obtain the electrolyte solution.

[0045] The electrolyte solution formulations provided in Examples 2-16 and Comparative Examples 1-5 are essentially the same as in Example 1, and the differences are as follows: The molar concentrations of the first lithium salt used in Examples 2-3 are different; the molar concentrations of the first lithium salts used in Examples 4-5 are different, and the second lithium salt used contains only LiODFP or LiODFB; the concentrations of the first and second lithium salts used in Examples 6-7 are different; the concentrations of the first additive used in Examples 8-10 are different; the mass ratios of the second lithium salts LiODFP and LiODFB in Examples 11-12 are different; Example 13 does not contain the second additive; the concentration of the second additive in Example 14 is different. The types of the second additives in examples 15-16 are different;Comparative example 1 does not contain the second lithium salt and the first additive; and comparative examples 2-5 contain only one of the second lithium salt and the first additive. The specific differences are listed in Table 1. Table 1. Composition of the electrolyte solutions provided in Examples 1-16 and Comparative Examples 1-5 First lithium salt (mol / l) Second lithium salt (wt%) First additive (wt%) Second additive Example 1 1 M LiPF6 + 0.2 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,5 0.5% vinyl carbonate Example 2 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,5 0.5% vinyl carbonate Example 3 0.6 M LiPF6 + 0.6 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,5 0.5% vinyl carbonate Example 4 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP 0,5 0.5% vinyl carbonate Example 5 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFB 0,5 0.5% vinyl carbonate Example 6 0.8 M LiPF6 + 0.4 M LiFSI 0.25% LiODFP + 0.25% LiODFB 0,5 0.5% vinyl carbonate Example 7 0.8 M LiPF6 + 0.4 M LiFSI 0.8% LiODFP + 0.8% LiODFB 0,5 0.5% vinyl carbonate Example 8 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,2 0.5% vinyl carbonate Example 9 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP + 0.5% LiODFB 1 0.5% vinyl carbonate Example 10 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP + 0.5% LiODFB 2 0.5% vinyl carbonate Example 11 0.8 M LiPF6 + 0.4 M LiFSI 0.2% LiODFP + 0.8% LiODFB 0,5 0.5% vinyl carbonate Example 12 0.8 M LiPF6 + 0.4 M LiFSI 0.8% LiODFP + 0.2% LiODFB 0,5 0.5% vinyl carbonate Example 13 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,5 0.5% vinyl carbonate Example 14 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,5 0.5% vinyl carbonate Example 15 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,5 0.5% vinyl carbonate Example 16 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,5 0.5% vinyl carbonate Example 17 1.2 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,5 0.5% vinyl carbonate Example 18 1 M LiPF6 + 0.2 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,05 0.5% vinyl carbonate Example 19 1 M LiPF6 + 0.2 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,5 0.5% vinyl carbonate Example 20 0.2 M LiPF6 + 1 M LiFSI 0.5% LiODFP + 0.5% LiODFB 0,5 0.5% vinyl carbonate Comparative example 1 0.8 M LiPF6 + 0.4 M LiFSI / / 0.5% vinyl carbonate Comparative example 2 0.8 M LiPF6 + 0.4 M LiFSI / 0,5 0.5% vinyl carbonate Comparative example 3 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP / 0.5% vinyl carbonate Comparative example 4 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFB / 0.5% vinyl carbonate Comparative example 5 0.8 M LiPF6 + 0.4 M LiFSI 0.5% LiODFP + 0.5% LiODFB / 0.5% vinyl carbonate

[0046] Lithium-ion batteries were fabricated by matching the electrolyte solutions provided in Examples 1-16 and Comparison Examples 1-5 with positive electrode plates, negative electrode plates, and separators. Specifically, the positive electrode active material lithium nickel cobalt manganate (purchased from Zhenhua E-Chem Inc.), the conductive carbon black, the conductive carbon nanotube, and the binder polyvinylidene fluoride were dispersed in the solvent N-methylpyrrolidone in a mass ratio of 94.5:3.5:0.5:1.5 to obtain the positive electrode active material slurry. The positive electrode active material slurry was uniformly applied to the surface of the aluminum foil of the positive current collector, and the positive electrode plate was obtained after drying, rolling, burning, cutting, and spot welding of tabs.The total thickness of the positive electrode plate was 90 µm.

[0047] The negative active material graphite (acquired from Jiangxi Zichen Technology Co., Ltd.), the conductive agent carbon black, the binder polyvinylidene fluoride, and sodium carboxymethylcellulose were dispersed and uniformly stirred in deionized water in a mass ratio of 94.5:2:2:1.5 to obtain a slurry of active material for the negative electrode layer. This slurry was uniformly applied to the surface of the copper foil of the negative current collector, and the negative electrode plate was obtained after drying, rolling, burning, cutting, and spot welding of tabs. The total thickness of the negative electrode plate was 128 µm.

[0048] The manufactured positive electrode plate, negative electrode plate, and separator were stacked on top of each other. The separator was inserted between the positive and negative electrode plates and then wound to form a battery cell. The battery cell was placed in the outer casing, and the electrolyte solution was injected into the battery cell in a glove box. The manufacturing of the lithium-ion battery was completed after packaging, conditioning, aging, and grading.

[0049] The lithium-ion batteries produced in Examples 1-16 and Comparative Examples 1-5 were tested for normal temperature cycle performance and high temperature performance, and the test procedures were as follows.

[0050] Test procedure for normal temperature cycle performance: The temperature was measured at 25 °C with a constant current of 1 C and a constant voltage of 4.4 V. The battery was left to rest for 5 minutes and then discharged to 2.75 V with a constant current of 1 C. The capacity retention rate was calculated after 500 cycles. The calculation method is: Capacity retention rate (%) = (500 discharge capacity / first discharge capacity) x 100%.

[0051] High-temperature storage performance test procedure: The battery was charged at a constant current of 1C and a constant voltage of 4.4V at 25°C. The initial thickness of the lithium-ion battery at this time was measured. The battery was then stored at 60°C for 15 days, and its thickness was measured again. The battery swelling rate was calculated using the following formula: Swelling rate (%) = (Thickness after storage - initial thickness) / initial thickness x 100%.

[0052] Test procedure for high-temperature cycle performance: The lithium-ion battery, stored at high temperature, was discharged at 1C to 2.75 V, and the battery's capacity retention rate was measured and calculated. The calculation formula is as follows: Capacity retention rate (%) = Retention capacity / Initial capacity x 100%.

[0053] The test results are shown in Table 2. Table 2. Performance test results of lithium-ion batteries produced in Examples 1-16 and Comparison Examples 1-5 Capacity retention rate (%) after 500 cycles at normal temperature Capacity retention rate (%) after 15 days of storage at 60 °C Swelling rate (%) after 15 days of storage at 60 °C Example 1 95,4 91,4 3,5 Example 2 97,2 92,4 3,5 Example 3 97,4 92,8 3,4 Example 4 95,8 90,8 4,0 Example 5 95,5 90,6 4,2 Example 6 96,1 91,3 3,8 Example 7 95,2 91,6 3,5 Example 8 95,5 91,8 3,6 Example 9 96,0 89,1 3,8 Example 10 95,0 88,4 4,0 Example 11 96,5 91,8 3,8 Example 12 96,8 91,9 3,7 Example 13 96,8 92,0 3,6 Example 14 95,8 92,4 3,5 Example 15 95,8 92,4 3,5 Example 16 97,1 91,9 3,5 Example 17 95,0 91,4 3,8 Example 18 94,2 91,1 4,0 Example 19 94,7 91,4 4,1 Example 20 95,1 91,5 3,8 Comparative example 1 87,8 82,4 3,3 Comparative example 2 92,5 88,9 2,7 Comparative example 3 93,1 89,5 4,2 Comparative example 4 93,5 89,6 4,1 Comparative example 5 94,0 90,8 3,9

[0054] According to Table 2, in comparison to Comparison Example 1, the addition of the second lithium salt or the first additive to the electrolyte solution helps to improve the normal-temperature cycle performance of lithium-ion batteries. The effect of adding the second lithium salt is better than that of the first additive; however, the high-temperature performance of lithium-ion batteries containing the second lithium salt is poor. In comparison to Comparison Examples 1-6, the electrolyte solution provided by Examples 1-16 includes both the second lithium salt and the first additive, which helps to improve the normal-temperature cycle performance and high-temperature performance of lithium-ion batteries.

[0055] According to Examples 1-3, provided the total molar concentration of the first lithium salt remains unchanged, the normal-temperature cycle performance and the high-temperature storage performance of the lithium-ion battery are improved by increasing the molar concentration of LiFSI. However, when the molar concentration of LiFSI reaches 0.6 M, the performance improvement of the lithium-ion battery is limited, while the manufacturing costs of the battery increase. For this reason, the molar concentration of LiFSI is preferably 0.4 mol / l. According to Examples 4-6, if the second lithium salt also includes LiODFP, the effect on improving the battery's performance is clearly better than that of adding only a second lithium salt.According to Examples 2 and 6-7, the normal-temperature cycle performance and the high-temperature cycle performance are improved by increasing the content of the second lithium salt; however, if the content exceeds 1.6%, both the normal-temperature cycle performance and the high-temperature performance of the lithium-ion battery are reduced, so the content of the second lithium salt is preferably 1%. According to Examples 2 and 8-10, the normal-temperature cycle performance and the high-temperature storage performance of the lithium-ion battery are improved by increasing the content of the first additive; however, if the content of the first additive reaches 1%, the performance of the lithium-ion battery is reduced, so the content of the first additive is preferably 0.5%.According to Examples 11-12, the normal-temperature cycle performance and the high-temperature storage performance of the battery improve when the mass ratio of the second lithium salts, LiODFP and LiODFB, is 1:1. According to Examples 2 and 13-14, the second additive is helpful in improving the normal-temperature cycle performance of lithium-ion batteries; however, if its content exceeds 2%, it does not contribute to improving the normal-temperature cycle performance of batteries, so the content of the second additive is preferably 0.1%-2% and more preferably 0.5%. According to Examples 15-16, different second additives have different effects on the normal-temperature cycle performance of the battery, with vinylene carbonate exhibiting the best effect.

[0056] Ultimately, it is understood that the foregoing examples are used only to illustrate, but are not limited to, the technical solution of the present application. Although the present application has been described in detail with reference to the foregoing examples, it is understood by the person skilled in the art that the technical solution described in the foregoing examples can be modified, and some or all of the technical features can be replaced by equivalents; however, these modifications or substitutions do not result in the essence of the corresponding technical solutions differing from the scope of the technical solutions of various examples of the present application. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] CN 202310932718.3

[0001]

Claims

[1] Electrolyte solution comprising a first lithium salt, a second lithium salt and a first additive, wherein the first lithium salt includes at least lithium bis(fluorosulfonyl)imide and the second lithium salt is selected from the group consisting of lithium difluoro(oxalato)borate, lithium difluorobis(oxalato)phosphate and a combination thereof; and the first additive is methylenemethanedisulfonate. [2] Electrolyte solution according to claim 1, wherein the molarity of the first lithium salt in the electrolyte solution is in the range of 0.3 mol / l to 2 mol / l. [3] Electrolyte solution according to claim 1 or 2, wherein the first lithium salt further comprises lithium hexafluorophosphate. [4] Electrolyte solution according to claim 3, wherein the molar ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is (0.2-1):

1. [5] Electrolyte solution according to claim 1, wherein the mass of the second lithium salt is in the range of 0.1% to 3% of the total mass of the electrolyte solution. [6] Electrolyte solution according to claim 1 or 5, wherein the second lithium salt further comprises lithium difluoro(oxalato)borate and lithium difluorobis(oxalato)phosphate. [7] Electrolyte solution according to claim 6, wherein the mass ratio of lithium difluorobis(oxalato)phosphate to lithium difluoro(oxalato)borate is 1:(0.2-4). [8] Electrolyte solution according to claim 1, wherein the mass of the first additive is in the range of 0.1% to 10% of the total mass of the electrolyte solution. [9] Electrolyte solution according to claim 1, wherein the electrolyte solution further comprises a second additive selected from one of vinylene carbonate, vinylethylene carbonate, ethylene sulfate, propylene carbonate, fluoroethylene carbonate, 1,3-propanesultone, prop-1-ene-1,3-sultone, 1,4-butanesultone, succinic anhydride, maleic anhydride, 2-methylmaleic anhydride, methylprop-2-ynyl carbonate, tetravinylsilane, triallyl isocyanurate, hexamethylene diisocyanate, o-phenanthroline, 1,4-phenylene diisocyanate, toluene-2,4-diisocyanate, N-phenylbis(trifluoromethanesulfonimide), 4,4'-bi-1,3,2-dioxathiolane-2,2,2'2'-tetraoxide, phenylmethanesulfonate, 2,4,8,10- Tetraoxa-3,9-Dithiaspiro[5.5]undecane-3,3,9,9-tetraoxide, hydroquinone bisfluorosulfate, triallyl phosphate, tripropargyl phosphate, 2,4-butanesultone, 2-isocyanatoethyl methacrylate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris[ethenyl(dimethyl)silyl]phosphate, 4,4'-Bi-1,3-dioxolane-2,2'-dione, propyldiprop-2-ynyl phosphate, ethyldiprop-2-ynyl phosphate, (2-allylphenoxy)trimethylsilane, tetramethylmethylene diphosphonate or 2-fluoropyridine. [10] Electrolyte solution according to claim 9, wherein the mass of the second additive is in the range of 0.1% to 5% of the total mass of the electrolyte solution. [11] Battery comprising the electrolyte solution according to any one of claims 1-10.