Lithium-ion battery electrolyte and lithium ion battery

Abstract

A lithium-ion battery electrolyte and a lithium-ion battery. In order to solve the problem of poor high-temperature performance and normal-temperature cycle performance of a high-voltage NCM system lithium-ion battery, the electrolyte comprises: an organic solvent, a lithium salt, and an additive, wherein the organic solvent comprises a fluorinated carboxylic ester and a carbonate excluding ethylene carbonate, and wherein the additive comprises one or more of an alkynyl carbonate derivative, a dioxane compound, and a cyclic anhydride, and one or more of vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, lithium difluorophosphate, lithium difluoro bis(oxalato) phosphate, and tris(trimethylsilyl) phosphate. The stability of the high-voltage NCM system lithium-ion battery at a high voltage is greatly improved by means of optimizing the combination of a solvent system and an additive, wherein the solvent system has a mixture of a fluorinated carboxylic ester and a carbonate excluding EC, such that the normal-temperature cycle performance, high-temperature cycle performance, high-temperature storage, and other such capabilities of said high-voltage NCM system lithium-ion battery are all improved.

Description

Lithium ion battery electrolyte and lithium ion battery TECHNICAL FIELD

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

[0002] NCM ternary material as a positive material of lithium ion battery has the advantages of high specific capacity, good cycle performance, good safety and small environmental pollution. In order to further meet the demand of people for high energy density, NCM ternary positive material is also developing in two directions: 1) high nickelization, higher Ni content can bring higher capacity; 2) high voltage, the increase of voltage can improve the capacity of the material on the one hand, and can also improve the voltage platform of the material. However, with the increase of charging voltage, the stability of the positive material / electrolyte interface will decrease, which will cause the increase of side reaction and seriously affect the cycle performance of lithium ion battery.

[0003] The electrolyte plays a decisive role in the performance of high-nickel and high-voltage lithium ion batteries. The traditional electrolyte using carbonate as solvent for high-voltage NCM system lithium ion battery has not obtained ideal results, the main reason is that carbonate solvent is catalyzed by transition metal ions in the positive material, which will be oxidized and decomposed at a lower potential (about 4.5V), especially cyclic carbonate EC, which is easy to oxidize and decompose at high temperature and high voltage, resulting in electrolyte loss and battery gas production, thus leading to rapid deterioration of battery performance.

[0004] Therefore, in order to popularize and apply high specific energy system battery, it is necessary to develop electrolyte matched with high-voltage positive material. SUMMARY

[0005] The purpose of the present application is to provide an electrolyte which can improve the room temperature and high temperature cycle performance and high temperature storage performance of high-voltage NCM battery at the same time.

[0006] Another purpose of the present application is to provide a high-voltage lithium ion battery with excellent electrochemical performance, especially excellent room temperature, high temperature cycle and high temperature storage performance.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] The present application provides a kind of lithium ion battery electrolyte, including organic solvent, lithium salt and additive, the organic solvent includes fluorinated carboxylic acid ester and carbonate, the fluorinated carboxylic acid ester includes one or more of 2,2-difluoroethyl acetate, 3,3-difluoropropyl acetate and 2,2-difluoroethyl propionate, the carbonate does not include ethylene carbonate, the additive includes first additive and second additive, the first additive includes one or more of alkyne carbonate derivative, oxane compound, cyclic anhydride, the alkyne carbonate derivative includes one or more of dipropargyl carbonate, di (2-alkynyl butyl) carbonate, di (3-alkynyl butyl) carbonate, di (2-alkynyl pentyl) carbonate, di (1-methyl-2-alkynyl butyl) carbonate and 2-alkynyl propyl-2'-alkynyl butyl carbonate, the oxane compound includes 1,3-dioxane and / or 1,4-dioxane, the cyclic anhydride includes citraconic anhydride and / or maleic anhydride, the second additive includes one or more of vinyl carbonate (VC), fluorinated ethylene carbonate (FEC), vinyl sulfate (DTD), lithium difluorophosphate (LiDFP), lithium difluorodioxalate phosphate (LiDODFP), tris (trimethylsilyl) phosphate (TMSP).

[0009] Further, the carbonate is one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate.

[0010] Further, the mass ratio of the fluorinated carboxylic acid ester and the carbonate is (0.8-1.2):1, for example 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1.

[0011] In some embodiments of the present application, the organic solvent is a mixture of 2,2-difluoroethyl acetate, propylene carbonate and methyl ethyl carbonate in a mass ratio of (2-3):1:(1-2).

[0012] Further preferably, the mass ratio of 2,2-difluoroethyl acetate, propylene carbonate and methyl ethyl carbonate is (2.5-3):1:(1-1.5).

[0013] In some embodiments of the present application, the first additive consists of the alkyne carbonate derivative, the oxane compound and the cyclic anhydride.

[0014] In some embodiments of the present application, the first additive includes two or three of the alkyne carbonate derivative, the oxane compound and the cyclic anhydride.

[0015] Further preferably, the mass ratio of the alkyne carbonate derivative, the oxane compound and the cyclic anhydride is (0.8-1.2):1:(0.8-1.2).

[0016] Still further preferably, the mass ratio of the acetylene carbonate derivative, the oxane compound and the cyclic anhydride is (0.8-1) : 1 : (0.8-1).

[0017] According to some preferred embodiments, the first additive is a combination of dipropargyl carbonate, citraconic anhydride and 1,3-dioxane.

[0018] In some embodiments of the application, the second additive comprises two or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate, tris(trimethylsilyl) phosphate.

[0019] In some embodiments of the application, the second additive comprises three or more of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate, tris(trimethylsilyl) phosphate.

[0020] According to some preferred embodiments, the second additive consists of vinylene carbonate, vinyl sulfate, lithium difluorophosphate and / or lithium difluorodioxalate phosphate.

[0021] Further preferably, the mass ratio of the vinyl sulfate, the vinylene carbonate, the lithium difluorophosphate and / or the lithium difluorodioxalate phosphate is (1.8-2.2) : 1 : (1.8-2.2).

[0022] Still further preferably, the mass ratio of the vinyl sulfate, the vinylene carbonate, the lithium difluorophosphate and / or the lithium difluorodioxalate phosphate is (1.8-2) : 1 : (1.8-2).

[0023] In embodiments of the application, the first additive is present in an amount of 0.5% to 5% by mass of the total electrolyte.

[0024] In embodiments of the application, the first additive is present in an amount of 1% to 5% by mass of the total electrolyte.

[0025] Further preferably, the first additive is present in an amount of 1.5% to 3% by mass of the total electrolyte.

[0026] In embodiments of the application, the second additive is present in an amount of 1% to 15% by mass of the total electrolyte.

[0027] Further preferably, the second additive is present in an amount of 1% to 10% by mass of the total electrolyte.

[0028] Still further preferably, the second additive is present in an amount of 2% to 5% by mass of the total electrolyte.

[0029] In the embodiment of the present application, the lithium salt is lithium hexafluorophosphate.

[0030] In the embodiment of the present application, the molar concentration of the lithium salt in the electrolyte is 0.8M-1.5M.

[0031] Further preferably, the molar concentration of the lithium salt in the electrolyte is 1M-1.5M, for example 1M, 1.1M, 1.2M, 1.3M, 1.4M or 1.5M.

[0032] In theory, the oxidation resistance of ethylene carbonate (EC) is good, which can meet the needs of 5V high-voltage batteries. However, in the actual lithium ion battery system, PF6 - The anion of the electrolyte lithium salt will produce HF or transfer fluorine ions to the solvent molecules in the electrolyte; at the same time, due to the high dielectric constant of EC, it will be complexed with PF6 - , and then quickly reach the positive electrode surface and be preferentially oxidized, which will seriously reduce the oxidation stability of the solvent molecules, so that the oxidation stability of the actual electrolyte system containing PF6 - is lower than the theoretical calculation value. The high melting point (36.4℃) of EC seriously limits the ion transport below 0℃, and causes energy loss and lithium precipitation. The present application improves the electrochemical performance of the electrolyte by optimizing the combination of organic solvents and additives without using EC, that is, avoids the oxidation and decomposition of EC at high temperature and high voltage in the conventional solvent system, improves the stability of the solvent system at high voltage and the poor low temperature effect caused by the high melting point of EC; mainly, after replacing EC with fluorinated carboxylic acid ester and fluorinated carbonate, the electrochemical window is widened, the stability at high temperature and high voltage is improved, and no gas is produced by decomposition; at the same time, under the synergistic action of the high-temperature additive combination (such as dipropargyl carbonate and citraconic anhydride), the interface between the positive electrode and the electrolyte is stabilized, the gas production and internal resistance change of the lithium ion battery are inhibited, so that the normal temperature and high temperature cycle performance of the high-voltage lithium ion battery system is simultaneously considered.

[0033] The present application also provides a high-voltage lithium ion battery comprising the above-mentioned lithium ion electrolyte.

[0034] In the embodiment of the present application, the positive electrode of the high-voltage lithium ion battery uses NCM ternary material and the charge cut-off voltage is 4.35V and above.

[0035] Further, the charge cut-off voltage is 4.45V and below.

[0036] Preferably, the positive electrode of the lithium ion battery uses artificial graphite or artificial graphite composite silicon-based material.

[0037] Further preferably, the negative electrode has a compaction density of not less than 1.65g / cm 3 .

[0038] The high-voltage lithium ion battery of the present application has improved normal-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance at high voltage.

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

[0040] The present application greatly improves the stability of high-voltage NCM system lithium ion battery at high voltage by combining the solvent system mixed with fluorocarboxylate and carbonate and free of EC with additive combination optimization, so that the normal-temperature cycle performance, high-temperature cycle performance and high-temperature storage performance at high voltage are all improved. DETAILED DESCRIPTION

[0041] The present application will be further described below in combination with examples. However, the present application is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to different requirements of specific use, and the implementation conditions not mentioned are the conventional conditions in the industry. The technical features involved in each embodiment of the present application can be combined with each other as long as there is no conflict between them.

[0042] Unless otherwise specified, the raw materials involved in the following examples and comparative examples are all commercially available products.

[0043] The configuration method of the electrolyte in the following examples and comparative examples refers to the prior art, and the present application will not be discussed in detail.

[0044] Example 1

[0045] The present example provides an electrolyte, the formula of which is as follows:

[0046] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0047] Electrolyte lithium salt: LiPF6 with a final concentration of 1 mol / L;

[0048] Additives: DTD with an addition amount of 1% of the total mass of the electrolyte, VC with an addition amount of 0.5% of the total mass of the electrolyte, dipropargyl carbonate with an addition amount of 0.5% of the total mass of the electrolyte, and LiDFP with an addition amount of 1% of the total mass of the electrolyte.

[0049] Example 2

[0050] The present example provides an electrolyte, the formula of which is as follows:

[0051] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0052] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L;

[0053] Additives: DTD with an addition amount of 1% of the total mass of the electrolyte, VC with an addition amount of 0.5% of the total mass of the electrolyte, citraconic anhydride with an addition amount of 0.5% of the total mass of the electrolyte, LiDFP with an addition amount of 1% of the total mass of the electrolyte.

[0054] Example 3

[0055] This example provides an electrolyte with the following formula:

[0056] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0057] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L;

[0058] Additives: DTD with an addition amount of 1% of the total mass of the electrolyte, VC with an addition amount of 0.5% of the total mass of the electrolyte, 1,3-dioxane with an addition amount of 0.5% of the total mass of the electrolyte, LiDFP with an addition amount of 1% of the total mass of the electrolyte.

[0059] Example 4

[0060] This example provides an electrolyte with the following formula:

[0061] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0062] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L;

[0063] Additives: DTD with an addition amount of 1% of the total mass of the electrolyte, VC with an addition amount of 0.5% of the total mass of the electrolyte, dipyridyl carbonate with an addition amount of 0.5% of the total mass of the electrolyte, 1,3-dioxane with an addition amount of 0.5% of the total mass of the electrolyte, LiDFP with an addition amount of 1% of the total mass of the electrolyte.

[0064] Example 5

[0065] This example provides an electrolyte with the following formula:

[0066] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0067] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L;

[0068] Additives: DTD at 1% of the total mass of the electrolyte, VC at 0.5% of the total mass of the electrolyte, dipropargyl carbonate at 0.5% of the total mass of the electrolyte, citraconic anhydride at 0.5% of the total mass of the electrolyte, LiDFP at 1% of the total mass of the electrolyte.

[0069] Example 6

[0070] This example provides an electrolyte with the following formulation:

[0071] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0072] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L;

[0073] Additives: DTD at 1% of the total mass of the electrolyte, VC at 0.5% of the total mass of the electrolyte, 1,3-dioxane at 0.5% of the total mass of the electrolyte, citraconic anhydride at 0.5% of the total mass of the electrolyte, LiDFP at 1% of the total mass of the electrolyte.

[0074] Example 7

[0075] This example provides an electrolyte with the following formulation:

[0076] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0077] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L;

[0078] Additives: DTD at 1% of the total mass of the electrolyte, VC at 0.5% of the total mass of the electrolyte, dipropargyl carbonate at 0.5% of the total mass of the electrolyte, 1,3-dioxane at 0.5% of the total mass of the electrolyte, citraconic anhydride at 0.5% of the total mass of the electrolyte, LiDFP at 1% of the total mass of the electrolyte.

[0079] Example 8

[0080] This example provides an electrolyte with the following formulation:

[0081] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0082] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L;

[0083] Additives: DTD at 1% of the total mass of the electrolyte, VC at 0.5% of the total mass of the electrolyte, carbonic acid dipropargyl ester at 0.5% of the total mass of the electrolyte, 1,3-dioxane at 0.5% of the total mass of the electrolyte, citraconic anhydride at 0.5% of the total mass of the electrolyte, LiDFP at 1% of the total mass of the electrolyte, LiDODFP at 1% of the total mass of the electrolyte, TMSP at 0.5% of the total mass of the electrolyte, FEC at 3% of the total mass of the electrolyte.

[0084] Example 9

[0085] This example provides an electrolyte with the following formulation:

[0086] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, methyl ethyl carbonate mixed in a mass ratio of 50:20:30;

[0087] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L;

[0088] Additives: DTD at 1% of the total mass of the electrolyte, VC at 0.5% of the total mass of the electrolyte, carbonic acid dipropargyl ester at 1% of the total mass of the electrolyte, 1,3-dioxane at 1% of the total mass of the electrolyte, citraconic anhydride at 1% of the total mass of the electrolyte, LiDFP at 1% of the total mass of the electrolyte, LiDODFP at 1% of the total mass of the electrolyte, TMSP at 0.5% of the total mass of the electrolyte, FEC at 3% of the total mass of the electrolyte.

[0089] Example 10

[0090] This example provides an electrolyte with the following formulation:

[0091] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, methyl ethyl carbonate mixed in a mass ratio of 50:20:30;

[0092] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L;

[0093] Additives: DTD at 1% of the total mass of the electrolyte, VC at 0.5% of the total mass of the electrolyte, carbonic acid dipropargyl ester at 1% of the total mass of the electrolyte, 1,3-dioxane at 1% of the total mass of the electrolyte, citraconic anhydride at 1% of the total mass of the electrolyte, LiDFP at 1% of the total mass of the electrolyte, LiDODFP at 1% of the total mass of the electrolyte, TMSP at 0.5% of the total mass of the electrolyte, FEC at 3% of the total mass of the electrolyte.

[0094] Example 11

[0095] This example provides an electrolyte, the formulation of which is as follows:

[0096] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0097] Electrolyte lithium salt: LiPF6 with a final concentration of 1 mol / L;

[0098] Additives: DTD with an added amount of 1% of the total mass of the electrolyte, VC with an added amount of 0.5% of the total mass of the electrolyte, dipropargyl carbonate with an added amount of 0.5% of the total mass of the electrolyte, 1,3-dioxane with an added amount of 0.5% of the total mass of the electrolyte, maleic anhydride with an added amount of 0.5% of the total mass of the electrolyte, LiDFP with an added amount of 1% of the total mass of the electrolyte.

[0099] Example 12

[0100] This example provides an electrolyte, the formulation of which is as follows:

[0101] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0102] Electrolyte lithium salt: LiPF6 with a final concentration of 1 mol / L;

[0103] Additives: DTD with an added amount of 1% of the total mass of the electrolyte, VC with an added amount of 0.5% of the total mass of the electrolyte, dipropargyl carbonate with an added amount of 0.5% of the total mass of the electrolyte, 1,4-dioxane with an added amount of 0.5% of the total mass of the electrolyte, citraconic anhydride with an added amount of 0.5% of the total mass of the electrolyte, LiDFP with an added amount of 1% of the total mass of the electrolyte.

[0104] Example 13

[0105] This example provides an electrolyte, the formulation of which is as follows:

[0106] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0107] Electrolyte lithium salt: LiPF6 with a final concentration of 1 mol / L;

[0108] Additives: DTD at 1% of the total mass of the electrolyte, VC at 0.5% of the total mass of the electrolyte, dipropargyl carbonate at 0.5% of the total mass of the electrolyte, 1,3-dioxolane at 0.5% of the total mass of the electrolyte, citraconic anhydride at 0.5% of the total mass of the electrolyte, LiDFP at 1% of the total mass of the electrolyte.

[0109] Comparative Example 1

[0110] This comparative example is a conventional additive, whose formulation is as follows:

[0111] Organic solvent: ethylene carbonate and methyl ethyl carbonate mixed at a mass ratio of 30:70;

[0112] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L.

[0113] Comparative Example 2

[0114] This comparative example provides an electrolyte, whose formulation is as follows:

[0115] Organic solvent: ethylene carbonate and methyl ethyl carbonate mixed at a mass ratio of 30:70;

[0116] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L.

[0117] Additives: dipropargyl carbonate at 0.5% of the total mass of the electrolyte.

[0118] Comparative Example 3

[0119] This comparative example provides an electrolyte, whose formulation is as follows:

[0120] Organic solvent: ethylene carbonate and methyl ethyl carbonate mixed at a mass ratio of 30:70;

[0121] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L.

[0122] Additives: citraconic anhydride at 0.5% of the total mass of the electrolyte.

[0123] Comparative Example 4

[0124] This comparative example provides an electrolyte, whose formulation is as follows:

[0125] Organic solvent: ethylene carbonate and methyl ethyl carbonate mixed at a mass ratio of 30:70;

[0126] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L.

[0127] Additive: 1,3-dioxolane, added in an amount of 0.5% of the total mass of the electrolyte.

[0128] Comparative Example 5

[0129] This comparative example provides an electrolyte with the following formulation:

[0130] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0131] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L.

[0132] Comparative Example 6

[0133] This comparative example provides an electrolyte with the following formulation:

[0134] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0135] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L.

[0136] Additive: dipropargyl carbonate, added in an amount of 0.5% of the total mass of the electrolyte.

[0137] Comparative Example 7

[0138] This comparative example provides an electrolyte with the following formulation:

[0139] Organic solvent: 2,2-difluoroethyl acetate, propylene carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 50:20:30;

[0140] Electrolyte lithium salt: LiPF6with a final concentration of 1 mol / L.

[0141] Additive: DTD added in an amount of 1% of the total mass of the electrolyte, VC added in an amount of 0.5% of the total mass of the electrolyte, and LiDFP added in an amount of 1% of the total mass of the electrolyte.

[0142] The electrolytes of the above examples and comparative examples are used to prepare 2500 mAh lithium-ion soft pack batteries of the NCM622 / artificial graphite system. The preparation method of the lithium-ion soft pack batteries refers to the prior art, and the present application is not specifically limited.

[0143] The cycle performance of the above lithium-ion soft pack batteries is tested using a Shenzhen Xinwei battery tester, including:

[0144] Normal temperature cycle performance test:

[0145] After the above lithium ion soft package batteries of Examples 1 to 12 and Comparative Examples 1 to 7 were formed, the batteries were tested for cycle performance at 1C in the voltage range of 2.75-4.4V at room temperature (25℃); after the above lithium ion soft package battery of Example 13 was formed, the battery was tested for cycle performance at 1C in the voltage range of 2.75-4.45V at room temperature (25℃).

[0146] Capacity retention rate (%) after 1000 cycles at 25℃ = discharge capacity at the 1000th cycle / discharge capacity at the first cycle x 100%.

[0147] 45℃ high temperature cycle performance test:

[0148] After the above lithium ion soft package batteries of Examples 1 to 12 and Comparative Examples 1 to 7 were formed, the batteries were tested for cycle performance at 1C in the voltage range of 2.75-4.4V at 45℃; after the above lithium ion soft package battery of Example 13 was formed, the battery was tested for cycle performance at 1C in the voltage range of 2.75-4.45V at 45℃.

[0149] Capacity retention rate (%) after 1000 cycles at 45℃ = discharge capacity at the 1000th cycle / discharge capacity at the first cycle x 100%.

[0150] Thickness expansion rate (%) after 1000 cycles at 45℃ = (thickness of the battery after the 1000th cycle - initial thickness of the battery) / initial thickness of the battery x 100%.

[0151] 60℃ high temperature storage performance test:

[0152] After the above lithium ion soft package batteries of Examples 1 to 12 and Comparative Examples 1 to 7 were charged at 1C to 4.4V and fully charged at constant voltage, the batteries were stored in a high-low temperature test chamber with the temperature set at 60℃ for 56 days, and the volume change rate, internal resistance change rate and capacity recovery rate were tested. After the above lithium ion soft package battery of Example 13 was charged at 1C to 4.45V and fully charged at constant voltage, the battery was stored in a high-low temperature test chamber with the temperature set at 60℃ for 56 days, and the volume change rate, internal resistance change rate and capacity recovery rate were tested.

[0153] Volume change rate (%) = (volume after high temperature storage - initial volume) / initial volume x 100%;

[0154] Internal resistance change rate (%) = (internal resistance after high temperature storage - initial internal resistance) / initial internal resistance x 100%;

[0155] Capacity recovery rate (%) = battery capacity after high temperature storage / initial capacity x 100%. The results of the room temperature cycle and high temperature cycle performance tests of the above lithium ion soft package batteries are shown in Table 1.

[0156] Table 1

[0157] The 60℃ high-temperature storage performance test results of the above lithium ion soft package battery are shown in Table 2.

[0158] Table 2

[0159] According to Tables 1 and 2, it is shown that with the replacement of ethylene carbonate (EC) with 2,2-difluoroethyl acetate and the optimization of the combination of additives, the normal-temperature cycle performance, high-temperature cycle performance, thickness expansion in high-temperature cycle, and high-temperature storage performance of the 4.4V high-voltage ternary NCM622 battery are all improved, among which the electrolyte of Example 7 has the best improvement effect on the comprehensive performance of the 4.4V high-voltage ternary NCM622 battery; the electrolyte formulation of Example 13 is consistent with that of Example 7, and after the charging voltage is increased to 4.45V, the electrochemical performance is still relatively excellent, which is slightly reduced compared with the charging voltage at 4.4V, indicating that there is still a challenge to the battery performance after the voltage is further increased.

[0160] The present application will now be described by reference to the following items:

[0161] 1. A lithium ion battery electrolyte, comprising an organic solvent, a lithium salt and an additive, the organic solvent comprising a fluorinated carboxylic acid ester and a carbonate,

[0162] the fluorinated carboxylic acid ester comprising one or more of 2,2-difluoroethyl acetate, 3,3-difluoropropyl acetate and 2,2-difluoroethyl propionate, and the carbonate not comprising ethylene carbonate,

[0163] the additive comprising a first additive and a second additive,

[0164] the first additive comprising one or more of an alkyne carbonate derivative, an oxane compound and a cyclic anhydride, the alkyne carbonate derivative comprising one or more of dipropargyl carbonate, di(2-vinylbutyl) carbonate, di(3-vinylbutyl) carbonate, di(2-vinylpentyl) carbonate, di(1-methyl-2-vinylbutyl) carbonate and 2-vinylpropyl-2'-vinylbutyl carbonate, the oxane compound comprising 1,3-dioxane and / or 1,4-dioxane, and the cyclic anhydride comprising citraconic anhydride and / or maleic anhydride,

[0165] the second additive comprising one or more of vinylene carbonate, fluorinated vinylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate and tris(trimethylsilyl) phosphate.

[0166] 2. The lithium ion battery electrolyte of item 1, wherein the carbonates are one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0167] and / or the fluorinated carboxylic acid ester and the carbonate are in a mass ratio of (0.8-1.2): 1.

[0168] 3. The lithium ion battery electrolyte of item 1 or 2, wherein the organic solvent is a mixture of 2,2-difluoroethyl acetate, propylene carbonate, and methyl ethyl carbonate in a mass ratio of (2-3): 1: (1-2).

[0169] 4. The lithium ion battery electrolyte of any one of items 1-3, wherein the first additive comprises two or three of an alkyne carbonate derivative, an oxane compound, and a cyclic anhydride.

[0170] 5. The lithium ion battery electrolyte of any one of items 1-4, wherein the first additive consists of the alkyne carbonate derivative, the oxane compound, and the cyclic anhydride.

[0171] 6. The lithium ion battery electrolyte of item 5, wherein the alkyne carbonate derivative, the oxane compound, and the cyclic anhydride are in a mass ratio of (0.8-1.2): 1: (0.8-1.2).

[0172] 7. The lithium ion battery electrolyte of any one of items 1-6, wherein the second additive comprises two or more of vinylene carbonate, fluorinated vinylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate, and tris(trimethylsilyl)phosphate.

[0173] 8. The lithium ion battery electrolyte of any one of items 1-7, wherein the second additive comprises three or more of vinylene carbonate, fluorinated vinylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate, and tris(trimethylsilyl)phosphate.

[0174] 9. The lithium ion battery electrolyte of items 1-8, wherein the second additive consists of vinylene carbonate, vinyl sulfate, lithium difluorophosphate, and / or lithium difluorodioxalate phosphate.

[0175] 10. The lithium ion battery electrolyte of item 9, wherein the vinyl sulfate, the vinylene carbonate, the lithium difluorophosphate, and / or lithium difluorodioxalate phosphate are in a mass ratio of (1.8-2.2): 1: (1.8-2.2).

[0176] 11. The lithium-ion battery electrolyte according to any one of items 1 to 10, wherein the first additive is present in an amount of 0.5% to 5% by mass of the total electrolyte.

[0177] 12. The lithium-ion battery electrolyte according to any one of items 1 to 10, wherein the first additive is present in an amount of 1% to 5% by mass of the total electrolyte.

[0178] and / or the second additive is present in an amount of 1% to 15% by mass of the total electrolyte.

[0179] 13. The lithium-ion battery electrolyte according to any one of items 1 to 12, wherein the lithium salt is lithium hexafluorophosphate; and / or the molar concentration of the lithium salt in the electrolyte is 0.8M to 1.5M.

[0180] 14. A lithium-ion battery comprising the lithium-ion battery electrolyte according to any one of items 1 to 13, wherein the positive electrode of the lithium-ion battery employs a NCM ternary material and the charge cut-off voltage is at 4.35V and above.

[0181] 15. The lithium-ion battery according to item 14, wherein the charge cut-off voltage is at 4.45V and below.

[0182] The foregoing detailed description of the application has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the application to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teachings. The described embodiments were chosen in order to best illustrate the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application.

Claims

1. A lithium-ion battery electrolyte comprising an organic solvent, a lithium salt and an additive, characterized in that: The organic solvent comprises fluorinated carboxylic acid ester and carbonate, The fluorinated carboxylic acid ester comprises one or more of 2,2-difluoroethyl acetate, 3,3-difluoropropyl acetate and 2,2-difluoroethyl propionate, and the carbonate does not comprise ethylene carbonate, The additive comprises a first additive and a second additive, The first additive comprises one or more of acetylenic carbonate derivative, oxane compound and cyclic anhydride, the acetylenic carbonate derivative comprises one or more of dipropargyl carbonate, di(2-propargyl) carbonate, di(3-propargyl) carbonate, di(2-pentynyl) carbonate, di(1-methyl-2-propargyl) carbonate and 2-propargyl-2'-propargyl carbonate, the oxane compound comprises 1,3-dioxane and / or 1,4-dioxane, and the cyclic anhydride comprises citraconic anhydride and / or maleic anhydride, The second additive comprises one or more of vinylene carbonate, fluorinated vinylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate and tris(trimethylsilyl) phosphate.

2. The electrolyte for lithium ion batteries according to claim 1, characterized in that: The carbonate is one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; The mass ratio of the fluorinated carboxylic acid ester and the carbonate is (0.8-1.2):

1.

3. The electrolyte for a lithium-ion battery according to claim 1 or 2, characterized in that: The organic solvent is a mixture of 2,2-difluoroethyl acetate, propylene carbonate and methyl ethyl carbonate in a mass ratio of (2-3):1:(1-2).

4. The lithium-ion battery electrolyte according to any one of claims 1 to 3, characterized in that: The first additive comprises two or three of the acetylenic carbonate derivative, the oxane compound and the cyclic anhydride.

5. The lithium-ion battery electrolyte according to any one of claims 1 to 4, characterized in that: The first additive consists of the acetylenic carbonate derivative, the oxane compound and the cyclic anhydride.

6. The electrolyte for lithium-ion batteries according to claim 5, characterized in that: The mass ratio of the acetylenic carbonate derivative, the oxane compound and the cyclic anhydride is (0.8-1.2):1:(0.8-1.2).

7. The lithium-ion battery electrolyte according to any one of claims 1 to 6, characterized in that: The second additive comprises two or more of vinylene carbonate, fluorinated vinylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate and tris(trimethylsilyl) phosphate.

8. The lithium-ion battery electrolyte according to any one of claims 1 to 7, characterized in that: The second additive comprises three or more of vinylene carbonate, fluorinated vinylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate and tris(trimethylsilyl) phosphate.

9. The electrolyte for lithium-ion batteries according to claims 1 to 8, characterized in that: The second additive consists of vinylene carbonate, vinyl sulfate, lithium difluorophosphate and / or lithium difluorodioxalate phosphate.

10. The lithium-ion battery electrolyte of claim 9, wherein: The mass ratio of the vinyl sulfate, the vinylene carbonate, the lithium difluorophosphate and / or lithium difluorodioxalate phosphate is (1.8-2.2):1:(1.8-2.2).

11. The lithium-ion battery electrolyte according to any one of claims 1 to 10, characterized in that: The first additive accounts for 0.5%-5% of the total mass of the electrolyte.

12. The lithium-ion battery electrolyte according to any one of claims 1 to 10, characterized in that: The first additive accounts for 1%-5% of the total mass of the electrolyte. The second additive accounts for 1%-15% of the total mass of the electrolyte.

13. The lithium-ion battery electrolyte according to any one of claims 1 to 12, characterized in that: The lithium salt is lithium hexafluorophosphate; and / or the molar concentration of the lithium salt in the electrolyte is 0.8M-1.5M.

14. A lithium-ion battery, characterized by: The lithium ion battery comprises the lithium ion battery electrolyte as claimed in any one of claims 1 to 13, and the positive electrode of the lithium ion battery adopts NCM ternary material and the charge cut-off voltage is at 4.35 V and above.

15. The lithium-ion battery of claim 14, wherein: The charge cut-off voltage is at 4.4 V and below.

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