Lithium ion battery

Abstract

The invention relates to a lithium ion battery. In order to solve the problem that the performance of the battery is influenced by solvent decomposition and gas production due to the fact that active oxygen is released in the using process when a lithium supplementing agent is added, a solvent ethylene carbonate in an electrolyte is promoted to be subjected to a ring-opening reaction, and the lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and the electrolyte, the positive electrode comprises a positive electrode active material and a lithium supplement agent, the electrolyte comprises an organic solvent, a lithium salt and an additive, the organic solvent comprises fluoro carboxylic ester, fluoro ether and carbonic ester and does not contain ethylene carbonate, and the additive comprises trimethylsiloxyethyl isocyanate and / or 2-(1, 1-thiophane-3-dioxide)-2, 2-methyl difluoroacetate. Through the synergistic effect of the solvent system and the additive, the stability of the electrolyte in a battery containing a lithium supplement agent is improved, the wettability and low-temperature performance of the battery, especially a high-compaction battery, are improved, and meanwhile, the lithium ion battery has relatively good normal-temperature cycle performance and high-temperature performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium ion battery. Background Art

[0002] Lithium-ion secondary batteries are increasingly used in the power and energy storage markets. As people's requirements for quality of life increase, the requirements for the endurance, mileage and service life of digital devices and electric vehicles are getting higher and higher, which has led to an increasing demand for the energy density of lithium-ion batteries. When a lithium-ion battery is charged for the first time, some of the Li+ released from the positive electrode will not be embedded in the negative electrode but will participate in the formation of the SEI film on the surface of the negative electrode, thereby consuming this part of the active lithium and reducing the energy density of the battery. In order to make up for this part of the lithium loss, lithium supplementation is usually carried out. Commonly used lithium supplements such as Li 2 NiO 2 (LNO).

[0003] Conventional electrolyte systems contain cyclic carbonates: ethylene carbonate (EC). Theoretically, cyclic carbonates have better antioxidant properties than chain carbonates, but in actual lithium-ion battery systems, PF6 － The electrolyte lithium salt anions will generate HF in the electrolyte or undergo a fluoride ion transfer reaction to the solvent molecules; at the same time, solvents with higher dielectric constants (such as EC) will also react with PF6 － The complex then quickly reaches the positive electrode surface and is preferentially oxidized. These reactions will seriously reduce the oxidation stability of the solvent molecules, making the PF6 － The oxidative stability of the actual electrolyte system is lower than the theoretical calculated value. In addition, the high melting point of EC (36.4°C) severely limits the ion transport below 0°C, resulting in energy loss and lithium precipitation.

[0004] The addition of lithium supplements will release active oxygen during use, thereby promoting the ring-opening reaction of the solvent ethylene carbonate (EC) in the electrolyte, causing the electrolyte solvent to decompose and produce a large amount of gas, which will significantly reduce the battery's electrical performance and safety performance. Therefore, it is imperative to develop an electrolyte that is free of EC and has good compatibility with positive and negative electrodes so that battery systems containing lithium supplements can be promoted and applied. Summary of the invention

[0005] The object of the present invention is to provide a lithium ion battery containing a lithium supplementing agent with good stability, high and low temperature performance and good normal temperature cycle performance.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A lithium ion battery comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises an organic solvent, a lithium salt and an additive, the positive electrode comprises a positive electrode active material and a lithium supplement, the organic solvent comprises a fluorocarboxylic acid ester, a fluoroether and a carbonate ester, the organic solvent does not contain ethylene carbonate, and the additive comprises trimethylsilylethyl isocyanate and / or 2-(1,1-dioxytetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester.

[0008] Since fluorine atoms have strong electronegativity and weak polarity, fluorinated solvents have high electrochemical stability. Scholars have studied a series of organic carbonate solvents partially or completely substituted with fluorine, and confirmed that after the introduction of fluorine, the physical properties of ordinary organic solvents have changed greatly, such as the freezing point of the solvent is lowered, the anti-oxidation stability is improved, and it is conducive to the formation of SEI film on the surface of graphite negative electrode. The present invention adopts a new type of fluorinated solvent to replace ethylene carbonate, and through the combined use with additives, the oxidative decomposition of the solvent caused by the oxygen release of the lithium supplement agent is inhibited, the stability of the solvent system in the presence of the lithium supplement agent is improved, and the wettability and low temperature performance of the battery, especially the high-density battery, are improved.

[0009] Preferably, the trimethylsilylethyl isocyanate and 2-(1,1-dioxytetrahydrothiophene-3-yl)-2,2-difluoroacetate each independently account for 0.05% to 3% of the total mass of the electrolyte, more preferably 0.05% to 1%, and even more preferably 0.1% to 0.5%.

[0010] Preferably, the additive further includes a cyclic carbonate compound.

[0011] Preferably, the cyclic carbonate compound includes one or more of vinylene carbonate (VC) and fluorovinylene carbonate (FEC).

[0012] Preferably, the cyclic carbonate compound accounts for 1% to 4% of the total mass of the electrolyte.

[0013] In some embodiments, the cyclic carbonate compound is vinylene carbonate.

[0014] Furthermore, the vinylene carbonate accounts for 1% to 3% of the total mass of the electrolyte, and more preferably 1.5% to 2.5%.

[0015] In some embodiments, the cyclic carbonate compound is vinylene carbonate and fluorovinylene carbonate.

[0016] Furthermore, the vinylene carbonate accounts for 1.5% to 2.5% of the total mass of the electrolyte, and the fluorovinylidene carbonate accounts for 0.5% to 1.5% of the total mass of the electrolyte.

[0017] Preferably, the additive further comprises cyclic sulfate compounds and / or cyclic sulfonate compounds.

[0018] In some embodiments, the cyclic sulfate ester compound includes dithiothreitol disulfide (DTD).

[0019] In some embodiments, the cyclic sulfonate compound includes one or more of methylene methanedisulfonate (MMDS) and 1,3-propylene sultone (PRS).

[0020] Preferably, the cyclic sulfate ester compound and the cyclic sulfonate ester compound each independently account for 0.5% to 2% of the total mass of the electrolyte, and more preferably 0.5 to 1.5%.

[0021] Preferably, the additive further comprises a lithium-containing compound.

[0022] Further preferably, the lithium-containing compound includes one or more of lithium difluorophosphate (LiDFP), lithium difluorooxalatophosphate (LiFOP), and lithium difluorooxalatoborate (LiODFB).

[0023] Preferably, the lithium-containing compound accounts for 0.1% to 1% of the total mass of the electrolyte, and more preferably 0.5% to 1%.

[0024] Preferably, the additive further includes a phosphate compound.

[0025] More preferably, the phosphate compound includes tris(trimethylsilyl)phosphate (TMSP).

[0026] Preferably, the phosphate compound accounts for 0.5% to 2% of the total mass of the electrolyte, more preferably 0.5% to 1.5%, and further preferably 0.8% to 1.2%.

[0027] Preferably, the fluorocarboxylic acid ester includes one or more of 2,2-difluoroethyl acetate, methyl fluorosulfonyldifluoroacetate, methyl trifluoropropionate, and methyl 3,3,3-trifluoroalanine.

[0028] Preferably, the fluoroether includes one or more of difluoromethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

[0029] Preferably, the carbonate includes one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0030] Preferably, the mass ratio of the fluorocarboxylic acid ester, the fluoroether and the carbonate is (0.2-0.6):(0.4-0.8):1.

[0031] More preferably, the mass ratio of the fluorocarboxylic acid ester, the fluoroether and the carbonate is (0.3-0.5):(0.5-0.7):1.

[0032] More preferably, the mass ratio of the fluorocarboxylic acid ester, the fluoroether and the carbonate is (0.35-0.45):(0.55-0.65):1, for example 0.4:0.6:1.

[0033] In some embodiments, the fluorocarboxylic acid ester is selected from any one of 2,2-difluoroethyl acetate, methyl fluorosulfonyl difluoroacetate, methyl trifluoropropionate, and methyl 3,3,3-trifluoroalanine; the fluoroether is selected from any one of difluoromethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether; and the carbonate is ethyl methyl carbonate.

[0034] Preferably, the organic solvent may further include one or more of carboxylic acid esters, ethers, and sulfones.

[0035] Further preferably, the carboxylic acid ester includes one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, methyl butyrate, and ethyl butyrate.

[0036] More preferably, the ether includes one or more of dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, and 1,3-dioxolane.

[0037] More preferably, the sulfone includes one or more of dimethyl sulfoxide, sulfolane, and dimethyl sulfone.

[0038] Preferably, the lithium supplement is selected from Li 2 NiO 2 (LNO), Li 5 FeO 4 (LFO), Li 2 MnO 3 (LMO), Li 6 CoO 4 Any of (LCO).

[0039] Preferably, the lithium supplement accounts for 0.5% to 5% of the total mass of the positive electrode active material, more preferably 1.5% to 4.5%, further preferably 2% to 4%, and even more preferably 2.5% to 3.5%.

[0040] Preferably, the positive electrode active material is selected from lithium iron phosphate or lithium manganese iron phosphate.

[0041] Further preferably, when the positive electrode active material is lithium manganese iron phosphate, the compaction density of the positive electrode is not less than 2.3 g / cm 3 When the positive electrode active material is lithium iron phosphate, the compaction density of the positive electrode is not less than 2.5g / cm 3 .

[0042] Preferably, the negative electrode comprises a negative electrode active material, and the negative electrode active material is artificial graphite or a silicon-graphite composite material.

[0043] Further preferably, the compaction density of the negative electrode is not less than 1.65 g / cm 3 .

[0044] Preferably, the lithium salt is lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide.

[0045] In some embodiments, the lithium salt is lithium hexafluorophosphate.

[0046] In some embodiments, the lithium salt is lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0047] Preferably, the molar concentration of the lithium salt in the electrolyte is 0.5M-2M, further 0.8M-1.5M, further 0.9M-1.2M.

[0048] In the present invention, the material of the diaphragm refers to the prior art, and the present invention does not impose any specific limitation.

[0049] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0050] The present invention improves the stability of the electrolyte in the battery containing the lithium supplement system through the synergistic effect of the solvent system and the additive, improves the wettability and low-temperature performance of the battery, especially the high-density battery, and the lithium-ion battery of the present invention also has better room-temperature cycle performance and high-temperature performance. DETAILED DESCRIPTION

[0051] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0052] Unless otherwise specified, the raw materials involved in the following examples and comparative examples are all commercially available products.

[0053] In order to more intuitively compare the electrolyte effect, unless otherwise specified, the batteries in the following comparative examples and embodiments uniformly use 1000mAh soft-pack batteries of lithium iron phosphate (LFP) / artificial graphite system, and the preparation method of the soft-pack batteries is as follows:

[0054] Positive electrode: lithium iron phosphate / lithium supplement LNO / conductive graphite / binder PVDF are mixed and coated in a ratio of 90.8% / 2.7% / 3.5% / 3% to form a positive electrode sheet for standby use (the lithium supplement accounts for about 3% of the total mass of the positive electrode active material);

[0055] Negative electrode: artificial graphite / conductive graphite / binder SBR (styrene-butadiene rubber) / thickener CMC (carboxymethyl cellulose) are mixed and coated in a ratio of 95.5% / 1% / 2% / 1.5% to form a negative electrode sheet for standby use;

[0056] The positive electrode sheet is rolled to a compaction density of 2.55g / cm 3 The negative electrode sheet is rolled to a compaction density of 1.7g / cm 3 After welding the tabs in strips, the strips are wound on a semi-automatic winding machine to form bare cells, which are then packaged with aluminum-plastic film to form AHB083048 cell models for standby use. The configuration methods of the electrolytes in the following comparative examples and embodiments refer to the prior art, and the present invention will not elaborate on them in detail.

[0057] Comparative Example 1

[0058] Electrolyte: The organic solvent is ethylene carbonate (EC) and ethyl methyl carbonate (EMC), with a mass ratio of 30:70; the electrolyte lithium salt is lithium hexafluorophosphate (LiPF 6 ), the concentration of lithium salt was 1 mol / L, and no other functional additives were added.

[0059] Comparative Example 2

[0060] Electrolyte: The organic solvent is ethylene carbonate and ethyl methyl carbonate, with a mass ratio of 30:70; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

[0061] 0.3% trimethylsilylethyl isocyanate (CAS No.: 22503-22-1, Shanghai Biyang Industrial) was added based on the total mass of the electrolyte.

[0062] Comparative Example 3

[0063] Electrolyte: The organic solvent is 2,2-difluoroethyl acetate (CAS No.: 1550-44-3), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (CAS No.: 16627-68-2), and ethyl methyl carbonate, with a mass ratio of 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L.

[0064] Comparative Example 4

[0065] Electrolyte: The organic solvent is 2,2-difluoroethyl acetate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and ethyl methyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

[0066] 2% vinylene carbonate (VC) was added based on the total mass of the electrolyte.

[0067] Example 1

[0068] Electrolyte: The organic solvent is 2,2-difluoroethyl acetate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and ethyl methyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

[0069] 2% vinylene carbonate (VC) and 0.1% trimethylsiloxyethyl isocyanate were added based on the total mass of the electrolyte.

[0070] Example 2

[0071] Electrolyte: The organic solvent is methyl fluorosulfonyl difluoroacetate (CAS No.: 680-15-9), 2,2,3,3-tetrafluoropropyl difluoromethyl ether (CAS No.: 35042-99-0), and ethyl methyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

[0072] Based on the total mass of the electrolyte, 2% VC, 0.1% 2-(1,1-dioxidotetrahydrothiophen-3-yl)-2,2-difluoroacetic acid methyl ester (CAS No.: 1783700-24-2, Shanghai Haohong Biological) and 1% lithium difluorooxalatoborate (LiODFB) were added.

[0073] Example 3

[0074] Electrolyte: The organic solvent is 3,3,3-trifluoroalanine methyl ester (CAS No.: 27240-44-4), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and ethyl methyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

[0075] Based on the total mass of the electrolyte, 2% VC, 0.3% 2-(1,1-dioxidotetrahydrothiophen-3-yl)-2,2-difluoroacetic acid methyl ester and 1% dithiodisulfate (DTD) were added.

[0076] Example 4

[0077] Electrolyte: The organic solvent is methyl fluorosulfonyl difluoroacetate, difluoromethyl-2,2,2-trifluoroethyl ether (CAS No.: 1885-48-9), and ethyl methyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L,

[0078] Based on the total mass of the electrolyte, 1% DTD, 2% VC, 1% fluoroethylene carbonate (FEC) and 0.2% trimethylsilylethyl isocyanate were added.

[0079] Example 5

[0080] Electrolyte: The organic solvent is methyl trifluoropropionate (CAS No.: 18830-44-9), 2,2,3,3-tetrafluoropropyl difluoromethyl ether, and ethyl methyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

[0081] 1% DTD, 2% VC, 1% FEC and 0.2% trimethylsiloxyethyl isocyanate were added based on the total mass of the electrolyte.

[0082] Example 6

[0083] Electrolyte: The organic solvent is methyl trifluoropropionate, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and ethyl methyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

[0084] 1% DTD, 2% VC, 1% FEC, 0.2% trimethylsilylethyl isocyanate and 0.5% LiODFB were added based on the total mass of the electrolyte.

[0085] Example 7

[0086] Electrolyte: The organic solvent is methyl trifluoropropionate, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and ethyl methyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

[0087] 1% DTD, 2% VC, 1% FEC, 0.2% trimethylsilylethyl isocyanate, 0.5% LiODFB and 1% tris(trimethylsilyl)phosphate (TMSP) were added based on the total mass of the electrolyte.

[0088] Example 8

[0089] Electrolyte: The organic solvent is methyl trifluoropropionate, difluoromethyl-2,2,2-trifluoroethyl ether, and ethyl methyl carbonate, with a mass ratio of 20:30:50; the electrolyte lithium salt is 0.7M LiPF 6 and 0.3 M lithium bis(fluorosulfonyl)imide (LiFSI);

[0090] Based on the total mass of the electrolyte, 1% DTD, 2% VC, 1% FEC, 0.2% trimethylsilylethyl isocyanate, 0.5% LiODFB and 1% TMSP were added.

[0091] Example 9

[0092] Electrolyte: The organic solvent is 2,2-difluoroethyl acetate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and ethyl methyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

[0093] 0.1% trimethylsilylethyl isocyanate was added based on the total mass of the electrolyte.

[0094] Example 10

[0095] Electrolyte: The organic solvent is 2,2-difluoroethyl acetate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and ethyl methyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

[0096] 0.1% of methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate was added based on the total mass of the electrolyte.

[0097] Lithium-ion battery performance test

[0098] The electrolytes in the above embodiments and comparative examples were respectively poured into soft-pack batteries for performance testing. The cycle performance of the batteries was tested using a Shenzhen Xinwei battery tester, and the high and low temperature test was performed using an ESPEC high and low temperature chamber.

[0099] (1) Normal temperature cycle performance test:

[0100] After the lithium-ion soft-pack batteries in all comparative examples and embodiments were formed, the batteries were tested at room temperature (25° C.) for 0.5C cycle performance in the voltage range of 2.75-3.7V.

[0101] Capacity retention rate after 5000 cycles at 25° C. (%)=discharge capacity at 5000th cycle / discharge capacity at first cycle×100%.

[0102] (2) -20℃ low temperature discharge test:

[0103] All experimental batteries were fully charged at room temperature and 0.5C, and then discharged at 0.5C. The discharge capacity was recorded as A. 0 After the experimental battery is fully charged at room temperature at 0.5C, it is placed in a high and low temperature box set at -20℃ for 8 hours, and then discharged at 0.5C. The discharge capacity is recorded as A 1 , and compared with the discharge capacity at room temperature:

[0104] -20℃ low temperature discharge rate (%) = A 1 / A 0 ×100%.

[0105] (3) 60℃ high temperature storage performance test:

[0106] After all the experimental batteries were fully charged at 0.5C constant current and constant voltage, they were stored in a high and low temperature box set at 60°C for 56 days. The volume expansion rate of the gas produced by the experimental batteries was tested during the storage process. The volume expansion rate test referred to the existing technology.

[0107] The data of normal temperature cycle capacity retention rate, high temperature storage expansion rate and low temperature discharge of all comparative examples and embodiments were collected and compared, and the results are shown in Table 1 below.

[0108] Table 1

[0109]

[0110]

[0111] The control example is substantially the same as Example 1, except that the control example battery does not contain the lithium supplement LNO.

[0112] The comparison of the data of each embodiment and comparative example in the table shows that the room temperature cycle performance, high temperature storage performance and low temperature discharge performance of LFP / AG (artificial graphite) battery are improved through the synergistic effect of fluorinated solvents and various functional additives. Through the combination optimization of additives, a stable solid electrolyte interface film is formed on the surface of the positive and negative electrode materials of the battery, which prevents the direct contact between the material and the electrolyte, and avoids the catalytic decomposition of the electrolyte solvent by the positive electrode material and the lithium supplement under high temperature conditions. At the same time, fluorinated carboxylic acid esters and fluorinated ethers replace EC with a high melting point, reducing the viscosity of the electrolyte, so that the room temperature, high temperature and low temperature performance of the LFP battery are significantly improved.

[0113] By comparing Comparative Examples 1 to 3, it is found that the solvent system of the present invention has better performance than the solvent system containing ethylene carbonate. By comparing Comparative Example 3 and the Examples, it is found that only using a fluorinated solvent to replace EC without adding any functional additives has limited improvement on the room temperature cycle performance and high and low temperature performance of the battery. The synergistic effect of the solvent system of fluorinated carboxylic acid esters and fluorinated ethers and additives can improve the high and low temperature performance and cycle performance of the battery to a greater extent.

[0114] By comparing Comparative Example 3, Comparative Example 4, Example 1, Example 9 and Example 10, it is found that the use of VC alone can improve the room temperature cycle performance of the battery, but the improvement on the high and low temperature performance is limited. The use of trimethylsilylethyl isocyanate or 2-(1,1-dioxidotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester alone can improve the high and low temperature performance of the battery, but the improvement on the room temperature cycle performance is limited. The combined use of VC with trimethylsilylethyl isocyanate and 2-(1,1-dioxidotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester can improve the room temperature cycle performance and the high and low temperature performance at the same time, and the effect is better than the superposition of the two used alone.

[0115] By comparing Examples 1 to 3, it is found that on the basis of using a fluorocarboxylic acid ester and a fluoroether solvent system and an additive of trimethylsilylethyl isocyanate or 2-(1,1-dioxidotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester, the addition of lithium-containing compounds and / or cyclic sulfate compounds can further improve the high and low temperature performance and cycle performance of the battery. The addition of cyclic sulfate compounds has a more obvious improvement on the room temperature cycle performance and high temperature performance of the battery, and the addition of lithium-containing compounds has a more obvious improvement on the low temperature performance of the battery.

[0116] By comparing Examples 3 to 6, on the basis of using a fluorocarboxylic acid ester and a fluoroether solvent system and an additive of trimethylsilylethyl isocyanate or 2-(1,1-dioxidotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester, a cyclic sulfate compound and / or a lithium-containing compound, adding fluorovinylidene carbonate can further improve the room temperature cycle performance and low temperature performance of the battery, and further introducing a phosphate compound is helpful to improve the battery performance, and further by optimizing the lithium salt system, the battery can obtain better performance.

[0117] By comparing Example 1 and the control example, it is found that adding a lithium supplement to the battery can effectively improve the room temperature cycle performance of the battery.

[0118] The above detailed description of the present invention is intended to enable persons familiar with the art to understand the contents of the present invention and implement them. It does not limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises an organic solvent, a lithium salt and an additive, Features: The positive electrode includes a positive electrode active material and a lithium supplement, the organic solvent includes a fluorocarboxylic acid ester, a fluoroether and a carbonate, the organic solvent does not contain ethylene carbonate, and the additive includes trimethylsilylethyl isocyanate and / or 2-(1,1-dioxidotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester.

2. The lithium ion battery according to claim 1, Features: The trimethylsilyloxyethyl isocyanate and 2-(1,1-dioxidotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester each independently account for 0.05% to 3% of the total mass of the electrolyte.

3. The lithium ion battery according to claim 1, Features: The additives also include cyclic carbonate compounds.

4. The lithium ion battery according to claim 3, Features: The cyclic carbonate compound includes one or more of vinylene carbonate and fluorovinylene carbonate; and / or, The cyclic carbonate compound accounts for 1% to 4% of the total mass of the electrolyte.

5. The lithium ion battery according to claim 1, Features: The additives also include cyclic sulfate compounds and / or cyclic sulfonate compounds.

6. The lithium ion battery according to claim 5, Features: The cyclic sulfate ester compound includes vinyl sulfate; and / or, The cyclic sulfonate compound includes one or more of methylene disulfonate and 1,3-propylene sultone; and / or, The cyclic sulfate ester compound and the cyclic sulfonate ester compound each independently account for 0.5% to 2% of the total mass of the electrolyte.

7. The lithium ion battery according to claim 1, Features: The additives also include lithium-containing compounds.

8. The lithium ion battery according to claim 7, Features: The lithium-containing compound includes one or more of lithium difluorophosphate, lithium difluorobisoxalatephosphate, and lithium difluorooxalateborate; and / or, The lithium-containing compound accounts for 0.1% to 1% of the total mass of the electrolyte.

9. The lithium ion battery according to claim 1, Features: The additives also include phosphate compounds.

10. The lithium ion battery according to claim 9, Features: The phosphate compound includes tris(trimethylsilyl)phosphate; and / or, The phosphate compound accounts for 0.5% to 2% of the total mass of the electrolyte.

11. The lithium ion battery according to claim 1, Features: The fluorinated carboxylic acid ester includes one or more of 2,2-difluoroethyl acetate, methyl fluorosulfonyldifluoroacetate, methyl trifluoropropionate, and methyl 3,3,3-trifluoroalanine; and / or, The fluoroether includes one or more of difluoromethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether; and / or, The carbonate comprises one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and / or, The mass ratio of the fluorocarboxylic acid ester, the fluoroether and the carbonate is (0.2-0.6):(0.4-0.8):

1.

12. The lithium ion battery according to claim 1, Features: The lithium supplement agent is selected from Li 2 NiO 2 , Li 5 FeO 4 , Li 2 MnO 3 , Li 6 CoO 4 Any of; and / or, The lithium supplement accounts for 0.5% to 5% of the total mass of the positive electrode active material.

13. The lithium ion battery according to claim 1, Features: The positive electrode active material is selected from lithium iron phosphate or lithium manganese iron phosphate; and / or, The negative electrode comprises a negative electrode active material, and the negative electrode active material is artificial graphite or a silicon-graphite composite material.

14. The lithium ion battery according to claim 1, Features: The lithium salt is lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide; and / or, The molar concentration of the lithium salt in the electrolyte is 0.5M-2M.

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