Lithium ion battery electrolyte without ec and lithium ion battery

Abstract

The present application relates to a kind of EC-free lithium ion battery electrolyte and lithium ion battery.To solve the problem of poor high-low temperature performance and room temperature cycle performance of high-voltage NCM system lithium ion battery, the present application provides an electrolyte, comprising organic solvent, lithium salt and additive, wherein the organic solvent comprises fluorinated carboxylic acid ester, fluorinated ether and carbonate, and the organic solvent does not contain ethylene carbonate;The additive comprises first additive and / or second additive, the first additive comprises dimethoxydivinylsilane and / or dimethyl (dimethylamino) vinylsilane, and the second additive comprises one or more of hexamethylene diisocyanate, trimethylsiloxane ethyl isocyanate and 2- (1, 1-dioxotetrahydrothiophene-3-yl) -2, 2-difluoroethyl acetate.The stability of high-voltage NCM system lithium ion battery under high voltage is improved by the synergistic effect of EC-free solvent system and additive, so that the lithium ion battery has better high-low temperature performance and room temperature cycle performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to a lithium ion battery electrolyte without EC and a lithium ion battery. BACKGROUND

[0002] The lithium ion battery positive electrode material such as NCM ternary material has the advantages of high specific capacity, good cycle performance, good safety and small environmental pollution, and gradually attracts people's attention, and is expected to become one of the mainstream positive electrode materials of the future lithium ion battery. In order to meet the demand of people for high energy density, the NCM ternary positive electrode 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 electrode material / electrolyte interface will be reduced, which will cause the increase of side reactions and seriously affect the cycle performance of the lithium ion battery.

[0003] The performance of high-nickel and high-voltage lithium ion batteries is mainly determined by the structure and properties of active materials and electrolytes. Among them, the matching of electrolyte is very important.

[0004] Traditional carbonates as electrolyte solvents, such as ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC) and the like, have become the ideal choice of organic electrolyte solvents due to the advantages of high ionic conductivity, good solubility to lithium salt and the ability to form stable solid electrolyte interface (SEI) film. Although the oxidation potential of this kind of solvent is as high as 5V, however, under the catalysis of transition metal ions in the positive electrode material, these solvents are oxidized and decomposed at a lower potential (about 4.5V), which leads to the rapid deterioration of the battery performance. Therefore, the development of high-voltage electrolyte matched with high-voltage positive electrode material has become the research focus of enterprises and research institutions.

[0005] A small amount of functional additive is added to carbonate-based electrolyte, which makes it preferentially to solvent molecules to undergo oxidation / reduction decomposition reaction, and forms an effective protective film on the electrode surface, which can inhibit the subsequent decomposition of carbonate-based solvent. The film formed by the excellent performance of the additive can even inhibit the dissolution of the positive material metal ions and the deposition at the negative electrode, thereby significantly improving the electrode / electrolyte interface stability and the cycle performance of the battery. In addition to the excellent functional additive, fluorinated solvent is also a selection direction in high-voltage system; because the fluorine atom has strong electronegativity and weak polarity, which makes the fluorinated solvent have higher electrochemical stability. Scholars have confirmed that the physical properties of ordinary organic solvents have changed a lot after introducing fluorine elements, such as the freezing point of the solvent is reduced, the oxidation stability is improved, and it is beneficial to form SEI film on the carbon negative electrode surface. The HOMO energy of fluorinated ethylene carbonate (FEC) is-12.33eV, which is much lower than that of EC and other non-fluorinated carbonate solvents. The oxidation potential of methyl 2,2,2-trifluoroethyl carbonate and ethyl 2,2,2-trifluoroethyl carbonate (TFEEC) is as high as 5.8-5.9V (vs. Li / Li+), which is much higher than that of non-fluorinated EMC and DEC. In theory, the oxidation resistance of cyclic carbonate is better than that of chain carbonate, which can meet the demand of 5V high-voltage battery. However, in the actual lithium ion battery system, PF6 － The anion of the electrolyte lithium salt in the electrolyte will produce HF or undergo fluorine ion transfer reaction to the solvent molecule; at the same time, the solvent with high dielectric constant (such as EC) will also be complexed with PF6 － Then quickly reach the positive electrode surface and be preferentially oxidized, these reactions will seriously reduce the oxidation stability of the solvent molecule, so that the oxidation stability of the actual electrolyte system containing PF6 － Is lower than the theoretical calculation value. And the high melting point (36.4℃) of EC seriously limits the ion transport below 0℃, and leads to energy loss and lithium precipitation, the use of new fluorinated solvents and functional additives is the most economical and effective method to improve the compatibility of electrode and electrolyte and improve the performance of the battery.

[0006] Therefore, it is urgent to provide a functional electrolyte to solve the above problems, so that the high specific energy system battery can be widely applied. SUMMARY

[0007] The purpose of the present application is to provide an electrolyte suitable for high-voltage lithium ion batteries, which can improve the high and low temperature performance and room temperature cycle performance of the battery.

[0008] The second purpose of the present application is to provide a lithium ion battery with better high and low temperature performance and room temperature cycle performance.

[0009] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0010] An electrolyte for lithium ion battery without EC, comprising organic solvent, lithium salt and additive, the organic solvent comprises fluorinated carboxylic acid ester, fluorinated ether and carbonate, the organic solvent does not contain vinyl carbonate; the additive comprises first additive and / or second additive, the first additive comprises dimethoxydivinylsilane and / or dimethyl(dimethylamino)vinylsilane, the second additive comprises one or more of hexamethylene diisocyanate, trimethylsiloxylethyl isocyanate and 2-(1,1-dioxothiofuran-3-yl)-2,2-difluoroethyl acetate.

[0011] Preferably, the first additive accounts for 0.1% to 3% of the total mass of the electrolyte.

[0012] Further preferably, the first additive accounts for 0.5% to 2% of the total mass of the electrolyte.

[0013] More preferably, the first additive accounts for 0.5% to 1.5% of the total mass of the electrolyte, for example 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.3% or 1.5%.

[0014] Preferably, the second additive accounts for 0.1% to 1% of the total mass of the electrolyte.

[0015] Further preferably, the second additive accounts for 0.1% to 0.5% of the total mass of the electrolyte, for example 0.1%, 0.2%, 0.3%, 0.4% or 0.5%.

[0016] Preferably, the additive further comprises a third additive, the third additive being selected from one or more of cyclic sulfate compounds.

[0017] Further preferably, the cyclic sulfate compound comprises vinyl sulfate (DTD).

[0018] Preferably, the third additive accounts for 0.1% to 2% of the total mass of the electrolyte.

[0019] Further preferably, the third additive accounts for 0.5% to 1.5% of the total mass of the electrolyte, for example 0.5%, 0.8%, 1%, 1.3%, 1.5%.

[0020] Preferably, the additive further comprises a fourth additive, the fourth additive being selected from one or more of lithium-containing compounds.

[0021] Further preferably, the lithium-containing compound comprises lithium difluorophosphate (LiDFP) and lithium difluorodioxalate phosphate (LiFOP).

[0022] Preferably, the fourth additive comprises 0.5% to 2.5% of the total mass of the electrolyte.

[0023] Further preferably, the fourth additive comprises 1% to 2% of the total mass of the electrolyte.

[0024] In some embodiments, the fourth additive is lithium difluorophosphate, which comprises 1% to 1.5% of the total mass of the electrolyte.

[0025] In some embodiments, the fourth additive is lithium difluorophosphate and lithium difluorophosphate dioxalate, which comprises 0.5% to 1% of the total mass of the electrolyte.

[0026] Preferably, the additive further comprises a fifth additive, which is selected from one or more of phosphate ester compounds.

[0027] Further preferably, the phosphate ester compound comprises tris(trimethylsilyl) phosphate.

[0028] Preferably, the fifth additive comprises 0.5% to 2% of the total mass of the electrolyte.

[0029] Further preferably, the fifth additive comprises 0.5% to 1.5% of the total mass of the electrolyte.

[0030] Preferably, the additive further comprises a sixth additive, which is selected from one or more of carbonate compounds.

[0031] Further preferably, the carbonate compound comprises vinylene carbonate (VC), fluoroethylene carbonate (FEC).

[0032] Preferably, the sixth additive comprises 0.1% to 15% of the total mass of the electrolyte.

[0033] Further preferably, the sixth additive comprises 0.1% to 11% of the total mass of the electrolyte.

[0034] In some embodiments, the sixth additive is vinylene carbonate, which comprises 0.1% to 0.5% of the total mass of the electrolyte.

[0035] In some embodiments, the sixth additive is vinylene carbonate and fluoroethylene carbonate, which comprises 1% to 10% of the total mass of the electrolyte.

[0036] Further, the fluoroethylene carbonate comprises 1% to 5% of the total mass of the electrolyte.

[0037] Preferably, the fluoro-carboxylic acid ester comprises one or more of 2,2-difluoroethyl acetate, methyl fluorosulfonyl difluoroacetate, methyl trifluoropropionate, methyl 3,3,3-trifluoropropionate.

[0038] Preferably, the fluoro-ether comprises 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.

[0039] Preferably, the carbonate comprises one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate.

[0040] Preferably, the fluoro-carboxylic acid ester, fluoro-ether and carbonate are in a mass ratio of (0.2-0.6):(0.4-0.8):1.

[0041] In some embodiments, the fluoro-carboxylic acid ester is selected from any one of 2,2-difluoroethyl acetate, methyl fluorosulfonyl difluoroacetate, methyl trifluoropropionate, methyl 3,3,3-trifluoropropionate, the fluoro-ether 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, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and the carbonate is ethyl methyl carbonate.

[0042] In some embodiments, the fluoro-carboxylic acid ester is selected from any one of 2,2-difluoroethyl acetate, methyl fluorosulfonyl difluoroacetate, methyl trifluoropropionate, methyl 3,3,3-trifluoropropionate, the fluoro-ether 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, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and the carbonate is ethyl methyl carbonate and propylene carbonate.

[0043] Preferably, the organic solvent can further comprise one or more of a carboxylic acid ester, an ether, a sulfone.

[0044] Further preferably, the carboxylic acid ester comprises one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, methyl butyrate, ethyl butyrate.

[0045] Further preferably, the ether comprises one or more of dimethoxymethane, 1,2- dimethoxyethane, tetrahydrofuran, 1,3-dioxolane.

[0046] Further preferably, the sulfone comprises one or more of dimethyl sulfoxide, sulfolane, dimethyl sulfone.

[0047] Preferably, the lithium salt is lithium hexafluorophosphate.

[0048] Preferably, the molar concentration of the lithium salt in the electrolyte is 0.8M-1.5M.

[0049] 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.

[0050] The present application also provides a lithium ion battery comprising the electrolyte as described above.

[0051] Preferably, the positive electrode of the lithium ion battery uses NCM ternary material and the charge cut-off voltage is ≥4.35V.

[0052] Preferably, the positive electrode of the lithium ion battery uses artificial graphite or artificial graphite composite silicon-based material.

[0053] Further preferably, the negative electrode has a compaction density of not less than 1.65g / cm 3 .

[0054] Thanks to the above technical solution, the present application has the following advantages compared with the prior art:

[0055] The present application improves the stability of high-voltage NCM system lithium ion battery at high voltage through the synergistic effect of EC-free solvent system and additives, so that the lithium ion battery has better high and low temperature performance and room temperature cycle performance. DETAILED DESCRIPTION

[0056] The present application will be further described below in conjunction 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 specified 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.

[0057] Unless otherwise specified, the raw materials involved in the following examples and comparative examples are all commercially available products.

[0058] In order to more intuitively compare the effect of the electrolyte, the following comparative examples and examples use 2500mAh soft package battery of 4.4V NCM622 / artificial graphite system for the battery, and the soft package battery is a commercially available product or the preparation method of the soft package battery can refer to the prior art, and the present application does not make specific limitations.

[0059] The electrolyte of the following comparative examples is configured by referring to the prior art, and the present application is not discussed in detail.

[0060] Comparative Example 1

[0061] Electrolyte: organic solvent is ethylene carbonate (EC) and methyl ethyl carbonate (EMC) with a mass ratio of 30:70; electrolyte lithium salt is lithium hexafluorophosphate (LiPF6) with a lithium salt concentration of 1 mol / L, and no other functional additives are added.

[0062] Comparative Example 2

[0063] Electrolyte: organic solvent is ethylene carbonate and methyl ethyl carbonate with a mass ratio of 30:70; electrolyte lithium salt is LiPF6 with a lithium salt concentration of 1 mol / L;

[0064] 0.5% dimethyl(dimethylamino)vinylsilane (CAS No.: 13391-72-5) based on the total mass of the electrolyte is added.

[0065] Comparative Example 3

[0066] Electrolyte: organic solvent is ethylene carbonate and methyl ethyl carbonate with a mass ratio of 30:70; electrolyte lithium salt is LiPF6 with a lithium salt concentration of 1 mol / L;

[0067] 0.3% hexamethylene diisocyanate (CAS No.: 822-06-0) based on the total mass of the electrolyte is added.

[0068] Comparative Example 4

[0069] Electrolyte: 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 methyl ethyl carbonate with a mass ratio of 20:30:50; electrolyte lithium salt is LiPF6 with a lithium salt concentration of 1 mol / L, and no other functional additives are added.

[0070] Comparative Example 5

[0071] Electrolyte: organic solvent is methyl fluorosulfonyl difluoroacetate (CAS No.: 680-15-9), 2,2,3,3-tetrafluoropropyl difluoromethyl ether (CAS No.: 35042-99-0), and methyl ethyl carbonate with a mass ratio of 20:30:50; electrolyte lithium salt is LiPF6 with a lithium salt concentration of 1 mol / L, and no other functional additives are added.

[0072] Comparative Example 6

[0073] Electrolyte: organic solvent is methyl trifluoropropionate (CAS No.: 18830-44-9), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (CAS No.: 406-78-0), methyl ethyl carbonate, and the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L, and no other functional additives are added.

[0074] Example 1

[0075] Electrolyte: organic solvent is methyl 3,3,3-trifluoropropionate (CAS No.: 27240-44-4), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl ethyl carbonate, and the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L;

[0076] Add 1% DTD, 0.5% dimethoxydivinylsilane (CAS No.: 129762-81-8), 0.1% hexamethylene diisocyanate and 1% lithium difluorophosphate (LiDFP) based on the total mass of the electrolyte.

[0077] Example 2

[0078] Electrolyte: organic solvent is methyl fluorosulfonyl difluoroacetate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, methyl ethyl carbonate, and the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L;

[0079] Add 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% trimethylsiloxylethyl isocyanate (CAS No.: 22503-22-1, Shanghai Biyang Industry), 1% lithium difluorophosphate (LiFOP) based on the total mass of the electrolyte.

[0080] Example 3

[0081] Electrolyte: organic solvent is 2,2-difluoroethyl acetate, difluoromethyl-2,2,2-trifluoroethyl ether (CAS No.: 1885-48-9), methyl ethyl carbonate, and the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L;

[0082] Add 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.2% 2-(1,1-dioxotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester (CAS No.: 1783700-24-2, Shanghai Haohong Biological) and 1% LiDFP based on the total mass of the electrolyte.

[0083] Example 4

[0084] Electrolyte: organic solvent is methyl trifluoropropionate, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methyl ethyl carbonate, the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L;

[0085] Add 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% 2-(1,1-dioxotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester, 1% LiDFP, 1% LiFOP and 1% tris(trimethylsilyl) phosphate (TMSP) based on the total mass of the electrolyte.

[0086] Example 5

[0087] Electrolyte: organic solvent is methyl trifluoropropionate, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methyl ethyl carbonate, the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L;

[0088] Add 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% 2-(1,1-dioxotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester, 1% LiDFP, 1% LiFOP and 1% tris(trimethylsilyl) phosphate (TMSP) based on the total mass of the electrolyte.

[0089] Example 6

[0090] Electrolyte: organic solvent is methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, methyl ethyl carbonate, the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L;

[0091] Add 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% 2-(1,1-dioxotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester, 0.5% LiDFP, 1% LiFOP, 1% TMSP and 0.5% vinylene carbonate (VC) based on the total mass of the electrolyte.

[0092] Example 7

[0093] Electrolyte: organic solvent is methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, methyl ethyl carbonate, the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1.1 mol / L,

[0094] Add 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% 2-(1,1-dioxotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester, 0.5% LiDFP, 1% LiFOP, 1% TMSP and 0.5% vinylene carbonate (VC) based on the total mass of the electrolyte.

[0095] Example 8

[0096] Electrolyte: organic solvent is methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, methyl ethyl carbonate, the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1.3mol / L;

[0097] Add 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% 2-(1,1-dioxotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester, 0.5% LiDFP, 1% LiFOP, 1% TMSP and 0.5% VC based on the total mass of electrolyte.

[0098] Example 9

[0099] Electrolyte: organic solvent is methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, methyl ethyl carbonate, the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1.3mol / L;

[0100] Add 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% 2-(1,1-dioxotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester, 0.5% LiDFP, 1% LiFOP, 1% TMSP, 0.5% VC and 10% fluoroethylene carbonate (FEC) based on the total mass of electrolyte.

[0101] Example 10

[0102] Electrolyte: organic solvent is propylene carbonate, methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, methyl ethyl carbonate, the mass ratio of the four is 5:15:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1.1mol / L;

[0103] Add 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.5% 2-(1,1-dioxotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester, 1% LiDFP, 1% LiFOP, 1% TMSP, 0.5% VC and 5% FEC based on the total mass of electrolyte.

[0104] Example 11

[0105] Electrolyte: organic solvent is methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, methyl ethyl carbonate, the mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1mol / L;

[0106] 1% dimethyl(dimethylamino)vinylsilane and 0.3% of 2-(1,1-dioxidothiopyran-3-yl)-2,2-difluoroacetic acid methyl ester based on the total mass of the electrolyte.

[0107] Example 12

[0108] Electrolyte: organic solvent is methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, ethyl methyl carbonate, mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L;

[0109] 1% dimethyl(dimethylamino)vinylsilane and 0.3% of 3-(dimethylamino)propyl methacrylate based on the total mass of the electrolyte.

[0110] Example 13

[0111] Electrolyte: organic solvent is methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, ethyl methyl carbonate, mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L;

[0112] 1% DTD, 1% dimethyl(dimethylamino)vinylsilane and 0.3% of 2-(1,1-dioxidothiopyran-3-yl)-2,2-difluoroacetic acid methyl ester based on the total mass of the electrolyte.

[0113] Example 14

[0114] Electrolyte: organic solvent is methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, ethyl methyl carbonate, mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L;

[0115] 1% dimethyl(dimethylamino)vinylsilane, 0.3% of 2-(1,1-dioxidothiopyran-3-yl)-2,2-difluoroacetic acid methyl ester, 0.5% LiDFP and 1% LiFOP based on the total mass of the electrolyte.

[0116] Example 15

[0117] Electrolyte: organic solvent is methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, ethyl methyl carbonate, mass ratio of the three is 20:30:50; electrolyte lithium salt is LiPF6, the concentration of lithium salt is 1 mol / L;

[0118] 1% DTD, 1% dimethyl(dimethylamino)vinylsilane and 1% LiDFP based on the total mass of the electrolyte.

[0119] Example 16

[0120] Electrolyte: the organic solvent is methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, and methyl ethyl carbonate, and the mass ratio of the three is 20:30:50; the electrolyte lithium salt is LiPF6, and the concentration of the lithium salt is 1 mol / L;

[0121] Add 1% DTD, 0.3% 2-(1,1-dioxothiofuran-3-yl)-2,2-difluoroacetic acid methyl ester and 1% LiDFP based on the total mass of the electrolyte.

[0122] Lithium ion battery performance test

[0123] The cycle performance of the battery was tested by a Shenzhen Xinwei battery tester, and the high and low temperature test was performed by an ESPEC high and low temperature chamber.

[0124] (1) Normal temperature cycle performance test:

[0125] After the lithium ion soft package battery in all the comparative examples and examples was formed, the cycle performance test of the battery was performed at 1C in the voltage range of 2.75-4.4V at normal temperature (25℃).

[0126] Capacity retention rate (%) after 1000 cycles at 25℃ = discharge capacity of the 1000th cycle / discharge capacity of the first cycle x 100%.

[0127] (2) 45℃ high temperature cycle performance test:

[0128] After the lithium ion soft package battery in all the comparative examples and examples was formed, the cycle performance test of the battery was performed at 1C in the voltage range of 2.75-4.4V at 45℃.

[0129] Capacity retention rate (%) after 1000 cycles at 45℃ = discharge capacity of the 1000th cycle / discharge capacity of the first cycle x 100%.

[0130] Thickness expansion rate (%) after 1000 cycles at 45℃ = thickness of the battery after the 1000th cycle / initial thickness of the battery x 100%.

[0131] (3) 60℃ high temperature storage performance test:

[0132] After the experimental battery was fully charged at 1C, it was stored in a high and low temperature chamber set at 60℃ for 56 days, and the internal resistance, gas production and capacity recovery rate of the experimental battery were tested during the storage process. The test methods of internal resistance, gas production and capacity recovery rate refer to the prior art.

[0133] (4) -20℃ low temperature discharge test:

[0134] All experimental batteries were fully charged at 1C at room temperature, then discharged at 0.5C, and the discharge capacity was recorded as A0. After being fully charged at 1C at room temperature, the experimental batteries were placed in a high-low temperature chamber set at -20℃ for 8 hours, then discharged at 0.5C, and the discharge capacity was recorded as A1. The discharge capacity was then compared with the discharge capacity at room temperature for calculation.

[0135] -20℃ low temperature discharge rate (%) = A1 / A0 × 100%.

[0136] Data on the room temperature cycling capacity retention rate, high temperature cycling capacity retention rate, and expansion rate before and after high temperature cycling of all comparative examples and embodiments were collected and compared. The results are shown in Table 1 below.

[0137] Table 1

[0138]

[0139]

[0140] Data on capacity recovery rate, volume expansion, and internal resistance changes after 8 weeks of high-temperature storage at 60°C for all comparative examples and embodiments, as well as low-temperature discharge rate data at -20°C, were collected and compared. The results are shown in Table 2 below.

[0141] Table 2

[0142]

[0143]

[0144] The comparison of the data from the various examples and comparative examples in the table shows that the synergistic effect of replacing EC with fluorinated solvents and various functional additives improves the room temperature cycling performance, high temperature cycling performance, thickness expansion during high temperature cycling, high temperature storage, and low temperature discharge performance of the 4.4V high-voltage ternary NCM622 battery. Through the optimization of the additive combination, a stable solid electrolyte interface film is formed on the surface of the positive and negative electrode materials, preventing direct contact between the materials and the electrolyte and avoiding the catalytic decomposition of the electrolyte solvent by the positive electrode material under high voltage and high temperature conditions. Simultaneously, the addition of fluorinated carboxylic acid esters and fluorinated ethers reduces the electrolyte viscosity, thereby significantly improving the room temperature, high temperature, and low temperature performance of the high-voltage NCM battery.

[0145] Comparison of Comparative Examples 1 and 4 to 6 revealed that simply replacing EC with fluorinated solvents without adding any functional additives resulted in limited improvement in the battery's room temperature cycle performance and high and low temperature performance.

[0146] By comparing Comparative Examples 4 to 6 and the Examples, it was found that the synergistic effect of fluorinated solvents and additives can greatly improve the room temperature cycle performance and high and low temperature performance of batteries.

[0147] Further comparison of Comparative Examples 4 to 6 and Examples 11 and 12 finds that the addition of the first additive and the second additive can significantly improve the battery cycle performance, high-temperature performance and low-temperature performance; comparison of Comparative Examples 1 to 4, Examples 11 to 14 finds that the addition of any one of the third additive and the fourth additive helps to improve the battery cycle performance and low-temperature performance, and the simultaneous addition of the third additive and the fourth additive improves the low-temperature performance more obviously, but causes the high-temperature performance of the battery to deteriorate, especially causes the high-temperature storage volume, internal resistance of the battery to increase and the high-temperature capacity recovery rate to decrease; comparison of Examples 5 to 10 finds that the addition of the fifth additive and the sixth additive is beneficial to improve the battery cycle performance at room temperature and high temperature, but when the fluoroethylene carbonate is added and the content of the fluoroethylene carbonate is increased to more than 10%, the battery expansion rate after high-temperature cycle increases and the internal resistance increases obviously, so the content of the fluoroethylene carbonate is preferably less than 10%; comparison of Example 7 and Example 8 finds that when the electrolyte simultaneously adds the first to sixth additives and the additives are the same, with the increase of the concentration of the lithium salt of the electrolyte, the high and low temperature performance and the cycle performance at room temperature of the battery are further improved.

[0148] The above has described the present application in detail, the purpose is to let the person who is familiar with this field technology can understand the content of the present application and implement, and cannot limit the protection scope of the present application with this, all equivalent changes or modifications according to the spirit of the present application should be covered in the protection scope of the present application.

Claims

1. An EC-free lithium-ion battery electrolyte, comprising an organic solvent, a lithium salt, and additives, characterized in that: The organic solvent includes fluorocarboxylic acid esters, fluoroethers, and carbonates, and does not contain ethylene carbonate; the additive includes a first additive and / or a second additive, the first additive including dimethoxydivinylsilane and / or dimethyl(dimethylamino)vinylsilane, and the second additive being methyl 2-(1,1-tetrahydrothiophene-3-yl)-2,2-difluoroacetate.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that: The first additive accounts for 0.1% to 3% of the total mass of the electrolyte; and / or, The second additive accounts for 0.1% to 1% of the total mass of the electrolyte.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that: The additive also includes a third additive, which is selected from one or more cyclic sulfate compounds.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that: The cyclic sulfate compounds include vinyl sulfate; and / or, The third additive accounts for 0.1% to 2% of the total mass of the electrolyte.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that: The additive also includes a fourth additive, which is selected from one or more lithium-containing compounds.

6. The lithium-ion battery electrolyte according to claim 5, characterized in that: The lithium-containing compounds include lithium difluorophosphate and lithium difluorodioxarate phosphate; and / or, The fourth additive accounts for 0.5% to 2.5% of the total mass of the electrolyte.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that: The additive also includes a fifth additive, which is selected from one or more phosphate ester compounds.

8. The lithium-ion battery electrolyte according to claim 7, characterized in that: The phosphate ester compounds include tris(trimethylsilane) phosphates; and / or, The fifth additive accounts for 0.5% to 2% of the total mass of the electrolyte.

9. The lithium-ion battery electrolyte according to claim 1, characterized in that: The additive also includes a sixth additive, which is selected from one or more carbonate compounds.

10. The lithium-ion battery electrolyte according to claim 9, characterized in that: The carbonate compounds include vinylene carbonate and fluorovinyl carbonate; and / or, The sixth additive accounts for 0.1% to 15% of the total mass of the electrolyte.

11. The lithium-ion battery electrolyte according to claim 1, characterized in that: The fluorocarboxylic acid esters include one or more of 2,2-difluoroethyl acetate, methyl fluorosulfonyl difluoroacetate, methyl trifluoropropionate, and methyl 3,3,3-trifluoroalanine; and / or The fluoroethers include 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; and / or, The carbonate includes one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

12. The lithium-ion battery electrolyte according to claim 1 or 11, characterized in that: The mass ratio of the fluorocarboxylic acid ester, fluoroether, and carbonate is (0.2~0.6):(0.4~0.8):

1.

13. The lithium-ion battery electrolyte according to claim 1, 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 in that: The lithium-ion battery includes the electrolyte as described in any one of claims 1 to 13.

15. The lithium-ion battery according to claim 14, characterized in that: The positive electrode of the lithium-ion battery is made of NCM ternary material and has a charging cut-off voltage ≥4.35V.

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