Lithium ion battery electrolyte without EC and lithium ion battery

Abstract

The invention relates to an EC-free lithium ion battery electrolyte and a lithium ion battery. In order to solve the problem that a high-voltage NCM system lithium ion battery is poor in high and low temperature performance and normal temperature cycle performance, the invention provides an electrolyte, the electrolyte comprises an organic solvent, a lithium salt and an additive, the organic solvent comprises fluorocarboxylate, fluoroether and carbonate, and the organic solvent does not contain ethylene carbonate; the additives comprise a first additive and / or a second additive, the first additive comprises dimethoxydivinylsilane and / or dimethyl (dimethylamino) vinylsilane, and the second additive comprises hexamethylene diisocyanate, trimethylsiloxyethyl isocyanate, 2-(1, 1-thiophane-3-yl)-2, 2, 4-triazole-3-yl)-1, 2, 4-triazole-3-yl)-1, 2, 4-triazole-3-yl)-1, 2, 4-triazole-3-yl)-1, 2, 4-triazole-3-yl)-1, 2, 4- the solvent is one or more of methyl 2, 2-difluoroacetate. Through the synergistic effect of the EC-free solvent system and the additive, the stability of the high-voltage NCM system lithium ion battery under high voltage is improved, so that the lithium ion battery has better high and low temperature performance and normal temperature cycle performance.

Description

Technical Field

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

[0002] Lithium-ion battery cathode materials such as NCM ternary materials have the advantages of high specific capacity, good cycle performance, good safety and low environmental pollution. They are gradually gaining attention and are expected to become one of the mainstream cathode materials for lithium-ion batteries in the future. In order to meet people's demand for high energy density, NCM ternary cathode materials are also developing in two directions: 1) high nickel content, higher Ni content can bring higher capacity; 2) high voltage, the increase in voltage can increase the capacity of the material on the one hand, and the voltage platform of the material on the other hand. However, as the charging voltage increases, the stability of the cathode material / electrolyte interface will decrease, causing an increase in side reactions, which will seriously affect the cycle performance of lithium-ion batteries.

[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 which the matching of electrolytes is very important.

[0004] Traditional carbonates, such as ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc., are ideal choices for organic electrolyte solvents due to their high ionic conductivity, good solubility in lithium salts, and ability to form a stable solid electrolyte interface (SEI) film. Although the oxidation potential of these solvents is as high as 5V, they are oxidized and decomposed at a lower potential (about 4.5V) due to the catalytic effect of transition metal ions in the positive electrode material, resulting in rapid deterioration of battery performance. Therefore, the development of high-voltage electrolytes that match high-voltage positive electrode materials is becoming a hot topic for research by various companies and research institutes.

[0005] Adding a small amount of functional additives to carbonate-based electrolytes allows them to undergo oxidation / reduction decomposition reactions before solvent molecules, and forms an effective protective film on the electrode surface, which can inhibit the subsequent decomposition of carbonate-based solvents. The film formed by additives with excellent performance can even inhibit the dissolution of metal ions in the positive electrode material and their deposition on the negative electrode, thereby significantly improving the electrode / electrolyte interface stability and the battery's cycle performance. In addition to excellent functional additives, fluorinated solvents are also a choice in high-voltage systems; due to the strong electronegativity and weak polarity of fluorine atoms, fluorinated solvents have high electrochemical stability. By studying a series of organic carbonate solvents that are partially or completely substituted with fluorine, scholars have confirmed that the physical properties of ordinary organic solvents have changed greatly after the introduction of fluorine, such as the lowering of the solvent's freezing point, the improvement of its antioxidant stability, and the formation of an SEI film on the surface of the carbon negative electrode. The HOMO energy of fluoroethylene carbonate (FEC) is -12.33 eV, which is much lower than non-fluorinated carbonate solvents such as EC. The oxidation potential of methyl 2,2,2-trifluoroethyl carbonate and ethyl 2,2,2-trifluoroethyl carbonate (TFEEC) is as high as 5.8-5.9 V (vs. Li / Li+), which is much higher than non-fluorinated EMC and DEC. Theoretically, cyclic carbonates have better oxidation resistance than chain carbonates, and both can meet the needs of 5V high-voltage batteries. However, 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 oxidation stability of the actual electrolyte system is lower than the theoretical calculated value. The high melting point of EC (36.4℃) severely 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 way to improve the compatibility of electrodes and electrolytes and improve battery performance.

[0006] In view of this, there is an urgent need to provide a functional electrolyte to solve the above problems so that high specific energy system batteries can be promoted and applied. Summary of the invention

[0007] The object of the present invention is to provide an electrolyte suitable for high voltage lithium ion batteries and capable of improving the high and low temperature performance and room temperature cycle performance of the battery.

[0008] The second object of the present invention 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 solution adopted by the present invention is as follows:

[0010] A lithium-ion battery electrolyte without EC comprises an organic solvent, a lithium salt and an additive, wherein the organic solvent comprises a fluorocarboxylic acid ester, a fluoroether and a carbonate, and the organic solvent does not contain ethylene carbonate; the additive comprises a first additive and / or a second additive, wherein the first additive comprises dimethoxydivinylsilane and / or dimethyl (dimethylamino) vinylsilane, and the second additive comprises one or more of hexamethylene diisocyanate, trimethylsilyloxyethyl isocyanate and 2-(1,1-dioxidotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester.

[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, and the third additive is selected from one or more cyclic sulfate compounds.

[0017] More preferably, the cyclic sulfate ester compound includes dithiothreitol disulfide (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%, or 1.5%.

[0020] Preferably, the additive further includes a fourth additive, and the fourth additive is selected from one or more lithium-containing compounds.

[0021] More preferably, the lithium-containing compound includes lithium difluorophosphate (LiDFP) and lithium difluorobis(oxalate) phosphate (LiFOP).

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

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

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

[0025] In some embodiments, the fourth additive is lithium difluorophosphate and lithium difluorobisoxalate phosphate, and the lithium difluorophosphate accounts for 0.5% to 1% of the total mass of the electrolyte.

[0026] Preferably, the additive further includes a fifth additive, and the fifth additive is selected from one or more phosphate compounds.

[0027] More preferably, the phosphate compound includes tris(trimethylsilyl)phosphate.

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

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

[0030] Preferably, the additive further includes a sixth additive, and the sixth additive is selected from one or more carbonate compounds.

[0031] More preferably, the carbonate compound includes vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

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

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

[0034] In some embodiments, the sixth additive is vinylene carbonate, and the vinylene carbonate accounts for 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, and the fluoroethylene carbonate accounts for 1% to 10% of the total mass of the electrolyte.

[0036] Furthermore, the fluoroethylene carbonate accounts for 1% to 5% of the total mass of the electrolyte.

[0037] Preferably, the fluorocarboxylic acid ester includes one or more of 2,2-difluoroethyl acetate, methyl fluorosulfonyldifluoroacetate, methyl trifluoropropionate, and methyl 3,3,3-trifluoroalanine.

[0038] 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.

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

[0040] Preferably, the mass ratio of the fluorocarboxylic acid ester, the fluoroether and the carbonate is (0.2-0.6):(0.4-0.8):1.

[0041] 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.

[0042] 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 and propylene carbonate.

[0043] Preferably, the organic solvent may further include one or more of carboxylic acid esters, ethers, and sulfones.

[0044] 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.

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

[0046] More preferably, the sulfone includes one or more of dimethyl sulfoxide, sulfolane, and 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 to 1.5M.

[0049] Further preferably, the molar concentration of the lithium salt in the electrolyte is 1M to 1.5M, for example, 1M, 1.1M, 1.2M, 1.3M, 1.4M or 1.5M.

[0050] The present invention also provides a lithium ion battery, which comprises the electrolyte as described above.

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

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

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

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

[0055] The present invention improves the stability of a high-voltage NCM system lithium-ion battery under high voltage through the synergistic effect of the 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 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.

[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 electrolyte effect, the batteries in the following comparative examples and embodiments uniformly use 2500mAh soft-pack batteries of 4.4V NCM622 / artificial graphite system. The soft-pack batteries are commercially available products or the preparation method of the soft-pack batteries can refer to the prior art, and the present invention is not specifically limited.

[0059] The configuration methods of the electrolytes in the following comparative examples and embodiments refer to the prior art and are not discussed in detail in the present invention.

[0060] Comparative Example 1

[0061] 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.

[0062] Comparative Example 2

[0063] Electrolyte: organic solvent is ethylene carbonate and ethyl methyl carbonate, with a mass ratio of 30:70; electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

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

[0065] Comparative Example 3

[0066] Electrolyte: organic solvent is ethylene carbonate and ethyl methyl carbonate, with a mass ratio of 30:70; electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1 mol / L;

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

[0068] Comparative Example 4

[0069] 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, and no other functional additives are added.

[0070] Comparative Example 5

[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, and no other functional additives are added.

[0072] Comparative Example 6

[0073] Electrolyte: The 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), 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, and no other functional additives are added.

[0074] Example 1

[0075] Electrolyte: The organic solvent is 3,3,3-trifluoroalanine methyl ester (CAS No.: 27240-44-4), 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;

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

[0077] Example 2

[0078] Electrolyte: The organic solvent is methyl fluorosulfonyl difluoroacetate, 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;

[0079] Based on the total mass of the electrolyte, 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% trimethylsiloxyethyl isocyanate (CAS No.: 22503-22-1, Shanghai Biyang Industrial), and 1% lithium difluorobisoxalate phosphate (LiFOP) were added.

[0080] Example 3

[0081] Electrolyte: The organic solvent is 2,2-difluoroethyl acetate, 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;

[0082] Based on the total mass of the electrolyte, 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.2% methyl 2-(1,1-dioxidotetrahydrothiophen-3-yl)-2,2-difluoroacetate (CAS No.: 1783700-24-2, Shanghai Haohong Biology) and 1% LiDFP were added.

[0083] Example 4

[0084] Electrolyte: The organic solvent is methyl fluorosulfonyl difluoroacetate, 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;

[0085] Based on the total mass of the electrolyte, 1% DTD, 1% dimethoxydivinylsilane, 0.2% methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate and 1% LiDFP were added.

[0086] Example 5

[0087] 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;

[0088] 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate, 1% LiDFP and 1% LiFOP were added based on the total mass of the electrolyte.

[0089] Example 6

[0090] Electrolyte: The organic solvent is methyl trifluoropropionate, 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;

[0091] 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate, 0.5% LiDFP, 1% LiFOP and 1% tris(trimethylsilyl)phosphate (TMSP) were added based on the total mass of the electrolyte.

[0092] Example 7

[0093] Electrolyte: The organic solvent is methyl trifluoropropionate, 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 1.1 mol / L,

[0094] Based on the total mass of the electrolyte, 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate, 0.5% LiDFP, 1% LiFOP, 1% TMSP and 0.5% vinylene carbonate (VC) were added.

[0095] Example 8

[0096] Electrolyte: The organic solvent is methyl trifluoropropionate, 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 1.3 mol / L;

[0097] Based on the total mass of the electrolyte, 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate, 0.5% LiDFP, 1% LiFOP, 1% TMSP and 0.5% VC were added.

[0098] Example 9

[0099] Electrolyte: The organic solvent is methyl trifluoropropionate, 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 1.3 mol / L;

[0100] Based on the total mass of the electrolyte, 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.3% methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate, 0.5% LiDFP, 1% LiFOP, 1% TMSP, 0.5% VC and 10% fluoroethylene carbonate (FEC) were added.

[0101] Example 10

[0102] Electrolyte: The organic solvent is propylene carbonate, methyl trifluoropropionate, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, and ethyl methyl carbonate, and the mass ratio of the four is 5:15:30:50; the electrolyte lithium salt is LiPF 6 , the concentration of lithium salt is 1.1 mol / L;

[0103] Based on the total mass of the electrolyte, 1% DTD, 1% dimethyl(dimethylamino)vinylsilane, 0.5% methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate, 1% LiDFP, 1% LiFOP, 1% TMSP, 0.5% VC and 5% FEC were added.

[0104] Embodiment 11

[0105] Electrolyte: The organic solvent is methyl trifluoropropionate, 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;

[0106] 1% of dimethyl(dimethylamino)vinylsilane and 0.3% of methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate were added based on the total mass of the electrolyte.

[0107] Example 12

[0108] Electrolyte: The organic solvent is methyl trifluoropropionate, 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;

[0109] 1% of dimethyl(dimethylamino)vinylsilane and 0.3% of trimethylsilylethyl isocyanate were added based on the total mass of the electrolyte.

[0110] Example 13

[0111] Electrolyte: The organic solvent is methyl trifluoropropionate, 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;

[0112] 1% DTD, 1% dimethyl(dimethylamino)vinylsilane and 0.3% methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate were added based on the total mass of the electrolyte.

[0113] Embodiment 14

[0114] Electrolyte: The organic solvent is methyl trifluoropropionate, 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;

[0115] 1% of dimethyl(dimethylamino)vinylsilane, 0.3% of methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate, 0.5% of LiDFP and 1% of LiFOP were added based on the total mass of the electrolyte.

[0116] Embodiment 15

[0117] Electrolyte: The organic solvent is methyl trifluoropropionate, 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;

[0118] 1% DTD, 1% dimethyl(dimethylamino)vinylsilane and 1% LiDFP were added 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 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;

[0121] 1% DTD, 0.3% methyl 2-(1,1-dioxytetrahydrothiophen-3-yl)-2,2-difluoroacetate and 1% LiDFP were added based on the total mass of the electrolyte.

[0122] Lithium-ion battery performance test

[0123] The battery cycle performance 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.

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

[0125] 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 1C cycle performance within a voltage range of 2.75-4.4V.

[0126] Capacity retention rate after 1000 cycles at 25° C. (%)=discharge capacity at 1000th cycle / discharge capacity at first cycle×100%.

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

[0128] After the lithium-ion soft-pack batteries in all comparative examples and embodiments were formed, the batteries were tested at 45° C. for 1C cycle performance in the voltage range of 2.75-4.4V.

[0129] Capacity retention rate after 1000 cycles at 45° C. (%)=discharge capacity at 1000th cycle / discharge capacity at first cycle×100%.

[0130] Thickness expansion ratio after 1000 cycles at 45° C. (%)=thickness of the battery after the 1000th cycle / initial thickness of the battery×100%.

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

[0132] After all the experimental batteries were fully charged at 1C constant current and constant voltage, they were stored in a high and low temperature box set at 60°C for 56 days. During the storage process, the internal resistance, gas production and capacity recovery rate of the experimental batteries were tested. The testing methods for internal resistance, gas production and capacity recovery rate were based on the existing technology.

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

[0134] All experimental batteries were fully charged at 1C at room temperature 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 1C, 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:

[0135] -20℃ low temperature discharge rate (%) = A 1 / A 0 ×100%.

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

[0137] Table 1

[0138]

[0139]

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

[0141] Table 2

[0142]

[0143]

[0144] The comparison of the data of each embodiment and comparative example in the table shows that the synergistic effect of replacing EC with fluorinated solvents and various functional additives improves the room temperature cycle performance, high temperature cycle performance, thickness expansion in high temperature cycle, high temperature storage and low temperature discharge of the 4.4V high voltage ternary NCM622 battery. By optimizing the combination of additives, a stable solid electrolyte interface film is formed on the surface of the positive and negative electrode materials of the battery, preventing the direct contact between the material and the electrolyte, avoiding the catalytic decomposition of the electrolyte solvent by the positive electrode material under high voltage and high temperature conditions, and at the same time, the addition of fluorinated carboxylic acid esters and fluorinated ethers can reduce the viscosity of the electrolyte, thereby significantly improving the room temperature, high temperature and low temperature performance of the high voltage NCM battery.

[0145] By comparing Comparative Example 1 with Comparative Examples 4 to 6, it is found that when only a fluorinated solvent is used to replace EC without adding any functional additives, the improvement of the room temperature cycle performance and high and low temperature performance of the battery is limited.

[0146] By comparing Comparative Examples 4 to 6 and the Examples, it is found that the room temperature cycle performance and high and low temperature performance of the battery can be improved to a great extent through the synergistic effect of the fluorinated solvent and the additive.

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

[0148] 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. An EC-free lithium-ion battery electrolyte comprising an organic solvent, a lithium salt and an additive, Features: The organic solvent includes fluorocarboxylates, fluoroethers and carbonates, and the organic solvent does not contain vinyl carbonate; the additive includes a first additive and / or a second additive, the first additive includes dimethoxydivinylsilane and / or dimethyl (dimethylamino) vinylsilane, and the second additive includes one or more of hexamethylene diisocyanate, trimethylsilyloxyethyl isocyanate, and 2-(1,1-dioxidotetrahydrothiophene-3-yl)-2,2-difluoroacetic acid methyl ester.

2. The lithium ion battery electrolyte according to claim 1, Features: 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, Features: The additives further include a third additive, and the third additive is selected from one or more cyclic sulfate compounds.

4. The lithium ion battery electrolyte according to claim 3, Features: The cyclic sulfate ester compound includes 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, Features: The additives further include a fourth additive, and the fourth additive is selected from one or more lithium-containing compounds.

6. The lithium ion battery electrolyte according to claim 5, Features: The lithium-containing compound includes lithium difluorophosphate and lithium difluorobisoxalate 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, Features: The additives further include a fifth additive, and the fifth additive is selected from one or more phosphate compounds.

8. The lithium ion battery electrolyte according to claim 7, Features: The phosphate compound includes tris(trimethylsilyl)phosphate; 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, Features: The additives further include a sixth additive, and the sixth additive is selected from one or more carbonate compounds.

10. The lithium ion battery electrolyte according to claim 1 or 9, Features: The carbonate compounds include vinylene carbonate and fluoroethylene 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, 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 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, Features: The mass ratio of the fluorocarboxylic acid ester, the fluoroether and the carbonate is (0.2-0.6):(0.4-0.8):

1.

13. The lithium ion battery electrolyte according to claim 1, Features: The lithium salt is lithium hexafluorophosphate; and / or the molar concentration of the lithium salt in the electrolyte is 0.8M to 1.5M.

14. A lithium ion battery, Features: The lithium ion battery comprises the electrolyte according to any one of claims 1 to 13.

15. The lithium ion battery according to claim 14, Features: The positive electrode of the lithium-ion battery adopts NCM ternary material and the charging cut-off voltage is ≥4.35V.

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