Wide-temperature lithium ion battery electrolyte and lithium ion battery thereof

Abstract

The application provides a wide-temperature lithium ion battery electrolyte and a lithium ion battery thereof, wherein the lithium ion battery electrolyte comprises a lithium salt, a nonaqueous organic solvent and an additive; the nonaqueous organic solvent comprises a first carbonate, a second carbonate, a third carbonate, a fourth carbonate and a carboxylic acid ester; the first carbonate is dimethyl carbonate and the volume percentage is 39-51%; the second carbonate is propylene carbonate and the volume percentage is 10-15%; the third carbonate is ethylene carbonate and the volume percentage is 8-15%; the fourth carbonate is methyl ethyl carbonate and / or diethyl carbonate and the volume percentage is 8-10%; and the carboxylic acid ester is one or more of propyl acetate, propyl propionate and ethyl propionate and the volume percentage is 19-26%. On the basis of the synergistic effect of dimethyl carbonate and propylene carbonate, the addition of ethylene carbonate, the fourth carbonate and the linear carboxylic acid ester can make the lithium ion battery have better high and low temperature performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a lithium ion battery, and more particularly to a wide-temperature lithium ion battery electrolyte and a lithium ion battery thereof. BACKGROUND

[0002] The working temperature of conventional lithium ion batteries is generally -20-60℃. When the temperature is lower than -20℃, the charge-discharge performance of the lithium ion battery is poor, the battery is difficult to charge, and the discharge capacity is only about 10% of that at normal temperature. When the temperature is higher than 60℃, there is a high safety risk. The main reason is that the non-aqueous organic solvent used in the conventional electrolyte has a high melting point, a low boiling point, or a large viscosity. The high melting point leads to easy solidification at a low temperature, which reduces the diffusion ability of lithium ions in the electrolyte, thereby greatly reducing the discharge performance at a low temperature. The low boiling point has poor high-temperature storage capacity at a temperature higher than 60℃, and generates more gas, which easily causes the safety device of the lithium ion battery to be opened, thereby causing the lithium ion battery to fail at a high temperature. The large viscosity leads to difficult ion migration and low conductivity at a low temperature, which also greatly reduces the low-temperature discharge performance.

[0003] In particular, the non-aqueous organic solvent of the conventional lithium ion battery electrolyte contains a high content of dimethyl carbonate, which has a high melting point (3℃) and a low boiling point (90℃), so its storage capacity at a high temperature is poor, which easily causes the safety device of the battery to be opened, thereby causing the battery to fail at a high temperature. Below 0℃, it is easy to solidify, which reduces the diffusion ability of lithium ions in the electrolyte, greatly reducing the discharge performance at a low temperature.

[0004] However, the working temperature of lithium ion batteries required by some military or special equipment often exceeds this temperature range, as low as -40℃ and as high as 95℃. At this working temperature, the conventional electrolyte containing a large amount of dimethyl carbonate as a solvent does not have high-temperature resistance and low-temperature ionic conductivity. SUMMARY

[0005] Based on the above problems, the purpose of the present application is to provide a wide-temperature lithium ion battery electrolyte and a lithium ion battery thereof that can be normally used at an extreme temperature of -40-95℃, thereby expanding the use field of lithium ion batteries.

[0006] To achieve the above object, the first aspect of the present application provides a wide-temperature lithium ion battery electrolyte, comprising a lithium salt, a non-aqueous organic solvent and an additive, wherein the non-aqueous organic solvent comprises a first carbonate, a second carbonate, a third carbonate, a fourth carbonate and a carboxylic acid ester, the first carbonate is dimethyl carbonate, and the percentage of the first carbonate in the volume of the non-aqueous organic solvent is 39-51%, the second carbonate is propylene carbonate, and the percentage of the second carbonate in the volume of the non-aqueous organic solvent is 10-15%, the third carbonate is ethylene carbonate, and the percentage of the third carbonate in the volume of the non-aqueous organic solvent is 8-15%, the fourth carbonate is methyl ethyl carbonate and / or diethyl carbonate, and the percentage of the fourth carbonate in the volume of the non-aqueous organic solvent is 8-10%, and the carboxylic acid ester is one or more of propyl acetate, propyl propionate and ethyl propionate, and the percentage of the carboxylic acid ester in the volume of the non-aqueous organic solvent is 19-26%.

[0007] The electrolyte of the present application introduces non-aqueous organic solvents with different melting points and boiling points to ensure that the lithium ion battery can be normally used at the extreme temperature of -40-95℃. Specifically, 39-51 vol.% of dimethyl carbonate is added, which has a lower viscosity (0.59 cP.s), is conducive to the penetration of the electrolyte in the lithium ion battery, and improves the cycle performance and consistency of the lithium ion battery. However, the melting point of dimethyl carbonate is relatively high (3℃), and the boiling point is relatively low (90℃), which easily solidifies below 0℃, resulting in a significant decrease in low-temperature discharge performance, and a poor long-term storage capacity at high temperature, which easily causes the safety device on the battery to be opened, thereby causing the battery to fail at high temperature. Therefore, the volume content of dimethyl carbonate in the electrolyte solvent cannot exceed 51%. The addition of propylene carbonate can compensate for the defects of the higher melting point and lower boiling point of dimethyl carbonate. Propylene carbonate is a special solvent, which has a very high boiling point (242℃) and a relatively low melting point (-49℃), which can ensure the high and low temperature performance of the battery at the extreme temperature of -40-95℃, and has a relatively high dielectric constant, which is conducive to improving the lithium ion dissociation capacity of the lithium salt in the electrolyte and improving the conductivity of the electrolyte. However, the viscosity of propylene carbonate is relatively high, so its content cannot exceed 15%, otherwise it will easily cause the electrolyte to penetrate poorly in the lithium ion battery. On the basis of the synergistic effect of dimethyl carbonate and propylene carbonate, vinyl carbonate and fourth carbonate are further added. Vinyl carbonate can fully dissociate the lithium ions of the lithium salt in the electrolyte, improve the lithium ion conductivity of the electrolyte, but the melting point of vinyl carbonate is too high (37℃), which is solid at room temperature, and too much addition is not conducive to the penetration of the electrolyte in the battery, so the addition amount in the electrolyte cannot exceed 15%. The fourth carbonate is methyl ethyl carbonate and / or diethyl carbonate, which has a low viscosity. The addition of the fourth carbonate can further reduce the viscosity of the electrolyte to improve the penetration, improve the temperature window of the electrolyte, reduce the impedance of the battery, and improve the cycle performance. In addition, linear carboxylic acid esters such as propyl acetate, propyl propionate and ethyl propionate are further added. Such linear carboxylic acid esters have the characteristics of low viscosity, high boiling point and low melting point, which can further consider the high and low temperature performance. That is, on the basis of the synergistic effect of dimethyl carbonate and propylene carbonate, the addition of vinyl carbonate, fourth carbonate and linear carboxylic acid ester can make the lithium ion battery still have good high and low temperature performance at the extreme temperature of -40-95℃.

[0008] Further, the lithium salt accounts for 10-20% of the mass percentage of the electrolyte.

[0009] Further, the lithium salt comprises one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0010] Further, the additive accounts for 1-10% of the mass percentage of the electrolyte.

[0011] Further, the additive comprises one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone and 1,3,6-hexane trinitrile. Among them, fluoroethylene carbonate is a good negative electrode film-forming additive, which is beneficial to prolong the cycle life, but it is easy to decompose to produce hydrogen fluoride above 50℃, which on the one hand makes the high-temperature cycle worse, and on the other hand produces gas easily, and the combination of the non-aqueous organic solvent of the present application can weaken the influence of fluoroethylene carbonate on high-temperature gas production. Vinylene carbonate is a good negative electrode film-forming additive, which forms a dense and uniform SEI film on the negative electrode, improves the consistency and cycle performance of the battery, but the film-forming impedance of the negative electrode is too large, and the discharge capacity at low temperature below 0℃ is poor, and the combination of linear carboxylate such as propyl acetate, propyl propionate and ethyl propionate in the non-aqueous organic solvent of the present application can overcome the problem of poor low-temperature discharge capacity. 1,3-Propane sultone is a good positive electrode film-forming additive, which can improve the high-temperature cycle and storage performance of lithium ion battery. 1,3,6-Hexane trinitrile is a positive electrode film-forming protective additive, which has the ability to complex transition metal ions in the positive electrode, can improve the high-temperature storage performance of lithium ion battery and improve the safety performance of the battery.

[0012] Further, the additive comprises fluoroethylene carbonate accounting for 3-5% of the mass percentage of the electrolyte, vinylene carbonate accounting for 0.5-1.2%, 1,3-propane sultone accounting for 1-2% and 1,3,6-hexane trinitrile accounting for 0.5-1.5%.

[0013] The second aspect of the present application provides a lithium ion battery comprising a positive electrode material, a negative electrode material and an electrolyte, wherein the electrolyte is the electrolyte described above. The electrolyte of the present application introduces non-aqueous organic solvents with different melting points and boiling points, so that the lithium ion battery still has good high and low temperature performance at an extreme temperature of-40-95℃.

[0014] Further, the positive electrode material is nickel-cobalt-manganese oxide or nickel-cobalt-aluminum oxide, and the chemical formula of the nickel-cobalt-manganese oxide is LiNi x Coy Mn z M (1-x-y-z) O2, the chemical formula of the nickel cobalt aluminum oxide is LiNi x Co y Al z N (1-x-y-z) O2, wherein M is at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, N is at least one of Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V and Ti, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z ≤ 1.

[0015] Further, the battery of the present application is a cylindrical lithium ion battery, and the working temperature is -40-95℃. DETAILED DESCRIPTION

[0016] For the convenience of description, some substances in the present application are abbreviated. For example, dimethyl carbonate is abbreviated as DMC, propylene carbonate is abbreviated as PC, ethylene carbonate is abbreviated as EC, methyl ethyl carbonate is abbreviated as EMC, diethyl carbonate is abbreviated as DEC, propyl acetate is abbreviated as PA, propyl propionate is abbreviated as PP, ethyl propionate is abbreviated as EP, fluoroethylene carbonate is abbreviated as FEC, vinylene carbonate is abbreviated as VC, and 1,3-propane sultone is abbreviated as 1,3-PS.

[0017] In the wide-temperature lithium ion battery electrolyte and the lithium ion battery of the present application, the wide-temperature refers to the working temperature range of the battery, which can be -40-95℃. The battery of the present application is particularly suitable for a cylindrical lithium ion battery. Due to the structural characteristics of the cylindrical battery, the wicking performance of the electrolyte is poor, and it is usually difficult to work at a temperature lower than -20℃ and a high temperature higher than 60℃. However, when the electrolyte composed of non-aqueous organic solvents with different melting points and boiling points is used, the high and low temperature performance is greatly improved, and the battery can still be used normally at the extreme working temperature of -40-95℃.

[0018] The lithium ion battery of the present application comprises a positive electrode material, a negative electrode material and an electrolyte, wherein the electrolyte is a wide-temperature lithium ion battery electrolyte.

[0019] The positive electrode material is preferably a nickel cobalt manganese oxide or a nickel cobalt aluminum oxide, and the chemical formula of the nickel cobalt manganese oxide is LiNi x Co y Mn z M (1-x-y-z) O2, the chemical formula of the nickel cobalt aluminum oxide is LiNi x Co y Al z N (1-x-y-z)O2, wherein M is at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti, N is at least one of Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V and Ti, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z < 1. The electrolyte can greatly improve the high and low temperature performance of the nickel-cobalt-manganese and nickel-cobalt-aluminum ternary material system battery.

[0020] The negative electrode material is selected from at least one of artificial graphite, natural graphite, mesocarbon microbeads, lithium titanate, silicon-carbon composite material and silicon monoxide.

[0021] The electrolyte can include a lithium salt, a non-aqueous organic solvent and an additive.

[0022] The lithium salt accounts for 10-20% of the mass percentage of the electrolyte, and can be specifically but not limited to 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%. The lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl imide) and lithium bis(trifluoromethylsulfonyl imide). Preferably, the lithium salt includes lithium hexafluorophosphate accounting for 11.25-15% of the mass percentage of the electrolyte, lithium difluorophosphate accounting for 0.3-1%, and imide lithium salt accounting for 0.5-1%, the imide lithium salt being lithium bis(fluorosulfonyl imide) and / or lithium bis(trifluoromethylsulfonyl imide). Through the joint action of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl imide) and lithium bis(trifluoromethylsulfonyl imide), the electrolyte can have a high ionic conductivity while improving the high temperature performance.

[0023] The non-aqueous organic solvent includes a first carbonate, a second carbonate, a third carbonate, a fourth carbonate and a carboxylic acid ester.

[0024] The first carbonate is dimethyl carbonate, and the first carbonate accounts for 39-51% of the volume percentage of the non-aqueous organic solvent, and can be specifically but not limited to 39%, 40%, 41%, 42%, 44%, 45%, 46%, 48%, 50%, 51%.

[0025] The second carbonate is propylene carbonate, and the second carbonate accounts for 10-15% of the volume percentage of the non-aqueous organic solvent, and can be specifically but not limited to 10%, 11%, 12%, 13%, 14%, 15%.

[0026] The third carbonate is ethylene carbonate, and the third carbonate accounts for 8-15% of the volume percentage of the non-aqueous organic solvent, and can be specifically but not limited to 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%.

[0027] The fourth carbonate is methyl ethyl carbonate and / or diethyl carbonate, i.e. the fourth carbonate is methyl ethyl carbonate, the fourth carbonate is diethyl carbonate, or the fourth carbonate is a mixture of methyl ethyl carbonate and diethyl carbonate. The percentage of the fourth carbonate in the non-aqueous organic solvent is 8-10%, and can be but is not limited to 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0028] The carboxylic acid ester is one or more of propyl acetate, propyl propionate, and ethyl propionate, and the percentage of the carboxylic acid ester in the non-aqueous organic solvent is 19-26%, and can be but is not limited to 19%, 20%, 21%, 22%, 23%, 24%, 25%, or 26%.

[0029] The electrolyte additive can be 1-10% of the electrolyte, and can be but is not limited to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The additive can include one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, and 1,3,6-hexanetricarbonitrile. Further, the additive includes 3-5% of fluoroethylene carbonate, 0.5-1.2% of vinylene carbonate, 1-2% of 1,3-propane sultone, and 0.5-1.5% of 1,3,6-hexanetricarbonitrile of the electrolyte. The fluoroethylene carbonate is a good negative electrode film-forming additive, which is beneficial to prolong the cycle life, but is prone to decomposition to produce hydrogen fluoride at 50°C or above, which on the one hand makes the high-temperature cycle worse, and on the other hand is prone to gas production. The non-aqueous organic solvent of the present application can reduce the influence of fluoroethylene carbonate on high-temperature gas production. The vinylene carbonate is a good negative electrode film-forming additive, which forms a dense and uniform SEI film on the negative electrode, improves the consistency and cycle performance of the battery, but the film-forming impedance of the negative electrode is too large, and the discharge capacity at low temperature below 0°C is poor. The linear carboxylic acid ester such as propyl acetate, propyl propionate, and ethyl propionate in the non-aqueous organic solvent of the present application can overcome the problem of poor low-temperature discharge capacity. The 1,3-propane sultone is a good positive electrode film-forming additive, which can improve the high-temperature cycle and storage performance of the lithium ion battery. The 1,3,6-hexanetricarbonitrile is a positive electrode film-forming protective additive, which has the ability to complex transition metal ions in the positive electrode, can improve the high-temperature storage performance of the lithium ion battery, and improve the safety performance of the battery.

[0030] The purposes, technical solutions, and beneficial effects of the present application are further illustrated by specific examples below, but do not constitute any limitation on the present application. If no specific conditions are indicated in the examples, the conventional conditions or the conditions recommended by the manufacturer can be used. If no manufacturer of the reagent or instrument is indicated, it is a conventional product that can be obtained by market purchase.

[0031] Example 1

[0032] Preparation of electrolyte: In an argon atmosphere, various non-aqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, followed by the addition of various additives, the dissolution and sufficient stirring of lithium salt, and the mixing to obtain electrolyte. Among them, the non-aqueous organic solvents accounted for 81% of the mass of the electrolyte and included DMC, PA, PC, EC and DEC, with the volume percentage of each being 39%, 25%, 11%, 15% and 10% respectively. The additives included FEC accounting for 3% of the mass of the electrolyte, VC 1%, 1,3-propane sultone 1% and 1,3,6-hexane trinitrile 1%. The lithium salt included lithium hexafluorophosphate 12%, lithium difluorophosphate 0.5% and lithium bis(fluorosulfonylimide) 0.5% of the mass of the electrolyte respectively.

[0033] Example 2

[0034] Preparation of electrolyte: In an argon atmosphere, various non-aqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, followed by the addition of various additives, the dissolution and sufficient stirring of lithium salt, and the mixing to obtain electrolyte. Among them, the non-aqueous organic solvents accounted for 81% of the mass of the electrolyte and included DMC, PA, PC, EC and DEC, with the volume percentage of each being 51%, 19%, 10%, 10% and 10% respectively. The additives included FEC accounting for 3% of the mass of the electrolyte, VC 1%, 1,3-propane sultone 1% and 1,3,6-hexane trinitrile 1%. The lithium salt included lithium hexafluorophosphate 12%, lithium difluorophosphate 0.5% and lithium bis(fluorosulfonylimide) 0.5% of the mass of the electrolyte respectively.

[0035] Example 3

[0036] Preparation of electrolyte: In an argon atmosphere, various non-aqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, followed by the addition of various additives, the dissolution and sufficient stirring of lithium salt, and the mixing to obtain electrolyte. Among them, the non-aqueous organic solvents accounted for 81% of the mass of the electrolyte and included DMC, PA, PC, EC and DEC, with the volume percentage of each being 39%, 26%, 15%, 12% and 8% respectively. The additives included FEC accounting for 3% of the mass of the electrolyte, VC 1%, 1,3-propane sultone 1% and 1,3,6-hexane trinitrile 1%. The lithium salt included lithium hexafluorophosphate 12%, lithium difluorophosphate 0.5% and lithium bis(fluorosulfonylimide) 0.5% of the mass of the electrolyte respectively.

[0037] Example 4

[0038] Preparation of electrolyte: Under argon atmosphere, various nonaqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing uniformly. Among them, the nonaqueous organic solvents accounted for 81% of the mass of the electrolyte and included DMC, PA, PC, EC, and DEC, and the volume percentages were 45%, 22%, 12%, 8%, and 13%, respectively. The additives included 3% of FEC, 1% of VC, 1% of 1,3-propane sultone, and 1% of 1,3,6-hexanetricarbonitrile bis(fluorosulfonyl imide) lithium, accounting for 3% of the mass of the electrolyte. The lithium salt included 12% of lithium hexafluorophosphate, 0.5% of lithium difluorophosphate, and 0.5% of lithium bis(fluorosulfonyl imide), accounting for 12% of the mass of the electrolyte, respectively.

[0039] Example 5

[0040] Preparation of electrolyte: Under argon atmosphere, various nonaqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing uniformly. Among them, the nonaqueous organic solvents accounted for 81% of the mass of the electrolyte and included DMC, PA, PC, EC, DEC, and EMC, and the volume percentages were 39%, 25%, 11%, 15%, 6%, and 4%, respectively. The additives included 3% of FEC, 1% of VC, 1% of 1,3-propane sultone, and 1% of 1,3,6-hexanetricarbonitrile bis(fluorosulfonyl imide) lithium, accounting for 3% of the mass of the electrolyte. The lithium salt included 12% of lithium hexafluorophosphate, 0.5% of lithium difluorophosphate, and 0.5% of lithium bis(fluorosulfonyl imide), accounting for 12% of the mass of the electrolyte, respectively.

[0041] Example 6

[0042] Preparation of electrolyte: Under argon atmosphere, various nonaqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing uniformly. Among them, the nonaqueous organic solvents accounted for 81% of the mass of the electrolyte and included DMC, PA, PC, EC, and EMC, and the volume percentages were 39%, 25%, 11%, 15%, 6%, and 4%, respectively. The additives included 3% of FEC, 1% of VC, 1% of 1,3-propane sultone, and 1% of 1,3,6-hexanetricarbonitrile bis(fluorosulfonyl imide) lithium, accounting for 3% of the mass of the electrolyte. The lithium salt included 12% of lithium hexafluorophosphate, 0.5% of lithium difluorophosphate, and 0.5% of lithium bis(fluorosulfonyl imide), accounting for 12% of the mass of the electrolyte, respectively.

[0043] Example 7

[0044] Preparation of electrolyte: In a vacuum glove box with water content <1 ppm under argon atmosphere, various nonaqueous organic solvents were mixed, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing. Among them, nonaqueous organic solvents accounted for 80% of the mass of the electrolyte, and included DMC, PA, PC, EC and DEC, and the volume percentages were 39%, 25%, 11%, 15% and 10%, respectively. The additives included 5% FEC of the mass of the electrolyte. The lithium salt included 14% lithium hexafluorophosphate and 1% lithium bis(fluorosulfonylimide) of the mass of the electrolyte, respectively.

[0045] Example 8

[0046] Preparation of electrolyte: In a vacuum glove box with water content <1 ppm under argon atmosphere, various nonaqueous organic solvents were mixed, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing. Among them, nonaqueous organic solvents accounted for 81% of the mass of the electrolyte, and included DMC, PA, PC, EC and DEC, and the volume percentages were 39%, 25%, 11%, 15% and 10%, respectively. The additives included 3% FEC, 1% VC, 1% 1,3-propane sultone and 1% 1,3,6-hexanetricarbonitrile bis(fluorosulfonylimide) of the mass of the electrolyte. The lithium salt included 13% lithium hexafluorophosphate of the mass of the electrolyte.

[0047] Comparative Example 1

[0048] Preparation of electrolyte: In a vacuum glove box with water content <1 ppm under argon atmosphere, various nonaqueous organic solvents were mixed, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing. Among them, nonaqueous organic solvents accounted for 81% of the mass of the electrolyte, and included EMC, DMC and EC, and the volume percentages were 10%, 80% and 10%, respectively. The additives included 3% FEC, 1% VC, 1% 1,3-propane sultone and 1% 1,3,6-hexanetricarbonitrile bis(fluorosulfonylimide) of the mass of the electrolyte. The lithium salt included 12% lithium hexafluorophosphate, 0.5% lithium difluorophosphate and 0.5% lithium bis(fluorosulfonylimide) of the mass of the electrolyte, respectively.

[0049] Comparative Example 2

[0050] Preparation of electrolyte: under argon atmosphere, various non-aqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing uniformly. Among them, non-aqueous organic solvents accounted for 81% of the mass of the electrolyte, and included EMC, PA, PC, EC and DEC, and the volume percentage of each was 45%, 22%, 12%, 8% and 13% respectively. Additives included FEC accounting for 3% of the mass of the electrolyte, VC 1%, 1,3-propane sultone 1% and 1,3,6-hexanetricarbonitrile bis(fluorosulfonylimide) lithium 1%. Lithium salt included lithium hexafluorophosphate 12%, lithium difluorophosphate 0.5% and bis(fluorosulfonylimide) lithium 0.5% of the mass of the electrolyte respectively.

[0051] Comparative Example 3

[0052] Preparation of electrolyte: under argon atmosphere, various non-aqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing uniformly. Among them, non-aqueous organic solvents accounted for 81% of the mass of the electrolyte, and included DMC, PA, PC, EC and DEC, and the volume percentage of each was 39%, 19%, 20%, 12% and 10% respectively. Additives included FEC accounting for 3% of the mass of the electrolyte, VC 1%, 1,3-propane sultone 1% and 1,3,6-hexanetricarbonitrile bis(fluorosulfonylimide) lithium 1%. Lithium salt included lithium hexafluorophosphate 12%, lithium difluorophosphate 0.5% and bis(fluorosulfonylimide) lithium 0.5% of the mass of the electrolyte respectively.

[0053] Comparative Example 4

[0054] Preparation of electrolyte: under argon atmosphere, various non-aqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing uniformly. Among them, non-aqueous organic solvents accounted for 81% of the mass of the electrolyte, and included DMC, PA, PC and DEC, and the volume percentage of each was 50%, 25%, 15% and 10% respectively. Additives included FEC accounting for 3% of the mass of the electrolyte, VC 1%, 1,3-propane sultone 1% and 1,3,6-hexanetricarbonitrile bis(fluorosulfonylimide) lithium 1%. Lithium salt included lithium hexafluorophosphate 12%, lithium difluorophosphate 0.5% and bis(fluorosulfonylimide) lithium 0.5% of the mass of the electrolyte respectively.

[0055] Comparative Example 5

[0056] Preparation of electrolyte: under argon atmosphere, various non-aqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing uniformly. Among them, the non-aqueous organic solvent accounted for 81% of the mass of the electrolyte, and included DMC, PA, PC and EC, and the volume percentage of each was 49%, 25%, 11% and 15% respectively. The additives included FEC accounting for 3% of the mass of the electrolyte, VC 1%, 1,3-propane sultone 1% and lithium 1,3,6-hexanetricarbonitrile bis(fluorosulfonylimide) 1%. The lithium salt included lithium hexafluorophosphate 12%, lithium difluorophosphate 0.5% and lithium bis(fluorosulfonylimide) 0.5% of the mass of the electrolyte respectively.

[0057] Comparative Example 6

[0058] Preparation of electrolyte: under argon atmosphere, various non-aqueous organic solvents were mixed in a vacuum glove box with water content <1 ppm, then various additives were added, and after dissolution and sufficient stirring, lithium salt was added, and the electrolyte was obtained after mixing uniformly. Among them, the non-aqueous organic solvent accounted for 81% of the mass of the electrolyte, and included DMC, PA, PC and EC, and the volume percentage of each was 49%, 25%, 11% and 15% respectively. The additives included FEC accounting for 3% of the mass of the electrolyte, VC 1%, 1,3-propane sultone 1% and lithium 1,3,6-hexanetricarbonitrile bis(fluorosulfonylimide) 1%. The lithium salt included lithium hexafluorophosphate 12%, lithium difluorophosphate 0.5% and lithium bis(fluorosulfonylimide) 0.5% of the mass of the electrolyte respectively.

[0059] The electrolytes prepared in Examples 1-8 and Comparative Examples 1-6 were assembled into lithium ion batteries, and low-temperature discharge, high-temperature storage and high-temperature cycle tests were carried out respectively, and the results are shown in Table 1.

[0060] Preparation method of lithium ion battery: single crystal lithium nickel cobalt manganese oxide NCM622 was used as the positive electrode material, the negative electrode used mesocarbon microbeads, the positive and negative electrode current collectors were aluminum foil and copper foil respectively, and ceramic separator was used to form a cylindrical lithium ion battery, and the battery was provided with a cylindrical battery conventional CID (current interrupt device) structure, after injecting the electrolyte, sealing, activation, formation and full charge to 4.2V.

[0061] Low-temperature discharge test: the battery was charged to 4.2V at 25±2℃ using 0.5C constant current and constant voltage, and the cutoff current was 0.05C, then it was placed in a -40±2℃ constant temperature box for 24h, and discharged to 2.0V at 0.2C, and the discharge capacity ratio was calculated.

[0062] High temperature storage test: the battery was charged to 4.2V by 0.5C constant current and constant voltage, the cut-off current was 0.05C, and then was left for 5h, and then was put into a constant temperature oven of 95±2℃, the voltage was tested once a day until the battery CID was disconnected, and the disconnected days were recorded.

[0063] High temperature cycle test: the battery was discharged to 3.0V by 0.5C constant current at 65±2℃, left for 30min, and then was charged to 4.2V by 0.5C constant current and constant voltage, the cut-off current was 0.05C, and then was left for 30min, and the cycle was repeated, and the discharge capacity of the first cycle and the discharge capacity of the last cycle were recorded, and the capacity retention rate was calculated.

[0064] Capacity retention rate = discharge capacity of the last cycle / discharge capacity of the first cycle x 100%.

[0065] Table 1 performance of lithium ion battery using electrolyte of examples 1-8 and comparative examples 1-6

[0066]

[0067]

[0068] From the results of Table 1, it can be seen that the electrolyte of the present application has better discharge performance at -40℃, 0.2C, based on the synergistic effect of dimethyl carbonate and propylene carbonate, and further adding ethylene carbonate, fourth carbonate and linear carboxylate, and by introducing non-aqueous organic solvents with different melting points and boiling points, the voltage is still above 3.9V after 20 days of storage at high temperature of 95℃, and the capacity retention rate is still above 80% after 400 cycles at 65℃. Therefore, the lithium ion battery using the electrolyte of the present application has better high and low temperature performance at the extreme temperature of -40-95℃, and can still be used normally.

[0069] From comparative example 1 and examples 6-7, it can be seen that the electrolyte of the present application has better high and low temperature performance based on the introduction of non-aqueous organic solvents with different melting points and boiling points, and further adding additives, and especially when the additives include FEC, VC, 1,3-PS and 1,3,6-hexanetricarbonitrile, the battery performance is the best.

[0070] In comparative examples 1 and 3-6, due to the high content of dimethyl carbonate, or due to the lack of the synergistic effect of second, third and fourth carbonates or carboxylate, the low temperature discharge, high temperature storage and high temperature cycle performance of the lithium ion battery cannot be considered simultaneously. In comparative example 2, the content of EMC is 45%, and the boiling point of EMC is relatively low (108℃), and it is still easy to produce gas and disconnect at high temperature of 95℃. In addition, due to the lack of DMC, the wetting effect of the electrolyte is poor, and lithium precipitation is easy to occur, the cycle performance of the battery after lithium precipitation is poor, and the long-term high temperature storage performance is also affected.

[0071] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the present application.

Claims

1. A lithium-ion battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, characterized in that, This is a cylindrical lithium-ion battery with an operating temperature of -40 to 95°C. The electrolyte is a wide-temperature lithium-ion battery electrolyte, comprising lithium salt, a non-aqueous organic solvent, and additives. The non-aqueous organic solvent comprises a first carbonate, a second carbonate, a third carbonate, a fourth carbonate, and a carboxylic acid ester. The first carbonate is dimethyl carbonate, and the first carbonate accounts for 39-51% of the volume of the non-aqueous organic solvent. The second carbonate is propylene carbonate, and the second carbonate accounts for 10-15% of the volume of the non-aqueous organic solvent. The third carbonate is ethylene carbonate. The third carbonate comprises 8-15% of the volume of the non-aqueous organic solvent; the fourth carbonate is ethyl methyl carbonate and / or diethyl carbonate, and comprises 8-10% of the volume of the non-aqueous organic solvent; the carboxylic acid ester is one or more of propyl acetate, propyl propionate, and ethyl propionate, and comprises 19-26% of the volume of the non-aqueous organic solvent; the additives include 3-5% fluoroethylene carbonate, 0.5-1.2% vinylene carbonate, 1-2% 1,3-propanesulfonate lactone, and 0.5-1.5% 1,3,6-hexanetrionitrile, by mass percentage of the electrolyte.

2. The lithium-ion battery as described in claim 1, characterized in that, The lithium salt accounts for 10-20% of the mass percentage of the electrolyte.

3. The lithium-ion battery as described in claim 1, characterized in that, The lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonylimide), and lithium bis(trifluoromethylsulfonylimide).

4. The lithium-ion battery as described in claim 1, characterized in that, The lithium salt comprises 11.25-15% lithium hexafluorophosphate, 0.3-1% lithium difluorophosphate, and 0.5-1% lithium imine salt, which are lithium bis(fluorosulfonyl)imine and / or lithium bistrifluoromethylsulfonylimine, accounting for 0.5-1% of the mass percentage of the electrolyte.

5. The lithium-ion battery according to claim 1, characterized in that, The positive electrode material is nickel cobalt manganese oxide or nickel cobalt aluminum oxide, and the chemical formula of the nickel cobalt manganese oxide is LiNi. x Co y Mn z M (1-x-y-z) O2, the chemical formula of the nickel-cobalt-aluminum oxide is LiNi x Co y Al z N (1-x-y-z) O2, wherein M is at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, and N is at least one of Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, and Ti. <x<1,0<y<1,0<z<1,x+y+z≤1。

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