Electrolyte, preparation method of electrolyte and lithium battery

Abstract

The invention relates to the technical field of batteries, in particular to an electrolyte, a preparation method of the electrolyte and a lithium battery. The electrolyte comprises a lithium salt, an organic solvent and an additive, the organic solvent comprises an ether solvent, the ether solvent comprises cyclic ether, non-halogen substituted chain ether and halogen substituted chain ether, and the halogen substituted chain ether is at least one of chlorinated chain ether, brominated chain ether and iodinated chain ether. By configuring at least one of cyclic ether, non-halogen substituted chain ether and chlorinated chain ether, brominated chain ether and iodinated chain ether in a lithium battery electrolyte system for cooperation, the interface impedance is reduced, the low-temperature conductivity is improved, the problem of low-temperature lithium precipitation is relieved, the adverse effect of high temperature on the lithium battery is improved, and the service life of the lithium battery is prolonged. And the charge-discharge performance, the cycle performance and the safety performance of the lithium battery at relatively low temperature and relatively high temperature are improved. The lithium battery using the electrolyte provided by the invention has better performance at normal temperature, lower temperature and higher temperature, and a better application temperature range of the battery is widened.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrolyte, a method for preparing the electrolyte, and a lithium battery. Background Art

[0002] Lithium batteries have the advantages of high energy density, portability, fast charging and no memory effect, and have been widely used in mobile phones, laptops, electric vehicles, energy storage systems and other fields. However, the performance of lithium batteries is greatly affected by temperature. Under low temperature conditions, the kinetic process of metal lithium slows down, which can easily cause uneven deposition of metal lithium and lithium precipitation. Under high temperature conditions, the side reactions in lithium batteries intensify, the cycle performance deteriorates more significantly, and even overheating and explosion may occur. Therefore, too low temperature and too high temperature can easily reduce the charging and discharging performance, cycle performance and safety performance of lithium batteries.

[0003] Improving the performance of lithium batteries under low or high temperature conditions is an important research direction in this field. Summary of the invention

[0004] The present application aims to provide an electrolyte, a method for configuring the electrolyte, and a lithium battery to improve the low-temperature performance and high-temperature performance problems of the lithium battery.

[0005] The embodiment of the present application is implemented as follows:

[0006] In a first aspect, an embodiment of the present application provides an electrolyte comprising a lithium salt, an organic solvent and an additive, wherein the organic solvent comprises an ether solvent, wherein the ether solvent comprises a cyclic ether, a non-halogen-substituted chain ether and a halogen-substituted chain ether, and the halogen-substituted chain ether is at least one of a chlorinated chain ether, a brominated chain ether and an iodinated chain ether.

[0007] In one embodiment of the present application, the number of carbon atoms of the non-halogen substituted chain ether is ≤10.

[0008] In one embodiment of the present application, the number of carbon atoms of the halogen-substituted chain ether is ≤10.

[0009] In one embodiment of the present application, the number of halogen atoms substituted in the halogen-substituted chain ether is ≤12.

[0010] In one embodiment of the present application, the number of oxygen atoms in the cyclic ether is ≤3, and the number of carbon atoms is ≤10.

[0011] In one embodiment of the present application, the non-halogen substituted chain ether includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0012] In one embodiment of the present application, the halogen-substituted chain ether includes at least one of 1,2-dichloroethane; 1,3-dichloropropane; 1,2-dibromopropane; 1,3-dibromobutane; and 1,2-diiodoethane.

[0013] In one embodiment of the present application, the cyclic ether includes at least one of ethylene oxide, propylene oxide, 1,2-butylene oxide, 1,4-butylene oxide, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, and 1,2-hexylene oxide.

[0014] In one embodiment of the present application, the mass proportion of the non-halogen substituted chain ether in the ether solvent is 5-50%.

[0015] In one embodiment of the present application, the mass proportion of the halogen-substituted chain ether in the ether solvent is 0.1-50%.

[0016] In one embodiment of the present application, the mass proportion of the cyclic ether in the ether solvent is 10-60%.

[0017] In one embodiment of the present application, the mass proportion of the ether solvent in the electrolyte is 30-80%.

[0018] In one embodiment of the present application, the mass proportion of the lithium salt in the electrolyte is 5-30%.

[0019] In one embodiment of the present application, the additive accounts for 0-5% by mass in the electrolyte.

[0020] In one embodiment of the present application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(pentafluoroethylsulfonyl)imide.

[0021] In one embodiment of the present application, the additive includes at least one of lithium nitrate, lithium carbonate, lithium fluoride, lithium bromide, lithium iodide, fluoroethylene carbonate, difluoroethylene carbonate, propane sultone, propene sultone, propene sultone, vinylene carbonate, vinyl carbonate, trifluoromethyl vinyl carbonate, vinyl sulfate, and vinyl sulfite.

[0022] In one embodiment of the present application, the organic solvent further comprises carboxylic acid ester, and the mass proportion of the carboxylic acid ester in the electrolyte is 5-40%.

[0023] In one embodiment of the present application, the organic solvent further includes carboxylic acid ester, and the number of carbon atoms of the carboxylic acid ester is ≤8.

[0024] In one embodiment of the present application, the organic solvent further includes carbonate, and the mass proportion of the carbonate in the electrolyte is 1-30%.

[0025] In one embodiment of the present application, the organic solvent further includes carbonate, and the number of carbon atoms of the carbonate is ≤6.

[0026] In a second aspect, an embodiment of the present application provides a method for preparing an electrolyte, mixing a lithium salt and an organic solvent, wherein the organic solvent includes an ether solvent, the ether solvent includes cyclic ether, non-halogen-substituted chain ether and halogen-substituted chain ether, and the halogen-substituted chain ether is at least one of chlorinated chain ether, brominated chain ether and iodinated chain ether.

[0027] In one embodiment of the present application, a lithium salt is first added to an organic solvent having a cyclic ether, and then non-halogen-substituted chain ether and halogen-substituted chain ether are added after mixing.

[0028] In a third aspect, an embodiment of the present application provides a lithium battery, comprising the electrolyte described in any one of the second aspects; or, comprising an electrolyte prepared by the method for preparing the electrolyte described in any one of the second aspects.

[0029] The technical solution of the present application reduces interfacial impedance, improves the conductivity of the electrolyte at low temperatures, alleviates the problem of low-temperature lithium precipitation, and improves the adverse effects of high temperature on lithium batteries, thereby improving the charge and discharge performance, cycle performance and safety performance of lithium batteries at lower and higher temperatures by configuring cyclic ethers, non-halogen-substituted chain ethers, and at least one of chlorinated chain ethers, brominated chain ethers and iodinated chain ethers in the organic solvent of the electrolyte system of the lithium battery.

[0030] After applying the electrolyte provided in the present application, the lithium battery has better performance at room temperature, lower temperature and higher temperature, thereby expanding the optimal application temperature range of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 A flow chart of a method for preparing an electrolyte provided in one embodiment of the present application;

[0033] Figure 2A flow chart of a method for preparing an electrolyte provided in another embodiment of the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0036] In this application, unless otherwise stated, directional words such as "upper" and "lower" generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device. In addition, in the description of this application, the term "including" means "including but not limited to". The terms first, second, third, etc. are used only as labels and do not impose numerical requirements or establish an order.

[0037] In this application, "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0038] In the present application, "at least one" means one or more, and "plurality" means two or more. "One or more", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0039] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0040] Metallic lithium has a high theoretical specific capacity, low density and low electrochemical potential, which makes lithium-ion batteries have the advantages of high energy density, lightness, fast charging and no memory effect. They are widely used in mobile phones, laptops, electric vehicles, energy storage systems and other fields. At the same time, these characteristics of metallic lithium may also produce some unfavorable phenomena in some cases, which restricts its application. For example, the application temperature range of lithium batteries. Lithium-ion batteries are generally set to be used at an ambient temperature of -20-55°C, and the optimal operating temperature is generally 0-40°C. As the temperature drops to -20°C or lower, the lower temperature causes the kinetic process to slow down, which can easily cause uneven deposition of metallic lithium and lithium precipitation. As the temperature gradually rises to 55°C or higher, it is easy for side reactions to intensify, resulting in deterioration of cycle performance and even overheating and explosion.

[0041] In view of this, the present application provides a technical solution, which improves the electrolyte system of lithium batteries, alleviates the low-temperature lithium precipitation phenomenon and the reduction of high-temperature cycle performance, improves the cycle performance and safety performance of lithium batteries at lower and higher temperatures, and makes lithium batteries have better performance at room temperature, lower temperature and higher temperature, thereby expanding the optimal application temperature range of the battery.

[0042] In a first aspect, an embodiment of the present application provides an electrolyte, the electrolyte comprising a lithium salt, an organic solvent and an additive, the organic solvent comprising an ether solvent, the ether solvent comprising a cyclic ether, a non-halogen substituted chain ether and a halogen substituted chain ether, the halogen substituted chain ether being at least one of a chlorinated chain ether, a brominated chain ether and an iodinated chain ether.

[0043] By configuring cyclic ether and non-halogen substituted chain ether, as well as at least one of chlorinated chain ether, brominated chain ether and iodinated chain ether in an organic solvent, the interfacial impedance is reduced, the conductivity of the electrolyte at low temperature is improved, the problem of low-temperature lithium precipitation is alleviated, and the adverse effects of high temperature on lithium batteries are improved, thereby improving the cycle performance and safety performance of lithium batteries at lower and higher temperatures.

[0044] In some embodiments, the non-halogen substituted linear ether has ≤10 carbon atoms.

[0045] Illustratively, the non-halogen substituted chain ether includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0046] In some embodiments, the halogen-substituted linear ether has ≤10 carbon atoms.

[0047] In some embodiments, the number of halogen atoms substituted in the halogen-substituted linear ether is ≤12.

[0048] Illustratively, the halogen-substituted chain ether includes at least one of 1,2-dichloroethane; 1,3-dichloropropane; 1,2-dibromopropane; 1,3-dibromobutane; and 1,2-diiodoethane.

[0049] In some embodiments, the cyclic ether has ≤3 oxygen atoms and ≤10 carbon atoms.

[0050] Illustratively, the cyclic ether includes at least one of ethylene oxide, propylene oxide, 1,2-butylene oxide, 1,4-butylene oxide, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, and 1,2-hexylene oxide.

[0051] In some embodiments, the mass proportion of non-halogen substituted chain ether in ether solvent is 5-50%. For example, the mass proportion of non-halogen substituted chain ether in ether solvent is 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 22%, 24%, 25%, 26%, 28%, 29%, 30%, 31%, 33%, 35%, 37%, 39%, 40%, 41%, 42%, 44%, 45%, 47%, 48% or 50%, etc.

[0052] In some embodiments, the mass proportion of the halogen-substituted chain ether in the ether solvent is 0.1-50%. For example, the mass proportion of the halogen-substituted chain ether in the ether solvent is 0.1%, 0.3%, 0.5%, 0.6%, 0.8%, 1.0%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.0%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 2.9%, 3.0%, 3.2%, 3.5%, 3.7%, 3.8%, 4.0%, 4.2%, 4.4%, 4.5%, 4.7%, 4.9%, 5.0%, 5.2%, 5.5%, 5.6%, 5.8%, 6.0%, 6.2%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8.0%, 8.1%, 8.2%, 8.5%, 8.7%, 8.8%, 8.9%, 9.1%, 9.2%, 9.3%, 9.4%, 9.5%, 9.6%, 9.7%, 9.8%, 9.9%, 10.1%, 10.2%, 10.3%, 10.4%, 10.5%, 10.6%, 10.7%, 10.8%, 10.9%, 10. .1%, 6.3%, 6.5%, 6.8%, 6.9%, 7.0%, 7.2%, 7.5%, 7.8%, 8.0%, 8.3%, 8.5%, 8.8%, 9.0%, 9.2%, 9.5%, 9.6%, 9.8%, 10%, 12%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 22%, 24%, 25%, 26%, 28%, 29%, 30%, 32%, 34%, 35%, 36%, 38%, 40%, 42%, 45%, 47%, 48% or 50%, etc.

[0053] In some embodiments, the mass proportion of the cyclic ether in the ether solvent is 10-60%. For example, the mass proportion of the cyclic ether in the ether solvent is 10%, 12%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 22%, 24%, 25%, 26%, 28%, 29%, 30%, 31%, 33%, 35%, 37%, 39%, 40%, 42%, 45%, 47%, 48%, 50%, 51%, 53%, 55%, 57%, 58%, 59% or 60%, etc.

[0054] In some embodiments, the mass proportion of the ether solvent in the electrolyte is 30-80%. For example, the mass proportion of the ether solvent in the electrolyte is 30%, 32%, 34%, 35%, 36%, 38%, 40%, 41%, 43%, 45%, 47%, 49%, 50%, 52%, 55%, 54%, 55%, 56%, 58%, 59%, 60%, 62%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 73%, 75%, 76%, 78%, 79% or 80%, etc.

[0055] In some embodiments, the mass proportion of lithium salt in the electrolyte is 5-30%. For example, the mass proportion of lithium salt in the electrolyte is 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 22%, 24%, 25%, 26%, 28%, 29% or 30%.

[0056] In some embodiments, the mass proportion of the additive in the electrolyte is 0-5%. For example, the mass proportion of the additive in the low-temperature electrolyte is 0.1%, 0.3%, 0.5%, 0.6%, 0.8%, 1.0%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.0%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 2.9%, 3.0%, 3.2%, 3.5%, 3.7%, 3.8%, 4.0%, 4.2%, 4.4%, 4.5%, 4.7%, 4.9% or 5.0%, etc.

[0057] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(pentafluoroethylsulfonyl)imide.

[0058] In some embodiments, the additive includes at least one of lithium nitrate (Li NO3), lithium carbonate (Li2CO3), lithium fluoride (Li F), lithium bromide (Li Br), lithium iodide (Li I), fluoroethylene carbonate (FEC), bisfluoroethylene carbonate (DFEC), propane sultone (PS), propene sultone (PST), propene sultone (RPS), vinylene carbonate (VC), vinyl vinyl carbonate (VEC), trifluoromethyl vinyl carbonate (TFPC), vinyl sulfate (DTD), and vinyl sulfite (ES).

[0059] In some embodiments, the organic solvent further comprises carboxylic acid ester, and the mass proportion of carboxylic acid ester in the electrolyte is 5-40%. For example, the mass proportion of carboxylic acid ester in the electrolyte is 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 22%, 24%, 25%, 26%, 28%, 29%, 30%, 31%, 33%, 35%, 37%, 39% or 40%, etc.

[0060] In some embodiments, the organic solvent further comprises carboxylic acid ester, and the number of carbon atoms of the carboxylic acid ester is ≤ 8. Exemplarily, the carboxylic acid ester comprises at least one of methyl formate, ethyl formate, methyl acetate, methyl propionate, and ethyl propionate.

[0061] In some embodiments, the organic solvent further comprises carbonate, and the mass proportion of carbonate in the electrolyte is 1-30%. For example, the mass proportion of carbonate in the electrolyte is 1%, 3%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 22%, 24%, 25%, 26%, 28%, 29% or 30%, etc.

[0062] In some embodiments, the organic solvent further comprises carbonate, and the number of carbon atoms of the carbonate is ≤ 6. Exemplarily, the carbonate comprises at least one of ethyl methyl carbonate, diethyl carbonate, and methyl propyl carbonate.

[0063] The present application configures 30-80% by weight of an ether solvent in the electrolyte system of a lithium battery, selects specific cyclic ethers, non-halogen substituted chain ethers, and at least one of chlorinated chain ethers, brominated chain ethers and iodinated chain ethers for combination, and configures the ether solvent to 10-60% of cyclic ethers, 5-50% of non-halogen substituted chain ethers and 0.1-10% of halogen substituted chain ethers according to the mass ratio, thereby reducing interfacial impedance, improving the conductivity of the electrolyte at low temperatures, alleviating the problem of low-temperature lithium precipitation, and improving the adverse effects of high temperature on lithium batteries, thereby improving the charge and discharge performance, cycle performance and safety performance of lithium batteries at lower and higher temperatures.

[0064] In a second aspect, an embodiment of the present application provides a method for preparing an electrolyte, mixing a lithium salt and an organic solvent, wherein the organic solvent includes an ether solvent, the ether solvent includes cyclic ether, non-halogen-substituted chain ether and halogen-substituted chain ether, and the halogen-substituted chain ether is at least one of chlorinated chain ether, brominated chain ether and iodinated chain ether.

[0065] In some embodiments, Figure 1 As shown, lithium salt is first added to an organic solvent having a cyclic ether, and then non-halogen-substituted chain ether and halogen-substituted chain ether are added after mixing, wherein the halogen-substituted chain ether is at least one of chlorinated chain ether, brominated chain ether and iodinated chain ether.

[0066] The present application further improves the solvation structure of the electrolyte through a specific configuration method, which is beneficial for the full dissolution of lithium salts and additives.

[0067] In other embodiments, Figure 2 As shown, an electrolyte for lithium-ion batteries is prepared, and the steps are as follows:

[0068] S1, mixing the cyclic ether and the carboxylic acid ester, and adding the lithium salt and the additive to obtain a pre-formulated solution;

[0069] S2, mixing carbonate, non-halogen substituted chain ether, and at least one of chlorinated chain ether, brominated chain ether, and iodinated chain ether with the pre-prepared liquid to obtain the desired electrolyte.

[0070] In a third aspect, an embodiment of the present application provides a lithium battery, which includes the electrolyte of any one of the second aspect; or, includes the electrolyte prepared by the method for preparing the electrolyte of any one of the second aspect.

[0071] The lithium battery provided in the embodiment of the present application uses the electrolyte provided in the second aspect or the third aspect, and the charging and discharging performance, cycle performance and safety performance at room temperature, lower temperature and higher temperature are improved, and has a wider and better application temperature range.

[0072] The present application is described in detail below through specific embodiments. The following embodiments are only partial embodiments of the present application and are not limitations of the present application.

[0073] Example 1

[0074] In a dry room with a dew point of -50°C, ethyl methyl carbonate, 1,4-butylene oxide, diethylene glycol dimethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are uniformly mixed in a mass ratio of 1:4:3:0.5, and then lithium bis(fluorosulfonyl)imide is added and stirred thoroughly to obtain the desired electrolyte, in which the lithium salt accounts for 15% of the total mass of the electrolyte.

[0075] Example 2

[0076] In a dry room with a dew point of -50°C, ethyl methyl carbonate, 1,4-butylene oxide, tetraethylene glycol dimethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are uniformly mixed in a mass ratio of 1:4:3:0.5, and then lithium bis(fluorosulfonyl)imide is added and stirred thoroughly to obtain the desired electrolyte, in which the lithium salt accounts for 15% of the total mass of the electrolyte.

[0077] Example 3

[0078] In a dry room with a dew point of -50°C, ethyl methyl carbonate, 1,4-butylene oxide, diethylene glycol dimethyl ether, and tetrafluoroethyl methyl ether are uniformly mixed in a mass ratio of 1:4:3:0.5, and then lithium bis(fluorosulfonyl)imide is added and stirred thoroughly to obtain the desired electrolyte, in which the lithium salt accounts for 15% of the total mass of the electrolyte.

[0079] Example 4

[0080] In a dry room with a dew point of -50°C, ethyl methyl carbonate, 3-methyltetrahydrofuran, diethylene glycol dimethyl ether and 1,3-dibromobutane are uniformly mixed in a mass ratio of 1:4:3:0.5, and then lithium bis(fluorosulfonyl)imide is added and stirred thoroughly to obtain the desired electrolyte, in which the lithium salt accounts for 15% of the total mass of the electrolyte.

[0081] Example 5

[0082] In a dry room with a dew point of -50°C, ethyl methyl carbonate, 1,4-butylene oxide, diethylene glycol dimethyl ether, and 1,3-dibromobutane are evenly mixed in a mass ratio of 1:4:3.4:0.1, and then lithium bis(fluorosulfonyl)imide is added and stirred thoroughly to obtain the desired electrolyte, in which the lithium salt accounts for 15% of the total mass of the electrolyte.

[0083] Example 6

[0084] In a dry room with a dew point of -50°C, ethyl methyl carbonate, 1,4-butylene oxide, diethylene glycol dimethyl ether, and 1,3-dibromobutane are evenly mixed in a mass ratio of 1:4:2.8:0.7, and then lithium bis(fluorosulfonyl)imide is added and stirred thoroughly to obtain the desired electrolyte, in which the lithium salt accounts for 15% of the total mass of the electrolyte.

[0085] Example 7

[0086] In a dry room with a dew point of -50°C, methyl formate, 1,4-butylene oxide, diethylene glycol dimethyl ether, and 1,3-dibromobutane are uniformly mixed in a mass ratio of 1:4:3:0.5, and then lithium bis(fluorosulfonyl)imide is added and stirred thoroughly to obtain the desired electrolyte, in which the lithium salt accounts for 15% of the total mass of the electrolyte.

[0087] Example 8

[0088] In a dry room with a dew point of -50°C, methyl propionate, ethyl methyl carbonate, 1,4-butylene oxide, diethylene glycol dimethyl ether, and 1,3-dibromobutane are evenly mixed in a mass ratio of 1:1:4:3:0.5, and then lithium bis(fluorosulfonyl)imide is added and stirred thoroughly to obtain the desired electrolyte, in which the lithium salt accounts for 15% of the total mass of the electrolyte.

[0089] Example 9

[0090] In a dry room with a dew point of -50°C, ethyl methyl carbonate, 1,4-butylene oxide, diethylene glycol dimethyl ether, 1,3-dibromobutane and lithium bis(fluorosulfonyl)imide were weighed in a mass ratio of 1:4:3:0.5:1.5, and then the electrolyte was prepared in the dry room with a dew point of -50°C in the following order:

[0091] Lithium bis(fluorosulfonyl)imide is added to 1,4-butylene oxide and mixed evenly, and then ethyl methyl carbonate, diethylene glycol dimethyl ether and 1,3-dibromobutane are added and mixed evenly to obtain the desired electrolyte.

[0092] Example 10

[0093] In a dry room with a dew point of -50°C, methyl propionate, ethyl methyl carbonate, 1,4-butylene oxide, diethylene glycol dimethyl ether, 1,3-dibromobutane and lithium bis(fluorosulfonyl)imide were weighed in a mass ratio of 1:1:4:3:0.5:1.5, and then the electrolyte was prepared in the dry room with a dew point of -50°C in the following order:

[0094] Lithium bis(fluorosulfonyl)imide is added to methyl propionate and 1,4-butylene oxide and mixed evenly, and then ethyl methyl carbonate, diethylene glycol dimethyl ether and 1,3-dibromobutane are added and mixed evenly to obtain the desired electrolyte.

[0095] Comparative Example 1

[0096] In a dry room with a dew point of -50°C, diethyl carbonate (DEC), ethylene carbonate (EC) and dimethyl carbonate (DMC) are evenly mixed in a mass ratio of 1:4:3.5, and then lithium bis(fluorosulfonyl)imide is added and stirred thoroughly to obtain the desired electrolyte, in which the lithium salt accounts for 15% of the total mass of the electrolyte.

[0097] Comparative Example 2

[0098] In a dry room with a dew point of -50°C, lithium difluorooxalatoborate (LiODFB), polyethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL) and lithium nitrate (Li NO3) after dehydration are configured into an electrolyte, wherein the volume ratio of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) is 1:1, the concentration of lithium difluorooxalatoborate (LiODFB) is 1.0 mol / L, and the concentration of lithium nitrate (Li NO3) is 0.1 mol / L.

[0099] Comparative Example 3

[0100] A 0.3 M electrolyte was prepared in a dry room with a dew point of -50°C. Bis(fluorosulfonyl)imide lithium salt, ethylene glycol dimethyl ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were prepared into an electrolyte in which the volume ratio of ethylene glycol dimethyl ether to 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether was 15.7. The electrolyte was stirred in a glove box until a uniform transparent solution was obtained.

[0101] 52 soft-pack lithium batteries of the same type were selected and divided into 13 groups, with 4 batteries in each group. A total of 13 electrolytes of Examples 1-10 and Comparative Examples 1-3 were injected into 13 groups of soft-pack lithium batteries respectively, and after standing and converting into different capacities, the low-temperature internal resistance, low-temperature cycle stability, volume expansion rate after high-temperature storage, and high-temperature cycle stability of the batteries were tested. The specific test conditions are as follows:

[0102] Low temperature internal resistance: After the soft-pack battery is placed in a low-temperature box at minus 20 degrees for 12 hours, the resistance of the soft-pack battery is measured with a battery internal resistance tester to compare the internal resistance of soft-pack batteries corresponding to different electrolytes.

[0103] Low temperature cycle stability: The soft pack battery was placed in a low temperature box at -20 degrees Celsius for 12 hours and then subjected to low temperature cycle test: first, 0.2C (1mA / cm 2 ) rate current density to 4.3V and then 0.2C (1mA / cm 2 ) was set to a current density of 2.5 V, and the charge and discharge cycles were carried out according to the above steps to compare the capacity retention rates of different electrolyte systems after 50 cycles.

[0104] Battery expansion rate after high-temperature storage: After the soft-pack battery is placed in an explosion-proof oven at 60 degrees for 7 days, the battery cell is taken out of the oven and the thickness expansion rate of the battery is tested.

[0105] High temperature cycle stability: The soft pack battery was placed in an explosion-proof oven at 55 degrees for 2 hours and then subjected to a high temperature cycle test: first, 0.2C (1mA / cm 2 ) rate current density to 4.3V and then charged with 1C (5mA / cm 2 ) was set to a current density of 2.7 V, and the charge and discharge cycles were carried out according to the above steps to compare the capacity retention rates of different electrolyte systems after 50 cycles.

[0106] The mean of each group of test results is shown in Table 1.

[0107] Table 1

[0108]

[0109] From this we can see that:

[0110] Comparing Examples 1-10 with Comparative Examples 1-3, the internal resistance of Examples 1-10 under low temperature conditions of -20°C is basically maintained at a relatively low state, and it is not easy to have too fast performance degradation caused by excessive internal resistance, and after 50 cycles at a low temperature of -20°C, the low-temperature cycle capacity retention rate is relatively high, indicating that the technical solution provided by the present application can effectively improve the charge and discharge performance, cycle performance and safety performance of lithium batteries at low temperatures, and alleviate the problem of performance degradation of lithium batteries at low temperatures; and, the expansion rate of Examples 1-10 under high temperature conditions of 60°C is much lower than that of Comparative Examples 1, 2 and 3. After 50 cycles at a high temperature of 55°C, the high-temperature cycle capacity retention rate is also relatively high, indicating that the technical solution provided by the present application can effectively improve the charge and discharge performance, cycle performance and safety performance of lithium batteries at high temperatures.

[0111] Comparing Example 1 with Example 2, Example 3, and Example 4, it can be seen that changing the selection of non-halogen substituted ether, halogen substituted ether, and cyclic ether within the limited conditions of this application can still achieve a good improvement effect. Comparing Example 1 with Example 5 and Example 6, it is shown that adjusting the proportion of each component of the ether solvent within a certain range can still achieve a good effect.

[0112] Comparing Example 1 with Example 7 and Example 8, it can be seen that replacing or increasing carbonate ester and carboxylic acid ester within a certain range can achieve a higher effect.

[0113] Comparing Example 1 with Example 9 and Example 10, it is shown that in the process of preparing the electrolyte provided in the present application, the order of adding each solvent can be adjusted successively.

[0114] The technical solutions provided by the embodiments of the present application are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. An electrolyte, characterized in that: The invention comprises a lithium salt and an organic solvent, wherein the organic solvent comprises an ether solvent, and the ether solvent comprises a cyclic ether, a non-halogen-substituted chain ether and a halogen-substituted chain ether, and the halogen-substituted chain ether is at least one of a chlorinated chain ether, a brominated chain ether and an iodinated chain ether.

2. The electrolyte according to claim 1, characterized in that: The number of carbon atoms of the non-halogen substituted chain ether is ≤ 10; and / or The number of carbon atoms of the halogen-substituted chain ether is ≤10; and / or The number of halogen atoms substituted in the halogen-substituted chain ether is ≤ 12; and / or The cyclic ether has ≤3 oxygen atoms and ≤10 carbon atoms.

3. The electrolyte according to claim 1, characterized in that: The non-halogen substituted chain ether includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; and / or The halogen-substituted chain ether includes at least one of 1,2-dichloroethane; 1,3-dichloropropane; 1,2-dibromopropane; 1,3-dibromobutane; 1,2-diiodoethane; and / or The cyclic ether includes at least one of ethylene oxide, propylene oxide, 1,2-butylene oxide, 1,4-butylene oxide, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, and 1,2-hexylene oxide.

4. The electrolyte according to any one of claims 1 to 3, characterized in that: The mass percentage of the non-halogen substituted chain ether in the ether solvent is 5-50%; and / or The mass percentage of the halogen-substituted chain ether in the ether solvent is 0.1-50%; and / or The mass proportion of the cyclic ether in the ether solvent is 10-60%.

5. The electrolyte according to claim 4, characterized in that The mass percentage of the ether solvent in the electrolyte is 30-80%; and / or The lithium salt accounts for 5-30% by mass in the electrolyte; and / or The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(pentafluoroethylsulfonyl)imide.

6. The electrolyte according to claim 1, characterized in that The electrolyte also includes additives: The mass percentage of the additive in the electrolyte is 0-5%; and / or The additive includes at least one of lithium nitrate, lithium carbonate, lithium fluoride, lithium bromide, lithium iodide, fluoroethylene carbonate, bisfluoroethylene carbonate, propane sultone, propene sultone, propene sultone, vinylene carbonate, vinyl carbonate, trifluoromethyl vinyl carbonate, vinyl sulfate, and vinyl sulfite.

7. The electrolyte according to claim 1, characterized in that: The organic solvent further comprises carboxylic acid ester, and the mass percentage of the carboxylic acid ester in the electrolyte is 5-40%; and / or The organic solvent further comprises a carboxylate, wherein the carbon number of the carboxylate is ≤8; and / or The organic solvent further comprises carbonate, and the mass percentage of the carbonate in the electrolyte is 1-30%; and / or The organic solvent further comprises carbonate, and the carbon number of the carbonate is ≤6.

8. A method for preparing an electrolyte, characterized in that: A lithium salt and an organic solvent are mixed, wherein the organic solvent comprises an ether solvent, the ether solvent comprises a cyclic ether, a non-halogen substituted chain ether and a halogen substituted chain ether, and the halogen substituted chain ether is at least one of a chlorinated chain ether, a brominated chain ether and an iodinated chain ether.

9. The method for preparing an electrolyte according to claim 8, characterized in that: Firstly, lithium salt is added into an organic solvent having cyclic ether, and then non-halogen substituted chain ether and halogen substituted chain ether are added after mixing.

10. A lithium battery, characterized in that: The electrolyte comprises the electrolyte described in any one of claims 1 to 7; or, the electrolyte prepared by the method for preparing the electrolyte described in claim 8 or 9.

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