Non-aqueous lithium battery electrolyte and secondary lithium battery

Abstract

The present application relates to a kind of non-aqueous lithium battery electrolyte and secondary lithium battery, mainly solve the high concentration lithium salt electrolyte viscosity, low conductivity, the problem of poor cycle performance.The present application adds additive and halogenated alkane to high concentration lithium salt electrolyte, by the synergistic cooperation of additive and halogenated alkane, not only reduce the viscosity of high concentration lithium salt electrolyte, improve the conductivity of high concentration lithium salt electrolyte, also improve the cycle performance of battery at room temperature and low temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to a non-aqueous lithium battery electrolyte and a secondary lithium battery. BACKGROUND

[0002] Lithium ion battery technology is more and more important in people's daily life, with the development of new energy, clean energy is more and more widely used, small to electronic components, large to cars and planes, almost all places using power need to use lithium ion battery, the broad market provides more development opportunities and also brings greater challenges. The extensive use leads to higher requirements for the adaptability of battery technology to the environment of the battery, the market needs the battery to maintain good performance in different harsh environments, and a larger temperature range has become an important issue for the development of the battery. At the same time, the extensive use puts forward higher requirements for the capacity performance and safety performance of the battery, and the generation of lithium dendrites in the battery cycle brings great challenges to the safety performance of the battery.

[0003] High-concentration lithium salt electrolyte has the effects of inhibiting the corrosion of current collector and inhibiting the growth of lithium dendrites, and is more and more concerned, however, the high-concentration lithium salt electrolyte has high viscosity and low conductivity, which is not conducive to the infiltration between the electrolyte and the electrode. People often use partial dilution of organic solvents to reduce the viscosity of high-concentration lithium salt electrolyte, however, the existing diluents such as fluorine-based organic solvents are expensive and not suitable for commercialization. In addition, although the addition of diluents can reduce the viscosity of the electrolyte, it will also affect the cycle performance of the battery.

[0004] Therefore, how to reduce the viscosity of high-concentration lithium salt electrolyte while improving the conductivity and cycle performance of the battery has become a research focus. SUMMARY

[0005] The purpose of the present application is to provide a non-aqueous lithium battery electrolyte and a secondary lithium battery, which solves the problems of high viscosity, low conductivity and poor cycle performance of high-concentration lithium salt electrolyte.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A non-aqueous lithium battery electrolyte, the non-aqueous lithium battery electrolyte comprises a lithium salt, an organic solvent, an additive and a diluent, the molar concentration of the lithium salt in the non-aqueous lithium battery electrolyte is greater than or equal to 3mol / L, the additive comprises one or more of ethylene carbonate, ethylene sulfate, fluorinated ethylene carbonate, ethylene carbonate, butanedinitrile and lithium difluorophosphate, and the diluent comprises a halogenated alkane.

[0008] Preferably, the halogen in the halogenated alkane is one or more of fluorine, chlorine and bromine.

[0009] Further preferably, the halogenated alkane has a carbon atom number of 1-3.

[0010] Further preferably, the halogenated alkane comprises one or more of monochloromethane, dichloromethane, dichloroethane, and tetrachloroethane.

[0011] Preferably, the halogenated alkane has a mass content of 10-20% in the non-aqueous lithium battery electrolyte.

[0012] Preferably, the additive has a mass content of 0.5-6% in the non-aqueous lithium battery electrolyte.

[0013] According to some preferred embodiments, the additive comprises ethylene carbonate, vinyl sulfate, and fluoroethylene carbonate.

[0014] Further preferably, the ethylene carbonate has a mass content of 0.5-3% in the non-aqueous lithium battery electrolyte.

[0015] Further preferably, the vinyl sulfate has a mass content of 0.1-1% in the non-aqueous lithium battery electrolyte.

[0016] Further preferably, the fluoroethylene carbonate has a mass content of 0.5-3% in the non-aqueous lithium battery electrolyte.

[0017] Preferably, the lithium salt comprises one or more of LiPF6, LiFSI, LiTFSI, LiBF4, LiClO4, LiCH3SO3, LiSCN, LiNO3, LiO3SCF2CF3, LiAsF6, and LiAlCl4.

[0018] Further preferably, the lithium salt has a molar concentration of 3-5 mol / L in the non-aqueous lithium battery electrolyte.

[0019] Preferably, the organic solvent comprises one or more of carbonates, carboxylic acid esters, ethers, and sulfones. When the organic solvent is a mixture of two or more, the organic solvent can be compounded in any weight ratio.

[0020] Further preferably, the carbonates comprise one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propylene carbonate.

[0021] Further preferably, the carboxylic acid esters comprise one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, methyl butyrate, and ethyl butyrate.

[0022] Further preferably, the ether includes one or more of dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane.

[0023] Further preferably, the sulfone includes one or more of dimethyl sulfoxide, sulfolane, dimethyl sulfone.

[0024] According to some preferred embodiments, the organic solvent is a mixed solvent of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and propylene carbonate in a mass ratio of (2-6):(5-11):(1-2):1.

[0025] Further preferably, the organic solvent is a mixed solvent of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and propylene carbonate in a mass ratio of (2-3):(5-7):(1-1.5):1.

[0026] Another aspect of the present application provides a secondary lithium battery including the non-aqueous lithium battery electrolyte as described above.

[0027] Thanks to the above technical solution, the present application has the following advantages compared with the prior art:

[0028] The present application, through the synergistic cooperation of the additive and the halogenated alkane, not only reduces the viscosity of the high-concentration lithium salt electrolyte, improves the electrical conductivity of the high-concentration lithium salt electrolyte, but also improves the cycle performance of the battery at room temperature and low temperature. DETAILED DESCRIPTION

[0029] A non-aqueous lithium battery electrolyte includes a lithium salt, an organic solvent, an additive, and a diluent.

[0030] In the present application, the non-aqueous lithium battery electrolyte is a high-concentration lithium salt electrolyte, in which the molar concentration of the lithium salt in the non-aqueous lithium battery electrolyte is greater than or equal to 3 mol / L. Specifically, the molar concentration of the lithium salt in the non-aqueous lithium battery electrolyte is 3-5 mol / L, for example, it can be 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, etc.

[0031] In the present application, the additive includes one or more of ethylene carbonate, ethylene sulfate, fluoroethylene carbonate, ethylene carbonate, butanedinitrile, lithium difluorophosphate, and the mass content of the additive in the non-aqueous lithium battery electrolyte is 0.5-6%, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, etc.

[0032] As preferred, the additive comprises ethylene carbonate, vinyl sulfate and fluoroethylene carbonate. Among them, the mass content of ethylene carbonate in the non-aqueous lithium battery electrolyte is 0.5-3%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3% and the like. The mass content of vinyl sulfate in the non-aqueous lithium battery electrolyte is 0.1-1%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% and the like. The mass content of fluoroethylene carbonate in the non-aqueous lithium battery electrolyte is 0.5-3%, for example, it can be 0.5%, 0.7%, 1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3% and the like.

[0033] For high-concentration lithium salt electrolyte, only adding an additive to the electrolyte cannot reduce the viscosity and improve the conductivity of the electrolyte; while only adding a diluent to the electrolyte can reduce the viscosity of the electrolyte, but the prepared electrolyte often has poor cycle performance. The present application improves the high viscosity and low conductivity of high-concentration lithium salt electrolyte by compounding the additive and the diluent, and greatly improves the cycle performance of the battery at room temperature and low temperature.

[0034] In the present application, the diluent comprises a halogenated alkane. As preferred, the halogen in the halogenated alkane is one or more of fluorine, chlorine and bromine, and the number of carbon atoms in the halogenated alkane is 1-3. Specifically, the halogenated alkane includes but is not limited to one or more of methyl chloride, dichloromethane, dichloroethane and tetrachloroethane.

[0035] The addition of halogenated alkane can improve the stability of electrolyte at low temperature, the higher the amount of halogenated alkane, the better the cycle performance of electrolyte at low temperature, but the higher the amount of halogenated alkane, the cycle performance of electrolyte at room temperature will be reduced. The present application controls the mass content of halogenated alkane in the non-aqueous lithium battery electrolyte to be between 10-20%, so that the electrolyte has better cycle performance at room temperature and low temperature. The mass content of halogenated alkane in the non-aqueous lithium battery electrolyte can be, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% and the like.

[0036] The organic solvent in the present application includes one or more of carbonates, carboxylic acid esters, ethers, sulfones. When the organic solvent is two or more kinds of mixture, the organic solvent can be compounded in any weight ratio. Specifically, the carbonates include one or more of vinyl carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate; the carboxylic acid esters include one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, methyl butyrate, ethyl butyrate; the ethers include one or more of dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane; the sulfones include one or more of dimethyl sulfoxide, sulfolane, dimethyl sulfone. As a preferred, the organic solvent is a mixed solvent of vinyl carbonate, methyl ethyl carbonate, dimethyl carbonate, propylene carbonate with a mass ratio of (2-6):(5-11):(1-2):1.

[0037] A secondary lithium battery comprising the non-aqueous lithium battery electrolyte as described above.

[0038] The application will be further described in conjunction with the following examples. However, the application is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to different requirements of specific use, and the implementation conditions not mentioned are the conventional conditions in the industry. The technical features involved in each embodiment of the application can be combined with each other as long as there is no conflict.

[0039] Comparative Example 1

[0040] The lithium salt LiFSI was dissolved in a mixed solvent of vinyl carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration was 1 mol / L, and 1% ethylene carbonate, 0.5% vinyl sulfate, 2% fluoro-vinyl carbonate were added in the solution respectively to obtain the electrolyte of the comparative example, based on the total mass of the electrolyte.

[0041] Comparative Example 2

[0042] The lithium salt LiFSI was dissolved in a mixed solvent of vinyl carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration was 5 mol / L, and 1% ethylene carbonate, 0.5% vinyl sulfate, 2% fluoro-vinyl carbonate were added in the solution respectively to obtain the electrolyte of the comparative example, based on the total mass of the electrolyte.

[0043] Comparative Example 3

[0044] The lithium salt LiPF6 was dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiPF6 concentration was 1 mol / L, and 1% ethylene carbonate, 0.5% vinyl sulfate, and 2% fluoroethylene carbonate were added to the solution to obtain the electrolyte of the comparative example.

[0045] Comparative Example 4

[0046] The lithium salt LiFSI was dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration was 5 mol / L, and 20% dichloromethane was added to the solution to obtain the electrolyte of the comparative example.

[0047] Comparative Example 5

[0048] The lithium salt LiFSI was dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration was 5 mol / L, and 20% dichloroethane was added to the solution to obtain the electrolyte of the comparative example.

[0049] Comparative Example 6

[0050] The lithium salt LiFSI was dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration was 5 mol / L, and 20% tetrachloroethane was added to the solution to obtain the electrolyte of the comparative example.

[0051] Example 1

[0052] The lithium salt LiFSI was dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration was 3 mol / L, and 10% dichloromethane was added to the solution, and then 1% ethylene carbonate, 0.5% vinyl sulfate, and 2% fluoroethylene carbonate were added to obtain the electrolyte of the example.

[0053] Example 2

[0054] The lithium salt LiFSI is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration is 3 mol / L, 20% of dichloromethane is added in the solution according to the total mass of the electrolyte, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of this example.

[0055] Example 3

[0056] The lithium salt LiFSI is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration is 3 mol / L, 10% of dichloroethane is added in the solution according to the total mass of the electrolyte, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of this example.

[0057] Example 4

[0058] The lithium salt LiFSI is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration is 3 mol / L, 20% of dichloroethane is added in the solution according to the total mass of the electrolyte, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of this example.

[0059] Example 5

[0060] The lithium salt LiFSI is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration is 3 mol / L, 10% of tetrachloroethane is added in the solution according to the total mass of the electrolyte, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of this example.

[0061] Example 6

[0062] The lithium salt LiFSI is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10), wherein the LiFSI concentration is 3 mol / L, 20% of tetrachloroethane is added in the solution according to the total mass of the electrolyte, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of this example.

[0063] Example 7

[0064] The lithium salt LiPF6 is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10) with a LiPF6 concentration of 3 mol / L. 10% of dichloromethane is added to the solution, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of this example.

[0065] Example 8

[0066] The lithium salt LiPF6 is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10) with a LiPF6 concentration of 3 mol / L. 20% of dichloromethane is added to the solution, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of this example.

[0067] Example 9

[0068] The lithium salt LiPF6 is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10) with a LiPF6 concentration of 3 mol / L. 20% of tetrachloroethane is added to the solution, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of this example.

[0069] Example 10

[0070] The lithium salt LiFSI is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10) with a LiFSI concentration of 5 mol / L. 20% of dichloromethane is added to the solution, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of this example.

[0071] Example 11

[0072] The lithium salt LiFSI is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10) with a LiFSI concentration of 5 mol / L. 20% of dichloroethane is added to the solution, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of this example.

[0073] Example 12

[0074] The lithium salt LiFSI is dissolved in a mixed solvent of ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate / propylene carbonate (mass ratio 25 / 50 / 15 / 10) with a LiFSI concentration of 5 mol / L, 20% of tetrachloroethane is added in the solution based on the total mass of the electrolyte, and then 1% of ethylene carbonate, 0.5% of vinyl sulfate, and 2% of fluoroethylene carbonate are added respectively to obtain the electrolyte of the example.

[0075] Experimental results

[0076] The viscosities and conductivities of the electrolytes obtained by testing Comparative Examples 1 and 2 and Examples 1-6 at room temperature are measured, and the electrolytes are injected into lithium cobalt oxide soft pack batteries of the same batch and model, and the cycle performance of the batteries at 2.75-4.2V at room temperature 25℃ and low temperature 0℃ is tested at 1C, and the specific results are shown in Table 1.

[0077] Table 1

[0078]

[0079] The electrolytes obtained by testing Comparative Examples 1, 3-6 and Examples 7-12 are injected into lithium cobalt oxide soft pack batteries of the same batch and model, and the cycle performance of the batteries at 2.75-4.2V at room temperature 25℃ and low temperature 0℃ is tested at 1C, and the specific results are shown in Table 2.

[0080] Table 2

[0081] Comparative Examples and Examples 1C 25°C 300 cycles discharge capacity retention rate % 1C 0°C 300 cycles discharge capacity retention rate % Comparative Example 1 86.72 82.39 Comparative Example 3 87.62 83.49 Comparative Example 4 72.49 86.22 Comparative Example 5 76.62 87.22 Comparative Example 6 79.43 89.06 Example 7 90.72 91.68 Example 8 91.69 93.26 Example 9 91.79 92.94 Example 10 91.06 90.94 Example 11 91.39 92.06 Example 12 93.65 93.07

[0082] The above has described the present application in detail, the purpose is to let the person who is familiar with this field technology can understand the content of the present application and implement, and cannot limit the protection scope of the present application with this, all equivalent changes or modifications according to the spirit of the present application should be covered in the protection scope of the present application.

Claims

1. A non-aqueous lithium battery electrolyte, characterized in that: The non-aqueous lithium battery electrolyte comprises lithium salt, organic solvent, additives, and diluent. The molar concentration of the lithium salt in the non-aqueous lithium battery electrolyte is greater than or equal to 3 mol / L. The additives include ethylene carbonate, vinyl sulfate, and fluoroethylene carbonate. The mass content of ethylene carbonate in the non-aqueous lithium battery electrolyte is 0.5-3%, the mass content of vinyl sulfate in the non-aqueous lithium battery electrolyte is 0.1-1%, the mass content of fluoroethylene carbonate in the non-aqueous lithium battery electrolyte is 0.5-3%, and the diluent includes haloalkanes, the mass content of which is 10-20%.

2. The non-aqueous lithium battery electrolyte according to claim 1, characterized in that: The halogen in the haloalkane is one or more of fluorine, chlorine, and bromine, and the number of carbon atoms in the haloalkane is 1 to 3.

3. The non-aqueous lithium battery electrolyte according to claim 1, characterized in that: The haloalkane includes one or more of chloromethane, dichloromethane, dichloroethane, and tetrachloroethane.

4. The non-aqueous lithium battery electrolyte according to claim 1, characterized in that: The lithium salt includes one or more of LiPF6, LiFSI, LiTFSI, LiBF4, LiClO4, LiCH3SO3, LiSCN, LiNO3, LiO3SCF2CF3, LiAsF6, and LiAlCl4.

5. The non-aqueous lithium battery electrolyte according to claim 1 or 4, characterized in that: The molar concentration of the lithium salt in the non-aqueous lithium battery electrolyte is 3–5 mol / L.

6. The non-aqueous lithium battery electrolyte according to claim 1, characterized in that: The organic solvent includes one or more of carbonates, carboxylic esters, ethers, and sulfones. The carbonate includes one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propylene carbonate. The carboxylic acid esters include one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, methyl butyrate, and ethyl butyrate. The ether comprises one or more of dimethoxymethane, 1,2-dimethoxyethane, tetrahydrofuran, and 1,3-dioxolane; The sulfone includes one or more of dimethyl sulfoxide, sulfolane, and dimethyl sulfone.

7. A secondary lithium battery, characterized in that: It includes the non-aqueous lithium battery electrolyte as described in any one of claims 1 to 6.

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