Electrolyte and lithium ion battery containing same

Abstract

The application provides an electrolyte and a lithium ion battery containing the same. The electrolyte comprises an organic solvent, a lithium salt and an additive, the additive comprises a first additive, the first additive is an overcharge prevention additive, and the overcharge prevention additive comprises 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and / or cyclohexylbenzene. Through the cooperation of 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and cyclohexylbenzene, the overcharge resistance of the battery cell is effectively improved, the overcharge problem of the battery cell is greatly improved, and the electrochemical performance stability is not affected.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more particularly to an electrolyte and a lithium-ion battery containing the electrolyte. Background Technology

[0002] Every year, electric vehicle fires caused by battery thermal runaway are common occurrences. Overcharging is a major contributing factor. This is because when lithium-ion batteries are overcharged, excessive lithium ions are released from the positive electrode material, causing a rapid increase in battery voltage and temperature, releasing large amounts of oxygen and heat. When a certain potential is reached, the electrolyte undergoes oxidative decomposition, resulting in a violent chemical reaction that generates a significant amount of heat, potentially leading to a dangerous situation. Therefore, researching anti-overcharge additives for electrolytes is essential.

[0003] CN108470947A discloses an overcharge prevention additive for lithium battery electrolytes and a lithium battery electrolyte containing the additive. The overcharge prevention additive is mainly composed of biphenyl, cyclohexylbenzene, difluorobiphenyl, fluorobenzene, and lithium difluorophosphate. Among these, biphenyl, cyclohexylbenzene, and difluorobiphenyl, as electropolymerizable compounds, can continuously generate corresponding overcharge additive reactions in the battery cell at different overcharge voltage ranges. The lithium battery electrolyte containing the above-mentioned overcharge prevention additive can gently block thermal collapse that may occur during overcharging, thereby avoiding performance degradation of the battery cell under overcharge conditions. However, using multiple overcharge prevention additives results in high battery manufacturing costs and high costs for large-scale production.

[0004] CN108565514A discloses an electrolyte overcharge protection additive and its application in a lithium-ion battery. The overcharge protection additive is an organosilicon derivative with a silicon-oxygen bond main chain and four anisole ether structures in its main molecular structure. It can more rapidly and efficiently undergo oxidation at the positive electrode during overcharging, and then migrate to the negative electrode for reduction. This repeated redox reaction at both electrodes, with a reversible overcharge protection mechanism, results in better overcharge protection. Furthermore, the addition of this overcharge protection additive does not reduce the battery's low-temperature and cycle performance. However, current research on organosilicon-based overcharge protection agents is not yet in-depth, and they are not suitable for large-scale production.

[0005] Therefore, how to prepare an overcharge prevention additive that can be mass-produced is an important research direction in this field. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an electrolyte and a lithium-ion battery containing the electrolyte.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] One objective of this invention is to provide an electrolyte comprising an organic solvent, a lithium salt, and an additive, wherein the additive comprises a first additive, which is an overcharge prevention additive comprising 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and / or cyclohexylbenzene.

[0009] The structure of the electrolyte 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene in this invention is shown in Formula 1. The structure of cyclohexylbenzene is shown in Formula 2. This invention effectively improves the overcharge resistance of battery cells by using the combined use of 2,5-di-tert-butyl-1,4-di(2-methoxyethoxy)benzene (Formula 1) and cyclohexylbenzene (Formula 2). This significantly improves the overcharge resistance of battery cells without affecting their electrochemical performance stability. For the cyclohexylbenzene additive, when the battery voltage exceeds the electropolymerization voltage of the additive, the additive monomer undergoes a polymerization reaction, generating a black substance called polycyclohexylbenzene. This forms a blocking layer on the electrode surface, rapidly increasing the battery's internal resistance and thus slowing down or preventing further decomposition of the electrolyte. This significantly reduces the generation of gas and heat, preventing thermal runaway. However, as the amount of cyclohexylbenzene added gradually increases, it affects the cycle performance of the battery cell. Therefore, it is necessary to use 2,5-di-tert-butyl-1,4-di(2-methoxyethoxy)benzene. Although this additive has slightly inferior overcharge resistance, it has good electrode compatibility. Therefore, experiments further verified that the combined use of these additives can reduce gas generation without affecting the cycle performance of the battery cell.

[0010] As a preferred embodiment of the present invention, the overcharge prevention additive is 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and cyclohexylbenzene.

[0011] As a preferred embodiment of the present invention, the additive further includes a second additive.

[0012] Preferably, the second additive comprises fluoroethylene carbonate.

[0013] As a preferred embodiment of the present invention, the electrolyte comprises 100% by mass, and the 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene accounts for 2-3% of the electrolyte by mass. The mass fraction can be 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] Preferably, with the electrolyte comprising 100% by mass, the cyclohexylbenzene accounts for 2-3% of the electrolyte by mass, wherein the mass fraction can be 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3%, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0015] Preferably, with the electrolyte accounting for 100% by mass, the second additive accounts for 4-6% of the electrolyte by mass fraction. The mass fraction can be 4%, 4.2%, 4.4%, 4.6%, 4.8%, 5.0%, 5.2%, 5.3%, 5.4%, 5.6%, 5.8%, or 6%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] As a preferred embodiment of the present invention, the organic solvent includes carbonate solvents.

[0017] Preferably, the carbonate solvent includes any one or a combination of at least two of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, or diethyl carbonate. Typical but non-limiting examples of such combinations include combinations of dimethyl carbonate and ethylene carbonate, combinations of ethylene carbonate and ethyl methyl carbonate, combinations of ethyl methyl carbonate and ethylene carbonate, combinations of ethylene carbonate and propylene carbonate, or combinations of propylene carbonate and diethyl carbonate.

[0018] As a preferred technical solution of the present invention, the electrolyte accounts for 100% by mass, and the organic solvent accounts for 70-80% by mass fraction of the electrolyte. The mass fraction can be 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] As a preferred technical solution of the present invention, the lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium difluorophosphate, or lithium bisfluorosulfonylimide. Typical but non-limiting examples of such combinations include combinations of lithium hexafluorophosphate and lithium difluorophosphate, combinations of lithium difluorophosphate and lithium bisfluorosulfonylimide, or combinations of lithium hexafluorophosphate and lithium bisfluorosulfonylimide, etc.

[0020] As a preferred technical solution of the present invention, the electrolyte is 100% by mass, and the lithium salt accounts for 10-20% of the electrolyte by mass fraction. The mass fraction can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] A second objective of this invention is to provide a lithium-ion battery, the lithium-ion battery comprising the electrolyte as described in one objective, and the lithium-ion battery further comprising a positive electrode and a negative electrode.

[0022] As a preferred technical solution of the present invention, the active material of the positive electrode includes any one or a combination of at least two of lithium cobalt oxide, lithium iron phosphate, nickel cobalt manganese ternary positive electrode material, lithium manganese oxide, or lithium iron phosphate. Typical but non-limiting examples of the combination include: a combination of lithium cobalt oxide and lithium iron phosphate, a combination of lithium iron phosphate and nickel cobalt manganese ternary positive electrode material, a combination of nickel cobalt manganese ternary positive electrode material and lithium manganese oxide, or a combination of lithium manganese oxide and lithium iron phosphate, etc.

[0023] Preferably, the active material of the negative electrode sheet includes natural graphite and / or artificial graphite.

[0024] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The electrolyte of this invention, by adding 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and cyclohexylbenzene as overcharge prevention additives, can effectively improve the overcharge resistance of the battery cell, which can significantly improve the overcharge problem of the battery cell without affecting the stability of electrochemical performance. Detailed Implementation

[0027] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0028] Example 1

[0029] This embodiment provides an electrolyte:

[0030] The electrolyte consists of organic solvents, lithium salts, and additives:

[0031] Organic solvents include: dimethyl carbonate and ethylene carbonate;

[0032] Lithium salts include: lithium hexafluorophosphate;

[0033] Additives: First additive: 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and cyclohexylbenzene; Second additive: fluoroethylene carbonate;

[0034] With the electrolyte mass as 100%, dimethyl carbonate mass fraction as 30%, ethylene carbonate mass fraction as 45%, lithium hexafluorophosphate mass fraction as 15%, 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene mass fraction as 2.5%, cyclohexylbenzene mass fraction as 2.5%, and fluoroethylene carbonate mass fraction as 5%.

[0035] Example 2

[0036] This embodiment provides an electrolyte:

[0037] The electrolyte consists of organic solvents, lithium salts, and additives:

[0038] Organic solvents include: ethyl methyl carbonate and ethylene carbonate;

[0039] Lithium salts include: lithium difluorophosphate;

[0040] Additives: First additive: 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and cyclohexylbenzene; Second additive: fluoroethylene carbonate.

[0041] With the electrolyte mass as 100%, the mass fraction of ethyl methyl carbonate as 30%, the mass fraction of ethylene carbonate as 40%, the mass fraction of lithium difluorophosphate as 20%, the mass fraction of 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene as 2%, the mass fraction of cyclohexylbenzene as 2%, and the mass fraction of fluoroethylene carbonate as 6%.

[0042] Example 3

[0043] This embodiment provides an electrolyte:

[0044] The electrolyte consists of organic solvents, lithium salts, and additives:

[0045] Organic solvents include: propylene carbonate and diethyl carbonate;

[0046] Lithium salts include: lithium difluorosulfonylimide;

[0047] Additives: First additive: 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and cyclohexylbenzene; Second additive: fluoroethylene carbonate.

[0048] With the electrolyte mass as 100%, the mass fractions of propylene carbonate, diethyl carbonate, lithium bis(fluorosulfonyl)imide, 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene, cyclohexylbenzene, and fluoroethylene carbonate as 4%.

[0049] Example 4

[0050] In this embodiment, all conditions are the same as in Example 1, except that cyclohexylbenzene is not added and the mass fraction of 2,5-di-tert-butyl-1,4-di(2-methoxyethoxy)benzene is replaced with 5%.

[0051] Example 5

[0052] In this embodiment, the conditions are the same as in Example 1, except that 2,5-di-tert-butyl-1,4-di(2-methoxyethoxy)benzene is not added and the mass fraction of cyclohexylbenzene is replaced with 5%.

[0053] Example 6

[0054] In this embodiment, except that the second additive fluoroethylene carbonate is not added and the mass fraction of the organic solvent dimethyl carbonate is replaced with 35%, all other conditions are the same as in Example 1.

[0055] Comparative Example 1

[0056] The conditions for this comparative example are the same as those in Example 1, except that 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and cyclohexylbenzene are not added, and the mass fraction of dimethyl carbonate is replaced with 35%.

[0057] The electrolytes from Examples 1-6 and Comparative Example 1 were added to the same soft-pack battery cell with a capacity of 45Ah. The battery cells from Examples 1-6 and Comparative Example 1 were charged and discharged at a current of 45Ah for 50 cycles. The upper limit voltage was set to 4.83V (overcharge voltage 115%, greater than GB standard 110%). After 50 cycles, the appearance of the battery cell was observed, and the gas production and capacity of the battery cell were recorded. The test results are shown in Table 1.

[0058] Table 1

[0059] Example 1 Mild bloating 66 44.05 Example 2 Mild bloating 78 44.08 Example 3 Mild bloating 61 43.20 Example 4 Mild bloating 75 43.72 Example 5 Mild bloating 68 42.55 Example 6 Mild bloating 72 38 Comparative Example 1 Severe bloating 163 40.38

[0060] The results above show that Example 1 performs better overall. In the presence of the second additive, fluoroethylene carbonate film-forming additive, the combined use of 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and cyclohexylbenzene can reduce the gas production to a minimum, while there is basically no significant difference in capacity, and it does not affect the overall performance of the cell.

[0061] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes an organic solvent, a lithium salt, and an additive. The additive includes a first additive, which is an overcharge prevention additive. The overcharge prevention additive is 2,5-di-tert-butyl-1,4-di(2-methoxyethoxy)benzene and cyclohexylbenzene. The additive also includes a second additive; The second additive includes fluoroethylene carbonate; With the electrolyte comprising 100% by mass, the 2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene comprises 2-3% by mass of the electrolyte, the cyclohexylbenzene comprises 2-3% by mass of the electrolyte, and the second additive comprises 4-6% by mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, The organic solvents include carbonate solvents.

3. The electrolyte according to claim 2, characterized in that, The carbonate solvents include any one or a combination of at least two of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, or diethyl carbonate.

4. The electrolyte according to claim 1, characterized in that, With the electrolyte comprising 100% by mass, the organic solvent comprises 70-80% by mass of the electrolyte.

5. The electrolyte according to claim 1, characterized in that, The lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium difluorophosphate, or lithium bis(fluorosulfonyl)imide.

6. The electrolyte according to claim 1, characterized in that, With the electrolyte comprising 100% by mass, the lithium salt comprises 10-20% by mass of the electrolyte.

7. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte as described in any one of claims 1-6, and the lithium-ion battery further includes a positive electrode and a negative electrode.

8. The lithium-ion battery according to claim 7, characterized in that, The active material of the positive electrode includes any one or a combination of at least two of lithium cobalt oxide, lithium iron phosphate, nickel-cobalt-manganese ternary positive electrode materials, or lithium manganese oxide.

9. The lithium-ion battery according to claim 7, characterized in that, The active material of the negative electrode sheet includes natural graphite and / or artificial graphite.