Electrolyte additive for improving high-temperature performance of lithium ion battery and application of electrolyte additive

Abstract

The invention provides an electrolyte additive for improving the high-temperature performance of a lithium ion battery, an electrolyte containing the electrolyte additive and application of the electrolyte. The additive structure of the electrolyte provided by the invention is provided with the unsaturated cyclic alkene compound with a three-dimensional structure, and the lithium ion battery prepared by using the electrolyte provided by the invention can improve the high-temperature cycle and high-temperature storage performance of the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to an electrolyte additive, an electrolyte containing the additive and application thereof, and belongs to the technical field of lithium ion batteries. Background Art

[0002] Lithium-ion batteries, due to their high energy density, excellent cycle performance, and lack of memory effect, have become the primary choice for high-performance electronic components and new energy vehicles. During use, batteries inevitably experience temperature increases, making their performance stability at high temperatures particularly important. The electrolyte, the "blood" of lithium-ion batteries, determines their performance. However, lithium hexafluorophosphate, the primary lithium salt used in current electrolytes, readily decomposes at high temperatures, resulting in a shortened battery cycle life, reduced capacity, and serious consequences such as gassing and bulging.

[0003] Adding a small amount of additives to the electrolyte can significantly improve the high-temperature performance of the battery. For example, Chinese patent CN 11691426 B provides an electrolyte formula that can improve the high-temperature cycling performance of the battery. By adding a heterocyclic compound with a benzenesulfonyl group to the electrolyte, the capacity retention rate of the battery during high-temperature cycling can be greatly improved. However, these heterocyclic compound additives with benzenesulfonyl groups are difficult to obtain, which will seriously affect cost-effectiveness. In addition, their large molecular weight will greatly increase the viscosity of the electrolyte. Chinese patent CN 116675650B adds an additive containing a pyrazine structure to the electrolyte to improve the cycling performance of the battery while removing HF. However, the synthesis process of this additive is very complicated and the reaction conditions are harsh, which may not be suitable for industrial production. Therefore, it is very necessary to find an additive that can improve high-temperature performance, is economical, and is easy to use. Summary of the Invention

[0004] In view of the existing problems, the present invention provides a high-temperature electrolyte additive, comprising an unsaturated cyclic olefin compound as shown in Formula 1.

[0005] The present invention provides an electrolyte, which can improve the high-temperature cycle performance and high-temperature storage performance of a lithium-ion battery.

[0006] The present invention provides a lithium ion battery having excellent high-temperature cycle performance and high-temperature storage performance.

[0007] In one aspect, the present invention provides a compound for use in an electrolyte additive, wherein the compound having the structure shown in Formula 1 is:

[0008]

[0009] Wherein R1, R2, R3, R4, R5, R6, R7, and R8 are each independently selected from substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C2-C5 unsaturated hydrocarbon, cyano, carbonyl, and derivatives thereof.

[0010] Specifically, selected from the compounds shown in A-1 to A-6;

[0011]

[0012] On the other hand, the present invention further provides an electrolyte, wherein the mass percentage of the compound of formula 1 is 0.2-5%, preferably 0.3-1%, based on the total mass of the electrolyte.

[0013] In a specific embodiment, based on the total percentage of the electrolyte, the electrolyte comprises 70-90% organic solvent, 5-20% lithium salt, 0.2-5% additives shown in Formula 1, and 0.2-5% other additives.

[0014] The organic solvent is selected from one or more of carbonates, ethers, sulfones, hydrofluoroethers, and carboxylic acid ester compounds; preferably, one or more of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, sulfolane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate;

[0015] The lithium salt is one or more of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, lithium bis(trifluoromethyl)sulfonyl imide, lithium tetrafluoroborate, and lithium bisoxalatoborate, preferably one or more of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, and lithium bis(trifluoromethyl)sulfonyl imide;

[0016] The additive represented by formula 1 is selected from any one of A-1 to A-6, preferably A-1 and A-6;

[0017] Other additives are selected from one or more of fluorinated carbonates, unsaturated carbonates, trialkylsilyl phosphates, trialkylsilyl borate, alkyl sulfates, alkyl or olefin sultones, fluorinated sulfonates or esters, lithium fluorinated phosphates, alkyl fluorinated phosphates, and nitriles, preferably one or more of vinylene carbonate, 1,3-propane sultone, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, vinyl sulfate, methylene methanedisulfonate, fluorinated ethylene carbonate, lithium fluorinated sulfonate, lithium difluorophosphate, diethyl fluorinated phosphate, lithium difluorobis(oxaloyl)phosphate, and adiponitrile. Finally, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and the electrolyte.

[0018] The beneficial effects of the present invention are:

[0019] The lithium-ion battery prepared using the electrolyte of the present invention has good high-temperature cycle performance and high-temperature storage performance.

[0020] The electrolyte of the present invention can combine the advantages of the compound of formula 1 and the additive. On the one hand, the compound of formula 1 contains multiple unsaturated bonds and a cyclic structure, and can easily undergo a ring-opening polymerization reaction. After being added to the electrolyte, it can preferentially form a protective film on the positive and negative electrodes. Moreover, due to the synergistic effect of multiple unsaturated bonds, the formed interface film has a certain three-dimensional structure, which can well isolate the contact between the electrolyte and the positive and negative electrodes, avoid the occurrence of side reactions, and improve high-temperature cycle performance.

[0021] On the other hand, the use of additives can reduce battery resistance, reduce polarization, and improve capacity retention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0023] Raw materials and sources: Solvents and lithium salts were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Other additives can be purchased from Shanghai McLean Biochemical Technology Co., Ltd., Shanghai Aladdin Biochemical Technology Co., Ltd., Shanghai Myrel Biochemical Technology Co., Ltd., Duoduo Reagent Network and other channels.

[0024] Table 1 Electrolyte components of Examples and Comparative Examples

[0025]

[0026] In Table 1, TMSP is tris(trimethylsilyl)phosphate, TMSB is tris(trimethylsilyl)borate, LiDFP is lithium difluorophosphate, LiDFOP is lithium difluorobis(oxalatophosphate), DTD is vinyl sulfate, and MMDS is methylene methanedisulfonate.

[0027] The lithium-ion batteries obtained in the examples and comparative examples were subjected to the following tests, respectively, and the test results are shown in Tables 2 and 3. Battery cycle and storage tests were conducted using a Xinwei charge and discharge instrument.

[0028] (1) Room temperature cycle performance test

[0029] At 25°C, the lithium-ion batteries obtained in the examples and comparative examples were charged at a constant current density of 1C to 4.25V, then charged at a constant voltage of 4.25V to a current density ≤0.05C. After standing for 5 minutes, they were discharged at a constant current density of 1C to 2.75V. The above constituted one charge / discharge cycle. The lithium-ion batteries were cycled 800 times at 25°C under the above conditions.

[0030] Capacity retention rate (%) of lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%.

[0031] (2) 45℃ high temperature cycle performance test

[0032] At 45°C, the lithium-ion batteries obtained in the examples and comparative examples were charged at a constant current density of 1C to 4.25V, then charged at a constant voltage of 4.25V to a current density ≤0.05C. After standing for 5 minutes, they were discharged at a constant current density of 1C to 2.75V. The above constituted one charge / discharge cycle. The lithium-ion batteries were cycled 800 times at 45°C under the above conditions.

[0033] Capacity retention rate (%) of lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%.

[0034] (3) 60℃ high temperature storage test

[0035] The lithium-ion batteries obtained in the examples and comparative examples were subjected to five charge-discharge cycles at room temperature at a charge / discharge rate of 1C / 1C, and then charged to 4.25V at a current density of 1C. The 1C capacity Q and the DC resistance R of the battery were recorded respectively. The fully charged batteries were placed in a 60°C environment for long-term storage for 56 days, and the 1C discharge capacity Q of the battery was recorded on the 7th, 14th, 28th and 56th days respectively. 7-a , Q 14-a , Q 28-a , Q 56-a , and DC resistors R7, R 14 、R28 and R 56 The battery was then cycled five times at room temperature with a charge / discharge rate of 1C / 1C, and the 1C discharge capacity Q was recorded. 7-b , Q 14-b , Q 28-b , Q 56-b , the battery high temperature storage residual capacity retention rate, recovery capacity retention rate and DC resistance increase rate are calculated.

[0036] The calculation formulas are as follows:

[0037] Residual capacity retention rate = Q n-a / Q×100%; Capacity recovery retention rate = Q n-b / Q×100%; DC resistance growth rate = R n / R×100%.

[0038] Where n is the measurement result after the storage of the nth day.

[0039] Table 2 Cyclic test results

[0040]

[0041] Table 3 Storage test results

[0042]

[0043]

[0044] As can be seen from Table 2, when comparing Comparative Examples 2-5 with Comparative Example 1, the addition of the compound of Formula 1 or the additive alone slightly improved the high-temperature cycling performance of the lithium-ion battery, but this was not significant. When comparing Examples 1-6 with Comparative Examples 2-4, the addition of the compound of Formula 1 and the additive together significantly improved the high-temperature performance of the lithium-ion battery. It can be seen from Examples 1-10 and Comparative Examples 5-8 that when the compound of Formula 1 or the additive is added in excess, the performance will deteriorate to a certain extent, so the addition amount must be controlled within a certain range.

[0045] As can be seen from Table 3, adding the compound of Formula 1 and the additive can greatly improve the high-temperature storage performance of the lithium-ion battery. At the same time, the additive can significantly reduce the DC resistance growth rate of the lithium-ion battery and improve the reversible capacity of the lithium-ion battery.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. Use of a compound in an electrolyte, wherein the compound has a structure shown in Formula 1: Wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10 are each independently selected from a halogen atom, a substituted or unsubstituted C1-C4 alkyl group, a substituted or unsubstituted C2-C5 unsaturated hydrocarbon group, a cyano group, and derivatives thereof.

2. Use of the compound according to claim 1 in an electrolyte, characterized in that: The compound is selected from the compounds shown in A-1 to A-6; 3. An electrolyte, wherein Based on the total mass of the electrolyte, the mass percentage of the compound of formula 1 is 0.2-5%, preferably 0.3-1%; The structure of the compound of formula 1 is: wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10 are each independently selected from a halogen atom, a substituted or unsubstituted C1-C4 alkyl group, a substituted or unsubstituted C2-C5 unsaturated hydrocarbon group, a cyano group, and derivatives thereof, preferably a compound represented by A-1 to A-6; 4. The electrolyte according to claim 3, wherein According to the total percentage of the electrolyte, the electrolyte contains 70-90% organic solvent, 5-20% lithium salt, 0.2-5% additive of formula 1, and 0.2-5% other additives.

5. The electrolyte according to claim 4, wherein The organic solvent is selected from one or more of carbonates, ethers, sulfones, hydrofluoroethers, and carboxylic acid ester compounds; preferably one or more of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, cyclopentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

6. The electrolyte according to claim 4 or 5, characterized in that The lithium salt is one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethyl)sulfonyl imide, lithium tetrafluoroborate, and lithium bis(oxalatoborate), preferably one or more of lithium hexafluorophosphate and lithium bis(fluorosulfonyl imide).

7. The electrolyte according to any one of claims 4 to 6, characterized in that Other additives are selected from one or more of fluorocarbonates, unsaturated carbonates, trialkylsilyl phosphates, trialkylsilyl borate, alkyl sulfates, alkyl or olefin sultones, fluorosulfonates or esters, lithium fluorophosphates, alkyl fluorophosphates, and nitriles, preferably one or more of vinylene carbonate, 1,3-propane sultone, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, vinyl sulfate, methylene methanedisulfonate, fluoroethylene carbonate, lithium fluorosulfonate, lithium difluorophosphate, diethyl fluorophosphate, lithium difluorobis(oxaloyl)phosphate, and adiponitrile.

8. A secondary battery comprising a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 4 to 7.

Images