Lithium ion battery electrolyte and lithium ion battery

Abstract

The invention relates to a lithium ion battery electrolyte and a lithium ion battery. In order to prolong the cycle life of a lithium ion battery and improve the high-temperature performance of the lithium ion battery, the invention provides a lithium ion battery electrolyte which comprises a lithium salt, an organic solvent and an additive, the additive comprises a first additive, the structural formula of the first additive is # imgabs0 # R1, R2, R3, R4, R5 and R6, at least one group in the first additive is selected from-(CH2) n-O-(CH2) m-CN, the remaining groups are respectively and independently selected from hydrogen, halogen or alkyl, wherein n and m are respectively and independently selected from 0 or positive integers. The first additive is added into the electrolyte, so that the electrochemical performance of the lithium ion battery is improved, and the lithium ion battery has better high-temperature cycle performance and high-temperature capacity retention rate.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a lithium-ion battery electrolyte and a lithium-ion battery. Background Art

[0002] Due to characteristics such as high energy density, high power density, good cycle performance, no memory effect, and environmental friendliness, lithium-ion batteries are widely used in various electronic products such as mobile communication devices like mobile phones, mobile cameras, laptops, and mobile phones, and are also strong candidates for the energy supply system of future electric vehicles. The chain-like organic solvents commonly used in lithium-ion battery electrolytes include: dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, etc., as well as mixtures of two or more of them. The lithium salts commonly used are: lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, etc., as well as mixtures of two or more of them. Since lithium hexafluorophosphate has the property of being easily decomposed, especially in the presence of trace amounts of water in non-aqueous electrolytes, the decomposition rate will further accelerate. In addition, the high-temperature use environment of lithium-ion batteries will also cause a significant increase in the HF content of the electrolyte, and HF will damage the SEI film on the surfaces of the positive and negative electrodes of the lithium battery, thus seriously affecting the electrochemical performance of the lithium-ion battery.

[0003] With the expansion of the application fields of lithium-ion batteries, especially the rapid development of electric vehicles, the market has put forward high energy density requirements for the performance of power batteries. To achieve this goal, the positive and negative electrode materials need to further improve their capacities. The positive electrode material can increase the nickel content and raise the charging cut-off potential to improve the discharge capacity of the material. Under high voltage conditions, the electrolyte will undergo an oxidation reaction on the surface of the positive electrode material, resulting in poor cycle performance of the material and the battery. Especially under high-temperature conditions, the oxidation reaction of the electrolyte will be further aggravated. It should be noted that for high-voltage positive electrode materials, at present, the cycle performance and high-temperature shelf performance of the battery are mainly improved by adjusting the electrolyte additives. For example, in patent CN105428719A, the organic solvent consists of a cyclic carbonate solvent, a fluorinated solvent, and a carbonate solvent, and the additive is 3-fluoro-1,3-propylene sulfonic acid lactone. The prepared electrolyte can effectively improve the cycle life and high-temperature performance of high-voltage wide-temperature lithium-ion batteries when applied to lithium-ion batteries with lithium cobalt oxide positive electrode materials. However, through practice, it is found that its high-temperature cycle performance still needs to be improved when applied to lithium-ion batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a lithium-ion battery electrolyte and a lithium-ion battery with better high-temperature performance.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A lithium-ion battery electrolyte, comprising a lithium salt, an organic solvent and an additive, wherein the additive comprises a first additive, and the structural formula of the first additive is At least one of R1, R2, R3, R4, R5, and R6 is selected from -(CH2) n -O-(CH2) m -CN, and the remaining groups are independently selected from hydrogen, halogen or alkyl, where n and m are independently selected from 0 or positive integers.

[0007] Preferably, n and m are independently selected from 0, 1, 2, and 3.

[0008] More preferably, n and m are independently selected from 0 or 1.

[0009] Preferably, the alkyl group is an alkyl group having 1 to 3 carbon atoms, such as methyl, ethyl or propyl.

[0010] More preferably, the alkyl group is methyl.

[0011] Preferably, the halogen is fluorine.

[0012] In some embodiments, one or two of R1, R2, R3, R4, R5, and R6 are selected from -O-CN, -CH2-O-CN, -O-CH2-CN, and the remaining groups are independently selected from hydrogen, fluorine or methyl.

[0013] Further, when one of R1, R2, R3, R4, R5, and R6 is -O-CN, -CH2-O-CN, -O-CH2-CN, two of the remaining groups are methyl and the remaining other groups are hydrogen, or one of the remaining groups is fluorine and the remaining other groups are hydrogen, or all of the remaining groups are hydrogen;

[0014] When two of R1, R2, R3, R4, R5, and R6 are selected from -O-CN, -CH2-O-CN, -O-CH2-CN, the remaining other groups are hydrogen.

[0015] In some specific and preferred embodiments, the first additive comprises One or more of.

[0016] Preferably, the first additive accounts for 0.5 to 3% of the total mass of the electrolyte, such as 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8% or 3%.

[0017] Preferably, the additive further comprises a second additive, which includes one or more of vinylene carbonate (VC), ethylene vinylene carbonate, 1,3 - propane sultone (PS), 1,3-(1 - propylene) sultone, methylene methanedisulfonate, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, methyl maleic anhydride, succinic anhydride, biphenyl, cyclohexylbenzene, trioctyl phosphate, fluoroethylene carbonate, 1,2 - bis(2 - cyanoethoxy) ethane, 1,4 - dicyano - 2 - butene, 1,2,3 - tris(2 - cyanoethoxy) propane, succinonitrile, adiponitrile, 1,3,6 - hexanetricarbonitrile, sebaconitrile.

[0018] Preferably, the second additive accounts for 0.1 - 10% of the total mass of the electrolyte, more preferably 0.5 - 5%.

[0019] Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, anhydrous lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium difluoro bis(oxalato) phosphate, lithium 4,5 - dicyano - 2 - trifluoromethylimidazole, lithium fluorosulfonate, lithium bis(oxalato) borate, lithium difluorooxalato borate.

[0020] More preferably, the lithium salt contains lithium hexafluorophosphate.

[0021] Even more preferably, the lithium hexafluorophosphate accounts for 10 - 15% of the total mass of the electrolyte.

[0022] In some embodiments, the lithium salt further contains one or more of lithium tetrafluoroborate, lithium hexafluoroarsenate, anhydrous lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium difluoro bis(oxalato) phosphate, lithium 4,5 - dicyano - 2 - trifluoromethylimidazole, lithium fluorosulfonate, lithium bis(oxalato) borate, lithium difluorooxalato borate.

[0023] Preferably, the lithium salt accounts for 10 - 20% of the total mass of the electrolyte.

[0024] Preferably, the organic solvent is selected from one or more of carbonates and / or carboxylates.

[0025] More preferably, the carbonate includes one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

[0026] More preferably, the carboxylate includes ethyl propionate (EP) and / or propyl propionate (PP).

[0027] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and the lithium-ion battery electrolyte as described above.

[0028] Preferably, the positive electrode active material is LiCoO2, and the voltage ≥ 4.40V.

[0029] Preferably, the negative electrode active material is selected from carbon materials, alloy materials, metal materials, carbon-silicon materials, carbon-silicon dioxide materials, carbon-silicon monoxide materials, carbon-tin materials, or carbon-tin oxide materials.

[0030] More preferably, the negative electrode active material is selected from artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, or soft carbon.

[0031] Preferably, the lithium-ion battery includes, but is not limited to, a soft-pack, square, or cylindrical battery.

[0032] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0033] By adding a first additive to the electrolyte, the present invention improves the electrochemical performance of the lithium-ion battery, enabling the lithium-ion battery to have better high-temperature cycling performance and high-temperature capacity retention rate. Specific Embodiments

[0034] The present invention will be further described below in conjunction with embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions adopted in the embodiments can be further adjusted according to different requirements of specific uses, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0035] Unless otherwise specified, the raw materials involved in the following examples and comparative examples are commercially available products. Among them, the structural formula of S1 is CAS No.: 1125-43-5; the structural formula of S2 is CAS No.: 75403-69-9; the structural formula of S3 is CAS No.: 137988-23-9; the structural formula of S4 is CAS No.: 27165-72-6.

[0036] Unless otherwise specified, "%" in Table 1 below represents mass percentage.

[0037] Example 1

[0038] Battery Preparation Process: Lithium cobalt oxide (LiCoO2): polyvinylidene fluoride (PVDF): conductive carbon (SP) = 95:3.5:1.5 was added to N-methylpyrrolidone (NMP) and stirred evenly to form a slurry. The slurry was coated on an aluminum foil current collector using a coater, dried at 120 °C, rolled, and slit to obtain a positive electrode sheet. Using the same process, artificial graphite: sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) with a mass ratio of 95:3:2 was added to secondary water and stirred evenly to form a slurry. The slurry was coated on a copper foil current collector using a coater, dried at 120 °C, rolled, and slit to obtain a negative electrode sheet. The positive electrode sheet, negative electrode sheet, and PP separator were wound into an electrode core, and then the electrode core was placed into an aluminum-plastic film and sealed at the edges. After vacuum drying, electrolyte was injected and sealed to obtain a soft-pack polymer lithium-ion battery, abbreviated as LCO / AG.

[0039] Electrolyte Preparation: 20% ethyl methyl carbonate (DEC), 30% ethylene carbonate (EC), 20% ethyl propionate (EP), and 30% propyl propionate (PP) were taken by weight ratio and thoroughly mixed evenly in a glove box with a humidity less than 1% to prepare an electrolyte solvent. Then, based on the total mass of the electrolyte, lithium hexafluorophosphate LiPF6 with a mass fraction of 13.5% and lithium difluoro(oxalato)borate LiODFB with a mass fraction of 0.5% were added in portions. After the electrolyte salts were fully dissolved, S1 with a mass content of 0.5% was added, and then left standing for 24 hours to obtain the electrolyte of Example 1.

[0040] The above electrolyte was injected into the soft-pack battery LCO / AG for performance testing.

[0041] Battery High-Temperature Test Conditions: The assembled LCO / AG battery was first formed. The formation conditions were: constant current charging at 0.1C to 4.45V, then constant voltage charging at 4.45V for 2h, standing for 10min, and then constant current discharging at 0.2C to 3.0V. The test conditions for the high-temperature cycling performance of the lithium-ion battery were: at a high temperature of 45 °C, constant current charging at 1C to 4.45V, then constant voltage charging at 4.45V for 2h, standing for 10min, constant current discharging at 1C to 3.0V, standing for 10min, and then performing 500 cycles. The capacity retention rate at 500 cycles % = capacity at the 500th cycle / capacity at the 1st cycle × 100%.

[0042] Battery High-Temperature Storage Conditions: After formation, the LCO / AG battery was charged at a constant current of 0.1C to 4.45V, then charged at a constant voltage of 4.45V for 2h, and left standing for 10min. The charging capacity of the battery was Q 充 ; the fully charged LCO / AG battery was stored at 80 °C for 4 hours and then discharged at a constant current of 0.2C to 3.0V. The discharging capacity of the battery was Q 放 . The capacity retention rate after high-temperature storage = Q 放 / Q 充 × 100%.

[0043] For Examples 2 to 22, except for the changes in the electrolyte components as shown in Table 1, the electrolyte preparation and battery tests were carried out in the same manner as in Example 1.

[0044] Comparative Examples 1 to 9

[0045] Except for the changes in the electrolyte components as shown in Table 1, the electrolyte preparation and battery tests were carried out in the same manner as in Example 1.

[0046] Table 1 Battery Formulations of Examples 1 - 22 and Comparative Examples 1 - 9

[0047]

[0048]

[0049] Table 2 Battery Performances of Examples 1 - 22 and Comparative Examples 1 - 9

[0050]

[0051]

[0052] By comparing the examples and comparative examples, it was found that adding the first additive could significantly improve the high - temperature cycling performance and high - temperature capacity retention rate of the battery, and with the increase in the addition amount of the first additive, the improvement of the battery performance became more obvious. The inventor speculated that: the first additive has better film - forming performance, which can effectively improve the composition of the CEI film on the surface of the electrode material, thereby improving the electrochemical performance of the battery, especially the high - temperature cycling performance and high - temperature capacity retention rate.

[0053] Further comparing Examples 1 to 22, it was found that adding additive S1, S2, S3, or S4 alone could effectively improve the high - temperature cycling performance and high - temperature capacity retention rate of the battery. At the same addition amount, the effect of adding S4 alone was better. Compared with the single addition of additives S1, S2, S3, or S4, the combined addition of two or more of them was better for improving the high - temperature cycling performance and / or high - temperature capacity retention rate of the battery. Especially the combination of S1 and S4 was better for improving the high - temperature cycling performance and high - temperature capacity retention rate. Further adding VC and / or PS to the electrolyte was helpful for improving the high - temperature cycling performance and / or high - temperature capacity retention rate of the battery, and the simultaneous addition of VC and PS was more obvious for improving the high - temperature cycling performance and high - temperature capacity retention rate of the battery.

[0054] The above has made a detailed description of the present invention, aiming to enable those skilled in this field of technology to understand the content of the present invention and implement it. However, it should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A lithium-ion battery electrolyte, comprising a lithium salt, an organic solvent, and an additive, characterized in that: The additive includes a first additive, and the structural formula of the first additive is At least one of the groups R1, R2, R3, R4, R5, and R6 is selected from -(CH2) n -O-(CH2) m -CN, and the remaining groups are each independently selected from hydrogen, halogen, or alkyl, where n and m are each independently selected from 0 or a positive integer.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that: n and m are each independently selected from 0, 1, 2, 3; and / or, the alkyl group is an alkyl group having 1 to 3 carbon atoms; and / or, the halogen is fluorine.

3. The lithium-ion battery electrolyte according to claim 2, characterized in that: One or two of R1, R2, R3, R4, R5, and R6 are selected from -O-CN, -CH2-O-CN, -O-CH2-CN, and the remaining groups are each independently selected from hydrogen, fluorine, or methyl.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that: When one of R1, R2, R3, R4, R5, and R6 is -O-CN, -CH2-O-CN, or -O-CH2-CN, two of the remaining groups are methyl and the other remaining groups are hydrogen, or one of the remaining groups is fluorine and the other remaining groups are hydrogen, or all of the remaining groups are hydrogen; When two of R1, R2, R3, R4, R5, and R6 are selected from -O-CN, -CH2-O-CN, -O-CH2-CN, the other remaining groups are hydrogen.

5. The lithium-ion battery electrolyte according to claim 4, characterized in that: The first additive includes one or more of 6. The lithium-ion battery electrolyte according to any one of claims 1 to 5, characterized in that: The first additive accounts for 0.5 to 3% of the total mass of the electrolyte.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that: The additive further includes a second additive, and the second additive includes one or more of vinylene carbonate, ethylene vinylene carbonate, 1,3-propane sultone, 1,3-(1-propene) sultone, methylene methanedisulfonate, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, methyl maleic anhydride, succinic anhydride, biphenyl, cyclohexylbenzene, trioctyl phosphate, fluorinated ethylene carbonate, 1,2-bis(2-cyanoethoxy) ethane, 1,4-dicyano-2-butene, 1,2,3-tris(2-cyanoethoxy) propane, succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, sebaconitrile; and / or, The second additive accounts for 0.1 to 10% of the total mass of the electrolyte.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that: The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, anhydrous lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium difluoro(bis(oxalato))phosphate, lithium 4,5-dicyano-2-trifluoromethylimidazole, lithium fluorosulfonate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate; and / or, The lithium salt accounts for 10 to 20% of the total mass of the electrolyte.

9. The lithium-ion battery electrolyte according to claim 1, characterized in that: The organic solvent is selected from one or more of carbonates and / or carboxylates.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that: The lithium ion battery further includes the lithium ion battery electrolyte according to any one of claims 1 to 9.

Images