WO2024104049A1 - 电解液及锂离子电池 - Google Patents

电解液及锂离子电池 Download PDF

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WO2024104049A1
WO2024104049A1 PCT/CN2023/125696 CN2023125696W WO2024104049A1 WO 2024104049 A1 WO2024104049 A1 WO 2024104049A1 CN 2023125696 W CN2023125696 W CN 2023125696W WO 2024104049 A1 WO2024104049 A1 WO 2024104049A1
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electrolyte
carbonate
lithium
compound
toluenesulfonyl
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PCT/CN2023/125696
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English (en)
French (fr)
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黄波
梁大宇
李道聪
杨茂萍
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合肥国轩高科动力能源有限公司
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Publication of WO2024104049A1 publication Critical patent/WO2024104049A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0088—Composites
    • H01M2300/0091—Composites in the form of mixtures
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte and a lithium ion battery.
  • the main purpose of the present invention is to provide an electrolyte and a lithium ion battery to solve the problem of high impedance of lithium ion batteries in the prior art.
  • an electrolyte comprising an organic solvent, LiPF6 and an additive, wherein the additive comprises a trifluoromethanesulfonic acid compound and a p-toluenesulfonyl compound.
  • trifluoromethanesulfonic acid compound is a compound having structural formula I:
  • R1 is selected from any one of silane group, substituted or unsubstituted phenyl group, substituted or unsubstituted C 1 to C 4 straight chain alkyl group, substituted or unsubstituted C 3 to C 6 branched chain alkyl group, and preferably the trifluoromethanesulfonic acid compound is selected from Any one or more of .
  • the trifluoromethanesulfonic acid compound is selected from Any one or more of .
  • the p-toluenesulfonyl compound is a compound having structural formula II,
  • R2 is selected from any one of cyano, halogen, and amino, and preferably the p-toluenesulfonyl compound is selected from Any one or more of .
  • the mass of the above-mentioned additive is 0.1-5wt% of the total mass of the electrolyte, and preferably the mass ratio of the trifluoromethanesulfonic acid compound to the p-toluenesulfonyl compound is 1:5-5:1.
  • the above-mentioned organic solvent includes any one or more of cyclic carbonates, chain carbonates and carboxylates, preferably the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate and ⁇ -butyrolactone, preferably the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl carbonate, preferably the carboxylate is selected from one or more of methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate and ethyl butyrate, preferably the organic solvent is selected from the combination of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, preferably the mass
  • the electrolyte further comprises a lithium salt additive, preferably the concentration of the lithium salt additive is 0.3 to 1 mol/L, and the lithium salt additive is preferably selected from lithium bis(fluorosulfonyl)imide, LiBF 4 , lithium bis(oxalatoborate), lithium difluorooxalatoborate, difluorooxalatophosphoric acid, Any one or more of lithium, lithium bis(trifluoromethylsulfonyl imide), phenyl sulfone, tris(trimethylsilyl)phosphite, vinyl sulfate, and methylene disulfonate.
  • a lithium salt additive preferably the concentration of the lithium salt additive is 0.3 to 1 mol/L
  • the lithium salt additive is preferably selected from lithium bis(fluorosulfonyl)imide, LiBF 4 , lithium bis(oxalatoborate), lithium difluorooxalatoborate, difluorooxalato
  • the preferred lithium salt additive is lithium bis(trifluoromethylsulfonyl imide), vinyl sulfate, and methylene disulfonate, or the preferred lithium salt additive is phenyl sulfone, tris(trimethylsilyl)phosphite, vinyl sulfate, and methylene disulfonate.
  • the concentration of the above-mentioned LiPF 6 is 0.5-1.5 mol/L
  • the preferred electrolyte includes: ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, LiPF 6 , vinyl sulfate, methylene disulfonate, bis(fluorosulfonyl)imide lithium salt and in, 2.5wt% of the electrolyte, 0.5wt% of the electrolyte; or 0.5wt% of the electrolyte, 2.5 wt% of the electrolyte; or 0.8wt% of the electrolyte, 2.2 wt% of the electrolyte; or 1.2wt% of the electrolyte, It is 1.8wt% of the electrolyte.
  • a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte is the electrolyte described above.
  • the positive electrode sheet comprises a positive electrode material, and preferably the positive electrode material is LiNi (1-xy) CoxMny , wherein 0 ⁇ x ⁇ 1 , 0 ⁇ y ⁇ 1.
  • the strong electron-withdrawing property of the trifluoromethyl group in the trifluoromethanesulfonic acid compound makes the mesyl group directly connected thereto have stronger reactivity, and the combined use with the toluenesulfonyl compound can form a stable interface film on the surface of the NCM ternary positive electrode and the graphite negative electrode.
  • the interface film is not only thin and dense, but also the benzene ring structure of the p-toluenesulfonyl compound has great rigidity, which makes the interface film more stable, thereby improving the ionic conductivity of the interface film, hindering the generation of harmful products such as HF in the electrolyte and the dissolution of the cathode transition metal during the cycle, and thus to a certain extent not only reducing the impedance of the lithium ion battery, but also significantly improving the comprehensive performance of the lithium ion battery such as the cycle performance.
  • the lithium ion battery in the prior art has the problem of high impedance.
  • the present invention provides an electrolyte and a lithium ion battery.
  • an electrolyte which includes an organic solvent, LiPF 6 and an additive, wherein the additive includes a trifluoromethanesulfonic acid compound and a p-toluenesulfonyl compound.
  • the strong electron-withdrawing property of the trifluoromethyl group in trifluoromethanesulfonic acid compounds makes the mesyl group directly connected to it have stronger reactivity.
  • a stable interface film can be formed on the surface of the NCM ternary positive electrode and the graphite negative electrode.
  • the interface film is not only thin and dense, but also the benzene ring structure of p-toluenesulfonyl compounds has great rigidity, which makes the interface film more stable, thereby improving the ionic conductivity of the interface film, hindering the generation of harmful products such as HF in the electrolyte and the dissolution of the cathode transition metal during the cycle, and thus to a certain extent not only reducing the impedance of the lithium-ion battery, but also significantly improving the comprehensive performance of the lithium-ion battery such as the cycle performance.
  • the trifluoromethanesulfonic acid compound is preferably a compound having structural formula I:
  • R1 is selected from any one of silane group, substituted or unsubstituted phenyl group, substituted or unsubstituted C 1 to C 4 straight chain alkyl group, substituted or unsubstituted C 3 to C 6 branched chain alkyl group, and preferably the trifluoromethanesulfonic acid compound is selected from Any one or more of .
  • trifluoromethanesulfonic acid compounds are selected from Any one or more of .
  • the p-toluenesulfonyl compound is a compound having structural formula II,
  • R2 is selected from any one of cyano, halogen, and amino, and preferably the p-toluenesulfonyl compound is selected from Any one or more of .
  • the p-toluenesulfonyl compounds containing the above substituents have higher redox properties, and the synergistic effect with trifluoromethanesulfonic acid compounds makes it easier for the two to form thinner and denser CEI and SEI protective films on the surfaces of NCM cathodes and graphite anodes, thereby greatly improving the cycle stability of NCM cathodes and the power of graphite anodes.
  • the functional groups of p-toluenesulfonyl compounds can inhibit the hydrolysis reaction of LiPF 6 , thereby hindering the generation of harmful products HF and the dissolution of transition metals in the NCM cathode during the cycle, thereby significantly improving the cycle life of the NCM/graphite full battery.
  • the mass of the above-mentioned additive is 0.1-5wt% of the total mass of the electrolyte, and the mass ratio of the trifluoromethanesulfonic acid compound to the p-toluenesulfonyl compound is preferably 1:5-5:1, which is more conducive to the synergistic effect between the trifluoromethanesulfonic acid compound and the p-toluenesulfonyl compound.
  • the above-mentioned organic solvent preferably includes any one or more of cyclic carbonates, chain carbonates and carboxylates, preferably the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate and ⁇ -butyrolactone, preferably the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl carbonate, preferably the carboxylate is selected from one or more of methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate and ethyl butyrate, preferably the organic solvent is selected from a combination of ethylene carbonate, diethyl carbonate and ethyl
  • the above-mentioned types of organic solvents can better avoid the damage of water to the electrolyte, and at the same time help to promote the more complete dissolution of the components in the electrolyte, thereby improving the synergy between the components and obtaining an electrolyte with excellent electrical properties.
  • the above-mentioned electrolyte preferably also includes a lithium salt additive, and the concentration of the lithium salt additive is preferably 0.3-1 mol/L.
  • the lithium salt additive is preferably selected from any one or more of bis(fluorosulfonyl)imide lithium salt, LiBF4 , lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorooxalatophosphate, lithium bis(trifluoromethylsulfonyl)imide, phenyl sulfone, tris(trimethylsilane)phosphite, vinyl sulfate, and methylene disulfonate.
  • the lithium salt additive is preferably bis(fluorosulfonyl)imide lithium salt, vinyl sulfate, and methylene disulfonate, or the lithium salt additive is preferably phenyl sulfone, tris(trimethylsilane)phosphite, vinyl sulfate, and methylene disulfonate.
  • LiPF 6 as an electrolyte can enhance the conductivity, energy storage and environmental protection of lithium-ion batteries.
  • the present application preferably has a concentration of LiPF 6 of 0.5 to 1.5 mol/L.
  • the preferred electrolyte includes: ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, LiPF 6 , vinyl sulfate, methylene disulfonate, lithium bis(fluorosulfonyl)imide salt and in, 2.5wt% of the electrolyte, 0.5wt% of the electrolyte; or 0.5wt% of the electrolyte, 2.5 wt% of the electrolyte; or 0.8wt% of the electrolyte, 2.2 wt% of the electrolyte; or 1.2wt% of the electrolyte, It is 1.8wt% of the electrolyte.
  • the mass ratio of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate is 1:1:2, the concentration of LiPF 6 is 0.7mol/L, and the concentrations of vinyl sulfate, methylene disulfonate and bis(fluorosulfonyl)imide lithium salt are each independently 0.1mol/L.
  • a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte is the aforementioned electrolyte.
  • the lithium-ion battery using the above electrolyte has lower impedance and can significantly improve the comprehensive performance of the lithium-ion battery, such as the cycle performance.
  • the positive electrode sheet preferably includes a positive electrode material, and the positive electrode material is preferably LiNi (1-xy) Co x Mn y , wherein 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1.
  • Nickel cobalt lithium manganese oxide ternary material LiNi 0.7 Co 0.1 Mn 0.2 , conductive agent Super P, adhesive PVDF and carbon nanotubes (CNT) are mixed uniformly at a mass ratio of 97.5:0.5:1:1 to prepare a lithium ion battery positive electrode slurry of a certain viscosity, which is coated on aluminum foil for current collector with a coating amount of 360 g/m 2 , dried at 85°C and then cold pressed; then striped and sliced, and then dried at 85°C in vacuum for 4 hours to prepare a lithium ion battery positive electrode sheet that meets the requirements.
  • Preparation of lithium-ion battery The positive electrode sheet, negative electrode sheet and separator prepared according to the above process are stacked to form a lithium-ion battery with a thickness of 0.5 mm, a width of 8 mm, and a length of 10 mm.
  • the capacity is 3 Ah.
  • the battery is vacuum-baked at 85°C for 48 hours, and the above electrolyte is injected to complete the battery production.
  • Examples 2 to 17 and Comparative Examples 1 to 4 changed the ratio and type of specific substances in the electrolyte, and obtained lithium-ion batteries with reference to the preparation method of Example 1.
  • the electrolyte formula is shown in Table 1 below.
  • Example 10 The difference between Example 10 and Example 4 is that
  • Example 11 The difference between Example 11 and Example 4 is that,
  • Example 12 The difference between Example 12 and Example 4 is that,
  • Trifluoromethanesulfonic acid compounds are Finally, a lithium-ion secondary battery is obtained.
  • Example 13 The difference between Example 13 and Example 4 is that,
  • Trifluoromethanesulfonic acid compounds are Finally, a lithium-ion secondary battery is obtained.
  • Example 14 The difference between Example 14 and Example 4 is that,
  • Toluenesulfonyl compounds are Finally, a lithium-ion secondary battery is obtained.
  • Example 15 The difference between Example 15 and Example 4 is that
  • Toluenesulfonyl compounds are Finally, a lithium-ion secondary battery is obtained.
  • Example 16 The difference between Example 16 and Example 4 is that the solvent is ethyl propionate (EP), and a lithium ion secondary battery is finally obtained.
  • EP ethyl propionate
  • Example 17 The difference between Example 17 and Example 4 is that the lithium salt additive is 0.1 mol/L LiFSI, 0.1 mol phenyl sulfone (PS) and 0.1 mol tris(trimethylsilyl)phosphite (TMSP), and finally a lithium ion secondary battery is obtained.
  • the lithium salt additive is 0.1 mol/L LiFSI, 0.1 mol phenyl sulfone (PS) and 0.1 mol tris(trimethylsilyl)phosphite (TMSP), and finally a lithium ion secondary battery is obtained.
  • the experimental batteries in Examples 1 to 17 and Comparative Examples 1 to 4 were respectively charged to a charge state of 50% SOC, and after being rested for 30 minutes, the sampling voltage V0 at the beginning of discharge was recorded, and then the sampling voltage V1 at the end of discharge was recorded after discharging at a current I of 2C for 10 seconds, and the initial DC discharge internal impedance DCR of the experimental battery was calculated as (V1-V0)/I.
  • the strong electron-withdrawing property of the trifluoromethyl group in trifluoromethanesulfonic acid compounds makes the mesyl group directly connected to it have stronger reactivity.
  • a stable interface film can be formed on the surface of the NCM ternary positive electrode and the graphite negative electrode.
  • the interface film is not only thin and dense, but also the benzene ring structure of p-toluenesulfonyl compounds has great rigidity, which makes the interface film more stable, thereby improving the ionic conductivity of the interface film, hindering the generation of harmful products such as HF in the electrolyte and the dissolution of the cathode transition metal during the cycle, and thus to a certain extent not only reducing the impedance of the lithium-ion battery, but also significantly improving the comprehensive performance of the lithium-ion battery such as the cycle performance.

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Abstract

提供了一种电解液及锂离子电池。该电解液包括有机溶剂、LiPF6以及添加剂，添加剂包括三氟甲烷磺酸类化合物和对甲苯磺酰类化合物。三氟甲烷磺酸类化合物与甲苯磺酰类化合物的联合使用，可在NCM三元正极及石墨负极表面形成稳定的界面膜，通过三氟甲烷磺酸类化合物和对甲苯磺酰类化合物的充分协同作用，界面膜不仅薄而致密，且对甲苯磺酰类化合物的苯环结构具有很大的刚性，使得界面膜更加稳定，从而提高了界面膜离子电导率，阻碍电解液中的HF等有害产物的产生和循环过程中阴极过渡金属的溶解，进而在一定程度上降低了锂离子电池的阻抗、改善了锂离子电池的循环性能。

Description

电解液及锂离子电池
本申请是以CN申请号为202211417646.0，申请日为2022年11月14日的中国申请为基础，并主张其优先权，该CN申请的公开内容再次作为整体引入本申请中。
技术领域
本发明涉及锂离子电池技术领域，具体而言，涉及一种电解液及锂离子电池。
背景技术
近年来，锂离子电池成为新的研究热点，并受到广泛关注。电动汽车领域关注混合动力汽车和移动设备电源用品等，这是由于其高能量密度、环境友好和经济友好决定的。众所周知，循环性能是电池的重要指标之一。随着电池的持续充电，会导致内阻的持续增长并且产生大量的热，通常在多次循环充电过程中恶化循环寿命。
发明内容
本发明的主要目的在于提供一种电解液及锂离子电池，以解决现有技术中的锂离子电池阻抗高的问题。
为了实现上述目的，根据本发明的一个方面，提供了一种电解液，电解液包括有机溶剂、LiPF6以及添加剂，添加剂包括三氟甲烷磺酸类化合物和对甲苯磺酰类化合物。
进一步地，上述三氟甲烷磺酸类化合物为具有结构式I所示的化合物：
其中，R1选自硅烷基、取代或非取代的苯基、取代或非取代的C1～C4的直链烷基、取代或非取代的C3～C6的支链烷基中的任意一种，优选三氟甲烷磺酸类化合物选自 中的任意一种或多种。
进一步地，上述三氟甲烷磺酸类化合物选自 中的任意一种或多种。
进一步地，上述对甲苯磺酰类化合物为具有结构式II所示的化合物，
其中，R2选自氰基、卤素、氨基中的任意一种，优选对甲苯磺酰类化合物选自中的任意一种或多种。
进一步地，上述添加剂的质量为电解液总质量的0.1～5wt％，优选三氟甲烷磺酸类化合物和对甲苯磺酰类化合物的质量比为1:5～5:1。
进一步地，上述有机溶剂包括环状碳酸酯、链状碳酸酯和羧酸酯中的任意一种或多种，优选环状碳酸酯选自碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、γ-丁内酯中的一种或几种，优选链状碳酸酯选自碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、碳酸甲丙酯、碳酸乙丙酯中的一种或几种，优选羧酸酯选自甲酸甲酯、甲酸乙酯、甲酸丙酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯中的一种或几种，优选有机溶剂选自碳酸乙烯酯、碳酸二乙酯和碳酸甲乙酯的组合，优选碳酸乙烯酯、碳酸二乙酯和碳酸甲乙酯质量比为1～2：1～2：2～5。
进一步地，上述电解液还包括锂盐添加剂，优选锂盐添加剂的浓度为0.3～1mol/L，优选锂盐添加剂选自双氟磺酰亚胺锂盐、LiBF4、双草酸硼酸锂、二氟草酸硼酸锂、二氟草酸磷酸 锂、双三氟甲基磺酰亚胺锂、苯砜、三(三甲基硅烷)亚磷酸酯、硫酸乙烯酯、甲基二磺酸亚甲酯中的任意一种或多种，进一步地，优选锂盐添加剂为双氟磺酰亚胺锂盐、硫酸乙烯酯、甲基二磺酸亚甲酯，或优选锂盐添加剂为苯砜、三(三甲基硅烷)亚磷酸酯、硫酸乙烯酯、甲基二磺酸亚甲酯。
进一步地，上述LiPF6的浓度为0.5～1.5mol/L，优选电解液包括：碳酸乙烯酯、碳酸二乙酯和碳酸甲乙酯、LiPF6、硫酸乙烯酯、甲基二磺酸亚甲酯、双氟磺酰亚胺锂盐以及其中，为电解液的2.5wt％，为电解液的0.5wt％；或为电解液的0.5wt％，为电解液的2.5wt％；或为电解液的0.8wt％，为电解液的2.2wt％；或为电解液的1.2wt％，为电解液的1.8wt％。
根据本发明的一个方面，提供了一种锂离子电池，包括正极片、负极片以及电解液，电解液为上述的电解液。
进一步地，上述正极片包括正极材料，优选正极材料为LiNi(1-x-y)CoxMny，其中，0≤x≤1，0≤y≤1。
应用本发明的技术方案，三氟甲烷磺酸类化合物中三氟甲基的强吸电子性使得与其直接相连的甲磺酰基具有更强的反应活性，与甲苯磺酰类化合物的联合使用，可在NCM三元正极及石墨负极表面形成稳定的界面膜，通过三氟甲烷磺酸类化合物和对甲苯磺酰类化合物的充分协同作用，界面膜不仅薄而致密，且对甲苯磺酰类化合物的苯环结构具有很大的刚性，使得界面膜更加稳定，从而提高了界面膜离子电导率，阻碍电解液中的HF等有害产物的产生和循环过程中阴极过渡金属的溶解，进而在一定程度上不仅降低了锂离子电池的阻抗，同时明显改善了锂离子电池的循环性能等综合性能。
具体实施方式
需要说明的是，在不冲突的情况下，本申请中的实施例及实施例中的特征可以相互组合。下面将结合实施例来详细说明本发明。
如背景技术所分析的，现有技术中的锂离子电池存在阻抗高的问题，为解决该问题，本发明提供了一种电解液及锂离子电池。
在本申请的一种典型的实施方式中，提供了一种电解液，该电解液包括有机溶剂、LiPF6以及添加剂，添加剂包括三氟甲烷磺酸类化合物和对甲苯磺酰类化合物。
三氟甲烷磺酸类化合物中三氟甲基的强吸电子性使得与其直接相连的甲磺酰基具有更强的反应活性，与甲苯磺酰类化合物的联合使用，可在NCM三元正极及石墨负极表面形成稳定的界面膜，通过三氟甲烷磺酸类化合物和对甲苯磺酰类化合物的充分协同作用，界面膜不仅薄而致密，且对甲苯磺酰类化合物的苯环结构具有很大的刚性，使得界面膜更加稳定，从而提高了界面膜离子电导率，阻碍电解液中的HF等有害产物的产生和循环过程中阴极过渡金属的溶解，进而在一定程度上不仅降低了锂离子电池的阻抗，同时明显改善了锂离子电池的循环性能等综合性能。
为提高三氟甲烷磺酸类化合物的成膜性，优选上述三氟甲烷磺酸类化合物为具有结构式I所示的化合物：
其中，R1选自硅烷基、取代或非取代的苯基、取代或非取代的C1～C4的直链烷基、取代或非取代的C3～C6的支链烷基中的任意一种，优选三氟甲烷磺酸类化合物选自 中的任意一种或多种。
为进一步地提高三氟甲烷磺酸类化合物与对甲苯磺酰类化合物的协同配合作用，优选上述三氟甲烷磺酸类化合物选自 中的任意一种或多种。
在本申请的一种实施例中，上述对甲苯磺酰类化合物为具有结构式II所示的化合物，
其中，R2选自氰基、卤素、氨基中的任意一种，优选对甲苯磺酰类化合物选自中的任意一种或多种。
包含以上取代基的对甲苯磺酰类化合物使得其具有较高的氧化还原性，与三氟甲烷磺酸类化合物的协同配合作用使得二者更容易在NCM阴极和石墨阳极表面生成更加薄而致密的CEI和SEI保护膜，从而大大提高了NCM阴极的循环稳定性和石墨阳极的功率性。另一方面，对甲苯磺酰类化合物官能团可以抑制LiPF6的水解反应，从而阻碍有害产物HF的产生和循环过程中NCM阴极过渡金属的溶解，进而显著提高了NCM/石墨全电池的循环寿命。
优选上述添加剂的质量为电解液总质量的0.1～5wt％，优选三氟甲烷磺酸类化合物和对甲苯磺酰类化合物的质量比为1:5～5:1，从而更有利于三氟甲烷磺酸类化合物和对甲苯磺酰类化合物之间进行协同配合作用。
在本申请的一种实施例中，优选上述有机溶剂包括环状碳酸酯、链状碳酸酯和羧酸酯中的任意一种或多种，优选环状碳酸酯选自碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、γ-丁内酯中的一种或几种，优选链状碳酸酯选自碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、碳酸甲丙酯、碳酸乙丙酯中的一种或几种，优选羧酸酯选自甲酸甲酯、甲酸乙酯、甲酸丙酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯中的一种或几种，优选有机溶剂选自碳酸乙烯酯、碳酸二乙酯和碳酸甲乙酯的组合，优选碳酸乙烯酯、碳酸二乙酯和碳酸甲乙酯的体积比为1～2:1～2:2～5。
上述种类的有机溶剂可以更好地规避水对电解液的破坏，同时有利于促进电解液中的各组分更充分的进行溶解，从而提高各组分之间的协同性，得到电学性能优良的电解液。
为增强锂盐添加剂与锂盐以及添加剂之间的配合作用，从而提高电解液的综合性能，优选上述电解液还包括锂盐添加剂，优选锂盐添加剂的浓度为0.3～1mol/L，优选锂盐添加剂选自双氟磺酰亚胺锂盐、LiBF4、双草酸硼酸锂、二氟草酸硼酸锂、二氟草酸磷酸锂、双三氟甲基磺酰亚胺锂、苯砜、三(三甲基硅烷)亚磷酸酯、硫酸乙烯酯、甲基二磺酸亚甲酯中的任意一种或多种，进一步地，优选锂盐添加剂为双氟磺酰亚胺锂盐、硫酸乙烯酯、甲基二磺酸亚甲酯，或优选锂盐添加剂为苯砜、三(三甲基硅烷)亚磷酸酯、硫酸乙烯酯、甲基二磺酸亚甲酯。
LiPF6作为电解液的电解质，可增强锂离子电池的导电性、储能性以及环保性，为进一步地发挥LiPF6的作用，本申请优选LiPF6的浓度为0.5～1.5mol/L，优选电解液包括：碳酸乙烯酯、碳酸二乙酯和碳酸甲乙酯、LiPF6、硫酸乙烯酯、甲基二磺酸亚甲酯、双氟磺酰亚胺锂盐以及其中，为电解液的2.5wt％，为电解液的0.5wt％；或为电解液的0.5wt％，为电解液的2.5wt％；或为电解液的0.8wt％，为电解液的2.2wt％；或为电解液的1.2wt％，为电解液的1.8wt％。进一步地，优选碳酸乙烯酯、碳酸二乙酯和碳酸甲乙酯的质量比为1:1:2，LiPF6的浓度为0.7mol/L，硫酸乙烯酯、甲基二磺酸亚甲酯和双氟磺酰亚胺锂盐的浓度各自独立地为0.1mol/L。
在本申请的另一种典型的实施方式中，提供了一种锂离子电池，包括正极片、负极片以及电解液，该电解液为前述的电解液。
采用上述电解液的锂离子电池具有较低的阻抗，可以明显改善锂离子电池的循环性能等综合性能。
为提高电解液与正极片的配合作用，从而使得锂离子电池的循环稳定性、较低的内阻等性能，优选上述正极片包括正极材料，优选正极材料为LiNi(1-x-y)CoxMny，其中，0≤x≤1，0≤y≤1。
以下将结合具体实施例和对比例，说明本申请的有益技术效果。
结构式I和结构式II的化合物从阿拉丁试剂官网上购得。
实施例1
电解液(以1L电解液计)的制备：将碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和碳酸甲乙酯(EMC)按质量比为EC:DEC:EMC＝1:1:2进行混合，混合后加入0.7mol的六氟磷酸锂(LiPF6)，0.1mol硫酸乙烯酯(DTD)、0.1mol甲基二磺酸亚甲酯(MMDS)、0.1mol双氟磺酰亚胺锂盐(LiFSI)，待锂盐完全溶解，加入2wt％1wt％
正极片的制备：将镍钴锰酸锂三元材料LiNi0.7Co0.1Mn0.2、导电剂Super P、粘接剂PVDF和碳纳米管(CNT)按质量比97.5:0.5:1:1混合均匀制成一定粘度的锂离子电池正极浆料，涂布在集流体用铝箔上，其涂布量为360g/m2，在85℃下烘干后进行冷压；然后进行分条，切片，然后在真空85℃烘4h，制成满足要求的锂离子电池正极片。
负极片的制备：将人造石墨与导电剂Super P、增稠剂CMC、粘接剂SBR(丁苯橡胶乳液)按质量比95:1.5:1.0:2.5的比例制成浆料，混合均匀，用混制的浆料涂布在铜箔的两面后，烘干、辊压后得到负极片，然后在真空85℃烘4h制成满足要求的锂离子电池负极片。
锂离子电池的制备：将根据上述工艺制备的正极片、负极片和隔膜经叠片工艺制作成厚度为0.5mm，宽度为8mm，长度为10的锂离子电池，容量为3Ah，在85℃下真空烘烤48小时，注入上述电解液，完成电池制作。
实施例2至17、对比例1至4改变电解液中具体物质的配比和种类，并参考实施例1的制备方法得到锂离子电池，电解液配方如下表1所示。
表1


实施例10
实施例10与实施例4的区别在于，
加入0.83wt％和0.17wt％最终得到锂离子电池。
实施例11
实施例11与实施例4的区别在于，
加入4.17wt％和0.83wt％最终得到锂离子电池。
实施例12
实施例12与实施例4的区别在于，
三氟甲烷磺酸类化合物为最终得到锂离子二次电池。
实施例13
实施例13与实施例4的区别在于，
三氟甲烷磺酸类化合物为最终得到锂离子二次电池。
实施例14
实施例14与实施例4的区别在于，
对甲苯磺酰类化合物为最终得到锂离子二次电池。
实施例15
实施例15与实施例4的区别在于，
对甲苯磺酰类化合物为最终得到锂离子二次电池。
实施例16
实施例16与实施例4的区别在于，溶剂为丙酸乙酯(EP)，最终得到锂离子二次电池。
实施例17
实施例17与实施例4的区别在于，锂盐添加剂为0.1mol/L的LiFSI、0.1mol苯砜(PS)和0.1mol三(三甲基硅烷)亚磷酸酯(TMSP)，最终得到锂离子二次电池。
(1)初始直流内阻(DCR)测试
分容后，分别将实施例1～17和对比例1～4中的实验电池充电至50％SOC的荷电状态，静止30min后纪录开始放电时的采样电压V0，然后以2C电流I放电10s后纪录放电结束时的采样电压V1，计算实验电池的初始直流放电内阻抗DCR＝(V1-V0)/I。
(2)循环性能检测
在25℃测试条件下，将实施例1～17和对比例1～4中实验电池分别以1C充放电倍率进行充放电循环性能测试，充放电电压区间设置为2.8～4.25V，常温循环800周，将以上测试结果列于表1。
以上实施例与对比例的对比中可以看出，与传统添加剂相比，该发明的三氟甲烷磺酸类化合物和对甲苯磺酰类化合物组合作为添加剂可以极大地降低了锂离子电池的直流内阻，同时对循环有明显的改善。
从以上的描述中，可以看出，本发明上述的实施例实现了如下技术效果：
三氟甲烷磺酸类化合物中三氟甲基的强吸电子性使得与其直接相连的甲磺酰基具有更强的反应活性，与甲苯磺酰类化合物的联合使用，可在NCM三元正极及石墨负极表面形成稳定的界面膜，通过三氟甲烷磺酸类化合物和对甲苯磺酰类化合物的充分协同作用，界面膜不仅薄而致密，且对甲苯磺酰类化合物的苯环结构具有很大的刚性，使得界面膜更加稳定，从而提高了界面膜离子电导率，阻碍电解液中的HF等有害产物的产生和循环过程中阴极过渡金属的溶解，进而在一定程度上不仅降低了锂离子电池的阻抗，同时明显改善了锂离子电池的循环性能等综合性能。
以上所述仅为本发明的优选实施例而已，并不用于限制本发明，对于本领域的技术人员来说，本发明可以有各种更改和变化。凡在本发明的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (12)

  1. 一种电解液，其特征在于，所述电解液包括有机溶剂、LiPF6以及添加剂，所述添加剂包括三氟甲烷磺酸类化合物和对甲苯磺酰类化合物。
  2. 根据权利要求1所述的电解液，其特征在于，所述三氟甲烷磺酸类化合物为具有结构式I所示的化合物：
    其中，R1选自硅烷基、取代或非取代的苯基、取代或非取代的C1～C4的直链烷基、取代或非取代的C3～C6的支链烷基中的任意一种。
  3. 根据权利要求2所述的电解液，其特征在于，所述三氟甲烷磺酸类化合物选自
    中的任意一种或多种。
  4. 根据权利要求3所述的电解液，其特征在于，所述三氟甲烷磺酸类化合物选自中的任意一种或多种。
  5. 根据权利要求1至4中任一项所述的电解液，其特征在于，所述对甲苯磺酰类化合物为具有结构式II所示的化合物，
    其中，R2选自氰基、卤素、氨基中的任意一种。
  6. 根据权利要求5所述的电解液，其特征在于，所述对甲苯磺酰类化合物选自中的任意一种或多种。
  7. 根据权利要求6所述的电解液，其特征在于，所述添加剂的质量为所述电解液总质量的0.1～5wt％，和/或所述三氟甲烷磺酸类化合物和所述对甲苯磺酰类化合物的质量比为1:5～5:1。
  8. 根据权利要求6所述的电解液，其特征在于，所述有机溶剂包括环状碳酸酯、链状碳酸酯和羧酸酯中的任意一种或多种，所述环状碳酸酯选自碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、γ-丁内酯中的一种或几种，所述链状碳酸酯选自碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、碳酸甲丙酯、碳酸乙丙酯中的一种或几种，所述羧酸酯选自甲酸甲酯、甲酸乙酯、甲酸丙酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯中的一种或几种。
  9. 根据权利要求6所述的电解液，其特征在于，所述电解液还包括锂盐添加剂，所述锂盐添加剂的浓度为0.3～1mol/L，所述锂盐添加剂选自双氟磺酰亚胺锂盐、LiBF4、双草酸硼酸锂、二氟草酸硼酸锂、二氟草酸磷酸锂、双三氟甲基磺酰亚胺锂、苯砜、三(三甲基硅烷)亚磷酸酯、硫酸乙烯酯、甲基二磺酸亚甲酯中的任意一种或多种。
  10. 根据权利要求9所述的电解液，其特征在于，所述LiPF6的浓度为0.5～1.5mol/L，优选所述电解液包括：碳酸乙烯酯、碳酸二乙酯和碳酸甲乙酯、LiPF6、硫酸乙烯酯、甲基二磺酸亚甲酯、双氟磺酰亚胺锂盐以及其中，所述为所述电解液的2.5wt％，所述为所述电解液的0.5wt％；
    或所述为所述电解液的0.5wt％，所述为所述电解液的2.5wt％；
    或所述为所述电解液的0.8wt％，所述为所述电解液的2.2wt％；
    或所述为所述电解液的1.2wt％，所述为所述电解液的1.8wt％。
  11. 一种锂离子电池，包括正极片、负极片以及电解液，其特征在于，所述电解液为权利要求1至10中任一项所述的电解液。
  12. 根据权利要求11所述的锂离子电池，其特征在于，所述正极片包括正极材料，所述正极材料为LiNi(1-x-y)CoxMny，其中，0≤x≤1，0≤y≤1。
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