WO2023040119A1 - 电解液添加剂和含有该添加剂的电解液及锂离子电池 - Google Patents

电解液添加剂和含有该添加剂的电解液及锂离子电池 Download PDF

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WO2023040119A1
WO2023040119A1 PCT/CN2021/142642 CN2021142642W WO2023040119A1 WO 2023040119 A1 WO2023040119 A1 WO 2023040119A1 CN 2021142642 W CN2021142642 W CN 2021142642W WO 2023040119 A1 WO2023040119 A1 WO 2023040119A1
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lithium
electrolyte
additive
ion battery
temperature
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PCT/CN2021/142642
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English (en)
French (fr)
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欧霜辉
王霹霹
白晶
毛冲
黄秋洁
戴晓兵
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珠海市赛纬电子材料股份有限公司
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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
    • 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 application belongs to the technical field of lithium-ion batteries, and in particular relates to an electrolyte additive, an electrolyte containing the additive, and a lithium-ion battery.
  • Lithium-ion batteries are widely used in 3C digital, power tools, aerospace, energy storage, power vehicles and other fields due to their advantages such as high specific energy, no memory effect, and long cycle life.
  • Nickel-cobalt-manganese ternary cathode material (NCM material) has become the preferred material for the cathode active material of lithium-ion batteries due to its good safety and low price.
  • NCM material Nickel-cobalt-manganese ternary cathode material
  • lithium-ion batteries The electrical performance requirements are getting higher and higher.
  • lithium-ion batteries have some challenges in the high-voltage system (voltage of 4.45V and above): it is found that under the high-voltage system of 4.45V, high-nickel ternary materials face the problems of poor high-temperature storage, poor cycle performance, and serious cycle gas production . This may be because the newly developed coating or doping technology is not perfect. As the charging voltage increases, the transition metal dissolution of the ternary electrode material becomes more and more serious. On the other hand, it is the matching problem of the electrolyte. The conventional The electrolyte will be oxidized and decomposed on the surface of the positive electrode of the battery at a high voltage of 4.45V. Especially under high temperature conditions, it will accelerate the oxidative decomposition of the electrolyte and at the same time promote the deterioration of the positive electrode material.
  • the purpose of this application is to provide an electrolyte additive, which effectively inhibits cycle gas production and improves the high-temperature storage, cycle performance, and low-temperature discharge performance of lithium-ion batteries in high-voltage (4.45V and above) systems.
  • Another object of the present application is to provide an electrolyte solution containing the above-mentioned electrolyte additive, which effectively suppresses cycle gas production and improves the high-temperature storage and cycle performance of lithium-ion batteries under high-voltage (4.45V and above) systems. Low temperature discharge performance.
  • Another object of the present application is to provide a lithium-ion battery containing the above-mentioned electrolyte, which has good high-temperature storage, cycle performance, and low-temperature discharge performance under a high-voltage (4.45V and above) system, and can be used in The gas production is low during the high temperature and high voltage cycle.
  • an electrolyte additive including a compound shown in structural formula 1:
  • R 1 is selected from halogen atom, substituted or unsubstituted C1 ⁇ C12 alkyl, R 2 , R 3 , R 4 are all the same as R 1 , X is sulfur atom, dimethylsilyl, methylene Or a C2-C12 linear alkenyl group, m is an integer of 0-6.
  • the electrolyte additive of the present application includes the bis-sulfonimide compound shown in structural formula 1, which contains 2 bis-sulfonimide structures, and this structure makes it undergo multi-step oxidation at the interface,
  • the oxidation resistance of the electrolyte is further improved, the positive electrode/electrolyte interface is optimized, the surface activity of the positive electrode is reduced, the decomposition of the electrolyte under high voltage is suppressed, and the generation of gas is effectively suppressed, and the interface can effectively suppress the transition
  • the dissolution of metals (Ni, Co, and Mn) further inhibits the decomposition of the electrolyte under high voltage, and also inhibits the mixing of cations; at the same time, it undergoes multi-step oxidation at the interface to form a more protective electrode/electrolyte interface film , and the interface film is not easy to decompose under high voltage, has good stability, has a good conduction lithium ion channel, and will not cause the
  • R 1 is selected from a halogen atom, a halogen-substituted or unsubstituted C1-C5 alkyl group
  • X is a sulfur atom, a dimethylsilyl group, a methylene group or a C2-C4 linear alkenyl group
  • m is 0- Integer of 4.
  • the compound shown in structural formula 1 is selected from at least one of compound 1 ⁇ compound 7:
  • compound 6 can be prepared according to the following synthetic route:
  • the present application also provides an electrolyte, including a lithium salt, an organic solvent and additives, and the additives include the electrolyte additives mentioned above.
  • the mass of the electrolyte additive of the present application accounts for 0.1-5.0% of the sum of the mass of the lithium salt and the organic solvent.
  • the lithium salt of the present application is selected from lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (LiClO 4 ), lithium tetrafluoroborate (LiBF 4 ), lithium methanesulfonate (LiCH 3 SO 3 ), trifluoromethane Lithium sulfonate (LiCF 3 SO 3 ), lithium dioxalate borate (C 4 BLiO 8 ), lithium difluorooxalate borate (C 2 BF 2 LiO 4 ), lithium difluorophosphate (LiPO 2 F 2 ), difluorobis At least one of lithium oxalate phosphate (LiDFBP), lithium bisfluorosulfonyl imide (LiFSI), and lithium bistrifluoromethylsulfonyl imide (LiTFSI).
  • LiPF 6 lithium hexafluorophosphate
  • LiClO 4 lithium perchlorate
  • LiBF 4 lithium
  • the concentration of the lithium salt of the present application in the electrolyte is 0.5-1.5M.
  • the organic solvent of the present application is selected from at least one of chain carbonates, carboxylates, ethers and heterocyclic compounds.
  • the additive of the present application also includes a film-forming additive, and the film-forming additive is selected from vinylene carbonate (VC), vinylidene vinyl carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfite (ES), 1,3 propane sultone (PS) and vinyl sulfate (DTD).
  • the film-forming additive accounts for 0.1-6.0% of the sum of the mass of the lithium salt and the organic solvent, and the film-forming additive can further improve the electrical performance of the lithium-ion battery.
  • the present application also provides a lithium-ion battery, including a positive electrode and a negative electrode, and also includes the above-mentioned electrolyte, and the highest charging voltage is 4.45V, and the active material of the positive electrode includes nickel-cobalt-manganese oxide material.
  • the electrolyte of the lithium-ion battery of the present application contains the compound shown in the above-mentioned structural formula 1, which can be oxidized in multiple steps on the surface of the ternary positive electrode material, further improving the performance of the electrolyte.
  • Oxidation resistance optimizing the positive electrode/electrolyte interface, reducing the surface activity of the positive electrode, inhibiting the decomposition of the electrolyte under high-voltage and high-temperature conditions of 4.45V, thereby inhibiting the generation of gas during high-temperature and high-voltage cycling of lithium-ion batteries, and the The interface can effectively inhibit the dissolution of transition metals (Ni, Co, and Mn), further inhibit the decomposition of the electrolyte under high voltage, and also inhibit the mixing of cations; at the same time, it undergoes multi-step oxidation on the surface of the ternary cathode material to form a more protective Strong electrode/electrolyte interface film, the interface film is not easy to decompose under high voltage, has good stability, and has good conduction lithium ion channels, which will not cause the collapse of lithium ion channels during the cycle process of 4.45V high voltage and high temperature , which in turn improves the cycle performance of lithium-ion batteries under high voltage (4
  • the chemical formula of the nickel-cobalt-manganese oxide material of the present application is LiNi x Co y Mn( 1-xy ) M z O 2 , where 0.6 ⁇ x ⁇ 0.9, x+y ⁇ 1, 0 ⁇ z ⁇ 0.08, M is at least one of Al, Mg, Zr and Ti.
  • the anode of the present application is a carbon anode material or a silicon anode material or a silicon-carbon anode material,
  • the anode of the present application is a silicon-carbon anode material, wherein the mass ratio of carbon to silicon is 90:10.
  • LiPF 6 lithium hexafluorophosphate
  • LiNi 6 Co 2 Mn 2 Zr 0.3 O 2 ternary material LiNi 6 Co 2 Mn 2 Zr 0.3 O 2 , conductive agent SuperP, binder PVDF and carbon nanotube (CNT) were uniformly mixed at a mass ratio of 97.5:1.5:1:1 to make a certain Viscosity lithium-ion battery positive electrode slurry is coated on the aluminum foil for the current collector, and the coating amount is 324g/m 2 , dried at 85°C and then cold-pressed; then edge trimming, cutting, and slitting After slitting, dry at 85°C for 4 hours under vacuum conditions, and weld the tabs to make a lithium-ion battery positive sheet that meets the requirements.
  • Preparation of the negative electrode sheet After mixing artificial graphite and silicon in a mass ratio of 90:10, with a conductive agent SuperP, a thickener CMC, and an adhesive SBR (styrene-butadiene rubber emulsion) in a mass ratio of 95:1.5:1.0: The ratio of 2.5 is made into a slurry, mixed evenly, coated on both sides of the copper foil with the mixed slurry, dried and rolled to obtain a negative electrode sheet, and made into a lithium ion battery negative electrode sheet that meets the requirements.
  • a conductive agent SuperP a conductive agent
  • CMC thickener
  • an adhesive SBR styrene-butadiene rubber emulsion
  • lithium-ion battery The positive electrode sheet, negative electrode sheet and separator prepared according to the above process are laminated into a lithium-ion battery with a thickness of 4.7mm, a width of 55mm, and a length of 60mm. Vacuum drying at 75°C Bake for 10 hours and inject the above electrolyte. After standing for 24 hours, charge to 4.45V with a constant current of 0.1C (180mA), then charge at a constant voltage of 4.45V until the current drops to 0.05C (90mA); then discharge to 3.0V at 0.2C (180mA), Repeat charging and discharging twice, and finally charge the battery to 3.8V at 0.2C (180mA) to complete the production of lithium-ion batteries.
  • the components of the electrolyte solutions of Examples 2-10 and Comparative Examples 1-4 are shown in Table 1.
  • the preparation methods of the electrolyte solutions of Examples 2-10 and Comparative Examples 1-4 refer to the preparation method of Example 1.
  • Example 2-10 and Comparative Examples 1-4 refer to the battery preparation method of Example 1 to make a lithium-ion battery, and perform low-temperature discharge performance, normal-temperature cycle performance, and High-temperature cycle performance and high-temperature storage performance tests, the test results are shown in Table 2.
  • Low-temperature discharge performance test Under normal temperature (25°C), charge and discharge the lithium-ion battery once at 0.5C/0.5C (discharge capacity is denoted as C0), the upper limit voltage is 4.45V, and then at 0.5C constant current and constant voltage Charge the battery to 4.45V under the same conditions; put the lithium-ion battery in a low-temperature box at -20°C for 4 hours, and discharge it at 0.5C at -20°C (the discharge capacity is recorded as C1); use the following formula to calculate the low temperature of the lithium-ion battery discharge rate;
  • High temperature cycle test Under the condition of high temperature (45°C), charge and discharge the lithium-ion battery once at 1.0C/1.0C (battery discharge capacity is C0), the upper limit voltage is 4.45V, and then perform 1.0C at room temperature /1.0C charging and discharging for 300 cycles (battery discharge capacity is C1), use the following formula to calculate the capacity retention rate of the lithium-ion battery;
  • High-temperature storage test Under normal temperature (25°C), charge and discharge the lithium-ion battery once at 0.3C/0.3C (the battery discharge capacity is recorded as C0), and the upper limit voltage is 4.5V; place the battery in an oven at 60°C Set aside for 15 days, take out the battery, place the battery in an environment of 25°C, discharge at 0.3C, and record the discharge capacity as C1; then charge and discharge the lithium-ion battery once at 0.3C/0.3C (record the discharge capacity of the battery as C2), Use the following formula to calculate the capacity retention rate and capacity recovery rate of lithium-ion batteries;
  • High-temperature expansion test Under normal temperature (25°C), charge and discharge the lithium-ion battery once at 0.3C/0.3C, the upper limit voltage is 4.45V, measure the thickness of the battery after discharge, and record it as D0; place the battery in Leave it in an oven at 60°C for 15 days, take out the battery, measure the thickness of the battery, and record it as D1.
  • Thickness expansion rate ((D1-D0)/D0)*100%
  • Comparing Comparative Example 3 with Example 9 the high-temperature storage, cycle performance, and low-temperature discharge performance of the lithium-ion battery of Example 9 are better than those of Comparative Example 3, and the thickness expansion rate of the lithium-ion battery of Example 9 is also lower. This is because the compound (bissulfonylimide) shown in structural formula 1 can undergo multi-step oxidation on the surface of the ternary positive electrode material.
  • the overpotential of the positive electrode when the overpotential of the positive electrode is low, the N-X bond in the compound is unilaterally broken, forming Preliminary oxidation, the compounds produced by its decomposition continue to be oxidized after the overpotential of the positive electrode increases, producing small molecular group compounds, which act on the positive electrode/electrolyte interface, and multi-step oxidation occurs on the surface of the ternary positive electrode material to form A more protective electrode/electrolyte interface film, which is not easy to decompose under high voltage, improves the stability of the electrode/electrolyte interface, and enriches the element composition of the electrode/electrolyte interface, thereby improving the high-voltage three-phase Electrochemical performance of lithium-ion batteries.
  • compound 8 is a bissulfonylimide structure compound, it can also form preliminary oxidation when the overpotential of the positive electrode is low, but the applicant of the present application found that compound 8 will be reacted after the overpotential of the positive electrode increases, That is, compound 8 cannot undergo multi-step oxidation, so it cannot improve the oxidation resistance of the electrolyte, cannot effectively inhibit the decomposition of the electrolyte, and cannot form a stable electrode/electrolyte interface film on the surface of the ternary cathode material.
  • compound 8 is also added as an additive in the electrolyte system of lithium-ion batteries to improve carbon-silicon negative electrode lithium-ion batteries.
  • the ability to conduct lithium ions further reduces the internal resistance of the battery, and the bis-sulfonimide compound can also inhibit the generation of hydrofluoric acid from fluoroethylene carbonate.
  • Example 9 Comparing Comparative Examples 3 to 4 with Example 9, although the high-temperature storage, cycle performance, and low-temperature discharge performance of the lithium-ion battery of Comparative Example 4 are better than those of Comparative Example 3, the high-temperature storage and cycle performance of the lithium-ion battery of Comparative Example 4 Performance, low-temperature discharge performance are still poorer than Example 9, which shows that the concentration of Compound 7 is doubled, that is, the concentration of the sulfonimide group remains the same as Example 9, but the electrical performance of the lithium-ion battery is still better than that of Example 9.
  • Example 9 is poor, which shows why the compound shown in structural formula 1 can effectively improve the electrochemical performance of high-voltage ternary lithium-ion batteries, not only with the sulfonimide group on structural formula 1, but also with its own unique structure related.

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Abstract

一种电解液添加剂和含有该添加剂的电解液及锂离子电池，其中电解液添加剂包括结构式1所示的化合物：其中R1选自卤素原子、取代或未取代的C1～C12烷基，R2、R3、R4的基团皆与R1相同，X为硫原子、二甲基硅基、亚甲基或C2～C12直链烯烃基，m为0～6的整数。该电解液添加剂有效抑制循环产气，提高锂离子电池于高电压（4.45V及以上）体系下的高温存储、循环性能、低温放电性能。

Description

电解液添加剂和含有该添加剂的电解液及锂离子电池 技术领域
本申请属于锂离子电池技术领域，尤其涉及电解液添加剂和含有该添加剂的电解液及锂离子电池。
背景技术
锂离子电池由于具有高比能量、无记忆效应、循环寿命长等优点被广泛应用于3C数码、电动工具、航天、储能、动力汽车等领域。镍钴锰三元正极材料(NCM材料)由于安全性好以及价格低廉，成为锂离子电池的正极活性材料的首选材料，但随着更高电压体系的锂离子电池发展与普及，对锂离子电池的电性能要求越来越高。
目前锂离子电池于高电压体系下(4.45V及以上的电压)存在一些挑战：发现在4.45V高电压体系下，高镍三元材料面临高温存储差、循环性能差、循环产气严重的问题。这可能是因为新开发的包覆或掺杂技术不太完善，随着充电电压的提高，三元电极材料的过渡金属溶出越来越严重，另一方面即是电解液的匹配问题，常规的电解液在4.45V高电压下是会在电池正极表面氧化分解的，特别在高温条件下，会加速电解液的氧化分解，同时促使正极材料的恶化反应。
因此，亟需开发一种能有效抑制循环产气，提高锂离子电池于高电压(4.45V及以上)体系下的高温存储、循环性能、低温放电性能的电解液添加剂，进而保证三元锂离子电池电性能的优良发挥。
申请内容
本申请的目的是提供一种电解液添加剂，该电解液添加剂有效抑制循环产气，提高锂离子电池于高电压(4.45V及以上)体系下的高温存储、循环性能、 低温放电性能。
本申请的另一目的是提供一种含有上述电解液添加剂的电解液，该电解液有效抑制循环产气，提高锂离子电池于高电压(4.45V及以上)体系下的高温存储、循环性能、低温放电性能。
本申请的又一目的是提供一种含有上述电解液的锂离子电池，该锂离子电池于高电压(4.45V及以上)体系下具有较好的高温存储、循环性能、低温放电性能，且在高温高电压循环过程中产气量较低。
为实现以上目的，本申请提供了一种电解液添加剂，包括结构式1所示的化合物：
Figure PCTCN2021142642-appb-000001
其中R 1选自卤素原子、取代或未取代的C1～C12烷基，R 2、R 3、R 4的基团皆与R 1相同，X为硫原子、二甲基硅基、亚甲基或C2～C12直链烯烃基，m为0～6的整数。
与现有技术相比，本申请的电解液添加剂包括结构式1所示的联双磺酰亚胺化合物，其含有2个双磺酰亚胺结构，该结构使得其在界面处发生多步氧化，进一步地提高了电解液的耐氧化性，优化了正极/电解液界面，降低了正极的表面活性，抑制电解液在高电压下的分解，进而有效抑制气体的产生，而且该界面可有效抑制过渡金属(Ni、Co和Mn)溶出，进一步抑制电解液在高电压下的分解，也能抑制阳离子混排；同时其在界面处发生多步氧化形成了更具保护力的电极/电解液界面膜，且该界面膜在高电压下不易分解、稳定性较好，具有良好的传导锂离子通道，不致于在循环过程中产生锂离子通道的坍塌，循环性能得以改善；而且界面膜中含磺酰亚胺成分，具有较为稳定的锂离子传输通道，因此锂离子电池的低温放电性能也得到了提高；另，在两个双磺酰亚胺结构之 间引入硫原子、二甲基硅基、亚甲基或直链烯烃基，即引入了硫元素、碳元素或硅元素，这丰富了电极/电解液界面膜组分，进一步改善了界面膜的热稳定性，从而改善了锂离子电池的高温存储性能。
较佳地，R 1选自卤素原子、卤素取代或未取代的C1～C5烷基，X为硫原子、二甲基硅基、亚甲基或C2～C4直链烯烃基，m为0～4的整数。
较佳地，结构式1所示的化合物选自化合物1～化合物7中的至少一种:
Figure PCTCN2021142642-appb-000002
其中，化合物6可按照如下合成路线制得：
(CH 3) 2SiCl 2+2AgN(SO 2CH 3) 2→(CH 3) 2Si(N(SO 2CH 3) 2) 2+2AgCl
为实现以上目的，本申请还提供了一种电解液，包括锂盐、有机溶剂和添加剂，添加剂包括上述提及的电解液添加剂。
较佳地，本申请的电解液添加剂的质量占锂盐和有机溶剂质量之和的0.1～5.0％。
较佳地，本申请的锂盐选自六氟磷酸锂(LiPF 6)、高氯酸锂(LiClO 4)、四氟硼酸锂(LiBF 4)、甲基磺酸锂(LiCH 3SO 3)、三氟甲基磺酸锂(LiCF 3SO 3)、二草酸硼酸锂(C 4BLiO 8)、二氟草酸硼酸锂(C 2BF 2LiO 4)、二氟磷酸锂(LiPO 2F 2)、二氟双草酸磷酸锂(LiDFBP)、双氟磺酰亚胺锂(LiFSI)和双三氟甲基磺酰亚胺锂(LiTFSI)中的至少一种。
较佳地，本申请的锂盐于电解液中的浓度为0.5～1.5M。
较佳地，本申请的有机溶剂选自链状碳酸酯类、羧酸酯类、醚类和杂环化 合物的至少一种。
较佳地，本申请的添加剂还包括成膜添加剂，成膜添加剂选自碳酸亚乙烯酯(VC)、亚乙烯基碳酸乙烯酯(VEC)、氟代碳酸乙烯酯(FEC)、亚硫酸乙烯酯(ES)、1,3丙磺酸内酯(PS)和硫酸乙烯酯(DTD)中的至少一种。成膜添加剂占锂盐和有机溶剂质量之和的0.1～6.0％，成膜添加剂能够进一步地改善锂离子电池的电性能。
为实现以上目的，本申请还提供了一种锂离子电池，包括正极和负极，还包括上述提及的电解液，且最高充电电压为4.45V，正极的活性材料包括镍钴锰氧化物材料。
与现有技术相比，本申请的锂离子电池的电解液中含有上述提及的结构式1所示的化合物，该化合物可在三元正极材料表面发生多步氧化，进一步地提高了电解液的耐氧化性，优化了正极/电解液界面，降低了正极的表面活性，抑制电解液在4.45V高电压高温条件下的分解，进而抑制锂离子电池在高温高电压循环过程中产生气体，而且该界面可有效抑制过渡金属(Ni、Co和Mn)溶出，进一步抑制电解液在高电压下的分解，也能抑制阳离子混排；同时其在三元正极材料表面发生多步氧化形成了更具保护力的电极/电解液界面膜，该界面膜在高电压下不易分解、稳定性较好，具有良好的传导锂离子通道，不致于在4.45V高电压高温的循环过程中产生锂离子通道的坍塌，进而使得锂离子电池于高电压(4.45V及以上)体系下的循环性能得以改善；而且界面膜中含磺酰亚胺成分，具有较为稳定的锂离子传输通道，因此锂离子电池于高电压(4.45V及以上)体系下的低温放电性能也得到了提高；另，在两个双磺酰亚胺结构之间引入硫原子、二甲基硅基或亚甲基，即引入了硫元素、碳元素、直链烯烃基或硅元素，这丰富了三元正极材料表面的界面膜组分，进一步改善了界面膜的热稳定性，从而改善了锂离子电池于高电压(4.45V及以上)体系下的高温存储性能。
较佳地，本申请的镍钴锰氧化物材料的化学式为LiNi xCo yMn( 1-x-y)M zO 2，其中0.6≤x<0.9，x+y<1，0≤z<0.08，M为Al、Mg、Zr和Ti中的至少一种。优选地，采用x＝0.6，y＝0.2，M为Zr，z＝0.03。
较佳地，本申请的负极为碳负极材料或硅负极材料或硅碳负极材料，
较佳地，本申请的负极为硅碳负极材料，其中碳与硅的质量之比为90:10。
具体实施方式
为更好地说明本申请的目的、技术方案和有益效果，下面将结合具体实施例对本申请作进一步说明。需说明的是，下述实施所述方法是对本申请做的进一步解释说明，不应当作为对本申请的限制。
实施例1
1、电解液的制备
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＝29.16:29.16:29.16进行混合，制得87.48g有机溶剂，混合后加入1M的六氟磷酸锂(LiPF 6)，待锂盐完全溶解后，加入0.5g的化合物1。
2、正极片的制备
将镍钴锰酸锂三元材料LiNi 6Co 2Mn 2Zr 0.3O 2、导电剂SuperP、粘接剂PVDF和碳纳米管(CNT)按质量比97.5:1.5:1:1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324g/m 2，在85℃下烘干后进行冷压；然后进行切边、裁片、分条，分条后在真空条件下85℃烘干4小时，焊接极耳，制成满足要求的锂离子电池正极片。
3、负极片的制备：将人造石墨，硅按质量比90:10混合后，与导电剂SuperP、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，制成满足要求的锂离子电池负极片。
4、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4.7mm，宽度为55mm，长度为60mm的锂离子电池，在75℃下真空烘烤10小时，注入上述电解液。静置24小时后，用0.lC(180mA)的恒流充电至4.45V，然后以4.45V恒压充电至电流下降到0.05C(90mA)；然后以0.2C(180mA)放电至3.0V，重复2次充放电，最后再以0.2C(180mA)将电池充电至3.8V，完成锂离子电池制作。
实施例2～10和对比例1～4的电解液组成成分如表1所示，实施例2～10和对比例1～4的电解液配制方法参照实施例1的配制方法进行。
表1实施例和对比例的电解液组成成分
Figure PCTCN2021142642-appb-000003
上述化合物8的结构式如下所述：
Figure PCTCN2021142642-appb-000004
以实施例2～10和对比例1～4的电解液，参照实施例1的电池制备方法制成 锂离子电池，并按照下述测试方法分别对锂离子电池进行低温放电性能、常温循环性能、高温循环性能、高温存储性能测试，测试结果如表2所示。
低温放电性能测试:在常温(25℃)条件下，对锂离子电池进行一次0.5C/0.5C充电和放电(放电容量记为C0)，上限电压为4.45V,然后在0.5C恒流恒压条件下将电池充电至4.45V；将锂离子电池置于-20℃低温箱中搁置4h，在-20℃下进行0.5C放电(放电容量记为C1)；利用下面公式计算锂离子电池的低温放电率；
低温放电率＝C1/C0*100％
常温循环测试：在常温(25℃)条件下，对锂离子电池进行一次1.0C/1.0C充电和放电(电池放电容量为C0)，上限电压为4.45V,然后在常温条件下进行1.0C/1.0C充电和放电500周(电池放电容量为C1)，利用下面公式计算锂离子电池的容量保持率；
容量保持率＝(C1/C0)*100％
高温循环测试：在过高温(45℃)条件下，对锂离子电池进行一次1.0C/1.0C充电和放电(电池放电容量为C0)，上限电压为4.45V，然后在常温条件下进行1.0C/1.0C充电和放电300周(电池放电容量为C1)，利用下面公式计算锂离子电池的容量保持率；
容量保持率＝(C1/C0)*100％
高温存储测试：在常温(25℃)条件下，对锂离子电池进行一次0.3C/0.3C充电和放电(电池放电容量记录为C0)，上限电压为4.5V；将电池放置于60℃烘箱中搁置15d，取出电池，将电池放置于25℃环境中，进行0.3C放电，放电容量记录为C1；然后对锂离子电池进行一次0.3C/0.3C充电和放电(电池放电容量记录为C2)，利用下面公式计算锂离子电池的容量保持率和容量恢复率；
容量保持率＝(C1/C0)*100％
容量恢复率＝(C2/C0)*100％
高温膨胀度测试：在常温(25℃)条件下，对锂离子电池进行一次0.3C/0.3C充电和放电，上限电压为4.45V，放电结束后测量电池厚度，记录为D0；将电池放置于60℃烘箱中搁置15d，取出电池，测量电池厚度，记录为D1。
厚度膨胀率＝((D1-D0)/D0)*100％
表2锂离子电池性能测试结果
Figure PCTCN2021142642-appb-000005
将实施例1～10和对比例1相比，实施例1～10的锂离子电池的高温存储、循环性能、低温放电性能比对比例1好，且施例1～10的锂离子电池的厚度膨胀率比对比例1低，这是因为锂离子电池的电解液中含有上述提及的结构式1所示的化合物，该化合物可在三元正极材料表面发生多步氧化，进一步地提高了电解液的耐氧化性，优化了正极/电解液界面，降低了正极的表面活性，抑制电解液在4.45V高电压高温条件下的分解，进而抑制锂离子电池在高温高电压循环过程中产气，而且该界面可有效抑制过渡金属(Ni、Co和Mn)溶出，进一步抑制电解液在高电压下的分解，也能抑制阳离子混排；同时其在三元正极材料表面发生多步氧化形成了更具保护力的电极/电解液界面膜，且该界面膜稳定性较好，具有良好的传导锂离子通道，不致于在4.45V高电压高温的循环过程中产生锂离子通道的坍塌，进而使得锂离子电池于高电压(4.45V及以上)体系下的循环性能得以改善；而且界面膜中含磺酰亚胺成分，具有较为稳定的锂离子传输通道，因此锂离子电池于高电压(4.45V及以上)体系下的低温放电性能也得到了提高；另，在两个双磺酰亚胺结构之间引入硫原子、二甲基硅基或亚甲基，即引入了硫元素、碳元素或硅元素，这丰富了三元正极材料表面的界面膜组分，进一步改善了界面膜的热稳定性，从而改善了锂离子电池于高电压 (4.45V及以上)体系下的高温存储性能。
将对比例3和实施例9进行对比，实施例9的锂离子电池的高温存储、循环性能、低温放电性能比对比例3好，且实施例9的锂离子电池的厚度膨胀率也较低。这是因为结构式1所示的化合物(联双磺酰亚胺)可在三元正极材料表面发生多步氧化，具体地，当正电极过电位较低时，化合物中N-X键单侧断裂，形成初步氧化，其分解产生的化合物，在正电极过电位升高后，继续被氧化，产生小分子团化合物，作用于正电极/电解液界面处，在三元正极材料表面发生多步氧化形成了更具保护力的电极/电解液界面膜，该界面膜在高电压下不易分解，提高了电极/电解液界面的稳定性，且丰富了电极/电解液界面的元素组成，进而改善高电压三元锂离子电池的电化学性能。虽然化合物8为双磺酰亚胺结构化合物，其也可在正电极过电位较低时形成初步氧化，但是本申请的申请人发现化合物8在正电极过电位升高后却会被反应掉，即化合物8不能发生多步氧化，从而不能提高电解液的耐氧化性，不能有效抑制电解液分解，也无法在三元正极材料表面形成稳定的电极/电解液界面膜。
还要说明的是，目前在锂离子电池的电解液体系中也有加入化合物8作为添加剂使用以改善碳硅负极锂离子电池，主要利用双磺酰亚胺类化合物生成的含硫有机盐具有优异的传导锂离子的能力进而降低电池的内阻，同时双磺酰亚胺类化合物还能抑制氟代碳酸乙烯酯生成氢氟酸。但是对于碳硅负极材料来说：锂离子在脱嵌过程中产生的体积膨胀，导致硅负极/电解液界面不稳定，不断有新的界面生成，导致成膜添加剂和活性锂的过度消耗，造成锂离子电池电性能恶化；因此锂离子电池正负极材料的失效机理完全不同，因而这也能说明能改善碳硅负极锂离子电池的添加剂并不一定能适用于高电压体系下的锂离子电池的高镍三元正极材料。
将对比例3～4和实施例9相比，虽然对比例4的锂离子电池的高温存储、循环性能、低温放电性能比对比例3好，但是对比例4的锂离子电池的高温存储、循环性能、低温放电性能还是比实施例9差，这表明将化合物7的浓度增大一倍，即将磺酰亚胺基团的浓度保持和实施例9相同，但是锂离子电池的电性能仍比实施例9差，这表明结构式1所示的化合物之所以能有效改善高电压 三元锂离子电池的电化学性能，不仅和结构式1上的磺酰亚胺基团有关，还和其自身特有的结构有关。
最后应当说明的是，以上实施例仅用以说明本申请的技术方案而非对本申请保护范围的限制，尽管参照较佳实施例对本申请作了详细说明，本领域的普通技术人员应当理解，可以对本申请的技术方案进行修改或者等同替换，而不脱离本申请技术方案的实质和范围。

Claims (10)

  1. 一种电解液添加剂，其特征在于，包括结构式1所示的化合物：
    Figure PCTCN2021142642-appb-100001
    其中R 1选自卤素原子、取代或未取代的C1～C12烷基，R 2、R 3、R 4的基团皆与R 1相同，X为硫原子、二甲基硅基、亚甲基或C2～C12直链烯烃基，m为0～6的整数。
  2. 如权利要求1所述的电解液添加剂，其特征在于，R 1选自卤素原子、卤素取代或未取代的C1～C5烷基，X为硫原子、二甲基硅基、亚甲基或C2～C4直链烯烃基，m为0～4的整数。
  3. 如权利要求1所述的电解液添加剂，其特征在于，所述结构式1所示的化合物选自化合物1～化合物7中的至少一种:
    Figure PCTCN2021142642-appb-100002
  4. 一种电解液，包括锂盐、有机溶剂和添加剂，其特征在于，所述添加剂包括如 权利要求1～3任一项所述的电解液添加剂。
  5. 如权利要求4所述的电解液，其特征在于，所述电解液添加剂的质量占所述锂盐和所述有机溶剂质量之和的0.1～5.0％。
  6. 如权利要求4所述的电解液，其特征在于，所述锂盐选自六氟磷酸锂、高氯酸锂、四氟硼酸锂、甲基磺酸锂、三氟甲基磺酸锂、二草酸硼酸锂、二氟草酸硼酸锂、二氟磷酸锂、二氟双草酸磷酸锂、双氟磺酰亚胺锂和双三氟甲基磺酰亚胺锂中的至少一种。
  7. 如权利要求4所述的电解液，其特征在于，所述有机溶剂选自链状碳酸酯类、羧酸酯类、醚类和杂环化合物的至少一种。
  8. 如权利要求4所述的电解液，其特征在于，所述添加剂还包括成膜添加剂，所述成膜添加剂选自碳酸亚乙烯酯、亚乙烯基碳酸乙烯酯、氟代碳酸乙烯酯、亚硫酸乙烯酯、1,3-丙磺酸内酯和硫酸乙烯酯中的至少一种。
  9. 一种锂离子电池，包括正极和负极，其特征在于，还包括如权利要求4～8任一项所述的电解液，且最高充电电压为4.45V，所述正极的活性材料包括镍钴锰氧化物材料。
  10. 如权利要求9所述的锂离子电池，其特征在于，所述镍钴锰氧化物材料的化学式为LiNi xCo yMn( 1-x-y)M zO 2，其中0.6≤x<0.9，x+y<1，0≤z<0.08，M为Al、Mg、Zr和Ti中的至少一种。
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