WO2023045165A1 - 电解液添加剂及含该添加剂的低温非水电解液和锂离子电池 - Google Patents

电解液添加剂及含该添加剂的低温非水电解液和锂离子电池 Download PDF

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WO2023045165A1
WO2023045165A1 PCT/CN2021/142646 CN2021142646W WO2023045165A1 WO 2023045165 A1 WO2023045165 A1 WO 2023045165A1 CN 2021142646 W CN2021142646 W CN 2021142646W WO 2023045165 A1 WO2023045165 A1 WO 2023045165A1
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lithium
low
carbonate
electrolyte
structural formula
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French (fr)
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白晶
王霹霹
毛冲
黄秋洁
欧霜辉
张元青
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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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 relates to the field of secondary batteries, in particular to an electrolyte additive, a low-temperature non-aqueous electrolyte containing the additive, and a lithium-ion battery.
  • Lithium-ion batteries are widely used in 3C digital, electric 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. With the increasing use of lithium-ion batteries in some high-end fields, the requirements for the environmental adaptation of lithium-ion batteries are becoming more and more stringent. The Antarctic expedition team's electronic equipment, deep sea exploration equipment, aerospace equipment and other extreme field equipment all challenge the low temperature performance of lithium-ion batteries.
  • Li + needs to be desolvated first when it is embedded in the graphite material, it needs to consume a certain amount of energy, which hinders the diffusion of Li + into the interior of graphite.
  • the solvation process will first occur, and the solvation process does not need to consume energy.
  • Li + can quickly come out of the graphite, so the charge acceptance of the graphite material is lower. Significantly worse than discharge acceptance.
  • One of the purposes of the present application is to provide an electrolyte additive, which can greatly improve the low-temperature performance of lithium-ion batteries, inhibit low-temperature lithium precipitation, and enable lithium-ion batteries to operate relatively normally in extremely low-temperature environments.
  • the second purpose of the present application is to provide a low-temperature non-aqueous electrolyte containing the above-mentioned additives.
  • the third purpose of the present application is to provide a lithium-ion battery with good low-temperature performance and cycle performance.
  • the first aspect of the present application provides an electrolyte additive, including a compound shown in structural formula 1 or structural formula 2:
  • R 1 and R 2 are selected from hydrogen atom, hydrocarbon group, trimethylsilyl group, fluorosulfonyl group or trifluoromethylsulfonyl group; X 1 and X 2 are selected from alkali metal elements.
  • the alkali metal element is selected from any one of Li, Na, K, and Cs.
  • the number of carbon atoms in the hydrocarbon group is 1-5.
  • the compound represented by the structural formula 1 or structural formula 2 is selected from at least one of compound 1 to compound 8:
  • the synthetic method of compound 3 is the same as that of compound 2, except that the reaction substrate ethyl chloride is replaced by vinyl chloride; the synthetic method of compound 6 is the same as that of compound 5, except that the reaction substrate sulfonyl fluoride is replaced by three Fluoromethylsulfonyl chloride; the synthetic method of compound 8 is the same as that of compound 7, except that the reaction substrate lithium hydroxide is replaced by cesium hydroxide.
  • the electrolyte additive of the present application adopts the compound of this kind of special structure shown in structural formula 1 or structural formula 2, wherein, the sulfonyl group in this additive structure can be in the lithium-ion battery initial charging and discharging stage in the battery
  • the positive and negative electrodes generate SEI films rich in sulfur-containing compounds such as LiSO 3 , ROSO 2 Li, etc.
  • This type of SEI still has good ion conductivity at low temperatures, which can promote the diffusion of lithium ions in the positive and negative electrodes at low temperatures.
  • fluorine-containing lithium salts will generate LiF, which is not conducive to low-temperature performance.
  • LiPF 6 will generate a large amount of LiF to attach to the SEI film during the formation stage. Due to the low molecular weight of LiF, it will intercalate sulfur containing LiSO 3 , ROSO 2 Li, etc. In the ion transport channel formed by the compound, the impedance is increased, which is not conducive to the low temperature performance of the battery.
  • the trimethylsilyl group in the additive structure can consume part of LiF in the first formation stage to generate trimethylfluorosilane, and trimethylfluorosilane is a gas at room temperature, and when the formation is completed, it will be pumped and sealed with other gases. Being taken away together will not affect the performance of the battery itself.
  • the imine structure in the additive structure can play a role in removing water and acid, preventing the PF 5 and HF generated by LiPF 6 from destroying the SEI on the positive and negative electrodes, and further ensuring low temperature and high ion conductivity. Stability of SEI film. Therefore, through the obvious synergistic effect of the three functional groups of the compound shown in the above structural formula 1 or structural formula 2, the low-temperature performance of the lithium-ion battery is greatly improved, and the low-temperature lithium precipitation is inhibited, so that the lithium-ion battery can operate relatively normally in an extremely low-temperature environment. .
  • the second aspect of the present application provides a low-temperature non-aqueous electrolyte, including a lithium salt, a non-aqueous organic solvent and an additive, and the additive is the above-mentioned electrolyte additive.
  • the weight percentage of the electrolyte additive in the low-temperature non-aqueous electrolyte is 0.1-3%, which may be but not limited to 0.1%, 1%, 2%, or 3%.
  • the lithium salt is selected from lithium hexafluorophosphate (LiPF 6 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium bisoxalate borate (LiBOB), lithium difluorooxalate borate (LiODFB), lithium difluorooxalate phosphate (LiPF 2 (C 2 O 4 ) 2 ), lithium tetrafluoroborate (LiBF 4 ), lithium tetrafluorooxalate phosphate (LiPF 4 (C 2 O 4 )), lithium bistrifluoromethanesulfonyl imide (LiN(SO 2 At least one of CF 3 ) 2 ), lithium bisfluorosulfonyl imide (Li[N(SO 2 F) 2 ), and lithium tetrafluoromalonate phosphate.
  • LiPF 6 lithium hexafluorophosphate
  • LiPO 2 F 2 lithium bisoxalate borate
  • LiODFB lithium di
  • the content of the lithium salt accounts for 10-20% of the weight of the low-temperature non-aqueous electrolyte, specifically, but not limited to, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, the concentration of lithium salt in the non-aqueous electrolyte is 0.5-2.5mol/L.
  • the non-aqueous organic solvent is selected from ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), At least one of butyl acetate (n-BA), ⁇ -butyrolactone (GBL), propyl propionate (n-PP), ethyl propionate (EP) and ethyl butyrate (EB).
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • DEC diethyl carbonate
  • EMC ethyl methyl carbonate
  • PC propylene carbonate
  • n-BA butyl acetate
  • GBL ⁇ -butyrolactone
  • n-PP propyl propionate
  • EP ethyl propionate
  • EB ethyl butyrate
  • the non-aqueous organic solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC).
  • the non-aqueous organic solvent accounts for 60-80% of the weight of the non-aqueous electrolyte, specifically but not limited to 60%, 65%, 66%, 67%, 68%, 69%, 70%, 71% , 72%, 73%, 74%, 75%, 80%.
  • the low-temperature non-aqueous electrolyte also includes additives, which account for 0.5-10% of the weight of the non-aqueous electrolyte, specifically but not limited to 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.
  • the auxiliary agent is selected from 2,2,2-methylethyl trifluorocarbonate, 2,2,2-diethyl trifluorocarbonate, 2,2,2-ethylene-propylene trifluorocarbonate ester, vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), diethyl pyrocarbonate (DEPC), 1,3-propane sultone (PS) , vinyl sulfate (DTD), 1,2-difluoroethylene carbonate (DFEC), tris(trimethylsilane) phosphate (TMSP), tris(trimethylsilane) phosphite (TMSPi), 4 ,4'-bi-1,3-dioxolane-2,2'-dione (BDC), 3,3-bis-disulfuric acid vinyl ester (BDTD), 4,4-bis-dioxolane-2,2'-dione ester, phosphoric acid Triallyl ester (TA), t
  • additives can form a stable passivation film on the surface of the positive electrode, prevent the oxidative decomposition of the electrolyte on the surface of the positive electrode, inhibit the dissolution of transition metal ions from the positive electrode, improve the stability of the structure and interface of the positive electrode material, and significantly improve the high temperature of the battery. performance and cycle performance.
  • the auxiliary agent includes fluoroethylene carbonate (FEC).
  • FEC fluoroethylene carbonate
  • Adding FEC to the electrolyte can improve the cycle stability of the battery in a high-voltage system, and the compound shown in structural formula 1 or structural formula 2 can act with FEC to Adjust the decomposition rate of FEC to form an electronically insulating interfacial layer containing LiF, which is beneficial to improve the cycle performance and low-temperature performance of lithium-ion batteries under high voltage.
  • the auxiliary agent includes ethylene sulfate (DTD), and ethylene sulfate (DTD) is added to the electrolyte as an auxiliary agent to modify the SEI film components on the surface of the negative electrode of the lithium battery to improve the relative ratio between the sulfur atom and the oxygen atom.
  • DTD ethylene sulfate
  • sulfur atoms and oxygen atoms contain lone pairs of electrons, which can attract lithium ions, speed up the shuttle of lithium ions in the SEI film, and reduce the battery interface impedance, thereby further effectively improving the low-temperature charge and discharge performance of high-voltage lithium-ion batteries.
  • the auxiliary agent is selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), vinyl sulfate (DTD), 4,4'- -1,3-dioxolane-2,2'-diketone (BDC), 3,3-disulfuric acid vinyl ester (BDTD), 4,4-dioxolane-2,2'-dione ester, bisfluoroethylene carbonate (DFEC), and the contents are respectively 0.1-2%, 0.2-6%, 0.2-2%, 0.2-2%, 0.1-1.5%, 0.1-1.5%, 0.1-1.5%, 0.1-1.5%.
  • the third aspect of the present application also provides a lithium-ion battery, including a positive electrode material, a negative electrode material, and an electrolyte, and the electrolyte is the aforementioned low-temperature non-aqueous electrolyte.
  • the maximum charging voltage of the lithium-ion battery is 4.5V.
  • the positive electrode material is Li (1+a) Ni x Co y M z N 1-xyz O 2+b , wherein M is Mn or Al, and N is Mg, Cu, Zn, Sn, B, Any one of Ga, Cr, Sr, Ba, V and Ti, -0.10 ⁇ a ⁇ 0.50, 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1, 0.7 ⁇ x+y+z ⁇ 1, -0.05 ⁇ b ⁇ 0.10.
  • the negative electrode material is selected from graphite.
  • Capacity retention discharge capacity of the last cycle/initial capacity ⁇ 100%.
  • Capacity retention low temperature discharge capacity/initial capacity ⁇ 100%.
  • LiPF 6 will generate a large amount of LiF to attach to the SEI film during the formation stage. Due to the low molecular weight of LiF, it will intercalate ions formed by sulfur-containing compounds such as LiSO 3 and ROSO 2 Li. In the transmission channel, increasing the impedance is not conducive to the low temperature performance of the battery.
  • the trimethylsilyl group in the additive structure can consume part of LiF in the first formation stage to generate trimethylfluorosilane, and trimethylfluorosilane is a gas at room temperature, and when the formation is completed, it will be pumped and sealed with other gases. Being taken away together will not affect the performance of the battery itself.
  • the imine structure in the additive structure can play a role in removing water and acid, preventing the PF 5 and HF generated by LiPF 6 from destroying the SEI on the positive and negative electrodes, and further ensuring low temperature and high ion conductivity. Stability of SEI film. Therefore, through the obvious synergistic effect of the three functional groups of the compound shown in the above structural formula 1 or structural formula 2, the low-temperature performance of the lithium-ion battery is greatly improved, and the low-temperature lithium precipitation is suppressed, so that the lithium-ion battery can operate relatively normally in an extremely low-temperature environment. .
  • low-temperature performance of lithium-ion batteries can be further improved due to the introduction of additives in Examples 14-21, especially the introduction of fluoroethylene carbonate (FEC).
  • FEC fluoroethylene carbonate

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Abstract

一种电解液添加剂，包括结构式1或结构式2所示的化合物：其中R1、R2选自氢原子、碳原子数为1-5的烃基、三甲基硅基、氟磺酰基或三氟甲基磺酰基；X1、X2为选自碱金属元素。本申请采用了上述结构式1或结构式2所示的化合物作为添加剂，结构式1或结构式2含有磺酰基团、三甲基硅基和亚胺结构，该三官能团通过明显的协同作用，极大的提升了锂离子电池的低温性能，抑制低温析锂，使得锂离子电池在极端低温的环境下能相对正常运作。本申请还提供一种含该添加剂的低温非水电解液和锂离子电池。

Description

电解液添加剂及含该添加剂的低温非水电解液和锂离子电池 技术领域
本申请涉及二次电池领域，具体涉及一种电解液添加剂及含该添加剂的低温非水电解液和锂离子电池。
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。随着一些高端领域锂离子电池的使用越来越广泛，对于锂离子电池环境适应的要求也越来越苛刻。南极考察队的电子设备、深海探测设备、航空航天设备等极端领域设备无不对锂离子电池的低温性能提出挑战。
锂离子电池的性能受动力学特性影响比较大，由于Li +在嵌入到石墨材料中时需要首先进行去溶剂化，这需要消耗一定的能量，阻碍了Li +扩散到石墨内部。相反地，Li +在脱出石墨材料进入到溶液中，会首先发生溶剂化过程，而溶剂化过程不需要消耗能量，Li +可以快速的脱出石墨，因此也就导致了石墨材料的充电接受能力要明显差于放电接受能力。
在低温条件下，石墨负极的动力学特性进一步变差，因此在充电的过程中石墨负极的电化学极化明显加剧，很容易导致负极表面析出金属锂。德国慕尼黑工业大学的Christian von Lüders等研究显示在-2℃下，充电倍率超过C/2就会显著的增加金属锂的析出量，例如C/2倍率下，负极表面镀锂的数量约为整个充电容量的5.5％，但是在1C倍率下将达到9％。析出的金属锂可能会进一步发展，最终成为锂枝晶，穿破隔膜，导致正负极短路。因此，需要尽量避免锂离子电池在低温条件下充电，当电池必须在低温下充电时，需要尽可能选择小电 流对锂离子电池进行充电，并在充电后对锂离子电池进行充分的搁置，从而保证负极析出的金属锂能够与石墨反应，重新嵌入到石墨负极内部。故开发低温性电解液以应对极端环境是对电解液行业的又一挑战。
对此，非常有必要研发一种抑制低温析锂的添加剂以解决上述技术问题。
申请内容
本申请的目的之一是提供一种电解液添加剂，可极大的提升锂离子电池的低温性能，抑制低温析锂，使得锂离子电池在极端低温的环境下能相对正常运作。
本申请的目的之二是提供一种低温非水电解液，该电解液含上述添加剂。
本申请的目的之三是提供一种锂离子电池，具有很好的低温性能和循环性能。
为了实现上述目的，本申请第一方面提供了一种电解液添加剂，包括结构式1或结构式2所示的化合物：
Figure PCTCN2021142646-appb-000001
其中R 1、R 2选自氢原子、烃基、三甲基硅基、氟磺酰基或三氟甲基磺酰基；X 1、X 2为选自碱金属元素。
较佳地，碱金属元素选自Li、Na、K、Cs中的任意一种。
较佳地，烃基中碳原子数为1-5。
较佳地，所述结构式1或结构式2所示的化合物选自化合物1至化合物8中的至少一种：
Figure PCTCN2021142646-appb-000002
其中，化合物2、化合物4、化合物5、化合物7的合成方法分别如下：
Figure PCTCN2021142646-appb-000003
Figure PCTCN2021142646-appb-000004
化合物3的合成方法与化合物2的合成方法相同，不同在于反应底物氯乙烷换成氯乙烯；化合物6的合成方法与化合物5的合成方法相同，不同在于反应底物磺酰氟换成三氟甲基磺酰氯；化合物8合成方法与化合物7的合成方法相同，不同在于反应底物氢氧化锂换成氢氧化铯。
在上述技术方案中，本申请的电解液添加剂采用了结构式1或结构式2所示这一类特殊结构的化合物，其中，该添加剂结构中的磺酰基团能够在锂离子电池初次充放电阶段在电池正负极生成富含LiSO 3、ROSO 2Li等含硫化合物的SEI膜，这类SEI在低温下仍有很好的离子导电性，可以促进低温下锂离子在正负极的扩散。但是由于含氟锂盐会生成LiF，不利于低温性能，比如LiPF 6在化成阶段会生成大量的LiF附着在SEI膜上，LiF由于分子量较少，会嵌入含有LiSO 3、ROSO 2Li等含硫化合物形成的离子传输孔道中，增大阻抗，反而不利于电池的低温性能。而该添加剂结构中的三甲基硅基在首次化成阶段能消耗部分LiF，生成三甲基氟硅烷，而三甲基氟硅烷常温下为气体，在化成完毕抽气封口的时候随着其他气体一起被抽走，不会影响到电池本身性能。同时，该添加剂结构中的亚胺结构又能在其中起到除水除酸的作用，避免LiPF 6生成的PF 5和HF对正负极上的SEI进行破坏，进一步确保了低温高离子电导率SEI膜的稳定性。因此，上述结构式1或结构式2所示化合物三官能团通过明显的协同作用，极大的提升了锂离子电池的低温性能，抑制低温析锂，使得锂离子电池在极端低温的环境下能相对正常运作。
本申请第二方面提供了一种低温非水电解液，包括锂盐、非水有机溶剂和添加剂，添加剂为上述电解液添加剂。
较佳的，所述电解液添加剂在该低温非水电解液中的重量百分比为0.1～3％，可为但不限于为0.1％、1％、2％、3％。
较佳的，锂盐选自六氟磷酸锂(LiPF 6)、二氟磷酸锂(LiPO 2F 2)、双草酸硼酸锂(LiBOB)、二氟草酸硼酸锂(LiODFB)、二氟二草酸磷酸锂(LiPF 2(C 2O 4) 2)、四氟硼酸锂(LiBF 4)、四氟草酸磷酸锂(LiPF 4(C 2O 4))、双三氟甲基磺酰亚胺锂(LiN(SO 2CF 3) 2)、双氟代磺酰亚胺锂(Li[N(SO 2F) 2)和四氟丙二酸磷酸锂中的至少一种。
较佳的，锂盐的含量占该低温非水电解液重量的10～20％，具体可为但不限于为10％、11％、12％、13％、14％、15％、16％、17％、18％、19％、20％，锂盐在非水电解液中的浓度为0.5～2.5mol/L。
较佳的，所述非水有机溶剂选自碳酸乙烯酯(EC)、碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、碳酸丙烯酯(PC)、乙酸丁酯(n-BA)、γ-丁内酯(GBL)、丙酸丙酯(n-PP)、丙酸乙酯(EP)和丁酸乙酯(EB)中的至少一种。
更为优选地，非水有机溶剂为碳酸二甲酯(DMC)、碳酸二乙酯(DEC)。
较佳的，非水有机溶剂占非水电解液重量的60～80％，具体可为但不限于为60％、65％、66％、67％、68％、69％、70％、71％、72％、73％、74％、75％、80％。
较佳的，低温非水电解液还包括助剂，助剂占非水电解液重量的0.5～10％，具体可为但不限于为0.5％、1％、2％、3％、4％、5％、6％、7％、8％、9％、10％。
较佳的，所述助剂选自2,2,2-三氟代碳酸甲乙酯、2,2,2-三氟代碳酸二乙酯、2,2,2-三氟代碳酸乙丙酯、碳酸亚乙烯酯(VC)、氟代碳酸乙烯酯(FEC)、双氟代碳酸乙烯酯(DFEC)、焦碳酸二乙酯(DEPC)、1,3-丙烷磺酸内酯(PS)、硫酸乙烯酯(DTD)、1,2-二氟代碳酸乙烯酯(DFEC)，三(三甲基硅烷)磷酸酯(TMSP)、三(三甲基硅烷)亚磷酸酯(TMSPi)、4,4'-联-1,3-二氧戊环-2,2'-二酮(BDC)、3,3-联二硫酸乙烯酯(BDTD)、4,4-联二硫酸乙烯酯、磷酸三烯丙酯(TAP)、磷酸 三炔丙酯(TPP)、丁二腈(SN)、己二腈(ADN)、1,3,6-己烷三腈(HTCN)和1,2-双(氰乙氧基)乙烷(DENE)中的至少一种。助剂的加入能够在正极表面形成稳定的钝化膜，阻止电解液在正极表面的氧化分解，抑制过渡金属离子从正极中溶出，提高正极材料结构和界面的稳定性，进而显著提高电池的高温性能和循环性能。
优选的，助剂包含氟代碳酸乙烯酯(FEC)，添加FEC于电解液中可提高在高电压体系下电池的循环稳定性，且结构式1或结构式2所示的化合物可与FEC作用，以调节FEC的分解速率，形成含LiF的电子绝缘界面层，从而有利于提升高电压下锂离子电池的循环性能与低温性能。
优选的，助剂包含硫酸乙烯酯(DTD)，含硫酸乙烯酯(DTD)作为助剂加入到电解液中，可对锂电池负极表面SEI膜组分进行修饰，提高硫原子和氧原子的相对含量，硫原子和氧原子含有孤对电子，可以吸引锂离子，加快锂离子在SEI膜中穿梭，降低电池界面阻抗，从而进一步有效提升高电压锂离子电池的低温充放电性能。
优选的，助剂选自碳酸亚乙烯酯(VC)、氟代碳酸乙烯酯(FEC)、1,3-丙烷磺酸内酯(PS)、硫酸乙烯酯(DTD)、4,4'-联-1,3-二氧戊环-2,2'-二酮(BDC)、3,3-联二硫酸乙烯酯(BDTD)、4,4-联二硫酸乙烯酯、双氟代碳酸乙烯酯(DFEC)，且含量各自为0.1～2％、0.2～6％、0.2～2％、0.2～2％、0.1～1.5％、0.1～1.5％、0.1～1.5％、0.1～1.5％。
相应地，本申请第三方面还提供了一种锂离子电池，包括正极材料、负极材料和电解液，所述电解液为前述的低温非水电解液。
较佳的，锂离子电池的最高充电电压为4.5V。
较佳的，所述正极材料为Li (1+a)Ni xCo yM zN 1-x-y-zO 2+b，其中，M为Mn或Al，N为Mg、Cu、Zn、Sn、B、Ga、Cr、Sr、Ba、V和Ti中的任意一种，-0.10≤a≤0.50，0＜x＜1，0＜y＜1，0<z＜1，0.7＜x+y+z≤1，-0.05≤b≤0.10。
较佳的，所述负极材料选自石墨。
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
在充满氮气的手套箱(O 2＜1ppm，H 2O＜1ppm)中，将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)按照3:7比例混合均匀，制得79g非水有机溶剂，再加入1g的化合物1作为添加剂并得到混合溶液。将混合溶液密封打包放置急冻间(-4℃)冷冻2h之后取出，在充满氮气的手套箱(O 2＜1ppm，H 2O＜1ppm)中，向混合溶液中缓慢加入20g六氟磷酸锂，混合均匀后即制成电解液。
实施例2～21和对比例1～4的电解液配方如表1所示，配制电解液的步骤同实施例1。
表1各实施例和对比例中的电解液组分和含量
Figure PCTCN2021142646-appb-000005
Figure PCTCN2021142646-appb-000006
以最高充电电压为4.5V的NCM523为正极材料，天然石墨为负极材料，以实施例1～21和对比例1～4的电解液参照常规锂电池制备方法制成锂离子电池，并分别进行低温循环性能、低温循环析锂、极端低温放电性能进行测试，测试结果如下表2所示：
低温循环测试：
将电池置于恒温-10℃/-20℃/-30℃的烘箱中搁置4小时，后以0.5C的电流 恒流充电至4.5V，然后恒压充电至电流下至0.05C，然后以0.5C的电流恒流放电至3.0V，如此循环，记录未进低温箱之前电池的初始容量和最后一圈的放电容量。
容量保持率＝最后一圈的放电容量/初始容量×100％。
低温循环析锂：
将-20℃低温循环20周后并充满电的电池在手套箱拆解，观察负极是否出现析锂现象。
极端低温放电性能测试：
将电池充电至4.5V后置于恒温-40℃/-50℃的烘箱中搁置4小时，后以0.2C的电流放电至3.0V，记录未进低温箱之前电池初始容量和低温放电容量。
容量保持率＝低温放电容量/初始容量×100％。
表2电池低温性能
Figure PCTCN2021142646-appb-000007
Figure PCTCN2021142646-appb-000008
从表2结果可知，采用本申请添加剂的锂离子电池的实施例1-21的低温性能明显优于对比例1-4。由于本申请的电解液添加剂采用了结构式1或结构式2所示这一类特殊结构的化合物，其中，该添加剂结构中的磺酰基团能够在锂离子电池初次充放电阶段在电池正负极生成富含LiSO 3、ROSO 2Li等含硫化合物的SEI膜，这类SEI在低温下仍有很好的离子导电性，可以促进低温下锂离子在正负极的扩散。但是由于锂盐的影响不利于低温性能，比如LiPF 6在化成阶段会生成大量的LiF附着在SEI膜上，LiF由于分子量较少，会嵌入含有LiSO 3、ROSO 2Li等含硫化合物形成的离子传输孔道中，增大阻抗，反而不利于电池的低温性能。而该添加剂结构中的三甲基硅基在首次化成阶段能消耗部分LiF，生成三甲基氟硅烷，而三甲基氟硅烷常温下为气体，在化成完毕抽气封口的时候随着其他气体一起被抽走，不会影响到电池本身性能。同时，该添加剂结构中的亚胺结构又能在其中起到除水除酸的作用，避免LiPF 6生成的PF 5和HF对正负极上的SEI进行破坏，进一步确保了低温高离子电导率SEI膜的稳定性。因此，上述结构 式1或结构式2所示化合物三官能团通过明显的协同作用，极大的提升了锂离子电池的低温性能，抑制低温析锂，使得锂离子电池在极端低温的环境下能相对正常运作。
进一步可知，实施例14-21中由于引入了助剂，能进一步提升锂离子电池的低温性能，尤其是氟代碳酸乙烯酯(FEC)的引入。
由对比例2的数据可知，加入双氟磺酰亚胺，虽然也含有磺酰基团和亚胺基团，但其低温性能反而变差，主要是双氟磺酰亚胺带活泼氢，促进HF生成，在电解液中显中强酸性，反而破坏了SEI膜，破坏正负极与电解液界面，使得电解液低温性能变差。
由对比例3的数据可知，单一的三甲基硅基能略微改善低温性能，但对低温性能改善不明显。
由对比例4的数据可知，将双氟磺酰亚胺和三甲基硅基组合后，仍不能达到本申请采用结构式1或结构式2所示这一类特殊结构的化合物改善低温性能的效果。
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或结构式2所示的化合物：
    Figure PCTCN2021142646-appb-100001
    其中R 1、R 2选自氢原子、烃基、三甲基硅基、氟磺酰基或三氟甲基磺酰基；X 1、X 2为选自碱金属元素。
  2. 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或结构式2所示的化合物选自化合物1至化合物8中的至少一种：
    Figure PCTCN2021142646-appb-100002
    Figure PCTCN2021142646-appb-100003
  3. 一种低温非水电解液，包括锂盐、非水有机溶剂和添加剂，其特征在于，所述添加剂包括如权利要求1～2任一所述的电解液添加剂。
  4. 如权利要求3所述的低温非水电解液，其特征在于，所述电解液添加剂在该低温非水电解液中的重量百分比为0.1～3％。
  5. 如权利要求3所述的低温非水电解液，其特征在于，所述锂盐选自六氟磷酸锂、二氟磷酸锂、双草酸硼酸锂、二氟草酸硼酸锂、二氟二草酸磷酸锂、四氟硼酸锂、四氟草酸磷酸锂、双三氟甲基磺酰亚胺锂、双氟代磺酰亚胺锂和四氟丙二酸磷酸锂中的至少一种。
  6. 如权利要求3所述的低温非水电解液，其特征在于，所述非水有机溶剂选自碳酸乙烯酯、碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、碳酸丙烯酯、乙酸丁酯、γ-丁内酯、丙酸丙酯、丙酸乙酯和丁酸乙酯中的至少一种。
  7. 如权利要求3所述的低温非水电解液，其特征在于，还包括助剂，所述助剂选自2,2,2-三氟代碳酸甲乙酯、2,2,2-三氟代碳酸二乙酯、2,2,2-三氟代碳酸乙丙酯、碳酸亚乙烯酯、氟代碳酸乙烯酯、双氟代碳酸乙烯酯、焦碳酸二乙酯、1,3-丙烷磺酸内酯、硫酸乙烯酯、1,2-二氟代碳酸乙烯酯、三(三甲基硅烷)磷酸酯、三(三甲基硅烷)亚磷酸酯、4,4'-联-1,3-二氧戊环-2,2'-二酮、3,3-联二硫酸乙烯酯、4,4-联二硫酸乙烯酯、磷酸三烯丙酯、磷酸三炔丙酯、丁二腈、己二腈、1,3,6-己烷三腈和1,2-双(氰乙氧基)乙烷中的至少一种。
  8. 一种锂离子电池，包括正极材料、负极材料和电解液，其特征在于，所述电解液为权利要求3～7任一项所述的低温非水电解液。
  9. 如权利要求8所述的锂离子电池，其特征在于，所述正极材料为Li (1+a)Ni xCo yM zN 1-x-y-zO 2+b，其中，M为Mn或Al，N为Mg、Cu、Zn、Sn、B、Ga、Cr、Sr、Ba、V和Ti中的任意一种，-0.10≤a≤0.50，0＜x＜1，0＜y＜1，0<z＜1，0.7＜x+y+z≤1，-0.05≤b≤0.10。
  10. 如权利要求8所述的锂离子电池，其特征在于，所述负极材料选自石墨。
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