WO2018054153A1 - 电解液及二次电池 - Google Patents

电解液及二次电池 Download PDF

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WO2018054153A1
WO2018054153A1 PCT/CN2017/093748 CN2017093748W WO2018054153A1 WO 2018054153 A1 WO2018054153 A1 WO 2018054153A1 CN 2017093748 W CN2017093748 W CN 2017093748W WO 2018054153 A1 WO2018054153 A1 WO 2018054153A1
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group
carbon atoms
halogenated
electrolyte
carbonate
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PCT/CN2017/093748
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English (en)
French (fr)
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张明
韩昌隆
张翠
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宁德时代新能源科技股份有限公司
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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
    • H01M10/052—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
    • H01M10/05—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
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
    • 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
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • 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 field of battery technologies, and in particular, to an electrolyte and a secondary battery.
  • Secondary batteries especially lithium ion secondary batteries, have broad application prospects in consumer electronics, power vehicle batteries and energy storage power sources due to their high energy density, long cycle life and no pollution.
  • transition metal oxide cathode active materials have become a research hotspot because their theoretical specific capacity is higher than other cathode active materials.
  • the transition metal oxide positive active material has strong oxidizing property under high SOC state, which causes the electrolyte to easily undergo electrochemical oxidation reaction on the surface of the positive electrode, and at the same time causes changes in the structure of the transition metal oxide positive active material, resulting in nickel and cobalt.
  • the transition metal such as manganese is eluted by a reduction reaction to cause deterioration of the electrochemical performance of the lithium ion secondary battery. Therefore, it has been critical to develop an electrolyte that matches the transition metal oxide positive active material.
  • an object of the present invention is to provide an electrolyte and a secondary battery capable of simultaneously improving the normal temperature cycle performance and high-temperature storage performance of the secondary battery when the electrolyte is applied to the secondary battery. And high temperature thermal stability.
  • the present invention provides an electrolyte comprising an electrolyte salt, an organic solvent, and an additive.
  • the additive includes a cyclotriphosphazene compound and ethylene carbonate.
  • the invention provides a secondary battery comprising an electrolyte according to an aspect of the invention.
  • the electrolytic solution of the present invention contains both a cyclotriphosphazene compound and ethylene carbonate, and when it is applied to a secondary battery, it can simultaneously improve the normal temperature cycle performance, high temperature storage performance, and high temperature thermal stability of the secondary battery.
  • the electrolytic solution according to the first aspect of the invention includes an electrolyte salt, an organic solvent, and an additive.
  • the additive includes a cyclic triphosphazene compound and ethylene carbonate (VEC).
  • the cyclotriphosphazene compound means a six-membered cyclic compound which is alternately formed by P and N by a single double bond and a derivative thereof which is substituted.
  • the ethylene carbonate may form a network passivation film on the surface of the positive electrode active material, and effectively suppress oxidation of the electrolyte by the positive electrode active material, but ethylene carbonate
  • the ester easily forms a solid electrolyte interface film having a high impedance on the surface of the negative electrode, affecting the performance of the secondary battery.
  • the polyphosphate component produced by the decomposition of the cyclotriphosphazene compound can be embedded in the solid electrolyte interface film formed by ethylene carbonate on the surface of the negative electrode, thereby effectively reducing the solid electrolyte interface film formed by ethylene carbonate on the surface of the negative electrode. impedance.
  • the cyclotriphosphazene compound can also absorb hydrofluoric acid in the electrolyte to alleviate the corrosion of the positive and negative passivation films of hydrofluoric acid. Therefore, when the electrolyte contains both the cyclotriphosphazene compound and ethylene ethylene carbonate, a stable passivation film can be formed on both the positive and negative electrodes, and the solid electrolyte interface film on the surface of the negative electrode also has a low impedance. And better ion transport characteristics, so that the secondary temperature cycle performance, high temperature storage performance and high temperature thermal stability of the secondary battery are significantly improved.
  • the cyclotriphosphazene compound is selected from one or more of the compounds represented by Formula 1.
  • R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently selected from the group consisting of H, F, Cl, Br, I, an alkane group having 1 to 20 carbon atoms, and having 1 carbon atom; a halogenated alkane group of ⁇ 20, an olefin group having 2 to 20 carbon atoms, a halogenated olefin group having 2 to 20 carbon atoms, an aryl group having 6 to 26 carbon atoms, or a halogen having 6 to 26 carbon atoms; An aryl group, an alkoxy group having 1 to 20 carbon atoms, a halogenated alkoxy group having 1 to 20 carbon atoms, an aryloxy group having 6 to 26 carbon atoms, or a halogenated group having 6 to 26 carbon atoms.
  • One of aryloxy groups; at least one of R 1 , R 3 and R 5 is selected from the group consisting of an alkane group having 1 to 20 carbon atoms, a halogenated alkane group having 1 to 20 carbon atoms, and 2 to 2 carbon atoms.
  • R 2 and R 4 ; , at least two of R 6 are each independently selected from F, Cl, Br, I of Species.
  • R 1 , R 3 and R 5 is selected from an alkane group having 1 to 6 carbon atoms and having 1 to 6 carbon atoms.
  • R 2 , R 4 and R 6 are each selected from fluorine.
  • the cyclotriphosphazene compound may be selected from one or more of the following compounds;
  • the ethylene carbonate content may be from 0.1% to 3% by mass based on the total mass of the electrolyte.
  • the mass percentage of ethylene carbonate in the electrolyte is less than 0.1%, it cannot form a complete network passivation film on the surface of the positive electrode active material, thereby failing to effectively prevent the oxidation of the electrolyte on the surface thereof.
  • the mass percentage of ethylene carbonate in the electrolyte is higher than 3%, it will form an excessively thick passivation film on the surface of the positive and negative electrodes, so that the impedance of the passivation film is high, which is disadvantageous to ions.
  • the transmission in the passivation film increases the polarization of the battery, which in turn deteriorates the performance of the secondary battery.
  • the content of the cyclotriphosphazene compound may be from 0.1% to 10% by mass based on the total mass of the electrolyte.
  • the mass percentage of the cyclotriphosphazene compound in the electrolyte is 0.1%, the reaction of forming a solid electrolyte interface film on the surface of the negative electrode is insufficient, and the improvement of the performance of the secondary battery is not obvious; when the cyclotriphosphazene is improved
  • the mass percentage of the compound in the electrolyte is higher than 10%, the viscosity of the electrolyte is significantly increased, the electrical conductivity of the electrolyte is lowered, thereby slowing the migration of ions, and adversely affecting the performance of the secondary battery.
  • the organic solvent may be selected from the group consisting of ethylene carbonate (EC), propylene carbonate, butylene carbonate, fluoroethylene carbonate, and ethyl methyl carbonate (EMC). , dimethyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, ethylene propyl carbonate, 1,4-butyrolactone, ⁇ -butyrolactone, methyl propionate, butyric acid Methyl ester, ethyl acetate, ethyl propionate, butyrate B At least two of the esters.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • DEC dipropyl carbonate
  • methyl propyl carbonate ethylene propyl carbonate
  • 1,4-butyrolactone 1,4-butyrolactone
  • ⁇ -butyrolactone 1,4-butyrolactone
  • methyl propionate butyric acid
  • the electrolyte salt may be selected from a lithium salt, a sodium salt or a zinc salt, which varies depending on the secondary battery to which the electrolyte is applied.
  • the concentration of the electrolyte salt is from 0.5 M to 1.5 M.
  • the concentration of the electrolyte salt is from 0.8 M to 1.2 M.
  • the additive may further include vinylene carbonate (VC), vinyl sulfate (DTD), and 1,3-propane sultone (1,3-PS).
  • VC vinylene carbonate
  • DTD vinyl sulfate
  • TMSB tris(trimethylsilyl)borate
  • the electrolytic solution may be prepared by a conventional method, for example, mixing the respective materials in the electrolytic solution uniformly.
  • a secondary battery according to a second aspect of the invention includes the electrolytic solution according to the first aspect of the invention.
  • the secondary battery further includes a positive electrode sheet, a negative electrode sheet, and a separator.
  • the positive electrode sheet may include a positive electrode current collector and a positive electrode slurry layer provided on the positive electrode current collector and containing a positive electrode active material.
  • the negative electrode sheet may include a negative electrode current collector and a negative electrode slurry layer provided on the negative electrode current collector and containing the negative electrode active material.
  • the specific kind of the separator is not particularly limited, and may be any separator material used in the prior art, such as polyethylene, polypropylene, and polyvinylidene fluoride. Ethylene and their multilayer composite films are, but not limited to, these.
  • the secondary battery may be a lithium ion secondary battery, a sodium ion secondary battery, or a zinc ion secondary battery.
  • the cathode active material may be selected from one of lithium cobaltate, lithium iron phosphate, lithium manganate, nickel manganese cobalt ternary material, and nickel cobalt aluminum ternary material.
  • the negative active material may be selected from graphite and/or silicon
  • the electrolyte salt ie, lithium salt
  • LiPF 6 LiPF 6
  • LiClO 4 LiAsF 6
  • LiTFSI LiTFS
  • LiFSI LiDFOB
  • LiBOB LiBOB
  • the present application is further illustrated below in conjunction with the embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the application.
  • the present invention selects flexible packaging lithium ion secondary batteries for related testing.
  • the lithium ion secondary batteries of Examples 1-21 and Comparative Examples 1-6 were each prepared in the following manner.
  • the positive electrode active material LiNi 0.8 Co 0.15 Mn 0.15 O 2 , the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 97:1.4:1.6, and added to the solvent N-methylpyrrolidone (NMP).
  • NMP solvent N-methylpyrrolidone
  • the anode active material graphite, the conductive agent Super P, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber emulsion (SBR) are mixed according to a mass ratio of 96.4:1.5:0.5:1.6, and added to the solvent.
  • a negative electrode slurry was obtained under the action of a vacuum mixer, wherein the solid content of the negative electrode slurry was 54 wt%; the negative electrode slurry was uniformly coated on the negative electrode current collector copper foil and dried at 85 ° C, and then passed through a cold Pressing, trimming, cutting, and striping were finally dried under vacuum at 120 ° C for 12 h to obtain a negative electrode sheet.
  • the concentration of LiPF 6 was 1 mol/L.
  • Table 1 The specific types and contents of the additives used in the electrolyte are shown in Table 1. In Table 1, the additive is added in an amount of mass calculated based on the total mass of the electrolyte.
  • a polyethylene film (PE) having a thickness of 16 ⁇ m was used as the separator.
  • the positive electrode sheet, the separator film and the negative electrode sheet are stacked in order, so that the separator is in a function of isolating between the positive and negative electrodes, and then wound into a square bare cell, soldered to the ear, and the bare cell is loaded.
  • the packaging foil aluminum plastic film and then baked at 80 ° C to remove water, the corresponding electrolyte is injected and sealed, after which it is allowed to stand, hot and cold, and chemicalized (0.02C constant current charging to 3.3V, then 0.1C) Constant current charging to 3.6V), shaping, capacity testing and other processes, to obtain a finished flexible packaging lithium ion secondary battery, the thickness of which is 4.0mm, width of 60mm, length of 140mm.
  • the lithium ion secondary battery was charged to 4.2 V with a constant current of 1 C, further charged at a constant voltage of 4.2 V until the current was 0.05 C, and then discharged to a constant current of 1 C to 2.8 V, which was a charge and discharge cycle.
  • the discharge capacity of this time is the discharge capacity after the first cycle of the lithium ion secondary battery.
  • the lithium ion secondary battery was subjected to 500 cycles of charge/discharge test in accordance with the above method.
  • the capacity retention ratio (%) after the lithium ion secondary battery was cycled 500 times the discharge capacity after 500 cycles/the discharge capacity after the first cycle ⁇ 100%.
  • the lithium ion secondary battery was charged at a constant current of 1 C to a voltage of 4.2 V, and then charged at a constant voltage of 4.2 V until the current was 0.05 C, and then discharged at a constant current of 1 C to a voltage of 2.8 V, and the lithium was tested at this time.
  • the discharge capacity of the ion secondary battery is denoted as C 0 ; the lithium ion secondary battery is then charged at a constant current of 1 C to a voltage of 4.2 V, and then charged at a constant voltage of 4.2 V until the current is 0.05 C, and the lithium ion secondary battery is used.
  • the capacity retention ratio (%) of the lithium ion secondary battery after storage at 60 ° C for 90 days C 1 / C 0 ⁇ 100%.
  • the lithium ion secondary battery subjected to 500 cycles was charged at a constant current of 0.5 C to a voltage of 4.2 V at 25 ° C, further charged at a constant voltage of 4.2 V to a current of 0.05 C, and then the lithium ion secondary battery was placed.
  • the state of the lithium ion secondary battery was observed by maintaining it in a high temperature furnace at 150 ° C for 1 hour.
  • Comparative Examples 1-3 the normal temperature cycle of the lithium ion secondary battery is obtained when ethylene carbonate (Comparative Example 2) or a cyclotriphosphazene compound (Comparative Example 3) is separately added to the electrolytic solution.
  • the performance and high-temperature storage performance were slightly improved relative to Comparative Example 1, but the improvement effect was not obvious, and the high-temperature thermal stability of the lithium ion secondary battery was still poor.
  • ethylene carbonate and cyclotriphosphazene compound were simultaneously added to the electrolyte, and the room temperature cycle performance and high-temperature storage performance of the lithium ion secondary battery were remarkably improved, and the heat of the lithium ion secondary battery was improved. Stability is also significantly improved.
  • the electrolyte was further added with ethylene carbonate, cyclotriphosphazene compound, and also added with ethylene sulfate, 1,3-propane sultone, and tris(trimethylsilyl)phosphoric acid.
  • the esters at this time, the room temperature cycle performance and the high-temperature storage property of the lithium ion secondary battery are further improved, and the stability of the lithium ion secondary battery is not deteriorated.
  • Example 3 From the comparison of Example 3, Examples 6-9 and Comparative Example 5, it can be seen that when the content of the cyclotriphosphazene compound in the electrolyte is too high, since it will significantly increase the viscosity of the electrolyte, the conductance of the electrolyte is lowered. The rate of lithium ion migration is slowed down, and the normal temperature cycle performance, high temperature storage performance, and high temperature thermal stability of the lithium ion secondary battery are not improved but deteriorate.
  • the application of the electrolyte containing the cyclotriphosphazene compound and ethylene carbonate to the lithium ion secondary battery can improve not only the normal temperature cycle performance and the high temperature storage performance of the lithium ion secondary battery, but also It is possible to improve the thermal stability of a lithium ion secondary battery at a high temperature.

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Abstract

本发明提供一种电解液及二次电池。所述电解液包括电解质盐、有机溶剂以及添加剂。所述添加剂包括环三磷腈化合物以及碳酸乙烯亚乙酯。当本发明的电解液应用到二次电池中后，能够同时提高二次电池的常温循环性能、高温存储性能以及高温热稳定性。

Description

电解液及二次电池 技术领域
本发明涉及电池技术领域，尤其涉及一种电解液及二次电池。
背景技术
二次电池尤其是锂离子二次电池由于具有能量密度高、循环寿命长、无污染等特点，使得其在消费类电子、动力汽车电池及储能电源上具有广阔的应用前景。
无论在哪个应用领域，人们对锂离子二次电池的续航能力提出了更高的要求。为了提高锂离子二次电池的能量密度，开发具有高比容量的正极活性材料是有效办法之一。目前，过渡金属氧化物正极活性材料由于其理论比容量相比于其它正极活性材料更高，使得其成为研究热点。然而过渡金属氧化物正极活性材料在高SOC状态下具有很强的氧化性，导致电解液容易在正极表面发生电化学氧化反应，同时引起过渡金属氧化物正极活性材料结构的变化，导致镍、钴、锰等过渡金属发生还原反应而溶出，从而引起锂离子二次电池电化学性能的恶化。因此开发出一种与过渡金属氧化物正极活性材料相匹配的电解液非常关键。
发明内容
鉴于背景技术中存在的问题，本发明的目的在于提供一种电解液及二次电池，当所述电解液应用到二次电池中后，能够同时提高二次电池的常温循环性能、高温存储性能以及高温热稳定性。
为了达到上述目的，在本发明的一方面，本发明提供了一种电解液，其包括电解质盐、有机溶剂以及添加剂。所述添加剂包括环三磷腈化合物以及碳酸乙烯亚乙酯。
在本发明的另一方面，本发明提供了一种二次电池，其包括根据本发明一方面所述的电解液。
相对于现有技术，本发明的有益效果为：
本发明的电解液同时含有环三磷腈化合物以及碳酸乙烯亚乙酯，当将其应用到二次电池中后，能够同时提高二次电池的常温循环性能、高温存储性能以及高温热稳定性。
具体实施方式
下面详细说明根据本发明的电解液及二次电池。
首先说明根据本发明第一方面的电解液。
根据本发明第一方面的电解液包括电解质盐、有机溶剂以及添加剂。所述添加剂包括环三磷腈化合物以及碳酸乙烯亚乙酯(VEC)。
在根据本发明第一方面所述的电解液中，环三磷腈化合物是指由P和N通过单双键交替形成的六元环状化合物及其被取代得到的衍生物。
在根据本发明第一方面所述的电解液中，所述碳酸乙烯亚乙酯可在正极活性材料表面形成网状钝化膜，有效抑制正极活性材料对电解液的氧化，但是碳酸乙烯亚乙酯容易在负极表面形成阻抗较高的固体电解质界面膜，影响二次电池的性能。而环三磷腈化合物分解产生的多磷酸盐成分可以嵌入由碳酸乙烯亚乙酯在负极表面形成的固态电解质界面膜中，从而有效降低碳酸乙烯亚乙酯在负极表面形成的固态电解质界面膜的阻抗。此外，环三磷腈化合物还可以吸收电解液中的氢氟酸，减轻氢氟酸对正负极钝化膜的腐蚀。因此，当电解液中同时含有环三磷腈化合物和碳酸乙烯亚乙酯时，可同时在正负极表面形成稳定的钝化膜，同时负极表面的固态电解质界面膜还兼具较低的阻抗和较好的离子传输特性，使二次电池的常温循环性能、高温存储性能以及高温热稳定性均得到明显改善。
在根据本发明第一方面所述的电解液中，所述环三磷腈化合物选自式1所示的化合物中的一种或几种。其中，R1、R2、R3、R4、R5、R6各自独立地选自H、F、Cl、Br、I、碳原子数为1～20的烷烃基、碳原子数为1～20的卤代烷烃基、碳原子数为2～20的烯烃基、碳原子数为2～20的卤代烯烃基、碳原子数为6～26的芳基、碳原子数为6～26的卤代芳基、碳原子数为1～20的烷氧基、碳原子数为1～20的卤代烷氧基、碳原子数为6～26的芳氧基、碳原 子数为6～26的卤代芳氧基中的一种；R1、R3、R5中的至少一个选自碳原子数为1～20的烷烃基、碳原子数为1～20的卤代烷烃基、碳原子数为2～20的烯烃基、碳原子数为2～20的卤代烯烃基、碳原子数为6～26的芳基、碳原子数为6～26的卤代芳基、碳原子数为1～20的烷氧基、碳原子数为1～20的卤代烷氧基、碳原子数6～26的芳氧基、碳原子数为6～26的卤代芳氧基中的一种；R2、R4、R6中的至少两个各自独立地选自F、Cl、Br、I中的一种。
Figure PCTCN2017093748-appb-000001
在根据本发明第一方面所述的电解液中，优选地，R1、R3、R5中的至少一个选自碳原子数为1～6的烷烃基、碳原子数为1～6的卤代烷烃基、碳原子数为2～6的烯烃基、碳原子数为2～6的卤代烯烃基、苯基、卤代苯基、碳原子数为1～6的烷氧基、碳原子数为1～6的卤代烷氧基、苯氧基、卤代苯氧基中的一种。
在根据本发明第一方面所述的电解液中，优选地，R2、R4、R6均选自氟。
在根据本发明第一方面所述的电解液中，具体地，所述环三磷腈化合物可选自下述化合物中的一种或几种；
Figure PCTCN2017093748-appb-000002
Figure PCTCN2017093748-appb-000003
在根据本发明第一方面所述的电解液中，碳酸乙烯亚乙酯的含量可为所述电解液总质量的0.1％～3％。当碳酸乙烯亚乙酯在电解液中的质量百分含量低于0.1％时，其无法在正极活性材料的表面形成完整的网状钝化膜，从而不能有效阻止电解液在其表面的氧化副反应；当碳酸乙烯亚乙酯在电解液中的质量百分含量高于3％时，其会在正负极表面形成过厚的钝化膜，使得钝化膜的阻抗较高，不利于离子在钝化膜中的传输，增加了电池极化，反而恶化二次电池的性能。
在根据本发明第一方面所述的电解液中，所述环三磷腈化合物的含量可为所述电解液总质量的0.1％～10％。当环三磷腈化合物在电解液中的质量百分含量低0.1％时，其在负极表面生成固态电解质界面膜的反应不够充分，对二次电池性能的改善作用不明显；当环三磷腈化合物在电解液中的质量百分含量高于10％时，会显著增加电解液的粘度，降低电解液的电导率，从而减缓离子的迁移，反而恶化二次电池的性能。
在根据本发明第一方面所述的电解液中，所述有机溶剂可选自碳酸乙烯酯(EC)、碳酸丙烯酯、碳酸丁烯酯、氟代碳酸乙烯酯、碳酸甲乙酯(EMC)、碳酸二甲酯、碳酸二乙酯(DEC)、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、1,4-丁内酯、γ-丁内酯、丙酸甲酯、丁酸甲酯、乙酸乙酯、丙酸乙酯、丁酸乙 酯中的至少两种。
在根据本发明第一方面所述的电解液中，所述电解质盐可选自锂盐、钠盐或锌盐，依据所述电解液应用的二次电池的不同而不同。
在根据本发明第一方面所述的电解液中，所述电解质盐的浓度为0.5M～1.5M。优选地，所述电解质盐的浓度为0.8M～1.2M。
在根据本发明第一方面所述的电解液中，所述添加剂还可包括碳酸亚乙烯酯(VC)、硫酸乙烯酯(DTD)、1,3-丙磺酸内酯(1,3-PS)、三(三甲基硅烷)磷酸酯(TMSP)、三(三甲基硅烷)硼酸酯(TMSB)中的一种或几种，以进一步改善二次电池的性能。
在根据本发明第一方面所述的电解液中，电解液采用常规方法制备即可，比如将电解液中的各个物料混合均匀即可。
其次说明根据本发明第二方面的二次电池。
根据本发明第二方面的二次电池包括根据本发明第一方面所述的电解液。
在根据本发明第二方面所述的二次电池中，所述二次电池还包括正极片、负极片以及隔离膜。
在根据本发明第二方面所述的二次电池中，所述正极片可包括正极集流体和设置于所述正极集流体上且包含正极活性材料的正极浆料层。
在根据本发明第二方面所述的二次电池中，所述负极片可包括负极集流体和设置于所述负极集流体上且包含负极活性材料的负极浆料层。
在根据本发明第二方面所述的二次电池中，隔离膜的具体种类并不受到具体的限制，可以是现有技术中使用的任何隔离膜材料，例如聚乙烯、聚丙烯、聚偏氟乙烯以及它们的多层复合膜，但不仅限于这些。
在根据本发明第二方面所述的二次电池中，所述二次电池可为锂离子二次电池、钠离子二次电池或锌离子二次电池。当所述二次电池为锂离子二次电池时，所述正极活性材料可选自钴酸锂、磷酸铁锂、锰酸锂、镍锰钴三元材料、镍钴铝三元材料中的一种或几种，所述负极活性材料可选自石墨和/或硅，所述电解质盐(即锂盐)可选自LiPF6、LiClO4、LiAsF6、LiTFSI、LiTFS、LiFSI、LiDFOB以及LiBOB中的一种或几种。
下面结合实施例，进一步阐述本申请。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围，本发明选择了软包装锂离子二次电池进行相关的测试。
在实施例和对比例中所使用到的试剂、材料以及仪器如没有特殊的说明，均可商购获得。
实施例1-21以及对比例1-6中的锂离子二次电池均按照下述方法进行制备。
(1)正极片制备
将正极活性材料LiNi0.8Co0.15Mn0.15O2、导电剂Super P、粘结剂聚偏二氟乙烯(PVDF)按照质量比97:1.4:1.6进行混合，加入至溶剂N-甲基吡咯烷酮(NMP)中，在真空搅拌机作用下搅拌至体系成均一透明状，获得正极浆料，其中正极浆料中固体含量为77wt％；将正极浆料均匀涂覆于正极集流体铝箔上并在在85℃下烘干，然后经过冷压、切边、裁片、分条，最后在85℃的真空条件下烘干4h，得到正极片。
(2)负极片制备
将负极活性材料石墨、导电剂Super P、增稠剂羧甲基纤维素钠(CMC)、粘结剂丁苯橡胶乳液(SBR)按照质量比96.4:1.5:0.5:1.6进行混合，加入至溶剂去离子水中，在真空搅拌机作用下获得负极浆料，其中负极浆料中固体含量为54wt％；将负极浆料均匀涂覆在负极集流体铜箔上并在85℃下烘干，然后经过冷压、切边、裁片、分条，最后在120℃的真空条件下烘干12h，得到负极片。
(3)电解液制备
在含水量<10ppm的氩气气氛手套箱中，将EC、EMC、DEC按照质量比为EC:EMC:DEC＝30:50:20进行混合，作为有机溶剂，接着将充分干燥的锂盐LiPF6溶解于混合有机溶剂中，之后加入添加剂，混合均匀后获得电解液。其中，LiPF6的浓度为1mol/L。电解液中所用到的添加剂的具体种类以及含量如表1所示。在表1中，添加剂的添加量为基于电解液的总质量计算得到的质量百分数。
(4)隔离膜的制备
以厚度为16μm的聚乙烯膜(PE)作为隔离膜。
(5)锂离子二次电池的制备
将正极片、隔离膜、负极片按顺序叠好，使隔离膜处于正、负极片之间起到隔离的作用，然后卷绕成方形的裸电芯，焊接极耳，将裸电芯装入包装箔铝塑膜中，然后在80℃下烘烤除水后，注入相应的电解液并封口，之后经过静置、热冷压、化成(0.02C恒流充电到3.3V，再以0.1C恒流充电到3.6V)、整形、容量测试等工序，获得成品软包装锂离子二次电池，其厚度为4.0mm、宽度为60mm、长度为140mm。
表1 实施例1-21及对比例1-6的参数
Figure PCTCN2017093748-appb-000004
Figure PCTCN2017093748-appb-000005
接下来说明锂离子二次电池的测试过程。
(1)锂离子二次电池的常温循环性能测试
25℃下，将锂离子二次电池以1C恒流充电至4.2V，进一步以4.2V恒压充电至电流为0.05C，然后以1C恒流放电至2.8V，此为一个充放电循环过程，此次的放电容量为锂离子二次电池首次循环后的放电容量。将锂离子二次电池按照上述方法进行500次循环充电/放电测试。
锂离子二次电池循环500次后的容量保持率(％)＝循环500次后的放电容量/首次循环后的放电容量×100％。
(2)锂离子二次电池的高温存储性能测试
25℃下，将锂离子二次电池以1C恒流充电至电压为4.2V，之后以4.2V恒压充电至电流为0.05C，然后以1C恒流放电至电压为2.8V，测试此时锂离子二次电池的放电容量，记为C0；之后将锂离子二次电池以1C恒流充电至电压为4.2V，之后以4.2V恒压充电至电流为0.05C，将锂离子二次电池放 入60℃的恒温箱，保温90天，取出锂离子二次电池，以1C恒流放电至电压为2.8V，测试此时锂离子二次电池的放电容量，记为C1。
锂离子二次电池60℃存储90天后的容量保持率(％)＝C1/C0×100％。
(3)锂离子二次电池的高温热稳定性测试
在25℃下，将进行过500次循环的锂离子二次电池以0.5C恒流充电至电压为4.2V，进一步以4.2V恒压充电至电流为0.05C，然后将锂离子二次电池置于150℃的高温炉中保持1h，观察锂离子二次电池的状态。
表2 实施例1-21和对比例1-6的性能测试结果。
Figure PCTCN2017093748-appb-000006
Figure PCTCN2017093748-appb-000007
从对比例1-3中可以看出，当电解液中单独加入碳酸乙烯亚乙酯(对比例2)或单独加入环三磷腈化合物(对比例3)时，锂离子二次电池的常温循环性能和高温存储性能均相对对比例1略有改善，但改善效果不明显，且锂离子二次电池的高温热稳定性仍较差。在实施例1-18中，电解液中同时加入碳酸乙烯亚乙酯和环三磷腈化合物，锂离子二次电池的常温循环性能和高温存储性能得到显著提升，且锂离子二次电池的热稳定性也明显提高。在实施例19-21中，电解液在添加碳酸乙烯亚乙酯和环三磷腈化合物的同时还添加有硫酸乙烯酯、1,3-丙磺酸内酯、三(三甲基硅烷)磷酸酯中的一种或几种，此时锂离子二次电池的常温循环性能和高温存储性能进一步得到改善，且锂离子二次电池的稳定性未出现恶化。
从实施例1-5和对比例4的对比中可以看出，当电解液中碳酸乙烯亚乙酯的含量过高时，由于其会在正负极表面形成过厚的钝化膜，使得钝化膜的阻抗较高，不利于锂离子在钝化膜中的传输，锂离子二次电池的常温循环性能、高温存储性能以及高温热稳定性非但没有改善反而恶化。
从实施例3、实施例6-9和对比例5的对比中可以看出，当电解液中环三磷腈化合物的含量过高时，由于其会显著增加电解液的粘度，降低电解液的电导率，减缓锂离子的迁移，锂离子二次电池的常温循环性能、高温存储性能以及高温热稳定性非但没有改善反而恶化。
综上分析可知，将包含有环三磷腈化合物和碳酸乙烯亚乙酯的电解液应用到锂离子二次电池中后，不仅能够提高锂离子二次电池的常温循环性能和高温存储性能，而且能够改善锂离子二次电池在高温下的热稳定性。
以上所述，仅是本申请的几个实施例，并非对本申请做任何形式的限制，虽然本申请以较佳实施例揭示如上，然而并非用以限制本申请，任何熟悉本专业的技术人员，在不脱离本申请技术方案的范围内，利用上述揭示的技术内容做出些许的变动或修饰均等同于等效实施案例，均属于技术方案范围内。

Claims (10)

  1. 一种电解液，包括：
    电解质盐；
    有机溶剂；以及
    添加剂；
    其特征在于，
    所述添加剂包括环三磷腈化合物以及碳酸乙烯亚乙酯。
  2. 根据权利要求1所述的电解液，其特征在于，所述环三磷腈化合物选自式1所示的化合物中的一种或几种；
    Figure PCTCN2017093748-appb-100001
    其中，
    R1、R2、R3、R4、R5、R6各自独立地选自H、F、Cl、Br、I、碳原子数为1～20的烷烃基、碳原子数为1～20的卤代烷烃基、碳原子数为2～20的烯烃基、碳原子数为2～20的卤代烯烃基、碳原子数为6～26的芳基、碳原子数为6～26的卤代芳基、碳原子数为1～20的烷氧基、碳原子数为1～20的卤代烷氧基、碳原子数为6～26的芳氧基、碳原子数为6～26的卤代芳氧基中的一种；
    R1、R3、R5中的至少一个选自碳原子数为1～20的烷烃基、碳原子数为1～20的卤代烷烃基、碳原子数为2～20的烯烃基、碳原子数为2～20的卤代烯烃基、碳原子数为6～26的芳基、碳原子数为6～26的卤代芳基、碳原子数为1～20的烷氧基、碳原子数为1～20的卤代烷氧基、碳原子数6～26的芳氧基、碳原子数为6～26的卤代芳氧基中的一种；
    R2、R4、R6中的至少两个各自独立地选自F、Cl、Br、I中的一种。
  3. 根据权利要求2所述的电解液，其特征在于，
    R1、R3、R5中的至少一个选自碳原子数为1～6的烷烃基、碳原子数为1～6的卤代烷烃基、碳原子数为2～6的烯烃基、碳原子数为2～6的卤代烯烃基、苯基、卤代苯基、碳原子数为1～6的烷氧基、碳原子数为1～6的卤代烷氧基、苯氧基、卤代苯氧基中的一种；
    R2、R4、R6均选自氟。
  4. 根据权利要求3所述的电解液，其特征在于，所述环三磷腈化合物选自下述化合物中的一种或几种；
    Figure PCTCN2017093748-appb-100002
    Figure PCTCN2017093748-appb-100003
  5. 根据权利要求1所述的电解液，其特征在于，所述环三磷腈化合物的含量为所述电解液总质量的0.1％～10％。
  6. 根据权利要求1所述的电解液，其特征在于，所述碳酸乙烯亚乙酯的含量为所述电解液总质量的0.1％～3％。
  7. 根据权利要求1所述的电解液，其特征在于，所述有机溶剂选自碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、氟代碳酸乙烯酯、碳酸甲乙酯、碳酸二甲酯、碳酸二乙酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、1,4-丁内酯、γ-丁内酯、丙酸甲酯、丁酸甲酯、乙酸乙酯、丙酸乙酯、丁酸乙酯中的至少两种。
  8. 根据权利要求1所述的电解液，其特征在于，在所述电解液中，电解质盐的浓度为0.5M～1.5M，优选地，电解质盐的浓度为0.8M～1.2M。
  9. 根据权利要求1-8中任一项所述的电解液，其特征在于，所述添加剂还包括碳酸亚乙烯酯、硫酸乙烯酯、1,3-丙磺酸内酯、三(三甲基硅烷)磷酸酯、三(三甲基硅烷)硼酸酯中的一种或几种。
  10. 一种二次电池，其特征在于，包括根据权利要求1-9中任一项所述的电解液。
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