WO2018040763A1 - 一种添加剂，其制备方法及含有所述添加剂的锂离子电池 - Google Patents

一种添加剂，其制备方法及含有所述添加剂的锂离子电池 Download PDF

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WO2018040763A1
WO2018040763A1 PCT/CN2017/093186 CN2017093186W WO2018040763A1 WO 2018040763 A1 WO2018040763 A1 WO 2018040763A1 CN 2017093186 W CN2017093186 W CN 2017093186W WO 2018040763 A1 WO2018040763 A1 WO 2018040763A1
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additive
lithium ion
formula
ion battery
unsubstituted
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PCT/CN2017/093186
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English (en)
French (fr)
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余林峰
蒋治亿
许金梅
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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
    • H01M10/056—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
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • 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
    • 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
    • H01M2300/0017—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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present application relates to the field of lithium ion battery materials, and in particular to an additive, a preparation method thereof and a lithium ion battery containing the additive.
  • additives Adding a small amount of certain substances to a lithium ion battery can significantly improve the performance of the battery. These small amounts of substances are called additives. Additives have become a hot spot in the research field of lithium ion batteries.
  • a series of electrochemical reactions occur between the electrode material and the electrolyte to form a passivation layer covering the surface of the electrode material, that is, a solid electrolyte phase interface (SEI) film.
  • SEI solid electrolyte phase interface
  • a small amount of additives added to the lithium ion battery can preferentially react on the surface of the electrode to improve the composition and structure of the SEI film.
  • the excellent SEI film allows lithium ions to pass freely, solvent molecules cannot pass through, and further reaction between the electrolyte and the electrode material is prevented, thereby improving the rate performance and cycle performance of the battery.
  • the inside of the battery is prone to irreversible oxidative decomposition or thermal decomposition of the electrolyte, generating a large amount of flammable gas, which is prone to combustion and causes an explosion.
  • the combustion reaction of the electrolyte is usually a chain reaction involving hydroxyl radicals. Therefore, an additive is added to the lithium ion battery, and the additive decomposes and releases free radicals when heated to capture highly reactive hydrogen radicals, which can effectively reduce the electrolyte.
  • the flammability improves the safety of lithium-ion batteries.
  • the primary object of the present application is to propose an additive.
  • a second object of the present application is to propose a method of preparing the additive.
  • a third object of the present application is to propose a lithium ion battery containing the additive.
  • the present application relates to a lithium ion battery additive selected from at least one of the compounds of formula I:
  • R 1 and R 2 are each independently selected from substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 6 -C 26 aryl, substituted or unsubstituted C 5 -C 22
  • the aryl group, the substituent is a halogen; preferably a C 1 -C 8 alkyl group, more preferably a C 1 -C 3 alkyl group.
  • the present application also relates to a method of preparing the additive, the method comprising at least a lithium iodide and a phosphotriester as shown in Formula II, which are prepared by a substitution reaction to give a compound of formula I,
  • R 3 is selected from a substituted or unsubstituted C 1 -C 12 alkyl group, a substituted or unsubstituted C 6 -C 26 aryl group, a substituted or unsubstituted C 5 -C 22 aryl group, and the substituent is a halogen. .
  • the reaction is carried out in an inert gas atmosphere at a reaction temperature of 20 ° C to 30 ° C, a reaction time of 22 to 26 hours, and a molar ratio of lithium iodide to triethyl phosphate of 0.9 to 1.1: 0.9 to 1.1.
  • the solvent is acetone
  • the molar ratio of lithium iodide to triethyl phosphate is 1:1
  • the reaction temperature is normal temperature for 24 hours.
  • the present application also relates to a lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte containing an electrolyte, an organic solvent, and an additive described herein.
  • the additive is present in the electrolyte in an amount of from 0.1 to 0.5% by mass.
  • the additive according to the present application contributes to the formation of a stable SEI film on the surface of the electrode of a lithium ion battery, prevents co-intercalation of solvent molecules, and inhibits further reaction of the negative electrode with the electrolyte.
  • the addition of additives can improve the morphology and composition of the SEI film, promote and participate in the formation of the component Li x PO y F z , reduce the SEI film impedance, reduce polarization, and reduce the consumption of lithium ions. Due to the improvement of the SEI film by the additive of the present application, the lithium ion battery rate performance and cycle performance of the additive are improved.
  • the additive of the present invention is incorporated into a lithium ion battery, and when the battery is exposed to sparks or burns, the phosphorus compound decomposes to form a nonflammable liquid film of phosphoric acid. At the same time, phosphoric acid is further dehydrated to form metaphosphoric acid, and metaphosphoric acid is further polymerized to form polymetaphosphoric acid In this process, not only the coating layer formed by phosphoric acid plays a covering effect, but also because the produced polymetaphosphoric acid is a strong acid, it is a strong dehydrating agent, dehydrating and charring the polymer, changing the mode of the polymer combustion process and The surface of the surface forms a surface film to block the air, thereby exerting a stronger flame retardant effect and improving the safety of the lithium ion battery.
  • the present application relates to a lithium ion battery additive selected from at least one of the compounds of formula I:
  • R 1 and R 2 are each independently selected from substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 6 -C 26 aryl, substituted or unsubstituted C 5 -C 22 aromatic
  • the substituent is a halogen.
  • R 1 and R 2 are each independently selected from a C 1 - C 8 alkyl group, more preferably a C 1 - C 3 alkyl group.
  • R 1 and R 2 are the same substituents.
  • the alkyl group may be a chain alkyl group or a cycloalkyl group, and a hydrogen group on the ring of the cycloalkyl group may be substituted with an alkyl group.
  • the preferred lower limit of the number of carbon atoms is 1, 2, 3, 4, and the preferred upper limit is 3, 4, 5, 6, 8, 10, 12.
  • an alkyl group having 1 to 8 carbon atoms is selected, and more preferably, a chain alkyl group having 1 to 6 carbon atoms and a cycloalkyl group having 3 to 8 carbon atoms are selected, and still more preferably, A chain alkyl group having 1 to 3 carbon atoms is selected.
  • alkyl group examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, and new.
  • aryl group having 6 to 26 carbon atoms it is preferred to select an aryl group having 6 to 16 carbon atoms, more preferably an aryl group having 6 to 14 carbon atoms, and still more preferably, carbon is selected.
  • Specific examples of the aryl group include a phenyl group, a benzyl group, a biphenyl group, a p-tolyl group, an o-tolyl group, and an m-tolyl group.
  • An aryl group having 5 to 22 carbon atoms which may be selected from the group consisting of furyl, thienyl, pyrrolyl, thiazolyl, imidazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, fluorenyl and quinolinyl. Orolinic group and the like.
  • lithium ion battery of the present application is an improvement additive, when R 1 and R 2 is ethyl, the structural formula of the additive as shown in Formula I 1:
  • the additive molecule shown is a phosphate structure. Wherein, the two phosphorus-oxygen bonds of the phosphate ester are respectively connected to two ethyl groups, and the third phosphorus-oxygen bond forms a salt with the lithium ion.
  • the secondary battery additive of the present application may also be selected from at least one of the following compounds:
  • the additive of the present application is prepared by a substitution reaction of lithium iodide and a phosphate triester, and the reaction equation is as follows:
  • R 3 is selected from a substituted or unsubstituted C 1 -C 12 alkyl group, a substituted or unsubstituted C 6 -C 26 aryl group, a substituted or unsubstituted C 5 -C 22 aryl group, and the substituent is a halogen. .
  • R 1 , R 2 and R 3 are the same compound.
  • the additive of the present application can be prepared by the above method by changing the chemical structural formula of the starting material.
  • the specific conditions of the reaction are: the reaction is carried out in an inert gas atmosphere, the reaction temperature is 20 ° C to 30 ° C, the reaction time is 22 to 26 hours, preferably 24 hours, lithium iodide and phosphoric acid
  • the molar ratio of triethyl ester is from 0.9 to 1.1: 0.9 to 1.1.
  • the solvent is acetone
  • the molar ratio of lithium iodide to triethyl phosphate is 1:1
  • the reaction temperature is normal temperature
  • the time is 24 hours.
  • the present application provides a lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte containing the additive provided in the present application.
  • the additive has a mass content of 0.2 to 0.5% in the electrolyte. If the content of the additive is too low, a stable SEI film cannot be effectively formed on the electrode surface of the lithium ion battery, and further reaction between the negative electrode and the electrolyte cannot be effectively suppressed. At the same time, the addition of additives is too low, and the effect on the morphology and composition of the SEI film is not significant, and the SEI film impedance cannot be effectively reduced. Too low an additive content is not effective in improving the safety of the battery. If the additive content is too high, an excessively thick SEI film is easily formed on the electrode surface of the lithium ion battery, so that the SEI film impedance is increased.
  • the electrolyte contains electrolytes, organic solvents and additives, among which:
  • the organic solvent is selected from the group consisting of carbonates, sulfates, sulfones, nitriles, and the like, and the carbonate is selected from the group consisting of cyclic carbonates and chain carbonates; and sulfates are selected from the group consisting of cyclic sulfates, chain sulfates, and the like.
  • the organic solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, At least one of ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile or methyl sulfide.
  • the lithium ion battery is a wound lithium ion battery or a laminated lithium ion battery.
  • Step 1) In an argon atmosphere glove box, 134 g of lithium iodide was added to the reaction vessel, and 1 L of acetone was added. Then, 134 g of triethyl phosphate was added dropwise to the reaction system.
  • Step 2) The reaction system was stirred at normal temperature for 24 hours. After the reaction was completed, the crude reaction product was filtered to give a crude solid.
  • Step 3 The filtered solid was transferred into a reaction vessel, acetone was added, and stirred for 1 hour to dissolve and remove impurities. The crude product was filtered again for further purification.
  • Step 4) Step 3 was repeated twice, and the product was dried in a vacuum oven to obtain 138 g of a pure lithium ion battery additive compound in a yield of 86%.
  • the nuclear magnetic spectrum of the compound is as follows:
  • the additives in other embodiments of the present application are also prepared by the above methods using different raw materials.
  • the prepared additive was applied to a lithium ion battery, and the battery was prepared as follows:
  • mass ratio of graphite material: binder PVDF: conductive agent Super P 92:5:3 to prepare lithium ion battery anode pole piece.
  • the electrolyte is assembled into a lithium ion together with a cathode pole piece, an anode pole piece, and a polyethylene separator. battery.
  • the preparation steps of the other batteries were the same as in Example 1.
  • the preparation steps of the other batteries were the same as in Example 1.
  • the rate performance, cycle life and needling safety of the battery were tested in the test examples and comparative examples.
  • the detection methods are as follows:
  • Example 7 91.8 1064 No fire, no explosion Comparative example 1 86.2 972 Fire Comparative example 2 83.4 989 Fire Comparative example 3 81.2 991 Fire
  • the rate performance and cycle life test showed that the 3C discharge capacity and cycle life of the batteries in Examples 1 to 7 were higher than the comparative examples, indicating that the additive proposed in the present application is applied to a lithium ion battery, which can improve the film formation state of the SEI film and The composition reduces the polarization of the battery and improves the rate performance and cycle life of the battery.
  • the acupuncture test showed that the batteries in Examples 1 to 7 could not be fired and exploded, indicating that the additive proposed in the present application is applied to a lithium ion battery, and is more easily vaporized and decomposed when heated, releasing a phosphorus-containing radical, and the phosphorus-containing radical has The ability to capture hydrogen radicals in the system, thereby terminating the chain reaction, preventing the combustion or explosion of organic solvents, and improving the safety of lithium ion batteries.

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Abstract

本申请涉及一种添加剂，具体讲，添加剂选自如式(I)所示化合物中的至少一种。本申请还涉及该添加剂的制备方法及含有该添加剂的锂离子电池。本申请的添加剂有助于在锂离子电池的电极表面形成稳定的SEI膜，阻止溶剂分子的共嵌入，抑制负极与电解液的进一步反应；还可以在电极表面形成表面膜以隔绝空气，从而发挥更强的阻燃效果，提升电池的倍率性能、循环性能和安全性。

Description

一种添加剂，其制备方法及含有所述添加剂的锂离子电池 技术领域
本申请涉及锂离子电池材料领域，具体讲，涉及一种添加剂，其制备方法及含有所述添加剂的锂离子电池。
背景技术
在锂离子电池中添加少量的某些物质，能显著改善电池的性能，这些少量的物质称为添加剂。添加剂已成为当前锂离子电池研究领域的热点。
在锂离子电池充放电过程中，电极材料与电解液发生一系列电化学反应，生成了覆盖在电极材料表面的钝化层，即固体电解质相界面(SEI)膜。在锂离子电池中加入的少量添加剂能在电极表面优先发生反应，改善SEI膜组分及结构。优良的SEI膜允许锂离子自由通过，溶剂分子无法穿越，阻止电解液与电极材料的进一步反应，进而提高电池的倍率性能及循环性能。
锂离子电池在过充或受热时，电池内部易发生电解液的不可逆氧化分解或热分解，产生大量可燃性气体，易发生燃烧，并引起爆炸。电解液的燃烧反应通常是氢氧自由基参与的链式反应，因此在锂离子电池中加入添加剂，添加剂在受热时分解释放出自由基，以捕获高反应活性的氢自由基，可有效降低电解液的可燃性，提升锂离子电池的安全性。
鉴于此，特提出本申请。
发明内容
本申请的首要发明目的在于提出一种添加剂。
本申请的第二发明目的在于提出所述添加剂的制备方法。
本申请的第三发明目的在于提出含有所述添加剂的锂离子电池。
为了完成本申请的目的，采用的技术方案为：
本申请涉及一种锂离子电池添加剂，所述添加剂选自如式I所示化合物中的至少一种：
Figure PCTCN2017093186-appb-000001
其中，所述R1和R2各自独立地选自取代或未取代的C1～C12烷基、取代或未取代的C6～C26芳基，取代或未取代的C5～C22芳杂基，取代基为卤素；优选为C1～C8烷基，更优选为C1～C3烷基。
优选地，所述添加剂的结构式如式I1所示：
Figure PCTCN2017093186-appb-000002
本申请还涉及制备所述添加剂的方法，所述方法至少包括碘化锂与如式II所示的磷酸三酯通过取代反应制备得到如式I所示化合物，
Figure PCTCN2017093186-appb-000003
其中，R3选自取代或未取代的C1～C12烷基、取代或未取代的C6～C26芳基，取代或未取代的C5～C22芳杂基，取代基为卤素。
优选地，所述反应在惰性气体气氛中进行，反应温度为20℃～30℃，反应时间为22～26小时，碘化锂与磷酸三乙酯的摩尔比为0.9～1.1：0.9～1.1。
优选地，在惰性气体气氛中，向溶剂中加入碘化锂和磷酸三乙酯进行反应，得到式I1所示添加剂。
优选地，所述溶剂为丙酮，碘化锂与磷酸三乙酯的摩尔比为1：1，反应温度为常温，时间为24小时。
本申请还涉及一种锂离子电池，所述锂离子电池包括正极片、负极片、隔膜以及电解液，所述电解液中含有电解质、有机溶剂以及本申请所述的添加剂。
优选地，所述添加剂在电解液中的质量含量为0.1～0.5％。
本申请的技术方案至少具有以下有益的效果：
本申请涉及的添加剂有助于在锂离子电池的电极表面形成稳定的SEI膜，阻止溶剂分子的共嵌入，抑制负极与电解液的进一步反应。同时，添加剂的加入可以改善SEI膜的形貌及组成，促进并参与组分LixPOyFz的形成，降低SEI膜阻抗，减小极化，减小锂离子的消耗。由于本申请的添加剂对SEI膜的改善作用，加入该添加剂的锂离子电池倍率性能、循环性能得到提升。
在锂离子电池中，电解液在受热的情况下，容易发生氢氧自由基的链式反应。通过针刺实验体现本申请添加剂的安全性。进一步地，本申请的添加剂在受热时汽化分解，释放出含磷自由基，该含磷自由基具有捕获体系中氢自由基的能力，从而终止链式反应的继续进行，阻止有机溶剂的燃烧或爆炸，提升锂离子电池的安全性。
本发明的添加剂加入锂离子电池中，在电池出现火星或燃烧时，磷化合物分解生成磷酸的不燃性液态膜。同时，磷酸进一步脱水生成偏磷酸，偏磷酸进一步聚合生成聚偏磷酸。在这个过程中，不仅磷酸生成的覆盖层起到覆盖效应，而且由于生成的聚偏磷酸是强酸，是很强的脱水剂，使聚合物脱水而炭化，改变了聚合物燃烧过程的模式并在其表面形成表面膜以隔绝空气，从而发挥更强的阻燃效果，提升锂离子电池的安全性。
具体实施方式
下面结合具体实施例，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。
本申请涉及一种锂离子电池添加剂，所述添加剂选自如式I所示化合物中的至少一种：
Figure PCTCN2017093186-appb-000004
其中，R1和R2各自独立地选自取代或未取代的C1～C12烷基、取代或未取代的C6～C26芳基，取代或未取代的C5～C22芳杂基，取代基为卤素。
作为本申请锂离子电池添加剂的一种改进，R1和R2各自独立地选自C1～C8烷基，更优选为C1～C3烷基。
作为本申请锂离子电池添加剂的一种改进，R1和R2为相同的取代基。
在本申请的上述结构式中：
对于取代或未取代的C1～C12烷基，烷基可为链状烷基，也可为环烷基，位于环烷基的环上的氢可被烷基取代，所述烷基中碳原子数优选的下限值为1，2，3，4，优选的上限值为3，4，5，6，8，10，12。优选地，选择碳原子数为1～8的烷基，进一步优选地，选择碳原子数为1～6的链状烷基，碳原子数为3～8的环烷基，更进一步优选地，选择碳原子数为1～3的链状烷基。作为烷基的实例，具体可以举出：甲基、乙基、正丙基、异丙基、正丁基、异丁基、仲丁基、叔丁基、正戊基、异戊基、新戊基、己基、2-甲基-戊基、3-甲基-戊基、1,1,2-三甲基-丙基、3,3,-二甲基-丁基、庚基、2-庚基、3-庚基、2-甲基己基、3-甲基己基、异庚基、辛基、壬基、癸基。
对于碳原子数为6～26的芳基，优选地，选择碳原子数为6～16的芳基，进一步优选地，选择碳原子数为6～14的芳基，更进一步优选地，选择碳原子数为6～9的芳基。作为芳基的实例，具体可以举出：苯基、苄基、联苯基、对甲苯基、邻甲苯基、间甲苯基。
碳原子数为5～22的芳杂基，可选自：呋喃基、噻吩基、吡咯基、噻唑基、咪唑基、吡啶基、吡嗪基、嘧啶基、哒嗪基、吲哚基、喹啉基等。
作为本申请锂离子电池添加剂的一种改进，当R1和R2为乙基时，所述添加剂的结构式如式I1所示：
Figure PCTCN2017093186-appb-000005
所示添加剂分子为磷酸酯结构。其中，磷酸酯的两个磷氧键分别与两个乙基相连接，第三个磷氧键与锂离子成盐。
作为本申请锂离子电池添加剂的一种改进，本申请的二次电池添加剂还可选自以下化合物中的至少一种：
Figure PCTCN2017093186-appb-000006
为了实现本申请的第二目的，本申请的添加剂通过碘化锂与磷酸三酯通过取代反应制备得到，反应方程式如下所示：
Figure PCTCN2017093186-appb-000007
其中，R3选自取代或未取代的C1～C12烷基、取代或未取代的C6～C26芳基，取代或未取代的C5～C22芳杂基，取代基为卤素。
优选的，R1、R2、R3为相同的化合物。
本申请的添加剂，可通过改变初始原料的化学结构式，采用上述方法进行制备。
作为本申请制备方法的一种改进，反应的具体条件为：反应在惰性气体气氛中进行，反应温度为20℃～30℃，反应时间为22～26小时，优选24小时，碘化锂与磷酸三乙酯的摩尔比为0.9～1.1：0.9～1.1。
作为本申请制备方法的一种改进，所述如式I1所示添加剂的制备方法，至少包括：
在惰性气体气氛中，向溶剂中加入碘化锂和磷酸三乙酯进行反应，得到式I1所示化合物，其反应方程式如下所示：
Figure PCTCN2017093186-appb-000008
其中，溶剂为丙酮，碘化锂与磷酸三乙酯的摩尔比为1：1，反应温度为常温，时间为24小时。
为了实现本申请的第三目的，本申请提供一种锂离子电池，锂离子电池含有正极片、负极片、隔离膜以及电解液，电解液中含有本申请所提供的添加剂。
作为本申请锂离子电池的一种改进，添加剂在电解液中的质量含量为0.2～0.5％。如添加剂含量过低，则在锂离子电池的电极表面不能有效地形成稳定的SEI膜，不能有效地抑制负极与电解液的进一步反应。同时，添加剂的加入过低，对SEI膜的形貌及组成改善效果不显著，不能有效地降低SEI膜阻抗。过低的添加剂含量，对于电池安全性的改善效果也不明显。如添加剂含量过高，则在锂离子电池的电极表面易形成过厚的SEI膜，使SEI膜阻抗增加。
电解液中含有电解质、有机溶剂和添加剂，其中：
电解质选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、四氟草酸磷酸锂、LiN(SO2Rf)2、LiN(SO2F)(SO2Rf)、双三氟甲烷磺酰亚胺锂、双(氟磺酰)亚胺锂、双草酸硼酸锂、二氟草酸硼酸锂中的至少一种，其中，Rf＝–CnF2n+1，n为1～10的整数，优选六氟磷酸锂或LiN(SO2Rf)2。
有机溶剂选自碳酸酯、硫酸酯、砜类、腈类化合物等，碳酸酯选自环状碳酸酯、链状碳酸酯；硫酸酯选自环状硫酸酯、链状硫酸酯等。
具体可选自以下有机溶剂并不限于此：碳酸亚乙酯、碳酸亚丙酯、碳酸二甲酯、碳酸二乙酯、碳酸二丙酯、碳酸甲乙酯、甲酸甲酯、甲酸乙酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、乙酸乙酯、N-甲基吡咯烷酮、N-甲基甲酰胺、N-甲基乙酰胺、乙腈、甲硫醚中的至少一种。
优选地，所述锂离子电池为卷绕式锂离子电池或叠片式锂离子电池。
实施例1～7
实施例1～7的添加剂的结构式如由式I所示，其通过式II所示的磷酸三酯与碘化锂反应制备得到。式II所示的磷酸三酯中，取代基的具体选择如表1所示，制备得到的添加剂中的取代基如表2所示：
Figure PCTCN2017093186-appb-000009
表1
式II所示的磷酸三酯 R1 R2 R3
II1 乙基 乙基 乙基
II2 正丙基 正丙基 正丙基
II3 异丙基 异丙基 异丙基
II4 正丁基 正丁基 正丁基
II5 乙基 正丙基 乙基
II6 正己基 正己基 正己基
II7 苯基 苯基 苯基
表2
添加剂I R1 R2
I1 乙基 乙基
I2 正丙基 正丙基
I3 异丙基 异丙基
I4 正丁基 正丁基
I5 乙基 正丙基
I6 正己基 正己基
I7 苯基 苯基
具体地，式I1所示添加剂的制备方法为：
步骤1)：在氩气氛围的手套箱中，向反应容器中加入134g碘化锂，并加入1L丙酮。然后，将134g磷酸三乙酯滴加入反应体系中。
步骤2)：反应体系在常温下搅拌24小时。反应结束后，将反应粗产物过滤，得到粗产物固体。
步骤3)：将过滤后的固体转移入反应容器中，加入丙酮，搅拌1小时，以溶解并除去杂质。再次过滤粗产物，以进一步纯化。
步骤4)：重复步骤3两次，用真空烘箱干燥产物，得到纯净的锂离子电池添加剂化合物138g，产率86％。
所得产物的化学式和质量组成如下所示：
C4H10O4PLi(160.05g/mol)：C＝30.02％；H＝6.30％；O＝39.99％；P＝19.35％；Li＝4.34％。
所述化合物的核磁谱如下所示：
1H NMR(500MHz,CDCl3):δ4.11(4H),1.35(6H).
31P NMR(500MHz,D2O):δ2.97.
本申请其它实施例中的添加剂也通过上述方法，选用不同的原料进行制备。
将制备得到的添加剂应用于锂离子电池中，按以下方法制备电池：
按质量配比镍钴锰酸锂三元材料：粘结剂PVDF：导电剂Super P＝90:5:5制备锂离子电池阴极极片。按质量配比石墨材料：粘结剂PVDF：导电剂Super P＝92:5:3制备锂离子电池阳极极片。按质量配比碳酸乙烯酯：二甲基碳酸酯＝4：6配制电解液，其中六氟磷酸锂1.0mol/L，将实施例1～7制备的锂离子电池添加剂按0.1～0.5％的质量百分比加入该电解液中。将电解液分别与阴极极片、阳极极片、聚乙烯隔膜一起装配为锂离子 电池。
对比例1～3：
对比例1：按质量配比为碳酸乙烯酯：二甲基碳酸酯＝4：6配制电解液，其中六氟磷酸锂1.0mol/L，不使用添加剂，其它电池的制备步骤与实施例1相同。
对比例2：按质量配比为碳酸乙烯酯：二甲基碳酸酯＝4：6配制电解液，其中六氟磷酸锂1.0mol/L，将0.2％的三苯基亚磷酸酯加入该电解液中。其它电池的制备步骤与实施例1相同。
对比例3：按质量配比为碳酸乙烯酯：二甲基碳酸酯＝4：6配制电解液，其中六氟磷酸锂1.0mol/L，将0.2％的式III所示磷酸酯加入该电解液中。其它电池的制备步骤与实施例1相同。
Figure PCTCN2017093186-appb-000010
实施例和对比例的电解液中，各成分具体比例如表3所示。
表3
Figure PCTCN2017093186-appb-000011
其中，“-”表示未添加任何物质。
测试实施例和对比例制备电池的倍率性能、循环寿命和针刺安全性，检测方法如下：
电池倍率性能测试，按照如下步骤进行：
a)电池以3C倍率电流恒流充电至4.2V时，转恒压充电，至充电电流降至0.05C倍率电流时停止充电；
b)电池以3C倍率电流恒流放电至2.8V时停止放电；
c)计算电池放电容量与充电容量的百分比。
电池循环寿命测试，按照如下步骤进行：
a)电池以1C倍率电流恒流充电至4.2V时，转恒压充电，至充电电流降至0.05C倍率电流时停止充电；
b)电池以1C倍率电流恒流放电至2.8V时停止放电；
c)重复进行充放电循环至电池容量降至初始容量的80％时停止测试。
电池针刺试验，参照GB/T 31485-2015，按照如下步骤进行：
a)电池以1C倍率电流恒流充电至4.2V时，转恒压充电，至充电电流降至0.05C倍率电流时停止充电。
b)用直径5～8mm的耐高温钢针，以(25±5)mm/s的速度，从垂直于蓄电池极板的方向贯穿，贯穿位置宜靠近刺面的几何中心，钢针停留在蓄电池中；
c)观察1小时。
检测到的数据如表4所示。
表4
编号 3C放电容量/％ 循环寿命/次 针刺测试
实施例1 91.3 1016 不起火，不爆炸
实施例2 93.5 1005 不起火，不爆炸
实施例3 90.4 1053 不起火，不爆炸
实施例4 92.6 1047 不起火，不爆炸
实施例5 89.7 994 不起火，不爆炸
实施例6 92.1 1077 不起火，不爆炸
实施例7 91.8 1064 不起火，不爆炸
对比例1 86.2 972 起火
对比例2 83.4 989 起火
对比例3 81.2 991 起火
倍率性能及循环寿命测试表明，实施例1～7中电池的3C放电容量和循环寿命均高于对比例，说明本申请提出的添加剂应用于锂离子电池中，能够改善SEI膜的成膜状态及组成，降低电池的极化，提升电池的倍率性能及循环寿命。
针刺测试表明，实施例1～7中电池均不起火爆炸，说明本申请提出的添加剂应用于锂离子电池中，在受热时更易汽化分解，释放出含磷自由基，该含磷自由基具有捕获体系中氢自由基的能力，从而终止链式反应的继续进行，阻止有机溶剂的燃烧或爆炸，提升锂离子电池的安全性。
本申请虽然以较佳实施例公开如上，但并不是用来限定权利要求。任何本领域技术人员在不脱离本申请构思的前提下，都可以做出若干可能的变动和修改，因此本申请的保护范围应当以权利要求所界定的范围为准。

Claims (10)

  1. 一种添加剂，其特征在于，所述添加剂选自如式I所示化合物中的至少一种：
    Figure PCTCN2017093186-appb-100001
    其中，所述R1和R2各自独立地选自取代或未取代的C1～C12烷基、取代或未取代的C6～C26芳基，取代或未取代的C5～C22芳杂基，取代基为卤素。
  2. 根据权利要求1所述的添加剂，其特征在于，所述R1和R2各自独立地选自C1～C8烷基。
  3. 根据权利要求2所述的添加剂，其特征在于，所述R1和R2各自独立地选自C1～C3烷基。
  4. 根据权利要求1所述的添加剂，其特征在于，所述添加剂的结构式如式I1所示：
    Figure PCTCN2017093186-appb-100002
  5. 一种制备如权利要求1至3中任一项所述添加剂的方法，其特征在于，所述方法至少包括碘化锂与如式II所示的磷酸三酯通过取代反应制备得到如式I所示化合物，
    Figure PCTCN2017093186-appb-100003
    其中，R3选自取代或未取代的C1～C12烷基、取代或未取代的C6～C26芳基，取代或未取代的C5～C22芳杂基，取代基为卤素。
  6. 根据权利要求5所述的方法，其特征在于，所述反应在惰性气体气氛中进行，反应温度为20℃～30℃，反应时间为22～26小时，碘化锂与磷酸三乙酯的摩尔比为0.9～1.1：0.9～1.1。
  7. 根据权利要求5所述的方法，其特征在于，在惰性气体气氛中，向溶剂中加入碘化锂和磷酸三乙酯进行反应，得到式I1所示添加剂。
  8. 根据权利要求7所述的方法，其特征在于，所述溶剂为丙酮，碘化锂与磷酸三乙酯的摩尔比为1：1，反应温度为常温，时间为24小时。
  9. 一种锂离子电池，其特征在于，所述锂离子电池包括正极片、负极片、隔膜以及电解液，所述电解液中含有电解质、有机溶剂以及权利要求1至3中任一项所述的添加剂。
  10. 根据权利要求9所述的电池，其特征在于，所述添加剂在电解液中的质量含量为0.1～0.5％。
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