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注册: 2012-06-04
专业: 应用高分子化学与物理

[交流] 锂电池电解液阻燃添加剂技术进展已有1人参与

锂电池电解液阻燃添加剂技术进展

限制电动汽车普及的主要因素，主要包括价格、基础设施、续航里程和安全性。事实上，价格、基础设施和续航里程都可以通过其他方式进行弥补和改进；而安全性，是用户最关心的，也是电动汽车和锂电池生产商必须解决的重要问题。

锂电池电解液一般采用有机溶剂，在过热条件下易燃，因此在电解液中加入阻燃添加剂是提高电池安全性最经济有效的方法之一。目前用于锂离子电池阻燃的物质主要包括磷酸酯类、亚磷酸酯类、有机卤代物类和磷腈类等。

烷基磷酸酯类化合物（如TMP、TEP等）是最早研究用于锂离子电池的阻燃剂，但其粘度较大、电化学稳定性差，在提高电解液阻燃性的同时会对电解液的离子导电性和电池的循环可逆性造成负面影响。利用F元素取代烷基上的H得到氟代烷基磷酸酯（如TFP、BMP、TDP），可以提高化合物的还原稳定性及阻燃效果。此外，磷酸甲酚二苯酯（CDP）和磷酸二苯一辛酯(DPOF)等芳香基磷酸酯也具有良好的阻燃效果。

除了磷（V）化合物之外，磷（Ⅲ）化合物也是有效的阻燃添加剂。磷（Ⅲ）化合物与磷（V）化合物比较，更有利于SEI膜的生成，并且前者能使五氟化磷（PF5）失活。在磷（Ⅲ）化合物中，三（2，2，2-三氟乙基）亚磷酸酯（TTFP）不仅能够降低电解液的可燃性，而且能够提高锂离子电池的循环性能，是一种比较有潜力的阻燃剂。

有机卤代物阻燃剂主要是指氟代有机物，包括氟代环状碳酸酯、氟代链状碳酸酯和烷基-全氟代烷基醚等。氟代有机物具有较高的闪点，同时氟取代氢原子后会降低溶剂分子的含氢量及其可燃性，将其添加到有机电解液中可以提高电解液的安全性。氟代环状碳酸酯类化合物，如CH2F-EC、CHF2-EC 和CF3-EC 都具有较好的化学和物理稳定性，较高的闪点和介电常数，能够很好的溶解锂盐电解质并与其它有机溶剂混溶。

磷腈类化合物是指小分子的环状或高分子线性磷氮化合物，一些磷腈化合物自身有比较好的离子导电性，可单独用作锂离子电池电解液，如含寡居氧化乙烯侧链的线性多聚磷腈，离子导电率可达10-5S/cm。并且，这些聚合物有比较高的分解温度（约235℃），放热量适中。如寡聚环氧乙烯侧链的环状磷腈三聚体在保持离子导电性的同时具有很好的阻燃性能。

虽然很多种类的电解液添加剂都一定程度上起到了阻燃的效果，但是由于添加剂的物理性质（粘度大等）、化学或电化学不稳定等性质，它的加入往往又会对电池的其他方面性能造成负面影响。因此，在保持电池各方面电化学性能的同时，开发具有有效阻燃性能的添加剂是锂离子电池电解液阻燃添加剂未来发展的方向。

此外，热聚合添加剂也是锂离子电池安全性添加剂研究的一个重要方向。热聚合添加剂能够在一定温度下（如110～150℃）发生聚合反应，从而阻断电池充放电，阻止电池温度的上升，避免“热失控”的发生。热聚合的单体需满足电化学稳定性好、热稳定性好，且不影响锂离子电池内部锂离子传导。目前国内对该类热聚合型添加剂的研究尚少，在其实现应用之前还需投入大量的研究工作。

2013中国锂电池电解液研讨会将于7月25-26日在上海召开。来自国内电解液行业领军企业的专家将做《锂电池电解液阻燃添加剂技术进展》的主题报告。

Technical Progress of Lithium Battery Electrolyte Flame Retardant Additives

The major limits of promotion of electric vehicles (EV) include the price, infrastructure, mileage, and safety. Actually, price, infrastructure, mileage issues can be revamped or improved by other ways; while safety, is the most concerned by customers, also the must be solved problem of EV and lithium battery manufacturers.

Lithium battery electrolyte commonly used organic solvents, it is flammable in overheat condition. Therefore, adding flame retardant additives into the electrolyte is one of the most cost-effective ways to improve battery safety. Currently, the LIB flame retardant additives include phosphate ester, phosphite ester, organic halides and phosphazene etc.

Alkyl phosphate ester compounds (such as TMP, TEP etc.) are the firstly studied flame retardant additive for lithium ion batteries. But its viscosity is high and electrochemical stability is poor. Although it can improve the electrolyte flame retardance; while at the same time, it may cause negative effects to the electrolyte ionic conductivity and battery cycle reversibility. Use the F element to substitute the H element of the alkyl phosphate ester then get the fluoroalkyl phosphate ester (such as TFP, BMP, TDP) can improve its reduction stability and flame retardant. In addition, cresyl diphenyl phosphate (CDP), diphenyl isooctyl phosphate (DPOF) and other aromatic phosphate ester also has good flame retardant effect.

In addition to phosphorus (V) compounds, phosphorus (Ⅲ) compounds are also effective flame retardant additives. Phosphorus (Ⅲ) compounds compared with phosphorus (V) compounds, it is more conducive to the formation of SEI membrane and it can make the phosphorus pentafluoride (PF5) loss of activity. In phosphorus (Ⅲ) compounds, Tris(2,2,2-trifluoroethyl) phosphite ester (TTFP) can not only reduce the flammability of the electrolyte, but also improve the cycle performance of lithium-ion batteries, it is a potential flame retardant additive.

The organic halide flame retardant additive mainly refers to organic fluorine compounds, includes the fluorinated cyclic carbonate ester, fluorinated chain carbonate ester and alkyl - perfluoroalkyl ether etc. Fluorinated organic compounds have a high flash point and a fluorine atom substituted for a hydrogen atom will reduce the hydrogen content and flammability of the solvent molecules. Adding it to the organic electrolyte can improve its safety. Fluorinated cyclic carbonate ester compounds such as CH2F-EC, CHF2-EC and CF3-EC have high chemical and physical stability, high flash point and permittivity. They are capable of dissolving lithium salt well and miscible with other organic solvents.

Phosphazene compounds refer to small molecule cyclic or macromolecule linear phosphorus-nitrogen compounds. Some phosphazene compounds have good ionic conductivity, can be used alone as a lithium-ion battery electrolyte. For example, the ionic conductivity of the linear multi polyphosphazene with widowed ethylene oxide side chain can reach 10-5S/cm. Moreover, these polymers have relatively high decomposition temperature (about 235 ℃) and moderate heat release. For instance, cyclic phosphazene trimer with oligomeric oxirene side chains has excellent flame retardant while keeping good ionic conductivity.

Although many kinds of electrolyte additives have played a certain extent of flame retardant effect, but they may bring negative effects to the other performance of battery due to their peculiar physical properties (such as high viscosity etc.), chemical or electrochemical instability and other characteristics. So to develop an effective flame retardant additive and maintaining all the electrochemical performances of the battery is the future direction.

In addition, the thermal polymerization additive is also an important research direction of lithium-ion battery safety additives. Thermal polymerization additives can produce polymerization reaction at a certain temperature (such as 110 ~ 150 ℃), thus blocking the battery charge and discharge, prevent the battery temperature rise and avoid thermal runaway. The monomer that used for thermal polymerization must be with high electrochemical stability, thermal stability, and does not influence the internal lithium ion conductive of the lithium ion battery. At present, the domestic study on the thermal polymerization additive are very few, we need to invest a lot of research work to make it become applied.

2013 China LIB Electrolytes Conference will be held on 25-26 July in Shanghai, China. In the upcoming conference, expert from LIB Electrolytes industry leading company will deliver a speech on “Technical Progress of Lithium Battery Electrolyte Flame Retardant Additives”

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2013-07-01

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