双层界面膜成膜添加剂的设计与成膜机理研究

The enhancement of energy density, safety and endurance is an important key on the development of power lithium ion battery. It’s an effective way to improve the energy density of lithium ion battery utilizing the high voltage cathode materials. However, electrolyte solvents and organic carbonate esters sustain decomposition on highly oxidative surfaces of these charged cathodes. The aim of this project is to solve this problem by using new type electrolyte additives to avoid the interface reaction between them. The design of the new type electrolyte additives and formation mechanism are studied by theoretical calculation and experimental methods. Density functional theory and linear sweep voltammetry are utilized to calculate and test the oxidation potential of the additives. Organic electro-oxidation technique is adopted to prepare interfacial film and analyze its component, formation mechanism, thermostability and chemical stability. The feature of this project is the design of new double-layer interfacial film formation additives. The electrodes with the double-layer interface films formed through different methods are studied to find out an effective method to prepare low cost high stability film. The rate capability, cycle stability and safety of battery with new type film additives were characterized using electrochemistry methods. Finally, the improvement on the battery performance of the power lithium ion battery can be achieved through the application of the new type additives.

提高动力锂离子电池的能量密度、安全性和耐久性是其大规模应用的前提，高电压正极材料的使用是提高锂离子电池能量密度的有效途径。本研究针对锂离子电池高电压正极材料与电解液易于发生界面反应而导致电池性能恶化的问题，采取理论计算和具体实验、测试技术相结合的方法，从密度泛函理论计算出发，结合线性扫描伏安法等电化学技术设计并优选高电压正极成膜添加剂，采用有机电氧化技术重现并制备界面膜，分析其成分、探讨成膜机理。本项目的特色之处在于，利用双电位成膜或组装高稳定性链尾，开发新型高稳定双层界面膜正极成膜添加剂。比较研究不同功能化手段形成的双层界面膜对电池性能的影响，探索制备高稳定性双层界面膜添加剂的便捷途径。完成新型高电压电解液在半电池及全电池中的全性能应用评估和优化，考察其对电池循环性能、倍率性能及安全性的影响规律。最终实现基于高电压正极材料的高能量密度动力电池性能的整体提升。

电子类产品更新换代及电动汽车的快速发展对锂离子电池的能量密度要求日益剧增。采用高比容量或高工作电压的正极材料可以提高锂离子电池的能量密度。但高的工作电压总是伴随着严重的电解液分解和正极材料中金属离子的溶解。这些问题源于正极材料和电解液之间差的界面稳定性，最终导致电池低的库伦效率和差的循环性能。本项目采取理论计算和具体实验技术相结合的方法，从密度泛函理论计算出发，结合线性扫描伏安法等电化学技术设计并开发出系列高电压正极成膜添加剂，并分析与探讨了添加剂在电池体系中的成膜机理。三（五氟苯基）硼具有较高的LUMO和较低的HOMO，能先与电解液氧化和还原，是一种良好的成膜添加剂。实验证实，这种化合物能在正极和负极表面同时成膜，促进电池体系的循环。三（五氟苯基）膦（TPFPP）作为电解液添加剂用于改善Li1.17Ni0.25Mn0.58O2 (OLO)/graphite 全电池的高压循环性能。充放电测试表明添加TPFPP 显著提高了OLO/graphite 全电池的容量保持性能。在电解液中加入0.5 wt. % TPFPP 后，电池在0.3 C 下循环200次后容量保持率由62.6%提高到90.6%。含Ti的化合物四（三甲基硅基）钛酸酯作为电解液成膜添加剂，可以产生有机无机复合的双层界面膜，有机成分能有效隔离电解液与电极的持续接触，其中的无机成分可以迅速消耗电解液中的水和酸，避免电极的刻蚀，有效促进电池的循环稳定性。在执行过程中，发现一些反常现象，如“变质”的电解液效果更好，并对其进行了机理探索。在顺利完成计划的同时，还增加了聚合物固体电解质修饰界面的研究内容，并取得了一定成果。