双键功能化的离子液体与电极表界面作用机理的研究

The dissolution of positive active material into electrolyte and the oxidative decomposition of electrolyte on the electrode surface cause poor cycling performance and safety for lithium-ion batteries. In order to improve the above problem, ionic liquids which can form a passivating film on the electrode are used as new electrolyte solvents to replace the conventional organic carbonate in lithium-ion batteries.The SEI film can effectively suppress the secondary reaction occurred between electroyte and electrode. A series of double bond functionalized ionic liquids with low viscosity are prepared in this project,which can be designed by changing the structure of anion and cation and then used as solvents in electrolyte for lithium-ion batteries. This project is focused on the surface film formation on LiNi0.5Mn1.5O4 cathode material in different kinds of ionic liquid electrolyte and discuss the influencing factors to the surface film such as kinds of ionic liquid and temperature. The microstructure of ionic liquid, bonds broken and polymerization reaction are also investigated by the method ofquantum chemical calculation in order to confirm the formation of surface film on LiNi0.5Mn1.5O4 cathode material. At last, the interactional mechanism beween ionic liquid electrolyte and LiNi0.5Mn1.5O4 cathode material is illustrated by the results both of quantum chemistry calculation and experimental method so that the cycling performance and the safety of lithium-ion batteries can be enhanced. The expect results in this project will promote the development of commercial progress of electrolyte and provide the scientific proof and rationale for lithium-ion batteries.

针对正极活性物质在电解液中的溶解及电解液组分在电极表面的氧化分解，导致锂离子电池的循环性能和安全性能较差等问题，本项目旨在采用具有成膜作用的离子液体作为溶剂，在电极材料表面形成SEI膜，从而有效地抑制电解液与电极材料间的副反应发生。利用离子液体的可设计性，对阴阳离子结构进行调变，设计合成一系列低粘度的双键功能化的离子液体，并将其应用于锂离子电池电解液中。重点研究低粘度双键功能化的离子液体与镍锰正极表界面SEI膜的形成规律，分析离子液体的种类、组分及温度对正极表面SEI膜的影响。同时借助理论计算和分子模拟手段对离子液体的微观结构、化学键的断裂及聚合历程进行系统地研究，从理论上验证镍锰正极表面上SEI膜的形成。最终采用实验和理论计算相结合的方法，阐明离子液体与镍锰正极材料表界面的相互作用机理，提高锂离子电池的电性能，为锂离子电池商品化和性能提高提供重要的理论依据。

针对正极活性物质在电解液中的溶解及电解液组分在电极表面的氧化分解，导致锂离子电池的循环性能和安全性能较差等问题，本项目以设计合成具有成膜作用的双键功能化的离子液体为切入点，构建了高性能的锂离子电池离子液体电解液体系并对其进行了相关拓展研究。相关研究结果如下：(1) 合成了双键功能化的吡咯和哌啶离子液体，获得了性能优异的耐4.95V的离子液体电解液，在100周后较空白电解液的容量提高了5.6%，从机理上揭示了双键功能化离子液体在电极表面的作用。(2) 进行双键的拓展研究，设计合成了两种碳氧双键功能化的离子液体，获得了4.0V以上电池的LiTFSI基离子液体电解液体系，功能化的离子液体在电极表面形成稳定的保护膜，抑制了LiTFSI对集流体的腐蚀，提高了4.0V以上电池的性能，100个循环后，容量保持率为94%。而对于无离子液体添加的电解液来说，Li/LiMn2O4半电池的放电比容量在前10个循环，迅速地衰减至21mAh/g左右。此外，碳氧双键功能化的离子液体也有效地提高了磷酸铁锂电池的倍率性能，在1.5C时，放电比容量发挥率较无碳氧双键功能化的[N2224][TFSI]的提高了70%。通过研究工作证明了双键功能化离子液体均具有成膜作用，可在电极表面形成稳定的SEI膜，从而提高锂离子电池的电化学性能，为动力电池的发展提供了理论依据和应用基础。