基于LCST型聚甲基丙烯酸酯/离子液体凝胶的可逆温敏性智能锂离子电池电解质的制备及其性能研究

安全性问题严重制约了锂离子电池在动力与储能领域的规模应用，其产生机制是电池热失控。早前的防过热技术多属于“自杀式”的不可逆保护。目前为发展可逆热保护技术，报道了基于聚（N-异丙基丙烯酰胺）或甲基纤维素等温敏性水凝胶的热自保护电解质。然而，受限于水的电化学窗口窄（1.23V）的缺点，这些水凝胶较难应于现有有机电解质体系。为此，本项目将具有最低临界溶解温度的温敏性聚合物/离子液体凝胶引入电池中，制备温敏性电解质实现锂离子电池的过热保护；通过设计合成一系列不同的聚甲基丙烯酸酯和咪唑类离子液体，探索电解质体系的温敏特性与其聚合物和离子液体种类、聚合物及锂盐浓度等的关系，筛选出合适的聚合物/离子液体凝胶体系。在此基础上，制备温敏聚合物凝胶电解质，构建温敏性锂离子电池，考察该温敏性凝胶在实际电池环境中的电化学稳定性、温度响应机制及实际响应速率等相关应用性能，为发展可逆热自保护锂离子电池提供基础数据。

Lithium-ion batteries (LIBs) are successfully used as power sources in most of today’s portable electronics because they have high energy density, acceptable cycle life and low self-discharging. However, their safety issues are a major obstacle impeding the large-scale and high-power applications such as electric vehicles and renewable power stations. With the increasing of energy-density, battery safety issues are becoming more and more prominent. It is now well recognized that control of thermal runaway is very important for the development of safe LIBs. However, some early efforts are irreversible, one-time thermal protections and the LIBs are no longer functional afterwards. To develop reversible thermal runaway control strategies, nowadays, almost all these temperature-sensitive batteries were based on a typical thermo-responsive polymer, poly (N-isopropylacrylamine) (PNIPAM) and its copolymers in aqueous solutions. Although these strategies based on PNIPAM-type hydrogels achieve innate intelligent batteries with dynamic charge and discharge rate with respect to temperature variation and provide active thermal self-protection. However, these aqueous systems are clearly not directly applicable to LIBs that use organic electrolytes. In this project, similar to the above sol-gel transition mechanism of PNIPAM-type hydrogels, a new concept to achieve a non-volatile, thermoreversible, and self-protective polymer/ionic liquid (PIL) system with the lower critical solution temperature (LCST) behaviour is proposed. Introducing an unusual LCST behaviour of polymer (methacrylate) in imidazolium-based ionic liquids (ILs) can lead to new electrolytes that can timely sense the temperature changes in the microenvironment of LIBs, promptly trigger shutdown to protect the battery at risky temperatures, and allow the battery to resume normal function on cooling. Instead of the volatility and flammability of organic electrolytes, some imidazolium-based ILs are utilized as solvents and improve the ionic conductivity of polymer solutions. A series of poly(methacrylate) derivatives with different chemical structure and molecular weight and imidazolium-based ILs with different alkyl chains are designed and synthesized, and theirs phase separation behaviors and physicochemical and electrochemical properties of prepared different PILs are investigated. Thermoresponsive phenomena and structure-property relationships of the PIL systems will be uncovered. The mechanism of control over the responsive temperature, the response time, and reversibility of the PIL system and corresponding thermal responsive and electrochemical performance in the real battery are investigated. It can be expected that the research results from this project would provide scientific basis and theoretical supports for building smart lithium-ion batteries in the future.