离子液晶基二维快速锂离子传导通道的设计、构筑及其导电机理研究

Common lithium salts such as LiPF6, LiClO4, and LiBF4 used in lithium secondary battery are insulators at solid state unless they are dissolved in organic solvents or plasticizers like flammable dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate. It means that such electrolyte composed of lithium salts and flammable solvents reveals the disadvantages of poor thermal stability, inflammability and the risk of explosibility. To the best of our knowledge, there is no relevant report regarding the research and application of safe and self-conductive lithium salts. In this project, a series of new non-flammable ionic-liquid-crystal based lithium salts (LiILCs) are particularly designed and synthesized by the reaction of boric acid, lithium hydrate and alkyl substituted two carboxyl imidazole with the characteristic of ionic liquid crystal, showing self-conductivity and the similar molecular structure with the promising lithium bis(oxalato)borate (LiBOB). Hot-stage polarizing microscope, small angle X-ray scattering, X-ray diffraction, differential scanning calorimetry, electrochemical workstation and thermogravimetric analysis are used to evaluate the comprehensive properties of the resulting LiILCs, such as the self-assembly behavior, crystallization, ionic conductivity, electrochemical stability, thermal stability and so on. In addition, the combination of time-resolved Fourier transform infrared (FTIR) with two-dimensional correlation FTIR spectroscopy is used to detect the microcosmic conductive mechanism and probe the relationship between the self-assembly and the conducting mechanism of the prepared LiILCs.

LiPF6、LiClO4、LiBF4等常见锂盐自身不具备锂离子导电能力，使用前需将其溶解于碳酸酯类小分子溶剂或增塑剂。由此获得的“电解质”表现出热稳定性差、易燃、易爆等缺陷，目前尚未见安全型、自身可导电锂盐的开发与应用报道。本项目在大量文献调研及前期工作基础上，以具有离子液晶特性的烷基取代二羧基咪唑、硼酸、氢氧化锂等为主要原料，设计并合成出与最具应用潜质的新型锂盐（LiBOB）有类似分子结构，同时自身可导电的难燃性离子液晶型锂盐（LiILCs）。采用热台偏光显微镜、示差扫描量热分析、电化学工作站、热重分析等手段全面评价所得LiILCs的自组装行为（二维快速离子传导通道的构筑与控制）、离子导电性、电化学稳定性、热稳定性等综合性能；采用时间分辨及二维相关红外技术剖析所得LiILCs在外电场作用下的微观离子导电机理，探索LiILCs的自组装行为与其微观离子导电机理。

以具有离子液晶特性的烷基取代咪唑衍生物、硼酸、氢氧化锂为主要原料，设计并成功合成了一系列与双草酸硼酸锂具有类似分子结构，同时自身又具有优异离子导电性及难燃性质的离子液晶型锂离子导体，采用核磁共振技术表征了所得离子导体的化学结构。通过等温结晶技术构筑并改变锂离子导体内的二维快速传导通道，并采用示差扫描量热分析、X射线衍射、二维相关红外光谱、电化学分析等方法系统地研究了所开发离子液晶基二维快速离子传导通道的微观信息，阐明了高速离子传导通道的构效关系，推导了离子传输的本构方程，为全固态安全型可充放锂离子电池的开发提供了理论指导和数据支持。