New Ionic Liquid Electrolytes And Their Applications In Lithium Secondary Battery

With the improving demand of higher power systems for electric vehicle (EV) and other large-scale electrochemical applications, Ionic liquids(ILs) electrolytes have attracted attention due to their unique properties, such as nonvolatility, nonflammability ,good thermal and electrochemical stability and high ionic conductivity. As a group of chemicals whose structure can be designed by our needs, they are considered as potential safe electrolyte. Besides, cathode materials and collectors are important parts for lithium secondary batteries. Before we apply these new kind of electrolytes in lithium secondary batteries, we must investigate compatibility of them .In this work, we investigated the polarization behavior of Al, Ta and Nb foil were was investigated in BF4- anion based ILs, BMI-BF4, PP14-BF4 and BMI-BF4·PC. Using SEM, EDX and XPS to analyse the whole polarization process. We found the high breakdown potential properties of Al foil in BMI-BF4, PP14-BF4 and the mixture of BMI-BF4·PC during the anodic polarization can be favored for high performance electrochemical devices. Second, we synethesized a guanidinium IL and investigated it's properties, including melting point ,thermal stablility ,viscosity, conductivity and electrochemical window. We found that 1g14TFSI have a melting point below -60℃, conductivity is 1.91mS cm-1, and it's electrochemical window is 4.2V at 25℃. Then we investigated the charge/disacharge capacities in three kinds of batteries including LiCoO2/Li, LiMn2O4/Li and LiFePO4/Li.We used several ways to improve their performances, such as the process of soaking , mixing ,and the addition of two electrolyte additives. Finally we found with the addition of GBL, this kind of electrolytes had best performances at a race of 1C in LiFePO4/Li batteries.