Research on ternary electrolyte systems with N-butyl,methyl-piperidinium bis((trifluoromethyl)sulfonyl)imide ionic liquid based on radical polymerization method for lithium ion battery

• Method of radical polymerization is used to prepare electrolytes.
• PP14TFSI + LiTFSI + PMMA electrolytes have good electrochemical properties.
• Conductivity of 6.8 × 10−4 S cm−1 and tLi+tLi+ of 0.37 are achieve at room temperature.
• XPS show passivating film comprises multilayer films: Li2O and Li2CO3 layer.
• Model describing Li electrode/electrolyte interface are developed.

A kind of ternary electrolyte systems containing N-butyl,methyl-piperidinium bis((trifluoromethyl)sulfonyl)imide (PP14TFSI), LiTFSI and poly(methyl methacrylate) (PMMA) are prepared by the radical polymerization method. The resultant electrolyte displays the room temperature conductivity of 6.8 × 10−4 S cm−1 and the lithium ions transference number (tLi+tLi+) of 0.37. The composition and the status of the passivating film are very important for the process of the charge transfer and of the conduction. XPS analysis shows that the passivating film comprises Li2O and Li2CO3. The ternary electrolytes possess the electrochemical stability window of 4.5 V and better compatibility. The discharge curves of a Li/electrolyte/LiFePO4 cell at different rate indicate that, in generally, the capacity decreases gradually with the increasing of the rate and the cycle number. While the 30th cycle, the discharge capacity of 152.4 mA h g−1 (0.1 C), 126.5 mA h g−1 (0.2 C), 112.8 mA h g−1 (0.5 C) and 107.5 mA h g−1 (1 C) is still achieved. These properties allow the effective use of these films as electrolytes for the development of advanced polymer lithium ion batteries based on a LiFePO4 cathode.