Chapter 10 - Fluorinated electrolytes based on lithium salts of strong brønsted acids

Abstract

Ionic conductivity in solvent-free solid polymer electrolytes (SPEs) has been extensively studied because of the potential applications for such materials in electrochemical power sources and devices, particularly in high-energy density rechargeable lithium batteries. The SPEs have many advantageous properties for such applications including good dimensional and thermal stability, a wide electrochemical stability window, better shape flexibility and manufacturing integrity, and improved safety. The present chapter focuses both on the synthesis of novel lithium salts based on polyanions with structures similar to that of LiTFSI and the structural, thermal, and electrochemical characterization of SPEs prepared using these salts in polyether hosts. The effect of cross-linking on ionic conductivity is also explored for several of the new lithium salts. SPEs were prepared from a series of new bis[(perfluoroalkyl) sulphonyl]diimide dilithium salts based on LiTFSI motifs (n _ 1, x _ 2, 4, 6, 8; Scheme 1) using either high-molecular-weight poly(ethylene oxide) (PEO) or cross-linked low-molecular-weight poly(ethylene glycol) (PEG) as polymeric hosts. Ionic conductivities for the SPEs were measured over a temperature range between ambient and 120°C and the findings have been shared in the chapter.