Lithium Ion Conductivity of Polymer Electrolytes Based on Insoluble Lithium Tetrakis(pentafluorobenzenethiolato)borate and Poly(ethylene oxide)

Lithium ion conductivity and the ion transport mechanism for heterogeneous polymer electrolytes composed of insoluble lithium tetrakis(pentafluorobenzenethiolato)borate (LiTPSB), which has weak interaction between the lithium ion and the counteranion, and high molecular weight poly(ethylene oxide) (PEO) have been investigated. In addition, the ionic conductivity of polymer electrolytes based on low molecular weight poly(ethylene glycol) dimethyl ether (PEGDME) or amorphous poly[tetra(ethylene glycol) methyl ether methacrylate] (PEGM) was also researched. LiTPSB is not soluble in any solvents and polymers, however its composites with poly(ether)s exhibited ionic conductivity. The lithium ion transport mechanism in the interfacial phase between LiTPSB and PEO was proposed. The apparent activation energy of ionic conductivity was smaller for LiTPSB/PEO (salt ) than lithium trifluoromethanesulfonate (Litrif)/PEO. A high lithium ion transference number of 0.65–0.75 was also obtained for the insoluble LiTPSB/PEO system. A new peak of the melting point of PEO was observed in differential scanning calorimetry measurements of LiTPSB/PEO polymer electrolytes, and it suggested the formation of a new ion conducting phase in the interfacial region between LiTPSB and PEO.