A QuaternaryPoly(ethylene carbonate)-Lithium Bis(trifluoromethanesulfonyl)imide-Ionic Liquid-Silica Fiber Composite Polymer Electrolyte for Lithium Batteries

Abstract

Poly(ethylene carbonate) (PEC) is known as an alternating copolymer derived from carbon dioxide (CO2) and an epoxide as monomers. Here, we describe a new quaternary PEC-based composite electrolyte containing lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt, N-n-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyr14TFSI) ionic liquid, and an electrospun silica (SiO2) fiber (SiF) with a submicron diameter in view of its possible applications in solid-state Li polymer batteries. A free-standing electrolyte membrane is prepared by a solvent casting method. The Pyr14TFSI ionic liquid enhances the ionic conductivity of the electrolyte as a result of its plasticizing effect. The electrochemical properties, such as ionic conductivity and Li transference number (tLi+), as well as mechanical strength of the electrolyte, are further improved by the SiF. We show that the quaternary electrolyte has a conductivity of the order of 10−7Scm−1 at ambient temperature and a high tLi+ value of 0.36 with an excellent flexibility. A prototype Li polymer cell using LiFePO4 as a cathode material is assembled and tested. We demonstrate that this battery delivers a reversible charge-discharge capacity close to 100mAh g−1 at 75°C and C/15 rate. We believe that this work may pave the road to utilize CO2 as a carbon source for highly-demanded, functional battery materials in future.