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

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 (Pyr(14)TFSI) 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 freestanding electrolyte membrane is prepared by a solvent casting method. The Pyr(14)TFSI 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 (t(Li+)), 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(-7) S cm(-1) at ambient temperature and a high t(Li+) 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 100 mAh g(-1) at 75 degrees 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. (C) 2015 Elsevier Ltd. All rights reserved.