Melt-diffused binary solid-solid ionic mixture in a porous polymeric host as free-standing solid electrolyte for lithium batteries

Abstract Recently, ionic liquid based solid electrolytes is of great interest for the development of safe rechargeable lithium batteries. In this study, a solvent free approach to incorporate a novel type of binary mixture solid electrolyte composed of room temperature solid, crystalline, ionic liquid 1-butyl-1,4-diazabicyclo [2.2.2] octan-1-ium bis(trifluoromethanesulfonyl) imide (C4DTFSI) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) within an inert, porous host membrane is designed. The thermal, spectroscopic and electrochemical properties of the electrolyte at varied LiTFSI concentrations are studied. The Li+ transference number of the free-standing solid electrolyte is 0.49 at 25 ℃ having electrochemical stability of more than 5 V vs. Li/Li+. Moreover, the solid electrolyte assembled with LiFePO4 (LFP) cathode and Li anode in half cell configuration showed good cyclability (133 mAh g−1 after 100 cycles at 0.2 C) with Coulombic efficiency above 99 %.