Fluoroethylene Carbonate as an Additive for γ-Butyrolactone Based Electrolytes

Compared to the actual state of the art electrolyte (SOTA) for Lithium-ion batteries (LIBs), a novel electrolyte with better safety and lower costs and at the same time equal electrochemical performance was developed and investigated in this work. This electrolyte consists of a mixture of gamma-Butyrolactone (GBL) as a solvent with fluoroethylene carbonate (FEC) as solid electrolyte interphase (SET) additive and lithium tetrafluro borate (LiBF4) as electrolyte salt. Raman spectroscopy measurements indicated that the salt is completely dissociated by the solvent GBL which is the reason for the enhanced ionic conductivity compared to the SOTA electrolyte. Cyclic voltammetry with a T44 graphite electrode revealed the positive influence of the SET additive FEC. The addition of FEC (1% by wt) enabled fully reversible de-/ intercalation of lithium ions into graphite. Furthermore, 1 M LiBF4 in GBL FEC (1% by wt) improved the coulombic efficiency of T44 graphite in the first cycle of constant current cycling experiments and in addition, no capacity fading was observed after 50 cycles. On NCM electrodes a stable cycling was observed as well, obtaining similar performance compared to the SOTA electrolyte, even at an increased cutoff potential of 4.6 V vs. Li/Li+. (C) 2013 The Electrochemical Society.