Electrolyte performance of CH3-(OC2H4)(3)-CH3 (TG)/LiN(SO2F)(2) (LiFSI) 1: 1 molar mixture was investigated for high-safety lithium-ion secondary batteries by various physicochemical and electrochemical measurements. The TG-LiFSI electrolyte formed 1: 1 complex, and showed relatively high thermal stability. Stable charge/discharge (intercalation/deintercalation) of lithium ions with both LiFePO4 positive electrode and graphite negative electrode were enabled with high coulombic efficiency and long cycles. Moreover, long cycle charge/discharge operations of [LiFePO4 positive electrode vertical bar TG-LiFSI electrolyte graphite negative electrode] cell was achieved with 82% of capacity retention at 100 cycles. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3582822]