The electrochemical and battery performances of a CH3–O–(C2H4O)3–CH3/LiN(SO2CF3)2 1:1 equimolar complex electrolyte were evaluated using [Li metal|Li metal], [LiFePO4|Li metal], and [LiNi1/3Mn1/3Co1/3O2|Li metal] cells. A relatively favorable surface was formed at the Li metal/electrolyte interface revealed by observation of the storage time dependence of the electrochemical impedance spectroscopy. A 3V-class [LiFePO4|Li metal] cell exhibited favorable capacity retention with little degradation after 600 cycles (2.5–4.0 V). A 4V-class [LiNi1/3Mn1/3Co1/3O2|Li metal] cell also exhibited good capacity retention of approximately 60% of the initial discharge capacity after 400 cycles (2.7–4.2 V), while the capacity retention decreased markedly upon increasing the upper charge cutoff voltage above 4.4 V.