Influence of mixing carbonate-modified siloxane into 1 M (M: mol L−1) LiPF6-ethylene carbonate (EC)/ethylmethyl carbonate (EMC) (mixing volume ratio = 3:7) mixed solvent electrolytes on charge–discharge cycling properties of lithium is examined. As siloxane, 4-(2-bis(trimethylsilyloxy)methylsilylethyl)-1,3-dioxolan-2-one is investigated. Charge–discharge cycling efficiencies of lithium metal anodes are improved and impedance of anode/electrolyte interface decreases by mixing siloxane, compared with those in 1 M LiPF6-EC/EMC alone. Mechanism of enhancement of lithium cycling efficiency is considered to be due to the suppression of excess reduction of LiPF6-EC/EMC by lithium and growth of surface film (SEI, solid electrolyte interphase) on lithium. Infrared study indicates that SEI formed in LiPF6-EC/EMC with siloxane contains more inorganic compounds than that in LiPF6-EC/EMC alone. Better cycling behavior of α-Fe2O3 and Si–SiO2–carbon composite anodes is obtained by mixing siloxane. Thermal behavior of electrolyte solutions toward graphite-lithium anodes is evaluated with a differential scanning calorimeter. Heat-output of graphite–lithium anodes with 1 M LiPF6-EC/EMC electrolyte solutions tends to decrease by mixing siloxane.