Application of Si–C–O glass-like compounds as negative electrode materials for lithium hybrid capacitors

The Si-C-O glass-like compound (a-SiCO) was applied to a negative electrode of a lithium hybrid capacitor (LHC) with activated carbon positive electrodes. The performance as a negative electrode (by a three-electrode system) and LHC (by a two-electrode system) was evaluated in LiClO4 (EC-DEC) and LiBF4 (PC) electrolytes. With a-SiCO reversible insertion/extraction of lithium ions at high current densities (0.5-2.0 A g^[-1]) was possible. By prior short-circuiting of the negative electrode with lithium metal in the electrolytes for appropriate periods, the charge/discharge performance of the assembled LHC compared favorably with an electric double layer capacitor (EDLC) made of the activated carbon used for LHC. The cycle performance of the LHC was better but the capacitance was smaller in the LiBF4 (PC) electrolyte than in LiClO4 (EC-DEC) electrolyte. Smaller capacitance is mainly due to lower electric conductivity and higher viscosity of LiBF4 (PC) electrolyte than LiClO4 (EC-DEC) electrolyte. The energy density of the assembled LHC reached a maximum of about three times that of EDLC, with the power density comparable to that of the EDLC.