Structures and lithium storage performance of Si-O-C composite materials depending on pyrolysis temperatures

A polymer blend of a partially-branched phenyl-substituted polysilane, (Ph2Si)0.85(PhSi)0.15, and polystyrene (1:1 by weight) has been prepared to produce silicon oxycarbide (Si-O-C) composite materials through pyrolysis in the temperature range 700-1200 °C under an argon atmosphere. According to elemental analysis results, carbon is a major constituent in a series of Si-O-C composite materials obtained in this study. Completely amorphous features were observed for the composite materials obtained between 700 and 1100 °C, while a clearly discernible crystalline evolution of silicon carbide (SiC) phases was found in a glass network of the composite material obtained at 1200 °C. This paper also deals with electrochemical lithiation and delithiation for the series of Si-O-C composite materials. The first delithiation capacities of these composite materials were highly dependent on pyrolysis temperatures. The composite material obtained at 700 °C had the maximum delithiation capacity of ca. 800 mA h g−1, while the composite material obtained at 1200 °C showed the minimum delithiation capacity of ca. 330 mA h g−1. The crystalline evolution of SiC phases is thought to cause such a drastic decrease in delithiation capacity at 1200 °C.