Silicon Oxycarbides in Hard-Carbon Microstructures and Their Electrochemical Lithium Storage

Silicon oxycarbide (Si–O–C) glasses have been obtained by pyrolysis of powdery blends, composed of polysiloxane resin and phenol aralkyl resin, to 1000°C. Chemical and structural analyzes were conducted to investigate the characteristics of Si–O–C glass networks and disordered graphitic components. In the completely amorphous nature of the Si–O–C glasses, the carbon content largely increased with increasing the blend ratio of phenol aralkyl resin in a way contrary to the silicon content. The Si–O–C glasses have been evaluated as a negative electrode material for rechargeable lithium-ion batteries. Electrochemical measurements showed that delithiation capacities linearly increased to >800 mA h g −1 with increasing the silicon content in these Si–O–C glasses. Interestingly, the carbon-rich Si–O–C glasses had delithiation capacities of up to 580 mA h g −1 with good cyclability. 7 Li NMR analyzes indicated that the carbon-rich Si–O–C glasses have more hard carbon-like features and that at least two electrochemically active sites store lithium species.