Polysilane/Acenaphthylene Blends Toward Si–O–C Composite Anodes for Rechargeable Lithium-Ion Batteries

Silicon oxycarbide (Si–O–C) composite materials have been prepared by pyrolysis of polysilane–acenaphthylene powdery blends to 1000°C under an inert gas atmosphere. Two branched polysilanes, (Ph₂Si)_0.85(PhSi)_0.15 and (MePhSi)_0.70(Ph₂Si)_0.15(MeSi)_0.15, were used in this study. Our thermal analyses confirm a high possibility that acenaphthylene significantly affects the microstructure of the Si–O–C composite materials that can be represented as SiC _x O_2(1–x) + yC (free carbon). The powdery blends in a weight ratio of 1:1 produced the Si–O–C composite materials with a high lithium storage capacity (ca. 500 mA h g₋₁ or higher) and excellent cyclability. These composite materials clearly showed a pseudo-voltage plateau upon electrochemical delithiation, as seen in the case of hard carbon. ₇Li NMR analyses showed the presence of at least two electrochemically active sites for lithium storage in the Si–O–C composite materials. Structural and electrochemical analyses support the idea that the Si–O–C composite materials have micropores where less-ionic lithium species can be formed. Increasing the ratio of acenaphthylene in the powdery blends resulted in low electrochemical performance because the free carbon contributed greatly to the microstructure of the resulting composite materials.