Structural and electrochemical characterization of glassy carbon prepared from silicon-doped polymethacrylonitrile/divinylbenzene copolymer

There has been a great deal of discussion on the potential role of heteroat oms in carbons intended for lithium ion intercalation. Previous observation s have been mixed, ranging from beneficial to detrimental effects on interc alation capacity, irreversible losses, and charge efficiencies. The introdu ction or substitution of silicon into a carbon matrix prepared by chemical vapor deposition has demonstrated a positive effect. The present study conc erns substitutional effects in disordered carbons synthesized from polymer precursors. Solid-state nuclear magnetic resonance, photoacoustic IR spectr oscopy, X-ray fluorescence, and high-resolution transmission electron micro scopy were used to follow the modified carbon synthesis. Silicon is success fully incorporated into the polymer matrix by copolymerizing the precursors with tetravinylsilane. On oxidative stabilization and pyrolysis, however, the Si-C connectivity is replaced by Si-O coordination. These silicon speci es appear to be discrete, and no evidence for either a crystalline or amorp hous secondary SiO2 phase is seen. These silicon species have a profound ef fect on the electrochemical performance. Irreversible loss processes are gr eatly increased, and charge efficiencies are decreased when compared to non substituted controls. (C) 1999 The Electrochemical Society. S0013-4651(98)1 0-010-1. All rights reserved.