Pyrolysed pitch-polysilane blends for use as anode materials in lithium ion batteries II: the effect of oxygen

As previously reported, blends of pitch and polysilanes, (Me₂Si)_x(PhMeSi)_y, with various pitch/polysilane ratios were pyrolysed at 1000 °C [W. Xing, A.M. Wilson, G. Zank, J.R. Dahn, Solid State Ionics 93 (1997) 239]. Some of the pyrolysed mixtures demonstrated large reversible capacities for lithium insertion (600 mA h g⁻¹), small irreversible capacities (150–200 mA h g⁻¹) and small hysteresis between charge and discharge cycles. Here, we investigate the role of the oxygen in these materials. The magnitude of the irreversible capacity and hysteresis are correlated to the oxygen content. This suggests that these materials are disordered carbons containing nanodispersed silicon oxycarbide clusters and not nanodispersed silicon, as was previously suggested. This does not change our opinion that pyrolysed pitch-polysilane blends are good alternatives to carbons for anode materials in lithium ion batteries.