We describe the characteristics of materials prepared by the pyrolysis of over 50 different silicon-containing polymers, including polysilanes, polysiloxanes, and pitch silane blends. We investigate the electrochemical behaviour and structural properties of these materials as a function of their stoichiometry. Based on our findings we propose a structural phase diagram which illustrates possible structures of these materials Our results suggest that the electrochemical behaviour of these materials, as might be expected, varies with stoichiometry and structure. We recommend stoichiometric ranges to be avoided for lithium-ion battery applications.