Carbon anodes for Li-ion cells were prepared by the in situ polymerization of olefins such as propylene and ethylene in the channels of a sepiolite clay mineral. Upon dissolution of the inorganic framework, a disordered carbon was obtained. The carbon was tested as an anode in coin cells, yielding an average reversible capacity of 633 mAh/g discounting the first cycle, which is 1.70 times higher than the capacity delivered by graphitic carbon assuming 100% efficiency. The coulombic efficiency was higher than 90%. Morphologies of the clay, carbon/clay composite, and final carbon were examined by TEM. The structure of the carbon and its electrochemical performance were monitored in situ by small angle x-ray scattering.