On the origin of the extra electrochemical capacity displayed by MO/Li cells at low potential

We report that the room temperature cycling of CoO/Li cells involving two processes, the reduction of CoO-->Co-0 and the growth of a polymer/gel-like film at high and low potentials, respectively, is extremely sensitive to cycling voltage ranges with the best results obtained when the cells are fully discharged. The low-voltage process is quite reversible over the 0.02 to 1.8 V range with a sustained capacity of about 150 mAh/g over a few hundred cycles. Within such a range of potential the polymer/gel-like is barely evolving while it vanishes as the oxidation potential is increased above 2 V. From the cyclic-voltammogram profiles we conclude that the origin of the low-voltage capacity is nested in the pseudocapacitive character of the in situ made polymeric/gel film. Tentative explanations based on comparisons with existing literature are made to explain such an unusual finding. (C) 2002 The Electrochemical Society.