Rechargeable Alkaline Manganese Dioxide Batteries: I . In Situ X‐Ray Diffraction Investigation of the (EMD‐Type) Insertion System

The electrochemical insertion and deinsertion of H + was investigated by studying its influence on the evolution of the crystallographic structure of of EMD type (electrochemical method deposition) during the discharge and recharge processes of an alkaline battery, using in situ x‐ray diffraction. During the first discharge, proton insertion up to H + per with concomitant electron transfer causes an expansion of the crystalline cell. The lattice expansion is attributed to the reduction of Mn 4+ ions to Mn 3+ ions which have a larger ionic radius. Between 0.5 to 0.8 H + inserted the long‐range order is lost and the presence of a quasi‐amorphous phase which could not be identified is detected. This amorphous phase is reduced to (or ) and to when more than 0.8 H + is inserted. On recharge, the is oxidized to (or ) leading to poor cycling of the battery. When the discharge is limited to 0.8 H + the battery can be recharged and cycled many times. Still more cycles can be obtained when the discharge is limited to 0.5 H + , corresponding to the range where the structure is retained. In this range, strong hysteresis in the voltage curves indicated that while there is structural reversibility, structural changes arise at different voltages on discharge and recharge.