Morphology and spatial distribution of ZnO formed in discharged alkaline Zn/MnO2 AA cells

A novel experimental technique was developed to extract the KOH solution from the porous zinc electrode in an inert environment. This technique permits the ZnO/electrolyte interface, the ZnO/Zn particle interface, and the spatial distribution of ZnO in the porous anode in commercial alkaline Zn/MnO2 AA batteries to be characterized for the first time by optical and scanning electron microscopy. Both type I and type II ZnO, previously observed in oxidation of planar zinc electrodes, were found in each completely discharged zinc particle in the porous electrode. The morphology, size, and location of these two ZnO forms strongly suggested that they were produced by a solution-precipitation route. The drain rate had a significant impact on the spatial distribution of ZnO in the anode. The segregation of ZnO near the separator became dominant at drain rates higher than 500 mA. The mechanisms by which the morphology and segregation of ZnO within the porous electrode could result in the reduced battery runtime are discussed. (C) 2003 The Electrochemical Society.