Hetaerolite Profiles in Alkaline Batteries Measured by High Energy EDXRD

Energy dispersive X-ray diffraction (EDXRD) with photons of high energy and high flux is used to map crystalline discharge products within alkaline AA cells following discharge at various rates: C/160, C/80, C/40, C/20, C/10, and C/5. During the study, the sealed cells are never opened and thus never exposed to air. The technique's resolution allows the various manganese oxide discharge products to be distinguished, which has previously proven difficult. In particular, colocalized Mn3O4 (hausmannite) and ZnMn2O4 (hetaerolite) phases are resolved at C/160, C/80, and C/40 rates. Following more rapid discharge at C/20, no hausmannite is observed: instead, two well-defined zones result, one consisting only of hetaerolite, and the other only of alpha-MnOOH (groutite), with a small transition region where both phases are detected. Modeling suggests the observed hetaerolite-groutite boundary positions are consistent with hetaerolite formation in regions of greater active material utilization. Radial hetaerolite and hausmannite profiles are calculated and found to be a function of the discharge current, which also determines discharge capacity. Results also show formation of a alpha-MnOOH phase from oxidation states MnO(1.)7 to MnO(1.)53 with relatively little gamma-MnOOH character. (C) 2014 The Electrochemical Society. All rights reserved.