[sup 2]H MAS NMR and SPECS Studies of γ-MnO[sub 2] Reduction in Zinc Alkaline Primary Batteries

Abstract

2H2H magic-angle spinning (MAS) NMR spectroscopy was used, in conjunction with step potential electrochemical spectroscopy (SPES), to investigate the reduction and H-insertion mechanisms of γ­MnO2γ­MnO2 in primary zinc alkaline batteries. Three electrolytic manganese dioxides (EMDs) were discharged in a deuterated alkaline electrolyte: a commercial EMD, and two synthetic EMDs, one prepared in a static electrolyte, and the other in a deuterated static electrolyte. Five distinct discharge processes were observed in the SPES plots, which were assigned to reduction of MnO2MnO2 near defects (1.45 V), reduction of ramsdellite and pyrolusite domains (1.1-1.3 V), formation of ZnMn2O4ZnMn2O4 (1.05 V), and reduction of Mn(III) to Mn(II) (0.95 V). The 2H2H signal intensities increase up to ca. 50% of discharge and then decrease on further discharge due to the growth of non-proton-containing oxides, such as Mn2O3,Mn2O3, Mn3O4,Mn3O4, and ZnMn2O4.ZnMn2O4. The 2H2H MAS NMR spectra of the 1.4 V discharged products of all γ­MnO2γ­MnO2 samples were dominated by an isotropic resonance at around 300 ppm, which is assigned to deuteron environments near defects (e.g., Mn-vacancy sites). The results were compared to those for three γ­MnO2γ­MnO2 model compounds with different levels of De Wolff disorder, Pr≈0.25,Pr≈0.25, 0.61, 0.99. © 2004 The Electrochemical Society. All rights reserved.