Role of TiB2 and Bi2O3 additives on the rechargeability of MnO2 in alkaline cells

With an aim to understand the role of recently reported Ti-containing additives like TiB2 on the rechargeability of manganese oxide cathodes in alkaline cells, a redox reaction involving the chemical oxidation of Mn(OH)2 with H2O2 in KOH solution and a non-redox reaction involving the reaction of Mn(III) acetate with KOH have been carried out in the presence and absence of 1 wt% TiB2 and 0.5 wt% TiB2 + 4.5 wt% Bi2O3 additives. The solid products formed during the reactions have been analyzed by X-ray diffraction and a redox titration to determine the oxidation state of manganese while the filtrate has been analyzed to determine the amount of dissolved manganese with reaction time. The results suggest that irreversible reactions that follow the disproportionation reaction of dissolved Mn3+, which leads to the formation of electrochemically inactive phases like birnessite (δ-MnO2) and hausmannite (Mn3O4) and a consequent decline in capacity retention, are suppressed in the presence of the TiB2 additive, with the suppression being more effective when Bi2O3 is present along with TiB2.