Improved performance of Bi2O3-doped MnO2 cathode on rechargeability in LiOH aqueous cell

Many attempts have been made to make the zinc-manganese dioxide (Zn-MnO₂) alkaline cell rechargeable, but all investigations are pertained to the proton insertion mechanism into MnO₂. In this paper, a new class of rechargeable bismuth oxide-doped MnO₂ electrode in lithium hydroxide (LiOH) electrolyte is described. The doping and the appropriate pH selection of the aqueous electrolyte improved the electrochemical performance of the aqueous cell. Hence, with an aim to understand the role of bismuth oxide (Bi₂O₃) during the discharge process, doped MnO₂ cathodes are characterized by various techniques like secondary ion mass spectrometry, X-ray diffraction, Fourier transform infra-red spectroscopy, and transmission electron microscopy analysis. The results suggest that the influence of the large radius of the cation (Bi₂O₃; Bi (III) ion (0.96 Å)) cannot be integrated into the spinel structure, thereby, improving the rechargeability. The electrode reaction of doped MnO₂ in LiOH electrolyte is shown to be lithium insertion while preventing the formation of a spinel structure that leads to a major formation of manganese oxy hydroxides.