Studies on electrochemical performance of partially reduced MnO2 used as cathode for MH–MnO2 rechargeable battery

Cyclic voltammograms show that the reversibility of the manganese dioxide (MnO2) electrode is improved by means of using partially reduced samples. The crystal lattice of the intermediate is transformed by reduction. Formation of the manganous ion is very limited before the electrode potential reaches −0.4 V (versus Hg/HgO), thus the formation of Mn3O4 is prevented. The addition of Ni(OH)2 to partially reduced samples can further improve the reversibility of the MnO2 electrode, Ni(OH)2 delays the 2e− discharge step and decreases the opportunity for the co-existence of Mn(III) and Mn(II) ions and, thereby, prevents the formation of Mn3O4. The capacity retention of a cathode of partially reduced MnO2 (pr-MnO2) or pr-MnO2+Ni(OH)2 is much better than that of the MnO2 cathode. This demonstrates the feasibility of using pr-MnO2 as a cathode material.