Optimising heat treatment environment and atmosphere of electrolytic manganese dioxide for primary Li/MnO2 batteries

The influence of various conditions on the heat treatment step in preparing manganese dioxide for primary lithium batteries is reported. Heating environments considered are static air, flowing air and mechanical tumbling, while the heating atmospheres are flowing gases of air, O2, N2, Ar, 9:1 N2/H2, and under vacuum. The heat treated materials are characterised by the percentage of electrochemically active Mn(IV), cation vacancy and pyrolusite fractions, and BET surface area, which are the most influential parameters. Many materials made in this study show better electrochemical performance than literature materials, with primary capacities up to 263 mAh g−1 (2 mA g−1 discharge rate), which is 85% of the nominal MnO2 utilisation, but 98% utilisation of the electrochemically active Mn(IV) species. In particular, changing the environment from static air to mechanical tumbling results in a significant increase in primary capacity, with the additional utilisation of 3-13% of the material across the 2-20 mA g−1 discharge rates, and up to 98% utilisation of Mn(IV). In addition, flowing air and oxygen atmospheres were also advantageous, with high primary capacities (260-262 mA g−1 at 2 mA g−1) and excellent utilisation of the active material (up to 97% for flowing oxygen).