The rechargeable aqueous zinc ion battery (ZIB) has many advantages over the Li-ion batteries for grid scale energy storage, such as high abundance and low cost of Zn, as well as much safer battery chemistry of aqueous electrolytes. Manganese dioxides (MnO2s) are promising cathodes for ZIBs due to their high theoretical capacity, voltage, and abundance of Mn. However, MnO2s suffer from severe capacity fading over time as the battery is put through extended charge-discharge cycles. Here, we investigate the influence of the ZnSO4 electrolyte concentration on the galvanostatic charge-discharge cycling performance of cryptomelane type manganese dioxide (a-MnO2). Low-electrolyte concentrations (&lt;0.2M) demonstrate higher capacities and capacity retentions after extended battery cycling. At 0.1M ZnSO4, α-MnO2 delivered 62 and 103mAh/g capacities at 1st and 100th cycles, respectively (166% capacity retention). Conversely, at high electrolyte concentrations (&gt;1.0M), the capacity retentions were below 30% and capacities fell below 60mAh/g after 100 cycles. It is also shown that as electrolyte concentration is lowered below 0.2M, there is a notable capacity increase that occurs from the first cycle to the ~50th cycle and no capacity fading from that point forward. Better electrochemical performance of a-MnO2 at low electrolyte concentrations is attributed to the suppression of cathode dissolution and the mitigation of the formation of impurity phases such as ZnMn2O4 and ZnMn3O7.2H2O.

Effect of electrolyte concentration on the cycle life of cryptomelane type manganese dioxide cathodes in aqueous zinc ion batteries

2019 Spring National Meeting

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