Joint Charge Storage for High-Rate Aqueous Zinc-Manganese Dioxide Batteries

Aqueous rechargeable zinc-manganese dioxide batteries show great promise for large-scale energy storage due to their use of environmentally friendly, abundant, and rechargeable Zn metal anodes and MnO₂ cathodes. In the literature various intercalation and conversion reaction mechanisms in MnO₂ have been reported, but it is not clear how these mechanisms can be simultaneously manipulated to improve the charge storage and transport properties. A systematical study to understand the charge storage mechanisms in a layered δ-MnO₂ cathode is reported. An electrolyte-dependent reaction mechanism in δ-MnO₂ is identified. Nondiffusion controlled Zn²⁺ intercalation in bulky δ-MnO₂ and control of H⁺ conversion reaction pathways over a wide C-rate charge-discharge range facilitate high rate performance of the δ-MnO₂ cathode without sacrificing the energy density in optimal electrolytes. The Zn-δ-MnO₂ system delivers a discharge capacity of 136.9 mAh g^-1 at 20 C and capacity retention of 93% over 4000 cycles with this joint charge storage mechanism. This study opens a new gateway for the design of high-rate electrode materials by manipulating the effective redox reactions in electrode materials for rechargeable batteries.