Sodium-potassium co-doped layered manganese dioxide cathode material for high performance aqueous zinc-ion batteries

Abstract

Manganese dioxide with high operating voltage and satisfactory energy density have been identified as the promising cathode materials for aqueous zinc-ion batteries (AZIBs). However, the structural instability of manganese-based materials during the (dis)charging process limits their further development. Herein, sodium-potassium co-doped layered K0.37Na0.18MnO2·xH2O (KNMOH) are synthesized by a liquid-phase synthesis method at room temperature. The co-doping of Na+ and K+ stabilizes the layered structure, widens the layer spacing and has the effect of electrostatic shielding to facilitate the (de)intercalation of Zn2+. Benefiting from the stable structure and nanoscale size, the flower-like KNMOH cathode maintained a high specific capacity of 239.1 mAh·g−1 after 700 cycles at 500 mA·g−1. Simultaneously, this work firstly reveals that the presence of K8(SO4)(SO3OH)6 suppressed the generation of Zn4SO4(OH)6·0.5H2O, resulting in more free Zn2+ and high reversibility. This co-doped design of bimetallic ions insertion enhances the electrochemical performance and provides a new idea for the improvement of the manganese-based cathode materials for AZIBs.