Facile electrode additive stabilizes structure of electrolytic MnO2 for mild aqueous rechargeable zinc-ion battery

MnO2 is a potential cathode material for aqueous zinc-ion battery (ZIB) because of its high capacity, low toxicity and low cost. Though, MnO2 electrode suffers from capacity fading during cycling mainly due to Mn dissolution and structural change. The addition of Mn2+ into the mild acidic electrolyte is a common method to suppress Mn dissolution, though it cannot prevent the formation of inactive ZnMn2O4 from reaction between MnO2 and zincate ions. Here, we show that Bi2O3 additive in the electrode can suppress ZnMn2O4 formation and improve cyclability of electrolytic manganese dioxide (EMD). EMD electrode with 10 wt% Bi2O3 in ZnSO4 electrolyte without Mn2+ additive maintains a high capacity of 229 mAh g−1 at 100 mA g−1 after 100 cycles, with a capacity retention of 78%, in comparison with the 8% capacity retention for EMD electrode without Bi2O3. Characterizations suggest that bismuth is able to interact with zinc under alkaline condition and reduce the amount of zincate ions in the electrolyte. Combining both Bi2O3 electrode additive and Mn2+ electrolyte additive, EMD can give a base capacity of about 300 mAh g−1 at 0.3C and maintain a stable capacity of 190 mAh g−1 for 1000 cycles at 1000 mA g−1 (about 3.3C).