Regulating proton distribution by ion exchange resin to achieve long lifespan aqueous Zn-MnO2 battery

Despite progress in aqueous rechargeable Zn/MnO2 batteries, mechanism of the complicated cathode reactions is not fully understood. Therefore, the battery system still suffers from some operation issues, such as unsatisfactory cyclability, especially at small current densities (<1C). In this work, we report that the side product from pH fluctuation, Zn4(OH)6SO4∙xH2O (ZHS), can react with Mn2+ during charge process at over 1.55 V (vs. Zn/Zn2+) to form a lowly crystallized Woodruffite ((Zn,Mn)2Mn5O12∙4H2O, or ZMO), which severely hinders the electrochemical performance of MnO2 cathode and causes rapid capacity fading. To tackle this issue, we demonstrate that the introduction of ion exchange resin (IER) can regulate proton distribution in the electrolyte and eliminate the ZHS at 1.55 V during charge process, thus effectively inhibit the generation of ZMO. In Mn2+-additive free electrolyte, the proposed battery with IER provides a reversible specific capacity of 170 mAhg−1 over 200 cycles (>1450 h continuous discharging/charging) at 50 mAg−1. When Mn2+ is pre-added in the electrolyte, a specific capacity of 384 mAhg−1 and a capacity retention of 77.7% after 900 cycles can be obtained at 100 mAg−1 and 5 Ag−1, respectively. This study shows a general approach to the design of long lifespan aqueous Zn/MnO2 batteries.