Distinguish MnO₂/Mn²⁺ Conversion/ Zn²⁺ Intercalation/ H⁺ Conversion Chemistries at Different Potentials in Aqueous Zn∥MnO₂ Batteries

The rechargeable aqueous Zn parallel to MnO2 chemistry has been extensively explored, but its electrochemical reaction mechanisms, especially in the context of MnO2/Mn2+ conversion and Zn2+/H+ intercalation chemistry, remain not fully understood. Here, we designed an amphiphilic hydrogel electrolyte, which distinguished the MnO2/Mn2+ conversion, Zn2+ intercalation, and H+ intercalation and conversion processes at three distinct discharge plateaus of an aqueous Zn parallel to MnO2 battery. The amphiphilic hydrogel electrolyte is featured with an extended electrochemical stability window up to 3.0 V, high ionic conductivity, Zn2+-selective ion tunnels, and hydrophobic associations with cathode materials. This specifically designed electrolyte allows the MnO2/Mn2+ conversion reaction at a discharge plateau of 1.75 V. More interesting, the discharge plateaus of similar to 1.33 V, previously assigned as the co-intercalation of Zn2+ and H+ ions in the MnO2 cathode, are specified as the exclusive intercalation of Zn2+ ions, leading to an ultra-flat voltage plateau. Furthermore, with a distinct three-step electrochemical energy storage process, a high areal capacity of 1.8 mAh cm(-2) and high specific energy of 0.858 Wh cm(-2), even at a low MnO2 loading mass of 0.5 mg cm(-2) are achieved. To our knowledge, this is the first report to fully distinguish different mechanisms at different potentials in aqueous Zn parallel to MnO2 batteries.