Distinguish MnO 2 /Mn 2+ Conversion/ Zn 2+ Intercalation/ H + Conversion Chemistries at Different Potentials in Aqueous Zn||MnO 2 Batteries.

The rechargeable aqueous Zn||MnO 2 chemistry has been extensively explored, but its electrochemical reaction mechanisms, especially in the context of MnO 2 /Mn 2+ conversion and Zn 2+ /H + intercalation chemistry, remain not fully understood. Here, we designed an amphiphilic hydrogel electrolyte, which distinguished the MnO 2 /Mn 2+ conversion, Zn 2+ intercalation, and H + intercalation and conversion processes at three distinct discharge plateaus of an aqueous Zn||MnO 2 battery. The amphiphilic hydrogel electrolyte is featured with an extended electrochemical stability window up to 3.0 V, high ionic conductivity, Zn 2+ -selective ion tunnels, and hydrophobic associations with cathode materials. This specifically designed electrolyte allows the MnO 2 /Mn 2+ conversion reaction at a discharge plateau of 1.75 V. More interesting, the discharge plateaus of ~1.33 V, previously assigned as the co-intercalation of Zn 2+ and H + ions in the MnO 2 cathode, are specified as the exclusive intercalation of Zn 2+ 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 MnO 2 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||MnO 2 batteries.