High‐Voltage Aqueous Manganese‐Ion Batteries Enabled by a Semi‐Crystalline Polyaniline Cathode and Mn Metal Anode

ABSTRACT Aqueous manganese‐ion batteries (AMIBs) are emerging as promising candidates for large‐scale, safe, and low‐cost energy storage owing to the natural abundance and much lower redox potential of manganese compared with zinc. Here, we realize a high‐voltage AMIB by pairing a semi‐crystalline, porous polyaniline (PANI) cathode with a Mn metal anode. Exploiting the intrinsically lower Mn potential (−1.19 V vs. SHE) than Zn (−0.76 V) enables an average cell voltage of 1.27 V—over 30% higher than conventional Zn‐based aqueous batteries—while keeping PANI within its stable electrochemical window. The PANI cathode delivers a high reversible capacity of 88.3 mAh/g and retains 67.9% capacity after 1000 cycles, with ex situ spectroscopy revealing a highly reversible Mn 2 + /H + hybrid storage mechanism and exceptional structural stability. Full Mn//PANI cells markedly outperform Zn analogues not only in voltage but also in rate capability and cycle life, maintaining 81.3% capacity after 500 cycles at 1.0 A/g. These findings position PANI as a high‐performance organic cathode and establish clear system‐level advantages of Mn over Zn for next‐generation high‐voltage aqueous batteries.