Investigations on Tunnel‐Structure MnO2 for Utilization as a High‐Voltage and Long‐Life Cathode Material in Aqueous Ammonium‐Ion and Hybrid‐Ion Batteries

Abstract Recently, nonmetal NH 4 + ions have attracted extensive attention for use as charge carries in the field of energy storage due to their abundant resources, environmental friendliness, and low cost. However, the development of aqueous ammonium‐ion batteries (AAIBs) is constrained by the absence of high‐voltage and long‐life materials. Herein, different tunnel‐structure MnO 2 materials (α‐, β‐, and γ‐MnO 2 ) are utilized as cathodes for AAIBs and hybrid‐ion batteries and compared, and α‐MnO 2 is demonstrated to exhibit the most remarkable electrochemical performance. The α‐MnO 2 cathode material delivers the highest discharge capacity of 219 mAh g −1 at a current density of 0.1 A g −1 and the best cyclability with a capacity retention of 95.4% after 10 000 cycles at 1.0 A g −1 . Moreover, aqueous ammonium‐ion and hybrid‐ion (ammonium/sodium ions) full batteries are successfully constructed using α‐MnO 2 cathodes. This work provides a novel direction for the development of aqueous energy storage for practical applications.