MnAl Layered Double Hydroxides: A Robust Host for Aqueous Ammonium‐Ion Storage with Stable Plateau and High Capacity

Abstract Rechargeable aqueous batteries based on ammonium‐ions shows great potential in low‐cost energy storage systems owing to their prominent superior characteristics, including ultrafast kinetics, long‐term lifespan, and environmental friendliness. Nevertheless, their development is severely challenged by the fact that the as‐reported cathode materials generally fail to satisfy the requirements on high capacity and stable working voltage simultaneously. Herein, the first NH 4 + storage behavior in a MnAl layered double hydroxide (LDH) series is reported. Intriguingly, stable working voltage at 0.2 V is observed in the optimized Mn 3 Al 1 ‐LDH sample with a high discharge capacity of 183.7 mAh g −1 at 0.1 A g −1 . When assembling the rocking‐chair battery using a 3,4,9,10‐perylenetetracarboxylic diimide anode, the full battery delivers a high energy density of 45.8 Wh kg −1 , surpassing most of its recently reported counterparts. A rapid amorphization conversion of the LDH cathode during the first charge process is revealed, which should be beneficial to NH 4 + isotropic transport accompanied by a highly reversible building/breaking process of hydrogen bonds. The results realize a novel layered inorganic cathode material with superior performance for aqueous ammonium‐ion batteries, and the amorphization conversion to facilitate ion storage provides new insight into electrode design for aqueous batteries.