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

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 NH₄⁺ 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 Mn₃Al₁-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 NH₄⁺ 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.