Decoding Dual Redox-Active Ammonium Molybdenum Sulfide for High-Capacity Hydrated Ammonium-Ion Storage

Aqueous nonmetallic ammonium-ion (NH 4 + ) batteries (AmIBs) have emerged as one of the promising electrochemical energy storage candidates. However, their advancements have been hindered by the scarcity of high-performance host materials. Herein, a sulfur-rich ammonium molybdenum sulfide ((NH 4 ) 2 Mo 3 S 13 ·H 2 O, NMSH) is developed as an anode host for AmIBs. Theoretical and experimental results demonstrate that NMSH possesses a dual redox-active center (i.e., Mo 4+ and S 2 2– ) displaying a high reversible specific capacity of ∼275 mAh g –1 at 0.1 A g –1, which outperforms the most reported ammonium-ion storage hosts. Even at 10 A g –1, this material shows a great rate capacity of 121 mAh g –1 . Notably, the hydrated ammonium-ion storage mechanism with water co-intercalation/extraction is verified by various characterization technologies and theoretical simulation. The sulfur-rich NMSH facilitates ammonium-ion storage, thereby paving the way for exploring more energetic, efficient, and sustainable ammonium-ion batteries.