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

Aqueous nonmetallic ammonium-ion (NH₄⁺) 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 ((NH₄)₂Mo₃S₁₃·H₂O, NMSH) is developed as an anode host for AmIBs. Theoretical and experimental results demonstrate that NMSH possesses a dual redox-active center (i.e., Mo⁴⁺and S₂^2–) displaying a high reversible specific capacity of ∼275 mAh g^–1at 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.