Ultrastable and High‐Capacity Aqueous Ammonium‐Ion Storage in {Mo 7 }@ CNTs via a Pseudocapacitive Hydrogen‐Bonding Network

Comprehensive Summary Aqueous ammonium‐ion (NH 4 + ) batteries (AAIBs) hold great promise for sustainable energy storage owing to their high safety, low cost, and dendrite‐free characteristics. However, existing electrode materials generally suffer from insufficient active sites, poor structural stability, and sluggish charge‐transfer kinetics. Here we report a composite {Mo 7 }@CNTs, in which heptamolybdate polyoxometalate ({Mo 7 }) clusters are uniformly anchored on the surface of carbon nanotubes (CNTs). The {Mo 7 } cluster, composed of seven MoO 6 octahedra, establishes an electron‐delocalized network and provides abundant terminal oxygen (Mo=O t ) sites that form reversible hydrogen bonds with NH 4 + , enabling fast surface capacitance‐dominated charge storage. The highly conductive CNTs network effectively suppresses the aggregation and dissolution of {Mo 7 } and reduces the kinetic barrier. The optimized {Mo 7 }@CNTs delivers a specific capacity of 325.1 mAh·g –1 , with negligible capacity decay over 20,000 cycles and a Coulombic efficiency remaining at nearly 100%. An asymmetric full cell assembled with {Mo 7 }@CNTs as the anode and MoO 3 as the cathode achieves an energy density of 81.4 Wh·kg –1 at an operating voltage of 1.6 V and retains nearly 100% of its initial capacity after 20,000 cycles at 10 A·g –1 . This work provides a surface‐interface synergy strategy for designing high‐capacity, ultra‐long‐life aqueous non‐metallic ion energy storage materials.