Unlocking High‐Energy and Freeze‐Tolerant Aqueous Ammonium‐Ion Batteries via Phase‐Reconstructed Low‐Strain Amorphous Vanadium Oxides

ABSTRACT Aqueous ammonium‐ion batteries (AAIBs) are promising for sustainable energy storage but suffer from sluggish solid‐state diffusion, structural degradation, and severe performance deterioration under subzero conditions. To overcome these limitations, we report a defect‐rich amorphous composite, A‐V2O4.7•1.6H2O anchored on N‐doped carbon nanosheets (A‐VOx@NC), synthesized via scalable in situ electrochemical reconstruction of a two‐dimensional vanadium nitride anchored on N‐doped carbon (2D VN@NC) precursor. This architecture synergistically integrates highly disordered amorphous VOx, oxygen vacancies, structural water, and a conductive N‐doped carbon framework. This design narrows the bandgap to 0.56 eV, broadens ion diffusion pathways, and accelerates reversible NH4+/H+ co‐insertion kinetics. The flexible amorphous lattice effectively buffers mechanical strain, reducing volume expansion to 4.64% versus 18.9% for pristine V2O5. Consequently, A‐VOx@NC delivers an exceptional reversible capacity of 462 mAh g −1 (normalized to VN@NC precursor mass; 449 mAh g −1 after subtracting the carbon contribution) at 0.1 A g −1 , retains 84.98% capacity after 2500 cycles at 5 A g −1 , and maintains >82% capacity after 1000 cycles at −20°C. The assembled symmetric cell achieves an energy density of 177.6 Wh kg −1 (based on total active mass) over 2800 cycles. This work establishes a defect‐ and interface‐engineering blueprint for high‐energy‐density, climate‐resilient aqueous energy storage.