Light-Induced NH 4 + Deprotonation Drives NH 4 + /H + Hybrid Storage Toward Near-Theoretical Capacity in NH 4 V 4 O 10 Electrodes

Ammonium-ion batteries (AIBs) utilize the earth abundance, low molar mass, and small hydrated radius of NH4+ to achieve high gravimetric specific capacity, offering a sustainable alternative to metal-ion systems for large-scale energy storage. However, achieving high capacity in AIB electrodes remains challenging due to inefficient NH4+ intercalation. Here, we demonstrate that photodriven NH4+ deprotonation on the NH4V4O10 electrodes enables near-theoretical capacity through hybrid NH4+/H+ storage. Light irradiation modulates the ions intercalation kinetics, enhancing the ion diffusion contribution while maintaining pseudocapacitive behavior, boosting capacity by 76.6%. The capacity of the NH4V4O10 electrode reaches 539 mAh g–1 at 1 A g–1, approaching its theoretical capacity (589 mAh g–1). TOF-SIMS and in situ Raman spectroscopy revealed that light triggers NH4+ deprotonation at the electrode/electrolyte interface, enabling proton intercalation as the primary capacity enhancement mechanism. DFT calculations rationalize this effect by showing that photoexcitation of NH4V4O10 reduces the NH4+ deprotonation barrier on surface, and facilitates proton intercalation. Such interfacial photocontrol of NH4+ dynamics explores new pathways toward efficient ammonium-ion batteries with photo assistance.