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.