Fluorine‐Doped NaTi2(PO4)3 Via Electronic Orbital Modulation and Bandgap Engineering for Aqueous Li/Na/K‐Ion Batteries

Sodium titanium phosphate (NaTi 2 (PO 4 ) 3 , NTP) has emerged as a promising electrode material due to its three‐dimensional open framework. This study investigates the use of NTP in aqueous dilute Li + /Na + electrolytes and extends its application to high‐concentration K + electrolytes. X‐ray photoelectron spectroscopy, X‐ray absorption near‐edge structure analysis, and density functional theory calculations revealed that highly electronegative fluorine partially substitutes for oxygen in the NTP lattice, resulting in the formation of Ti‐F bonds. The substitution effectively modulates the electronic structure of Ti 4+ , alters the local coordination environment, and influences the redox dynamics. Enhanced long‐term cycling stability and rate performance were demonstrated across aqueous sodium‐ion, lithium‐ion, and potassium‐ion half‐cells. Among the investigated systems, the aqueous sodium‐ion system exhibited the best electrochemical performance, characterized by a single, well‐defined charge–discharge plateau, stable cycling behavior with 88.7% capacity retention after 500 cycles at 1 A g −1 , and an initial specific discharge capacity of 121.7 mAh g −1 at 0.2 A g −1 . The results establish F‐doped NTP as a promising candidate for advanced energy storage applications in aqueous alkali metal‐ion batteries.