Deciphering Crystal Structure-Lithium Storage Behaviors in Niobium Tungsten Oxides Toward High-Power Lithium-Ion...

Lithium-ion capacitors (LICs) bridge the gap between batteries and supercapacitors, offering high energy/power density and long cycle life. However, their practical performance is limited by the scarcity of battery-type anodes combining fast lithium-storage kinetics with structural robustness, and by the difficulty of matching such anodes with capacitive cathodes of comparable rate capability. Here, a family of niobium tungsten oxides with distinct crystal structures, Wadsley-Roth phases (Nb₁₂WO₃₃, Nb₁₄W₃O₄₄, and Nb₁₆W₅O₅₅) and a tungsten-bronze phase (Nb₁₈W₁₆O₉₃), are systematically evaluated as high-rate anodes. Their open frameworks endow high lithium intercalation potentials (1.57-1.67 V vs. Li/Li⁺) and excellent rate capability. Among these, Nb₁₆W₅O₅₅ exhibits the lowest lithium-ion migration energy barrier (0.15 eV), reflecting superior lithium-storage kinetics. Pairing Nb₁₆W₅O₅₅ with capacitive carbon cathodes yields high-performance LICs in both aqueous and organic systems: the aqueous Nb₁₆W₅O₅₅//APDC device delivers 62.8 Wh kg^-1 at 3.3 kW kg^-1, while the optimized organic Nb₁₆W₅O₅₅-CNT//GO device operates over 0.01-3.7 V, achieving an ultrahigh energy density of 300.6 Wh kg^-1 and a maximum power density of 33.3 kW kg^-1, with excellent rate capability and cycling stability. This work elucidates the structure-kinetics relationship governing fast lithium storage in niobium tungsten oxides and offers a strategy for next-generation high-energy, high-power LICs.