Deciphering Crystal Structure‐Lithium Storage Behaviors in Niobium Tungsten Oxides Toward High‐Power Lithium‐Ion Capacitors

ABSTRACT

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 (Nb ₁₂ WO ₃₃ , Nb ₁₄ W ₃ O ₄₄ , and Nb ₁₆ W ₅ O ₅₅ ) and a tungsten‐bronze phase (Nb ₁₈ W ₁₆ O ₉₃ ), 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, Nb ₁₆ W ₅ O ₅₅ exhibits the lowest lithium‐ion migration energy barrier (0.15 eV), reflecting superior lithium‐storage kinetics. Pairing Nb ₁₆ W ₅ O ₅₅ with capacitive carbon cathodes yields high‐performance LICs in both aqueous and organic systems: the aqueous Nb ₁₆ W ₅ O ₅₅ //APDC device delivers 62.8 Wh kg ⁻¹ at 3.3 kW kg ⁻¹ , while the optimized organic Nb ₁₆ W ₅ O ₅₅ ‐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.