Tuning Electrochemical Behaviors of AC//Nb ₂ O ₅ Lithium‐Ion Capacitors by Prelithiation and N/P Ratio With LiFePO ₄

Niobium pentoxide (Nb ₂ O ₅ ) is a promising anode material for lithium‐ion capacitors (LICs) due to its unique crystal structure enabling rapid and stable Li ⁺ insertion/extraction. However, the kinetic mismatch between the capacitive‐type cathode and Nb ₂ O ₅ anode, coupled with severe gas evolution, has hindered its practical commercialization. Herein, a novel three‐electrode LIC was constructed with an activated carbon (AC) cathode, Nb ₂ O ₅ anode, and LiFePO ₄ (LFP) reference electrode, where LFP serves dual functions as a stable reference and controllable lithium source for anode prelithiation. Prelithiation treatment significantly reduces charge transfer resistance and enhances Li ⁺ diffusion kinetics, effectively mitigating the kinetic mismatch. By systematically regulating the N/P ratio and prelithiation degree, the optimized LIC (1.5 N/P ratio, 50% prelithiation) achieves 87.3% capacity retention at the 100 C/1 C ratio, 86.2% capacity retention after 30,000 cycles, 48.7 Wh kg ⁻¹ energy density at 27.8 W kg ⁻¹ , and 89.7% capacity retention at –20 °C. Additionally, postcycling gas evolution decreases with increasing prelithiation degree but increases with larger N/P ratios, which is attributed to the reduced operating potential of the AC cathode. This work provides an innovative strategy to balance LIC electrochemical performance and gas production, offering valuable insights for the rational design of high‐performance LICs toward practical applications.