Lithium Storage in Carbon Cloth–Supported KNb₃O₈ Nanorods Toward a High‐Performance Lithium‐Ion Capacitor

Exploration of novel anodes with a high capacity and fast charge rate is crucial for developing high‐energy‐density lithium‐ion capacitors. Herein, high‐rate Li⁺ insertion into KNb₃O₈ nanorods grown on conductive carbon cloth (CC) by a facile electrodeposition technique is reported. The hierarchically porous network and the enhanced conductivity enable the CC‐KNb₃O₈ electrode to deliver a high discharge capacity of 271 mA h g⁻¹ at 0.01 A g⁻¹ with a low yet safe voltage (1.2 V versus Li/Li⁺) while exhibiting outstanding cycling stability (225 mA h g⁻¹ after 100 cycles) and superior rate capability (159 mA h g⁻¹ at 0.5 A g⁻¹). Electrochemical results and X‐ray photoelectron spectroscopy (XPS) analysis show that accompanying mutielectron transfers involving the Nb⁵⁺/Nb⁴⁺ and Nb⁴⁺/Nb³⁺ redox reactions, KNb₃O₈ remains in the stable orthorhombic phase without notable volume expansion during the whole charging and discharging process. A lithium‐ion capacitor built with a CC‐KNb₃O₈ anode and active carbon cathode delivers a maximum energy density of 69 W h kg⁻¹ at a power output of 346 W kg⁻¹ and retains 88% capacity after 1000 cycles at 2.0 A g⁻¹. This work opens up a new avenue for designing high‐capacity niobium‐based electrodes toward a high‐performance charge storage device.