Oxygen‐Defective TiNb2O7‐x Nanochains with Enlarged Lattice Spacing for High‐Rate Lithium Ion Capacitor

Abstract Titanium niobium oxide (TiNb 2 O 7 ) is considered as a promising candidate for lithium‐ion capacitors (LICs) due to its high reversible capacity, low cost, and safety. However, it is limited by ineffective ion diffusivity and low intrinsic conductivity. Herein, in situ defect engineering in TiNb 2 O 7‐ x nanochains is successfully achieved by a facile electro‐spinning technique to improve their electrochemical performance. Remarkably, the oxygen vacancies can enhance the electronic conductivity, while the enlarged lattice spacing is conducive to the Li + insertion/extraction, consequently enhancing the electron and ion transport kinetics. Moreover, such oxygen vacancies and enlarged lattice spacing can supply more active sites for lithium storage. Consequently, the TiNb 2 O 7‐ x nanochains exhibit a remarkable specific capacity of 440 mAh g −1 at 0.1 A g −1 , superior rate capability (126 mAh g −1 at a high current density of 5.0 A g −1 ), and cycling stability (92% retention over 2000 cycles at 1.0 A g −1 ). In addition, the TiNb 2 O 7‐ x ‐based LIC delivers high energy/power densities of 114 Wh kg −1 and 22502.4 W kg −1 with high‐rate performance and long cycle lifespan. This work provides new insights on in situ formation of defects to enhance the electrochemical behavior for high‐rate LICs.