Unveiling TiNb₂O₇ as an insertion anode for lithium ion capacitors with high energy and power density

This is the first report of the utilization of TiNb₂O₇ as an insertion-type anode in a lithium-ion hybrid electrochemical capacitor (Li-HEC) along with an activated carbon (AC) counter electrode derived from a coconut shell. A simple and scalable electrospinning technique is adopted to prepare one-dimensional TiNb₂O₇ nanofibers that can be characterized by XRD with Rietveld refinement, SEM, and TEM. The lithium insertion properties of such electrospun TiNb₂O₇ are evaluated in the half-cell configuration (Li/TiNb₂O₇) and it is found that the reversible intercalation of lithium (≈3.45 mol) is feasible with good capacity retention characteristics. The Li-HEC is constructed with an optimized mass loading based on the electrochemical performance of both the TiNb₂O₇ anode and AC counter electrode in nonaqueous media. The Li-HEC delivers very high energy and power densities of approximately 43 Wh kg^-1 and 3 kW kg^-1, respectively. Furthermore, the AC/TiNb₂O₇ Li-HEC delivers a good cyclability of 3000 cycles with about 84 % of the initial value. Spinning to capacity: High-energy-density lithium-ion hybrid electrochemical capacitors are fabricated by using an insertion-type TiNb₂O₇ anode, prepared by a scalable electrospinning technique, with an activated carbon (AC) counter electrode.