Excellent Zinc-Ion Hybrid Capacitor Based on the Nb₂CT_<i>x</i> Anode and CNTs@MnO₂ Nanocomposite Cathode

The zinc-ion hybrid capacitor (ZIHC) is an emerging energy storage device that has attracted intense interest for the inherent merits of relatively higher energy density and power density. Herein, an excellent ZIHC based on the Nb2CTx anode and CNTs@MnO2 cathode has been rationally designed and fabricated successfully in this work. MnO2 nanoflakes were grown on carbon nanotubes (CNTs) directly with a hydrothermal approach. Then, the CNTs@MnO2 nanocomposite acted as a cathode in a zinc-ion battery. Nb2CTx, a kind of new layered compound in the MXene family, demonstrates excellent ion storage capability. The large interlayer space dramatically improves zinc-ion accessibility. A ZIHC with a Nb2CTx anode and a CNTs@MnO2 cathode displays an energy density of 96.7 Wh kg–1 (with 183.2 W kg–1) and a power density of 1156.3 W kg–1 (with 61 Wh kg–1), a capacitance retention of about 88.7% after 10,000 cycles, and a Coulombic efficiency of more than 98.5% in the whole cycling process. This strategy of designing the ZIHC may provide a promising route to create novel energy storage devices.