Mesoporous NiCo2O4 nanoneedle arrays as supercapacitor electrode materials with excellent cycling stabilities

Abstract

In this work, mesoporous NiCo₂O₄ nanoneedle arrays grown on a nickel foam substrate are fabricated by a facile hydrothermal route. The as-synthesized NiCo₂O₄ products as binder-free electrodes for supercapacitors show a superior discharge areal capacity of 0.998 C cm⁻² at a current density of 2 mA cm⁻², excellent rate performance (60.25% retention with current density increasing from 2 mA cm⁻² to 200 mA cm⁻²) and outstanding cycling stability (about 19.3% loss after 12 000 cycles at a current density of 20 mA cm⁻²). An assembled supercapacitor using a NiCo₂O₄ electrode as the positive electrode delivers a volumetric energy density of 0.33 mW h cm⁻³ at a volumetric power density of 12 mW h cm⁻³ and still achieves 63.6% retention with the volumetric power density increasing to 120 mW h cm⁻³. Surprisingly, 140.6% capacity retention is attained after 8000 cycles at 10 mA cm⁻².