Ionic-liquid-assisted one-pot synthesis of Cu 2 O nanoparticles/multi-walled carbon nanotube nanocomposite for high-performance asymmetric supercapacitors.

Finding earth-abundant and high-performance electrode materials for supercapacitors is a demanding challenge in the energy storage field. Cuprous oxide (Cu 2 O) has attracted increasing attention due to its theoretically high specific capacitance, however, the development of Cu 2 O-based electrodes with superior capacitive performance is still challenging. We herein report a simple and effective ionic-liquid-assisted sputtering approach to synthesizing the Cu 2 O nanoparticles/multi-walled carbon nanotubes (Cu 2 O/MWCNTs) nanocomposite for high-performance asymmetric supercapacitors. The Cu 2 O/MWCNTs nanocomposite delivers a high specific capacitance of 357 F g -1 , good rate capability and excellent capacitance retention of about 89% after 20 000 cycles at a current density of 10 A g -1 . The high performance is attributed to the uniform dispersion of small-sized Cu 2 O nanoparticles on conductive MWCNTs, which offers plenty of redox active sites and thus improve the electron transfer efficiency. Oxygen vacancies are further introduced into Cu 2 O by the NaBH 4 treatment, providing the oxygen-deficient Cu 2 O/MWCNTs (r-Cu 2 O/MWCNTs) nanocomposite with significantly improved specific capacitance (790 F g -1 ) and cycling stability (∼93% after 20 000 cycles). The assembled asymmetric supercapacitor based on the r-Cu 2 O/MWCNTs//activated carbon (AC) structure achieves a high energy density of 64.2 W h kg -1 at 825.3 W kg -1 , and long cycling life. This work may form a foundation for the development of both high capacity and high energy density supercapacitors by showcasing the great potential of earth-abundant Cu-based electrode materials.