Two-step hydrothermal synthesis of NiCo2S4/Co9S8 nanorods on nickel foam for high energy density asymmetric supercapacitors

Abstract

It is still a huge challenge to obtain a high-energy-density asymmetric supercapacitors and develop an active electrode material with excellent electrochemical characteristics. Although NiCo2S4 has been considered as one of the promising positive electrode materials for asymmetric supercapacitors, the electrochemical performance of the NiCo2S4-based positive electrodes is still relatively low and cannot meet the demand in the devices. Herein, NiCo2S4/Co9S8 nanorods with a large capacitance are synthesized via a simple two-step hydrothermal treatment. A high-performance asymmetric supercapacitor operating at 1.6V is successfully assembled using the NiCo2S4/Co9S8 nanorods as positive electrode and activated carbon as negative electrode in 3M KOH aqueous electrolyte, which demonstrates a fairly high energy density of 49.6Whkg−1 at a power density of 123Wkg−1, an excellent capacitance of 0.91Fcm−2 (139.42Fg−1) at current density of 1mAcm−2 as well as a remarkable cycling stability due to the high physical strength, the large specific surface area, and the good conductivity for NiCo2S4/Co9S8 nanorods and the brilliant synergistic effect for NiCo2S4 and Co9S8 electrode materials. The as-prepared NiCo2S4/Co9S8 nanorods open up a new platform as positive electrode material for high-energy-density asymmetric supercapacitors in energy-storage.