A cycle-durable hollow nanoneedle structure with a nanosheet as a conductive substrate CoS1.097/Ni9S8@RGO to enhance supercapacitor performance

Abstract

Metal sulfides are promising supercapacitor electrode materials with a large theoretical capacity and rich operability. However, its unsatisfactory cycle stability and rate performance are tough problems to be solved. Therefore, the preparation of metal sulfide-based electrode materials with a stable structure, long cycle life, and high-rate performance is an effective strategy to solve these problems. Herein, metal sulfides were first crystallized into crosslinked nanosheet and nanotube structures, which ensure abundant active sites for redox reactions. Then, the further modification of the prepared material by spraying graphene was carried out, which, as demonstrated by combining experimental data and physical characterization, leads to a more complete hollow structure, enlarged electrochemical reaction sites, and reduced electrolyte transport distance, thus improving the charge transfer kinetics. In the early stage of the charge–discharge cycle test, the electrode material undergoes a self-activation process, which transforms the electrode material from one equilibrium state to a new equilibrium state. Therefore, 2-CSNS@RGO electrode capacitance was 1650.13 C g⁻¹ at 1 A g⁻¹ with remarkable cycling of 3000 cycles at 10 A g⁻¹, and it retains 186.1% capacity of the initial value. An asymmetric supercapacitor (2-CSNS@RGO//AC) was prepared by coupling 2-CSNS@RGO as the positive electrode and activated carbon (AC) as the negative electrode. 2-CSNS@RGO//AC has an energy density of 88 W h kg⁻¹ at a power density of 0.8 kW kg⁻¹, and the capacity retention rate is 131.6% after 30 000 cycles at 10 A g⁻¹.