Three-dimensional hollow microtubular carbonized kapok fiber/cobalt-nickel binary oxide composites for high-performance electrode materials of supercapacitors

Abstract

Three-dimensional hollow microtubular carbonized kapok fiber/cobalt-nickel binary oxide hybrid composites were successfully prepared based on the low-cost natural kapok fiber by combining a simple hydrothermal technique and calcination method. The three-dimensional hollow tubular structure was kept well during the preparation process. The surface morphologies of the as-prepared three-dimensional carbonized kapok fiber/cobalt-nickel binary oxide hybrids changed from the cross-linked fibrous network to the nanoflakes with the increase in the calcination temperature. The composites prepared at 600°C for 2h exhibited a high specific capacity with 502.4Cg−1 at discharge currents of 0.25Ag−1 in 6.0M KOH, and the capacity retention was still maintained at 97.5% after 5000 cycles demonstrating good electrochemical stability. In addition, a hybrid supercapacitor device was also assembled using active carbon and the as-prepared composite as negative and positive electrodes, respectively. It could be operated within a wide potential window of 0.0–1.6V with a high specific energy of 23.2Whkg−1. In addition, the hybrid supercapacitor also exhibited excellent rate capability as well as long-term stability after 5000 cycles. The high reversible capacity of the obtained electroactive hybrid composites can be ascribed to the unique hollow tubular structure, the large surface area, the high defective carbon matrix and the synergetic effect of hybrid electroactive components. Therefore, the as-prepared three-dimensional hollow microtubular hybrids are expected to develop high-performance supercapacitor.