High-performance layered NiCo2S4@rGO/rGO film electrode for flexible electrochemical energy storage

The rapid development of portable and wearable electronic devices requires novel energy storage devices. Flexible, high-performance electrode materials are critical for meeting the demands yet remain challenging. Here, a rationally designed flexible NiCo2S4@rGO/rGO film constructed with NiCo2S4@rGO frameworks is successfully prepared through a step-wise process (hydrothermal, freeze-drying, vacuum filtration, and then sulfurization/reduction). The NiCo2S4@rGO/ rGO film as flexible electrode shows typical battery-type faradaic redox features and exhibits a high specific capacitance of 1100.0 F g(-1) at 1 Ag-1, a good rate performance of 89.1% capacity retention at 10 A g(-1) coupled with long cycling stability of 90.2% after 5000 cycles. The good electrochemical performance is mainly attributed to the loose layered structure and strong interaction between NiCo2S4 and rGO nanosheets, which enhance the diffusion of electrolyte ions/electrons and decreases intrinsic resistance and contact resistance. A flexible hybrid supercapacitor assembled using the NiCo2S4@rGO/rGO film as cathode and the rGO film as anode shows a high energy density of 30.0 Wh kg(-1) at a power density of 857.6W kg(-1) at an extended operating voltage of 1.8 V. The method can also be readily adapted for loading other bimetallic sulfides on rGO films, indicative of its feasibility and flexibility to prepare rGO-based hybrid film for high-performance flexible electrochemical energy storage. (C) 2019 Elsevier Ltd. All rights reserved.