Synergistic MXene/NiCo2S4 composite for high-performance flexible all-solid-state supercapacitors

The scientific community has been captivated by flexible all-solid-state supercapacitors, which can meet the growing demand for portable electronic devices. In this study, a novel MXene/NiCo2S4 (MNCS) composite material was synthesized via the hydrothermal method, with NiCo2S4 uniformly distributed on the surface or within the interlayers of MXene. The aim of this study was to enhance energy storage applications by developing a positive electrode material using a composite of MNCS. The architecture of the composite was carefully designed to prevent the stacking of MXene and the accumulation of NiCo2S4 nanoparticles, effectively suppressing these issues. It is worth noting that when utilized in a three-electrode system, the MNCS electrode demonstrates outstanding electrochemical performance. Specifically, at a current density of 1 A g-1, the electrode exhibits a specific capacity of 2675 F g-1 (equivalent to 1070 C g-1). Furthermore, even after undergoing 10,000 cycles of charging and discharging, the electrode retains an impressive 96.51 % of its initial capacity. These results clearly indicate that the exceptional performance observed in this supercapacitor can be attributed to the synergistic collaboration between NiCo2S4 nanoparticles and MXene nanosheets which significantly enhances charge transfer during both charging and discharging processes. Moreover, we synthesized MNCS composites for use as positive electrodes in asymmetric flexible solid-state supercapacitors while employing activated carbon (AC) as negative electrodes. The resulting device exhibits high specific capacitance (256 F g-1) and impressive energy density (61 Wh kg-1) at a power density of 763 W kg-1 under a large voltage window (1.7 V) and current density (1 A g-1). Additionally, favorable cycling stability is observed with minimal capacitance variation even under various bending deformations. This study presents an innovative approach for developing composite materials with superior electrochemical properties and flexible devices with high energy density and power density.