Boosting the safety and energy density of MoS2/CNTs based solid-state sodium-ion supercapacitor with an ionogel electrolyte

ABSTRACT Solid-state energy storage devices exhibit superior safety and energy density. However, their practical applications are still limited by the lower conductivity and ion transfer rate. The performances of sodium ion capacitors (SICs) are determined combinational by the device configuration, electrodes, and electrolyte. Therefore, the configuration optimization of solid-state sodium-ion supercapacitor (SS-SIC) is critically important. Here, the fabrication of a safer high-energy-density solid-state sodium-ion supercapacitor is demonstrated by using flake-shaped MoS2/carbon nanotubes (CNTs) nanohybrids and sodium-ion ionogel electrolyte. The microstructures of nanohybrids can support shortened migration paths for sodium ions and can buffer the volume change of electrochemical reactions. Moreover, the optimized sodium-ion ionogel electrolyte was found to exhibit improved flame-retardant ability, accelerated ionic conductivity, and excellent sodium migration rate. Electrochemical analysis and molecular simulation methods of energy storage behaviors were employed to uncover the origin of improved performances at higher temperatures. The optimized SS-SIC could deliver a high energy density up to 115.7 W h kg−1 at 70 °C, and excellent durability with 81% retention after 8000 cycles. Therefor a new energy supply device is provided for equipment operating at higher temperatures.