Untapped Potential of Polymorph MoS2: Tuned Cationic Intercalation for High-Performance Symmetric Supercapacitors.

Supercapacitors have been the key target as energy storage devices for modern technology that need fast charging. Although supercapacitors have large power density, modifications should be done to manufacture electrodes with high energy density, longer stability, and simple device structure. The polymorph MoS2 has been one of the targeted materials for supercapacitor electrodes. However, it was hard to tune its phase and stability to achieve the maximum possible efficiency. Herein, we demonstrate the effect of the three main phases of MoS2 (the stable semiconductor 2H, the metastable semiconductor 3R, and the metastable metallic 1T) on the capacitance performance. The effect of the cation intercalation on the capacitance performance was also studied in Li2SO4, Na2SO4, and K2SO4 electrolytes. The performance of the electrode containing the metallic 1T outperforms those of the 2H and 3R phases in all electrolytes, with the order 1T > 3R > 2H. The 1T/2H phase showed a maximum performance in the K2SO4 electrolyte with a specific capacitance of 590 F g-1 at a scan rate of 5 mV s-1. MoS2 showed a good performance in both positive and negative potential windows allowing the fabrication of symmetric supercapacitor devices. The 1T MoS2 symmetric device showed a power density of 225 W/kg with an energy density of 4.19 Wh/kg. The capacitance retention was 82% after 1000 cycles, which is an outstanding performance for the metastable 1T-containing electrode.