Can mixed anion transition metal dichalcogenide electrodes enhance the performance of electrochemical energy storage devices? The case of MoS2xSe2(1-x)

A significant enhancement in performance of electrochemical energy storage devices has been achieved by optimizing the S:Se ratio in electrodes made from MoS2xSe2(1-x) alloys synthesized through a facile hydrothermal technique. In symmetric two electrode configuration, the transition metal dichalcogenide with S: Se ratio of 1:1 exhibits a battery type behavior and delivers high specific capacitance of 1020F g−1 and a capacity value of 85 mAh at 10 A g−1. The electrochemical energy storage device exhibits an excellent rate capability of 96 % over the current density range of 10 to 20 A g−1. The enhanced performance is largely due to the reduced contact resistance brought in by an enhancement of electrical conductivity in the mixed cation system, in addition to the enhanced surface area of the two-dimensional material. Analysis of the electronic structure using density functional theory calculations reveals that anion vacancies created during synthesis of the material enhance the electrical conductivity of MoSSe by reducing the bandgap, which is confirmed by electrochemical impedance spectroscopy studies. The work demonstrates the importance of fine-tuning the electrical properties and morphology of the electrode material in improving the performance of electrochemical energy storage devices.