Two-dimensional transition metal dichalcogenides in supercapacitors and secondary batteries

Supercapacitors and secondary batteries are indispensable and widely used energy storage components in modern electrical and electronic facilities/devices. However, they both suffer from different technical weaknesses which need to be thoroughly addressed to satisfy the increasing demand for clean energy technologies. For many years efforts to overcome these technical challenges have reached their practical limits, but recent progress on two dimensional (2D) materials, such as thin transition metal dichalcogenides (TMDs), has been considered more encouraging. Owing to their thin and flexible aspects, large electrochemical active surface area (EASA), high surface tunability, rich coordination sites, and both "Faradaic" and "Non-Faradaic" electrochemical behaviours, 2D TMDs play particular roles in improving many aspects of energy storage devices. This concise review summarizes current challenges facing both supercapacitors and secondary batteries, and discusses how 2D TMDs can be utilized to improve their performance. Building on their thin and flexible features, we further discuss how the emerging flexible and thin energy storage devices can benefit from the 2D TMDs, and make suggestions as to how these 2D TMDs can be engineered for future energy storage applications.