Boosting the cycling stability of transition metal compounds-based supercapacitors

As an important electrochemical energy storage system, supercapacitors (SCs) possess advantages of high power density, long cycling life and great safety to meet the requirements of particular applications. Current commercial SCs that are mainly based on activated carbon materials generally have low energy density. Development of alternative electrode materials with a high specific capacitance is critical to achieving a high energy density of SCs. In the past decades, transition metal compounds have been explored as promising electrode materials for SCs with high energy density by taking advantage of faradaic charge storage process of transition metal cations. Nevertheless, SCs with transition metal based electrode materials normally suffer sluggish electrochemical reaction kinetics and poor electron conductivity, which result in unsatisfactory cycling stability and rate capability. In this review, we focus on the analysis of recent research breakthroughs in the development of high electrochemical performance SCs using transition metal oxides/hydroxides, sulfides, selenides and phosphides. The majority of the devices demonstrated outstanding cycling lifetime of over 10,000 times and excellent capacity retention rate along with high energy density. A critical analysis of the factors that contribute to the electrochemical performance of these star-performing SCs such as material morphology, crystal structure, composition, interfacial properties and key chemical reactions are presented. This timely review sheds light on the most effective possible paths towards design and fabrication of high performance SCs using transition metal electrode materials.