Materials design and preparation for high energy density and high power density electrochemical supercapacitors

Electrochemical supercapacitors process ultra-high power density and long lifetime, but the relatively low en-ergy density hinder the wide application. Therefore, supercapacitors with high energy density and high power density ("dual high") have attracted great attentions. New active materials with high pseudocapacitance beyond electronic double layer capacitance and novel devices with high working voltage, are two approaches toward "dual high" supercapacitors. In this review, we briefly introduce the history, classification, basic mechanism, and device architecture of supercapacitors. Then, the key issues and design strategies for "dual high" supercapacitors will be proposed. The recent methodical advances will also be highlighted on the material with outstanding specific capacitance and the corresponding electrolyte systems with expanded operating voltage. Besides, the recent progresses of current collectors and separators for supercapacitors are also included. Finally, we will provide our insights regarding the major challenges and prospective solutions in this highly exciting field. We believe such a review will significantly expand the horizons in ever-deepening understanding toward "dual high" supercapacitors