Due to outstanding storage capacity, ultra-high power density, super long cycle life time, moderate energy density and high safety, supercapacitors have enthusiastically become a new type of energy storage device and energy storage technology after lithium ion battery. In the recent decade, scientists and engineers around the world have extensively and thoroughly studied physics, chemistry, materials, chemical engineering, electronics, transportation engineering, energy science and technology, aeronautical and astronautics science and technology, which promoted the rapid application of supercapacitors in electric automobile, engineering machinery, industrial energy saving, wind power and many other fields. This monograph focuses on three reviews and fifteen original research papers, highlighting main research progress in micro-supercapacitors (MSCs), graphene-based supercapacitors, flexible supercapacitors, hybrid supercapacitors, covering the new energy storage principle, novel electrode materials, neoteric electrolyte, and late-model device technology.

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Although we only introduced several typical applications of supercapacitors here, energy density is a key factor restricting the development of other applications of supercapacitors under the premise of guaranteeing long-term cycling stability, high-rate performance, and power density. Thereby, designing supercapacitors configuration with high energy density to achieve the excellent electrochemical capacitance performance is the major issue and challenge. We hope that this special issue brings readers a timely overview on the latest breakthroughs in the related area.
Finally, we would like to express our sincere thanks to all the authors, referees and Editorial Board. We always welcome any comment, suggestion, and feedback.