As a new type of energy storage device, supercapacitors have attracted wide attention because of their excellent performance, such as high charge and discharge speed, high power density, and long cycle life. The electrolytes have been considered as one of the most important factors affecting the performance of supercapacitors, whose ionic type and size, ion mobility, ionic conductivity, viscosity, thermal/electrochemical stability and the operating voltage window have the important influence on the working voltage, energy density and cycle life of the device. In view of recent research status of electrolytes, this paper summarizes the charge storage mechanism, key parameters of performance evaluation and the research progress of electrolytes in supercapacitors. The classification of electrolytes is specially presented, including liquid electrolytes which incorporate aqueous, organic, ionic liquid, redox-active electrolytes and solid-state/quasi-solid-state electrolytes which cover inorganic solid-state electrolytes, solid polymer electrolytes, and gel polymer electrolytes. The latest research and development of various electrolytes are reviewed and discussed, and the influences of electrolyte properties on the performance of supercapacitors are discussed in detail. The methods of design and optimization of electrolytes for supercapacitors are emphasized in this paper. The difficulties of producing high-performance electrolytes are pointed out, and the future research directions are put forward to overcome these difficulties without sacrificing existing advantages.
Contents
1 Introduction
2 Electrolytes and their categories
2.1 Liquid electrolytes
2.2 Solid-state/quasi-solid-state electrolytes
3 Conclusion