A review of advanced electrolytes for supercapacitors

As a novel energy storage technology, supercapacitors (SCs) have excellent cycling stability and high power density. However, their energy density is inferior as compared to batteries. Electrolytes are critical for improving the electrochemical performance of supercapacitors, which could directly affect the energy density, power density, cycling stability, and safety. Electrolytes mainly include aqueous electrolytes, organic electrolytes, solid or quasi-solid electrolytes, and ionic liquid electrolytes. Regulating the composition of electrolytes or developing advanced electrolytes are significant for supercapacitors. Therefore, this work reviews the advanced electrolytes used in supercapacitors in recent years, including aqueous electrolytes, organic electrolytes, solid/quasi-solid electrolytes, and ionic liquid electrolytes. Additionally, the development of electrolytes for metal-ion hybrid supercapacitors is introduced. This paper summarizes the current researches, including critical issues and possible solutions. And the challenges faced by the development of electrolytes in the future are also highlighted and discussed. This study is of great importance to the development of high-quality electrolytes and supercapacitors with demanded performance and functions.