Perspective on High-Energy Carbon-Based Supercapacitors

Supercapacitors based on carbon materials have advantages such as high power density, fast charging/discharging capability, and long lifetime stability, playing a vital role in the field of electrochemical energy storage technologies. To further expand the practical applications of carbon-based supercapacitors, their energy density, which is essentially determined by the specific capacitance and operating voltage, should be improved. This review provides fundamental knowledge on achieving high energy density of supercapacitors. We first address the relationship of the features of carbon materials, such as the surface area, pore size distribution, and surface functional groups, with their electrochemical performances, such as the gravimetric and volumetric capacitance, surface pseudocapacitance, and operating voltage. Then, we discuss the properties of electrolytes from non-aqueous and aqueous to hybrid one from the thermodynamic and kinetic aspects, and present their effects on capacitance and operating voltage. Finally, we illustrate different cell design strategies and their basic principles for increasing operating voltage. We also highlight the recent advances related to these fields and provide our insight into high-energy supercapacitors.