Critical evaluation of hybrid and organic electrolytes for supercapacitors with optimized porous carbon

Abstract

Applying aqueous/organic hybrid electrolytes for carbon supercapacitors has recently attracted much attention owing to their wider stability window than aqueous electrolytes and moisture-tolerant and non-flammable properties. Hence, a critical evaluation of hybrid electrolytes vs. common organic electrolytes used in supercapacitors concerning their electrochemical performance is warranted. This work analyzed the capacitive performance of hybrid and organic electrolytes for a model carbon with a range of porosity. It was found that there was a trade-off between the gravimetric capacitance (and energy density) and rate capability (and power density) when the pores were widened by increasing the activation temperature from 800°C to 900°C. The carbon activated at 800°C showed higher capacitance at low rates, but the latter (900°C) caught up at high rates. Considering the volumetric performance, the carbon activated at 800°C outperformed its counterpart activated at 900°C owing to its higher density. It was found that the water/acetonitrile hybrid electrolyte with sodium perchlorate, having a small size of ions, displayed superior capacitance, rate performance, and power density, but comparable energy density when compared with a common organic electrolyte for any given porous carbon. As such, a supercapacitor containing the hybrid electrolyte and activated carbon with an optimized porosity at 800°C demonstrated a record capacitance of 51.3 F/g (20.9 F/cm3) at 0.1 A/g. It is expected that this crucial analysis could guide the design and applications of hybrid electrolytes for practical supercapacitors.