Boosting the volumetric energy of supercapacitors using polytetrafluoroethylene pyrolysis gas

Abstract

Increasing the volumetric energy of carbon-based supercapacitors is of practical importance for the advancement of high-powered energy storage. Herein, we use the gases evolved from polytetrafluoroethylene pyrolysis at 800 °C to fluorine-dope an activated carbon, and directly synthesize a fluorine-doped highly porous graphite in the same environment. As supercapacitor materials in organic electrolyte, both resultant fluorine-doped carbons outperform their non-doped counterparts, delivering up to 40% gain in cell volumetric energy at high power cycling. F-doping increases volumetric capacitance (F cm−3) via increase in “real” areal capacity (uF cm−2) and/or increase in “real” volumetric surface area (m2 cm−3), and increases electron conductivity. Considering current collector and separator volume fractions, cells containing the fluorine-doped activated carbon electrode films of 100 and 50 μm deliver an impressive 12.9 Wh L−1 at 0.1 kW L−1 and 6.7 Wh L−1 at 2.15 kW L−1 respectively. We conclude that the gas-based F-doping method affords an effective and less hazardous route to produce fluorine-doped carbons for increased volumetric energy storage.