High
cost, low capacitance, and complicated synthesis process are
still the key limitations for carbon-negative materials to meet their
industrial production and application in high-energy-density asymmetric
supercapacitors (ASCs). In this work, we demonstrate the facile preparation
of ultrahigh-surface-area free-standing carbon material from low-cost
industrial carbon felt (CF) and its application for flexible supercapacitor
electrode with outstanding performance. Through a simple freeze-drying-assisted
activation method, the as-prepared activated CF (ACF) was endowed
with satisfactory flexibility, ultrahigh specific surface area of
2109 m2 g–1, good electric conductivity
(311 S m–1), and excellent wettability to aqueous
electrolyte. Owing to these merits, the ACF expressed an ultrahigh
areal capacitance of 1441 mF cm–2, a high specific
capacitance (C
s) of 280 F g–1 based on the mass of the whole electrode, and an impressive cycling
stability (87% retention after 5000 cycles). When applied as a flexible
freestanding electrode for MnO2//ACF ASCs, the ACF-based
device provided satisfactory areal energy densities of 0.283 and 0.104
mWh cm–2 in aqueous and quasi-solid electrolytes,
respectively. The values outperform many previously reported carbon-based
electrochemical devices. The low cost of raw material and the facile
fabrication process, together with the high electrochemical performance,
make our ACF electrode highly applicable for the mass production of
flexible energy-storage devices.