Temperature Tolerant, Anti-Drying Supercapacitor Based on Organohydrogel Electrolyte

According to the increased demand for wearable devices, there has been extensive research on flexible energy storage devices including batteries and supercapacitors. Among them, flexible supercapacitors based on hydrogel electrolytes can be facilely applied to various wearable electronic devices. However, hydrogel easily freezes at sub-zero temperatures and evaporates at high temperatures due to water contents, limiting the operation temperatures for the supercapacitors. As an alternative to hydrogels, organohydrogels with anti-freezing and evaporation resistance have been paid a vast attention.<br/>We report on the fabrication of a temperature-resistant, anti-drying, flexible supercapacitor based on polyacrylamide/poly(2-acrylamido-2-methyl-1-propanesulfonic acid) PAAM/PAMPS organohydrogel. The organohydrogel electrolyte is synthesized via UV initiated one-pot polymerization of a precursor solution containing acrylamide, 2-acrylamido-2-methyl-1-propanesulfonic acid, water, ethlyene glycol, LiCl, a cross-linker of N,N‘-methylenebisacrylamide and an initiator of ammonium persulfate. As temperature tolerant conductive electrodes, polyaniline/multi-walled carbon nanotubes deposited on a flexible graphite substrate is used. Using such prepared electrodes and organohydrogel electrolyte, a stack-type supercapacitor is assembled, exhibiting a high areal capacitance of 50 mF cm^-2, energy density of 8 μWh cm^-2 and power density of 90 μW cm^-2 at room temperature. The initial capacitance at room temperature remains at over 75% in the temperature range between -20 and 80 °C. Three repeated cycles of cooling and heating from -20 to 80 °C recovers the capacitance at room temperature, indicating the high temperature tolerance of our fabricated supercapacitor. Furthermore, 80% of the initial capacitance also remains even after 5,000 cycles of charging/discharging in the whole temperature range. These results demonstrate the potential application of our PAAM/PAMPS organohydrogel based supercapacitor to wearable electronics as an integrated energy storage device under extreme temperature conditions.