Abstract
Expanding the range of supercapacitor operation to temperatures above 100°C is important because this would enable capacitors to operate under the severe conditions required for next-generation energy storage devices. In this study, we address this challenge by the fabrication of a solid-state supercapacitor with a proton-conducting Sn0.95Al0.05H0.05P2O7 (SAPO)-polytetrafluoroethylene (PTFE) composite electrolyte and a highly condensed H3PO4 electrode ionomer. At a temperature of 200°C, the SAPO-PTFE electrolyte exhibits a high proton conductivity of 0.02 S cm−1 and a wide withstanding voltage range of ±2 V. The H3PO4 ionomer also has good wettability with micropore-rich activated carbon, which realizes a capacitance of 210 F g−1 at 200°C. The resulting supercapacitor exhibits an energy density of 32 Wh kg−1 at 3 A g−1 and stable cyclability after 7000 cycles from room temperature to 150°C.
Highlights
Expanding the range of supercapacitor operation to temperatures above 1006C is important because this would enable capacitors to operate under the severe conditions required for next-generation energy storage devices
Both aqueous electrolytes (H2SO4 or KOH) and organic electrolytes limit the operation temperature to typically 100uC or lower, due to their low boiling points[8,9,10]. In contrast to these electrolytes, room-temperature ionic liquids (RTILs) are stable even at 300uC, due to the absence of solvent[11]; the ionic conductivity of these materials at room temperature is as low as a few millisiemens per centimeter[12], which results in low power densities
No abrupt decrease in the ionic conductivity with temperature was observed in the temperature range tested, which is similar to the case for H3PO4
Summary
Expanding the range of supercapacitor operation to temperatures above 1006C is important because this would enable capacitors to operate under the severe conditions required for next-generation energy storage devices. (Separators such as cellulose papers, polymers, and glass wool shrink under such conditions, causing electrical shorts in the device.) For next-generation automotive applications, high ionic conductivity and stability of the electrolyte over a wide temperature range (230 to preferably #200uC) will be crucial for the operation of high-temperature supercapacitors. The high-temperature performance of EDL-type supercapacitors with these electrolytes has not been studied thoroughly In spite of these efforts, the capacitance of so-called solid-state supercapacitors still remains strongly dependent on the protonics of the electrode employed because the EDL is formed only at the interface of the electrolyte and electrode. The goals of the present work were to (1) optimize the electrolyte and ionomer materials, (2) improve the surface utilization of microor mesoporous carbon, and (3) conduct capacitor tests using an optimized combination of electrolyte, ionomer, and carbon from room temperature to 200uC
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