While flexible supercapacitors with high capacitance and energy density is highly desired for outdoor wearable electronics, their application under low-temperature environments, like other energy storage devices, remains an urgent challenge. Solar thermal energy converts solar light into heat and has been extensively applied for solar desalination and power generation. In the present work, to address the failure problem of energy storage devices in a cold environment, solar thermal energy was used to improve flexible supercapacitor performance at low temperature. As a proof of concept presented here, a typical all-solid-state supercapacitor composed of activated carbon electrodes and gel polymer electrolyte was coated by a carbonized melamine sponge. Due to the ability of photothermal conversion of carbonized melamine sponge, the capacitance of the supercapacitor was greatly enhanced, which could be further improved by adding surface plasmonic nanomaterials, for example, Ag nanowires. Compared with the device without photothermal conversion layers, the specific capacitance increased 3.48 times at -20 °C and retained 87% capacitance at room temperature and the specific capacitance increased 6.69 times at -50 °C and retained 73% capacitance at room temperature. The present work may provide new insights on the application of solar energy and the design of energy storage devices with excellent low-temperature resistance.
Keywords: carbonized sponge; energy storage; low-temperature resistance; photothermal conversion; supercapacitor.