Pure Aqueous Planar Microsupercapacitors with Ultrahigh Energy Density under Wide Temperature Ranges

Abstract Currently, limited by factors such as low working voltage (≤1 V), poor temperature tolerance, and underutilization of electrolytes, pure aqueous symmetric planar microsupercapacitors (PMSCs) show unsatisfactory energy density under wide temperature ranges. To address these issues, a novel strategy is introduced to construct pure aqueous PMSCs with an ultrahigh energy density under wide temperature ranges through the development of high‐performance carbon nanotube‐MnO 2 microelectrodes and high‐voltage aqueous polyacrylamide polyelectrolyte with exceptional temperature tolerance and redox‐enhanced function. Notably, the capacitance contribution of alizarin red S redox additives and the outstanding ability to withstand high voltage of polyacrylamide polyelectrolyte play the crucial roles in improving the electrochemical performance of PMSCs. As a result, the constructed microdevice achieves a record‐high working voltage of 2 V at temperatures from −15 °C to 100 °C and ultrahigh areal energy densities of 12.9 μWh cm –2 at −15 °C, 17.4 μWh cm –2 at room temperature and 24 μWh cm –2 at 100 °C, which are superior to those of previously reported pure aqueous PMSCs at the temperature. Meanwhile, it also shows good flexibility and excellent cycling stability (92.7% after 25 000 cycles at −15 °C and 81% after 20 000 cycles at 100 °C).