LAUSR

Symmetric aqueous microsupercapacitors (MSCs) generally show a low working voltage (≤1 V) and narrow operating temperature window in the vicinity of 25 °C due to the poor temperature tolerance and instability of conventional aqueous electrolytes under high voltage. It is challenging to develop MSCs that can offer a high‐voltage output (>2 V) under complex ambient temperature. In this work, a symmetric MSC is fabricated by using the anti‐freezing and heat‐tolerant aqueous polyacrylamide polyelectrolyte (HVTT‐PAM‐10.5) and carbon nanotube microelectrodes, which achieves a record high output voltage of 2.3 V and the widest operating temperature window of −40 to 100 °C among the aqueous MSCs reported previously. It can deliver an ultrahigh areal energy density of above 4.9 μWh cm−2 at temperatures from −40 to 100 °C, outperforming the previous carbon‐based MSCs with aqueous electrolytes at room temperature. Additionally, even after 324 000 cycles at −40 °C and 10 000 cycles at 100 °C, the MSC still retains the high capacitance retention of 92.6% and 90.4%, respectively. Impressively, the HVTT‐PAM‐10.5 polyelectrolyte can also be paired with other electrode materials such as CNT/polyaniline to obtain the highest energy density of 48.6 μWh cm−2 among all symmetric/asymmetric MSCs with aqueous electrolytes.