MnO₂|activated carbon supercapacitors are attractive power devices that rival the electric double-layer capacitors (EDLCs) due to high reachable voltage. However, they greatly suffer from performance loss at low temperature as most of aqueous electrolytes freeze below ca. -10°C. Here, a concentrated choline nitrate-based (5 mol/L aqueous ChNO₃) electrolyte is applied to extend the working temperature range due to its eutectic-like properties. In such electrolyte, water acts as hydrogen bond donor for nitrate anion and low hydration energy for large choline cations favors ionic transport. The MnO₂/CNT composite electrode with a hierarchical structure has been synthesized by hydrothermal process. The presence of CNTs as core component facilitates the electron conduction, while the two-dimensional MnO₂ flakes grown on the surface provide electrolyte transport pathways and improve the interfacial processes (pseudocapacitive charge/discharge). Thanks to the low hydration of choline cation, the individual activated carbon (AC, negative) and MnO₂/CNT (positive) electrodes are charged symmetrically up to a cell voltage of 1.8 V. Overall, due to the wide electrochemical stability window (∼2.0 V) and anti-freezing properties of ChNO₃-based aqueous electrolyte and the hierarchical design of the MnO₂/CNT composite, the asymmetric supercapacitor operates down to -40 °C and displays excellent energy and coulombic efficiency with no loss of performance after several thousand cycles. This work provides a new possibility on the low temperature application of high voltage supercapacitors.

MnO ₂ |活性炭超级电容器是极具吸引力的功率器件，可与双电层电容器 (EDLC) 相媲美，因为它具有高可达电压。然而，由于大多数水性电解质在低于 ca 时结冰，它们在低温下的性能损失很大。-10℃。在这里，一种浓缩的硝酸胆碱基（5 mol/L ChNO ₃水溶液）电解质由于其类似共晶的特性而被用于扩展工作温度范围。在这种电解质中，水充当硝酸根阴离子的氢键供体，大胆碱阳离子的低水合能有利于离子传输。_二氧化锰采用水热法合成了具有分级结构的/CNT复合电极。碳纳米管作为核心成分的存在促进了电子传导，而在表面生长的二维 MnO ₂薄片提供了电解质传输途径并改善了界面过程（赝电容充电/放电）。由于胆碱阳离子的低水合作用，单个活性炭（AC，负极）和 MnO ₂ /CNT（正极）电极对称充电至 1.8 V 的电池电压。总体而言，由于宽电化学稳定性窗口（~ 2.0 V)和ChNO ₃基水系电解质的抗冻性能和MnO ₂的分层设计/CNT 复合材料，这种不对称超级电容器的工作温度可低至 -40 °C，并显示出出色的能量和库伦效率，在数千次循环后不会损失性能。该工作为高压超级电容器的低温应用提供了新的可能。