A Supercapacitor Architecture for Extreme Low‐Temperature Operation Featuring MXene/Carbon Nanotube Electrodes with Vertically Aligned Channels and a Novel Freeze‐Resistant Electrolyte

• Published in: Advanced functional materials Vol. 34; no. 24
• Main Authors: Zhao, Tianyu, Yang, Dongzhi, Li, Bai‐Xue, Shi, Yongzheng, Quan, Qiuyan, Koratkar, Nikhil, Yu, Zhong‐Zhen
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.06.2024
• Subjects: Capacitance; Carbon nanotubes; Channels; Charge transfer; Electrochemical analysis; electrode architecture; Electrodes; Electrolytes; Energy storage; Feasibility studies; Freezing; Ion currents; Ion transport; Ionic liquids; ionogels; Low temperature; low‐temperature resistance; MXene/carbon nanotube film; MXenes; Supercapacitors; Synthesis; Temperature; Tortuosity
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202314825

The electrochemical performance of supercapacitors drops precipitously at extreme low temperatures due to a multitude of reasons, which includes electrolyte freezing, sluggish ion transport in the electrode and electrolyte, and high charge transfer resistance at electrode–electrolyte interfaces. To address high interface resistance, a new supercapacitor architecture is reported, in which MXene/carbon nanotube electrodes with vertically aligned channels are synthesized to reduce tortuosity and maximize the electrode–electrolyte contact area. These electrodes are fabricated using a directional‐freezing strategy, generating direct and fast ion transport pathways. Further, a freeze‐resistant electrolyte which shows high ionic conductivity is synthesized by designing a double‐crosslinked polymer network in a binary solvent consisting of ionic liquid and water, which exhibits an ultralow freezing temperature of −54 °C. An all‐in‐one supercapacitor is assembled by an integrated polymerization strategy to minimize interfacial resistances. The resulting device delivers a specific capacitance of 231 F g−1 at 2 mV s−1 and a maximum energy density of 10.17 Wh kg−1, while maintaining a capacitance retention of 92%, even at an extreme low temperature of −50 °C. The supercapacitor architecture developed in this study, demonstrates the feasibility of electrochemical energy storage at extreme low temperatures. A novel supercapacitor for extreme low‐temperature operation is constructed, consisting of MXene/carbon nanotube electrodes with vertically aligned channels to generate direct and fast ion transport pathways, and a freeze‐resistant ionogel electrolyte. The device delivers a specific capacitance of 231 F g−1 at 2 mV s−1 and maintains a capacitance retention of 92% even at −50 °C.