A Supercapacitor Architecture for Extreme Low‐Temperature Operation Featuring MXene/Carbon Nanotube Electrodes with Vertically Aligned Channels and a Novel Freeze‐Resistant Electrolyte
Tianyu Zhao, Dongzhi Yang, Bai‐Xue Li, Yongzheng Shi, Qiuyan Quan, Nikhil Koratkar, Zhong‐Zhen Yu
Abstract
Abstract 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.