Improved volumetric pseudocapacitance electrode obtained by solvothermal treatment of diethanolamine and different auxiliary solvents with MXene

Abstract Flexible supercapacitors (SCs) can usually be used as potential candidates for small flexible electronic devices, due to their good flexibility, rapid charge-discharge ability, and long-term cycling stability. Here, a facile solvothermal approach has been developed to prepare flexible and high-performance nitrogen-doped Ti3C2 MXene film electrodes for symmetric SCs. The effects of different solvents on the atomic structure, surface microstructure, and charge storage mechanism of N-doped Ti3C2 films were studied to explore the defect engineering of MXene for the enhancement of capacitive performance. Because of the comprehensive effects of the mixed solvents (diethanolamine (DEA) and isopropyl alcohol (IPA)) and the large inner pressure under the ex situ solvothermal process, the as-prepared N-doped Ti3C2 film fabricated from DEA and IPA with a volume ratio of 1:1 (IPAD-Ti3C2) shows a superhigh capacitance of 2,846.5 F cm−3 at 5 mV s−1 and excellent stability. In addition, the IPAD-Ti3C2 film-assembled symmetric SC delivers a relatively large volumetric energy density of 64.0 Wh L−1 and a superhigh volumetric power density of 118,033.3 W L−1 at 1,000 mV s−1. This work provides a feasible solution to improve the application potential of MXenes and, more broadly, binary metal carbides by ex situ nitrogen doping with mixed solvents.