Hierarchical Vertically Aligned Titanium Carbide (MXene) Array for Flexible All-Solid-State Supercapacitor with High Volumetric Capacitance

The traditional method for fabricating film electrodes may cause the restacking of the nanomaterials, which leads to the severe reduction of specific surface area and hinders the contact of ions with active sites. Herein, a vertically aligned hierarchical array structure is achieved with the accordion-structured MXene particles as the building block, and high-performance flexible all-solid-state supercapacitors (ASSSs) are fabricated with this original structure. These electrodes not only retain the accordion structure of MXene but also possess a micron-scale array structure, which could both avoid the restacking of the two-dimensional nanomaterials and facilitate the ion migration and electron transport in the solid-state devices. The as-prepared ASSSs exhibited a high volumetric capacitance of 485 F cm^–3 at 1 A cm^–3 with an ultrahigh energy density of 9.6 mWh cm^–3, and a power density of 2800 mW cm^–3 under the optimal conditions, and demonstrate high flexibility and weakened correlation between capacitance properties with material thickness. This hierarchical array structure achieves a remarkable increase in specific capacitance by ∼200% compared with that of the film counterpart, which demonstrates a valid way to design electrodes for electrochemical energy storage and generation devices.