Constructing expanded ion transport channels in flexible MXene film for pseudocapacitive energy storage

Abstract 2D transition metal carbide (MXene) based flexible films have received increasing attention in the application of energy storage for portable and wearable electronic devices. However, the self-restacking caused by Van der Waals interactions between the layers lead to insufficient access to allow the electrolyte ions to contact the active material. Herein, we rationally utilized the freeze-drying technique to prepare MXene film electrode for alleviating its self-restacking and improving the electrochemical performances. Through freeze-drying treatment, the frozen solvent molecules were removed by sublimation, and alleviating the adverse effect of van der Waals forces and contributing to the enlarged layer space. The constructed freeze-dried MXene (f-MXene) films generate unique porous architecture, which can provide highly efficient ion diffusion and transport channels. Consequently, the typical f-MXene-10 film exhibit good specific capacitance (341.5 F g−1/922.1 F cm−3 at 1 A g−1) and desired capacitance retention of 60.4% from 1 to 10 A g−1. Moreover, the assembled asymmetric device delivered a maximal gravimetric energy density of 6.1 Wh Kg−1, volumetric energy density of 16.4 Wh L−1 and a good capacitance retention of 89.3% after 10,000 cycles. The rationally designed synthesizing route has attractive promise to promote MXene materials for diverse energy and environmental applications.