Crumpled MXene Electrodes for Ultrastretchable and\nHigh-Area-Capacitance Supercapacitors

In\nspite of the excellent electrical and electrochemical properties,\ntwo-dimensional transition metal carbide (MXene) is often limited\nby the high stiffness for the direct implementation in next-generation\nstretchable and wearable energy storage devices. The improved deformability\nhas been achieved in ultrathin composite electrodes utilizing additives\nthat substantially reduce the specific capacitance. Here, we demonstrate\nan ultrastretchable and high-performing supercapacitor based on MXene\nelectrodes with crumpled textures. After screening on the thickness,\nthe crumpled MXene film of ∼3 μm in thickness is identified\nas the optimal choice to mitigate the crack formations under large\nand repetitive mechanical strains. The as-prepared symmetric supercapacitor,\ntherefore, demonstrates a high specific capacitance of ∼470\nmF cm^–2, ultrahigh stretchability up to 800% area\nstrain, and >90% retention of the initial capacitance after 1000\nstretch–relaxation\ncycles. The developments offer an attractive avenue to design stretchable\nelectrodes based on various two-dimensional nanomaterials and their\ncomposites.