A facile “thick to thin” strategy for integrating high volumetric energy density and excellent flexibility into MXene/wood free-standing electrode for supercapacitors

Wood-based thick electrodes (>400 μm) always exhibit low volumetric loading of active material and poor flexibility. Herein, a “thick to thin” strategy including densification and low-temperature heating treatment is innovatively proposed and then applied in a MXene (Ti 3 C 2 T x )/wood thick electrode (500 μm) to simultaneously realize large volumetric loading and excellent flexibility. It is found that the densification can significantly increase the volumetric mass loading of Ti 3 C 2 T x by 10 times owing to the great reduction of the electrode thickness (50 μm), and endow the electrode with excellent flexibility by changing porous microstructure to compact microstructure. Furthermore, the low-temperature heating treatment greatly improves the electrochemical performances of the electrode by generating meso -/macropores for ion transport and exposing more active sites to the electrolyte. After conducting our proposed strategy, the optimized electrode exhibits 9 times higher volumetric capacitance (reaching 187F cm −3 ) than the control electrode, and still has a high rate capability of 77 % when the current density increases by 100 folds. Additionally, the optimized free-standing electrode is used to fabricate a quasi-solid-state supercapacitor which demonstrates stable capacitive behaviors during bending and a large volumetric energy density of 3 mWh cm −3 at 30.6 mW cm −3 .