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 (Ti3C2Tx)/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 Ti3C2Tx 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.