A morphology control engineered strategy of TiCT/sulfated cellulose nanofibril composite film towards high-performance flexible supercapacitor electrode.

2D TiCT MXene is an ideal material for fabricating supercapacitor electrodes due to its excellent physical-chemical properties. However, the inherent self-stacking, narrow interlayer spacing, and low general mechanical strength limit its application in flexible supercapacitors. Herein, facile structural engineering strategies by drying (vacuum drying, freeze drying, and spin drying) were proposed to fabricate 3D high-performance TiCT/sulfated cellulose nanofibril (SCNF) self-supporting film supercapacitor electrodes. Compared with other composite films, the freeze-dried TiCT/SCNF composite film exhibited a looser interlayer structure with more space which was conducive to charge storage and ion transport in the electrolyte. Therefore, the freeze-dried TiCT/SCNF composite film exhibited a higher specific capacitance (220 F/g) compared to the vacuum-dried TiCT/SCNF composite film (191 F/g) and the spin-dried TiCT/SCNF composite film (211 F/g). After 5000 cycles, the capacitance retention rate of the freeze-dried TiCT/SCNF film electrode was close to 100 %, showing excellent cycle performance. Meanwhile, the tensile strength of freeze-dried TiCT/SCNF composite film (13.7 MPa) was much greater than that of the pure film (7.4 MPa). This work demonstrated a facile strategy for control of TiCT/SCNF composite film interlayer structure by drying for fabricating well-designed structured flexible and free-standing supercapacitor electrodes.