Nacre-inspired composite films with high mechanical strength constructed from MXenes and wood-inspired hydrothermal cellulose-based nanofibers for high performance flexible supercapacitors

Two dimensional MXenes with fascinating characteristics of high electrical conductivity, high density and electroactivity show promising applications in various fields. However, the direct applications of MXenes have been limited due to their inferior mechanical properties and easy restacking. Herein, a kind of nacre-like composite film constructed with Ti3C2Tx, cellulose nanofiber (HCNF) and sodium lignosulfonate (Lig) obtained through the hydrothermal process, named Ti3C2Tx/HCNF@Lig, has been successfully synthesized. The hydrothermal cellulose nanofiber (HCNF) film shows an enhanced mechanical strength (114 MPa) compared to that of the CNF film (95 MPa). Wood-inspired HCNF@Lig composite films present an enhanced mechanical tensile strength of up to 133 MPa. Nacre-like deformable Ti3C2Tx/HCNF@Lig(3@1) composite films exhibit high conductivity (up to 1.75 × 105 S m-1) and mechanical properties (up to 258 MPa). The electrodes of Ti3C2Tx/HCNF@Lig(3@1)97/3 composite film assembled flexible solid-state supercapacitors possess an excellent volumetric specific capacitance of 748.96 F cm-3. The corresponding deformable supercapacitors show an excellent energy density of 16.2 W h L-1 and outstanding electrochemical cycling stability. The as-prepared nacre-like Ti3C2Tx/HCNF@Lig composite films with high mechanical properties and electrochemical performance are expected to be practically applied in flexible/wearable energy storage devices.