Mxene (Ti3C2T )/cellulose nanofiber/porous carbon film as free-standing electrode for ultrathin and flexible supercapacitors

Traditional porous carbon (PC)-based supercapacitors (SCs) are generally stiff and heavy owing to their rigid components and bulky additives, such as binders, conducting materials, and current collectors. Herein, a porous (574.5 m2 g−1), conductive (83.1 S cm−1), and flexible MXene (Ti3C2Tx)/cellulose nanofiber (CNF)/PC hybrid film is prepared by strong interfacial interactions among its components via a facile vacuum-filtration method. Three-dimensional PC provides abundant micropores for charge storage and considerable amount of meso/macropores for fast diffusion of ions. Two-dimensional Ti3C2Tx offers a significantly high conductivity of 2.6 × 103 S cm−1 and a good film-forming ability. A one-dimensional CNF ensures high mechanical properties with a tensile strength of 38.6 MPa for the hybrid film by binding the adjacent Ti3C2Tx flakes and PC. Additionally, the presence of CNF and PC increases the interlayer distance between Ti3C2Tx flakes, thereby providing more ion-accessible surface areas on Ti3C2Tx and creating open gaps for fast ion transport. Benefiting from these electrochemically attractive properties, this film is further employed as a free-standing electrode to fabricate a high-performance quasi-solid-state SC, which demonstrates an ultrathin thickness of 0.2 mm, a high flexibility, a significantly high areal capacitance of 143 mF cm−2 at 0.1 mA cm−2, and a large areal energy density of 2.4 μWh cm−2 at 17.5 μW cm−2, with a high retention of ~50% even after increasing the power density by ~100 fold. This work will pave the way for developing free-standing MXene-based hybrid films that simultaneously possess excellent conductivity, good mechanical properties, and large charge storage capacity for flexible and high-performance SCs.