3D Cross-linked Ti3C2Tx-Ca-SA films with expanded Ti3C2Tx interlayer spacing as freestanding electrode for all-solid-state flexible pseudocapacitor

Ti3C2Tx, a member of the MXene, has attracted extensive interest because of its high conductivity, unique two-dimensional (2D) structure and intrinsic pseudocapacitance for supercapacitors. Flexible and freestanding Ti3C2Tx films are promising electrodes for functioned supercapacitors used in wearable and portable electronic devices. However, the severe self-restacking of 2D Ti3C2Tx nanosheets restraints their practical application. Herein, freestanding and flexible three-dimensional (3D) cross-linked Ti3C2Tx-Ca-SA (sodium alginate) films with expanded Ti3C2Tx interlayer spacing are reported. The expanded interlayer spacing allows more electrolyte ions to quickly intercalate providing more intercalation pseudocapacitance, while the 3D cross-linked microstructure ensures a continuous conductive network facilitating charges transport. Attributing to the unique structure, the Ti3C2Tx-Ca-SA film delivers an outstanding areal capacitance (633 mF cm-2 at 5 mV s-1). Meanwhile, the assembled all-solid-state pseudocapacitor shows good flexibility and capacity stability under various bending conditions. The device exhibits a high energy density up to 12.6 µWh cm-2 at the power density of 375 µW cm-2 and excellent cycling stability, which are much better than prior reported state-of-the-art supercapacitors. This research exploits a simple method to optimize the structure of MXene as state-of-the-art electrodes for high-performance flexible energy-storage devices.