Self-Standing Ti3C2Tx/MoO3-x Composite Films with High Volumetric and Gravimetric Capacitance Performances for Flexible Solid-State Supercapacitors

Two-dimensional MXene materials have received a great deal of attention for their use in energy storage. However, MXene usually suffers from severe self-restacking, which leads to the active sites being covered, hinders the electrolyte ion transport, and thus affects the electrochemical performance. In the present work, molybdenum trioxide with oxygen vacancy (MoO3-x) nanobelts as the interspacer and active electrode material were introduced into Ti3C2Tx, a member of MXenes family, by the vacuum-assisted filtration method to form the self-standing film. Conductive Ti3C2Tx nanosheets bridge MoO3-x nanobelts to facilitate electron transfer, and MoO3-x nanobelts are randomly intercalated between Ti3C2Tx nanosheets to effectively prevent self-restacking of Ti3C2Tx, provide pseudocapacitance, and promote wettability. The Ti3C2Tx/MoO3-x-50% displays high volumetric/gravimetric capacitance performances (1893.2 F cm(-3) and 733.8 F g(-1) at 1 A g(-1) and at 20 A g(-1) with 1578.7 F cm(-3) and 611.9 F g(-1)), outperforming reported Ti3C2Tx, Ti3C2Tx-based, or MoO3-based composites. Furthermore, Ti3C2Tx/MoO3-x-50% presents capacitance retention of 90.2% after 2000 cycles, showing good cycling stability. The assembled Ti3C2Tx/MoO3-x-50%//Ti3C2Tx/MoO3-x-50% flexible solid-state supercapacitor using a PVA/H2SO4 gel electrolyte displays high volumetric/gravimetric energy densities (25.8 W h L-1 at 448.7 W L-1 and 10.0 W h kg(-1) at 173.9 W kg(-1)) and good cycling stability. In addition, the supercapacitor shows little significant capacitance loss after 100th bending cycle of 180 degrees, demonstrating excellent flexibility. Such a self-standing Ti3C2Tx/MoO(3-x )composite film and its flexible solid-state symmetric supercapacitor show great potential in wearable and portable electronic devices.