Self-Standing Ti₃C₂T_x/MoO_3–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°, demonstrating excellent flexibility. Such a self-standing Ti3C2Tx/MoO3–x composite film and its flexible solid-state symmetric supercapacitor show great potential in wearable and portable electronic devices.