Highly conductive V4C3Tx MXene-enhanced polyvinyl alcohol hydrogel electrolytes for flexible all-solid-state supercapacitors

Hydrogel electrolytes are an integral part of flexible solid-state supercapacitors. To further improve the low ionic conductivity, large interfacial resistance and poor cycling stability for hydrogel electrolytes, the V₄C₃T _<i>x</i> MXene-enhanced polyvinyl alcohol hydrogel electrolyte was fabricated to enhance its mechanical and electrochemical performance. The high-conductivity V₄C₃T _<i>x</i> MXene (16,465.3 S m^-1) bonding transport network was embedded into the PVA-H₂SO₄ hydrogel electrolyte (PVA- H₂SO₄-V₄C₃T _<i>x</i> MXene). Results indicate that compared to the pure PVA-H₂SO₄ hydrogel electrolyte (105.3 mS cm^-1, 48.4%@2,800 cycles), the optimal PVA-H₂SO₄-V₄C₃T _<i>x</i> MXene hydrogel electrolyte demonstrates high ionic conductivity (133.3 mS cm^-1) and commendable long-cycle stability for the flexible solid-state supercapacitors (99.4%@5,500 cycles), as well as favorable mechanical flexibility and self-healing capability. Besides, the electrode of the flexible solid-state supercapacitor with the optimal PVA-H₂SO₄-V₄C₃T _<i>x</i> MXene hydrogel as the solid-state electrolyte has a capacitance of 370 F g^-1 with almost no degradation in capacitance even under bending from 0° to 180°. The corresponding energy density for flexible device is 4.6 Wh kg^-1, which is twice for that of PVA-H₂SO₄ hydrogel as the solid-state electrolyte.