High-Performance Flexible Quasi-Solid-State Supercapacitors Realized by Molybdenum Dioxide@Nitrogen-Doped Carbon and...

Flexible quasi-/all-solid-state supercapacitors have elicited scientific attention to fulfill the explosive demand for portable and wearable electronic devices. However, the use of electrode materials faces several challenges, such as intrinsically slow kinetics and volume change upon cycling, which impede the energy output and electrochemical stability. This study presents well-aligned molybdenum dioxide@nitrogen-doped carbon (MoO₂@NC) and copper cobalt sulfide (CuCo₂S₄) tubular nanostructures grown on flexible carbon fiber for use as electrode materials in supercapacitors. Benefiting from the chemically stable interfaces, affluent active sites, and efficient 1D electron transport, the MoO₂@NC and CuCo₂S₄ nanostructures integrated on conductive substrates deliver excellent electrochemical performance. A flexible quasi-solid-state asymmetric supercapacitor composed of MoO₂@NC as the negative electrode and CuCo₂S₄ as the positive electrode achieves an ultrahigh energy density of 65.1 W h kg^-1 at a power density of 800 W kg^-1 and retains a favorable energy density of 27.6 W h kg^-1 at an ultrahigh power density of 12.8 kW kg^-1. Moreover, it demonstrates good cycling performance with 90.6% capacitance retention after 5000 cycles and excellent mechanical flexibility by enabling 92.2% capacitance retention after 2000 bending cycles. This study provides an effective strategy to develop electrode materials with superior electrochemical performance for flexible supercapacitors.