Hierarchically layered nanocomposite electrodes formed by spray-injected MXene nanosheets for ultrahigh-performance flexible supercapacitors

Abstract Although MXenes with outstanding electrical conductivity possess great potential as energy-storage materials for flexible supercapacitors (SCs), the electrochemical performance of the pure MXene-based SCs are often restricted by inherent limitations such as inferior energy densities and serious aggregation. Alternatively, it will be an effective strategy to develop rationally designed composite electrodes that can simultaneously provide both high electrical conductivity and large surface area via complementary functions of each constituent. Here, hierarchically layered MXene nanosheets on nickel cobalt sulfide/carbon cloth (Ti3C2Tx/NiCo2S4@CC, herein TNSC) was prepared through spray injection of MXene on nickel cobalt sulfide, which not only achieved an excellent specific capacitance at high current densities but also possess improved cycling stability. The optimized TNSC electrode shows maximum specific capacities of 2326F g−1 at a current density of 1 A g−1, and excellent cycling stability of 93.8% at 10 A g−1. We show that these outstanding electrochemical performances can be achieved by a proper loading amount of surface-coated Ti3C2Tx, which can simultaneously enhance electrical conductivity and permeate ions to nickel cobalt sulfide. Furthermore, a quasi-solid‐state flexible SC (QFSC) based on TNSC presents a high energy density of 57.5 W h kg−1 at a power density of 800 W kg−1 in a wide potential window of 1.6 V. Therefore, the excellent electrochemical performances of the TNSC electrode makes it as a prominent candidate for high-performance and flexible energy storage devices.