High energy density of two-dimensional MXene/NiCo-LDHs interstratification assembly electrode: Understanding the role of interlayer ions and hydration

The application of two-dimensional layered hybrid materials in supercapacitor electrodes has high energy density. However, the hybrid assembly and electrochemical energy storage mechanism of multifarious layered electrode materials are still unclear. In this work, a two-dimensional interstratification assembly hybrid electrode by using electrostatic assembly between MXene modified with cetyl trimethylammonium bromide cation (CTAB) and NiCo-LDHs modified with dodecyl benzene sulfonic acid anion (DBS) is presented. As a result, the self-restacking of MXene and NiCo-LDHs nanosheets are effectively prevented, leading to a regular interstratification structure and large interlayer spacing, which accelerate diffusion of electrolyte ions and possess more electrochemical activity sites. The freestanding MXene/NiCo-LDHs electrode displays a much higher specific capacitance of 1207 F g(-1) at a scan rate of 0.5 A g(-1), an impressive rate capability with 93% capacitance retention after 5000 cycles. Moreover, it shows maximum energy density of 107.3 Wh kg(-1) (98.5 mWh cm(-3)) at a power density of 571 W kg(-1) (524 mW cm(-3)), which is among the highest values reported for MXene and NiCo-LDHs based materials in aqueous electrolytes. This significant electrochemical performance is mainly attributed to hydration of two-dimensional electrodes and exchange or adsorption of interlayer anion-cation.