Free-standing cotton-derived carbon microfiber@nickel-aluminum layered double hydroxides composite and its excellent capacitive performance

The main bottleneck of supercapacitor is its low energy density, mainly arising from the low capacity of the electrode materials. Although some pseudocapacitive metal oxide/hydroxides have been selected to improve the energy density of supercapacitor, their low conductivity and inferior reversibility still need to be considered. In this work, we prepared a free-standing composite comprised of NiAl-layered double hydroxide (LDH) nanoflakes decorated on a cotton derived carbon microfiber (CMF@NiAl-LDH) via a facile hydrothermal method. The large-scale and compressible cotton derived carbon fiber with connected three-dimensional pores served as conductive backbones for the growth of the NiAl-LDH nanoflakes. It can not only improve the conductivity of NiAl-LDH, but also amend the distribution of NiAl-LDH nanosheets, leading to both rapid electron and electrolyte ions transport kinetics. The abundant space among NiAl-LDH nanoflakes as well as developed 3D pores of CMF can accommodate the volume expansion of NiAl-LDH during long lifespan cycling. Benefited from these rational design, the as-prepared CMF@NiAl-LDH electrode exhibited significantly improved capacitive performance in terms of high specific capacitance (1667 F g⁻¹ at 1 A g⁻¹), excellent rate performance (68.7% retained at 15 A g⁻¹) and remarkable cyclic stability (105.4% maintained after 2000 cycles) in aqueous electrolytes. The assembled CMF@NiAl-LDH//porous carbon asymmetric supercapacitor can deliver a large energy density of 45.2 Wh Kg⁻¹. This investigation suggests that the prepared CMF@NiAl-LDH electrode offers a great potential in large-scale energy storage device applications.