Flower-like NiMn layered double hydroxide coupled with carbon nanotube arrays on nickel mesh as binder-free electrode for asymmetric supercapacitor

Flower-like nickel manganese layered double hydroxide coupled with carbon nanotube arrays in-situ grown on a nickel mesh (NiMn-LDH/CNTs@Ni) has been prepared by a facile hydrothermal method. By increasing the Mn/Ni ratio, the thickness of the LDH nanosheets increased while the spherical structure built up from the interconnected LDH nanosheets degraded. The optimized NiMn-LDH/CNTs@Ni exhibits a three-dimensional flower-like structure with the CNT arrays in-situ grown on nickel mesh by chemical vapor deposition method acting as stems to connect the NiMn-LDH nanoflowers. The prepared NiMn-LDH/CNTs@Ni exhibit high specific capacitance of 1367 F g−1 at 1 A g−1, capacitance retention of 76% at 10 A g−1 and excellent cycling performance in 3 M KOH aqueous solution. First-principles calculations show that Mn doping improves the electron transport and charge transfer capabilities by narrowing the energy gap and increasing the density of states near the Fermi level, which is conducive to enhancing the charge storage capacity. Asymmetric supercapacitors fabricated with NiMn-LDH/CNTs@Ni and nitrogen-doped carbon nanotubes exhibited energy densities as high as 31.8 W h kg−1 at a power density of 800 W kg−1, demonstrating the potential of the fabricated binder-free electrodes for practical applications. This study demonstrates that modulating the electronic structure and nanostructure by doping hetero metal atoms can effectively improve the charge storage capacity of LDHs.