Novel synthesis of manganese cobalt layered double hydroxide and sulfur-doped nickel cobalt layered double hydroxide composite as efficient active material of battery supercapacitor hybrids

Nickel and cobalt layered double hydroxide (NiCo-LDH) is one of promising active materials of battery supercapacitor hybrids (BSH) as the clean renewable energy. Designing composites and doping heteroatoms are widely applied to solve poor conductivity, serious agglomeration, and structural defects of NiCo-LDH. In this work, manganese cobalt LDH (MnCo-LDH) is firstly incorporated in sulfur-doped NiCo-LDH (S-NiCo-LDH) on Ni foam (NF) via the hydrothermal process as a binder-free electrode of BSH. Favorable morphology with nanowires covered on the vertical grown nanosheet array is successfully designed for MnCo-LDH/S-NiCo-LDH with the large specific surface area and the well-established pore structure. The specific capacitances (C_F) of 681.4, 953.9 and 1581.3 F/g are respectively achieved for the NiCo-LDH, S-NiCo-LDH, MnCo-LDH/S-NiCo-LDH electrodes at the current density of 1 A/g. The larger C_F value of MnCo-LDH/S-NiCo-LDH is due to larger conductivity and effective charge transfer paths. A BSH assembled using MnCo-LDH/S-NiCo-LDH/NF and graphene/NF electrodes shows a wide potential window of 1.6 V, a large maximum energy density of 46.6 Wh/kg at 0.8 kW/kg, and an excellent cyclic stability with the C_F retention of 81% and the Coulombic efficiency higher than 87% after 10,000 times charge/discharge process at the current density of 7 A/g.