Synthesis and electrochemical performance of graphene/metal oxide nanocomposite electrodes in lithium secondary batteries and supercapacitors

A graphene/NiO and graphene/NiO-MnO₂ nano-composites were prepared by simple chemical precipitation followed by thermal annealing and using a chelating agent and Ni and Mn hydroxides on graphene. The graphene/NiO-MnO₂ was pretreated by ultrasonication followed by thermal annealing at 300°C for 2 h. Graphene/MoO₂-MoS₂ composites were prepared by a hydrothermal reaction of molybdenum(IV) oxide with sodium sulfide and subsequent ball-milling with graphene. The results of XRD, FE-SEM, and FE-TEM analyses confirmed the presence of NiO, MnO₂, MoO₂-MoS₂ nanoparticles on the graphene surface. In the properties of anodes in lithium-ion batteries, the discharge capacities of graphene, graphene/NiO (59 wt.%) are about 302 and 856 mAh g^-1 at 5000 mA g^-1 (5 C), respectively. The cells containing 59 wt.% NiO show the best performance, and the graphene nanocomposite materials have high rate properties that are comparable to some of the good results reported in the literature using NiO. The mole ratios of MoO₂ and MoS₂ in the synthesized MoO₂-MoS₂ powder were found to be approximately 62.3:37.7. The graphene/MoO₂-MoS₂ composite anodes showed a high discharge capacity (~974 mAh g^-1) after 20 cycles and superior high-rate capability. In the properties of electrode in supercapacitor, the maximum specific capacitance of the graphene/NiO-MnO₂ electrode was 242.15 F g^-1 by cyclic voltammetry at a scan rate of 0.2 mV s^-1, which was significantly higher than that of a graphene electrode.