LiMn2O4/graphene composites as cathodes with enhanced electrochemical performance for lithium-ion capacitors

A LiMn2O4 microsphere (LMO-MS)/graphene nanosheet (GNS) composite has been synthesized using gamma-MnO2 microspheres as a precursor. It is characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). The test results suggest that the sphere-like LMO-MSs structures were successfully coated by the GNSs. A novel lithium-ion capacitor was fabricated using activated carbon as the anode electrode and LMO-MSs@GNSs composite as the cathode electrode. The electrochemical properties were investigated by galvanostatic charge/discharge cycling and cycling voltammetry. The electrochemical test results show that the energy density of the LMO-MSs@GNSs composite lithium-ion capacitor presents 38.8 W h kg(-1) at a power density 12.6 W kg(-1) with an organic electrolyte in the voltage range of 0-2.3 V. The synergistic effect of GNSs and LMO-MSs could significantly improve the electrical conductivity and provides more reaction sites, thereby resulting in the better electrochemical properties of the composites. The high rate capacity and longterm stability make the LMO-MSs@GNSs composite a suitable electrode material for high-performance lithium-ion capacitors.