Carbon/λ-MnO2 composites for supercapacitor electrodes

In the present work a composite of carbon with λ-MnO2 have been synthesized by a simple two-step route. In the first step, to obtain LiMn2O4/carbon material, mesoporous activated carbon was impregnated with the solution of precursor metal salts and heated subsequently. As-prepared materials were acid treated which resulted in the formation of λ-MnO2/carbon. Physical properties, structure and specific surface area of electrode materials were studied by TEM, X-ray diffraction and nitrogen sorption measurements. Voltammetry cycling, galvanostatic charge/discharge and impedance spectroscopy measurements performed in two- and three-electrode cells have been applied in order to measure electrochemical parameters. TEM images confirmed well dispersed λ-MnO2 particles on the surface of carbon material. The carbon in the composite plays an important role as the surface area enhancing component and a support of pseudocapacitive material. Furthermore, the through-connected porosity serves as a continuous pathway for electrolyte transport. A synergetic effect of the porous carbon framework and of the redox properties of the λ-MnO2 is at the origin of improvement of specific capacitance values which has been observed for composites after delithiation.