Dilute graphite-sulfates intercalation stages studied by simultaneous application of cyclic voltammetry, probe-beam deflection, in situ resistometry, and x-ray diffraction techniques

This paper describes the stoichiometry, kinetics, and electronic resistivity of dilute graphite-sulfates intercalation compounds (stages pristine to VIII) obtained during electrochemical oxidation of graphite in 4M H2SO4 solution. The stoichiometry of the reaction was determined by the use of cyclic voltammetry and in situ XRD. Dilute graphite-sulfates phases are formed continuously as solid solution in the graphite matrix. The electronic resistivity of the composite graphite electrode as a function of potential depends largely on parasitic reactions, i.e., partial oxidation of graphite particles. The ionic flux of the HSO4- species across the electrode-solution interface was traced by deflection of a probe-laser beam ("mirage", or PBD technique) measured simultaneously with cyclic voltammetry. Convolution of the resulting deflectograms, measured at different distances from the electrode, allowed the calculation of diffusion coefficient of the active species in solution. Basic electroanalytical features of Li-ion intercalation into graphite from Li+-containing aprotic electrolytes are compared with those for HSO4- in aqueous 4M H2SO4.