The electrochemical preparation and properties of ionic alkali metal-and NR 4-graphite intercalation compounds in organic electrolytes

Abstract

The preparation of graphite-alkali metal-solvent or graphite-NR 4-Solvent ternary intercalation compounds by electrochemical reduction of graphite is described. The reduction occurs stagewise and the complete formation of a defined stage can be recognized by a striking change in the potential of the graphite electrode. Under certain conditions the stoichiometry of intercalation compounds (e.g. C 48K(DMSO), C 24K(DMSO), C 18Li(DME) can be calculated from the coulombs consumed by a weighed graphite electrode until a step in potential occurs. The electrochemical intercalation of alkali metals into graphite is reversible. It may be reversed with a coulombic efficiency up to practically 100%, e.g. for C n K(DMSO). A considerable co-intercalation of alkali metal salts from the electrolyte was not observed. From a preparative point of view, a great advantage over the direct chemical reduction of graphite is that a desired degree of intercalation can be specifically prepared. A coulometric determination of the intercalated cations is possible by way of an electrochemical reoxidation. Potential measurements of electrochemically prepared intercalation compounds with a well-defined degree of intercalation represent a simple method for investigating the thermodynamics of these reactions. Furthermore, by means of dynamic electrochemical methods, such as cyclic voltammetry, information about the kinetics of intercalation reactions is obtainable.