Electrochemical Intercalation of PF[sub 6] into Graphite

Abstract

Nonaqueous electrochemical cells using carbon as both the negative and positive electrodes have been proposed in the literature. In such “dual graphite” cells, lithium intercalates into the negative electrode, and the anion intercalates into the positive electrode when the cells are charged, depleting the electrolyte of salt. Here, the origin of the cell potential is considered first. Then, using Li/graphite test cells, intercalation into graphite is studied using electrochemical methods and in situ X‐ray diffraction. We prove that intercalated graphite exists in a series of staged phases. Differential capacity vs. voltage measurements are used to determine the voltages of the staging transitions and the compositions of the staged phases. The cell potential during anion intercalation rises to over 5 V, and we have learned that cells with electrolytes using ethyl methyl sulfone solvent can give reliable results up to 5.5 V under these highly oxidizing conditions. By contrast, ethylene carbonate based electrolytes are strongly oxidized above about 5.2 V, preventing complete loading of graphite with . © 2000 The Electrochemical Society. All rights reserved.