Influence of graphite surface properties on the first electrochemical lithium intercalation

The electrochemical insertion of lithium ions into graphite materials having different surface chemistry and defect concentration was studied during the first cycle in half-cell containing 1 M LiPF₆ in an electrolytic solvent mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). The graphite surface properties were varied by thermal treatments in either hydrogen, oxygen, or nitrogen oxide or chemical treatment in boiling nitric acid. The influence of the surface modifications on the course of the first electrolyte reduction was investigated. The surface group chemistry was analyzed by temperature-programmed desorption coupled with mass spectrometry. The surface defect concentration was determined in terms of the active surface area (ASA) measured by oxygen chemisorption and a subsequent temperature-programmed desorption. The experimental results showed that the ASA parameter governs the exfoliation tendency of the graphite negative electrode material with the existence of a critical value below which the graphite systematically exfoliates. The specific charge loss during the first electrochemical insertion of lithium and the exfoliation behavior of the graphite negative electrode material are not influenced by the type and amount of oxygen surface groups. But hydrogen present on the graphite surface increased the graphite exfoliation tendency even for graphite materials with an ASA above the critical value.