Novel Impact of Short Term Aging on the Electrochemistry of CO[sub 2] Treated Synthetic Graphite

A study was conducted of graphite prepared from heat-treatment of synthetic graphite LK-702 in flowing CO2. Samples were characterized by percent mass loss, X-ray powder diffraction, scanning electron microscopy imaging, thermogravimetric analysis, Brunauer-Emmett-Teller surface area, and methylene blue adsorption surface area measurements. Treated graphites were studied as possible electrode materials for Li-ion cells. Cycle tests demonstrated that the reversible capacity and percent capacity retained were relatively unaffected by CO2 treatment, while the irreversible capacity as significantly influenced by CO2 treatment. The change in irreversible capacity was strongly dependent upon the age of the treated samples, where samples freshly treated in CO2 showed a decrease in irreversible capacity with treatment time, and treated samples aged for at least fourteen days (in a dry environment) showed an increase in irreversible capacity with treatment time. To our knowledge, this is the first report of the impact of short term aging on the electrochemistry of CO2 treated graphite. (C) 2004 The Electrochemical Society.