On the performance of graphitized meso carbon microbeads (MCMB)-meso carbon fibers (MCF) and synthetic graphite electrodes at elevated temperatures

The behavior of graphite electrodes comprising either synthetic flakes or round-shaped particles, meso carbon microbeads (MCMB) and meso carbon fibers (MCF), were studied at elevated temperatures (up to 80 degrees C) in standard solutions of ethylene carbonate-ethylmethylcarbonate (EC-EMC)/LiPF6. Electron microscopy, X-ray diffraction (XRD), and Raman spectroscopy were used in conjunction with standard electrochemical techniques, including impedance spectroscopy. While electrodes comprised of synthetic flakes demonstrated impressive stability, even at 80 degrees C, MCMB-MCF electrodes demonstrated a rapid capacity fading at elevated temperatures. This capacity fading is due to the formation of thick surface films that contain Li carbonate and Li oxalate as part of their components. The thick surface films are formed upon cycling because of the surface properties of round-shaped graphite particles, as discussed herein. The MCMB-MCF electrodes fail at high temperature because of the high impedance developed due to the formation of thick surface films. (C) 2007 Elsevier B.V. All rights reserved.