Modification of natural graphite for lithium ion batteries

A process was attempted to improve the performance of natural graphite for lithium ion batteries (LIB). The natural graphite was treated in a concentrated sulfuric acid solution at high temperature, followed by the coating of resorcinol-formaldehyde resin using in situ polymerization and heat-treatment over 800 degrees C. SEM, XRD, XPS and Raman spectroscopy were employed to investigate the samples. It was found that the sharp edges as well as other active sites were repaired and the thin pyrolytic carbon film coated on the surface of graphite led to the decrease of BET surface areas of coated graphite and depressed decomposition of electrolyte and co-intercalation of solvated ions, which led to an improved electrochemical performance of modified graphite. In fact, the modified natural graphite reached 90.3% of the initial coulombic efficiency, more than 350 mAh g(-1) of them reversible capacity and 96.4% of the charge capacity retention reached after 70 cycles. The results show that the proposed process is a promising and practicable way to improve natural graphite for LIB. (C) 2007 Elsevier Masson SAS. All rights reserved.