Electrochemical behavior of surface-fluorinated graphite

Electrochemical intercalation and deintercalation of lithium ions have been investigated using surface-fluorinated graphite electrodes in 1 M LiClO4-EC/DEC (1:1) at 25 degrees C. The 2 and 10 min-fluorinated graphite samples contained small amounts of fluorine, 0.5-2.2 at% and 0.6-3.7 at%, while their surface fluorine concentrations were 6.0-14.6 at% and 7.1-18.1 at%, respectively. Raman spectra indicated that the surface fluorination caused the surface disordering of graphite. The 2 min-fluorinated graphite samples showed the higher charge capacities than original graphite by about 5-10%, that is, 380-400 mA h g(-1) and the half of 10 min-fluorinated graphite samples also gave the high charge capacities of about 380 mA h g(-1). XPS and Raman spectroscopy revealed that the most of fluorine atoms were removed from graphite surface and the surface disordering of graphite was increased by charge-discharge cycling. Based on these results, the mechanism on the capacity increase by the surface fluorination of graphite was discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.