ABSTRACT
These differences were attributed to the crystal structure of LT and HT-CF, which is determined by the nature of the C-F bonds. In the LT-CF, it was shown from x-ray diffraction analysis that the carbon hexagons remain planar as in the parent graphite [6]. Therefore, the aromatic character has remained in this com pound. Since the electrode reduction involves accommodation of the lithium ion between the fluorinated carbon layers and the electron transfer to these layers, it was suggested that the electron may have been transferred to the delocalized irband, which originates the aromatic character [13]. Therefore, the C-F bond was left unbroken even if it has been weakened to some extent. In such a mechanism, a metastable and nonstoichiometric compound Lix(CFv) should reversibly be formed during the lithium intercalation (reduction) and deintercalation (oxidation). On the contrary, in the HT-CF, the strong C-F covalent bonding implies a drastic change in the carbon hybridization from sp2 (planar) to sp3 (puckered hexagons). The aromaticity has completely disappeared and the electron transfer during the cathodic reduction will involve the break of the C-F bond and the irreversible formation of C and LiF, as is the situation in liquid electrolyte.
