New electrochemical and chemical routes for the synthesis of lithium rich graphite intercalation compounds

Abstract

New lithium rich graphite intercalation compounds have been synthesized. They display a van der Waals space containing five alternating intercalated layers, three of lithium and two of oxygen corresponding to an interplanar distance d I equal to 665 pm. The compound ideally formulated as Li 2C 6O 0.5 has been obtained from the second-stage NaC 6O 0.5 either by its electrochemical reduction in LiClO 4-ethylene carbonate electrolyte or by its direct reduction with molten lithium. This yellow material, of biintercalation type, is characterized by a repeat distance along c-axis, I c, equal to 1035 pm. This value corresponds to the addition of an interplanar spacing of 370 pm resulting in lithium intercalation in the van der Waals gap of NaC 6O 0.5 and of another one of 665 pm, resulting in the exchange of sodium by lithium in the five intercalated layers of the starting material. Another compound, formulated as LiC 6O 0.5, is a classical stage 3 material in which the intercalated part is the five alternating lithium–oxygen layers also present in Li 2C 6O 0.5. Its repeat distance along c-axis is equal to 1340 pm. All these Li xC 6O 0.5 compounds contain sodium clusters trapped in their bulk. Lithium species appear to be organized to form a hexal structure as in LiC 6 while there is no occurrence for a structural organization of oxygen present as peroxide ions.