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

New lithium rich graphite intercalation compounds have been synthesized. Th ey display a van der Waals space containing five alternating intercalated l ayers, three of lithium and two of oxygen corresponding to an interplanar d istance d(I) equal to 665 pm. The compound ideally formulated as Li2C6O0.5 has been obtained from the second-stage NaC6O0.5 either by its electrochemi cal reduction in LiClO4-ethylene carbonate electrolyte or by its direct red uction 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 NaC6O0.5 and of another one of 665 pm, resulting in the exchange of sodium by lithium i n the five intercalated layers of the starting material. Another compound, formulated as LiC6O0.5, is a classical stage 3 material i n which the intercalated part is the five alternating lithium-oxygen layers also present in Li2C6O0.5. Its repeat distance along c-axis is equal to 13 40 pm. All these LixC6O0.5 compounds contain sodium clusters trapped in their bulk . Lithium species appear to be organized to form a hexal structure as in Li C6 while there is no occurrence for a structural organization of oxygen pre sent as peroxide ions. (C) 1999 Elsevier Science Ltd. All rights reserved.