Structure of the superdense LiC3 compound prepared by ball-milling

The intercalation of lithium into graphite by ball-milling leads to a powder whose X-ray pattern is close to that of LiC6, but the density of the powder indicates the presence of an intercalation phase close to LiC3. This compound is superdense since its volume concentration in lithium is twice that of LiC6, the repeat distance along the c-axis being identical in both compounds. Moreover, contrarily to an other compound, LiC2 synthesized under high pressure, which decomposes slightly (in several months) into LiC6 + Li, LiC3 is stable. The Li-7 NMR was very helpful to solve the different problems about this compound and the present work explains all the observations, how and why LiC3 remains stable at ambient pressure. (C) 2003 Elsevier Ltd. All rights reserved.