3.3. Annealing of LiC6
After annealing of LiC6 at 330 C for 72 h, two co-existing lithium
graphite intercalation compounds LiC6 and LiC12 can be identified
by XRD (Fig. 4). No reflexes of Li2C2 or graphite are observed.
Thus, a phase transformation from LiC6 to LiC12, which is obviously
not finished after 72 h, has taken place during the annealing process
at 330 C. There is a minuscule reflex at 33.5 which indicates
that also a minor volume fraction of Li2O may be present.
Due to the fact that discrete reflexes of LiC6 and LiC12 are observed
in the XRD scan, it can be concluded that the de-intercalation
process is accompanied by discrete phase transformations.
This observation is in line with results of galvanostatic reduction
experiments which display a voltage plateau in the composition
range between LiC6 and LiC12, indicating a two-phase region in
the Li–C phase diagram [22,23].
3.4. DSC and XRD on LiC6
The decay of the LiC6 compound is also found in the DSC analysis.
The DSC signal in the first cycle features an elongated exother-
Fig. 1. XRD pattern of the synthesized pure Li2C2. mic buckle with an onset around 250 C