Phase diagram of Li x C 6

Using lithium/graphite electrochemical cells and in situ x-ray diffraction, we have determined the phase diagram of ${\mathrm{Li}}_{\mathit{x}}$${\mathrm{C}}_{6}$ for 0x1 and 0 \ifmmode^\circ\else\textdegree\fi{}CT70 \ifmmode^\circ\else\textdegree\fi{}C. We find several differences between our results and previous work. For x0.04, the intercalated Li is randomly distributed throughout the graphite host in a dilute stage-1 phase. As x increases past 0.04, a clear coexistence between this phase and a stage-4 phase is observed. As x increases further at 21 \ifmmode^\circ\else\textdegree\fi{}C, transitions to stage 3, to a ``liquidlike'' stage-2 phase (denoted 2L), to stage 2, and finally to filled stage 1 occur sequentially as expected on the basis of previous work. We have been able to accurately determine the ranges in x and in T of the single-phase and the coexisting-phase regions. Clear coexisting-phase regions are observed (indicating first-order transitions) for all the transitions except for the stage-4 to -3 transition. We discuss the difference between this transition and the others. The average layer spacing of ${\mathrm{Li}}_{\mathit{x}}$${\mathrm{C}}_{6}$ has been measured as a function of x.