Thermodynamics and crystal structure anomalies in lithium-intercalated graphite

Abstract

We found anomalous behaviors during lithium electrochemical intercalation into graphite in the entropy curve and the crystal structure, especially, during the stages from 2 to 1 transition at x = 0.5 in Li_xC_6. The entropy first decreases monotonously, then re-increased sharply at the transition. The average interlayer spacing displays a hysteresis during intercalation and de-intercalation and departs from linearity. The results are discussed in relation with a contribution of the vibrational entropy and possible occurrence of intermediary phase(s) between the two lithium-rich intercalation stages.

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