Phase diagrams for systems with low free energy variation: A coupled theory/experiments method applied to Li-graphite

The paper presents a fast and efficient method to compute phase diagrams using first-principles methods, and statistical physics coupled with experimental techniques. The method is applied to lithium intercalated graphite for which evidence of experimental anomalies have recently questioned the currently accepted stage II/stage I two-phase transformation in the 0.5 <= x <= 1.0 composition range. Our coupled experimental and theoretical analysis has led to a full determination of the LixC6 phase diagram in this range of composition, revealing previously unknown phase transitions and the characterization of at least two new phases.