Li intercalation in graphite: A van der Waals density-functional study

• Published in: Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2014-10, Vol.90 (15), Article 155448
• Main Authors: Hazrati, E., de Wijs, G. A., Brocks, G.
• Format: Article
• Language: English
• Subjects: Condensed matter; Density; Dilution; Graphene; Graphite; Intercalation; Intercalation compounds; Lithium; Mathematical models
• ISSN: 1098-0121; 1550-235X
• DOI: 10.1103/PhysRevB.90.155448

Modeling layered intercalation compounds from first principles poses a problem, as many of their properties are determined by a subtle balance between van der Waals interactions and chemical or Madelung terms, and a good description of van der Waals interactions is often lacking. Using van der Waals density functionals we study the structures, phonons and energetics of the archetype layered intercalation compound Li-graphite. Intercalation of Li in graphite leads to stable systems with calculated intercalation energies of -0.2 to -0.3 eV/Li atom, (referred to bulk graphite and Li metal). The fully loaded stage 1 and stage 2 compounds LiC sub(6) and Li sub(1/2)C sub(6) are stable, corresponding to two-dimensional [radical]3 x [radical]3 lattices of Li atoms intercalated between two graphene planes. Stage N > 2 structures are unstable compared to dilute stage 2 compounds with the same concentration. At elevated temperatures dilute stage 2 compounds easily become disordered, but the structure of Li sub(3/16)C sub(6) is relatively stable, corresponding to a [radical]7 x [radical]7 in-plane packing of Li atoms. First-principles calculations, along with a Bethe-Peierls model of finite temperature effects, allow for a microscopic description of the observed voltage profiles.