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

• Published in: arXiv.org 2014-10
• Main Authors: Hazrati, E, de Wijs, G A, Brocks, G
• Format: Article
• Language: English
• Subjects: Adhesion; Density; Dilution; Dimensional stability; First principles; Graphene; Graphite; High temperature; Intercalation; Intercalation compounds; Lattices; Organic chemistry; Reptiles & amphibians; Temperature effects
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1410.5632

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\(_6\) and Li\(_{1/2}\)C\(_6\) are stable, corresponding to two-dimensional \(\sqrt3\times\sqrt3\) 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\(_{3/16}\)C\(_6\) is relatively stable, corresponding to a \(\sqrt7\times\sqrt7\) 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.