Abstract
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 to eV/Li atom, (referred to bulk graphite and Li metal). The fully loaded stage 1 and stage 2 compounds and are stable, corresponding to two-dimensional lattices of Li atoms intercalated between two graphene planes. Stage 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 is relatively stable, corresponding to a 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.
- Received 20 August 2014
- Revised 9 October 2014
DOI:https://doi.org/10.1103/PhysRevB.90.155448
©2014 American Physical Society