Electronic signatures of anharmonic dynamics and charge fluctuations in Lithiated graphite

Abstract Lithium graphite intercalation compounds (Li-GICs) are model energy storage systems and are essential materials for modern day portable electronics. Obtaining insights into their operando atomic structure and thermodynamics is thus of fundamental interest. Here we explore the electronic and atomic states of Li-GICs at varying degrees of Lithium loading (i.e., “staging”) by means of ab-initio molecular dynamics simulations and simulated X-ray adsorption spectroscopy (XAS). We analyze the atomic correlation functions and shows enhancements in the Lithium-ion entropy with staging, arising from anharmonic dynamics and charge fluctuations which activate low-energy phonon modes. This manifests electronically as modulations of the unoccupied π*/σ* orbital energy levels and modulations of the Carbon K-edge XAS spectra. Thus, we advance the idea that these “static” measurements in fact encodes the thermodynamic response of the system to electrochemical perturbation. This causal link between atomic and electronic structure, thermodynamics and spectroscopy, refines our understanding of electrochemical stability, and may suggest new degree of freedoms for tuning device performance.