Effect of temperature on the kinetics and thermodynamics of electrochemical insertion of Li-ions into a graphite electrode

We report on the potential and temperature dependences of the differential intercalation capacitance, Cdif, and the chemical diffusion coefficient, D, during Li intercalation into a graphite anode by a combined application of slow-scan rate cyclic voltammetry (SSCV) and the potentiostatic intermittent titration technique (PITT). Drastically different behavior was observed within the short-time ranges of the PITT response measured for a two-phase coexistence domain and a solid solution of phases 4 and 3. Electroanalytical evidence for small droplet formation (nucleation) of a new phase in the bulk of the old one was found for the former domain, showing good correlation with in situ XRD studies. SSCV data obtained in the 25–80 °C temperature range were in excellent agreement with the published temperature–concentration phase diagrams built on the basis of detailed XRD characterizations. The simultaneous appearance of maxima on Cdif versus E plots and minima on the related log D versus E plots in the two-phase domains was rationalized in terms of a lattice gas model with single site energy, and highly attractive interactions between the intercalated guest atoms. The electroanalytical behavior of graphite within the solid-solution domain (a mixture of phases 4 and 3) was interpreted semi-quantitatively on the basis of a model that took into account the presence of two sub-lattices of different energy (a model of “energetic heterogeneity”) for Li accommodation, and attractive interactions between the guest atoms on each sub-lattice, or, alternatively, due to in-plane order–disorder transitions because of short-range repulsive interactions between the intercalated guest species.