Polarizable continuum model for lithium interface transitions between a liquid electrolyte and an intercalation electrode

A model is described and used to calculate the energy of lithium when cross ing the interface between a liquid electrolyte and an electrode surface. Th e model is based on a classical treatment of the solute-solvent interaction s in terms of a polarizable continuum model (PCM), and of the Lithium cryst al interactions by electrostatic (Madelung) energy calculations including s hort-range closed shell repulsion. In addition, the coupling of Li+ with th e charge compensating electron on a neighbour Mn4+ site is taken into accou nt. A first application of the model to the Li-Mn2O4 (spinel) system shows that diffusion of Li from the surface to bulk of the electrode requires an activation energy, which is higher than the one for bulk diffusion. Surface charges, as deduced from electronegativity calculations are strongly reduc ed compared to the bulk ones. As a result, a barrier is also formed for the solvent to the surface Li+ diffusion. On the basis of the calculated energ y profiles we conclude that for Li/Mn2O4 bulk diffusion is considerably fas ter than lattice incorporation. Our results are in qualitative agreement wi th fits of equivalent circuits to alternating cut-rent impedance measuremen ts for Li+ intercalation in cubic and layered TiS2 and NiO2 and potential j ump kinetic experiments on Mn2O4:Li. (C) 1999 Elsevier Science B.V. All rig hts reserved.