Computational Study of Chemical and Electrochemical Intercalation of Li Into Li1+xTi2O4 Spinel Structures

Abstract

Li1+xTi2O4 spinel structures are used as model systems to study the complex environment of electrode/electrolyte interfaces in lithium-ion batteries. The lithiation pathways and the potential dependence of delithiation on the corresponding Li1+xTi2O4 surfaces were explored using the density functional theory. Low-index surfaces are found to be highly reactive, with Li forming a fully lithiated phase (Li2Ti2O4) before more Li can penetrate farther into the bulk. The calculated activation energies for the formation of Li2Ti2O4 at the surface are found to be much lower than those for Li diffusion through LiTi2O4, suggesting that a two-phase lithiation process takes place during cycling. Additionally, the delithiation reaction mechanism in Li2Ti2O4 is studied by evaluating the free energies for Li+ transfer to an ethylene carbonate electrolyte by employing a Born–Haber thermodynamic cycle. The effects of an applied (external) potential are effectively incorporated into the thermodynamic cycle and provides the...