Thermodynamic and kinetic approaches to lithium intercalation into a Li1-δMn2O4 electrode using Monte Carlo simulation

The thermodynamics and kinetics of electrochemical intercalation of lithium into a Li1 - deltaMn2O4 electrode have been investigated theoretically by a statistical thermodynamics concept using a Monte Carlo simulation based upon the lattice gas model. From the fluctuations in the internal energy and the number of lithium ions in the grand canonical ensemble, the partial molar internal energy and entropy of lithium ions were obtained theoretically at a fixed chemical potential. Both theoretical and experimental partial molar quantities alike showed a negative deviation from those quantities of the ideal solution below (1 - delta) = 0.5 and a positive deviation above (1 - delta) = 0.5. The component diffusivity of lithium ions was calculated with the aid of a random walk algorithm in the canonical ensemble. From the combination of the thermodynamic enhancement factor and the component diffusivity of lithium ions calculated theoretically by introducing the irreversible lithium trap sites into the Li1 - deltaMn2O4 electrode, the chemical diffusivity of lithium ions was determined and compared with that measured using the galvanostatic intermittent titration technique. From the good coincidence between the chemical diffusivities calculated theoretically and determined experimentally, it was inferred that the lithium ions trapped irreversibly near structural defects disturb locally the ordering of lithium ions and hence the chemical diffusion of lithium ions in the ordered phase is strongly enhanced. (C) 2001 Elsevier Science Ltd. All rights reserved.