Thermodynamic and kinetic approaches to lithium intercalation into a Li1-delta Mn2O4 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 u pon the lattice gas model. From the fluctuations in the internal energy and the number of lithium ions in the grand canonical ensemble, the partial mo lar internal energy and entropy of lithium ions were obtained theoretically at a fixed chemical potential. Both theoretical and experimental partial m olar 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 diff usivity of lithium ions calculated theoretically by introducing the irrever sible 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 coi ncidence between the chemical diffusivities calculated theoretically and de termined experimentally, it was inferred that the lithium ions trapped irre versibly near structural defects disturb locally the ordering of lithium io ns and hence the chemical diffusion of lithium ions in the ordered phase is strongly enhanced. (C) 2001 Elsevier Science Ltd. All rights reserved.