A series of computer simulations of the self-diffusion of lithium in pure and doped lithium-manganese spinel materials was performed. The molecular dynamics approach employed a fully ionic force field that accounted for electrostatic, repulsive and dispersion interactions among all ions. A reference unit cell comprising 56 ions (Li8Mn3+8Mn4+8O32) was used to perform the simulations under constant volume and constant pressure constraints. All of the atomic positions were allowed to vary during the simulation. Simulations were performed for undoped and doped LiMn2O4 at various levels of lithium content (based upon the number of lithium ions per unit cell and the manganese oxidation state). The molecular dynamics results indicated an activation energy of approximately 97kJ/mol for the self-diffusion of lithium in the undoped material. Lithium ion trajectories from the simulations provided diffusion coefficients that decreased by a factor of ten as the cathode accumulated lithium ions during discharge. Results for the doped spinel suggested a decrease in the diffusion rate with increasing dopant ions.

Molecular Dynamics Study of Lithium Diffusion in Lithium-Manganese Spinel Cathode Materials. Cygan, R.T., Westrich, H.R., Doughty, D.H.: Materials Research Society Symposium - Proceedings, 1998, 496, 109-14