The effect of mixed Mn valences on Li migration in LiMn2O4 spinel:: A molecular dynamics study

Previous molecular dynamics (MD) simulations have shown that, with good choice of potential shapes and parameters, the structure and properties of stoichiometric LiMn2O4 can be reproduced to good accuracy. In particular, the experimentally observed self-diffusion of Li ions was shown to occur only for a discrete, mixed Mn valence model. Here, those MD studies have been extended, demonstrating that periodically switching the Mn valence states, reflecting an electron hopping model, greatly facilitates the Li ion self-diffusion. The interaction is mediated by the O atoms, which coordinate both cations and temporarily adopt local distortions based on the three coordinating Mn valences. Although the O atoms continue to vibrate harmonically about a displaced mean, permitting the Li atoms to migrate, the time and spatial average remains that of the ideal spinel with distributed Li. (C) 2004 American Institute of Physics.