Analysing the Implications of Charging on Nanostructured Li2MnO3 Cathode Materials for Lithium-Ion Battery Performance.

Abstract

Capacity degradation and voltage fade of Li2MnO3 during cycling are the limiting factors for its practical use as a high-capacity lithium-ion battery cathode. Here, the simulated amorphisation and recrystallisation (A + R) technique is used, for generating nanoporous Li2MnO3 models of different lattice sizes (73 Å and 75 Å), under molecular dynamics (MD) simulations. Charging was carried out by removing oxygen and lithium ions, with oxygen charge compensated for, to restrain the release of oxygen, resulting in Li2−xMnO3−x composites. Detailed analysis of these composites reveals that the models crystallised into multiple grains, with grain boundaries increasing with decreasing Li/O content, and the complex internal microstructures depicted a wealth of defects, leading to the evolution of distorted cubic spinel LiMn2O4, Li2MnO3, and LiMnO2 polymorphs. The X-ray diffraction (XRD) patterns for the simulated systems revealed peak broadening in comparison with calculated XRD, also, the emergence of peak 2Θ ~ 18–25° and peak 2Θ ~ 29° were associated with the spinel phase. Lithium ions diffuse better on the nanoporous 73 Å structures than on the nanoporous 75 Å structures. Particularly, the Li1.00MnO2.00 shows a high diffusion coefficient value, compared to all concentrations. This study shed insights on the structural behaviour of Li2MnO3 cathodes during the charging mechanism, involving the concurrent removal of lithium and oxygen.