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

Tshidi Mogashoa; Raesibe Sylvia Ledwaba; Phuti Esrom Ngoepe

doi:10.3390/ma15165687

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

Materials (Basel). 2022 Aug 18;15(16):5687. doi: 10.3390/ma15165687.

Authors

Tshidi Mogashoa¹, Raesibe Sylvia Ledwaba¹, Phuti Esrom Ngoepe¹

Affiliation

¹ Materials Modelling Centre, University of Limpopo, Private Bag X 1106, Sovenga 0727, South Africa.

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 Li_2-xMnO_3-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 Li_1.00MnO_2.00 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.

Keywords: Li2MnO3; amorphisation; charging; energy storage; lithium-ion battery; nanoporous; recrystallisation.

Grants and funding

The study was funded by the South African Research Chair Initiative of the Department of Science and Innovation, and the National Research Foundation in Pretoria, grant number 136301.