Enhancing the Structural and Mechanical Properties of Li1.22-XNaxMn0.78o2 (0.00 ≤ X ≤ 0.05) by Doping with Sodium: DFT and FHI-Aims

• N. Sithole Materials Modelling Centre, University of Limpopo, South Africa https://orcid.org/0000-0002-5193-0828
• K.M. Kgatwane Materials Modelling Centre, University of Limpopo, South Africa https://orcid.org/0009-0005-3124-7270
• P.E. Ngoepe Materials Modelling Centre, University of Limpopo, South Africa https://orcid.org/0000-0003-0523-5602

DOI:

https://doi.org/10.7166/36-3-3348

Abstract

The study examined the properties of Li-rich layered oxide cathode material, xLi₂MnO₃-(1-x)LiMnO_2, in an attempt to improve its electrochemical performance and capacity. The process included the Li-Na pair potentials. Using first-principles density functional theory (DFT) calculations to fit the Li-Na pair potentials, the mechanical and structural characteristics of the LiNaO structure were created as a model to fit the pair potentials. The calculated values of the lattice parameters had less than 2% difference, and the elastic constants of LiNaO were in good agreement with the experimental values of Na₂O. The elastic constants suggested that the LiNaO system was mechanically stable. The Buckingham pair potential parameters A and rho were fitted to the DFT pair potential and were found to be 28250.500 and 0.231 respectively. After refining the Buckingham potential parameters with the GULP code, the values of A and rho were 38500.500 and 0.177 respectively. The obtained Li-Na pair potentials were used in amorphisation and recrystallisation studies to determine the structural stability and mobility of lithium ions on the Li_1.22-xNa_xMn_0.78O₂ (x = 0.00, 0.01, and 0.05) nanoparticles using the DL_POLY molecular dynamics simulation package. We observed that <5% Na doping results in an ordered structure with regular cubic morphology and larger Li layer spacing, preventing the layered structure from turning into spinel.