Unraveling the Effects of Al Doping on the Electrochemical Properties of LiNi_0.5Co_0.2Mn_0.3O₂Using First Principles

Abstract

One of the prevailing approaches to tune properties of materials is lattice doping with metal cations. Aluminum is a common choice, and numerous studies have demonstrated the ability of Al3+ doping to stabilize different positive electrode materials, such as Li[Ni-Co-Mn]O2 (NCMs). Currently, an atomic level understanding of the stabilizing effect of Al doping in NCMs is limited. In this work, we investigate the effect of Al doping on Ni-rich-NCM-523 (LiNi0.5Co0.2Mn0.3O2). Our results suggest that Al stabilizes the structure of the cathode material via strong Al-O iono-covalent bonding due to a significant Al(s)-O(p) overlap, as well as significant charge transfer capabilities of Al. The calculated formation energies suggest that Al doping results in stabilization of partially lithiated states of NCM-523. On the other hand, calculated voltages indicate only a minor change in the voltage profiles as a function of the state-of-charge due to Al doping, and a modest increase in the Li diffusion barrier was observed. We note that high doping concentrations might mitigate the Li diffusion rates.