DFT + U calculations of structural, magnetic, and electrochemical properties and Na+ diffusion barrier in the O3‐phase of NaTm0.5Ni0.5O2 (Tm = Ti, Mn)

Abstract

AbstractO3‐type sodium rich layered transition metal (TM) oxides namely NaTm0.5Ni0.5O2 (Tm = Ti, Mn) are theoretically explored in this work. The structural, magnetic and electrochemical properties are studied using first‐principles calculations at different Na‐intercalation levels. Cell parameters calculated using GGA, GGA + U and dispersion‐corrected GGA + U + D3 methods are compared with experimental data. The incorporation of Hubbard parameter (U) for 2p orbital of O with Hubbard parameters of Mn‐3d orbitals and Ni‐3d orbitals at GGA + U provides a good description of the electronic structure, cell parameter, magnetic moment and effective charge. Comparisons are also made to meta‐GGA functional (strongly constrained and appropriately normed) calculations. Ti‐based O3‐phase is found to be more stable than Mn‐based O3‐phase for all Na‐intercalation levels. However, the presence of Mn ions can significantly reduce the Na+ diffusion barrier as compared to Ti ions in O3‐type NaTm0.5Ni0.5O2 system. Both Ti and Mn ions act as structural stabilizers and do not participate in electrochemistry during charge/discharge. PBE + U + D3 functional is recommended to get reliable results for electronic and magnetic properties of these kind of systems.