Rational Tailoring of NASICON-Type Electrode Materials for Enhanced Ion Transport in Sodium- and Lithium-Ion Batteries

Sodium superionic conductor (NASICON)-structured type NaTi₂(PO₄)₃ and LiTi₂(PO₄)₃ battery materials are investigated and compared for their Na-ion and Li-ion transport properties. Classical molecular dynamics (MD) simulations using interatomic partial charge pair-potential models and density functional theory (DFT) calculations are applied to study these properties. Mean square displacement and density plots provide insights into the dynamics of ion transport. The self-diffusion coefficients calculated using vacancy-assisted mechanisms agree with the experimental data. The electronic properties, ion energetics, and ion diffusion barriers via ion hopping mechanisms are studied using DFT. To enhance the diffusivity of the Na-ion and Li-ion, uniaxial (x, y, and z) and biaxial (xy, xz, and yz) lattice strains, ranging from −3% to 3%, are applied and compared, utilizing MD simulations. Lattice strain effects on Na-/Li-ion self-diffusion coefficients indicate a positive correlation, with an increase in the self-diffusion coefficient under tensile strain compared to that of the unstrained crystal in both structures. Conversely, compressive strain results in decreased diffusion coefficients.