Revisiting the ionic diffusion mechanism in Li3PS4 via the joint usage of geometrical analysis and bond valence method

Abstract

Inorganic solid electrolytes have obvious advantages on safety and electrochemical stability compared to organic liquid electrolytes, but the advance on high ionic conductivity of typical electrolytes is still undergoing. Although the first-principles calculation in the ion migration simulation is an important strategy to develop high-performance solid electrolyte, the process is very time-consuming. Here, we propose an effective method by combining the geometrical analysis and bond valance sum calculation to obtain an approximate minimum energy path preliminarily, in parallel to pave the way for the interoperability of low-precision and high-precision ion transport calculation. Taking a promising electrolyte Li3PS4 as an example, we revisit its Li-ionic transport behavior. Our calculated Li-ion pathways and the activation energies (the corresponding values: 1.09 eV vs. 0.88 eV vs. 0.86 eV) in γ-, β- and α-Li3PS4 are consistent with the ones obtained from the first-principles calculations. The variations of the position of P-ions lead the rearrangement of the host PS4 tetrahedron, affecting the diffusion positions of Li-ions and further enabling high Li+ conductivity in β-Li3PS4. Keywords: Solid electrolyte, Conduction pathway, Crystal structure analysis, Geometric analysis, Bond valence method