Determining the Relationship Between Crystal Structure and Ionic Conductivity of Solid-State Electrolytes



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Solid-state electrolytes, or superionic conductors, are a promising method of energy storage as a safer alternative to conventional, flammable Li-ion batteries. However, the implementation of solid-state batteries is limited by their ionic conductivity and diffusivity (characteristics integral to battery performance) which are not yet commercially competitive. The objective of this research is to investigate the relationship between crystal structure and ionic conductivity of solid-state electrolytes to find specific criteria for systematically and reliably identifying superionic conductors based on structure. We study sulfur and oxygen sublattices with different volumes as simple models of superionic conductors to explain and predict lithium ionic conductivity. Energy pathways were investigated with density functional theory and nudged elastic band theory, and ionic conductivity was predicted with ab initio molecular dynamics. These energy reductions elucidate a relationship between ionic conductivity and crystal structure, and ab initio molecular dynamics simulations verify the actual ionic conductivity and diffusivity of various materials. Based on the 2015 publication “Design principles for solid-state lithium superionic conductors” by Wang et. al. concerning the relationship between ionic conductivity and crystal structure, the molecular dynamics simulations of materials with a bcc framework are anticipated to yield the best ionic conductivity and diffusivity results.