An Ab Initio Investigation of Structure-Function Relationships in Solid-State Electrolytes

Solid-state electrolytes (SSEs), or superionic conductors, are a promising method of energy storage and a safer alternative to conventional Li-ion batteries. However, the ionic conductivities of most known SSEs, a characteristic integral to battery performance, are not yet commercially competitive. Ionic conductivity in SSEs is often achieved through the interstitial hopping of the mobile cation, so understanding the energetics of the crystal structure is important. The objective of this thesis is to use density function theory (DFT) to investigate the relationships between crystal structure and ionic conductivity of SSEs. Activation energies were calculated using DFT and nudged elastic band theory for sulfide and oxide frameworks with either lithium or sodium cations. The energy pathways generated in this study were consistent with previous findings that materials with BCC structures have the lowest energy barriers and thus have the highest ionic conductivities due to their homogenous tetrahedral sites.