UC Santa Barbara

High-throughput density functional theory calculations can provide a method for predicting material properties in alkali-ion electrode and electrolyte chemistries. Through these calculations, paired with cluster expansion models and uncertainty quantification methods, we have tools to understand the fundamental thermodynamic origins of crystallographic deformation and alkali-ion phase stabilities in these materials. In this analysis, we use these methods to understand phase stability and lithiation mechanisms in a family of high power density electrode chemistries called the Wadsley-Roth crystallographic shear phases. Due to the complexity and large cell sizes of Wadsley-Roth phase materials, this combination of methods is useful for tapping the origin of the high charge rates and power densities in these unique structures. The study begins with an examination of stability of compounds in the Ti-Nb-O ternary where we examine the effect of electrostatics and distortions on phase stability of the Wadsley-Roth phases. We then examine the effect of chemical strain in the lithium site-filling mechanism in the highly reversible Wadsley-Roth material, PNb9O25. We extend our analysis to the high-power density, commercialized Wadsley-Roth phase, TiNb2O7, where we examine the effect of metal-metal electronic interactions and pair distances on the complex lithium site filling mechanism present in this compound. We then do an in depth analysis of the effect of lithiation on octahedral distortions to acquire a complete understanding of structural changes upon lithiation. These analyses are paired with experimental results to exhibit the validity of these calculations.