Origin of Outstanding Stability in the Lithium Solid Electrolyte Materials: Insights from Thermodynamic Analyses Based on First-Principles Calculations

First-principles calculations were performed to investigate the electrochemical stability of lithium solid electrolyte materials in all-solid-state Li-ion batteries. The common solid electrolytes were found to have a limited electrochemical window. Our results suggest that the outstanding stability of the solid electrolyte materials is not thermodynamically intrinsic but is originated from kinetic stabilizations. The sluggish kinetics of the decomposition reactions cause a high overpotential leading to a nominally wide electrochemical window observed in many experiments. The decomposition products, similar to the solid-electrolyte-interphases, mitigate the extreme chemical potential from the electrodes and protect the solid electrolyte from further decompositions. With the aid of the first-principles calculations, we revealed the passivation mechanism of these decomposition interphases and quantified the extensions of the electrochemical window from the interphases. We also found that the artificial coating layers applied at the solid electrolyte and electrode interfaces have a similar effect of passivating the solid electrolyte. Our newly gained understanding provided general principles for developing solid electrolyte materials with enhanced stability and for engineering interfaces in all-solid-state Li-ion batteries

First-Principles Study of Oxyhydride H^– Ion Conductors: Toward Facile Anion Conduction in Oxide-Based Materials

H^– ion conductor materials have the great potential to enable high-energy density electrochemical storage based on hydrogen. Fast H^– conduction has been recently demonstrated in the La_{2–<i>x</i>–<i>y</i>}Sr_{<i>x</i>+<i>y</i>}LiH_{1–<i>x</i>+<i>y</i>}O_3–<i>y</i> oxyhydride materials. However, little is known about the H^– diffusion mechanism in this new material and its unique structure. The origin of such exceptional H^– conduction in the oxide-based materials is of great interest. Using first-principles calculations, we studied the energetics and diffusion mechanisms of H^– ions as a function of structures and compositions in this oxyhydride system. Our study identified that fast H^– diffusion is mediated by H^– vacancies and that the fast two-dimensional or three-dimensional H^– diffusion is activated by different anion sublattices in different compositions. In addition, novel doping was predicted from ab initio computation to increase H^– conductivity in these materials. The unique two-anion-site feature in this structural framework enables highly tunable lattice and minimizes the blocking of anion diffusion by oxygen sublattice, allowing high mobile-carrier concentration and good diffusion network. This conclusion offers general guidance for future design and discovery of novel oxide-based anion conductors