First-Principles Prediction of Hydrogen Storage Energetics in the Li-B-N-H System*

In this talk, we describe recent efforts using first-principles density functional theory (DFT) based methods to elucidate the reaction energetics and phase stability in the Li-B-N-H hydrogen storage system. We have calculated DFT total energies of a large number of phases in this system, including Li$_{4}$BN$_{3}$H$_{10}$, Li$_{2}$BNH$_{6}$, and their decomposition products. We then use these DFT energies in the recently developed ``grand canonical linear programming'' (GCLP) approach to automatically detect the thermodynamically preferred decomposition paths of these compounds as functions of temperature and H$_{2}$ pressure. Using the combined DFT+GCLP approach we calculate thermodynamic phase diagrams in the LiBH$_{4}$ -- LiNH$_{2}$ phase space. Some phases (e.g., Li$_{3}$BN$_{2}$, BN) are found to be very energetically stable, but are often only seen experimentally at very high temperatures, presumably due to hindered kinetics. By removing these phases from the DFT+GCLP calculations and examining the resultant phase diagrams, we can provide insight into the experimental reaction mechanisms.