Structure and Defect Chemistry of Low- and High-Temperature Phases of LiBH4

• Published in: Journal of physical chemistry. C Vol. 116; no. 25; pp. 13488 - 13496
• Main Authors: Shevlin, S. A, Cazorla, C, Guo, Z. X
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 28-06-2012
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electron states; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Methods of electronic structure calculations; Physics; Solubility, segregation, and mixing; phase separation; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Hydrogen storage; Vacancies; Transport properties; Digital simulation; Solubility; Theoretical study; Monoclinic lattices; Hexagonal crystals; Density functional method; Orthorhombic lattices; Electrolytes; Defect structure; Crystal structure
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp3014805

Density functional theory simulations were performed to resolve the recent controversy regarding the crystal structure of the low-temperature and high-temperature phases of the hydrogen storage and Li ion electrolyte material LiBH4. It is demonstrated that, independent of hybrid free exchange-correlation functional, the experimentally proposed orthorhombic Pnma structure is energetically the most favorable low-T structure while the experimentally proposed hexagonal P63 mc structure is the most favorable high-T structure. Furthermore, we discover a new monoclinic C2/c structure for the high-temperature phase which is competitive in stability with the P63 mc structure. Both high-temperature P63 mc and C2/c structures are stable against dehydrogenation and formation of Li vacancies. For all high-temperature structures, the formation energy of the Li Frenkel defect is low at 0.50–0.90 eV, with major implications for Li ion transport properties.