NMR and X-ray Diffraction Studies of Phases in the Destabilized LiH-Si System

Hydrogen absorption and desorption isotherms have been measured on ballmilled mixtures of LiH+Si powders to evaluate the thermodynamic parameters of these reversible reactions. The phase compositions at the various stages of reaction have been examined by Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR) of the Li, H, and Si nuclei and powder x-ray diffraction (XRD). The initial mixtures of LiH and Si were found to convert into known Li-Si silicide intermetallics (i.e., Li12Si7, Li7Si3, and Li13Si4) as well as providing evidence for a previously unknown ternary Li-Si-H phase as hydrogen was first desorbed and then absorbed. While the absorption reactions are reversible over portions of the Li-Si-H composition range, incomplete recovery of the original LiH + Si phases was also observed under some test conditions.