The effects of moisture on LiD single crystals studied by temperature-programmed decomposition

Abstract

Temperature-programmed decomposition (TPD) technique was performed on LiOH powders and LiD single crystals previously exposed to different moisture levels. Our results show that the LiOH decomposition process is rate-limited by an inward moving reaction front mechanism with an activation energy barrier of ∼122–149 kJ/mol. The LiOH structure is stable even if kept at 320 K. However, LiOH structures formed on the surface of LiD single crystals during moisture exposure at low dosages may have multiple activation energy barriers, some of which may be much lower than 122 kJ/mol. The rate-limiting mechanism for the decomposition of LiOH structures with reduced activation energy barriers is consistent with a unimolecular nucleation model. We attribute the lowering of the activation energy barrier for the LiOH decomposition to the existence of sub-stoichiometric Li(OH) x with x<1 and cracks, broken bonds, and other disorders in the LiOH structures formed at low levels of moisture exposure. These defective LiOH structures may decompose significantly over many years of storage even at room temperature. At high moisture exposure levels, LiOH · H 2 O formation is observed. The release of H 2O molecules from LiOH · H 2 O structure has small activation energy barriers in the range of 48–69 kJ/mol and follows a unimolecular nucleation process. The loosely bonded H 2O molecules in the LiOH · H 2 O structure can be easily pumped away at room temperature in a reasonable amount of time. Our experiments also suggest that handling LiD single crystals at an elevated temperature of 340 K or more reduces the growth rate of LiOH and LiOH · H 2 O significantly.