Phase space investigation of the lithium amide halides

• The lower limits of halide incorporation in lithium amide have been investigated.
• The only amide iodide stoichiometry observed was Li3(NH2)2I.
• Solid solutions were observed in both the amide chloride and amide bromide systems.
• A 46% reduction in chloride content resulted in a new phase: Li7(NH2)6Cl.
• New low-chloride phase maintained improved H2 desorption properties of Li4(NH2)3Cl.

An investigation has been carried out into the lower limits of halide incorporation in lithium amide (LiNH2). It was found that the lithium amide iodide Li3(NH2)2I was unable to accommodate any variation in stoichiometry. In contrast, some variation in stoichiometry was accommodated in Li7(NH2)6Br, as shown by a decrease in unit cell volume when the bromide content was reduced. The amide chloride Li4(NH2)3Cl was found to adopt either a rhombohedral or a cubic structure depending on the reaction conditions. Reduction in chloride content generally resulted in a mixture of phases, but a new rhombohedral phase with the stoichiometry Li7(NH2)6Cl was observed. In comparison to LiNH2, this new low-chloride phase exhibited similar improved hydrogen desorption properties as Li4(NH2)3Cl but with a much reduced weight penalty through addition of chloride. Attempts to dope lithium amide with fluoride ions have so far proved unsuccessful.