First Principles Study of the LiNH₂/Li₂NH Transformation

On the basis of ab initio simulations, we propose a scenario for the decomposition pathway of Li amide into Li imide and ammonia (2LiNH₂ → Li₂NH + NH₃) which represents the first step of the dehydrogenation reaction of the LiNH₂/LiH₃ mixture. Activation energies for formation of NH₃ in LiNH₂, for diffusion of charged species (H⁺, Li⁺) in LiNH₂ and Li₂NH, for H⁺/Li⁺ transfer across the LiNH₂/Li₂NH interface and for NH₃ desorption at the surface of LiNH₂ and Li₂NH have been computed from first principles. The results actually suggest that the transformation path depends on the surface-to-volume ratio of the LiNH₂ crystallites.