Reassessing of the lithium intercalation mechanism in layered nickel

Abstract

The study of the powder diffraction diagrams of the Li xNiPS 3 intercalates has been reassessed using the highly sensitive INEL curve detector. This detector used in the Debye-Scherrer geometry and with a monochromated radiation allowed the accurate recording of the air sensitive nickel thiophosphate intercalates powder diffraction patterns and their subsequent processings, an experiment never done before. The study showed that the intercalation proceeds according to a macroscopic biphased mechanism, which was not found in previous works. The two phases implied are the starting phase NiPS 3 and the fully reduced end-compound Li 2NiPS 3. For this latter material, monoclinic and hexagonal cell parameters are proposed. The study of the pristine phase's Full Width at Half Maximum diffraction line variation during lithium intercalation shows that the non-intercalated grains are sensitive, through microstrain broadening or/and size decrease, to the formation of the Li 2NiPS 3 intercalate. These results answer earlier conflicting observations, in particular about the quasi-equilibrium discharge curves.