High-Temperature Structural Evolution of the Disordered LiMn1.5Ni0.5O4

In this work, we present our recent results about the changes induced on a crystalline bulk LiMn1.5Ni0.5O4 disordered cubic spinel phase by thermal treatments carried out under different back atmospheres (vacuum and air). Our aim is to describe the structural changes induced by temperature in various conditions both on the long range (by means of XRD) and on the short range around Mn/Ni metal sites (by means of EXAFS) and to investigate the reversible oxygen loss and adsorption upon heating and cooling, respectively. In summary, the LiMn1.5Ni0.5O4 phase suffers large structural modifications above 650°C both under vacuum and air. These alterations are closely related to the occurrence of large oxygen vacancies in the anionic sublattice due to spontaneous oxygen loss via the gas phase. Apparently, local and long-range distortions from the pristine disordered cubic spinel structure are completely reversible in air upon cooling from high temperature, whereas under vacuum, the structural alterations are permanent.