A comparative study of Fd-3m and P4332 “LiNi0.5Mn1.5O4”

“LiNi0.5Mn1.5O4” is generally reported to crystallize in the spinel structure within two different space groups (Fd-3m and P4332) depending on the oxygen stoichiometry/ordering of the Ni/Mn cations. This paper presents a contribution to the study of these two phases in order to have a better insight on how the preparation method influence their electrochemical properties. The phases were synthesized by a ceramic route and thoroughly characterized using X-ray diffraction (XRD), FTIR and Raman spectroscopy. This latter technique, together with the obtaining of the electrochemical signature, allows discriminating between the types of spinel phases. Based on thermal in situ XRD measurements, we further propose a peritectoid transformation as an explanation for the appearance of a nickel based rock salt phase during the preparation. Finally, we discuss on the electrochemical deinsertion mechanism.

Research highlights
► High voltage spinel "LiNi0.5Mn1.5O4"are prepared and thoroughly characterized.
► The formation of the rock salt impurity is explained through a peritectoid phase transition and the electrochemical de-insertion mechanism was investigated.
► We present the electrochemical deinsertion mechanism and discuss it in relation with recent reports on the effect of structural strains.