In situ synchrotron radiation diffraction study of the Li+ de/intercalation behavior in spinel LiNi0.5Mn1.5O4-δ

The oxygen vacancies are usually beneficial to Li-ion transport in high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) cathode material, but the influence of the oxygen deficiencies in the disordered spinel LNMO oxide on phase transition mechanism during charging/discharging remains unknown. Herein, the oxygen stoichiometry control of LNMO was achieved through a microwave annealing treatment. The prepared non-stoichiometric LiNi0.5Mn1.5O4-δ (Fd3-m) materials delivered a pronounced improvement of rate capability, e.g. the discharge capacity at an ultra-fast rate (10 C) is up to 104.3 mA h g−1. Instead of the typical two-step phase transformation process, a solid-solution-like reaction in the as-synthesized LiNi0.5Mn1.5O4-δ (Fd3-m) during cycling was deciphered by an in situ synchrotron radiation diffraction analysis. These findings shed light on the phase transition mechanism of defective spinel oxides with an enhanced electrochemical properties.