Octahedral and Porous Spherical Ordered LiNi0.5Mn1.5O4 Spinel: the Role of Morphology on Phase Transition Behavior and Electrode/Electrolyte Interfacial Properties.

LiNi0.5Mn1.5O4 compound as positive electrode of the lithium ion battery with high specific energy or high specific power, has a good application prospect in the field of electric vehicles such as PHEV/EVs. The influence of the morphology of ordered LiNi0.5Mn1.5O4 on phase transition behavior and electrode/electrolyte interfacial properties is investigated, including octahedral and porous spherical morphologies. Three phases named LiNi0.5Mn1.5O4 (Li1), Li0.5Ni0.5Mn1.5O4 (Li0.5) and Ni0.5Mn1.5O4 (Li0) are detected by in situ X-ray diffraction (XRD) measurement with high time resolution in the octahedral and porous spherical ordered LiNi0.5Mn1.5O4 materials during charge and discharge, and the phase transition kinetics of the two samples at high discharge rate and after charge-discharge cycles are elucidated. It is a clear demonstration that the high-rate capability and cycle life of LiNi0.5Mn1.5O4 material are influenced by crystal morphology. The porous spherical LiNi0.5Mn1.5O4 material exhibits better rate performance, associated with the fast reaction kinetic of Li0.5 phase formation. It is noticed that the coexistence of three cubic phases in the initial discharge stage is observed in the cycled octahedral sample, resulting in a higher capacity fading after 200 cycles at room temperature and 1 C. However, the porous spherical sample exhibits a poor cyclic performance at 55 °C and 1 C. This may be attributed to the fact that the porous spherical sample with high specific surface area leads to an accelerated decomposition of the electrolyte at 55 °C, and the thick interfacial film and high content of LiF on the electrode surface are formed.