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LiNi0.5Mn1.5O4compound 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 LiNi0.5Mn1.5O4on 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 LiNi0.5Mn1.5O4materials 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 LiNi0.5Mn1.5O4material are influenced by crystal morphology. The porous spherical LiNi0.5Mn1.5O4material 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.

A commercial Li4Ti5O12material was modified by NH4F using a facile and dry method at a low temperature in air. X-ray diffraction reveals that the fluorination did not change the bulk structure of Li4Ti5O12. X-ray photoelectron spectroscopy demonstrates that LiF was formed at the surface and Ti4+was partially changed into Ti3+. Microscopic images show that some nanoislands were formed on the surface, which enlarged the surface area. Consequently, the NH4F-modified Li4Ti5O12material exhibited significantly enhanced capacities and rate capabilities, even at low temperatures. The discharge capacity was increased from 149 to 167 mA h g–1at 1 C, and the capacity retention was increased from 17.8 to 52.0% at 15 C. The capacity retention of NH4F-modified Li4Ti5O12was greater than that of Li4Ti5O12at each low-temperature point. Additionally, the introduction of F can protect the Li4Ti5O12material from side reactions with the electrolyte and the atmosphere, enhancing the surface stability and reducing the release of gaseous products. It is believed that the NH4F-modified Li4Ti5O12with enhanced electrochemical performance is a promising anode material for lithium ion batteries. Furthermore, this facile surface fluorination strategy is amenable to large-scale production.