Improving electrochemical performance of spherical LiMn2O4 cathode materials for lithium ion batteries by Al-F codoping and AlF3 surface coating

In this paper, combination of both codoping and coating with Al, F compounds on spherical LiMn2O4 is studied to obtain an improved charge/discharge cycling performance. Firstly, Al, F-codoped Li-Mn-spinel compounds (LiMn1.96Al0.04O3.94F0.06) are synthesized via solid-state reaction followed by high-temperature treatment. The Al-F codoping spherical LiMn2O4 particles with uniform sizes of about 15 μm have high crystallinity and high tap density. The doped LiMn2O4 significantly improves the cycling performance and rate capability at room temperature. On the basis of codoped LiMn2O4, the AlF3 coating with LiMn1.96Al0.04O3.94F0.06 materials is prepared to further improve the cycling performance and rate capability at elevated temperature. Compared with pristine LiMn1.96Al0.04O3.94F0.06, the coated LiMn1.96Al0.04O3.94F0.06 shows no obvious changes on crystal structure as well as microstructure. The capacity retentions delivered by the coated samples are enhanced remarkably compared to those of the pristine one, especially at elevated temperature. It is proved that the 1 mol% AlF3-coated LiMn1.96Al0.04O3.94F0.06 shows not only improved capacity retention but also an acceptable initial capacity. At 0.5C rate, the bare and 1 mol%-coated samples have their respective capacity retentions of 86.4 and 92 % after 50 cycles at 55 °C. Meanwhile, the 1 mol% AlF3-coated LiMn1.96Al0.04O3.94F0.06 exhibits excellent rate capability at 4C and 6C at 55 °C.