Fluorine Doping of LiNi_(3/8)Co_(2/8)Mn_(3/8)O_2 Cathode Material for Lithium-ion Batteries

The layered LiNi3/8Co2/8Mn3/8O2-yFy(y=0, 0.05, 0.10, 0.20) samples were prepared by using the co-precipitated hydroxide as precursor, and characterized by means of XRD, XPS, SEM, cyclic voltammetry, charge/discharge tests, DSC etc techniques. The results show that fluorine doping can not induce the valence change of transition metal ions in LiNi3/8Co2/8Mn3/8O2-yFy samples. The samples with y=0.05, 0.10 show better cycling performance with no expense of capacity compared with undoped one, 97.5%, 96.2% capacity retention respectively after 30 cycles can be reached. The ch lattice expanding of samples with y=0.05, 0.10 reduces from 2.06% of undoped one to 1.017%, 1.018% respectively when lithium is de-intercalated, contributing to the improvement of structure stability and electrochemical cycle character. However, the sample with y=0.20 exhibits lower capacity and faster capacity fading upon cycling, due to high cation disordering and internal impedance. Fluorine doping also accelerates agglomeration of particles of the samples, enhancing operability of electrode preparation of the cathodes. In addition, fluorine-doped samples have better thermal stability than LiNi3/8Co2/8Mn3/8O2.