Effect of substitution of cobalt with iron on electrochemical behavior and solid electrolyte interface of LiNi0.8Co0.15Al0.05O2

Abstract Partial substitution of Co with Fe in LiNi 0.8 Co 0.15 Al 0.05 O 2 is carried out via ball-milling followed by a two-step solid reaction. The LiNi 0.8 Co 0.15-y Fe y Al 0.05 O 2 (0 ≤ y ≤ 0.15) samples exhibit significantly improved cyclic stability compared to pristine LiNi 0.8 Co 0.15 Al 0.05 O 2 , although the specific capacity decreases with increasing of the Fe content. In particular, the LiNi 0.8 Co 0.075 Fe 0.075 Al 0.05 O 2 material exhibits high capacity retention of 88.4% at 1 C after 350 cycles, relative to that of 55.7% for the pristine LiNi 0.8 Co 0.15 Al 0.05 O 2 . This phenomenon is more obvious at high rate and elevated temperature. The electrochemical impedance spectra and X-ray photoelectron spectra analysis demonstrate that less solid electrolyte interface film is formed on LiNi 0.8 Co 0.075 Fe 0.075 Al 0.05 O 2 than LiNi 0.8 Co 0.15 Al 0.05 O 2 . The significantly improved cyclability is mainly attributed to the effect of the FeO 6 octahedron on the edge-shared NiO 6 octahedra via enhanced electron localization. As a result, the tendency to generate reactive oxygen species at the interface could be reduced, leading to suppression of the oxidation of the electrolyte.