AlF3-coated Li(Li0.17Ni0.25Mn0.58)O2 as cathode material for Li-ion batteries

Li-rich layered oxide is prepared and coated with an AlF3 layer by a chemical deposition method. The as-prepared and AlF3-coated Li-rich materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The as-prepared Li-rich oxide has a typical layered structure with the chemical formula of Li(Li0.17Ni0.25Mn0.58)O2, and the AlF3 layer with a thickness of about 5–7 nm is coated on the surface of the Li(Li0.17Ni0.25Mn0.58)O2 grains. Galvanostatic charge–discharge tests at various rates show that the AlF3-coated Li(Li0.17Ni0.25Mn0.58)O2 has an obviously enhanced electrochemical performance compared with the as-prepared sample. At 0.2 C rate, the AlF3-coated sample provides a large capacity of more than 250 mAh g−1. The coulombic efficiency in the initial cycle is improved to 89.5% from 76.4%. At 5 C rate, the reversible capacity of the AlF3-coated sample is stable at above 104 mAh g−1 after 200 cycles, much higher than that of the as-prepared sample. According to the analysis from electrochemical impedance spectra (EIS), the improvements of the electrochemical performance are mainly attributed to the pre-activation of the Li-rich layered oxide induced by the AlF3 coating and the maintenance of more active sites for the lithium ion intercalation/extraction in the AlF3-coated sample.

► The AlF3 layer with a thickness of 5–7 nm is coated on the surface of the Li-rich oxide.
► The AlF3-coated Li(Li0.17Ni0.25Mn0.58)O2 delivers the excellent high-rate capability.
► The AlF3 coating can pre-activate the Li-rich layered oxide.