Surface fluorinated LiNi0.8Co0.15Al0.05O2 as a positive electrode material for lithium ion batteries

Abstract

LiNi_0.8Co_0.15Al_0.05O₂ is considered as an alternative to the commercial LiCoO₂ positive electrode material for lithium ion batteries because of its excellent cycling performance. However, its capacity fading and potential safety hazard still need to be improved. In this study, fluorination has been introduced for the first time to modify the surface of LiNi_0.8Co_0.15Al_0.05O₂ by a one-step facile and dry method. The crystalline structure, morphology, surface information and electrochemical performance were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectronic spectroscopy and electrochemical tests. The surface-fluorinated LiNi_0.8Co_0.15Al_0.05O₂ exhibits a reversible capacitance up to 220.5 mA h g⁻¹ at 0.1 C, good rate capability, and an excellent long-term cycling stability with 93.6% capacity retention after 80 cycles at 0.1 C, which is much better than that of the pristine commercial LiNi_0.8Co_0.15Al_0.05O₂. The main reason is that metal-fluorine (M–F) bond partially replaces the metal–oxygen (M–O) bond at the surface, enhancing the entire bond energy as well as the structure stability. In addition, the interfacial conductivity between the electrolyte and the positive electrode has been increased, leading to a faster kinetic process. These results show that fluorinated LiNi_0.8Co_0.15Al_0.05O₂ is a promising positive electrode material for high performance lithium ion batteries.