Surface coating and doping of single-crystal LiNi0.5Co0.2Mn0.3O2 for enhanced high-voltage electrochemical performances via Chemical Vapor Deposition

• The Al 2 O 3 is applied on the surface of single-crystal LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM) by Chemical Vapor Deposition (CVD). • The optimum CVD operation time for Al 2 O 3 is 30 min. • The electrochemical performance of NCM can be significantly improved by the Al 2 O 3 coating prepared by CVD. • The Al 2 O 3 is chemically bonded with the NCM substrate and a trace of Al exists as the dopant on the top surface of NCM. Due to the poor cycle stability at high operating voltage, layered transition-metal oxides (NCM) have limited industrial applications and cover up the appealing properties like high energy density and low price. In this work, Al 2 O 3 is deposited on the surface of single-crystal LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM) materials by Chemical Vapor Deposition (CVD) as the inorganic coating layer for the first time. By carefully controlling the deposition intervals, the varied thicknesses of Al 2 O 3 coating could be obtained. Furthermore, according to the CVD, the Al 2 O 3 coating is chemically bonded to the NCM substrates, and a trace of Al exists as a dopant on the top surface. The surface modification layer is detected by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectrometer. The results infer that the combination of Al doping and Al 2 O 3 coating on the top surface of substrate can significantly improve the capacity retention under high voltage up to 4.5 V. The optimum CVD deposition time is 30 min. The modified cathode renders a capacity of 191.9 mA h/g with a retention of 61.3% at 4.5 V after cycling for 100 cycles. The value is superior to its counterpart-the single-crystal NCM without CVD treatment. Surface treatment by controllable CVD paves a new and practical pathway for the broadly application of single-crystal cathode materials of Li ion battery.