An similar to 10 nm AlF3 layer was coated on the surface of a Li[Ni0.5Mn0.5]O-2 positive electrode material for lithium-ion batteries, and the effects of this coating on battery performances and thermal stability of the cathode materials were studied. Although no significant bulk structural differences were observed between the coated and pristine material, a slightly higher capacity was seen for the AlF3-coated Li[Ni0.5Mn0.5]O-2 electrode, and the rate capability was also greatly enhanced by the AlF3 coating. These improvements are mainly attributed to the suppression of the transition metal dissolution benefited from the AlF3 coating. This suppression contributed to the reduction in the charge-transfer resistance. Time-of-flight secondary ion mass spectroscopic analysis showed that insulating LiF, as a product of decomposed LiPF6, was deposited on the surface of pristine and AlF3-coated Li[Ni0.5Mn0.5]O-2. The deposition of LiF was greatly suppressed by AlF3 coating on the outer surface of Li[Ni0.5Mn0.5]O-2. The protection of the active material by the AlF3 coating substantially improved the capacity, capacity retention, and rate capability of the batteries. It also enhanced the thermal stabilities of the positive electrode material. (C) 2008 The Electrochemical Society.