Improvement of the Electrochemical Properties of Li[Ni[sub 0.5]Mn[sub 0.5]]O[sub 2] by AlF[sub 3] Coating

An layer was coated on the surface of a 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 -coated electrode, and the rate capability was also greatly enhanced by the coating. These improvements are mainly attributed to the suppression of the transition metal dissolution benefited from the 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 , was deposited on the surface of pristine and -coated . The deposition of LiF was greatly suppressed by coating on the outer surface of . The protection of the active material by the coating substantially improved the capacity, capacity retention, and rate capability of the batteries. It also enhanced the thermal stabilities of the positive electrode material.