Controlled nanoparticle metal phosphates (metal = Al, Fe, Ce, and Sr) coatings on LiCoO2 cathode materials

Abstract

Despite the fact that the same coating concentration and annealing temperature are used for MPO4 nanoparticle coatings (M = Al, Fe, Ce, and SrH) on a LiCoO2 cathode, the extent of the coating coverage is influenced by the nanoparticle size or morphology. Nanoparticles (AlPO 4 or FePO4) with a size smaller than 20 nm led to the complete encapsulation of LiCoO2, but those with sizes greater than 150 nm (CePO4) or with whisker shapes (SrHPO4) led to partial encapsulation. This difference affected the discharge capacity. The LiCoO2 completely encapsulated with AlPO4 or FePO 4 showed the highest discharge capacity of 230 mAh/g at 4.8 and 3 V at a rate of 0.1 C (=18 mA/g), which diminished with decreasing coating coverage in the order of Al ∼ Fe < SrH < Ce < bare cathode. However, the capacity retention during cycling increased in the order of Al > Ce > SrH > Fe > bare cathode. This is consistent with the capacity retention result obtained at 90°C storage for 4 h.