Cyclic performances of HT-LiCo_0.8M_0.2O₂ (M = Al, Ni) powders prepared by the molten salt synthesis method

Single phases of M-substituted lithium cobalt oxides, HT-LiCo_0.8M_0.2O₂ (M = Al, Ni), were prepared by molten salt synthesis (MSS) method using coprecipitated Co-M hydroxides in 0.59 LiNO₃-0.41 LiOH. The prepared powders consisted of well-developed particles with spherical shape and the particle size was around 150 nm in diameter. Among them, HT-LiCo_0.8Al_0.2O₂ showed an inferior cyclic performance and a smaller discharge capacity than HT-LiCo_0.8Ni_0.2O₂, even though the former is more structurally stable than the latter. Structural analysis of HT-Li_xCo_0.8Al_0.2O₂ indicated that the Al substitution, causing an enhanced internal resistance for lithium ion diffusion, is responsible for the capacity fading. In the meanwhile, HT-Li_xCo_0.8Ni_0.2O₂ with large c layer spacing showed as high as 146 mAh/g at the first cycle and 130 mAh/g at the twentieth cycle.