Preparation and Characterization of LiNi0.8Co0.2O2 Synthesized by an Emulsion Drying Method

A layered LiNi_0.8Co_0.2O₂ solid solution, which is a promising cathode material for secondary lithium batteries, was successfully synthesized by an emulsion drying method. Because electrochemical properties significantly depend on the conditions of the synthesis, the calcination temperature was carefully determined on the basis of X-ray diffraction and TG studies. The prepared cathodes were characterized by means of SEM, BET, X-ray diffraction, Rietveld refinement, cyclic voltammetry and a charge-discharge experiment. From the Rietveld analysis, it was found that powder calcined at 800 °C for 12 h exhibits a well ordered and lower cation mixed layered structure than the others. The cyclic voltammetry experiment shows that phase transformation can be suppressed considerably by increasing the calcination temperature to 800 °C. The highest discharge capacity of 188.4 mA h g⁻¹ was obtained from the sample prepared at 800 °C. Furthermore, a high capacity retention ratio of 88.1% was found for the initial value after 50 cycles at a constant current density of 40 mA g⁻¹ between 2.7 V_Li/Li⁺ and 4.3 V_Li/Li⁺. In the rate capability test, the cathode delivered a higher discharge capacity of 153.1 mA h g⁻¹ at a 4 C (800 mA g⁻¹) rate.