Synthesis of Cathode Materials LiNi1-yCoyO2from Various Starting Materials and their Electrochemical Properties

Abstract

The LiNi 1-y Co y O₂ samples were synthesized at 800℃ and 850℃, by the solid-state reaction method, from the various starting materials LiOH, Li₂CO₃, NiO, NiCO₃, Co₃O₄, CoCO₃, and their electrochemical properties are investigated. The LiNi 1-y Co y O₂ prepared from Li₂CO₃, NiO, and Co₃O₄ exhibited the α-NaFeO₂ structure of the rhombohedral system (space group; R3m). As the Co content increased, the lattice parameters a and c decreased. The reason is that the radius of Co ion is smaller than that of Ni ion. The increase in c/a shows that two-dimensional structure develops better as the Co content increases. The LiNi 0.7 Co 0.3 O₂ [HOO(800,0.3)] synthesized at 800℃ from LiOH, NiO, and Co₃O₄ exhibited the largest first discharge capacity 162 mAh/g. The size of particles increases roughly as the valve of y increases. The samples with the larger particles have the larger first discharge capacities. The cycling performances of the samples with the first discharge capacity larger than 150 mAh/g were investigated. The LiNi 0.9 Co 0.1 O₂[COO(850,0.1)] synthesized at 850℃ from Li₂CO₃, NiO, and Co₃O₄ showed an excellent cycling performance. The sample with the larger first discharge capacity will be under the more severe lattice destruction, due to the expansion and contraction of the lattice during intercalation and deintercalation, than the sample with the smaller first discharge capacity. As the first discharge capacity increases, the capacity fading rate thus increases.