Electrochemical properties of cathode materials LiNi1-yCoyO2 synthesized using various starting materials

摘要

LiNi1-yCoyO2 samples were synthesized at 800degreesC and 850degreesC, by the solid-state reaction method, using the starting materials LiOH.H2O, Li2CO3, NiO, NiCO3, Co3O4 and CoCO3. The LiNi1-yCoyO2 synthesized using Li2CO3, NiO and Co3O4 exhibited the alpha-NaFeO2 structure of the rhombohedral system (space group R (3) over barm). As the Co content increased, the lattice parameters a and c decreased. The reason is that the radius of the Co ion is smaller than that of the Ni ion. The increase in c/a shows that a two-dimensional structure develops better as the Co content increases. The LiNi0.7Co0.3O2 synthesized at 800degreesC using LiOH.H2O, NiO and Co3O4 exhibited a larger first discharge capacity of 162 mAh g(-1) than the other samples. The cycling performances of the samples with the first discharge capacity larger than 150 mAh g(-1) were investigated. LiNi0.9Co0.1O2 synthesized at 850degreesC using Li2CO3, NiO and Co3O4 showed excellent cycling performance. Samples with larger first discharge capacity will have a greater tendency for lattice destruction due to expansion and contraction during intercalation and deintercalation, than samples with smaller first discharge capacity. As the first discharge capacity increases, the capacity fading rate thus increases. [References: 27]