Synthesis and electrochemical characterization of gradient composite LiNi1-yCoyO2 used as cathode materials in lithium-ion battery

Gradient composites, LiNi1-yCoyO2, are synthesized from coated spherical Ni(OH)(2) precursor. These composites could be applied as new cathode materials in lithium-ion batteries because they have low cobalt content (yless than or equal to0.2) and exhibit excellent properties during high-rate charge/discharge cycles. The initial discharge capacity of coated composite of LiNi0.95Co0.05O2 is 186 mAh/g, and the decreasing rate of the capacity is 3.2% in 50 cycles at 1 C rate. It has been verified by TEM and EDX experiments that a core-shell structure of the composite particles develops because of the cobalt enrichment near the surfaces, and the formation of the cobalt enrichment layer is sensitive to sintering temperature. High cobalt surface concentration may reduce the undesired reactions and stabilize the structure of the particles.