Synthesis and electrochemical properties of lithium nickel oxysulfide (LiNiS_yO_2-y) material for lithium secondary batteries

The layered oxysulfide LiNiS_yO_2-y compounds were synthesized and characterized to investigate the effect of sulfur on the electrode performance of LiNiO₂. LiNiO₂ precursors were first synthesized by a sol-gel method using adipic acid as a chelating agent and then doped with sulfur powders by a solid-state reaction under the flow of oxygen to prepare LiNiS_yO_2-y compounds. Pure LiNiO₂ electrode showed a gradual decrease of discharge capacity with cycle number, whereas the capacity retention rate of LiNiS_yO_2-y electrodes significantly improved. The initial discharge capacity of the LiNiS_yO_2-y cells was lower than that of LiNiO₂ cell and decreased with the increasing content of sulfur substituted in LiNiS_yO_2-y.