The effect of oxygen flow rate and anion doping on the performance of LiNiO2 electrode for lithium secondary batteries

Abstract

Although LiNiO₂has some advantages over LiCoO₂such as low cost, environmental safety. However LiNiO₂has still had some problems in the practical application due to the difficulty in the synthesis of stoichiometric LiNiO₂and the thermal instability. This paper reports the effect of oxygen flow rate during the synthesis of LiNiO₂ using a sol-gel method as well as the effect of S-doping in LiNiO₂in the form of LiNiO₂-уSуon alleviation of capacity fading of LiNiO₂electrode. The structural and electrochemical characteristics were explored for layered LiNiO₂synthesised as a fuction of oxygen flow rate. XRD and discharge capacity measurements showed that high qualtity of LiNiO₂powders were prepared at 750 and 800 sccm O₂flow rate. It was found that LiNiO₂have a stable rock-salt structure when synthesized at oxygen flow rates above 400 sccm, but show an unstable structure at the flow rates of oxygen below 300 sccm. The electrochemical charicterization of LiNiO₂electrodes also showed a similar trend to that observed in the structure of LiNiO₂. Oxysulfide layered LiNiO₂-ySy powers were synthesized and characterized to investigate the effect of S-doping on the electrode performance of the material. It was found that sulfur powers can be more effectively used as a sulfur source to produce better quality of LiNiO powders. The dischrge capacity of LiNiO₂cell steadily decreased with the cycle number, but the capacity retention rate of LiNiO₂ySy cells was significantly improved. The merits of anion doping in LiNiO₂has been intensively disccused in this work.