Electrochemical Effects of Yttrium(Y) Doping on Rich-Nickel Cathode Materials for Lithium Ion Batteries

Abstract

Rich-nickel layered oxides are regarded as one of the most promising cathode materials for the next generation of high energy lithium-ion batteries due to its high discharge specific capacity. However, the practical application of the materials is limited by poor cyclic stability. In order to solve this severe problem, the spherical precursor Ni0.85Co0.075Mn0.075(OH)2 cathode materials are synthesized through co-precipitation, then Yttrium(Y) is added to synthesize high nickel layered oxides Li(Ni0.85Co0.075Mn0.075)0.98Y0.02O2 during crystallization by solid-state reaction at a certain calcination temperatures under oxygen atmosphere to improve the electrochemical properties of materials in this study. The microstructure, particle morphology and electrochemical properties of the materials are characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), constant current charge and discharge, cyclic voltammetry(CV), respectively. The XRD results show that both two samples are corresponding to the layered α-NaFeO2 structure with R3m space group, while the c/a ratio and the unit cell volume increased with the addition of Yttrium. As the unit cell size increases, the volumes of Li-ion transport pathways also increase, which further promote lithium diffusion rate in the channel and facilitate Li+ intercalation/de-intercalation. And the SEM results demonstrated that both precursor materials were spherical secondary particles formed by the aggregation of primary scale-like particles, and the particle size gradually decreased with the addition of yttrium. The CV determination results show that both materials have two pairs of redox peaks. Still ,the redox peak of the doped material is broader and without the sharpness of the original one. In addition to this, the doped sample exhibits the excellent electrochemical performance with first discharge specific capacity with 193.34 mAh·g-1 and capacity retention of 85.83% after 100 cycles at 0.5C, while the original material LiNi0.85Co0.075Mn0.075O2 has higher first discharge capacity of 195.86 mAh·g-1, and the capacity retention in the 100 cycles of original was only 78.06%. In a word, the results showed that Y-doping could significantly improve the cyclic stability of LiNi0.85Co0.075Mn0.075O2 due to it promoted the diffusion channel of Li+ and inhibited the side reactions between samples and electrolyte. Figure 1