Improving the cycling performance of LiNi0.8Co0.15Al0.05O2 cathode materials via zirconium and fluorine co-substitution

Abstract High-nickel layered transition-metal oxides with large reversible capacity typically suffer from crystal instability and fast capacity decay during cycling. Herein, we report a co-substitution strategy using traditional solid state sintering technology to incorporate zirconium (Zr) and fluorine (F) into LiNi0.8Co0.15Al0.05O2 cathode materials. The effects of the substitution on the crystal structure, morphology and electrochemical performance of LiNi0.8Co0.15Al0.05O2 were investigated by the combinations of XRD, SEM, EDS, XPS, CV, galvanostatic charge-discharge tests and EIS. The results show that F substitution stabilizes the crystal structure. However, it increases the degree of the cation mixing and degrades the reversible capacity. Zr substitution effectively stabilizes the crystal structure and reduces the cation mixing due to the strong bond dissociation energy of Zr–O. Our study suggests that the Zr and F co-substitution facilitates the transport of lithium ions, mitigates the electrochemical polarization and significantly enhances the structural stability. The Zr and F co-doped sample shows capacity retention of 90.5% after 200 cycles at 1 C, while that of bare sample remained only 75.8%. This work sheds lights on understanding the effects of multi-ion substitution on improving electrochemical performance of high-nickel layered cathodes.