An in-depth analysis detailing the structural and electrochemical properties within Br− modified LiNi0.815Co0.15A0.035O2 (NCA) cathode material

Abstract

The Br− modified LiNi0.815Co0.15Al0.035O2 (NCA) cathode materials areprepared via a situ doping method for the first time. The structural and electrochemical properties within Br− modified NCA cathode material are in an in-depth analysis. X-ray diffraction (XRD) results show enlarged interslab spacing due to the fact that partial Br− has doped into the bulk particles of NCA to replace O2− in 6c site. Density functional theory (DFT) calculations suggest that Br− doping mainly occurs in the surface layer. Moreover, the Br‒ modified NCA cathode materials present smaller primary particles than pure NCA, which is proved by calculations of particle size from random scanning electron microscopy (SEM) images. X-ray photoelectron spectroscopy (XPS) results certify that the the valence state of Ni3+ is partly reduced to Ni2+ and residual lithium acts as stable LiBr instead of unstable Li2CO3 at the surface of Br‒ modified NCA cathode materials. From the electrochemical tests, 0.2 mol% Br− modified NCA with reduced potential polarization, decreasing value of Rsf + Rct and increasing Li+ diffusion coefficient, exhibits excellent cycling performance, even at elevated temperature. These results clearly indicate that Br− modification contributes to the remarkable enhancement of structure stability and cycling performance of NCA.