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

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 R-sf + R-ct 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. (C) 2019 Elsevier Ltd. All rights reserved.