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

The Br − modified LiNi 0.815 Co 0.15 Al 0.035 O 2 (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 O 2− 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 Ni 3+ is partly reduced to Ni 2+ and residual lithium acts as stable LiBr instead of unstable Li 2 CO 3 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.