Facile Dry Coating Method of High‐Nickel Cathode Material by Nanostructured Fumed Alumina (Al2O3) Improving the Performance of Lithium‐Ion Batteries

Surface coating is a crucial method to mitigate the aging problem of high‐Ni cathode active materials (CAMs). By avoiding the direct contact of the CAM and the electrolyte, side reactions are hindered. Commonly used techniques like wet or ALD coating are time consuming and costly. Therefore, a more cost‐effective coating technique is desirable. Herein, a facile and fast dry powder coating process for CAMs with nanostructured fumed metal oxides are reported. As the model case, the coating of high‐Ni NMC (LiNi0.7Mn0.15Co0.15O2) by nanostructured fumed Al2O3 is investigated. A high coverage of the CAM surface with an almost continuous coating layer is achieved, still showing some porosity. Electrochemical evaluation shows a significant increase in capacity retention, cycle life and rate performance of the coated NMC material. The coating layer protects the surface of the CAM successfully and prevents side reactions, resulting in reduced solid electrolyte interface (SEI) formation and charge transfer impedance during cycling. A mechanism on how the coating layer enhances the cycling performance is hypothesized. The stable coating layer effectively prevents crack formation and particle disintegration of the NMC. In depth analysis indicates partial formation of LixAl2O3/LiAlO2 in the coating layer during cycling, enhancing lithium ion diffusivity and thus, also the rate performance. Nanostructured fumed Al2O3 is coated by a dry powder approach on high‐nickel cathode active material (CAM). The resulting porous coating enables an increased rate performance and long‐term cycling stability. The coating protects the surface of the CAM from side reactions, preventing crack formation. In depth analysis indicates an incorporation of lithium ions in the coating layer, enhancing the Li+ diffusivity.