Improved Cycling Performance of High‐Nickel NMC by Dry Powder Coating with Nanostructured Fumed Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub>, and ZrO<sub>2</sub>: A Comparison
Marcel J. Herzog, Daniel Esken, Jürgen Janek
Abstract
Abstract Surface coating is an effective concept to protect layered cathode active materials (CAMs) in lithium ion batteries from detrimental side reactions. Dry powder coating is a fast and cost‐effective coating process, and here we transfer this coating approach from Al 2 O 3 to nanostructured fumed TiO 2 and ZrO 2 coatings on the same NMC (Li[Ni,Mn,Co]O 2 ) material. Using similar processing, this allows a direct comparison of the characteristics of the achieved coating layers and their influence on the cycling performance of high‐nickel NMC. The nanostructured small oxide aggregates result in a quite homogeneous coating layer with a certain porosity around each CAM particle. Significantly enhanced long‐term cycling stability is observed, with a trend of increasing stability in the series ZrO 2 <TiO 2 <Al 2 O 3 . Fumed Al 2 O 3 and TiO 2 coating layers prevent cathode particle cracking and disintegration successfully, while fumed ZrO 2 only shows a moderate protection effect. Each coating material enhances the rate performance compared to uncoated NMC in the row TiO 2 <ZrO 2 <Al 2 O 3 . XPS measurements of cycled electrodes indicate a partial incorporation of lithium ions in the crystalline TiO 2 and ZrO 2 coating layers, contributing to the enhanced lithium‐ion transport across the CAM surface layer, as observed before for fumed γ ‐Al 2 O 3 coatings. Summarizing the results, the best overall cycling performance was achieved by coating high‐nickel NMC with fumed Al 2 O 3 , providing the highest rate capability and the best long‐term cycling stability.