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.

Considering the high theoretical energy density and improved safety, thiophosphate-based all-solid-state batteries (ASSBs) have become one of the most promising candidates for next-generation energy storage systems. However, the intrinsic electrochemical instability of thiophosphate-based solid electrolytes in contact with oxide-based cathodes results in rapid capacity fading and has driven the need of protective cathode coatings. In this work, for the first time, a fumed lithium titanate (LTO) powder-based coating has been applied to Ni-rich oxide-based cathode active material (CAM) using a newly developed dry-coating process. The LTO cathode coating has been tested in thiophosphate-based ASSBs. It exhibits a significantly improved C-rate performance along with superior long-term cycling stability. The improved electrochemical performance is attributed to a reduced interfacial resistance between coated cathode and solid electrolyte as deduced from in-depth electrochemical impedance spectroscopy analysis. These results open up a new, facile dry-coating route to fabricate effective protective CAM coatings to enable long-life ASSBs. This nondestructive coating process with no post-heat-treatment approach is expected to simplify the coating process for a wide range of coatings and cathode materials, resulting in much improved cathode/electrolyte interfacial stability and electrochemical performance of ASSBs.

Dry powder coating is an effective approach to protect the surfaces of layered cathode active materials (CAMs) in lithium-ion batteries. Previous investigations indicate an incorporation of lithium ions in fumed Al2O3, ZrO2, and TiO2 coatings on LiNi0.7Mn0.15Co0.15O2 during cycling, improving the cycling performance. Here, this coating approach is transferred for the first time to fumed ternary LiAlO2, Li4Zr3O8, and Li4Ti5O12 and directly compared with their lithium-free equivalents. All materials could be processed equally and their nanostructured small aggregates accumulate on the CAM surfaces to quite homogeneous coating layers with a certain porosity. The LiNi x Mn y Co z O2 (NMC) coated with lithium-containing materials shows an enhanced improvement in overall capacity, capacity retention, rate performance, and polarization behavior during cycling, compared to their lithium-free analogues. The highest rate performance was achieved with the fumed ZrO2 coating, while the best long-term cycling stability with the highest absolute capacity was obtained for the fumed LiAlO2-coated NMC. The optimal coating agent for NMC to achieve a balanced system is fumed Li4Ti5O12, providing a good compromise between high rate capability and good capacity retention. The coating agents prevent CAM particle cracking and degradation in the order LiAlO2 ≈ Al2O3 > Li4Ti5O12 > Li4Zr3O8 > ZrO2 > TiO2. A schematic model for the protection and electrochemical performance enhancement of high-nickel NMC with fumed metal oxide coatings is sketched. It becomes apparent that physical and chemical characteristics of the coating significantly influence the performance of NMC. A high degree of coating-layer porosity is favorable for the rate capability, while a high coverage of the surface, especially in vulnerable grain boundaries, enhances the long-term cycling stability and improves the cracking behavior of NMCs. While zirconium-containing coatings possess the best chemical properties for high rate performances, aluminum-containing coatings feature a superior chemical nature to protect high-nickel NMCs.

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 Al2O3 to nanostructured fumed TiO2 and ZrO2 coatings on the same NMC (Li[Ni,Mn,Co]O2) 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 ZrO2