Increased Performance Improvement of Lithium-Ion Batteries by Dry Powder Coating of High-Nickel NMC with Nanostructured Fumed Ternary Lithium Metal Oxides

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 Al 2 O 3, ZrO 2, and TiO 2 coatings on LiNi 0.7 Mn 0.15 Co 0.15 O 2 during cycling, improving the cycling performance. Here, this coating approach is transferred for the first time to fumed ternary LiAlO 2, Li 4 Zr 3 O 8, and Li 4 Ti 5 O 12 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 O 2 (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 ZrO 2 coating, while the best long-term cycling stability with the highest absolute capacity was obtained for the fumed LiAlO 2 -coated NMC. The optimal coating agent for NMC to achieve a balanced system is fumed Li 4 Ti 5 O 12, providing a good compromise between high rate capability and good capacity retention. The coating agents prevent CAM particle cracking and degradation in the order LiAlO 2 ≈ Al 2 O 3 > Li 4 Ti 5 O 12 > Li 4 Zr 3 O 8 > ZrO 2 > TiO 2 . 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.