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 Al₂O₃, ZrO₂, and TiO₂ coatings on LiNi_0.7Mn_0.15Co_0.15O₂ 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_xMn_yCo_zO₂ (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.