All-Dry Synthesis of Single Crystal NMC Cathode Materials for Li-Ion Batteries

Single crystal (SC) cathode materials with a layered structure are considered to be state-of-the-art for lithium ion batteries. However, their production involves many steps and can produce large amounts of wastewater. Here we report an all-dry method for making SC cathode materials, with LiNi_0.6Mn_0.2Co_0.2O₂ (SC-NMC) used as a specific example. It was found that a SC-NMC precursor in the form of a previously unobserved rock-salt (Ni, Mn, Co)O solid solution phase can be made phase pure by ball milling. This demonstrates that precursors with atomic scale mixing can be achieved by dry methods. It is furthermore shown that large precursor particle sizes are not necessary to form large SC-NMC particles, as is commonly believed. Instead, large crystallites could just as easily be made from submicron precursors by adjusting the sintering time in air. As a result, highly crystalline SC-NMC with precisely controlled average crystallite sizes ranging from ∼2–10 μm could be made from submicron precursor powders made using an all-dry process.