Ambient Storage Derived Surface Contamination of NCM811 and NCM111: Performance Implications and Mitigation Strategies

The quality of metal oxide-based battery active materials is compromised by surface contamination from storage and handling at ambient conditions. We present a detailed analysis of the true nature and the quantity of the surface contaminants on two different cathode active materials, the widely used LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111) and the Ni-rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811). We process these materials in three distinct conditions "wet" (excessive exposure to moisture), "dry" (standard drying of as-received materials), and "calcined" (heat-treatment of cathode powders). Surface contaminants are then quantified by thermogravimetric analysis coupled with mass spectrometry (TGA-MS), and their reactivity with an ethylene carbonate-based electrolyte is evaluated using on-line mass spectrometry (OMS). We demonstrate that not only the commonly assumed LiOH and Li 2 CO 3 residues account for NCM performance deterioration upon storage in moisture and CO 2 containing atmosphere, but also basic transition metal hydroxides/carbonates formed on the material surface. Eventually, we showcase a thermal treatment that removes these transition metal based surface contaminants and leads to superior cycling stability.