Stabilized Behavior of LiNi_0.85Co_0.10Mn_0.05O₂ Cathode Materials Induced by Their Treatment with SO₂

We present in this paper a modification and stabilization approach for the surface of a high specific capacity Ni-rich cathode material LiNi0.85Co0.10Mn0.05O2 (NCM85) via SO2 gas treatment at 250–400 °C, in order to enhance its electrochemical performance in advanced lithium-ion batteries. It was established that SO2 interactions with NCM85 result in the formation of a nanometer-sized Li2SO4 surface layer on the oxide particles with no impact on the bulk structure of the material and its morphology. We consider the above interactions as oxidation–reduction processes resulting in direct oxidation of sulfur and partial reduction of Ni3+ as revealed by high-resolution XPS and electron paramagnetic resonance studies. The important impacts of the SO2 treatment are a remarkably stable cycling performance of cathodes comprising this material with ∼10% increase in capacity retention and lesser voltage hysteresis upon cycling compared to untreated NCM85 cathodes. The SO2-treated NCM85 material is also significantly thermally stable, demonstrating lower heat evolution upon thermal reactions with standard EC-EMC/LiPF6 solutions by 12–20%, compared to untreated material. The proposed approach to modify the surface of Ni-rich NCM cathode materials by SO2 treatment is demonstrated to be a promising method to enhance their electrochemical performance. This work demonstrates a leap in performance of Ni-rich NCM cathode materials by increasing the content of nickel compared to any benchmark cathodes and is a promising approach for stabilization by surface modification.