Stabilized Behavior of LiNi_0.85Co_0.10Mn_0.05O₂Cathode 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.