Altering Surface Contaminants and Defects Influences the First-Cycle Outgassing and Irreversible Transformations of LiNi_0.6Mn_0.2Co_0.2O₂

By altering the surface of LiNi0.6Mn0.2Co0.2O2 (NMC622) we show that surface defects and contaminants dominate the outgassing and irreversible surface transformations during the first electrochemical cycle. To alter the surface defects and contaminants without changing the bulk structure of the NMC622, we perform mild methanol and water rinses, a water soak, a water rinse and subsequent heat treatment, as well as purposeful increase of the surface Li2CO3. By combining isotopic labeling; gas analysis; and peroxide, hydroxide, and carbonate titrations we observe that these alterations change the surface Li2CO3, surface hydroxides, and the local defects, which in turn alter the nature and extent of the outgassing to O2 and CO2. Our results highlight that outgassing of Li-ion cathode materials is highly dependent on the synthesis and storage routes and comparison of varying compositions must take into account these differences to make any meaningful conclusions. We also show that simple rinsing procedures may be an effective route to controlling interfacial reactivity of Li-ion active materials.