Controlling Residual Lithium in High‐Nickel (>90 %) Lithium Layered Oxides for Cathodes in Lithium‐Ion Batteries

Abstract The rampant generation of lithium hydroxide and carbonate impurities, commonly known as residual lithium, is a practical obstacle to the mass‐scale synthesis and handling of high‐nickel (>90 %) layered oxides and their use as high‐energy‐density cathodes for lithium‐ion batteries. Herein, we suggest a simple in situ method to control the residual lithium chemistry of a high‐nickel lithium layered oxide, Li(Ni 0.91 Co 0.06 Mn 0.03 )O 2 (NCM9163), with minimal side effects. Based on thermodynamic considerations of the preferred reactions, we systematically designed a synthesis process that preemptively converts residual Li 2 O (the origin of LiOH and Li 2 CO 3 ) into a more stable compound by injecting reactive SO 2 gas. The preformed lithium sulfate thin film significantly suppresses the generation of LiOH and Li 2 CO 3 during both synthesis and storage, thereby mitigating slurry gelation and gas evolution and improving the cycle stability.