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

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 )O₂ (NCM9163), with minimal side effects. Based on thermodynamic considerations of the preferred reactions, we systematically designed a synthesis process that preemptively converts residual Li₂ O (the origin of LiOH and Li₂ CO₃ ) into a more stable compound by injecting reactive SO₂ gas. The preformed lithium sulfate thin film significantly suppresses the generation of LiOH and Li₂ CO₃ during both synthesis and storage, thereby mitigating slurry gelation and gas evolution and improving the cycle stability.