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 )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. This simple and versatile approach is thus a promising practical solution to overcome the residual lithium issues currently encountered on mass production lines.