High nickel layered oxide cathodes are gaining increasing attention for lithium-ion batteries due to their higher energy density and lower cost compared to LiCoO2. However, they suffer from the formation of residual lithium on the surface in the form of LiOH and Li2CO3 on exposure to ambient air. The residual lithium causes notorious issues, such as slurry gelation during electrode preparation and gas evolution during cell cycling. In this review, we investigate the residual lithium issues through its impact on cathode slurry instability based on deformed polyvinylidene fluoride (PVdF) as well as its formation and reduction mechanism in terms of inherently off-stoichiometric synthesis of high nickel cathodes. Additionally, new analysis method with anhydrous methanol was introduced to exclude Li+/H+ exchange effect during sample preparation with distilled water. We hope that this review would contribute to encouraging the academic efforts to consider practical aspects and mitigation in global high-energy-density lithium-ion battery manufacturers.