Modified High-Nickel Cathodes with Stable Surface Chemistry Against Ambient Air for Lithium-Ion Batteries.

High-Ni layered oxides are promising next-generation cathodes for lithium-ion batteries owing to their high capacity and lower cost. However, as the Ni content increases over 70 %, they have a high dynamic affinity towards moisture and CO2 in ambient air, primarily reacting to form LiOH, Li2 CO3 , and LiHCO3 on the surface, which is commonly termed "residual lithium". Air exposure occurs after synthesis as it is common practice to handle and store them under ambient conditions. The air exposure leads to significant performance losses, and hampers the electrode fabrication, impeding their practical viability. Herein, we show that substituting a small amount of Al for Ni in the crystal lattice notably improves the chemical stability against air by limiting the formation of LiOH, Li2 CO3 , LiHCO3 , and NiO in the near-surface region. The Al-doped high-Ni oxides display a high capacity retention with excellent rate capability and cycling stability after being exposed to air for 30 days.