Stabilizing nickel-rich layered oxide cathodes by magnesium doping for rechargeable lithium-ion batteries

Nickel-rich layered transition metal oxides are attractive cathode materials for rechargeable lithium-ion batteries but suffer from inherent structural and thermal instabilities that limit the deliverable capacity and cycling performance on charging to a cutoff voltage above 4.3 V. Here we report LiNi0.90Co0.07Mg0.03O2 as a stable cathode material. The obtained LiNi0.90Co0.07Mg0.03O2 microspheres exhibit high capacity (228.3 mA h g-1 at 0.1C) and remarkable cyclability (84.3% capacity retention after 300 cycles). Combined X-ray diffraction and Cs-corrected microscopy reveal that Mg doping stabilizes the layered structure by suppressing Li/Ni cation mixing and Ni migration to interlayer Li slabs. Because of the pillar effect of Mg in Li sites, LiNi0.90Co0.07Mg0.03O2 shows decent thermal stability and small lattice variation until it is charged to 4.7 V, undergoing a H1-H2 phase transition without discernible formation of an unstable H3 phase. The results indicate that moderate Mg doping is a facile yet effective strategy to develop high-performance Ni-rich cathode materials.