Direct visualization of lattice oxygen evolution and related electronic properties of Li1.2Ni0.2Mn0.6O2 cathode materials

Abstract Li-rich layered manganese oxide-based cathodes have drawn much attention for the next-generation lithium-ion batteries due to the large discharge capacities and low cost. However, the lattice oxygen release and subsequent surface densification during cycling inevitably lead to their instability, which incurs capacity failure at high voltage. Herein, we have systematically explored the oxygen oxidation mechanisms in Li1.2Ni0.2Mn0.6O2 (0 0 3) surface by considering five possible different local oxygen coordination environments and investigate their oxidation process during the different degrees of delithiation. Based on the density functional theory calculations, we identify the triggering factors for the oxygen dimerization at the cathode surface. Our study reveals that the oxygen atoms linearly coordinated with two Li-ions (Li O Li geometries) are unstable and proceed oxidation via O2− to O− to O22− to O2− and finally O2 evolution occurred on the cathode surface at a higher degree of delithiation. Based on our theoretical results, we expect that the oxygen molecule release can be suppressed by modifying the surface's oxygen coordination environment. Such a comprehensive understanding is essential for developing the novel complex Li-rich layered manganese oxide cathodes.