Lattice Oxygen Instability in Oxide-Based Intercalation Cathodes: A Case Study of Layered LiNi_1/3Co_1/3Mn_1/3O₂

Oxide-based cathode materials are key components of secondary batteries, for example, alkali metal-ion and anion batteries, sufficient stability of which is thus vital for ensuring high energy density and safety. However, problems originating from the lattice oxygen instability in oxide-based intercalation cathodes are widely reported, such as capacity degradation, gas generation, and thermal runaway, highlighting the importance of deep insights into the critical factors for lattice oxygen stability. In this work, lattice oxygen stability in layered rock-salt LiNi_1/3Co_1/3Mn_1/3O_2−δ is investigated with a focus on oxygen release behavior and relevant changes in crystal and electronic structures. Release of lattice oxygen facilitates cation mixing, transition metal slab expansion, and Li slab contraction, thus deteriorating the layered structure. As is revealed by X-ray absorption spectroscopy, in the beginning stage of oxygen release, the charge balance is compensated by selective reduction of Ni³⁺. This strongly suggests that high valent Ni generated by delithiation or negative defect species, that is, lithium at the transition metal site ((Formula presented.) TM), aggravates oxygen release severely. The findings of this work provide a new research direction and guidelines for the stabilization of lattice oxygen in oxide-based intercalation cathodes.