Oxygen defects are closely related to the battery performance of oxide-based cathode active materials for lithium-ion batteries, and especially, positive influences have been reported in Li-rich cathode materials. However, the function of oxygen defects and its influence on electrochemical properties are poorly understood so far. Here, impacts of oxygen vacancy on electrochemical properties of a Li-rich cathode Li 1.2 Mn 0.6 Ni 0.2 O 2−δ are reported. Single-phase oxygen-deficient Li 1.2 Mn 0.6 Ni 0.2 O 1.97 was prepared by using the solid electrolyte reactor composed of an oxide ion conductor, and its electrochemical properties, crystal, and electronic structures were compared with those of the oxygen-stoichiometric Li 1.2 Mn 0.6 Ni 0.2 O 2 . In the initial charge, the oxygen-deficient Li 1.2 Mn 0.6 Ni 0.2 O 1.97 showed a larger oxidation current due to the oxygen release than the oxygen-stoichiometric Li 1.2 Mn 0.6 Ni 0.2 O 2 . This suggests that preliminary introduced oxygen vacancy promoted the further oxygen release during the initial charge possibly by accelerating the oxide ion diffusion in the active material via oxygen vacancy. Due to the oxygen release, heavily oxygen-deficient Li 1.2 Mn 0.6 Ni 0.2 O 2−δ phase (δ > 0.03) was formed at the near-surface region after the initial charge/discharge cycle. Vigorous Mn redox was observed in the heavily oxygen-deficient Li 1.2 Mn 0.6 Ni 0.2 O 2−δ phase during the charge/discharge in contrast to the oxygen-stoichiometric phase wherein Mn was almost inactive for the charge/discharge. The modulation of oxygen defects can be one of effective strategies to control redox species in battery active materials.
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 LiNi1/3Co1/3Mn1/3O2−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 (Li″ 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.
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