The occurrence of an apparent two-phase delithiation mechanism reported for LiNi_0.8Co_0.15Al_0.05O₂ (NCA)¹ is not intrinsic to the material but is due to a surface layer.

Ni-rich layered oxides like NCA are the most important class of positive electrodes for high-energy-density Li-ion batteries. These materials react with H₂O and CO₂ from air to form surface layers mainly composed of Li₂CO₃^2–5. The presence of such a surface layer is deleterious to the electrochemical performance of this class of material. We show, using in-situ synchrotron X-ray diffraction measurements, that this surface layer also induces the presence of a second phase during the 1^st electrochemical delithiation. Such a mechanism is however not intrinsic to NCA. Indeed, a sample stored and handled in an argon atmosphere presents a typical solid solution behavior, as expected for this class of material.

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