Reversible Oxygen Redox in High Voltage for Lithium-Rich Layered Oxides

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Abstract Lithium-rich layered oxides, characterized by Li ions in the transition-metal layers, can significantly increase battery energy density through the introduction of oxygen redox. However, these cathodes often suffer from substantial voltage hysteresis, leading to a considerable energy loss during discharge. Herein, we present an O3-type cathode, Li0.63[Li0.20Mn0.80]O2, through the spontaneous ion exchange of P3–Na0.60[Li0.20Mn0.80]O2 in the electrolyte, which retains the ribbon-ordered superstructure. This cathode exhibits a reversible oxygen reduction plateau within the 4.2–4.7 V voltage range, exhibiting minimal voltage loss (hysteresis) during the initial discharge. When the lower voltage limit is reduced to 3.0 V, the plateau disappears. In situ XRD and STEM indicate that there is no significant structural change. Further spectral tests and DFT calculations show that the reversible oxygen reaction is replaced by the Mn reaction during the charging process due to charge transfer, resulting in the disappearance of the discharging plateau. Our findings suggest the potential for lithium-rich layered oxide cathodes to operate without voltage hysteresis and suggest that structural degradation at high voltage is not the only factor causing irreversible oxygen reaction.

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