Low-Voltage Ligand-to-Metal Charge Transfer in LixCoO2

Abstract Oxygen redox in transition metal oxide cathodes is typically expected to occur at higher voltages. Here, we report an unexpected low-voltage oxygen redox mechanism in the archetypal LiCoO₂ (LCO) cathode. This mechanism is triggered by changes to the local atomic structure from a subtle phase change within the first 10% of delithiation. Our results indicate the formation of delocalized electron holes at oxygen 2p orbitals resulting in a reduction of cobalt ions via ligand-to-metal charge transfer. This reduction causes an anomalous change in LCO’s magnetic response with delithiation. This observation provides fundamental insight into the mechanism behind anion redox, offering a fresh perspective to take advantage of this additional redox center.