Tuning Local Structural Configurations to Improve Oxygen-Redox Reversibility of Li-Rich Layered Oxides.

Li-rich layered oxides (LLOs) are regarded as one of the most desirable cathode materials due to their high specific capacity. Nevertheless, the irreversible oxygen release associated with low oxygen stability prevents their widespread application. Herein, an improved oxygen redox reversibility was achieved by constructing Ni 2+ -O 2- -Ni 2+ configurations. Superconducting Quantum Interference Device (SQUID) magnetometry measurements are used to track the evolution of the Ni 2+ -O 2- -Ni 2+ configuration during the electrochemical process. The strongest 180° superexchange interaction in the Ni 2+ -O 2- -Ni 2+ configuration, derived from the inevitable Li/Ni mixing in LLOs, regulates the local structure to form the ferrimagnetic (FiM) structural units. Consequently, the FiM structural units prevent the irreversible oxygen release and endow LLOs with high initial Coulombic efficiency (ICE). This work emphasizes the importance of the Ni 2+ -O 2- -Ni 2+ configuration for LLOs with high reversible capacity and proposes a synthesis approach to modulate the amount of FiM structural units.