Oxygen Redox Activation at Initial Cycle to Improve Cycling Stability for the Na0.83Li0.12Ni0.22Mn0.66O2 System

Oxygen reactions are commonly used to increase the specific capacities of Na-ion batteries, especially for the NaxLiyTMO2 systems. Previous research focused on improving the stabilities of oxygen reactions to enhance cycling stability. However, the effects of oxygen reactions on the distribution of Li ions in the transition metal (TM) and alkali metal (AM) layers for the Na-ion battery are relatively unexplored and rarely employed. In this study, we employ a layered P2-Na0.83Li0.12Ni0.22Mn0.66O2 cathode to control the effects of the oxygen reactions on the distributions of Li ions in two layers. With oxygen-redox-activation-at-first-cycle (ORAFIC)-cycling, which cycled first within 2.0-4.6 V to activate oxygen redox and then cycled within 2.0-4.2 V, this cathode exhibited better cycling stability compared to low-voltage (LV)-cycling of 2.0-4.2 V and high-voltage (HV)-cycling of 2.0-4.6 V. Using nuclear magnetic resonance spectroscopy, electron paramagnetic resonance, inductively coupled plasma experiments, and X-ray diffraction, it is confirmed that ORAFIC-cycling stabilizes the crystal structure and distributions of Li ions in the TM and AM layers and reduces Li-ion loss, thus improving the cycling stability.