De-clustered nonbonding oxygen state inhibits oxygen dimerization for highly activated and stable anionic redox in sodium-based layered cathodes

Abstract

Manganese-based layered transition metal (TM) oxides with anionic redox reaction (ARR) activity hold great promise for low-cost and high-energy–density sodium-ion batteries cathodes. However, the unstable ARR charge compensation readily causes cycled capacity loss and voltage decay which severely restrict these materials’ commercial applications. Here, we show that a de-clustered distribution of nonbonding oxygen 2p state can enhance the stability of ARR and meanwhile increase its activity. The de-clustered nonbonding oxygen 2p state is achieved through regulating the ordered degree of cationic distributions that is superstructure in the TM layer. The designed cathode with relatively intact superstructure shows a record ARR activity and significantly suppressed voltage decay (0.52 mV per cycle). In-situ Raman indicates that the de-clustered nonbonding oxygen 2p state leads to an inhibited oxygen dimerization which is critical for stabilizing the ARR. Through employing in-situ X-ray diffraction, we reveal that the eliminated O–O dimers suppresses detrimental P2-P2′ phase transitions, leading to an ultralow volume change of 0.24% upon cycling. The robust Na-de/intercalation structure accompanying ARR process is further supported by theoretical calculations.