Realizing discrepant oxygen-redox chemistry in honeycomb superlattice cathode via manipulating oxygen-stacking sequences

Abstract

Anion redox chemistry in honeycomb-superlattice transition metal layer oxides plays a profound role on improving energy density in Na-defect P-type layer structure with pure cationic redox for sodium-ion batteries (SIBs). The correlation regarding variant oxygen-stacking sequences, discrepant oxygen-redox chemistry and electrochemical oxygen-layer sliding is vital, but is not established. Driving from controlling oxygen stacking sequences, the discrepant anionic redox chemistry is realized within Mg-Mn honeycomb-superlattice layer structure. Specifically, the P3-ABBCCA structure exhibits lower oxygen-redox trigger potential and higher oxygen-redox activity, resulting in a higher initial discharge capacity 202.0 mAh g−1 than 152.9 mAh g−1 of P2-ABBA structure. However, P3-ABBCCA stacking structure easily suffers grievous oxygen-sliding coupled with continuous oxygen activation at high cutting-off operation voltage 4.5 V, and finally transforms into O3-ABCABC structure. Compared with oxygen-stacking configuration of P2-ABBA structure, the oxygen-sliding of P3-ABBCCA structure is more irreversible, resulting in sluggish kinetics, rapid capacity degradation and discharge voltage fade during cycling. This study provides a new perspective and guidance on facilitating oxygen-redox chemistry reform in superlattice Na-defective layer cathode of SIBs.