Local Structure Regulation for Oxygen Redox and Structure Stability of P2-Type Cathodes

The local structure plays a crucial role in oxygen redox reactions, which boosts the capacity of layered oxide cathodes for sodium-ion batteries. While studies on local structural ordering have primarily focused on the intra-layer ordering, there has been limited research on the inter-layer stacking for the layered cathode materials for sodium-ion batteries. In this work, the impact of the intra-layer and inter-layer local structural regulation on anionic kinetics and the structure stability are explored through experimental analysis and theoretical calculations. Cu²⁺ substitution is introduced to adjust the transition metal inter-layer structure of P2-Na_0.67Mg_0.28Mn_0.72O₂, obtaining a zig-zag stacked honeycomb superlattice structure in P2- Na_0.67Cu_0.14Mg_0.14Mn_0.72O₂. The local structure regulation mitigates the cation migration, improves the structure reversibility even at a deeply desodiation state of Na_0.05, and the reductive coupling between cationic and anionic redox processes facilitates electron transfer from oxygen to copper ions and governs the properties of electrochemical kinetics and hysteresis. A full cell with hard carbon anode shows commendable energy density at high power density. This study paves an optional path for enhancing the structure stability and dynamics of oxygen redox chemistry in P2-type cathode materials for sodium-ion battery systems.