Achieving Stable Cycling Performance in a P2-Type Layered Oxide Cathode through a Synergic Li/Zn Doping for Sodium–Ion Batteries

It has been suggested that sodium layered transition metal oxides could potentially serve as excellent cathodes for sodium-ion batteries (SIBs) because of their appropriate operating potentials and high capacities. However, the growing reliance on energy requirements has necessitated a higher energy density of SIBs. It has been demonstrated that activating oxygen-related activities for SIBs is a viable method to improve energy density. Herein, we suggest applying the synergy of Li and Zn codoping to activate the anionic redox reactions (ARRs) and improve their reversibility in Na_0.75Ni_0.3Mn_0.7O₂. The dual ion doping alleviates the phase transition and inhibits the Na⁺/vacancy arrangements, consequently improving the rate capacity and cyclic stability. The Na_0.75Li_0.15Ni_0.1Zn_0.05Mn_0.7O₂ delivers a discharge capacity of 134 mA h g^-1 and no significant capacity loss at 100 mA g^-1 between 2 and 4.5 V after 200 cycles. More importantly, the density functional theory (DFT) calculation proves that the codoping strategy triggers more ARRs compared to single-element doping, thereby providing enhanced capacity. The codoping induced oxygen redox strategies will create a new path for rational design of cathodes to enhance the energy density for SIBs.