Controllable dual-substitution engineering enable high stability P2-type Mn-rich cathodes under high voltage

P2-type Na_0.67MnO₂ (NM) cathodes represent a cost-effective and promising material for sodium-ion batteries (SIBs). Suppressing undesirable phase transformations and Jahn-Teller is quite a challenge for the design of high stability Mn-rich cathodes. Herein, we design and optimize the preparation of Ni and Ti dual-substituted P2-type Mn-rich Na_0.67Ni_xMn_0.8Ti_0.2-xO₂ (0 ≤x ≤ 0.2), with the goal to enhancing structural stability and facilitating fast Na⁺ diffusion under high voltage. The Na_0.67Ni_0.15Mn_0.8Ti_0.05O₂ (NN_0.15M_0.8T_0.05) exhibits a narrower bandgap, stronger transition metal (TM)-O bonds, and lower Na⁺ migration energy barriers compared to P2-Na_0.67MnO₂ (NM) as demonstrated by DFT results. X-ray absorption spectroscopy (XAS) reveals the charge compensation mechanism of Ni, indicating that the average working voltage is enhanced by Ni. In-situ X-ray diffraction (XRD) show NN_0.15M_0.8T_0.05 efficiently suppressing the O-P stacking fault defect transitions observed in the Ni single composition by stabilizing the reversible P2/OP4 structure at high voltage. As a result, NN_0.15M_0.8T_0.05 achieves a high energy density of over 460 Wh/kg within the voltage range of 2–4.3 V, along with significantly improved capacity retention and rate capability. Altogether, the findings reveal that the controllable dual-substitution engineering strategy offers a promising and feasible approach for designing cathode materials in sodium-ion batteries (SIBs).