Preparation and Property Optimization of High Capacity O3-type NaNi_0.4Fe_0.2Mn_0.4O₂

O3-type NaNi 0.4 Fe 0.2 Mn 0.4 O 2 cathode materials are structurally stable and have a high nickel content, allowing for stable high-capacity output. However, their performance needs further improvement. First, we investigated the effects of different sodium contents on the structure, morphology, and electrochemical performance of Na x Ni 0.4 Fe 0.2 Mn 0.4 O 2 (x = 0.85, 0.9, 0.95, 1, 1.05) materials. The Na 0.9 Ni 0.4 Fe 0.2 Mn 0.4 O 2 material exhibited initial discharge specific capacities of 148.11 and 181.80 mAh·g −1 at voltage ranges of 2–4.1 V and 2–4.2 V, respectively. To further optimize the cycling performance of the material, we doped NaNi 0.4 Fe 0.2 Mn 0.4 O 2 with different calcium contents. Ca 2+ doping significantly enhanced the electrochemical performance of the material. Subsequently, we synthesized Na 0.96 Ca 0.02 (NMF) 0.95 Zn 0.05 O 2 , and the dual-doped NMF-Ca 0.02 Zn 0.05 maintains approximately 80% capacity retention at 1–4.05 V, and around 70% as the cut-off voltage increases to 4.15 V in full cells.