A novel O_3-NaMn0.42Fe0.42Ni0.17O2 cathode material for sodium-ion batteries is synthesized, for the first time, by a co-precipitation method followed by solid-state reaction. The effect of Ni~(2+), Cu~(2+) and Ca~(2+) substitution for Mn4+ and Fe~(3+) on the structural stability, rate capability and cycling performance of the cathode material are examined. Chemical titration results and powder X-ray diffraction patterns indicate that the substitution of Ni~(2+), Cu~(2+) and Ca~(2+) for Fe~(3+) and Mn4+ can inhibit the reaction of Na+ ions in the structure of O_3-NaMn_(0.33)Fe_(0.33)Ni_(0.21)Cu_(0.08)Ca_(0.04)O_2 with air. The Ni~(2+), Cu~(2+) and Ca~(2+)-substituted O_3-NaMn_(0.33)Fe_(0.33)Ni_(0.21)Cu_(0.08)Ca_(0.04)O_2 cathode material show a higher capacity and better cycling stability than that of O_3-NaMn0.42 Fe0.42Ni0.17O2, indicating that a small amount of Ni~(2+), Cu~(2+) and Ca~(2+) substitution can improve the structure/air stability and the electrochemical performance. When O_3-NaMn_(0.33)Fe_(0.33)Ni_(0.21)Cu_(0.08)Ca_(0.04)O_2 cathode material is combined with the hard carbon anode, a full cell gives 220 Wh kg~(-1) energy density and 100% capacity retention after 56 charge/discharge cycles at 0.5C. The O_3-NaMn_(0.33)Fe_(0.33)Ni_(0.21)Cu_(0.08)Ca_(0.04)O_2 can be thought of as a potential cathode active material to encourage progress toward sodium-ion battery commercialization due to the high industrial applicability of the synthesis process and good electrochemical performance. Prime Novelty Statement A novel O_3-NaMn0.42Fe0.42Ni0.17O2 cathode material for sod um on batter es is synthesized for the first time by a co-precipitation method with subsequent solid-state reaction. The substitution of Ni~(2+), Cu~(2+) and Ca~(2+) for Fe~(3+) and Mn4+ improves the air stability and electrochemical performance of O_3-NaMn_(0.33)Fe_(0.33)Ni_(0.21)Cu_(0.08)Ca_(0.04)O_2 cathode material. When O_3-NaMn0.33 Fe0.33Ni_(0.21)Cu_(0.08)Ca_(0.04)O_2 cathode material couples with the hard carbon anode, a full cell gives an energy density of 220 Wh kg~(-1) and the capacity retention of 100% after 56 charge/discharge cycles.
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