A novel air‐stable O3‐type layered oxide cathode material with low Ni content for sodium‐ion batteries

A novel O3‐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 Ni2+, Cu2+ and Ca2+ substitution for Mn4+ and Fe3+ 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 Ni2+, Cu2+ and Ca2+ for Fe3+ and Mn4+ can inhibit the reaction of Na+ ions in the structure of O3‐NaMn0.33Fe0.33Ni0.21Cu0.08Ca0.04O2 with air. The Ni2+, Cu2+ and Ca2+‐substituted O3‐NaMn0.33Fe0.33Ni0.21Cu0.08Ca0.04O2 cathode material show a higher capacity and better cycling stability than that of O3‐NaMn0.42Fe0.42Ni0.17O2, indicating that a small amount of Ni2+, Cu2+ and Ca2+ substitution can improve the structure/air stability and the electrochemical performance. When O3‐NaMn0.33Fe0.33Ni0.21Cu0.08Ca0.04O2 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 O3‐NaMn0.33Fe0.33Ni0.21Cu0.08Ca0.04O2 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.