Layered Co/Ni-free Mn-rich oxide P2-Na2/3Mn0.8Fe0.1Mg0.1O2 as high-performance cathode material for sodium-ion batteries

In this work, the Co/Ni-free Na2/3Mn0.8Fe0.1Mg0.1O2 has been synthesized and investigated as low-cost and high-Mn content layered oxide cathode material for sodium-ion batteries by x-ray diffraction and electrochemical techniques. Due to a larger ionic size of Mg2+ than of Fe3+, the lattice parameters a and c both increase and the Mg2+ doping results in an expanded space for sodium-ion diffusion with the improved diffusion coefficient of sodium ion compared with Na2/3Mn0.8Fe0.2O2. Na2/3Mn0.8Fe0.1Mg0.1O2 delivers a high initial discharge capacity of 168 mAh g(-1), and great rate capabilities of 102, 80, and 55 mAh g(-1) at high rates of 2 C, 5 C, and 10 C. Mg2+ doping also can alleviate the Jahn-Teller effect by Mn3+ and stabilize the crystal structure, thus enhancing the cyclic stability of Na2/3Mn0.8Fe0.1Ti0.1O2 with about 90% capacity retention at 0.1 C. Electrochemical inactive and low-cost Mg-ion doping is an effective approach to improve the layered oxide cathode materials for sodium-ion batteries.