Na[Ni0.4Fe0.2Mn0.4−xTix]O2: a cathode of high capacity and superior cyclability for Na-ion batteries

New electrode materials of layered oxides, Na[Ni0.4Fe0.2Mn0.4−xTix]O2, have been synthesized as positive electrodes for sodium-ion batteries. The partial substitution of Mn with Ti increases the lattice spacing without changing the lattice structure. A Na//Na[Ni0.4Fe0.2Mn0.2Ti0.2]O2 cell delivers a reversible capacity of 145 mA h g−1 with excellent long cycling performance.