Structural effects of the iron/manganese ratio in Li-doped layered oxide cathodes for sodium-ion batteries

Li-doped layered oxides with different Fe/Mn ratios corresponding to the Na0.67[Li0.07Fe0.3+xMn0.63-x]O2 (x = 0, 0.15, 0.25) series, prepared between 800 and 1000 °C, are evaluated as cathode for sodium-ion batteries. On increasing the iron content and temperature of synthesis, new P3 and O3 phases appear along with the pre-existing P2 phase. Unfortunately, these multiphase systems are detrimental to the kinetic response and eventually electrochemical performance of these cathode materials, also revealing structural degradation on cycling. Only samples with the highest contribution of P2 phase can perform high capacities which can be retained for a long cycling.