Novel K+-doped Na0.6Mn0.35Fe0.35Co0.3O2 cathode materials for sodium-ion batteries: synthesis, structures, and electrochemical properties

A series of novel KxNa0.6-xMn0.35Fe0.35Co0.3O2 (x = 0, 0.005, 0.01, 0.05, 0.1) materials were successfully synthesized by the solid-state reaction method. The newly prepared cathode materials were examined by means of X-ray diffraction. They were characterized by scanning electron microscopy (SEM-EDS) and inductively coupled plasma mass spectrometry (ICP-OES). Their electrochemical performances for sodium-ion batteries were tested. The effects of varying K+ doping content on the electrochemical battery performance on the prepared cathode materials were investigated. It was found that the potassium-doped K0.01Na0.59Mn0.35Fe0.35Co0.3O2 showed the best electrochemical performance with an initial discharge capacity of 138.0 mAh g(-1) among them. The capacity retention after 20 cycles for Na0.6Mn0.35Fe0.35Co0.3O2 (without K+ doping) was 87.6%. After the potassium doped, the capacity retentions for K0.01Na0.59Mn0.35Fe0.35Co0.3O2 and K0.005Na0.595Mn0.35Fe0.35Co0.3O2 compounds were 90.8% and 90.6% respectively. These results proved that the appropriate amount of K+ doping could be a feasible strategy to increase the cycling stability performance of layered cathode for sodium-ion battery.