A novel potassium-containing layered oxide for the cathode of sodium-ion batteries

Layered oxides are successful cathode materials for sodium-ion batteries. Many of these oxides show interesting kinetic behavior but have poor structural stability. To overcome this limitation, an alternative material containing potassium in the interlayer space in trigonal prismatic coordination is studied here. The transition-metal layers are formed by sustainable transition elements such as iron and manganese. The solid was prepared using a sol–gel procedure that led to a product with relatively high purity, with a Pʹ3-type structure indexable in the C2/m space group of the monoclinic system. Its electrochemical behavior was studied in sodium metal half-cells. When the cell is charged up to 4.3 V, it is observed that the potassium extraction is not complete. The subsequent discharge of the cell is associated with the intercalation of sodium from the electrolyte. Thus, it is possible to incorporate a greater number of alkaline ions than those extracted in the previous charge. The residual potassium in the structure was found to be favorable to maintaining the structural integrity of the compound upon cycling. This can be explained by the beneficial effect of potassium, which would act as a structural “pillar” in the interlayer, which would reduce structural degradation during cycling.