Pyrrhotite Fe1-x S microcubes as a new anode material in potassium-ion batteries.

Potassium-ion batteries are an emerging energy storage technology that could be a promising alternative to lithium-ion batteries due to the abundance and low cost of potassium. Research on potassium-ion batteries has received considerable attention in recent years. With the progress that has been made, it is important yet challenging to discover electrode materials for potassium-ion batteries. Here, we report pyrrhotite Fe1-x S microcubes as a new anode material for this exciting energy storage technology. The anode delivers a reversible capacity of 418 mAh g-1 with an initial coulombic efficiency of ~70% at 50 mA g-1 and a great rate capability of 123 mAh g-1 at 6 A g-1 as well as good cyclability. Our analysis shows the structural stability of the anode after cycling and reveals surface-dominated K storage at high rates. These merits contribute to the obtained electrochemical performance. Our work may lead to a new class of anode materials based on sulfide chemistry for potassium storage and shed light on the development of new electrochemically active materials for ion storage in a wider range of energy applications.