Self‐Assembled FeSe2 Microspheres with High‐Rate Capability and Long‐Term Stability as Anode Material for Sodium‐ and Potassium‐Ion Batteries.

Sodium‐ and potassium‐ion batteries have attracted intensive attention recently as low‐cost alternatives to lithium‐ion batteries with naturally abundant resources. However, the large ionic radii of Na+ and K+ render their slow mobility, leading to sluggish diffusion in host materials. Herein, hierarchical FeSe2 microspheres assembled by closely packed nano/microrods are rationally designed and synthesized through a facile solvothermal method. Without carbonaceous material incorporation, the electrode delivers a reversible Na+ storage capacity of 559 mA h g−1 at a current rate of 0.1 A g−1 and a remarkable rate performance with a capacity of 525 mA h g−1 at 20 A g−1. As for K+ storage, the FeSe2 anode delivers a high reversible capacity of 393 mA h g−1 at 0.4 A g−1. Even at a high current rate of 5 A g−1, a discharge capacity of 322 mA h g−1 can be achieved, which is among the best high‐rate anodes for K+ storage. The excellent electrochemical performance can be attributed to the favorable morphological structure and the use of an ether‐based electrolyte during cycling. Moreover, quantitative study suggests a strong pseudocapacitive contribution, which boosts fast kinetics and interfacial storage. [ABSTRACT FROM AUTHOR]