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

Abstract

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.

Revealing the Reaction and Fading Mechanism of FeSe2 Cathodes for Rechargeable Magnesium Batteries

“…Satellite peaks are also observed at 711.6 and 724.5 eV. In the Se 3d spectrum (Figure 1c), the peaks at 54.5 and 55.4 eV are respectively ascribed to Se 3d 5/2 and Se 3d 3/2 , signifying the Fe−Se and Se−Se bonds [28–29] . Besides, the peak at 58.9 eV is from the surface oxidation, which is a common phenomenon for synthesized selenides.…”

“…In the Se 3d spectrum (Figure 1c), the peaks at 54.5 and 55.4 eV are respectively ascribed to Se 3d 5/2 and Se 3d 3/2 , signifying the FeÀ Se and SeÀ Se bonds. [28][29] Besides, the peak at 58.9 eV is from the surface oxidation, which is a common phenomenon for synthesized selenides. The crystal structure of FeSe 2 could be described by Figure 1d, in which Fe atoms are bonded with six Se atoms in an octahedral arrangement.…”

Nanostructured metal selenides as anodes for potassium-ion batteries

“…8l). 68 As presented in Fig. 8m, the stable hierarchical structure effectively prevented the FeSe 2 microspheres from agglomeration and collapse.…”

“…For example, Xin et al prepared FeSe 2 microspheres by using ethanolamine as a reaction medium. 68 As shown in Fig. 2a and b, FeSe 2 nanospheres were assembled by tightly packed nanorods with diameters of 1–2 μm.…”

“…In addition, the hydro(solvo)thermal method can control the morphology and size of MSs by changing the property of solutions (polarity, viscosity, and softness), reaction temperatures, and reaction times. 49,68,76,85,86…”