Electrochemical Potassiation/Depotassiation Properties of Rare-Earth Antimonide/Antimony Composite Electrodes

Potassium-ion batteries have emerged as promising next-generation energy storage systems because of the abundance and low cost of potassium. However, achieving high capacity and long-term cycling stability remains challenging, especially for metal/alloy anodes such as antimony (Sb), which suffers from considerable volume changes during charge–discharge cycling. To address this challenge, herein, composite anodes were prepared by combining Sb with rare earth antimonides (RESbx, RE = Y, La, Ce, Sm, or Gd), which are known for their charge–discharge cycling stability. The electrochemical performances of RESbx/Sb composite electrodes were systematically evaluated in an ionic liquid electrolyte. Charge–discharge testing revealed that RESbx addition, even at 10 wt %, considerably suppressed the rapid capacity fading observed in pure Sb electrodes, leading to excellent cycling stability. Additionally, pure Sb made the highest contribution to the capacity of the composite electrodes, and RESbx effectively suppressed electrode degradation. Specifically, the cycle life of the CeSb/Sb electrode was over three times longer than that of the pure Sb electrode. Cross-sectional scanning electron microscopy demonstrated that the RESbx phase mitigated electrode expansion and cracking. Further investigation showed that the high K+ diffusion coefficient of CeSb, larger lattice parameters of CeSb, and mechanical softness (lower breaking strength) of CeSb played key roles in increasing the cycle life of the CeSb/Sb electrode. These properties facilitated uniform K+ distribution and reduced mechanical stress in the CeSb/Sb electrode. Our findings help advance high-performance, resource-efficient energy storage technologies.