Surface iodine modification inducing robust CEI enables ultra-stable Li-Se batteries

Lithium-selenium batteries (LSeBs) have attracted increasing attention due to their excellent electronic conductivity and high theoretical specific capacity. However, there are still difficult problems such as low utilization rate and fast capacity decay in the actual application process. Herein, a surface iodine modified three-dimensional (3D) nano hollow carbon fiber (I-NHCF) network is designed and synthesized as Se host (Se@I-NHCF) for highly stable LSeBs. The surface iodine species induce the formation of robust cathode electrolyte interface (CEI), thus preventing the transformation of amorphous selenium to low-activity crystalline selenium and enabling stable electrochemical performance. Moreover, the surface iodine species promote rapid charge transfer, enhancing the chemical reaction kinetics and improving the utilization of the active Se species. As a result, the Se@I-NHCF cathode exhibits superior specific capacity of 581.8 mAh g⁻¹ with a high stability (0.0054% capacity decay per cycle) after 500 cycles at 1C, and an excellent rate performance of 567.6 mAh g⁻¹ at 2C. This work addresses the problem of rapid capacity decay by the formation of uniform and robust CEI to conserve highly reactive amorphous Se species, improve Se utilization, and achieve ultra-stable Li-Se batteries with high energy and long cycle life.