Micropore engineering on hollow nanospheres for ultra-stable sodium-selenium batteries

Abstract

Attracted by high energy density and considerable conductivity of selenium (Se), Na-Se batteries have been deemed promising energy-storage systems. But, it still suffers from sluggish kinetic behaviors and similar “shuttling effect” to S-electrodes. Herein, utilizing uniform hollow carbon spheres as precursors, Se-material is effectively loaded through vapor-infiltration method. Owing to the distribution of optimized pores, the content of microspores could be up to ∼60% (<2 nm), serving important roles for the physical confinement effect. Meanwhile, the rich oxygen-containing groups and N-elements could be noted, inducing the evolution of electron-moving behaviors. More significantly, assisted by the interfacial C–Se bonds and tiny Se distributions, Se electrodes are activated during cycling. Used as cathodes for Na-Se systems, the as-resulted samples display a capacity of 593.9 mA h g−1 after 100 cycles at the current density of 0.1 C. Even after 6000 cycles, the capacity could be still kept at about 225 mA h g−1 at 5.0 C. Supported by the detailed kinetic analysis, the designed microspores size induces the increasing redox reaction of nano Se, whilst the surface traits further render the enhancement of pseudo-capacitive contributions. Moreover, after cycling, the product Sex (x < 4) in pores serves as the primary active material. Given this, the work is anticipated to provide an effective strategy for advanced electrodes for Na-Se systems.