CoSe2-decorated carbon nanofibers: A catalytic electrode for uniform Li2Se nucleation in lithium-selenium batteries

Selenium cathodes have attracted widespread attention due to their high electronic conductivity and considerable volume capacity. However, the harmful shuttle of lithium polyselenides and irregular deposition of lithium selenide (Li2Se) severely degrade the redox rate of active selenium, causing poor cycling stability. Toward overcoming these limitations, herein, a catalytic electrode based on carbon nanofibers loaded with CoSe2 nanoparticles (CoSe2@CNF) is designed and engineered to trap polyselenides and activate their conversion. Density functional theory (DFT) calculations show that the introduction of CoSe2 nanoparticles lowers the redox barrier for Li2Se growth. Even more important, the presence of a homogeneous distribution of CoSe2 provides abundant nucleation sites for uniform Li2Se deposition. As a result, Li-Se batteries based on Se/CoSe2@CNF free-standing electrodes exhibit outstanding cycle stability. After 800 cycles, Se/CoSe2@CNF electrodes display a high capacity of 435.1 mAh g−1 with a 0.032% capacity decay per cycle at 0.5C. Even at a selenium loading of 4.1 mg cm−2, a high capacity retention rate of 72.8% is measured. Overall, this work provides a new strategy for achieving high-performance Li-Se batteries by introducing efficient polyselenide electrocatalysts as selenium hosts to facilitate the conversion of polyselenides and regulate the homogenous growth of Li2Se.