From atom to device: an integrated Se cathode with atomic Co sites and dual-carbon confinement for ultrafast Li-Se batteries.

Lithium-selenium (Li-Se) batteries are attractive for high-energy-density storage because of the high volumetric capacity and relatively high electrical conductivity of selenium. However, their practical application is still hindered by severe volume expansion, limited active-material utilization, and sluggish redox kinetics. Herein, we report an integrated Se cathode (Se/Co-NC@CNFs) based on a dual-carbon confinement strategy. In this architecture, atomically dispersed Co sites are anchored on porous N-doped carbon cages (Co-NC), which are further embedded in conductive carbon nanofibers (CNFs). This configuration enables high selenium loading while providing a multifunctional framework in which the Co-N4 sites act as electrocatalytically active centers to accelerate the conversion between Se and Li2Se. Meanwhile, the dual-carbon confinement from the Co-NC cages and the CNFs network effectively alleviates volume changes and improves selenium retention during cycling. More importantly, the binder-free and current-collector-free electrode design greatly increases the active-material fraction, resulting in a markedly improved capacity based on the total cathode mass (347 mAh g-1versus 22 mAh g-1 for the conventional Se/NC cathode). Consequently, the Se/Co-NC@CNFs cathode delivers a high reversible capacity of 520 mAh g-1 at 50 A g-1 (≈74C) and retains 514 mAh g-1 after 3500 cycles at 15 A g-1. This work provides a rational design strategy for high-performance, Li-Se batteries through atomic-scale catalysis and integrated electrode engineering.