From Atom to Device: An Integrated Se Cathode with Atomic Co Sites and Dual Carbon Confinement for Ultrafast Li-Se Batteries

Abstract

Lithium-selenium (Li-Se) batteries are attractive for high-energy-density storage owing to the high volumetric capacity and conductivity of Se. However, their practical implementation is still hindered by severe volume expansion, low active material utilization, and sluggish redox kinetics. Herein, we designed a freestanding and integrated Se-based electrode (Se/Co-NC@CNFs) via a dual-carbon confinement strategy. This architecture is constructed by anchoring atomically dispersed cobalt sites onto porous nitrogen-doped carbon cages (Co-NC), which are further embedded within conductive carbon nanofibers (CNFs). This unique configuration enables high Se loading while providing a multi-functional framework, where the atomic Co-N4 moieties serve as highly active electrocatalytic centers that significantly accelerate the conversion kinetics between Se and Li2Se. Simultaneously, the dual-carbon confinement, provided by the Co-NC cages and the CNFs networks, effectively mitigates volume variation and suppresses polyselenide dissolution of Se. Furthermore, the binder-free and currentcollector-free electrode architecture remarkably increases the proportion of active material, leading to a substantial improvement in overall energy density (347 mAh g -1 compared to Se/NC cathode's 22 mAh g -1 ). As a result, the Se/Co-NC@CNFs cathode delivers a high reversible capacity of 520 mAh g -1 at an ultrahigh current density of 50 A g -1 (≈74 C), outstanding cycling stability with 514 mAh g -1 retained after 3500 cycles at 15 A g -1 , and excellent mechanical flexibility in soft-packaged batteries. This work provides a rational design strategy for high-performance, Li-Se batteries through atomicscale catalysis and integrated electrode engineering.