Ion-Exchange Route Induced Heterostructured CoS2/FeS Nanoparticles Confined in Hollow N-Doped Carbon Frameworks for Enhanced Sodium Storage Performance

As a result of the high theoretical capacities, transitionmetalsulfides have attracted increasing attention as potential anodes forsodium-ion batteries (SIBs), but severely suffer from large volumetricvariations, sluggish kinetics, and polysulfide shuttling. Herein,utilizing metal-organic frameworks (MOFs) as functional templates,heterostructured CoS2/FeS nanoparticles confined in a hollowN-doped carbon framework are successfully fabricated via a controlled ion-exchange reaction combined with subsequent carbonizationand sulfurization processes. The construction of CoS2/FeSheterointerfaces promotes electron transfer and provides more activesites, while the derived N-doped carbon framework with a unique hollowinterior effectively improves the electrical conductivity, alleviatesthe volumetric variations, and facilitates the sodium storage processwith shortened Na+ diffusion paths. As anodes for SIBs,the optimal CoS2/FeS hybrid composite exhibits a high initialCoulombic efficiency (ICE) of 89.3%, a prolonged cycle life with acapacity of 494 mAh g(-1) over 500 cycles under acurrent density of 1.0 A g(-1), and an excellent ratecapability of 428 mAh g(-1) at 5.0 A g(-1), showing the great promise for SIBs. This research offers an efficientand feasible approach for exploring and fabricating bimetallic sulfideheterostructures with a unique hollow structure for high-performancemetal-ion batteries.