Transition　metal　selenides　are　considered　as　one　of　the　most　promising　anode　materials　for　sodium-ion　batteries　(SIBs)　on　account　of　their　high　theoretical　specific　capacity.　However,　the　poor　conductivity,　sluggish　kinetics　and　volume　expansion　during　the　(de)sodiation　process　hinder　its　application.　Herein,　a　novel　heterostructure　of　CoSe2/Sb2Se3　nanocrystals　embedded　into　nanocage-in-nanofiber　carbon　framework　is　designed　and　constructed　via　electrospinning,　carbonization,　ion　exchange　and　selenization　processes.　In　this　structure,　bimetallic　selenide　heterostructure　accelerates　electron/ion　transfer　kinetics　and　Na+　adsorption　capacity,　carbon　nanocages　structure　alleviates　the　volume　expansion　and　maintains　structural　integrity　during　the　(de)sodiation　process,　and　carbon　nanofibers　connect　the　nanocages　in　series　to　shorten　the　electron　transmission　path　and　enhance　electrical　conductivity.　As　a　self-supporting　anode　for　SIBs,　as-synthesized　CoSe2/Sb2Se3@C@CNF　shows　a　high　reversible　capacity　of　406　mAh　g-1　at　0.2　A　g-1　after　200　cycles　and　displays　excellent　rate　capability.　More　remarkably,　the　CoSe2/Sb2Se3@C@CNF　anode　manifests　an　outstanding　cycling　stability　for　over　2000　and　12,000　cycles　at　1　and　5　A　g-1,　with　the　capacity　retention　being　97　%　and　103　%　respectively.　Meanwhile,　the　excellent　sodium　storage　performance　is　revealed　by　kinetic　analysis,　energy　level　analysis　and　density　functional　theory　calculations.　©　2024　Elsevier　B.V.