Sodium-selenium　(Na-Se)　battery　has　been　emerging　as　one　of　the　most　prospective　energy　storage　systems　owing　to　their　high　volumetric　energy　density　and　cost　effectiveness.　Nevertheless,　the　shuttle　effect　of　sodium　polyselenide　(NaPSe)　and　sluggish　electrochemical　reaction　kinetics　present　the　main　bottlenecks　for　its　practical　implementation.　Herein,　a　new　Se　host　of　3D　nitrogen-doped　hierarchical　multicavity　carbon　nanospheres　(3D　NHMCs)　is　designed　and　synthesized　via　a　facile　self-sacrifice　templating　strategy.　The　3D　NHMCs　are　verified　to　hold　a　favorable　structure　of　a　hollow　macropore　core　and　numerous　micro/mesopores　hollow　shell　for　hosting　Se,　which　can　not　only　maximize　Se　utilization　and　alleviate　the　volumetric　expansion　but　also　promote　the　electrical/ionic　conductivity　and　electrolyte　infiltration.　Moreover,　the　abundant　self-functionalized　surfaces　as　an　efficient　NaPSe　scavenger　via　robust　physical-chemical　dual　blocking　effects　demonstrate　high-efficiency　in　situ　anchoring-diffusion-conversion　of　NaPSe,　rendering　rapid　reaction　kinetics　and　remarkable　suppressive　shuttle　effect,　as　evidenced　by　systematic　experimental　analysis　and　density　functional　theory　calculations.　As　a　result,　the　high-Se-loading　3D　NHMCs/Se　cathode　exhibits　an　ultrahigh　volumetric　capacity　(863　mAh　cm(-3))　and　rate　capability　(377　mAh　g(-1)　at　20　C)　and　unexceptionable　stability　over　2000　cycles　at　2　C.