Li-CO2　batteries　that　integrate　energy　storage　with　greenhouse　gas　fixation　have　received　a　great　deal　of　attention　in　the　pursuit　of　carbon　neutrality.　However,　cyclic　accumulation　of　the　insulative　and　insoluble　Li2CO3　on　the　cathode　surface　severely　restrains　the　battery　cyclability,　especially　under　a　high　depth　of　discharge/charge.　Herein,　we　design　and　fabricate　a　microreactor-type　catalyst　by　embedding　Ru　nanoparticles　into　the　shells　of　mesoporous　hollow　carbon　spheres.　We　show　that　both　the　hollow　cavity　and　mesoporous　shell　are　indispensable　for　concertedly　furnishing　a　high　activity　to　catalyze　reversible　Li2CO3　formation/decomposition.　This　unique　structure　ensures　that　the　Ru　sites　masked　by　exterior　Li2CO3　deposits　during　charging　can　resume　the　redox　process　of　discharge　by　working　with　the　prestored　electrolyte　to　establish　an　inner　reaction　path.　The　thus　fabricated　Li-CO2　batteries　demonstrate　remarkable　cyclability　of　1085　cycles　under　0.5　Ah　g-1　and　326　cycles　under　2　Ah　g-1　at　1　A　g-1,　outshining　most　of　the　literature　reports.　This　study　highlights　a　smart　catalyst　design　to　boost　the　reversibility　and　cyclability　of　Li-CO2　batteries　through　an　“in　&　out”　strategy.　©　2023　American　Chemical　Society.