Bismuth　telluride-based　thermoelectric　(TE)　devices　were　widely　used　in　waste　heat　recovery　due　to　their　high　thermoelectric　figure　of　merit　(ZT),　but　the　severe　diffusion　between　Sn-based　solder　and　TE　pillar　generated　porous　and　brittle　Sn-Te　intermetallic　compound　(IMC),　which　seriously　restricted　the　reliable　service　of　devices.　Ni-based　coating　was　used　but　the　thick　Ni-Te　IMC　also　impaired　the　properties　of　TE　pillars.　In　this　work,　the　crystalline　Co-P　coating　was　inserted　between　the　p-type　TE　material　Bi0.5Sb1.5Te3　and　the　solder　by　electrodeposition,　and　the　power　generation　sustainability　of　the　TE　pillar　were　significantly　improved,　and　the　mechanism　was　revealed.　The　microstructural　characterization　proved　that　the　Co-P　coating　could　effectively　resist　the　diffusion　of　active　Sn,　Bi,　Sb,　Cu　atoms.　Co-P　coating　would　provide　support　for　the　structural　integrity　and　performance　sustainability　of　TE　pillars.　It　was　worth　noting　that　an　ultrathin　CoTe2　IMC　layer　was　formed　between　the　Co-P　coating　and　the　Bi-Sb-Te　pillar,　which　was　much　thinner　than　the　Ni-Te　IMC　layer　reported　in　the　literature.　This　indicated　that　Co-P　only　consumed　little　thermoelectric　elements,　but　also　a　good　metallurgical　bond　was　formed　between　the　Co-P　and　the　Bi-Sb-Te.　After　aging　at　423　K　for　150　h,　the　maximum　output　power　and　average　Seebeck　coefficient　of　the　TE　pillar　without　coating　dropped　significantly　by　74%　and　34%,　respectively,　and　the　internal　resistance　rose　by　67%.　Remarkably,　the　maximum　output　power　and　average　Seebeck　coefficient　of　the　TE　pillar　protected　by　the　Co-P　coating　only　decreased　by　14%　and　5%,　respectively,　and　the　internal　resistance　only　increased　by　6%.