Selenium　(Se),　a　congener　of　Sulphur　(S),　is　widely　used　as　a　cathode　material　for　high　energy-density　lithiumion　batteries,　named　Li-Se　batteries.　It　has　been　found　that　nanostructured　Se　confined　in　carbonaceous　can　lead　to　significantly　improved　rate　capability　and　cyclic　performance.　However,　the　underlying　mechanism　of　carbon　coatings　in　view　of　surface/interface　electro-chemo-mechanical　effect　at　nanoscale　remains　poorly　unexploited.　Herein,　equipped　with　in-situ　transmission　electron　microscopy　(TEM),　we　have　investigated　the　type　of　lithium　ions　transportation,　phase　transformation,　and　coupling　mechanical　behavior　of　carbon　conformably　coated　Se　nanowire　(NW)　cathode　reacted　with　Li.　Intriguingly,　We　find　a　unique　lithiation　mechanism　that　the　＂leapfrog　phase　transformation＂　occurs　at　interface　between　carbon　coating　and　Se　NW　cathode.　The　increasingly　accumulated　Li　ions　in　leapfrog　buckled　region　as　a　new　platform　would　react　with　Se　to　form　crystalline　Li2Se　from　surface　to　interior.　More　importantly,　this　interfacial　diffusion　pathway　of　Li　ions　uniquely　differs　from　the　surface-coating　directed　Li　transportation　engineered　where　in　Li　ions　initially　diffuse　into　coatings　and　then　react　with　core　materials　of　electrodes.　Furthermore,　we　note　a　threshold　diameter　region　of　Se　NWs　with　similar　to　115-120　nm,　above　which　the　uniform　carbon　coating　(similar　to　8.5　nm)　shows　remarkable　crack　and　even　delimitation　after　fully　lithiation　form.　These　observations　provide　reliable　guidelines　for　the　design　of　high-performance　lithium-ion　batteries　by　interface　and　surface　engineering.