Ceiling　jet　fire　is　a　common　phenomena　in　thermal　runaway　(TR)　accidents　of　electric　vehicle　and　energy　storage　power　station　scenarios　based　on　lithium-ion　battery,　which　is　a　potential　risk　of　inducing　large-scale　fire　spread　in　battery　modules,　but　it　is　not　been　known　clearly.　This　work　investigates　the　influence　of　ceiling　jet　fire　on　TR　propagation　of　lithium　nickel　cobalt　manganese　oxide　(NCM)　battery　module　by　arranging　a　ceiling-like　obstacle　directly　above　the　tested　module.　A　series　of　overheat-induced　TR　propagation　tests　under　different　height　(H)　of　ceiling-like　obstacle　are　conducted　to　gain　better　understanding　of　the　heat　transfer　mechanism.　The　heat　transfer　and　average　heating　power　of　ceiling　jet　fire　to　adjacent　cells　are　determined　for　the　first　time.　Results　indicate　the　TR　propagation　speed　of　the　module　accelerates　with　the　decrease　of　H,　and　the　TR　propagation　speed　inside　the　cell　is　not　affected　by　ceiling　jet　fire.　More　importantly,　the　heat　transferred　from　cell　experiencing　TR　to　adjacent　cells　through　ceiling　jet　fire　(Qfl)　decreases　from　11087.33　J　to　7872.02　J,　and　the　ratio　of　Qfl　to　the　total　heat　released　in　TR　(ΔEtot)　declines　from　4.02　%　to　2.85　%　as　H　increases　from　5　to　15　cm.　Finally,　the　change　process　of　contact　thermal　resistance　between　adjacent　cells　and　its　relationship　with　heating　power　are　revealed　during　TR　propagation.　This　work　provides　a　basic　understanding　of　the　influence　mechanism　of　ceiling　jet　fire　on　TR　propagation,　which　possess　important　guidance　for　the　safety　protection　of　lithium-ion　battery　system.　©　2024