The　conversion　of　Li2S4　to　Li2S　is　the　most　important　and　slowest　rate-limiting　step　in　the　complex　sulfur　reduction　reaction　(SRR)　for　Li-S　batteries,　the　adjustment　of　which　can　effectively　inhibit　the　notorious　＇shuttle　effect＇.　Herein,　a　CoSe2-FeSe2　heterostructure　embedded　in　3D　N-doped　nanocage　as　a　modified　layer　on　commercial　separator　is　designed　(CoSe2-FeSe2@NC//PP).　The　CoSe2-FeSe2　heterostructure　forms　a　built-in　electric　field　at　the　two-phase　interface,　which　leads　to　the　optimized　adsorption　force　on　polysulfides　and　the　accelerated　reaction　kinetics　for　Li2S4-Li2S　evolution.　Density　functional　theory　(DFT)　calculations　and　experimental　results　combine　to　show　that　the　liquid-solid　reaction　(Li2S4-Li2S2/Li2S)　is　significantly　enhanced　in　terms　of　thermodynamics　and　electrodynamics.　Consequently,　the　batteries　assembled　with　CoSe2-FeSe2@NC//PP　delivered　an　excellent　rate　capability　(606　mAh　g−1　under　8.0　C)　and　a　long　cycling　lifespan　(only　0.056%　at　1.0　C　after　1000　cycles).　In　addition,　the　cells　can　provide　high　initial　capacity　of　887　mAh　g−1　at　sulfur　loading　of　5.8 mg　cm−2　and　0.1　C.　This　work　would　provide　valuable　insights　into　binary　metal　selenide　heterostructures　for　liquid-solid　conversion　in　Li-S　batteries.　©　2024　Wiley-VCH　GmbH.