The　practical　applications　of　solid-state　electrolytes　in　lithium-ion　batteries　(LIBs)　are　hindered　by　their　low　ionic　conductivity　and　high　interfacial　resistance.　Herein,　an　ethoxylated　trimethylolpropane　triacrylate　based　quasi-solid-state　electrolyte　(ETPTA-QSSE)　with　a　three-dimensional　(3D)　network　is　prepared　by　a　one-step　in-situ　photopolymerization　method.　The　3D　network　is　designed　to　overcome　the　contradiction　between　the　plasticizer-related　ionic　conductivity　and　the　thickness-dependent　mechanical　property　of　quasi-solid-state　electrolytes.　The　ETPTA-QSSE　achieves　superb　room-temperature　ionic　conductivity　up　to　4.55×10−3　S　cm−1,　a　high　lithium　ion　transference　number　of　0.57,　along　with　a　wide　electrochemical　window　of　5.3　V　(vs.　Li+/Li),　which　outperforms　most　ever　of　the　reported　solid-state　electrolytes.　Owing　to　the　robust　network　structure　and　the　cathode-electrolyte　integrated　electrode　design,　Li　metal　symmetrical　cells　show　reduced　interface　resistance　and　reinforced　electrode/　electrolyte　interface　stability.　When　applying　the　ETPTA-QSSE　in　LiFePO4Li　cells,　the　quasi-solid-state　cell　demonstrates　an　enhanced　initial　discharge　capacity　(155.5　mAh　g−1　at　0.2　C)　accompanied　by　a　high　average　Coulombic　efficiency　of　greater　than　99.3%,　offering　capacity　retention　of　92%　after　200　cycles.　Accordingly,　this　work　sheds　light　on　the　strategy　of　enhancing　ionic　conductivity　and　reducing　interfacial　resistance　of　quasi-solid-state　electrolytes,　which　is　promising　for　high-voltage　LIBs.　©　2022,　Science　China　Press　and　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.