Due　to　the　increasingly　urgent　safety　and　energy　density　concerns　of　lithium-ion　batteries,　more　and　more　attention　has　been　attracted　by　the　Li7La3Zr2O12　(LLZO)-based　solid　electrolytes　with　high　ion　conductivity　and　chemical　stability　against　Li-metal.　However,　to　prepare　the　high-quality　LLZO　ceramic　electrolyte　with　high-ion　conductivity　and　density,　there　is　still　a　big　challenge　of　the　serious　“Li-loss”　and　the　abnormal　grain　growth　during　the　long-time　high-temperature　sintering　process.　A　novel　covered　sintering　method　is　put　forward　to　prepare　the　high-quality　Mo-doped　LLZO　(LLZMO)　ceramic　electrolyte.　The　sintering　strategy　effectively　suppresses　the　Li-loss　to　obtain　the　LLZMO　dense　ceramics　with　cubic　garnet　phase　and　tight　grain　boundaries.　The　LLZMO　ceramics　sintered　at　lower　temperature　of　1050 °C　for　2 h　via　the　novel　covered　sintering　exhibit　high　density　(ρr　=　92.3%)　and　high-ionic　conductivity　of　6.08　×　10–4 S cm−1　at　25 °C,　which　are　close　to　those　of　LLZO-based　ceramics　prepared　by　hot　pressing　sintering,　ultrafast　high-temperature　sintering　(UHS).　The　novel　covered　sintering　provides　an　energy-saving,　low-cost　and　high-efficient　strategy　to　prepare　the　high-quality　LLZO-based　ceramics　electrolyte.　©　The　Author(s),　under　exclusive　licence　to　Springer　Science+Business　Media,　LLC,　part　of　Springer　Nature　2024.