A　thin　free-standing　composite　solid　electrolyte　film　(CSE,　similar　to　15　mu　m)　is　prepared　by　a　tape　casting　and　solution　infusion　method,　which　owns　a　high　ionic　conductivity　(2.76　x　10(-4)　S　cm(-1)　at　25　degrees　C)　and　a　wide　electrochemical　stability　window　(4.8　V　vs.　Li+/Li).　The　CSE-based　solid-state　lithium　metal　batteries　with　the　LiCoO2　cathode　present　good　cycling　stability　and　capacity　retention　with　a　4.5　V　cut-off　voltage.