8-Hydroxyquinoline　(8-HDQN)　is　used　as　a　bifunctional　film-forming　additive　to　improve　the　capacity　retention　of　Li/LiNi0.5Mn1.5O4　(LNMO)　cell.　Electrochemical　analysis　and　ex-situ　analysis　prove　that　8-HDQN　can　preferentially　oxidize　on　the　surface　LNMO　cathode　to　modify　the　Cathode　Electrolyte　Interface　(CEI)　film.　The　modified　film　effectively　reduces　the　oxidation　reaction　of　the　electrolyte　and　the　increase　of　polarization　during　the　cycle.　The　CEI　film　derived　from　8-HDQN　also　inhibits　the　dissolution　of　transition　metals　ions　from　the　LNMO　electrode,　and　reduces　the　self-discharge　of　the　Li/　LNMO　cell.　Moreover,　8-HDQN　can　also　reduce　the　side　reaction　of　PF5　by　coordination　with　PF5　to　improve　the　thermal　stability　of　the　electrolyte.