A　novel　additive,　7-hydroxycoumarin　(7-HC),　is　employed　to　construct　a　stable　interface　film　on　the　LiNi0.5Mn1.5O4　cathode　to　improve　the　cyclic　stability　of　Li/LiNi0.5Mn1.5O4　cells　at　elevated　temperature　(ca.　55　degrees　C).　In　the　0.01　wt%　7-hydroxycoumarin-containing　electrolyte,　the　capacity　retention　of　Li/LiNi0.5Mn1.5O4　cell　increases　from　78.15　%　to　95.64　%　at　elevated　temperature　after　100　cycles　at　1　C　rate.　Through　theoretical　calculations　and　ex-situ　analysis,　it　suggests　that　7-HC　is　susceptible　to　oxidation　than　other　components　of　the　electrolyte　to　form　a　thin　and　stable　film　on　the　surface　of　LiNi0.5Mn1.5O4　cathode.　The　thin　and　stable　film　can　effectively　reduce　the　interface　oxidation　reaction　and　the　＂cross-talk＂　between　the　positive　electrode　and　negative　electrode　and　effectively　inhibit　the　structural　changes　of　LiNi0.5Mn1.5O4　caused　by　dissolved　transition　metals　in　subsequent　cycles,　thereby　improving　the　cyclic　stability　of　the　cell　at　elevated　temperature.