The effects of 1vol% and 2vol% Fluoroethylene carbonate (FEC) on the electrochemical performance of LiNi0.5Mn1.5O4 (LNMO) have been investigated, and the results show that the cycling performance and rate capability of LiNi0.5Mn1.5O4 have been improved. In base electrolyte, the capacities become 91.3mAhg−1 with a retention of 82.3% after 150cycles at 1C rate. In contrast, after 150cycles the 1% FEC system reaches 106.7mAhg−1 with a 91.1% capacity retention, and the 2% FEC system achieves 113.5mAhg−1 with a 96.2% retention. 2% FEC system can even maintain 105.7mAhg−1 at 2C rate. Series of measurements exhibit that the preferential decomposition of FEC is beneficial to form a conductive film, which contains less compositions with low ionic conductivity. What's more, 2% FEC is more useful in forming a uniform and dense film than 1% FEC.