Effect of MgF2 coating on the electrochemical performance of LiMn2O4 cathode materials

Abstract

Spinel LiMn2O4 cathode materials were coated with 1.0, 3.0 and 5.0 wt.% of MgF2 by precipitation, followed by heat treatment at 400 °C for 5 h in air. The effects of MgF2 coating on the structural and electrochemical properties of LiMn2O4 cathodes were investigated using XRD, SEM, and electrochemical tests. XRD and SEM results show that no significant bulk structural differences are observed between the coated and pristine LiMn2O4. The charge–discharge tests show that the discharge capacity of LiMn2O4 decreases slightly, but the cyclability of LiMn2O4 is clearly improved when the amount of the MgF2 coated was increased to 3.0 wt.%. The 3.0 wt.% MgF2-coated LiMn2O4 exhibits capacity retention of 80.1 and 76.7 % after 100 cycles at room temperature (25 °C) and elevated temperature (55 °C) at a rate of 1 C, respectively, much higher than those of the bare LiMn2O4 (70.1 and 61.6 %). The improvement of electrochemical performance is attributed to the suppression of Mn dissolution into the electrolyte via the MgF2 coating layer.