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

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.