Surface modification of spinel LiMn2O4 with FeF3 for lithium ion batteries

Abstract

Cycling performance and thermal stability of spinel LiMn2O4 cathode material synthesized by a sol–gel method are improved by surface modification with FeF3 through chemical deposition method. The phase structures, components and morphologies of pristine and FeF3-coated LiMn2O4 are investigated by X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM). The cycling performances are thoroughly investigated and compared at room and high temperatures. The FeF3-coated LiMn2O4 electrodes display enhanced cycling stabilities compared with that of pristine LiMn2O4. Especially, the 5wt.% FeF3-coated LiMn2O4 demonstrates the best cycling performance, with the capacity retentions of 68.2% after 200 cycles at room temperature (25°C) and 61.5% after 100 cycles at elevated temperature (55°C), much better than those of the pristine materials, 49.8 and 40.2%. Cyclic voltammetry (CV) confirms that FeF3 modification layer improves the structure stability of LiMn2O4. Electrochemical impedance spectroscopy (EIS) data illustrate that FeF3 coating can suppress the fast growth of undesirable solid electrolyte interfacial (SEI) film. Differential scanning calorimetry (DSC) tests show that the existence of FeF3 helps to enhance the thermal stability of LiMn2O4 cathode.