Effects of Al, F dual substitutions on the structure and electrochemical properties of lithium manganese oxide

Spinel LiMn2O4 and F, Al-doped spinel LiAl0.05Mn1.95O3.98F0.02 have been synthesized by a soft chemistry method using adipic acid as the chelating agent. The synthesized spinel materials were characterized by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and charge-discharge testing. The results indicate that all the samples have high phase purity, and fluorine is important in controlling the morphology; the doped aluminum enhances the stability of spinel LiMn2O4. The charge-discharge tests indicate that LiAl0.05Mn1.95O4 has high capacity retention, which is 92.60% of the initial after 50 cycles. It is found that the novel compound LiAl0.05Mn1.95O3.98F0.02 with smaller particles can offer much higher capacity, whose initial discharge capacity is 126.5 mAh·g−1. The cyclic voltammetric experiments disclose the enhanced reversibility of the F, Al3+-modified spinel as compared with the undoped spinel.