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

Spinel LiMn₂O₄ and F, Al-doped spinel LiAl_0.05Mn_1.95O_3.58F_0.02 have been synthesized by a soft chemistry method using adipic acid as the chelating agent. The synthesized spine/materials were characterized by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and chargedischarge 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 LiAl_0.05Mn_1.95O₄ has high capacity retention, which is 92.60% of the initial after 50 cycles. It is found that the novel compound LiAl_0.05Mn_1.95O_3.98F_0.02 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.