Physicochemical properties of LiAl x Mn2 − x O4 and LiAl0.05Mn1.95O4 − y F y cathode material by the citric acid-assisted sol–gel method

Abstract

LiAlxMn2 − xO4 and LiAl0.05Mn1.95O4 − yFy spinel have been successfully synthesized by citric acid-assisted sol–gel method. The structure and physicochemical properties of this as-prepared powder were investigated by electronic conductivity test, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge test in detail. The electronic conductivity decreases with increasing of the content of doped Al. XRD patterns show that the diffraction of LiAl0.05Mn1.95O4 − yFy samples is similar, with all the peaks indexable in the Fd3m space group, and a little impurity appears in the LiAl0.05Mn1.95O3.8F0.2 sample. SEM reveals that all LiAl0.05Mn1.95O4 − yFy powders have the uniform, nearly cubic structure morphology with narrow size distribution which is less than 500 nm. Galvanostatic charge–discharge test indicates that LiAl0.05Mn1.95O4 has the highest discharge capacity and electrochemical performance among all LiAlxMn2 − xO4 samples after 50 cycles, and the initial discharge capacity of LiAl0.05Mn1.95O4 − yFy (y = 0, 0.02, 0.05, 0.1) is 123.9, 124.6, 124.9, and 125.0 mAh g−1, respectively, and their capacity retention ratios are 94.2%, 94.9%, 91.7%, and 89.9% after 50 cycles, respectively. EIS indicates that LiAl0.05Mn1.95O3.98F0.02 have smaller charge transfer resistance than that of LiAl0.05Mn1.95O4 corresponding to the extraction of Li+ ions.