Synthesis and physicochemical properties of LiAl0.05Mn1.95O4 cathode material by the ultrasonic-assisted sol-gel method

Spinel LiAl0.05Mn1.95O4 has been successfully synthesized by a new ultrasonic-assisted sol-gel (UASG) method. The structure and physicochemical properties of this as-prepared powder compared with the pristine LiMn2O4 and LiAl0.05Mn1.95O4 synthesized by the traditional sol-gel method were investigated by differential thermal analysis (DTA) and thermogravimetery (TG), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), cyclic voltammetry (CV), and galvanostatic charge-discharge testing in detail. The results show that all samples have high phase purity, and ultrasonic process plays an important role in controlling morphology; LiAl0.05Mn1.95O4 has higher Mn oxidation state, and the absorption peak of Mn(III)O and Mn(IV)O bonds has blue shift because of the doped Al. CV confirms that the LiAl0.05Mn1.95O4 sample (UASG) has a good reversibility and its structure is very advantageous for the transportation of lithium ions. The charge-discharge tests indicate that LiAl0.05Mn1.95O4 (UASG) has nearly equal initial capacity with LiMn2O4 (sol-gel) at 1C discharge rate, but LiAl0.05Mn1.95O4 (UASG) has higher discharge potential than that of LiMn2O4 (sol-gel). In addition, LiAl0.05Mn1.95O4 (UASG) has higher discharge potential and capacity than that of LiAl0.05Mn1.95O4 (sol-gel) at 1C discharge rate, and LiAl0.05Mn1.95O4 (UASG) has high capacity retention at C/3 and 1C discharge rate among three samples after 50 cycles, which reveals that the sample obtained via UASG method, has the best electrochemical performance among three samples.