Synthesis and electrochemistry of 5 VLiNi0.4Mn1.6O4 cathode materials synthesized by different methods

Spinel LiNi0.4Mn1.6O4 has been successfully synthesized by ultrasonic-assisted co-precipitation (UACP) method. The structure and physicochemical properties of this as-prepared powder compared with the LiNi0.4Mn1.6O4 synthesized by co-precipitation method were investigated by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge test in detail. XRD and SEM show that all samples have high phase purity, and ultrasonic process plays an important role in controlling morphology; FT-IR reveals that the Mn(III)-O stretching band at 511 cm(-1) has a red shift to 503 cm(-1), and the Mn(IV)-O stretching band at 612 cm(-1) has a blue shift to 622 cm(-1) because of the doped Ni. CV confirms that the LiNi0.4Mn1.6O4 sample (UACP) has bigger area of the reduction peaks than that of sample synthesized by co-precipitation method, indicating that the former has higher discharge capacity than that of the latter. Galvanostatic charge-discharge test indicates that the initial discharge capacities for the LiNi0.4Mn1.6O4 (UACP) at C/5 and 1C are 129 and 116 mAh g(-1), respectively. After 100 cycles, their capacity retentions are 94.6% and 85.3%, respectively. EIS indicates that LiNi0.4Mn1.6O4 samples synthesized by UACP method have smaller charge transfer resistance than that of samples synthesized by co-precipitation method corresponding to the extraction of Li+ ions. (C) 2007 Elsevier Ltd. All rights reserved.