Synthesis and electrochemistry of 5 V LiNi0.4Mn1.6O4 cathode materials synthesized by different methods

Spinel LiNi_0.4Mn_1.6O₄ has been successfully synthesized by ultrasonic-assisted co-precipitation (UACP) method. The structure and physicochemical properties of this as-prepared powder compared with the LiNi_0.4Mn_1.6O₄ 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 LiNi_0.4Mn_1.6O₄ 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 LiNi_0.4Mn_1.6O₄ (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 LiNi_0.4Mn_1.6O₄ 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.