A hydrothermal synthesis of Ru-doped LiMn_1.5Ni_0.5O₄ cathode materials for enhanced electrochemical performance

Abstract

An Ru-doped spinel-structured LiNi_0.5Mn_1.5O₄ (LNMO) cathode has been prepared <i>via</i> a simple hydrothermal synthesis method. The as-prepared cathode is characterized <i>via</i> Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), laser particle size distribution analysis, X-ray photoelectron spectroscopy (XPS) and electrochemistry performance tests. The FTIR spectroscopy and XRD analyses show that the Ru-doped LNMO has a good crystallinity with a disordered <i>Fd</i>3̄<i>m</i> space group structure. The disordered structure in the cathode increased and the Li _<i>x</i> Ni_1-<i>x</i> O impurity phase decreased when Ru addition increased. SEM shows that all samples are octahedral particles with homogeneous sizes distribution, and the particle size analysis shows that the Ru-doped samples have smaller particle size. XPS confirms the existence of Ru ions in the sample, and reveals that the Ru induce to part of Mn⁴⁺ transfers to Mn³⁺ in the LNMO. The electrochemical property indicated that the Ru-doped cathode exhibits better electrochemical properties in terms of discharge capacity, cycle stability and rate performance. At a current density of 50 mA g^-1, the discharge specific capacity of the Ru-4 sample is 140 mA h g^-1, which is much higher than that of the other samples. It can be seen from the rate capacity curves that the Ru-doped samples exhibit high discharge specific capacity, particularly at high current density.