Ruthenium doped LiMn1.5Ni0.5O4 microspheres with enhanced electrochemical performance as lithium-ion battery cathode

Ruthenium doped LiNi0.5Mn1.5O4 (LNMO) microspheres has been prepared by a simple solid-state reaction process. The as-prepared sample was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and electrochemistry performance test. The sample shows a spinel crystal structure without RuO2 impurity phase, and Ru doped sample crystal plane spacing increases. Combined with EDS spectrum, it indicates that the Ru ion was doped in the LNMO and distributed homogeneously. The XPS also further confirm the existence of Ru ions, and Ru has no obvious influence on Ni and Mn elements. The SEM images show that all the samples are sphere-like, with many polyhedral particles attached to the surface. When doped with 4% Ru ion, many cavities appear on the surface to form a porous structure. Electrochemical analysis confirms that the Ru-doped sample exhibits better electrochemical properties regarding discharge capacity, cycle stability, and rate performance. The 4% Ru-doped sample owns an initial discharge capacity of 125 mAh g−1 at 0.25C rate, with a capacity retention of 92% after 50 charge–discharge cycles. Moreover, at high current density (1C), Ru doped sample’s discharge capacity is 103 mAh g−1 while the original is only 86 mAh g−1. The excellent electrochemical properties are attributed to the Ru doping that increases the interlayer spacing and reduces the charge-transfer impedance (Rct), which is beneficial to lithium ion-exchange.