Improved Electrochemical Performance of 0.5Li(2)MnO(3)·0.5LiNi(0.5)Mn(0.5)O(2) Cathode Materials for Lithium Ion Batteries Synthesized by Ionic-Liquid-Assisted Hydrothermal Method

Well-dispersed Li-rich Mn-based 0.5Li(2)MnO(3)·0.5LiNi0.5Mn(0.5)O(2) nanoparticles with diameter ranging from 50 to 100 nm are synthesized by a hydrothermal method in the presence of N-hexyl pyridinium tetrafluoroborate ionic liquid ([HPy][BF4]). The microstructures and electrochemical performance of the prepared cathode materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical measurements. The XRD results show that the sample prepared by ionic-liquid-assisted hydrothermal method exhibits a typical Li-rich Mn-based pure phase and lower cation mixing. SEM and TEM images indicate that the extent of particle agglomeration of the ionic-liquid-assisted sample is lower compared to the traditional hydrothermal sample. Electrochemical test results indicate that the materials synthesized by ionic-liquid-assisted hydrothermal method exhibit better rate capability and cyclability. Besides, electrochemical impedance spectroscopy (EIS) results suggest that the charge transfer resistance of 0.5Li(2)MnO(3)· 0.5LiNi0.5Mn(0.5)O(2) synthesized by ionic-liquid-assisted hydrothermal method is much lower, which enhances the reaction kinetics.