Effect of Mn doping on electrochemical properties of Li2FeSiO4/C cathode materials based on a vacuum solid-state method

Abstract

Li2Fe1−x Mn x SiO4/C (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) are prepared by a vacuum solid-state reaction of SiO2, CH3COOLi·2H2O, FeC2O4·2H2O, and Mn(CH3COO)2·4H2O. The crystalline structures, morphologies, and electrochemical performances are analyzed contrastively by X-ray diffraction (XRD), scanning electron microscopy, galvanostatic charging–discharging, and electrochemical impedance spectroscopy (EIS). The XRD and EIS results prove that Mn doping may be beneficial to the battery performances of Li2FeSiO4 materials, by reducing the crystallite sizes, decreasing transfer impedance (R ct), and increasing Li-ion diffusion coefficient (D Li+). However, the galvanostatic charge–discharge results indicate that only Li2Fe0.8Mn0.2SiO4/C shows the improved performance; its initial discharge capacity can reach to 190.7 mAh g−1. All things considered, the increased impurities after Mn doping, decided by reference intensity ratio (RIR) method, seem to impose more negative effects on the Li2Fe1−x Mn x SiO4/C performances. Under this premises, the Mn-doped content is particularly important for Li2FeSiO4 materials prepared by the vacuum solid-state method.