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

Li₂Fe_1?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 Li₂Fe_0.8Mn_0.2SiO₄/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 Li₂Fe_1?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.