A high-performance Li₂FeSiO₄/C cathode enhanced by a novel liquid-state carbon source

A novel liquid-state carbon source, [2-[(2R,3S,4R)-3,4-dihydroxytetrahydrofuran-2-yl]-2-hydroxy-ethyl] dodecanoate (sorbitan monolaurat, Span-20, C₁₈H₃₄O₆), is used to synthesize Li₂FeSiO₄/C by the sol-gel method. X-ray diffraction and scanning electron microscope measurements are carried out to determine the crystal structures, morphologies and particle sizes of the resulting products. The results show that Li₂FeSiO₄/C has pure phase and the average particle size of Li₂FeSiO₄ is in 20-30 nm. The result of Raman spectroscopy measurement indicates that the liquid-state carbon source can be prone to generate the carbon materials with high-ordered structure compared to the solid-state carbon source. The Li₂FeSiO₄/C cathode delivers an initial discharge capacity of 187 mAh g^-1 at 0.1 C rate, and it also shows good rate performance and stable cycle performance, indicating that the liquid-state carbon source helps to improve the electrochemical performance of the Li₂FeSiO₄/C cathode. By analyzing electrochemical impedance spectra, it is concluded that the carbon coating layer generated from the liquid-state Span-20 enhances the electrode/electrolyte interface characterization and improves the Li⁺ diffusion.