Tartaric acid assisted synthesis of Li2FeSiO4/C: Effect of carbon content on the electrochemical performance of Li2FeSiO4/C for lithium ion batteries

Li2FeSiO4/C composites were successfully prepared by tartaric acid assisted sol–gel route. Tartaric acid was used as both the chelating agent and carbon source. Effects of carbon content on the physical and electrochemical performances of the samples were studied in detail. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge–discharge and AC impedance spectroscopy, respectively. The particle size of Li2FeSiO4/C decreases with increasing content of carbon; however higher content of carbon will lead to poorer crystallinity and more impurities. When the carbon content is 4.0 wt.%, the Li2FeSiO4/C sample has the largest exchange current density (i° = 0.110 mA cm− 2) and highest diffusion coefficient of lithium ion (DLi+ = 1.01E − 12 cm2 s− 1). Thus, Li2FeSiO4/C with 4.0 wt.% carbon has the best electrochemical properties, in terms of discharge capacity and cycling stability. It exhibits an initial discharge capacity of 119.7 mAh g− 1 at C/16 rate at room temperature. When cycled at C/10 rate, the Li2FeSiO4/C sample with 4.0 wt.% carbon delivers an initial discharge capacity of 96.6 mAh g− 1, and 98.6% of the initial discharge capacity remained after 25 cycles.