To improve the electrochemical performance of Li 2 FeSiO 4 with low electric conductivity, the Li 2 FeSiO 4 /C composites with different carbon content are synthesized by a vacuum solid-state method. The experimental results show that the introduced carbon decrease the crystallite sizes of final products, but still keep the serious aggregated particles and make the Li 2 SiO 3 impurity further increased. The Li 2 FeSiO 4 with 4.15 wt.% carbon delivers the initial discharge capacity of 108.9 mAhg −1 at room temperature and retains 71.5% of the initial discharge capacity after 50 cycles. The transition phenomenon in charge–discharge curves and the variation in D Li+ values with the cycling number clearly indicate a transient process of phase transition for Li 2 FeSiO 4 , which requires at least 5–10 charge–discharge cycles.