Li2FeSiO4/C cathodes were synthesized by combination of wet-process method and solid-state reaction at high temperature, and effects of roasting temperature and modification on properties of the Li2FeSiO4/C cathode were investigated. The XRD patterns of the Li2FeSiO4/C samples indicate that all the samples are of good crystallinity, and a little Fe3O4 impurity was observed in them. The primary particle size rises as the roasting temperature increases from 600 to 750°C. The Li2FeSiO4/C sample synthesized at 650°C has good electrochemical performances with an initial discharge capacity of 144.9mAhg−1 and the discharge capacity remains 136.5mAhg−1 after 10 cycles. The performance of Li2FeSiO4/C cathode is further improved by modification of Ni substitution. The Li2Fe0.9Ni0.1SiO4/C composite cathode has an initial discharge capacity of 160.1mAhg−1, and the discharge capacity remains 153.9mAhg−1 after 10 cycles. The diffusion coefficient of lithium in Li2FeSiO4/C is 1.38×10−12 cm2 s−1 while that in Li2Fe0.9Ni0.1SiO4/C reaches 3.34×10−12 cm2 s−1.