Synthesis of Li2FeSiO4/carbon nano-composites by impregnation method

Nanocrystalline lithium iron silicate/carbon (Li2FeSiO4/C) composites were successfully prepared by impregnation of a commercial porous carbon using ethanolic solutions of the different metallic precursors, followed by thermal annealing at 600 °C. The effects of Li2FeSiO4 loading content on the structure and organization of the Li2FeSiO4/C composites at the nanoscale were investigated. Through optimization of the synthesis conditions, small Li2FeSiO4 nanocrystals (4-12 nm) are formed and well dispersed in the porous conductive carbon. The electrochemical performances of these composites were tested as positive electrodes for lithium-ion batteries. The Li2FeSiO4/C composite with the lowest Li2FeSiO4 loading exhibits the best rate capability with a significant capacity contribution from carbon. It was found that the presence of carbon delays the lowering of the Fe3+/Fe2+ redox voltage usually reported for Li2FeSiO4 (from 3.1/3.0 to 2.8/2.7 V vs. Li+/Li), due to a stabilization effect of the initial Li2FeSiO4 crystal structure. For the Li2FeSiO4/C composite (81/19 weight ratio), a discharge capacity of 81 mAh g−1 can be achieved at 55 °C for a charge/discharge rate of 2C, with 86% capacity retention after 500 cycles, showing the positive effect of the porous carbon addition for long term cycling stability.