Facile synthesis of Li2FeSiO4/C composites with triblock copolymer P123 and their application as cathode materials for lithium ion batteries

Phase-pure, monoclinic, and nanostructured Li2FeSiO4/C composite has been synthesized with poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer P123. The structure of the composite has been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The Li2FeSiO4/C composite exhibits superior electrochemical properties as the cathode materials for lithium ion batteries. The discharge specific capacities can reach 230 mAh g−1 at current density of 0.1 C (1 C = 166 mA g−1) at room temperature when cycled between 1.5 and 4.8 V (vs. Li+/Li). Discharge capacities of 185, 150, and 120 mAh g−1 are obtained at high rates of 1 C, 5 C, and 10 C, respectively. The high capacities are believed to be related to both Fe2+/Fe3+ and Fe3+/Fe4+ redox couples, as suggested by the Mössbauer spectra for the electrode materials. The Li2FeSiO4/C composite also shows excellent rate capability and cyclability. All these results suggest that Li2FeSiO4/C composite is a very promising candidate as a cheap and sustainable cathode material for the next generation of rechargeable lithium ion batteries.