Superior electrochemical capability of Li_2FeSiO_4/C/G composite as cathode material for Li-ion batteries

摘要

A novel graphene-containing Li_2FeSiO_4 composite (Li_2FeSiO_4/C/G) has been synthesized successfully which shows superior performance when used as the cathode material for lithium ion batteries. The Li_2FeSiO_4/C precursor was synthesized via a modified sol-gel method and mixed with graphene oxide nanosheets which were then reduced by annealing to obtain electron conductive graphene. The structure characterizations by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) show that phase-pure Li_2FeSiO_4/C nanoparticles are mixed homogeneously with graphene nanosheets. When used as the cathode materials for rechargeable lithium ion batteries, the composite Li_2FeSiO_4/C/G shows superior large capacities and long-time cyclabilities. Specific discharge capacities of 310 mAh g~(-1), corresponding to 1.86 Li~+ ions exchange per Li_2FeSiO_4 molecule, can be reached at the charging/discharging rate of 0.1 C (1 C = 166 mAg~(-1)). At the high rate of 30 C and 50 C, the composite still shows ～110 and ～50 mAh g~(-1) discharge capacities after 1000 charging-discharging cyclings. These superior-the best up to now-performances of the composite are believed to be the cooperative result of the 3D conducting network, formed by the flexible and planar graphene nanosheets, and the nanoscale sizes of the carbon-coated Li_2FeSiO_4 particles.