Improved Performance of Li2FeSiO4/C Composite with Highly Rough Mesoporous Morphology

The Li 2 FeSiO 4 /C composites were prepared using iron starting materials of either insoluble ferrous (FeC 2 O 4 ·2H 2 O) or soluble ferric (Fe(NO 3 ) 3 ·9H 2 O) compounds through sol-gel process and solid state reaction. The pure monoclinic P 2 1 / n with the rough surface consisting of a large amount of open pores was obtained using ferric iron source, while the sphere-like nanoparticles containing major impurities of Fe 3 O 4 (γ-Fe 2 O 3 ) and Li 2 SiO 3 were obtained using ferrous iron source. With less expensive ferric nitrate and faster heating rate, the excellent diffusion coefficients of 1.88 × 10 −8 cm 2 s −1 at 25°C and 1.42 × 10 −7 cm 2 s −1 at 55°C were obtained with the highly rough mesoporous morphology due to the enhanced interfacial kinetics with the apparent reductions in the charge transfer resistance and significant reductions in the migration resistance at the higher temperature. Coupled with higher degree of graphitized carbon, the initial and maximum discharge capacities of 213.9 and 239.2 mAh g −1 could be achieved at 55°C and C/16 based on 50 cycles of charge/discharge testing at 25°C.