The low temperature electrochemical performances of LiFePO4/C/graphene nanofiber with 3D-bridge network structure

Abstract

Three-dimensionally assembled LiFePO4/C/graphene nanofiber composites were successfully prepared via a suspension mixing method followed by heat-treatment at 400°C. A faster electron transfer, lower electrochemical polarization as well as higher diffusion coefficient of Li+ are obtained with the assistance of graphene nanofibers. The 5wt% graphene nanofibers modified electrode (G-5) delivers the best electrochemical kinetics including the lowest charge transfer resistance and highest diffusion coefficient of Li+ at 0°C and −20°C, respectively. Likewise, the G-5 exhibits the highest charge-discharge capability and the most stable cycling performance at low operation temperatures compared with those of LiFePO4/C, 3wt% and 7wt% graphene nanofibers modified LiFePO4/C (G-3 and G-7) composites. The G-5 electrode shows a capacity of 92.8mAhg−1 with 92.0% capacity retention after 200 cycles at 1C at −20°C. The reasons for the significant improvement of the low operation temperatures electrochemical performances can be ascribed to the enhanced conductivity and reduced agglomeration of pristine particles due to the introduction of graphene nanofibers. These excellent low temperature performances show that graphene nanofibers modified LiFePO4/C electrodes are promising cathode candidates for lithium-ion batteries applications at low temperatures.