Construction of highly conductive network for improving electrochemical performance of lithium iron phosphate

High performance lithium iron phosphate (LFP) cathode materials were synthesized using amorphous carbon, carbon nanotubes (CNTs), and graphene (G) as conductive materials via sand milling and spray drying processes and followed by calcination. The structural characterizations indicated that CNTs and G can well connected with LFP nanoparticles (NPs), which was coated with a thin layer of amorphous carbon, benefiting the construction of three-dimensional efficient conductive network. The electrochemical measurements confirmed that the introduction of CNTs and G can obviously decrease the charge transfer impedance of lithium ion battery and increase the discharge special capacity. The initial discharge special capacity increases in the order of LFP/C (150.3 mAh/g) < LFP/C/CNTs (155.7 mAh/g) < LFP/C/G (159.7 mAh/g) < LFP/C/G/CNTs (164.5 mAh/g) at 0.1 C. LFP/C/G/CNTs also exhibited considerable discharge special capacity (99.5 mAh/g) at high current of 5 C. Compared with LFP/C (248 Ω), LFP/C/G/CNTs (50 Ω) showed obviously decreased charge transfer impedance. Cycle performance test indicated that the specific capacity retention for LFP/C/G/CNTs was 99% after 200 cycles, displaying good cycle stability. The superior electrochemical performance of LFP/C/G/CNTs is attributed to the significantly synergistic effect of CNTs and G on decreasing charge transfer impedance by constructing highly three-dimensional conductive network. Besides, the effect of G to CNTs mass ratio and the calcination temperature on the electrochemical performance of LIBs were also discussed.