Journal of Materials Science, Vol.53, No.4, 2697-2708, 2018
In situ synthesis of Fe(1-x)Co (x) F-3/MWCNT nanocomposites with excellent electrochemical performance for lithium-ion batteries
Due to their high theoretical capacities and high energy densities, metal fluorides have attracted significant attention as cathodes for lithium-ion batteries. However, thus far, their low conductivities have limited the performance of these materials. In this work, the Fe(1-x)Co (x) F-3/MWCNT (multi-walled carbon nanotube) nanocomposites (x = 0, 0.02, 0.04 and 0.06) are obtained by an in situ solvothermal method with Co-doping and wrapping of the MWCNTs. The results indicate that Co-doping can adjust the crystal structure, decrease the band gaps and enhance the Li+ diffusion coefficient of FeF3. Additionally, the wrapped network of MWCNTs enhances the conductivity of the composites and improves their electrochemical performances. The Fe0.96Co0.04F3/MWCNT nanocomposites exhibit a high initial discharge capacity of 217.0 mAh g(-1) at rate of 0.2 C within the potential range of 2.0-4.5 V, which is much higher than that of the FeF3/MWCNT counterpart (192.1 mAh g(-1)). The discharge capacities of these two samples remain at 187.9 and 160.7 mAh g(-1) even after 50 cycles. Meanwhile, the EIS results reveal that both the Li+ charge transfer resistance (R (ct) = 31.25 Omega) and Li+ diffusion coefficient (1.40 x 10(-11) cm(2) s(-1)) are satisfactory from Co-doping and the in situ wrapping of the MWCNTs.