Structural influence of porous FeOx@C nanorods on their performance as anodes of lithium-ion batteries

Abstract

Two types of porous iron oxide nanorods, FeO_x synthesized by hydrothermal treatment (FeO_x-HY) with large internal voids and porous shells and FeO_x synthesized by annealing (FeO_x-AN) with mesopores of ∼4.0 nm, were obtained by hydrothermal or high temperature treatments of β-FeOOH nanorods, respectively. Their performance as anode materials in lithium ion batteries (LIBs) were evaluated and correlated with the specific features of the porous structures. FeO_x-HY with large internal voids and porous shell exhibited a better cyclability than FeO_x-AN. With the assistance of a carbon coating, the FeO_x-HY@C electrode exhibited a steadily increased specific capacity with the increase of cycles, and a high specific capacity of ∼1131 mA h g⁻¹ at a current density of 100 mA g⁻¹ after 50 cycles. In comparison, the FeO_x-AN@C electrode delivered a slightly decreased cycling performance in the specific capacity and a smaller specific capacity at each current density. The structural features of FeO_x-HY@C with the large internal voids, porous thin shells and the elastic carbon shell can effectively buffer volume swings and mechanical stresses, synchronize lithium diffusion and charge transport processes, and facilitate the lithium ion transport. These results suggest that the pore structure of the anode materials has a significant influence on their performance in LIBs.