Experimental Elucidation of a Graphenothermal Reduction Mechanism of Fe2O3: An Enhanced Anodic Behavior of an Exfoliated Reduced Graphene Oxide/Fe3O4 Composite in Li-Ion Batteries

The graphenothermal reduction mechanism of Fe 2 O 3 by graphene oxide (GO) is elucidated through careful experimental analysis. The degree of oxidation (DO) of GO plays a key role in controlling the reduction of Fe 2 O 3 by GO. GO with low DO follows a conventional three-stage reaction path, i.e., ′2GO + Fe 2 O 3 → EG/Fe 3 O 4 (Stage I) → EG/FeO (Stage II) → EG/Fe (Stage III)′ (where EG is exfoliated reduced graphene oxide), at temperatures 650 and 750 °C to reduce Fe 2 O 3, whereas the GO with higher DO transforms rapidly and ceases the reduction at Stage I, i.e., with the formation of EG/Fe 3 O 4 at 650 °C. It is also found that slow thermal treatment of GO continues the reduction to Stage II and further to Stage III depending on time of heating and temperature. EG/Fe 3 O 4 (synthesized at 550 °C, 5 h) by using GO with low DO showed superior cycling performance as an anode of Li-ion battery than its counterpart prepared (at 650 °C, 5 h) from GO with high DO owing to good contacts between EG and Fe 3 O 4 . EG/Fe 3 O 4 (synthesized at 550 °C, 5 h) exhibited reversible capacity as high as 860 mAh/g which is greater than the specific capacity of EG/Fe 3 O 4 synthesized (at 650 °C, 5 h) by 150 mAh/g. Overall, EG/Fe 3 O 4 (synthesized at 550 °C, 5 h) outperformed its counterpart (i.e., EG/Fe 3 O 4 synthesized at 650 °C, 5 h) by exhibiting excellent cycling stability and rate capability at current rates ranging from 0.5 to 3.0 C.