Structural evolution from mesoporous α-Fe2O3 to Fe3O4@C and γ-Fe2O3 nanospheres and their lithium storage performances

Abstract

Mesoporous α-Fe₂O₃ nanospheres were synthesized through a solvothermal route, with polyethylene glycol as soft templates. The mesoporous nanospheres were then coated with carbon through hydrothermal treatment of glucose. After being calcined at 500 °C under Ar atmosphere for 4 h, mesoporous Fe₃O₄@C nanospheres were obtained. When further heated at 260 °C in air for 2 h, Fe₃O₄@C was transformed into γ-Fe₂O₃ mesoporous nanospheres. Significant phase changes occurred without destroying the structure of mesoporous nanospheres. All the three mesoporous nanospheres showed superior Li storage performances at the initial charge and discharge cycle; however, the cyclic stabilities of the three samples were quite different; Fe₃O₄@C exhibited a stable discharge capacity of ∼570 mA h g⁻¹ after 30 cycles, while the discharge capacities of α-Fe₂O₃ and γ-Fe₂O₃ faded rapidly to ∼100 mA h g⁻¹ after 30 cycles.