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

Mesoporous alpha-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 degrees C under Ar atmosphere for 4 h, mesoporous Fe3O4@C nanospheres were obtained. When further heated at 260 degrees C in air for 2 h, Fe3O4@C was transformed into gamma-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 similar to 570 mA h g(-1) after 30 cycles, while the discharge capacities of alpha-Fe2O3 and gamma-Fe2O3 faded rapidly to similar to 100 mA h g(-1) after 30 cycles.