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Transition metal oxides with high theoretical capacities are widely investigated as potential anodes for alkali-metal ion batteries. However, the intrinsic conductivity deficiency and large volume changes during cycles result in poor cycling stability and low rate capabilities. Graphene has been widely used to support metal oxide for enhanced performance, but the cycling life is limited by the aggregation/collapse of active materials on graphene surface. Herein, we significantly improve the battery performance of graphene-metal oxide composite via pore engineering and surface protection. In this architecture, the mesoporous NiFe2O4 is designed for fast ion diffusion and volume accommodation, and the outer graphene protection can further enhance the electrical conductivity and prevent the aggregation during cycle. Thus, as-prepared G@p-NiFe2O4@G composite for lithium storage delivers high capacity (1244 mA h g−1 after 300 cycles at 0.2 A g−1), excellent rate performance (563 mA h g−1 at 4 A g−1), and outstanding cycling life up to 1200 cycles at 1.5 A g−1. For sodium storage, it also displays good cycling stability and superior rate performance. Moreover, the effects of various microstructures on the battery performance, the reaction kinetics of various electrodes, and the reaction mechanism of NiFe2O4 have been systematically investigated in this work. [ABSTRACT FROM AUTHOR]

In this work, we report a high-performance anode material created by rationally encapsulating multi-walled carbon nanotubes (MWNTs) within hollow Fe 3 O 4 nanotubes followed by applying a carbon coating. When tested for lithium storage, as-prepared MWNT@hollow Fe 3 O 4 @C coaxial nanotubes present high specific capacity, superior rate performance, and outstanding cycling stability. It is capable of delivering high capacities of 758 mA h g -1 at 500th cycle at 0.2 A g -1 , and 409 mA h g -1 after 1000 cycles at a high rate of 1.5 A g -1 . This excellent performance can be attributed to its unique architecture, which provides high electrical conductivity, offers enough void space for volume accommodation, and mitigates the pulverization of Fe 3 O 4 during cycles.