Marcasite (m-FeS) exhibits higher electronic conductivity than that of pyrite (p-FeS) because of its lower semiconducting gap (0.4 vs 0.7 eV). Meanwhile, as demonstrates stronger Fe-S bonds and less S-S interactions, the m-FeS seems to be a better choice for electrode materials compared to p-FeS. However, the m-FeS has been seldom studied due to its sophisticated synthetic methods until now. Herein, a hierarchical m-FeS and carbon nanofibers composite (m-FeS/CNFs) with grape-cluster structure was designed and successfully prepared by a straightforward hydrothermal method. When evaluated as an electrode material for lithium ion batteries, the m-FeS/CNFs exhibited superior lithium storage properties with a high reversible capacity of 1399.5 mAh g after 100 cycles at 100 mA g and good rate capability of 782.2 mAh g up to 10 A g. The Li-storage mechanism for the lithiation/delithiation processes of m-FeS/CNFs was systematically investigated by ex situ powder X-ray diffraction patterns and scanning electron microscopy. Interestingly, the hierarchical m-FeS microspheres assembled by small FeS nanoparticles in the m-FeS/CNFs composite converted into a mimosa with leaves open shape during Li insertion process and vice versa. Accordingly, a "CNFs accelerated decrystallization-recrystallization" mechanism was proposed to explain such morphology variations and the decent electrochemical performance of m-FeS/CNFs.

Herein, we develop a Co3O4-based anode material with a hierarchical structure similar to that of a lotus pod, where single yolk–shell-structured Co3O4@Co3O4 nanospheres are well embedded in a nitrogen-doped carbon (N–C) conductive framework (Co3O4@Co3O4/N–C). This distinctive architecture contains multiple advantages of both the yolk–shell structure and conductive N–C framework to improve the Li ion storage performance. Especially, the doping of the N atom in N–C increases the interaction between the carbon and adsorbents, which is confirmed by the theoretical calculations in this work, making the carbon framework much more electrochemically active. As a result, the Co3O4@Co3O4/N–C exhibits fast surface-controlled kinetics, which corroborate the high counterion mobility and the ultrafast electron-transfer kinetics of the electrode. Due to these synergetic effects, desired capacity stability (1169.6 mAh g–1 at 200 mA g–1 after 100 cycles) and superior rate performance (633.4 mAh g–1 at 10 A g–1) have been realized in this Co3O4@Co3O4/N–C electrode.

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Hierarchical FeS spheres coated with ultrathin graphitic carbon layer exhibit superior low-temperature Li/Na-storage properties.