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.

The intrinsic charge-transfer property bears the primary responsibility for the sluggish redox kinetics of the common electrode materials, especially operated at low temperatures. Herein, we report the crafting of homogeneously confined Fe7Se8 nanoparticles with a well-defined graphitic carbon matrix that demonstrate a highly efficient charge-transfer system in a designed natural coral-like structure (cl-Fe7Se8@C). Notably, the intricate architecture as well as highly conductive peculiarity of C concurrently satisfy the demands of achieving fast ionic/electrical conductivities for both Li/Na-ion batteries in a wide temperature range. For example, when cl-Fe7Se8@C is employed as the anode material to assemble full batteries with the cathode of Na3V2(PO4)2O2F (NVPOF), decent capacities of 323.1 and 175.9 mA h g–1 can be acquired at temperatures of 25 and −25 °C, respectively. This work is significant for further developing potential anode materials for advanced energy storage and conversion under low-temperature conditions.

Constructing potential anodes for sodium-ion batteries (SIBs) with a wide temperature property has captured enormous interests in recent years. Fe 1−x S, a zero-band gap material confirmed by density states calculation, is an ideal electrode for fast energy storage on account of its low cost and high theoretical capacity. Herein, Fe 1−x S nanosheet wrapped by nitrogen-doped carbon (Fe 1−x S@NC) is engineered through a post-sulfidation strategy using Fe-based metal-organic framework (Fe-MOF) as the precursor. The obtained Fe 1−x S@NC agaric-like structure can well shorten the charge diffusion pathway, and significantly enhance the ionic/electronic conductivities and the reaction kinetics. As expected, the Fe 1−x S@NC electrode, as a prospective SIB anode, delivers a desirable capacity up to 510.2 mA h g −1 at a high rate of 8000 mA g −1 . Additionally, even operated at low temperatures of 0 and −25°C, high reversible capacities of 387.1 and 223.4 mA h g −1 can still be obtained at 2000 mA g −1 , respectively, indicating its huge potential use at harsh temperatures. More noticeably, the full battery made by the Fe 1−x S@NC anode and Na 3 V 2 (PO 4 ) 2 O 2 F cathode achieves a remarkable rate capacity (186.8 mA h g −1 at 2000 mA g −1 ) and an impressive cycle performance (183.6 mA h g −1 after 100 cycles at 700 mA g −1 ) between 0.3 and 3.8 V. Such excellent electrochemical performance is mainly contributed by its pseudocapacitive-dominated behavior, which brings fast electrode kinetics and robust structural stability to the whole electrode.

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The inserted and cross-linked HCNFs in the MnO/HCNFs composites act like electrical “highways” through which electrons/Li ions are directly transferred to the inner parts of the MnO microspheres without obstruction.