Inner-Stress-Optimized High-Density Fe3O4 Dots Embedded in Graphitic Carbon Layers with Enhanced Lithium Storage

Double-Shelled Fe-Fe3C Nanoparticles Embedded on a Porous Carbon Framework for Superior Lithium-Ion Half/Full Batteries

Cost-effective and environmentally friendly Fe-based active materials offer exceptionally high energy capacity in lithium-ion batteries (LIBs) due to their multiple electron redox reactions. However, challenges, such as morphology degradation during cycling, cell pulverization, and electrochemical stability, have hindered their widespread use. Herein, we demonstrated a simple salt-assisted freeze-drying method to design a double-shelled Fe/Fe3C core tightly anchored on a porous carbon framework (FEC). The shell consists of a thin Fe3O4 layer (≈2 nm) and a carbon layer (≈10 nm) on the outermost part. Benefiting from the complex nanostructuring (porous carbon support, core-shell nanoparticles, and Fe3C incorporation), the FEC anode delivered a high discharge capacity of 947 mAh g-1 at 50 mA g-1 and a fast-rate capability of 305 mAh g-1 at 10 A g-1. Notably, the FEC cell still showed 86% reversible capacity retention (794 mAh g-1 at 50 mA g-1) at a high cycling temperature of 80 °C, indicating superior structural integrity during cycling at extreme temperatures. Furthermore, we conducted a simple solid-state fluorination technique using the as-prepared FEC sample and excess NH4F to prepare iron fluoride-carbon composites (FeF2/C) as the positive electrode. The full cell configuration, consisting of the FEC anode and FeF2/C cathode, reached a remarkable capacity of 200 mAh g-1 at a 20 mA g-1 rate or an energy density of approximately 530 Wh kg-1. Thus, the straightforward and simple experimental design holds great potential as a revolutionary Fe-based cathodic-anodic pair candidate for high-energy LIBs.

Yolk-shell porous Fe3O4@C anchored on graphene as anode for Li-ion half/full batteries with high rate capability and long cycle life

Iron oxides have been widely studied as anode materials for lithium-ion batteries (LIBs) due to their high conductivity (5 × 10⁴ S m^-1) and high capacity (ca. 926 mAh g^-1). However, having a large volume change and being highly prone to dissolution/aggregation during charge/discharge cycles hinder their practical application. Herein, we report a design strategy for constructing yolk-shell porous Fe₃O₄@C anchored on graphene nanosheets (Y-S-P-Fe₃O₄/GNs@C). This particular structure can not only introduce sufficient internal void space to accommodate the volume change of Fe₃O₄ but also afford a carbon shell to restrict Fe₃O₄ overexpansion, thus greatly improving capacity retention. In addition, the pores in Fe₃O₄ can effectively promote ion transport, and the carbon shell anchored on graphene nanosheets is capable of enhancing overall conductivity. Consequently, Y-S-P-Fe₃O₄/GNs@C features a high reversible capacity of 1143 mAh g^-1, an excellent rate capacity (358 mAh g^-1 at 10.0 A g^-1), and a prolonged cycle life with robust cycling stability (579 mAh g^-1 remaining after 1800 cycles at 2.0 A g^-1) when assembled into LIBs. The assembled Y-S-P-Fe₃O₄/GNs@C//LiFePO₄ full-cell delivers a high energy density of 341.0 Wh kg^-1 at 37.9 W kg^-1. The Y-S-P-Fe₃O₄/GNs@C is proved to be an efficient Fe₃O₄-based anode material for LIBs.

Carbon-coated Fe3O4 nanoparticles in situ grown on 3D cross-linked carbon nanosheets as anodic materials for high capacity lithium and sodium-ion batteries

Carbon coated Fe3O4 nanoparticles were grown in situ on 3D cross-linked carbon nanosheets, and exhibited excellent performance for lithium ion batteries.

Interfacing MXene Flakes on a Magnetic Fiber Network as a Stretchable, Flexible, Electromagnetic Shielding Fabric

A unique self-standing membrane composed of hierarchical thermoplastic polyurethane (TPU)/polyacrylonitrile (PAN) fibers is prepared by the electrospinning technique, followed by a simple dip-coating process. Fe₃O₄ nanoparticles are uniformly anchored on TPU/PAN fibers during the electrospinning process, enabling the membrane to achieve effective electromagnetic interference shielding (EMI SE) performance. Such a hybrid membrane has a high magnetization of 18.9 emu/g. When MXene (Ti₃C₂T_x) layers are further loaded on the TPU/PAN/Fe₃O₄NPs hybrid membrane, its EMI SE performance in the X band can exceed 30 dB due to the hydrogen bonds generated between the macromolecular chain of PAN and the functional group (T_x) on the surface of MXene. Simultaneously, the interfacial attraction between MXene and the TPU/PAN/Fe₃O₄NPs substrate is enhanced. The EMI SE mechanism of the hybrid membrane indicates that this film has great potential in the fields of wearable devices and flexible materials.

S-Decorated Porous Ti3 C2 MXene Combined with In Situ Forming Cu2 Se as Effective Shuttling Interrupter in Na-Se Batteries

Given natural abundance of Na and superior kinetics of Se, Na-Se batteries have attracted much attention but still face the problem of shuttling effect of soluble intermediates. The first-principle calculations reveal the S-decorated Ti₃ C₂ exhibits increased binding energy to sodium polyselenides, suggesting a better capture and restriction on intermediates. The obtained Se@S-decorated porous Ti₃ C₂ (Se@S-P-Ti₃ C₂ ) exhibits a high reversible capacity of 765 mAh g^-1 at 0.1 A g^-1 (calculated based on Se), ≈1.2, 1.3, and 1.7 times of Se@porous Ti₃ C₂ (Se@P-Ti₃ C₂ ), Se@Ti₃ C₂ , and Se, respectively. It gives considerable capacity of 664 mAh g^-1 at 20 A g^-1 and impressive cycling stability over 2300 cycles with an ultralow capacity decay of 0.003% per cycle. The excellent electrochemical performance can be ascribed to the S-modified porous Ti₃ C₂ , which provides effective immobilization toward polyselenides, makes full use of nanosized Se, and alleviates volume expansion during sodiation/desodiation. Additionally, in situ forming Cu₂ Se can generate Cu nanoparticles through discharge process and then transform polyselenides into solid-phase Cu₂ Se, further suppressing the shuttling effect. This work provides a practical strategy to immobilize and transform sodium polyselenides for high-capacity and long-life Na-Se batteries.

MXene-encapsulated hollow Fe3O4 nanochains embedded in N-doped carbon nanofibers with dual electronic pathways as flexible anodes for high-performance Li-ion batteries

Fe3O4 is one of the promising anode materials in Li-ion batteries and a potential alternative to graphite due to the high specific capacity, natural abundance, environmental benignity, non-flammability, and better safety. Nevertheless, the sluggish intrinsic reaction kinetics and huge volume variation severely limit the reversible capacity and cycling life. In order to overcome these hurdles and enhance the cycling life of Fe3O4, a one-dimensional (1D) nanochain structure composed of 2D Ti3C2-encapsulated hollow Fe3O4 nanospheres homogeneously embedded in N-doped carbon nanofibers (Fe3O4@MXene/CNFs) is designed and demonstrated as a high-performance anode in Li-ion batteries. The distinctive 1D nanochain structure not only inherits the high electrochemical activity of Fe3O4, but also exhibits excellent electron and ion conductivity. The Ti3C2 layer on the Fe3O4 hollow nanospheres forms the primary electron transport pathway and the N-doped carbon nanofiber network provides the secondary transport pathway. At the same time, Ti3C2 flakes partially accommodate the large volume change of Fe3O4 during Li+ insertion/extraction. Density functional theory (DFT) calculations demonstrate that the Fe3O4@MXene/CNFs electrode can efficiently enhance the adsorption of Li+ to promote Li+ storage. As a result of the electrospinning process, self-restacking of Ti3C2 flakes and aggregation of Fe3O4 nanospheres can be prevented resulting in a larger surface area and more accessible active sites on the flexible anode. The Fe3O4@MXene/CNFs anode has remarkable electrochemical properties at high current densities. For example, a reversible capacity of 806 mA h g-1 can be achieved at 2 A g-1 even after 500 cycles, corresponding to an area specific capacity of 1.612 mA h cm-2 at 4 mA cm-2 and a capacity as high as 613 mA h g-1 is retained at 5 A g-1, corresponding to an area capacity of 1.226 mA h cm-2 at 10 mA cm-2. The results indicate that the Fe3O4@MXene/CNFs anode has excellent properties for Li-ion storage.