A Core–Shell Fe/Fe2O3 Nanowire as a High‐Performance Anode Material for Lithium‐Ion Batteries

The preparation of novel one‐dimensional core–shell Fe/Fe₂O₃ nanowires as anodes for high‐performance lithium‐ion batteries (LIBs) is reported. The nanowires are prepared in a facile synthetic process in aqueous solution under ambient conditions with subsequent annealing treatment that could tune the capacity for lithium storage. When this hybrid is used as an anode material for LIBs, the outer Fe₂O₃ shell can act as an electrochemically active material to store and release lithium ions, whereas the highly conductive and inactive Fe core functions as nothing more than an efficient electrical conducting pathway and a remarkable buffer to tolerate volume changes of the electrode materials during the insertion and extraction of lithium ions. The core–shell Fe/Fe₂O₃ nanowire maintains an excellent reversible capacity of over 767 mA h g^?1 at 500 mA g^?1 after 200 cycles with a high average Coulombic efficiency of 98.6 %. Even at 2000 mA g^?1, a stable capacity as high as 538 mA h g^?1 could be obtained. The unique composition and nanostructure of this electrode material contribute to this enhanced electrochemical performance. Due to the ease of large‐scale fabrication and superior electrochemical performance, these hybrid nanowires are promising anode materials for the next generation of high‐performance LIBs.     

Exchange‐Coupled fct‐FePd/α‐Fe Nanocomposite Magnets Converted from Pd/Fe3O4 Core/Shell Nanoparticles

We report the controlled synthesis of exchange‐coupled face‐centered tetragonal (fct) FePd/α‐Fe nanocomposite magnets with variable Fe concentration. The composite was converted from Pd/Fe₃O₄ core/shell nanoparticles through a high‐temperature annealing process in a reducing atmosphere. The shell thickness of core/shell Pd/Fe₃O₄ nanoparticles could be readily tuned, and subsequently the concentration of Fe in nanocomposite magnets was controlled. Upon annealing reduction, the hard magnetic fct‐FePd phase was formed by the interdiffusion between reduced α‐Fe and face‐centered cubic (fcc) Pd, whereas the excessive α‐Fe remained around the fct‐FePd grains, realizing exchange coupling between the soft magnetic α‐Fe and hard magnetic fct‐FePd phases. Magnetic measurements showed variation in the magnetic properties of the nanocomposite magnets with different compositions, indicating distinct exchange coupling at the interfaces. The coercivity of the exchange‐coupled nanocomposites could be tuned from 0.7 to 2.8 kOe and the saturation magnetization could be controlled from 93 to 160 emu g^?1. This work provides a bottom‐up approach using exchange‐coupled nanocomposites for engineering advanced permanent magnets with controllable magnetic properties.     

Nitrogen‐Doped Mesoporous Carbon‐Encapsulated MoO2 Nanobelts as a High‐Capacity and Stable Host for Lithium‐Ion Storage

N‐doped mesoporous carbon‐capped MoO₂ nanobelts (designated as MoO₂@NC) were synthesized and applied to lithium‐ion storage. Owing to the stable core–shell structural framework and conductive mesoporous carbon matrix, the as‐prepared MoO₂@NC shows a high specific capacity of around 700 mA h g⁻¹ at a current of 0.5 A g⁻¹, excellent cycling stability up to 100 cycles, and superior rate performance. The N‐doped mesoporous carbon can greatly improve the conductivity and provide uninhibited conducting pathways for fast charge transfer and transport. Moreover, the core–shell structure improved the structural integrity, leading to a high stability during the cycling process. All of these merits make the MoO₂@NC to be a suitable and promising material for lithium ion battery.     

CNT@Fe3O4@C Coaxial Nanocables: One‐Pot,Additive‐Free Synthesis and Remarkable Lithium Storage Behavior

By using carbon nanotubes (CNTs) as a shape template and glucose as a carbon precursor and structure‐directing agent, CNT@Fe₃O₄@C porous core/sheath coaxial nanocables have been synthesized by a simple one‐pot hydrothermal process. Neither a surfactant/ligand nor a CNT pretreatment is needed in the synthetic process. A possible growth mechanism governing the formation of this nanostructure is discussed. When used as an anode material of lithium‐ion batteries, the CNT@Fe₃O₄@C nanocables show significantly enhanced cycling performance, high rate capability, and high Coulombic efficiency compared with pure Fe₂O₃ particles and Fe₃O₄/CNT composites. The CNT@Fe₃O₄@C nanocables deliver a reversible capacity of 1290 mA h g^?1 after 80 cycles at a current density of 200 mA g^?1, and maintain a reversible capacity of 690 mA h g^?1 after 200 cycles at a current density of 2000 mA g^?1. The improved lithium storage behavior can be attributed to the synergistic effect of the high electronic conductivity support and the inner CNT/outer carbon buffering matrix.     

One‐Pot Synthesis of Pomegranate‐Structured Fe3O4/Carbon Nanospheres‐Doped Graphene Aerogel for High‐Rate Lithium Ion Batteries

A unique hierarchically nanostructured composite of iron oxide/carbon (Fe₃O₄/C) nanospheres‐doped three‐dimensional (3D) graphene aerogel has been fabricated by a one‐pot hydrothermal strategy. In this novel nanostructured composite aerogel, uniform Fe₃O₄ nanocrystals (5–10 nm) are individually embedded in carbon nanospheres (ca. 50 nm) forming a pomegranate‐like structure. The carbon matrix suppresses the aggregation of Fe₃O₄ nanocrystals, avoids direct exposure of the encapsulated Fe₃O₄ to the electrolyte, and buffers the volume expansion. Meanwhile, the interconnected 3D graphene aerogel further serves to reinforce the structure of the Fe₃O₄/C nanospheres and enhances the electrical conductivity of the overall electrode. Therefore, the carbon matrix and the interconnected graphene network entrap the Fe₃O₄ nanocrystals such that their electrochemical function is retained even after fracture. This novel hierarchical aerogel structure delivers a long‐term stability of 634 mA h g^?1 over 1000 cycles at a high current density of 6 A g^?1 (7 C), and an excellent rate capability of 413 mA h g^?1 at 10 A g^?1 (11 C), thus exhibiting great potential as an anode composite structure for durable high‐rate lithium‐ion batteries.     

Confined Nanospace Pyrolysis for the Fabrication of Coaxial Fe3O4@C Hollow Particles with a Penetrated Mesochannel as a Superior Anode for Li‐Ion Batteries

In this study, a method is developed to fabricate Fe₃O₄@C particles with a coaxial and penetrated hollow mesochannel based on the concept of “confined nanospace pyrolysis”. The synthesis involves the production of a polydopamine coating followed by a silica coating on a rod‐shaped β‐FeOOH nanoparticle, and subsequent treatment by using confined nanospace pyrolysis and silica removal procedures. Typical coaxial hollow Fe₃O₄@C possesses a rice‐grain morphology and mesoporous structure with a large specific surface area, as well as a continuous and flexible carbon shell. Electrochemical tests reveal that the hollow Fe₃O₄@C with an open‐ended nanostructure delivers a high specific capacity (ca. 864 mA h g^?1 at 1 A g^?1), excellent rate capability with a capacity of about 582 mA h g^?1 at 2 A g^?1, and a high Coulombic efficiency (>97 %). The excellent electrochemical performance benefits from the hollow cavity with an inner diameter of 18 nm and a flexible carbon shell that can accommodate the volume change of the Fe₃O₄ during the lithium insertion/extraction processes as well as the large specific surface area and open inner cavity to facilitate the rapid diffusion of lithium ions from electrolyte to active material. This fabrication strategy can be used to generate a hollow or porous metal oxide structure for high‐performance Li‐ion batteries.     

A Carbon‐Sulfur Hybrid with Pomegranate‐like Structure for Lithium‐Sulfur Batteries

A carbon‐sulfur hybrid with pomegranate‐like core–shell structure, which demonstrates a high rate performance and relatively high cyclic stability, is obtained through carbonization of a carbon precursor in the presence of a sulfur precursor (FeS₂) and a following oxidation of FeS₂ to sulfur by HNO₃. Such a structure effectively protects the sulfur and leaves enough buffer space after Fe³⁺ removal and, at the same time, has an interconnected conductive network. The capacity of the obtained hybrid is 450 mA h g^?1 under the current density of 5 C. This work provides a simple strategy to design and prepare various high‐performance carbon‐sulfur hybrids for lithium‐sulfur batteries.     

Supercritical Carbon Dioxide Assisted Deposition of Fe3O4 Nanoparticles on Hierarchical Porous Carbon and Their Lithium‐Storage Performance

A composite of highly dispersed Fe₃O₄ nanoparticles (NPs) anchored in three‐dimensional hierarchical porous carbon networks (Fe₃O₄/3DHPC) as an anode material for lithium‐ion batteries (LIBs) was prepared by means of a deposition technique assisted by a supercritical carbon dioxide (scCO₂)‐expanded ethanol solution. The as‐synthesized Fe₃O₄/3DHPC composite exhibits a bimodal porous 3D architecture with mutually connected 3.7 nm mesopores defined in the macroporous wall on which a layer of small and uniform Fe₃O₄ NPs was closely coated. As an anode material for LIBs, the Fe₃O₄/3DHPC composite with 79 wt % Fe₃O₄ (Fe₃O₄/3DHPC‐79) delivered a high reversible capacity of 1462 mA h g^?1 after 100 cycles at a current density of 100 mA g^?1, and maintained good high‐rate performance (728, 507, and 239 mA h g^?1 at 1, 2, and 5 C, respectively). Moreover, it showed excellent long‐term cycling performance at high current densities, 1 and 2 A g^?1. The enhanced lithium‐storage behavior can be attributed to the synergistic effect of the porous support and the homogeneous Fe₃O₄ NPs. More importantly, this straightforward, highly efficient, and green synthetic route will definitely enrich the methodologies for the fabrication of carbon‐based transition‐metal oxide composites, and provide great potential materials for additional applications in supercapacitors, sensors, and catalyses.     

Two‐Dimensional Cobalt‐/Nickel‐Based Oxide Nanosheets for High‐Performance Sodium and Lithium Storage

Two‐dimensional (2D) nanomaterials are one of the most promising types of candidates for energy‐storage applications due to confined thicknesses and high surface areas, which would play an essential role in enhanced reaction kinetics. Herein, a universal process that can be extended for scale up is developed to synthesise ultrathin cobalt‐/nickel‐based hydroxides and oxides. The sodium and lithium storage capabilities of Co₃O₄ nanosheets are evaluated in detail. For sodium storage, the Co₃O₄ nanosheets exhibit excellent rate capability (e.g., 179 mA h g^?1 at 7.0 A g^?1 and 150 mA h g^?1 at 10.0 A g^?1) and promising cycling performance (404 mA h g^?1 after 100 cycles at 0.1 A g^?1). Meanwhile, very impressive lithium storage performance is also achieved, which is maintained at 1029 mA h g^?1 after 100 cycles at 0.2 A g^?1. NiO and NiCo₂O₄ nanosheets are also successfully prepared through the same synthetic approach, and both deliver very encouraging lithium storage performances. In addition to rechargeable batteries, 2D cobalt‐/nickel‐based hydroxides and oxides are also anticipated to have great potential applications in supercapacitors, electrocatalysis and other energy‐storage‐/‐conversion‐related fields.     

Efficient Noble‐Metal‐Free γ‐Fe2O3@NiO Core–Shell Nanostructured Photocatalysts for Water Oxidation

Flowerlike noble‐metal‐free γ‐Fe₂O₃@NiO core–shell hierarchical nanostructures have been fabricated and examined as a catalyst in the photocatalytic oxidation of water with [Ru(bpy)₃](ClO₄)₂ as a photosensitizer and Na₂S₂O₈ as a sacrificial electron acceptor. An apparent TOF of 0.29 μmols^?1 m^?2 and oxygen yield of 51 % were obtained with γ‐Fe₂O₃@NiO. The γ‐Fe₂O₃@NiO core–shell hierarchical nanostructures could be easily separated from the reaction solution whilst maintaining excellent water‐oxidation activity in the fourth and fifth runs. The surface conditions of γ‐Fe₂O₃@NiO also remained unchanged after the photocatalytic reaction, as confirmed by X‐ray photoelectron spectroscopy (XPS).     

Boron‐Doped,Carbon‐Coated SnO2/Graphene Nanosheets for Enhanced Lithium Storage

Heteroatom doping is an effective method to adjust the electrochemical behavior of carbonaceous materials. In this work, boron‐doped, carbon‐coated SnO₂/graphene hybrids (BCTGs) were fabricated by hydrothermal carbonization of sucrose in the presence of SnO₂/graphene nanosheets and phenylboronic acid or boric acid as dopant source and subsequent thermal treatment. Owing to their unique 2D core–shell architecture and B‐doped carbon shells, BCTGs have enhanced conductivity and extra active sites for lithium storage. With phenylboronic acid as B source, the resulting hybrid shows outstanding electrochemical performance as the anode in lithium‐ion batteries with a highly stable capacity of 1165 mA h g^?1 at 0.1 A g^?1 after 360 cycles and an excellent rate capability of 600 mA h g^?1 at 3.2 A g^?1, and thus outperforms most of the previously reported SnO₂‐based anode materials.     

α‐Fe2O3 Film with Highly Photoactivity for Non‐enzymatic Photoelectrochemical Detection of Glucose

A non‐enzyme photoelectrochemical (PEC) glucose sensor based on α‐Fe₂O₃ film is investigated. The α‐Fe₂O₃ film was fabricated via a simple spin coating method. The proposed glucose sensor exhibits good selectivity, a fast response time of <5 s, a linear range of 0.05 to 6.0 mM, sensitivity of 17.23 μA mM^?1 cm^?2 and a detection limit of 0.05 μM. Meanwhile, the excellent performances of the α‐Fe₂O₃ sensor were obtained in reproducibility and the long‐term stability under ambient condition. The linear amperometric response of the sensor covers the glucose levels in physiological and clinical for diabetic patients. Therefore, this non‐enzyme PEC sensor based on α‐Fe₂O₃ film has a great potential application in the development of glucose sensors.     

Fluorine‐Doped Fe2O3 as High Energy Density Electroactive Material for Hybrid Supercapacitor Applications

Nanostructured α‐Fe₂O₃ with and without fluorine substitution were successfully obtained by a green route, that is, microwave irradiation. The hematite phase materials were evaluated as a high‐performance electrode material in a hybrid supercapacitor configuration along with activated carbon (AC). The presence of fluorine was confirmed through X‐ray photoelectron spectroscopy and transmission electron microscopy. Fluorine‐doped Fe₂O₃ (F‐Fe₂O₃) exhibits an enhanced pseudocapacitive performance compared to that of the bare hematite phase. The F‐Fe₂O₃/AC cell delivered a specific capacitance of 71 F g^?1 at a current density of 2.25 A g^?1 and retained approximately 90 % of its initial capacitance after 15 000 cycles. Furthermore, the F‐Fe₂O₃/AC cell showed a very high energy density of about 28 W h kg^?1 compared to bare hematite phase (～9 W h kg^?1). These data clearly reveal that the electrochemical performance of Fe₂O₃ can be improved by fluorine doping, thereby dramatically improving the energy density of the system.     

MnO@Carbon Core–Shell Nanowires as Stable High‐Performance Anodes for Lithium‐Ion Batteries

A facile method is presented for the large‐scale preparation of rationally designed mesocrystalline MnO@carbon core–shell nanowires with a jointed appearance. The nanostructures have a unique arrangement of internally encapsulated highly oriented and interconnected MnO nanorods and graphitized carbon layers forming an external coating. Based on a comparison and analysis of the crystal structures of MnOOH, Mn₂O₃, and MnO@C, we propose a sequential topotactic transformation of the corresponding precursors to the products. Very interestingly, the individual mesoporous single‐crystalline MnO nanorods are strongly interconnected and maintain the same crystallographic orientation, which is a typical feature of mesocrystals. When tested for their applicability to Li‐ion batteries (LIB), the MnO@carbon core–shell nanowires showed excellent capacity retention, superior cycling performance, and high rate capability. Specifically, the MnO@carbon core–shell nanostructures could deliver reversible capacities as high as 801 mA h g^?1 at a high current density of 500 mA g^?1, with excellent electrochemical stability after testing over 200 cycles, indicating their potential application in LIBs. The remarkable electrochemical performance can mainly be attributed to the highly uniform carbon layer around the MnO nanowires, which is not only effective in buffering the structural strain and volume variations of anodes during repeated electrochemical reactions, but also greatly enhances the conductivity of the electrode material. Our results confirm the feasibility of using these rationally designed composite materials for practical applications. The present strategy is simple but very effective, and appears to be sufficiently versatile to be extended to other high‐capacity electrode materials with large volume variations and low electrical conductivities.     

Rational Construction of 2D Fe3O4@Carbon Core–Shell Nanosheets as Advanced Anode Materials for High-Performance Lithium-Ion Half/Full Cells

Transition metal oxides have vastly limited practical application as electrode materials for lithium-ion batteries (LIBs) due to their rapid capacity decay. Here, a versatile strategy to mitigate the volume expansion and low conductivity of Fe₃O₄ by coating a thin carbon layer on the surface of Fe₃O₄ nanosheets (NSs) was employed. Owing to the 2D core–shell structure, the Fe₃O₄@C NSs exhibit significantly improved rate performance and cycle capability compared with bare Fe₃O₄ NSs. After 200 cycles, the discharge capacity at 0.5 A g⁻¹ was 963 mA h g⁻¹ (93 % retained). Moreover, the reaction mechanism of lithium storage was studied in detail by ex situ XRD and HRTEM. When coupled with a commercial LiFePO₄ cathode, the resulting full cell retains a capacity of 133 mA h g⁻¹ after 100 cycles at 0.1 A g⁻¹, which demonstrates its superior energy storage performance. This work provides guidance for constructing 2D metal oxide/carbon composites with high performance and low cost for the field of energy storage.     

Hydrothermal Synthesis and Properties of Controlled α‐Fe2O3 Nanostructures in HEPES Solution

A facile, template‐free, and environmentally friendly hydrothermal strategy was explored for the controllable synthesis of α‐Fe₂O₃ nanostructures in HEPES solution (HEPES=2‐[4‐(2‐hydroxyethyl)‐1‐piperazinyl]ethanesulfonic acid). The effects of experimental parameters including HEPES/FeCl₃ molar ratio, pH value, reaction temperature, and reaction time on the formation of α‐Fe₂O₃ nanostructures have been investigated systematically. Based on the observations of the products, the function of HEPES in the reaction is discussed. The different α‐Fe₂O₃ nanostructures possess different optical, magnetic properties, and photocatalytic activities, depending on the shape and size of the sample. In addition, a novel and facile approach was developed for the synthesis of Au/α‐Fe₂O₃ and Ag/α‐Fe₂O₃ nanocomposites in HEPES buffer solution; this verified the dual function of HEPES both as reductant and stabilizer. This work provides a new strategy for the controllable synthesis of transition metal oxide nanostructures and metal‐supported nanocomposites, and gives a strong evidence of the relationship between the property and morphology/size of nanomaterials.     

Electrochemical and Structural Study of Layered P2‐Type Na2/3Ni1/3Mn2/3O2 as Cathode Material for Sodium‐Ion Battery

P2‐type Na_2/3Ni_1/3Mn_2/3O₂ was synthesized by a controlled co‐precipitation method followed by a high‐temperature solid‐state reaction and was used as a cathode material for a sodium‐ion battery (SIB). The electrochemical behavior of this layered material was studied and an initial discharge capacity of 151.8 mA h g^?1 was achieved in the voltage range of 1.5–3.75 V versus Na⁺/Na. The retained discharge capacity was found to be 123.5 mA h g^?1 after charging/discharging 50 cycles, approximately 81.4 % of the initial discharge capacity. In situ X‐ray diffraction analysis was used to investigate the sodium insertion and extraction mechanism and clearly revealed the reversible structural changes of the P2‐Na_2/3Ni_1/3Mn_2/3O₂ and no emergence of the O2‐Ni_1/3Mn_2/3O₂ phase during the cycling test, which is important for designing stable and high‐performance SIB cathode materials.     

Sodium‐Ion Storage Properties of FeS–Reduced Graphene Oxide Composite Powder with a Crumpled Structure

The sodium‐ion storage properties of FeS–reduced graphene oxide (rGO) and Fe₃O₄‐rGO composite powders with crumpled structures have been studied. The Fe₃O₄‐rGO composite powder, prepared by one‐pot spray pyrolysis, could be transformed to an FeS‐rGO composite powder through a simple sulfidation treatment. The mean size of the Fe₃O₄ nanocrystals in the Fe₃O₄‐rGO composite powder was 4.4 nm. After sulfidation, FeS nanocrystals of size several hundred nanometers were confined within the crumpled structure of the rGO matrix. The initial discharge capacities of the FeS‐rGO and Fe₃O₄‐rGO composite powders were 740 and 442 mA h g^?1, and their initial charge capacities were 530 and 165 mA h g^?1, respectively. The discharge capacities of the FeS‐rGO and Fe₃O₄‐rGO composite powders at the 50th cycle were 547 and 150 mA h g^?1, respectively. The FeS‐rGO composite powder showed superior sodium‐ion storage performance compared to the Fe₃O₄‐rGO composite powder.     

Cu3V2O8 Nanoparticles as Intercalation‐Type Anode Material for Lithium‐Ion Batteries

Cu₃V₂O₈ nanoparticles with particle sizes of 40–50 nm have been prepared by the co‐precipitation method. The Cu₃V₂O₈ electrode delivers a discharge capacity of 462 mA h g^?1 for the first 10 cycles and then the specific capacity, surprisingly, increases to 773 mA h g^?1 after 50 cycles, possibly as a result of extra lithium interfacial storage through the reversible formation/decomposition of a solid electrolyte interface (SEI) film. In addition, the electrode shows good rate capability with discharge capacities of 218 mA h g^?1 under current densities of 1000 mA g^?1. Moreover, the lithium storage mechanism for Cu₃V₂O₈ nanoparticles is explained on the basis of ex situ X‐ray diffraction data and high‐resolution transmission electron microscopy analyses at different charge/discharge depths. It was evidenced that Cu₃V₂O₈ decomposes into copper metal and Li₃VO₄ on being initially discharged to 0.01 V, and the Li₃VO₄ is then likely to act as the host for lithium ions in subsequent cycles by means of the intercalation mechanism. Such an “in situ” compositing phenomenon during the electrochemical processes is novel and provides a very useful insight into the design of new anode materials for application in lithium‐ion batteries.     

Preparation of Li4Ti5O12 Yolk–Shell Powders by Spray Pyrolysis and their Electrochemical Properties

We have reported for the first time the preparation of yolk–shell‐structured Li₄Ti₅O₁₂ powders for use as anode materials in lithium‐ion batteries. One Li₄Ti₅O₁₂ yolk–shell‐particle powder is directly formed from each droplet containing lithium, titanium, and carbon components inside the hot wall reactor maintained at 900 °C. The precursor Li₄Ti₅O₁₂ yolk–shell‐particle powders, which are directly prepared by spray pyrolysis, have initial discharge and charge capacities of 155 and 122 mA h g^?1, respectively, at a current density of 175 mA g^?1. Post‐treatment of the yolk–shell‐particle powders at temperatures of 700 and 800 °C improves the initial discharge and charge capacities. The initial discharge capacities of the Li₄Ti₅O₁₂ powders with a yolk–shell structure and a dense structure post‐treated at 800 °C are 189 and 168 mA h g^?1, respectively. After 100 cycles, the corresponding capacities are 172 and 152 mA h g^?1, respectively (retentions of 91 and 90 %).