Fe2O3/SnSSe Hexagonal Nanoplates as Lithium-Ion Batteries Anode

A synergistic heterojunction of SnS2/SnSSe nanosheets on GaN for advanced self-powered photodetectors

Tin-based TMDCs are gaining traction in optoelectronics due to their eco-friendliness and easy synthesis, contrasting Mo/W-based counterparts. This study pioneers the solvothermal synthesis of highly crystalline SnSSe alloy, akin to Janus structures, bridging a notable research gap. By integrating SnS2/SnSSe materials onto a GaN platform, a synergistic heterojunction is created, enhancing light absorption and the electron-hole pair separation efficiency, demonstrating a self-powered photodetection. The GaN/SnS2/SnSSe heterojunction showcases a staircase-like (type-II) band alignment and exceptional performance metrics: high photoresponsivity of 314.96 A W-1, specific detectivity of 2.0 × 1014 jones, and external quantum efficiency of 10.7 × 104% under 365 nm illumination at 150 nW cm-2 intensity and 3 V bias. Notably, the device displays intensity-dependent photocurrent and photoswitching behaviors without external bias, highlighting its unique self-powered attributes. This study underscores SnS2's significance in optoelectronics and explores SnSSe integration into van der Waals heterostructures, promising advanced photodetection devices and bias-free optoelectronics.

Progress and perspectives on iron-based electrode materials for alkali metal-ion batteries: a critical review

Iron-based materials with significant physicochemical properties, including high theoretical capacity, low cost and mechanical and thermal stability, have attracted research attention as electrode materials for alkali metal-ion batteries (AMIBs). However, practical implementation of some iron-based materials is impeded by their poor conductivity, large volume change, and irreversible phase transition during electrochemical reactions. In this review we critically assess advances in the chemical synthesis and structural design, together with modification strategies, of iron-based compounds for AMIBs, to obviate these issues. We assess and categorize structural and compositional regulation and its effects on the working mechanisms and electrochemical performances of AMIBs. We establish insight into their applications and determine practical challenges in their development. We provide perspectives on future directions and likely outcomes. We conclude that for boosted electrochemical performance there is a need for better design of structures and compositions to increase ionic/electronic conductivity and the contact area between active materials and electrolytes and to obviate the large volume change and low conductivity. Findings will be of interest and benefit to researchers and manufacturers for sustainable development of advanced rechargeable ion batteries using iron-based electrode materials.

High-Performance Sodium-Ion Batteries Enabled by 3D Nanoflowers Comprised of Ternary Sn-Based Dichalcogenides Embedded in Nitrogen and Sulfur Dual-Doped Carbon

To make sodium-ion batteries a realistic option for everyday energy storage, a practicable method is to enhance the kinetics of Na+ reactions through the development of structurally stable electrode materials. This study utilizes ternary Sn-based dichalcogenide (SnS1.5 Se0.5 ) in the design of electrode material to tackle several issues that adversely hinder the performance and longevity of sodium-ion batteries. First, the incorporation of Se into the SnS structure enhances its electrical conductivity and stability. Second, the ternary composition restricts the formation of intermediates during the desodiation/sodiation process, resulting in better electrode reaction reversibility. Finally, SnS1.5 Se0.5 lowers the diffusion barrier of Na, thereby facilitating rapid and efficient ion transport within the electrode material. Moreover, nitrogen and sulfur dual-doped carbon (NS-C) is used to enhance surface chemistry and ionic/electrical conductivity of SnS1.5 Se0.5 , leading to a pseudocapacitive storage effect that presents a promising potential for high-performance energy storage devices. The study has successfully developed a SnS1.5 Se0.5 /NS-C anode, exhibiting remarkable rate capability and cycle stability, retaining a capacity of 647 mAh g-1 even after 10 000 cycles at 5 A g-1 in half-cell tests. In full-cell tests, Na3 V2 (PO4 )3 //SnS1.5 Se0.5 /NS-C delivers a high energy density of 176.6 Wh kg-1 . In addition, the Na+ storage mechanism of SnS1.5 Se0.5 /NS-C is explored through ex situ tests and DFT calculations. The findings suggest that the ternary Sn-based dichalcogenides can considerably enhance the performance of the anode, enabling efficient large-scale storage of sodium. These findings hold great promise for the advancement of high-performance energy storage devices for practical applications.

Enabling Reversible Reaction by Uniform Distribution of Heterogeneous Intermediates on Defect-Rich SnSSe/C Layered Heterostructure for Ultralong-Cycling Sodium Storage

2D layered Sn-based materials have attracted enormous attention due to their remarkable performance in sodium-ion batteries. Nevertheless, this promising candidate involves a complex Na⁺ -storage process with multistep conversion-alloying reactions, which induces the uneven dispersion of heterogeneous intermediate accompanied by severe agglomeration of metallic Sn⁰ , inescapably resulting in poor reaction reversibility with sluggish rate capability and inferior cyclic lifespan. Herein, a delicately layered heterostructure SnSSe/C consisting of defect-rich SnSSe and graphene is designed and successfully achieved via a facile hydrothermal process. The equal anionic substitution of Se in SnSSe crystal can trigger numerous defects, which can not only facilitate Na⁺ diffusion but also accelerate the nucleation process by inducing quantum-dot-level uniform distribution of heterogeneous intermediates, Na₂ Se/Na₂ S and Sn⁰ . Concurrently, in situ formed uniform Na₂ Se/Na₂ S grain boundaries confined by this unique layered heterostructure may effectively suppress the agglomeration of metallic Sn⁰ nanograins and boost the reversibility of conversion-alloying reaction. As a result, the SnSSe/C displays significant improvement in Na-storage performance, in terms of remarkable rate capability and ultralong cycling lifespan. This work, focusing on controlling intermediate distribution, provides an effective strategy to boost reaction reversibility, which can be wildly employed in conversion-based electrodes for energy storage regions.

Heterostructure Fe2O3 nanorods@imine-based covalent organic framework for long cycling and high-rate lithium storage

Fe₂O₃ as an anode for lithium-ion batteries has attracted intense attention because of its high theoretical capacity, natural abundance, and good safety. However, the inferior cycling stability, low-rate performance, and limited composite varieties hinder the application of Fe₂O₃-based materials. In this work, an Fe₂O₃@COF-LZU1 (FO@LZU1) anode was prepared via an imine-based covalent organic framework (COF-LZU1) covering on the exterior surface of Fe₂O₃ after rational optimization. With its unique heterostructure, the COF-LZU1 layer not only effectively alleviated the volume expansion during cycling but also improved the charge-transfer capability because of the π-conjugated system. Moreover, the organic functional group (CN, benzene ring) for COF-LZU1 provided more redox-active sites for Li⁺ storage. Under the contributions of both Fe₂O₃ nanorods and COF-LZU1, the FO@LZU1_50% exhibited an ultrahigh initial capacity and long-term cycling performance with initial discharge capacities of 2143 and 2171 mA h g^-1 after 300 cycles under 0.1 A g^-1, and rate performance of 1310 and 501 mA h g^-1 at 0.3 and 3 A g^-1, respectively. In addition, a high retention capacity of 1185 mA h g^-1 was achieved at 1 A g^-1 after 500 cycles. Furthermore, a full-cell with the FO@LZU1_50% anode and LiCoO₂ cathode exhibited superior cycling and rate performance, which still maintained a reversible capacity of 260 mA h g^-1 after 200 cycles even at a current density of 1 A g^-1. The proposed strategy offers a new perspective for exploring the high-rate capability and designability of Fe₂O₃-based electrode materials.

Solution-Synthesized SnSe1-xSx: Dual-Functional Materials with Enhanced Electrochemical Storage and Thermoelectric Performance

The exploration of materials with multifunctional properties, such as energy harvesting and storage, is crucial in integrated energy devices and technologies. Herein, through an organic-free "soft chemical" solution method, a series of dual-functional SnSe_1-xS_x (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles have been developed toward high-performance electrochemical energy storage and thermoelectric conversion. Among the synthesized S-substituted SnSe, SnSe_0.5S_0.5 exhibits the highest rate capacity (546.1 mA h g^-1 at 2 A g^-1) and the best reversible capacity (556.2 mA h g^-1 at 0.1 A g^-1 after 100 cycles), which are much enhanced compared to those of SnSe. Density functional theory calculation confirms that the composition regulation by S substitution can lower the diffusion barrier of Li⁺, boost the diffusion rate of Li⁺, and in turn enhance the electrochemical kinetics, thus increasing the Li⁺ storage performance. Meanwhile, partially replacing Se by S decreases the lattice thermal conductivity, leading to an improved peak zT of 0.64 at 773 K in SnSe_0.9S_0.1, which is enhanced compared to the value for SnSe obtained at the same temperature. This study develops a combined composition tuning-nanostructuring approach for optimizing the electrochemical and thermoelectric performance of dual-functional SnSe.

Flowerlike Tin Diselenide Hexagonal Nanosheets for High-Performance Lithium-Ion Batteries

SnSe2 nanosheet is a common anode for lithium-ion batteries (LIBs), but its severe agglomeration hinders its practical application. Herein, a three-dimensional (3D) SnSe2 nanoflower (F-SnSe2) composed of non-stacking vertical upward hexagonal nanosheets was prepared through a colloidal method as an anode material for LIBs. Benefiting from the advantages of fast reaction-diffusion kinetics and buffering unavoidable volume variation during cycling, the F-SnSe2 electrode displays remarkable specific capacity of 795 mAh g-1 after 100 cycles at 100 mA g-1 and superior rate performance (282 mAh g-1 at 2,000 mA g-1). This work provides an effective way to get non-stacking nanosheets in energy storage field.

Facile and scalable synthesis of α-Fe2O3/γ-Fe2O3/Fe/C nanocomposite as advanced anode materials for lithium/sodium ion batteries

To develop low-cost advanced anode materials for lithium/sodium ion batteries, the chemical reaction equilibrium of Fe(NO₃)₃ and glucose in hot aqueous solution is creatively used to fabricate a new α-Fe₂O₃/γ-Fe₂O₃/Fe/C nanocomposite with the primary particle sizes concentrated at 25-80 nm. As anodes for lithium ion batteries, it exhibits a discharge capacity of ∼878 mAh g^-1 after 200 cycles at a current density of 200 mA g^-1. Moreover, even after 1000 cycles at a current density of 3200 mA g^-1, the discharge capacity is as high as ∼532 mAh g^-1, with a capacity retention of over than 100% against that of the second cycle. As anodes for sodium ion batteries, the nanocomposite displays a stable discharge capacity of ∼400 mAh g^-1 at a current density of 100 mA g^-1 and no obvious capacity degradation happens after 200 cycles. During cycling, the α-Fe₂O₃/γ-Fe₂O₃/Fe/C nanocomposite electrodes shows high structural stability and relatively faster reaction kinetics, which should be responsible for its excellent electrochemical performance. This work provides a facile and scalable route to synthesize high-performance and low-cost Fe₂O₃-based nanocomposite for the secondary batteries.

Micro/Nanoengineered α-Fe2 O3 Nanoaggregate Conformably Enclosed by Ultrathin N-Doped Carbon Shell for Ultrastable Lithium Storage and Insight into Phase Evolution Mechanism

The Fe-based transition metal oxides are promising anode candidates for lithium storage considering their high specific capacity, low cost, and environmental compatibility. However, the poor electron/ion conductivity and significant volume stress limit their cycle and rate performances. Furthermore, the phenomena of capacity rise and sudden decay for α-Fe₂ O₃ have appeared in most reports. Here, a uniform micro/nano α-Fe₂ O₃ nanoaggregate conformably enclosed in an ultrathin N-doped carbon network (denoted as M/N-α-Fe₂ O₃ @NC) is designed. The M/N porous balls combine the merits of secondary nanoparticles to shorten the Li⁺ transportation pathways as well as alleviating volume expansion, and primary microballs to stabilize the electrode/electrolyte interface. Furthermore, the ultrathin carbon shell favors fast electron transfer and protects the electrode from electrolyte corrosion. Therefore, the M/N-α-Fe₂ O₃ @NC electrode delivers an excellent reversible capacity of 901 mA h g^-1 with capacity retention up to 94.0 % after 200 cycles at 0.2 A g^-1 . Notably, the capacity rise does not happen during cycling. Moreover, the lithium storage mechanism is elucidated by ex situ XRD and HRTEM experiments. It is verified that the reversible phase transformation of α↔γ occurs during the first cycle, whereas only the α-Fe₂ O₃ phase is reversibly transformed during subsequent cycles. This study offers a simple and scalable strategy for the practical application of high-performance Fe₂ O₃ electrodes.

Heterostructured SnO2-SnS2@C Embedded in Nitrogen-Doped Graphene as a Robust Anode Material for Lithium-Ion Batteries

Tin-based anode materials with high capacity attract wide attention of researchers and become a strong competitor for the next generation of lithium-ion battery anode materials. However, the poor electrical conductivity and severe volume expansion retard the commercialization of tin-based anode materials. Here, SnO₂-SnS₂@C nanoparticles with heterostructure embedded in a carbon matrix of nitrogen-doped graphene (SnO₂-SnS₂@C/NG) is ingeniously designed in this work. The composite was synthesized by a two-step method. Firstly, the SnO₂@C/rGO with a nano-layer structure was synthesized by hydrothermal method as the precursor, and then the SnO₂-SnS₂@C/NG composite was obtained by further vulcanizing the above precursor. It should be noted that a carbon matrix with nitrogen-doped graphene can inhibit the volume expansion of SnO₂-SnS₂ nanoparticles and promote the transport of lithium ions during continuous cycling. Benefiting from the synergistic effect between nanoparticles and carbon matrix with nitrogen-doped graphene, the heterostructured SnO₂-SnS₂@C/NG further fundamentally confer improved structural stability and reaction kinetics for lithium storage. As expected, the SnO₂-SnS₂@C/NG composite exhibited high reversible capacity (1201.2 mA h g⁻¹ at the current rate of 0.1 A g⁻¹), superior rate capability and exceptional long-life stability (944.3 mAh g⁻¹ after 950 cycles at the current rate of 1.0 A g⁻¹). The results demonstrate that the SnO₂-SnS₂@C/NG composite is a highly competitive anode material for LIBs.

A Double-Buffering Strategy to Boost the Lithium Storage of Botryoid MnOx /C Anodes

Transition metal oxides (TMOs) are regarded as promising candidates for anodes of lithium ion batteries, but their applications have been severely hindered by poor material conductivity and lithiated volume expansion. As a potential solution, herein is presented a facile approach, by electrospinning a manganese-based metal organic framework (Mn-MOF), to fabricate yolk-shell MnO_x nanostructures within carbon nanofibers in a botryoid morphology. While the yolk-shell structure accomodates the lithiated volume expansion of MnO_x , the fiber confinement ensures the structural integrity during charge/discharge, achieving a so-called double-buffering for cyclic volume fluctuation. The formation mechanism of the yolk-shell structure is well elucidated through comprehensive instrumental characterizations and cogitative control experiments, following a combined Oswald ripening and Kirkendall process. Outstanding electrochemical performances are demonstrated with prolonged stability over 1000 cycles, boosted by the double-buffering design, as well as the "breathing" effect of lithiation/delithiation witnessed by ex situ imaging. Both the fabrication methodology and electrochemical understandings gained here for nanostructured MnO_x can also be extended to other TMOs toward their ultimate implementation in high-performance lithium ion batteries (LIBs).

Biomimetic Straw-Like Bundle Cobalt-Doped Fe2 O3 Electrodes towards Superior Lithium-Ion Storage

Biomimetic straw-like bundles of Co-doped Fe₂ O₃ (SCF), with Co²⁺ incorporated into the lattice of α-Fe₂ O₃ , was fabricated through a cost-effective hydrothermal process and used as the anode material for lithium-ion batteries (LIBs). The SCF exhibited ultrahigh initial discharge specific capacity (1760.7 mA h^-1  g^-1 at 200 mA g^-1 ) and cycling stability (with the capacity retention of 1268.3 mA h^-1  g^-1 after 350 cycles at 200 mA g^-1 ). In addition, a superior rate capacity of 376.1 mA h^-1  g^-1 was obtained at a high current density of 4000 mA g^-1 . The remarkable electrochemical lithium storage of SCF is attributed to the Co-doping, which increases the unit cell volume and affects the whole structure. It makes the Li⁺ insertion-extraction process more flexible. Meanwhile, the distinctive straw-like bundle structure can accelerate Li ion diffusion and alleviate the huge volume expansion upon cycling.

Constructing Three-Dimensional Porous Carbon Framework Embedded with FeSe2 Nanoparticles as an Anode Material for Rechargeable Batteries

Metal selenides have caused widespread concern due to their high theoretical capacities and appropriate working potential; however, they suffer from large volume variation during cycling and low electrical conductivity, which limit their practical applications. In this article, a three-dimensional (3D) porous carbon framework embedded with homogeneous FeSe₂ nanoparticles (3D porous FeSe₂/C composite) was synthesized by a facile calcined approach, following a selenized method without a template. As the uniformity of FeSe₂ nanoparticles and 3D porous structure are beneficial to accommodate volume stress upon cycling and shorten electrons/ions transport path, associated with carbon as a buffer matrix for increasing conductivity, the 3D porous FeSe₂/C composite displays excellent electrochemical properties with high reversible capacities of 798.4 and 455.0 mA h g^-1 for lithium-ion batteries and sodium-ion batteries, respectively, when the current density is 100 mA g^-1 after 100 cycles. In addition, the as-prepared composite exhibits good cycling stability as compared to bare FeSe₂ nanoparticles. Therefore, the facile synthetic strategy in the current work provides a new perspective in constructing a high-performance anode.

Low-Temperature Assembly of Ultrathin Amorphous MnO2 Nanosheets over Fe2O3 Spindles for Enhanced Lithium Storage

Carbon coating is an effective method to enhance the lithium storage of metal oxides, which, however, suffers from harsh conditions in high-temperature hydrolysis of organic mass at inert atmosphere and compromised capacity due to the presence of low-capacity carbon. We herein report a direct assembly of ultrathin amorphous MnO₂ nanosheets with thickness less than 3 nm over Fe₂O₃ nanospindle backbones at 95 °C as a mild-condition, short-process, and upscalable alternative to the classic carbon-coating method. The assembly of the amorphous MnO₂ nanosheets significantly increases the electrical conductivity of Fe₂O₃ nanospindles. When evaluated as an anode for lithium-ion batteries, the Fe₂O₃@amorphous MnO₂ electrode shows enhanced capacity retention compared to that of the Fe₂O₃ nanospindle electrode. In situ transmission electron microscopy and in situ X-ray diffraction observations of the electrochemically driven lithiation/delithiation of the Fe₂O₃@amorphous MnO₂ electrode indicate that the assembled amorphous MnO₂ nanosheets are in situ transformed into a Fe-Mn-O protection layer for better electrical conductivity, uncompromised Li⁺ penetration, and enhanced structural integration. The Fe₂O₃@amorphous MnO₂ electrode therefore has a reversible capacity of 555 mAh g^-1 after 100 galvanostatic charge/discharge cycles at 1000 mA g^-1, comparable with that of the Fe₃O₄@C electrode derived via the classic carbon-coating route.