Fabrication of SnS2/Mn2SnS4/Carbon Heterostructures for Sodium-Ion Batteries with High Initial Coulombic Efficiency and Cycling Stability

Dual-Driven Ion/Electron Migration and Sodium Storage by In Situ Introduction of Copper Ions and a Carbon-Conductive Framework in a Tin-Based Sulfide Anode

Tin sulfide (SnS) has emerged as a promising anode material for sodium ion batteries (SIBs) due to its high theoretical capacity and large interlayer spacing. However, several challenges, such as severe insufficient electrochemical reactivity, rapid capacity degradation, and poor rate performance, still hinder its application in SIBs. In this study, in situ introduction of copper ions and a carbon conductive framework to form SnS nanocrystals embedded in a Cu2SnS3 lamellar structure heterojunction composite (SnS/Cu2SnS3/RGO) with graphene as the supporting material is proposed to achieve dual-driven sodium ion/electron migration during the continuous electrochemical process. The designed structure facilitates the preferential electrochemical reduction of copper ions into copper nanocrystals during the discharge process and functions as a catalytically active center to promote multivalence tin sodiation reaction. Furthermore, during the charging process, the presence of copper nanocrystals also facilitates efficient desodiation of NaxSn and further activates to form higher valence state sulfides. As a result, the SnS/Cu2SnS3/RGO composite demonstrates high cycling stability with a high reversible capacity of 395 mAh g-1 at 5A g-1 after 500 cycles with a capacity retention of 85.6%. In addition, the assembled Na3V2(PO4)3∥SnS/Cu2SnS3/RGO sodium ion full cell achieves 93.7% capacity retention after 80 cycles at 0.5 A g-1.

Engineering (FeSn)/S nanocubes heterojunctions for improved sodium ion battery performance

Transition metal sulfides have emerged as compelling anode materials for sodium-ion batteries (SIBs), leveraging their abundant elemental reserves and high theoretical capacities. However, the reaction of sulfur with Na ions is usually accompanied by significant volume dilation, which hinders their further development and application. Hence, constructing bimetallic sulfide (FeSn)/S for SIBs anode material greatly alleviates the circulation attenuation caused by volume expansion. Through constructing bimetallic heterojunction materials from nanocube precursors, the (FeSn)/S anode material retains a high specific capacity of 578 mAh/g at an intense current density of 2 A/g after 1000 cycles, and exhibits an great rate capability, delivering 796 mAh/g at 100 mA/g. The excellent electrochemical performance of the heterojunction material presents a promising solution to the enduring quest for enhanced anode material for SIBs.

Template-Assisted Epitaxial Growth of Ordered SnO2 Nanorods Arrays with Different Hollow Structures for High-Performance Sodium Storage

Anode materials for sodium ion batteries (SIBs) are confronted with severe volume expansion and poor electrical conductivity. Construction of assembled structures featuring hollow interior and carbon material modification is considered as an efficient strategy to address the issues. Herein, a novel template-assisted epitaxial growth method, ingeniously exploiting lattice matching nature, is developed to fabricate hollow ordered architectures assembled by SnO2 nanorods. SnO2 nanorods growing along [100] direction can achieve lattice-matched epitaxial growth on (110) plane of α-Fe2O3. Driven by the lattice matching, different α-Fe2O3 templates possessing different crystal plane orientations enable distinct assembly modes of SnO2, and four kinds of hollow ordered SnO2@C nanorods arrays (HONAs) with different morphologies including disc, hexahedron, dodecahedron and tetrakaidecahedron (denoted as Di-, He-, Do-, and Te-SnO2@C) are achieved. Benefiting from the synergy of hollow structure, carbon coating and ordered assembly structure, good structural integrity and stability and enhanced electrical conductivity are realized, resulting in impressive sodium storage performances when utilized as SIB anodes. Specifically, Te-SnO2@C HONAs exhibit excellent rate capability (385.6 mAh·g-1 at 2.0 A·g-1) and remarkable cycling stability (355.4 mAh·g-1 after 2000 cycles at 1.0 A·g-1). This work provides a promising route for constructing advanced SIB anode materials through epitaxial growth for rational structural design.

Heterostructured Mn-Sn Bimetallic Sulfide Nanocubes Confined in N, S-co-Doped Carbon Framework as High-Performance Anodes for Sodium-Ion Batteries

Benefiting from its high theoretical capacity, tin disulfide (SnS2) draws abundant interest and attention for its promising practical prospect for sodium-ion batteries (SIBs). However, the huge volumetric variation in sodiation/desodiation reactions usually results in the fast decay of rate and cycling properties, which seriously obstructs its future applicable foregrounds. Herein, heterostructured Mn-Sn bimetallic sulfide nanocubes confined in N and S-codoped carbon (MSS@NSC) were rationally designed via a facile coprecipitation followed by a sulfurization strategy. When used as anodes for SIBs, the heterojunctions at the interfaces effectively accelerate the Na+ diffusion rate to promote the sodium-storage reaction kinetics. The N and S-codoped carbon provides a rapid conductive framework for the fast charge transport during the sodium-storage process. Moreover, the beneficial confinement effect of the NSC layer effectively guarantees a superb cycle property for the MSS@NSC anode. The favorable synergistic effects between the highly conductive framework of the NSC and MSS heterostructure endow the MSS@NSC anode with satisfactory electrochemical Na-storage properties.

Synergistically Coupling Atomic-Level Defect-Manipulation and Nanoscopic-Level Interfacial Engineering Enables Fast and Durable Sodium Storage

Through inducing interlayer anionic ligands and functionally modifying conductive carbon-skeleton on the transition metal chalcogenides (TMCs) parent to achieve atomic-level defect-manipulation and nanoscopic-level architecture design is of great significance, which can broaden interlayer distance, optimize electronic structure, and mitigate structural deformation to endow high-efficiency battery performance of TMCs. Herein, an intriguing 3D biconcave hollow-tyre-like anode constituted by carbon-packaged defective-rich SnSSe nanosheet grafting onto Aspergillus niger spores-derived hollow-carbon (ANDC@SnSSe@C) is reported. Systematically experimental investigations and theoretical analyses forcefully demonstrate the existence of anion Se ligand and outer-carbon all-around encapsulation on the ANDC@SnSSe@C can effectively yield abundant structural defects and Na+-reactivity sites, accelerate rapid ion migration, widen interlayer spacing, as well as relieve volume expansion, thus further resolving the critical issues throughout the charge-discharge processes. As anticipated, as-fabricated ANDC@SnSSe@C anode contributes extraordinary reversible capacity, wonderful cyclic lifespan with 83.4% capacity retention over 2000 cycles at 20.0 A g-1, and exceptional rate capability. A series of correlated kinetic investigations and ex situ characterizations deeply reveal the underlying springheads for the ion-transport kinetics, as well as synthetically elucidate phase-transformation mechanism of the ANDC@SnSSe@C. Furthermore, the ANDC@SnSSe@C-based sodium ion full cell and hybrid capacitor offer high-capacity contribution and remarkable energy-density output, indicative of its great practicability.

ZnSe/SnSe Heterostructure Incorporated with Selenium/Nitrogen Co-Doped Carbon Nanofiber Skeleton for Sodium-Ion Batteries

Effective strategies toward building exquisite nanostructures with enhanced structural integrity and improved reaction kinetics will carry forward the practical application of alloy-based materials as anodes in batteries. Herein, a free-standing 3D carbon nanofiber (CNF) skeleton incorporated with heterostructured binary metal selenides (ZnSe/SnSe) nanoboxes is developed for Na-ion storage anodes, which can facilitate Na+ ion migration, improve structure integrity, and enhance the electrochemical reaction kinetics. During the carbonization and selenization process, selenium/nitrogen (Se/N) is co-doped into the 3D CNF skeleton, which can improve the conductivity and wettability of the CNF matrices. More importantly, the ZnSe/SnSe heterostructures and the Se/N co-doping CNFs can have a synergistic interfacial coupling effect and built-in electric field in the heterogeneous interfaces of ZnSe/SnSe hetero-boundaries as well as the interfaces between the CNF matrix and the selenide heterostructures, which can enable fast ion/electron transport and accelerate surface/internal reaction kinetics for Na-ion storage. The ZnSe/SnSe@Se,N-CNFs exhibit superior Na-ion storage performance than the comparative ZnSe/SnSe, ZnSe and SnSe powders, which deliver an excellent rate performance (882.0, 773.6, 695.7, 634.2, and 559.0 mAh g-1 at current rates of 0.1, 0.2, 0.5, 1, and 2 A g-1) and long-life cycling stability of 587.5 mAh g-1 for 3500 cycles at 2 A g-1.

Coral-like CoSe2@N-doped carbon with a high initial coulombic efficiency as advanced anode materials for Na-ion batteries

Na-ion batteries (NIBs) have attracted great interest as a possible technology for grid-scale energy storage for the past few years owing to the wide distribution, low cost and environmental friendliness of sodium resources and similar chemical mechanisms to those of established Li-ion batteries (LIBs). Nonetheless, the implementation of NIBs is seriously hindered because of their low rate capability and cycling stability. This is mainly because the large ionic size of Na+ can reduce the structural stability and cause sluggish reaction kinetics of electrode materials. Herein, three-dimensional nanoarchitectured coral-like CoSe2@N-doped carbon (CL-CoSe2@NC) was synthesized through solvothermal and selenizing techniques. As a result, CL-CoSe2@NC for NIBs at 2 A g-1 exhibits an ultrahigh specific capacity of 345.4 mA h g-1 after 2800 cycles and a superhigh initial coulombic efficiency (ICE) of 93.1%. Ex situ XRD, HRTEM, SAED and XPS were executed to study the crystal structure evolution between Na and CoSe2 during sodiation/de-sodiation processes. The aforementioned results indicate that the improved sodium storage property of CL-CoSe2@NC could be attributed to better electrode kinetics and a stable SEI film because of the 3D nanoarchitecture and the existence of the NC layer.

Construction of ion-electron conduction network on FeS2 as high-performance cathodes enables all-solid-state lithium batteries

The all-solid-state lithium batteries (ASSLBs) with high energy density are considered to be one of the most promising candidates for next-generation lithium battery systems. Nevertheless, the low ionic and electronic conduction inside the cathode and the poor interfacial contact of the cathode/electrolyte seriously impede the large-scale application of ASSLBs. In this work, a novel multiple ion-electron conductive network is constructed on the FeS2 cathode to realize a high-energy all-solid-state battery. The internal disordered carbon matrix acts as electronic network to accelerate the electronic transmission. Meanwhile, reduced graphene oxide (rGO) tightly wrapping FeS2/C microspheres' surface serves as external electronic pathway. Moreover, the in-situ formed Li7P3S11 electrolyte infiltrates into the nanoparticles to improve lithium-ion transport kinetics. Therefore, the dual-carbon framework and Li7P3S11 coating layer strategies significantly enhance ion-electron transport kinetics and improve interfacial contact during cycling. As expected, the FeS2@C/rGO@Li7P3S11 cathode exhibits excellent rate capability and cycling stability, showing a reversible discharge capacity of 350.3 mAh/g at 0.5C after 200 cycles. More importantly, ex-situ XPS and dQ/dV results reveal that the synergistic effect of dual-carbon frameworks and Li7P3S11 coating layer not only provides fast electron-ion transfer channels, but also wraps the reaction products with poor electrochemical activity such as Fe0, FeSy, and S to accelerate the reaction kinetics and strengthens the reaction reversibility. This work provides valuable insights for improving the electrochemical performance and understanding the reaction mechanism of the conversion-type metal sulfide cathodes in ASSLBs.

A Brief Overview of Silicon Nanoparticles as Anode Material: A Transition from Lithium-Ion to Sodium-Ion Batteries

The successful utilization of silicon nanoparticles (Si-NPs) to enhance the performance of Li-ion batteries (LIBs) has demonstrated their potential as high-capacity anode materials for next-generation LIBs. Additionally, the availability and relatively low cost of sodium resources have a significant influence on developing Na-ion batteries (SIBs). Despite the unique properties of Si-NPs as SIBs anode material, limited study has been conducted on their application in these batteries. However, the knowledge gained from using Si-NPs in LIBs can be applied to develop Si-based anodes in SIBs by employing similar strategies to overcome their drawbacks. In this review, a brief history of Si-NPs' usage in LIBs is provided and discuss the strategies employed to overcome the challenges, aiming to inspire and offer valuable insights to guide future research endeavors.

Manipulating Molecular Structure to Trigger Ultrafast and Long-Life Potassium Storage of Fe0.4 Ni0.6 S Solid Solution

Currently, the main obstacle to the widespread utilization of metal chalcogenides (MSx ) as anode for potassium-ion batteries (PIBs) is their poor rate capability and inferior cycling stability as a result of the undesirable electrical conductivity and severe pulverization of the nanostructure during large K-ions intercalation-extraction processes. Herein, an ultrafast and long-life potassium storage of metal chalcogenide is rationally demonstrated by employing Fe0.4 Ni0.6 S solid-solution (FNS/C) through molecular structure engineering. Benefiting from improved electroactivity and intense interactions within the unique solid solution phase, the electrical conductivity and structure durability of Fe0.4 Ni0.6 S are vastly improved. As anticipated, the FNS/C electrode delivers superior rate properties (538.7 and 210.5 mAh g-1 at 0.1 and 10 A g-1 , respectively) and long-term cycle stability (180.8 mAh g-1 at 5 A g-1 after 2000 cycles with a capacity decay of 0.011% per cycle). Moreover, the potassium storage mechanisms of Fe0.4 Ni0.6 S solid solution are comprehensively revealed by several in situ characterizations and theoretical calculations. This innovative molecular structure engineering strategy opens avenues to achieve high-quality metal chalcogenides for future advanced PIBs.

Stannate-Based Materials as Anodes in Lithium-Ion and Sodium-Ion Batteries: A Review

Binary metal oxide stannate (M₂SnO₄; M = Zn, Mn, Co, etc.) structures, with their high theoretical capacity, superior lithium storage mechanism and suitable operating voltage, as well as their dual suitability for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), are strong candidates for next-generation anode materials. However, the capacity deterioration caused by the severe volume expansion problem during the insertion/extraction of lithium or sodium ions during cycling of M₂SnO₄-based anode materials is difficult to avoid, which greatly affects their practical applications. Strategies often employed by researchers to address this problem include nanosizing the material size, designing suitable structures, doping with carbon materials and heteroatoms, metal-organic framework (MOF) derivation and constructing heterostructures. In this paper, the advantages and issues of M₂SnO₄-based materials are analyzed, and the strategies to solve the issues are discussed in order to promote the theoretical work and practical application of M₂SnO₄-based anode materials.

Layer-Structured Anisotropic Metal Chalcogenides: Recent Advances in Synthesis, Modulation, and Applications

The unique electronic and catalytic properties emerging from low symmetry anisotropic (1D and 2D) metal chalcogenides (MCs) have generated tremendous interest for use in next generation electronics, optoelectronics, electrochemical energy storage devices, and chemical sensing devices. Despite many proof-of-concept demonstrations so far, the full potential of anisotropic chalcogenides has yet to be investigated. This article provides a comprehensive overview of the recent progress made in the synthesis, mechanistic understanding, property modulation strategies, and applications of the anisotropic chalcogenides. It begins with an introduction to the basic crystal structures, and then the unique physical and chemical properties of 1D and 2D MCs. Controlled synthetic routes for anisotropic MC crystals are summarized with example advances in the solution-phase synthesis, vapor-phase synthesis, and exfoliation. Several important approaches to modulate dimensions, phases, compositions, defects, and heterostructures of anisotropic MCs are discussed. Recent significant advances in applications are highlighted for electronics, optoelectronic devices, catalysts, batteries, supercapacitors, sensing platforms, and thermoelectric devices. The article ends with prospects for future opportunities and challenges to be addressed in the academic research and practical engineering of anisotropic MCs.

Crab Shell-Derived SnS2/C and FeS2/C Carbon Composites as Anodes for High-Performance Sodium-Ion Batteries

The demand for energy storage devices has increased significantly, and the sustainable development of lithium-ion batteries is limited by scarce lithium resources. Therefore, alternative sodium-ion batteries which are rich in resource may become more competitive in the future market. In this work, we synthesized low-cost SnS₂/C and FeS₂/C anode materials of sodium-ion batteries which used waste crab shells as biomass carbon precursor. The SnS₂ nanosheet and FeS₂ nanosphere structures are deposited on the crab shell-derived carbon through simple hydrothermal reaction. Due to the coexistence of transition metal dichalcogenides (TMDs) and crab-derived biomass carbon, the anode material has excellent cycle stability and rate performance. SnS₂/C and FeS₂/C deliver capacities of 535.4 and 479 mA h g^-1 at the current density of 0.1 A g^-1, respectively. This study explored an effective and economical strategy to use biomass and TMDs to construct high-performance sodium-ion batteries.

Core-shell-structured Mn2SnO4@Void@C as a stable anode material for lithium-ion batteries with long cycle life

Owing to its high theoretical specific capacity, Mn₂SnO₄ has been regarded as a promising electrode material for lithium-ion batteries. However, in suffering from huge volume expansion and pulverization amidst the alloying/dealloying processes, it presents difficulties in applications as an anode material. Herein, a core-shell-structured Mn₂SnO₄@Void@C anode material was successfully synthesized using a layer-wise assembly and selective etching method. Tetraethyl silicate (TEOS) and resorcinol formaldehyde resin, serving, respectively, as sacrificial template (SiO₂) and carbon layer sources, were coated successively onto Mn₂SnO₄ particles. Adopting an alkali etching process, the SiO₂ template was removed, and a Mn₂SnO₄@Void@C was therewith constructed. As Mn₂SnO₄ is well wrapped by a carbon shell and there are enough voids therein, its volume expansion whilst cycling can be significantly buffered. Moreover, the porous structure in Mn₂SnO₄@Void@C can provide convenient channels for ion transport and alleviate volume changes. Mn₂SnO₄@Void@C exhibits upgraded capacity and long cycling stability, since its specific capacity is maintained at 783.1 mA h g^-1 at 100 mA g^-1 after 150 cycles and at 553.3 mA h g^-1 at 1000 mA g^-1 after 1000 cycles.

Defective Bi2S3 Anchored on CuS/C as an Ultrafast and Long-Life Anode for Sodium-Ion Storage

Due to the high electrical conductivity and abundant redox active sites, bimetal sulfides are highly competitive anode materials for sodium storage with long-life and high-rate. Herein, a heterostructured metal sulfide (Bi₂S₃-CuS) with a carbon-based support is prepared by calcination and ion exchange methods. The synergistic effects of the heterostructure and defective structure provide facile diffusion channels, fast Na⁺ migration, and plentiful active sites for Na⁺, which reflect in the impressive electrochemical performance with a high reversible capacity of 592.2 mA h g^-1 after 1000 cycles at 8 A g^-1. Furthermore, the Na-ion full batteries exhibit an ultra-long cycling performance with a value of 216 mA h g^-1 after 4000 cycles at 10 A g^-1. Interestingly, the defective structure of Bi₂S₃ remains after cycling. Kinetic analyses and density functional theoretical calculations clarified that the heterointerfacial structure, especially on the interface containing sulfur defects in Bi₂S₃ of Bi₂S₃-CuS, could induce feasible ion adsorption and promote ion transfer, which lays the foundation for achieving ultrafast sodiation kinetics.

Recent Advances on Heterojunction-Type Anode Materials for Lithium-/Sodium-Ion Batteries

Rechargeable batteries are key in the field of electrochemical energy storage, and the development of advanced electrode materials is essential to meet the increasing demand of electrochemical energy storage devices with higher density of energy and power. Anode materials are the key components of batteries. However, the anode materials still suffer from several challenges such as low rate capability and poor cycling stability, limiting the development of high-energy and high-power batteries. In recent years, heterojunctions have received increasing attention from researchers as an emerging material, because the constructed heterostructures can significantly improve the rate capability and cycling stability of the materials. Although many research progress has been made in this field, it still lacks review articles that summarize this field in detail. Herein, this review presents the recent research progress of heterojunction-type anode materials, focusing on the application of various types of heterojunctions in lithium/sodium-ion batteries. Finally, the heterojunctions introduced in this review are summarized, and their future development is anticipated.

Rich Self-Generated Phase Boundaries of Heterostructured VS4 /Bi2 S3 @C Nanorods for Long Lifespan Sodium-Ion Batteries

Rationally designing on sundry multiphase compounds has come into the spotlight for sodium-ion batteries (SIBs) due to enhanced structural stability and improved electrochemical performances. Nevertheless, there is still a lack of thorough understanding of the reaction mechanism of high-active phase boundaries existing between multiphase compounds. Here, a VS₄ /Bi₂ S₃ @C composite anode for SIBs with rich phase boundaries in heterostructure is successfully synthesized. In situ X-ray diffraction analyses demonstrate a multistep redox mechanism in the heterostructures and ex situ transmission electron microscopy results confirm that tremendous self-generated phase boundaries are obtained and well-maintained during cycling, dramatically leading to stable reaction interfaces and better structural integrity. Combining experimental and theoretical results, a self-built-in electric field forming between phase boundaries acts as a dominate driving force for Na⁺ transport kinetics. Benefiting from the fast reaction kinetics of phase boundaries, the heterojunction provides an efficient approach to avoid abnormal voltage failure. As expected, the VS₄ /Bi₂ S₃ @C heterostructure displays superior sodium storage performances, especially an excellent long-term cycling stability (379.0 mAh g^-1 after 1800 cycles at a current density up to 2 A g^-1 ). This work confirms a critical role of phase boundaries on superior reversibility and structural stability, and provides a strategy for analogous conversion/alloying-type anodes.

Stability of FeF3-Based Sodium-Ion Batteries in Nonflammable Ionic Liquid Electrolytes at Room and Elevated Temperatures

Iron trifluoride (FeF3), a conversion-type cathode for sodium-ion batteries (SIBs), is based on cheap and abundant Fe and provides high theoretical capacity. However, the applications of FeF3-based SIBs have been hindered by their low-capacity utilization and poor cycling stability. Herein, we report greatly enhanced performance of FeF3 in multiple types of ionic liquid (IL) electrolytes at both room temperature (RT) and elevated temperatures. The Pyr1,4FSI electrolyte demonstrated the best cycling stability with an unprecedented decay rate of only ∼0.023% per cycle after the initial stabilization and an average coulombic efficiency of ∼99.5% for over 1000 cycles at RT. The Pyr1,3FSI electrolyte demonstrated the best cycling stability with a capacity decay rate of only ∼0.25% per cycle at 60 °C. Cells using Pyr1,3FSI and EMIMFSI electrolytes also showed promising cycling stability with capacity decay rates of ∼0.039% and ∼0.030% per cycle over 1000 cycles, respectively. A protective and ionically conductive cathode electrolyte interphase (CEI) layer is formed during cycling in ILs, diminishing side reactions that commonly lead to gassing and excessive CEI growth in organic electrolytes, especially at elevated temperatures. Furthermore, the increased ionic conductivity and decreased viscosity of ILs at elevated temperatures help attain higher accessible capacity. The application of ILs sheds light on designing a protective CEI for its use in stable SIBs.

Synergistic Engineering of Se Vacancies and Heterointerfaces in Zinc-Cobalt Selenide Anode for Highly Efficient Na-Ion Batteries

The exploitation of effective strategies to accelerate the Na⁺ diffusion kinetics and improve the structural stability in the electrode is extremely important for the development of high efficientcy sodium-ion batteries. Herein, Se vacancies and heterostructure engineering are utilized to improve the Na⁺ -storage performance of transition metal selenides anode prepared through a facile two-in-one route. The experimental results coupled with theoretical calculations reveal that the successful construction of the Se vacancies and heterostructure interfaces can effectively lower the Na⁺ diffusion barrier, accelerate the charge transfer efficiency, improve Na⁺ adsorption ability, and provide an abundance of active sites. Consequently, the batteries based on the constructed ZnSe/CoSe₂ -CN anode manifest a high initial Coulombic efficiency (97.7%), remarkable specific capacities (547.1 mAh g^-1 at 0.5 A g^-1 ), superb rate capability (362.1 mAh g^-1 at 20 A g^-1 ), as well as ultrastable long-term stability (1000 cycles) with a satisfied specific capacity (535.6 mAh g^-1 ) at 1 A g^-1 . This work facilitates an in-depth understanding of the synergistic effect of vacancies and heterojunctions in improving the Na⁺ reaction kinetics, providing an effective strategy to the rational design of key materials for high efficiency rechargeable batteries.

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.

A Versatile Strategy for Achieving Fast-Charging Batteries via Interfacial Engineering: Pseudocapacitive Potassium Storage without Nanostructuring

The rapid transport of alkali ions in electrodes is a long-time dream for fast-charging batteries. Though electrode nanostructuring has increased the rate-capability, its practical use is limited because of the low tap density and severe irreversible reactions. Therefore, development of a strategy to design fast-charging micron-sized electrodes without nanostructuring is of significant importance. Herein, a simple and versatile strategy to accelerate the alkali ion diffusion behavior in micron-sized electrode is reported. It is demonstrated that the diffusion rate of K⁺ ions is significantly improved at the hetero-interface between orthorhombic Nb₂ O₅ (001) and monoclinic MoO₂ (110) planes. Lattice distortion at the hetero-interface generates an inner space large enough for the facile transport of K⁺ ions, and electron localization near oxygen-vacant sites further enhances the ion diffusion behavior. As a result, the interfacial-engineered micron-sized anode material achieves an outstanding rate capability in potassium-ion batteries (KIBs), even higher than nanostructured orthorhombic Nb₂ O₅  which is famous for fast-charging electrodes. This is the first study to develop an intercalation pseudocapacitive micron-sized anode without nanostructuring for fast-charging and high volumetric energy density KIBs. More interestingly, this strategy is not limited to K⁺ ion, but also applicable to Li⁺ ion, implying the versatility of interfacial engineering for alkali ion batteries.

Superstructured Nanocrystals/Dual-Doped Mesoporous Carbon Anodes for High-Performance Sodium-Ion Batteries

Two-dimensional ordered superstructures have been attracting considerable attention due to their interesting properties and potential applications. However, designing ideal functional superstructures with excellent electrochemical properties is still a major challenge, and an in-depth understanding of the structure-activity relationship of electrodes remains to be achieved. To elucidate this critical issue, herein, we rationally designed and synthesized for the first time superstructured TiO₂/dual-doped mesoporous carbon anodes using confined space and surface coassembly strategies. Our method primarily relied on the larger interlayer space few-layered MXene and its negatively charged surface, allowing hexamethylenetetramine intercalation and surface electrostatic adsorption. The superstructured TiO₂/dual-doped mesoporous carbon was successfully assembled by the thermal decomposition of a confined carbon precursor. Subsequently, the comparison of Na⁺-storage properties of various anodes was carried out based on the results of structural characterization techniques and electrochemical analysis methods. The results showed that the optimized anode (N/O-C@TiO₂-20) can deliver a reversible capacity of 165 mA h g^-1 after 1000 cycles at a current density of 1 A g^-1, indicating excellent electrochemical properties. The enhancement can be attributed to the synergistic effect of carbon domains, defective nanocrystals, and a covalently coupled interface between TiO₂ and mesoporous carbon. Our work not only offered a new strategy for the assembly and regulation of superstructures to promote the electrochemical performance but also enlightened the rational design of advanced anodes for sodium-ion battery application.

Self-Sacrifice Template Construction of Uniform Yolk-Shell ZnS@C for Superior Alkali-Ion Storage

Secondary batteries have been widespread in the daily life causing an ever-growing demand for long-cycle lifespan and high-energy alkali-ion batteries. As an essential constituent part, electrode materials with superior electrochemical properties play a vital role in the battery systems. Here, an outstanding electrode of yolk-shell ZnS@C nanorods is developed, introducing considerable void space via a self-sacrificial template method. Such carbon encapsulated nanorods moderate integral electronic conductivity, thus ensuring rapid alkali-ions/electrons transporting. Furthermore, the porous structure of these nanorods endows enough void space to mitigate volume stress caused by the insertion/extraction of alkali-ions. Due to the unique structure, these yolk-shell ZnS@C nanorods achieve superior rate performance and cycling performance (740 mAh g-1 at 1.0 A g-1 after 540 cycles) for lithium-ion batteries. As a potassium-ion batteries anode, they achieve an ultra-long lifespan delivering 211.1 mAh g-1 at 1.0 A g-1 after 5700 cycles. The kinetic analysis reveals that these ZnS@C nanorods with considerable pseudocapacitive contribution benefit the fast lithiation/delithiation. Detailed transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses indicate that such yolk-shell ZnS@C anode is a typical reversible conversion reaction mechanism accomplished by alloying processes. This rational design strategy opens a window for the development of superior energy storage materials.

Engineering Ion Diffusion by CoS@SnS Heterojunction for Ultrahigh-Rate and Stable Potassium Batteries

Transitional metal sulfides (TMSs) are considered as promising anode candidates for potassium storage because of their ultrahigh theoretical capacity and low cost. However, TMSs suffer from low electronic, ionic conductivity and significant volume expansion during potassium ion intercalation. Here, we construct a carbon-coated CoS@SnS heterojunction which effectively alleviates the volume change and improves the electrochemical performance of TMSs. The mechanism analysis and density functional theory (DFT) calculation prove the acceleration of K-ion diffusion by the built-in electric field in the CoS@SnS heterojunction. Specifically, the as-prepared material maintains 81% of its original capacity after 2000 cycles at 500 mA g^-1. In addition, when the current density is set at 2000 mA g^-1, it can still deliver a high discharge capacity of 210 mAh g^-1. Moreover, the full cell can deliver a high capacity of 400 mAh g^-1 even after 150 cycles when paired with a perylene-3,4,9,10-tetracarboxydiimide (PTCDI) cathode. This work is expected to provide a material design idea dealing with the unstable and low rate capability problems of potassium-ion batteries.

NiS1−xSex Nanoparticles Anchored on Nitrogen-Doped Reduced Graphene Oxide as Highly Stable Anode for Sodium-Ion Battery

Nickel sulfides are regarded as one of the promising anode materials for sodium-ion batteries (SIBs), but the sluggish electrodes kinetics and rapid capacity decay, caused by their intrinsic low electrical conductivity and high bulk expansion, greatly limit their practical application. To overcome these obstacles, nano-sized, selenium-doped, nickel sulfide particles, anchored on nitrogen-doped reduced graphene oxide composites (NiS1−xSex@N–rGO), are rationally synthesized. The broad Na+ diffusion channels, resulting from Se doping, as well as the short Na+ transferring path, attributed from nano-size scale of NiS1−xSex particles, endow NiS1−xSex@N–rGO composites with ultrafast storage kinetics. Moreover, strong coupled effect between the NiS1−xSex and N–rGO is beneficial to the uniform dispersion of NiS1−xSex nanoparticles, improving electrical conductivity and suppressing the volume variation in charge/discharge process. Furthermore, the cut-off discharge voltage is modulated to realize the smaller volume change during cycle process. As a result, the fabricated anode of SIBs based on NiS1−xSex@N–rGO composites exhibits a high specific capacity of 300 mAh g−1, at the current density of 1 A g−1, after 1000 cycles with almost no capacity degradation.

Investigations on the Electrochemical and Mechanical Properties of Sb2 O3 Nanobelts by In Situ Transmission Electron Microscopy

Sb₂ O₃ shows great promise as a high-capacity anode material for sodium-ion batteries (SIBs) due to the combined mechanisms of intercalation, conversion, and alloying. In this work, the electrochemical performance and mechanical property of Sb₂ O₃ nanobelts during sodiation/desodiation are revealed by constructing nanoscale solid-state SIBs in a high-resolution transmission electron microscopy. It is found that the Sb₂ O₃ nanobelt exhibits an ultrahigh sodiation speed of ≈13.5 nm s^-1 and experiences a three-step sodiation reaction including the intercalation reaction to form Na_x Sb₂ O₃ , the conversion reaction to form Sb, and the alloying reaction to form NaSb. The alloying reaction is found to be reversible, while the conversion reaction is partially reversible. The Sb₂ O₃ nanobelt shows anisotropic expansion and the orientation of the Sb₂ O₃ nanobelt has great influence on the expansion ratio. It is found that the existence of a {010} plane with large d-spacing in the nanobelt leads to a surprisingly small expansion ratio (≈5%). The morphology of the Sb₂ O₃ nanobelt is well maintained during multiple electrochemical cycles. In situ bending experiments suggest that the sodiated Sb₂ O₃ nanobelts show improved toughness and flexibility compared to pristine Sb₂ O₃ nanobelts. These fundamental studies provide insight into the rational design of anode materials with improved electrochemical and mechanical performance in SIBs.

High-capacity CoP-Mn3P nanoclusters heterostructures derived by Co2MnO4 as advanced electrodes for supercapacitors

Although transition metal oxides (TMOs) have attracted enormous attention owing to their high performance in supercapacitors, it still remains challenging issues in terms of the poor electrical conductivity, sluggish redox kinetics and insufficient electrochemical active sites. Herein, the high-capacity CoP-Mn₃P nanoclusters featuring the heterogeneous interfaces have been successfully synthesized through hydrothermal method followed by annealing. The heterojunction formed between CoP and Mn₃P redistributes the charge at the interface between them, generating the built-in electric field to accelerate electron transfer, and thus the conductivity of the electrode is enhanced. Moreover, the unique morphology of nanoclusters composed of flake structures is beneficial to provide more electrochemical active sites. Consequently, the resultant CoP-Mn₃P nanoclusters electrode delivers an exceptional gravimetric specific capacity (2714 F g^-1 at 1 A g^-1) as well as a long cycle lifespan (83.1% of capacitance retention after 10,000 cycles). An asymmetric supercapacitor (ASC) device assembling with employing CoP/Mn₃P electrode presents an ultrahigh energy density value of 46.4 Wh kg^-1 at a power density of 800.0 W kg^-1 and a super capacitance retention of 86.2% after 30,000 cycles. This work paves an effective way for the investigation on the charge transfer kinetics of electrode materials.

Fabrication of MnSe/SnSe@C heterostructures for high-performance Li/Na storage

Novel heterostructured MnSe/SnSe@C nanoboxes display excellent electrochemical performance.

Nanoconfined bimetallic sulfides (CoSn)S heterostructure in carbon microsphere as a high-performance anode for half/full sodium-ion batteries

The development of high-capacity anode materials is crucial for sodium-ion batteries. Alloy-type anode materials have attracted tremendous attention due to their high theoretical capacities. Nonetheless, the realizations of high capacity and remarkable cycling stability are actually hindered by the sluggish reaction kinetics of sodium storage. Here, we report a binary metal sulfides CoS@SnS heterostructure confined in carbon microspheres (denoted as (CoSn)S/C) through a facile hydrothermal reaction combined with annealing treatment. The (CoSn)S/C with micro/nanostructure can shorten ion diffusion length and increase mechanical strength of electrode. Besides, the heterogeneous interface between CoS and SnS can improve the inherent conductivity and favor the rapid transfer of Na⁺. Benefitting from these advantages, (CoSn)S/C composite exhibits a high reversible capacity of 463 mAh g^-1 and superior durability (368 mAh g^-1 at 2 A g^-1 after 1000 cycles). Notably, the assembled Na₃V₂(PO₄)₃//(CoSn)S/C full cell delivers a reversible capacity of 386 mAh g^-1 at 0.2 A g^-1, proving that the (CoSn)S/C is a promising anode material for sodium-ion batteries. The density functional theory (DFT) calculations unveil the mechanism and significance of the constructed CoS@SnS heterostructure for the sodium storage at atomic level. This work provides an important reference for in-depth understanding of reaction kinetics of bimetallic sulfides heterostructure.

Metal-Organic Framework Derived Ultrafine Sb@Porous Carbon Octahedron via In Situ Substitution for High-Performance Sodium-Ion Batteries

Alloying-type anode materials are regarded as promising alternatives beyond intercalation-type carbonaceous materials for sodium storage owing to the high specific capacities. The rapid capacity decay arising from the huge volume change during Na⁺-ion insertion/extraction, however, impedes the practical application. Herein, we report an ultrafine antimony embedded in a porous carbon nanocomposite (Sb@PC) synthesized via facile in situ substitution of the Cu nanoparticles in a metal-organic framework (MOF)-derived octahedron carbon framework for sodium storage. The Sb@PC composite displays an appropriate redox potential (0.5-0.8 V vs Na/Na⁺) and excellent specific capacities of 634.6, 474.5, and 451.9 mAh g^-1 at 0.1, 0.2, and 0.5 A g^-1 after 200, 500, and 250 cycles, respectively. Such superior sodium storage performance is primarily ascribed to the MOF-derived three-dimensional porous carbon framework and ultrafine Sb nanoparticles, which not only provides a penetrating network for rapid transfer of charge carriers but also alleviates the agglomeration and volume expansion of Sb during cycling. Ex situ X-ray diffraction and in situ Raman analysis clearly reveal a five-stage reaction mechanism during sodiation and desodiation and demonstrate the excellent reversibility of Sb@PC for sodium storage. Furthermore, post-mortem analysis reveals that the robust structural integrity of Sb@PC can withstand continuous Na⁺-ion insertion/extraction. This work may provide insight into the effective design of high-capacity alloying-type anode materials for advanced secondary batteries.

Constructing NiS2/NiSe2 heteroboxes with phase boundaries for Sodium-Ion batteries

Reasonable design and synthesis of anode materials with high capacity, excellent rate capability and good cycling stability is vital for the pragmatic application of sodium-ion batteries (SIBs). Transition metal chalcogenides possess immense potential on account of their distinguished redox reversibility and high theoretical specific capacity. Herein, the hollow metal sulfide/metal selenide (NiS₂/NiSe₂) heteroboxes with rich phase boundaries have been manufactured as anode for SIBs. The lattice distortion and charge redistribution at the phase boundary of the as-prepared NiS₂/NiSe₂ heteroboxes can expose more active sites, which is profitable to the adsorption of Na⁺ and accelerate the sodium storage kinetics process, and the unique hollow porous structure is conducive to buffering the volume expansion and can facilitate the penetration of electrolyte during the repeated Na⁺ de-intercalation process. By virtue of these advantages, the NiS₂/NiSe₂ heteroboxes delivers a good rate capability, where the average capacity at 10 A g^-1 in comparison with 0.1 A g^-1 is 64.3%. Otherwise, it exhibits an ultralong reversible capacity of 292 mA h g^-1 after 2000 cycles at 10 A g^-1 with only 0.0125% average capacity decay per cycle. The rational construction of phase boundary with unique structure in this article has guiding significance for the manufacture of progressive SIBs anode materials.

SnSe2 /FeSe2 Nanocubes Capsulated in Nitrogen-Doped Carbon Realizing Stable Sodium-Ion Storage at Ultrahigh Rate

Metal selenides have attracted increasing attention recently as anodes for sodium-ion batteries (SIBs) because of their large capacities, high electric conductivity, as well as environmental benignity. However, the application of metal selenides is hindered by the huge volume variation, which causes electrode structure devastation and the consequent degrading cycling stability and rate capability. To overcome the aforementioned obstacles, herein, SnSe₂ /FeSe₂ nanocubes capsulated in nitrogen-doped carbon (SFS@NC) are fabricated via a facile co-precipitation method, followed by poly-dopamine wrapping and one-step selenization/carbonization procedure. The most remarkable feature of SFS@NC is the ultra-stability under high current density while delivering a large capacity. The synergistic effect of dual selenide components and core-shell architecture mitigates the volume effect, alleviates the agglomeration of nanoparticles, and further improves the electric conductivity. The as-prepared SFS@NC nanocubes present a high capacity of 408.1 mAh g^-1 after 1200 cycles at 6 A g^-1 , corresponding to an 85.3% retention, and can achieve a capacity of 345.0 mAh g^-1 at an extremely high current density of 20 A g^-1 . The outstanding performance of SFS@NC may provide a hint to future material structure design strategy, and promote further developments and applications of SIBs.

Conversion-Alloying Anode Materials for Sodium Ion Batteries

The past decade has witnessed a rapidly growing interest toward sodium ion battery (SIB) for large-scale energy storage in view of the abundance and easy accessibility of sodium resources. Key to addressing the remaining challenges and setbacks and to translate lab science into commercializable products is the development of high-performance anode materials. Anode materials featuring combined conversion and alloying mechanisms are one of the most attractive candidates, due to their high theoretical capacities and relatively low working voltages. The current understanding of sodium-storage mechanisms in conversion-alloying anode materials is presented here. The challenges faced by these materials in SIBs, and the corresponding improvement strategies, are comprehensively discussed in correlation with the resulting electrochemical behavior. Finally, with the guidance and perspectives, a roadmap toward the development of advanced conversion-alloying materials for commercializable SIBs is created.

Bimetallic Sulfide SnS2/FeS2 Nanosheets as High-Performance Anode Materials for Sodium-Ion Batteries

Transition-metal sulfide SnS₂ has aroused wide concern due to its high capacity and nanosheet structure, making it an attractive choice as the anode material in sodium-ion batteries. However, the large volume expansion and poor conductivity of SnS₂ lead to inferior cycle stability as well as rate performance. In this work, FeS₂ was in situ introduced to synchronously grow with SnS₂ on rGO to prepare a heterojunction bimetallic sulfide nanosheet SnS₂/FeS₂/rGO composite. The composition and distinctive structure facilitate the rapid diffusion of Na⁺ and improve the charge transfer at the heterogeneous interface, providing sufficient space for volume expansion and improving anode materials' structural stability. SnS₂/FeS₂/rGO bimetallic sulfide electrode boasts a capacity of 768.3 mA h g^-1 at the current density of 0.1 A g^-1, and 541.2 mA h g^-1 at the current density of 1 A g^-1 in sodium-ion batteries, which is superior to that of either single metal sulfide SnS₂ or FeS₂. TDOS calculation further confirms that the binding of FeS₂/SnS₂-Na is more stable than FeS₂ and SnS₂ alone. The superior electrochemical performance of the SnS₂/FeS₂/rGO composite material makes it a promising candidate for sodium storage.

Electrolyte/Structure-Dependent Cocktail Mediation Enabling High-Rate/Low-Plateau Metal Sulfide Anodes for Sodium Storage

As promising anodes for sodium-ion batteries, metal sulfides ubiquitously suffer from low-rate and high-plateau issues, greatly hindering their application in full-cells. Herein, exemplifying carbon nanotubes (CNTs)-stringed metal sulfides superstructure (CSC) assembled by nano-dispersed SnS₂ and CoS₂ phases, cocktail mediation effect similar to that of high-entropy materials is initially studied in ether-based electrolyte to solve the challenges. The high nano-dispersity of metal sulfides in CSC anode underlies the cocktail-like mediation effect, enabling the circumvention of intrinsic drawbacks of different metal sulfides. By utilizing ether-based electrolyte, the reversibility of metal sulfides is greatly improved, sustaining a long-life effectivity of cocktail-like mediation. As such, CSC effectively overcomes low-rate flaw of SnS₂ and high-plateau demerit of CoS₂, simultaneously realizes a high rate and a low plateau. In half-cells, CSC delivers an ultrahigh-rate capability of 327.6 mAh g^-1_anode at 20 A g^-1, far outperforming those of monometallic sulfides (SnS₂, CoS₂) and their mixtures. Compared with CoS₂ phase and SnS₂/CoS₂ mixture, CSC shows remarkably lowered average charge voltage up to ca. 0.62 V. As-assembled CSC//Na_1.5VPO_4.8F_0.7 full-cell shows a good rate capability (0.05 ~ 1.0 A g^-1, 120.3 mAh g^-1_electrode at 0.05 A g^-1) and a high average discharge voltage up to 2.57 V, comparable to full-cells with alloy-type anodes. Kinetics analysis verifies that the cocktail-like mediation effect largely boosts the charge transfer and ionic diffusion in CSC, compared with single phase and mixed phases. Further mechanism study reveals that alternative and complementary electrochemical processes between nano-dispersed SnS₂ and CoS₂ phases are responsible for the lowered charge voltage of CSC. This electrolyte/structure-dependent cocktail-like mediation effect effectively enhances the practicability of metal sulfide anodes, which will boost the development of high-rate/-voltage sodium-ion full batteries.

Emerging of Heterostructure Materials in Energy Storage: A Review

With the ever-increasing adaption of large-scale energy storage systems and electric devices, the energy storage capability of batteries and supercapacitors has faced increased demand and challenges. The electrodes of these devices have experienced radical change with the introduction of nano-scale materials. As new generation materials, heterostructure materials have attracted increasing attention due to their unique interfaces, robust architectures, and synergistic effects, and thus, the ability to enhance the energy/power outputs as well as the lifespan of batteries. In this review, the recent progress in heterostructure from energy storage fields is summarized. Specifically, the fundamental natures of heterostructures, including charge redistribution, built-in electric field, and associated energy storage mechanisms, are summarized and discussed in detail. Furthermore, various synthesis routes for heterostructures in energy storage fields are roundly reviewed, and their advantages and drawbacks are analyzed. The superiorities and current achievements of heterostructure materials in lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), lithium-sulfur batteries (Li-S batteries), supercapacitors, and other energy storage devices are discussed. Finally, the authors conclude with the current challenges and perspectives of the heterostructure materials for the fields of energy storage.

Unlocking Rapid and Robust Sodium Storage Performance of Zinc-Based Sulfide via Indium Incorporation

Zinc sulfide (ZnS) exhibits promise in sodium-ion batteries (SIBs) because of its low operation voltage and high theoretical specific capacity. However, pristine ZnS is not adequate in realizing rapid and robust sodium storage owing to its low reversibility, poor structure stability, and sluggish kinetics. To date, most efforts focus on utilizing carbonaceous incorporation to improve its electrochemical performances. Nevertheless, it remains an arduous challenge for realizing superior rate capability while obtaining stable cycling. Herein, inspired by the crystal structure of hexagonal ZnIn₂S₄, which possesses an intrinsic layered feature with larger unit-cell volume versus that of ZnS, indium incorporation is thus deployed as an immediate remedy. In/ex situ investigations combined with density functional theory calculations are conducted to reveal the superior kinetics, high reversibility, and good structure stability of ZnIn₂S₄. Notably, the formed indium-based derivatives during cycling manifest a Na⁺ (de)intercalation process, thereby exciting a synergetic mechanism to stabilize electrochemical cycling. As a result, the electrochemical performances of Zn-based sulfide are significantly improved via the indium incorporation. Furthermore, a full cell based on the ZnIn₂S₄ anode with the superior electrochemical performance is developed. This work provides an effective tactic of heteroatom incorporation for optimizing structure as well as exciting a complementary reaction process toward developing superior anodes for high-performance alkali-ion batteries.

Ultrafine ZnS Nanoparticles in the Nitrogen-Doped Carbon Matrix for Long-Life and High-Stable Potassium-Ion Batteries

Potassium-ion batteries (KIBs) have attracted researchers' widespread attention because of the luxuriant reserves of potassium salts and their low cost. Nevertheless, the absence of suitable electrode materials with a stable electrochemical property is a crucial issue, which seriously hampers the practical applications of KIBs. Herein, a scalable anode material consisting of ultrafine ZnS nanoparticles encapsulated in three-dimensional (3D) carbon nanosheets is explored for KIBs. This hierarchical anode is obtained via a simple and universal sol-gel method combined with a typical solid-phase sulfidation route. The special structure of this anode facilitates good contact with electrolytes and has enough voids to buffer the large volumetric stress changing during K⁺ insertion/extraction. Thus, the 3D ZnS@C electrode exhibitsour stable cycling performance (230 mAh g^-1 over 2300 cycles at 1.0 A g^-1) and superior rate capability. The kinetic analysis indicates that a ZnS@C anode with considerable pesoudecapactive contribution benefits a fast potassium/depotassium process. Detailed ex-situ and in-situ measurements reveal that this ZnS@C anode combines reversible conversion and alloying-type reactions. This rationally designed ZnS@C material is highly applicable for KIBs, and the current route opens an avenue for the development of highly stable K⁺ storage materials.

High-Safety and High-Voltage Lithium Metal Batteries Enabled by a Nonflammable Ether-Based Electrolyte with Phosphazene as a Cosolvent

The high reactivity between lithium metal and traditional carbonate electrolytes is a great obstacle to realize the long-term cycling ability of lithium metal batteries. Ether-based electrolytes have good stability toward lithium metal anodes. However, the oxidation stability of ether-based electrolytes is generally lower than 4 V, which limits the application of high-voltage (>4 V) cathodes and restricts the energy density. The high flammability of ether is another key issue that hinders the commercialization of ether-based electrolytes. To address these issues, herein, we report a high-voltage, nonflammable ether-based electrolyte with F-, N-, and P-rich hexafluorocyclotriphosphazene (HFPN) as a cosolvent. HFPN can not only act as a highly efficient flame-retarding agent but also form a dense and homogeneous solid electrolyte interphase (SEI) layer rich in LiF and Li₃N on the lithium metal anode, which stabilizes the lithium/electrolyte interface and inhibits the formation of lithium dendrites. Moreover, the HFPN-based electrolyte has a wider potential window than 4 V. As a result, with this electrolyte, high-voltage lithium metal batteries exhibit a capacity retention of ∼95% after 100 cycles. This study may provide a new pathway for developing safe, high-energy, and dendrite-free lithium metal batteries.

Recent Progress on the Alloy-Based Anode for Sodium-Ion Batteries and Potassium-Ion Batteries

High-energy batteries with low cost are urgently needed in the field of large-scale energy storage, such as grid systems and renewable energy sources. Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) with alloy-based anodes provide huge potential due to their earth abundance, high capacity, and suitable working potential, and are recognized as attractive alternatives for next-generation batteries system. Although some important breakthroughs have been reported, more significant improvements are still required for long lifetime and high energy density. Herein, the latest progress for alloy-based anodes for SIBs and PIBs is summarized, mainly including Sn, Sb, Ge, Bi, Si, P, and their oxides, sulfides, selenides, and phosphides. Specifically, the material designs for the desired Na⁺ /K⁺ storage performance, phase transform, ionic/electronic transport kinetics, and specific chemical interactions are discussed. Typical structural features and research strategies of alloy-based anodes, which are used to facilitate processes in battery development for SIBs and PIBs, are also summarized. The perspective of future research of SIBs and PIBs is outlined.

Heterostructure Engineering of Core-Shelled Sb@Sb2 O3 Encapsulated in 3D N-Doped Carbon Hollow-Spheres for Superior Sodium/Potassium Storage

In this work, the core-shelled Sb@Sb₂ O₃ heterostructure encapsulated in 3D N-doped carbon hollow-spheres is fabricated by spray-drying combined with heat treatment. The novel core-shelled heterostructures of Sb@Sb₂ O₃ possess a mass of heterointerfaces, which formed spontaneously at the core-shell contact via annealing oxidation and can promote the rapid Na⁺ /K⁺ transfer. The density functional theory calculations revealed the mechanism and significance of Na/K-storage for the core-shelled Sb@Sb₂ O₃ heterostructure, which validated that the coupling between the high-conductivity of Sb and the stability of Sb₂ O₃ can relieve the shortcomings of the individual building blocks, thereby enhancing the Na/K-storage capacity. Furthermore, the core-shell structure embedded in the 3D carbon framework with robust structure can further increase the electrode mechanical strength and thus buffer the severe volume changes upon cycling. As a result, such composite architecture exhibited a high specific capacity of ≈573 mA h g^-1 for sodium-ion battery (SIB) anode and ≈474 mA h g^-1 for potassium-ion battery (PIB) anode at 100 mA g^-1 , and superior rate performance (302 mA h g^-1 at 30 A g^-1 for SIB anode, while 239 mA h g^-1 at 5 A g^-1 for PIB anode).

Monolayer Amorphous Carbon-Bridged Nanosheet Mesocrystal: Facile Preparation, Morphosynthetic Transformation, and Energy Storage Applications

Self-assembly of nanoscale building units into mesoscopically ordered superstructures opens the possibility for tailored applications. Nonetheless, the realization of precise controllability related specifically to the atomic scale has been challenging. Here, first, we explore the key role of a molecular surfactant in adjusting the growth kinetics of two-dimensional (2D) layered SnS₂. Experimentally, we show that high pressure both enhances the adsorption energy of the surfactant sodium dodecylbenzene sulfonate (SDBS) on the SnS₂(001) surface at the initial nucleation stage and induces the subsequent oriented attachment (OA) growth of 2D crystallites with monolayer thickness, leading to the formation of a monolayer amorphous carbon-bridged nanosheet mesocrystal. It is notable that such a nanosheet-coalesced mesocrystal is metastable with a flowerlike morphology and can be turned into a single crystal via crystallographic fusion. Subsequently, direct encapsulation of the mesocrystal via FeCl₃-induced pyrrole monomer self-polymerization generates conformal polypyrrole (PPy) coating, and carbonization of the resulting nanocomposites generates Fe-N-S-co-doped carbons that are embedded with well-dispersed SnS/FeCl₃ quantum sheets; this process skillfully integrated structural phase transformation, pyrolysis graphitization, and self-doping. Interestingly, such an integrated design not only guarantees the flowerlike morphology of the final nanohybrids but also, more importantly, allows the thickness of petalous carbon and the size of the nanoconfined particles to be controlled. Benefiting from the unique structural features, the resultant nanohybrids exhibited the brilliant electrochemical performance while simultaneously acting as a reliable platform for exploring the structure-performance correlation of a Li-ion battery (LIB).

Heterogeneous interface design of bimetallic selenide nanoboxes enables stable sodium storage

The heterostructure SnSe2/CoSe2 core encapsulated in a carbon nanobox shell guarantees the structural stability and further ensures stable high performance for sodium ion batteries.

FeSe2@C Microrods as a Superior Long-Life and High-Rate Anode for Sodium Ion Batteries

Transition-metal selenides have emerged as promising anode materials for sodium ion batteries (SIBs). Nevertheless, they suffer from volume expansion, polyselenide dissolution, and sluggish kinetics, which lead to inadequate conversion reaction toward sodium and poor reversibility during the desodiation process. Therefore, the transition-metal selenides are far from long cycling stability, outstanding rate performance, and high initial Coulombic efficiency, which are the major challenges for practical application in SIBs. Here, an efficient anode material including an FeSe₂ core and N-doped carbon shell with inner void space as well as high conductivity is developed for outstanding rate performance and long cycle life SIBs. In the ingeniously designed FeSe₂@NC microrods, the N-doped carbon shell can facilitate mass transport/electron transfer, protect the FeSe₂ core from the electrolyte, and accommodate volume variation of FeSe₂ with the help of the inner void of the core. Thus, the FeSe₂@NC microrods can maintain strong structural integrity upon long cycling and ensure a good reversible conversion reaction of FeSe₂ during the discharge/charge process. As a result, the as-prepared FeSe₂@NC microrods exhibit excellent sodium storage performance and ultrahigh stability, achieving an excellent rate capability (411 mAh g^-1 at 10.0 A g^-1) and a long-term cycle performance (401.3 mAh g^-1 after 2000 cycles at 5.0 A g^-1).

Construction of series-wound architectures composed of metal-organic framework-derived hetero-(CoFe)Se2 hollow nanocubes confined into a flexible carbon skeleton as a durable sodium storage anode

Metal chalcogenides with structural pulverization/degradation and intrinsic low electrical conductivity trigger the challenging issues of serious capacity fading and inferior rate capability upon repeated de-/sodiation cycling. Multiple electroactive heterostructures can integrate the inherent advantages of a strong synergistic coupling effect to improve their electrochemical Na+-storage behavior and structural durability, showing robust mechanical features, fast Na+ immigration and abundant active insertion sites at intriguing heterointerfaces. Hence, a series-wound architecture of metal-organic framework (MOF)-derived heterogeneous (CoFe)Se2 hollow nanocubes confined into a one-dimension carbon nanofiber skeleton ((CoFe)Se2@CNS) was successfully developed via a template-assisted liquid phase anion exchange followed by electrospinning and conventional selenization treatment. When examined as an anode for sodium ion batteries, the (CoFe)Se2@CNS electrode exhibits remarkably enhanced electrochemical Na+-storage performance delivering a high sodiation capacity as high as 213.9 mA h g-1 after 3650 cycles at 5 A g-1 with a capacity degradation rate of only 0.0047% per cycle; specifically, it shows tremendous rate performance and ultrastable cycling durability of 194.7 mA h g-1 at a high rate of 8 A g-1 after 5630 cycles. This work can shed light on a fundamental approach for designing heterostructures of multiple electroactive components toward high-performance alkali metal ion batteries.

Promoting Ge Alloying Reaction via Heterostructure Engineering for High Efficient and Ultra-Stable Sodium-Ion Storage

Germanium (Ge)-based materials have been considered as potential anode materials for sodium-ion batteries owing to their high theoretical specific capacity. However, the poor conductivity and Na+ diffusivity of Ge-based materials result in retardant ion/electron transportation and insufficient sodium storage efficiency, leading to sluggish reaction kinetics. To intrinsically maximize the sodium storage capability of Ge, the nitrogen doped carbon-coated Cu3Ge/Ge heterostructure material (Cu3Ge/Ge@N-C) is developed for enhanced sodium storage. The pod-like structure of Cu3Ge/Ge@N-C exposes numerous active surface to shorten ion transportation pathway while the uniform encapsulation of carbon shell improves the electron transportation, leading to enhanced reaction kinetics. Theoretical calculation reveals that Cu3Ge/Ge heterostructure can offer decent electron conduction and lower the Na+ diffusion barrier, which further promotes Ge alloying reaction and improves its sodium storage capability close to its theoretical value. In addition, the uniform encapsulation of nitrogen-doped carbon on Cu3Ge/Ge heterostructure material efficiently alleviates its volume expansion and prevents its decomposition, further ensuring its structural integrity upon cycling. Attributed to these unique superiorities, the as-prepared Cu3Ge/Ge@N-C electrode demonstrates admirable discharge capacity, outstanding rate capability and prolonged cycle lifespan (178 mAh g-1 at 4.0 A g-1 after 4000 cycles).