Peapod-Like Carbon-Encapsulated Cobalt Chalcogenide Nanowires as Cycle-Stable and High-Rate Materials for Sodium-Ion Anodes

Multifunctional Separator Enables High-Performance Sodium Metal Batteries in Carbonate-Based Electrolytes

Sodium metal has become one of the most promising anodes for next-generation cheap and high-energy-density metal batteries; however, challenges caused by the uncontrollable sodium dendrite growth and fragile solid electrolyte interphase (SEI) restrict their large-scale practical applications in low-cost and wide-voltage-window carbonate electrolytes. Herein, a novel multifunctional separator with lightweight and high thinness is proposed, assembled by the cobalt-based metal-organic framework nanowires (Co-NWS), to replace the widely applied thick and heavy glass fiber separator. Benefitting from its abundant sodiophilic functional groups and densely stacked nanowires, Co-NWS not only exhibits outstanding electrolyte wettability and effectively induces uniform Na+ ion flux as a strong ion redistributor but also favors constructing the robust N,F-rich SEI layer. Satisfactorily, with 10 µL carbonate electrolyte, a Na|Co-NWS|Cu half-cell delivers stable cycling (over 260 cycles) with a high average Coulombic efficiency of 98%, and the symmetric cell shows a long cycle life of more than 500 h. Remarkably, the full cell shows a long-term life span (over 1500 cycles with 92% capacity retention) at high current density in the carbonate electrolyte. This work opens up a strategy for developing dendrite-free, low-cost, and long-life-span sodium metal batteries in carbonate-based electrolytes.

Metal Selenides Anode Materials for Sodium Ion Batteries: Synthesis, Modification, and Application

The powerful and rapid development of lithium-ion batteries (LIBs) in secondary batteries field makes lithium resources in short supply, leading to rising battery costs. Under the circumstances, sodium-ion batteries (SIBs) with low cost, inexhaustible sodium reserves, and analogous work principle to LIBs, have evolved as one of the most anticipated candidates for large-scale energy storage devices. Thereinto, the applicable electrode is a core element for the smooth development of SIBs. Among various anode materials, metal selenides (MSe_x ) with relatively high theoretical capacity and unique structures have aroused extensive interest. Regrettably, MSe_x suffers from large volume expansion and unwished side reactions, which result in poor electrochemistry performance. Thus, strategies such as carbon modification, structural design, voltage control as well as electrolyte and binder optimization are adopted to alleviate these issues. In this review, the synthesis methods and main reaction mechanisms of MSe_x are systematically summarized. Meanwhile, the major challenges of MSe_x and the corresponding available strategies are proposed. Furthermore, the recent research progress on layered and nonlayered MSe_x for application in SIBs is presented and discussed in detail. Finally, the future development focuses of MSe_x in the field of rechargeable ion batteries are highlighted.

Insights into Electrochemical Processes of Hollow Octahedral Co3Se4@rGO for High-Rate Sodium Ion Storage

Sodium ion batteries (SIBs), as an alternative and promising energy storage system, have attracted considerable attention due to the abundant reserves and low cost of sodium. However, it remains a great challenge to achieve high capacity and rate capability required for practical applications. Herein, hollow octahedral Co₃Se₄ particles encapsulated in reduced graphene oxide (Co₃Se₄@rGO) were designed and synthesized and exhibited excellent electrochemical performances as anodes of SIBs, especially rate capability. Sodiation/desodiation processes and involved mechanisms were investigated by using in situ TEM and in situ XRD. During sodiation, a crystalline Na₂Se layer with numerous amorphous fine Co nanoparticles dispersed on it was observed to appear on the surface of the original Co₃Se₄@rGO particles, and the movable Co-Na₂Se composites further migrated to the rGO network with high electron/ion dual conductivity, resulting in ultrafast sodium storage kinetics and remarkable rate performance of the Co₃Se₄@rGO anode evidenced by delivering a discharge capacity of 229.3 mAh g^-1 at a large current density of 50 A g^-1. Our findings reveal the fundamental mechanism behind the enhanced performance of the Co₃Se₄@rGO anode and offer valuable insights into the rational design of electrode materials for high-performance SIBs.

Ultrafine cobalt selenide nanowires tangled with MXene nanosheets as highly efficient electrocatalysts toward the hydrogen evolution reaction

Hydrogen energy has attracted sustainable attention in the exploitation and application of advanced power-generator devices, and electrocatalysts for the hydrogen evolution reaction (HER) have been regarded as one of the core components in the current electrochemical hydrogen production systems. In this work, a facile and cost-effective bottom-up strategy is developed for the construction of 1D ultrafine cobalt selenide nanowires tangled with 2D Ti₃C₂T_x MXene nanosheets (CoSe NW/Ti₃C₂T_x) through an in situ stereo-assembly process. Such an architectural design endows the hybrid system not only with a large accessible surface for the rapid transportation of reactants, but also with numerous exposed CoSe edge sites, thereby generating substantial synergic coupling effects. The as-derived CoSe NW/Ti₃C₂T_x hybrid demonstrates competitive electrocatalytic properties toward the HER with a small onset potential of 84 mV, a low Tafel slope of 56 mV dec^-1 and exceptional cycling performance, which are superior to those of bare CoSe and Ti₃C₂T_x materials. It is believed this promising nanoarchitecture may provide new possibilities for the design and construction of precious-metal-free electrocatalysts with high efficiency and great stability in the energy-conversion field.

Hierarchical Nanocapsules of Cu-Doped MoS2@H-Substituted Graphdiyne for Magnesium Storage

Hierarchical nanocomposites, which integrate electroactive materials into carbonaceous species, are significant in addressing the structural stability and electrical conductivity of electrode materials in post-lithium-ion batteries. Herein, a hierarchical nanocapsule that encapsulates Cu-doped MoS₂ (Cu-MoS₂) nanopetals with inner added skeletons in an organic-carbon-rich nanotube of hydrogen-substituted graphdiyne (HsGDY) has been developed for rechargeable magnesium batteries (RMB). Notably, both the incorporation of Cu in MoS₂ and the generation of the inner added nanoboxes are developed from a dual-template of Cu-cysteine@HsGDY hybrid nanowire; the synthesis involves two morphology/composition evolutions by CuS@HsGDY intermediates both taking place sequentially in one continuous process. These Cu-doped MoS₂ nanopetals with stress-release skeletons provide abundant active sites for Mg²⁺ storage. The microporous HsGDY enveloped with an extended π-conjugation system offers more effective electron and ion transfer channels. These advantages work together to make this nanocapsule an effective cathode material for RMB with a large reversible capacity and superior rate and cycling performance.

Rational Design of Yolk-Shell ZnCoSe@N-Doped Dual Carbon Architectures as Long-Life and High-Rate Anodes for Half/Full Na-Ion Batteries

Transition-metal selenides (TMSs) have emerged as prospective anode materials for sodium ion batteries (SIBs), owing to their considerable theoretical capacity and intrinsic high electronic conductivity. Whereas, TMSs still suffer from poor rate capability and inferior cycling stability induced by sluggish kinetics and severe volume changes during de/sodiation processes. Herein, a hierarchical composite consisting of a zinc-cobalt bimetallic selenide yolk and nitrogen-doped double carbon shell (denoted as ZnCoSe@NDC) is engineered and fabricated successfully. The architecture of the as-fabricated material improves the Na-ion storage performance via increasing the electron transfer kinetics, accommodating volume expansion, and mitigating the generation of by-products. As expected, the ZnCoSe@NDC electrode delivers superior sodium storage performance with long cycling stability (344.5 mAh g^-1 at 5.0 A g^-1 over 2000 long-term cycles) and high-rate performance (319.2 mAh g^-1 at 10.0 A g^-1 ). Meanwhile, the NVP@C//ZnCoSe@NDC full SIB cells are constructed successfully, retaining 96.3% of its initial capacity at 0.5A g^-1 after 200 loops. The outstanding electrochemical performance and the construction of hybrid SIBs will have far-reaching influences on the development of the various rechargeable batteries.

MOF-Derived Fe7 S8 Nanoparticles/N-Doped Carbon Nanofibers as an Ultra-Stable Anode for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have aroused wide concern due to their potential applications in large-scale energy-storage systems. In this work, a hybrid of Fe₇ S₈ nanoparticles/N-doped carbon nanofibers (Fe₇ S₈ /N-CNFs) is designed and synthesized via electrospinning. As an anode for SIBs, Fe₇ S₈ /N-CNFs exhibit a high reversible capacity of 649.9 mAh g^-1 at 0.2 A g^-1 after 100 cycles, and superior cycling stability for 2000 cycles at 1 A g^-1 with only 0.00302% capacity decay per cycle. Such excellent performance originates from: i) Fe₇ S₈ nanoparticles (average diameter of 17 nm), which shorten the Na⁺ diffusion distance; ii) the unique 3D N-CNFs, which enhance the conductivity, alleviate the self-agglomeration and large volume change of Fe₇ S₈ nanoparticles, and offer numerous active sites for Na⁺ adsorption and paths for electrolyte diffusion. The fascinating structure and superior electrochemical properties of Fe₇ S₈ /N-CNFs shed light on developing high-performance SIBs anode materials.

Reacquainting the Electrochemical Conversion Mechanism of FeS2 Sodium-Ion Batteries by Operando Magnetometry

In spite of the excellent electrochemical performance in lithium-ion batteries (LIBs), transition-metal compounds usually show inferior capacity and cyclability in sodium-ion batteries (SIBs), implying different reaction schemes between these two types of systems. Herein, coupling operando magnetometry with electrochemical measurement, we peformed a comprehensive investigation on the intrinsic relationship between the ion-embedding mechanisms and the electrochemical properties of the typical FeS₂/Na (Li) cells. Operando magnetometry together with ex-situ transmission electron microscopy (TEM) measurement reveal that only part of FeS₂ is involved in the conversion reaction process, while the unreactive parts form "inactive cores" that lead to the low capacity. Through quantification with Langevin fitting, we further show that the size of the iron grains produced by the conversion reaction are much smaller in SIBs than that in LIBs, which may lead to more serious pulverization, thereby resulting in worse cycle performance. The underlying reason for the above two above phenomena in SIBs is the sluggish kinetics caused by the larger Na-ion radius. Our work paves a new way for the investigation of novel SIB materials with high capacity and long durability.

Fabrication of CoSe@NC nanocubes for high performance potassium ion batteries

Potassium-ion batteries (PIBs) are considered as a promising candidate for large-scale energy storage. While exploring suitable anode materials are of vital need for the practical applications of PIBs. Herein, a well-designed heterostructured anode material CoSe nanocubes wrapped by N-doped carbon (CoSe@NC), has been successfully fabricated by simple annealing ZIF-67 nanocubes followed by in-situ selenization process. It is noted that ZIF-67 nanocubes are used as an effective template for the formation of porous structure, which can facilitate the construction of heterogeneous interface between CoSe and N-doped carbon (NC), effectively stabilizing CoSe with conversion reaction product Co⁰, increasing the diffusion mobility of electrons and K⁺-ions, and alleviating huge volume change. As expected, the heterostructured CoSe@NC nanocubes exhibit excellent K⁺-storage performance, which can display a rather high initial charge capacity (388.7 mAh g^-1 at 0.1 A g^-1 with the columbic efficiency of 70%), superior cyclic stability (309.6 mA h g^-1 after 500 cycles at 2 A g^-1), and exceptional rate capability (365.9 mAh g^-1 at 2 A g^-1). In terms of the low-cost and facile production approach for CoSe@NC, which makes the CoSe@NC a promising anode material for PIBs.

CoPSe: A New Ternary Anode Material for Stable and High-Rate Sodium/Potassium-Ion Batteries

The exploration of ideal electrode materials overcoming the critical problems of large electrode volume changes and sluggish redox kinetics induced by large ionic radius of Na⁺ /K⁺ ions is highly desirable for sodium/potassium-ion batteries (SIBs/PIBs) toward large-scale applications. The present work demonstrates that single-phase ternary cobalt phosphoselenide (CoPSe) in the form of nanoparticles embedded in a layered metal-organic framework (MOF)-derived N-doped carbon matrix (CoPSe/NC) represents an ultrastable and high-rate anode material for SIBs/PIBs. The CoPSe/NC is fabricated by using the MOF as both a template and precursor, coupled with in situ synchronous phosphorization/selenization reactions. The CoPSe anode holds a set of intrinsic merits such as lower mechanical stress, enhanced reaction kinetics, as well as higher theoretical capacity and lower discharge voltage relative to its counterpart of CoSe₂ , and suppressed shuttle effect with higher intrinsic electrical conductivity relative to CoPS. The involved mechanisms are evidenced by substantial characterizations and density functional theory (DFT) calculations. Consequently, the CoPSe/NC anode shows an outstanding long-cycle stability and rate performance for SIBs and PIBs. Moreover, the CoPSe/NC-based Na-ion full cell can achieve a higher energy density of 274 Wh kg^-1 , surpassing that based on CoSe₂ /NC and most state-of-the-art Na-ion full cells based on P-, Se-, or S-containing binary/ternary anodes to date.

Nanoengineering of 2D MXene-Based Materials for Energy Storage Applications

2D MXene-based nanomaterials have attracted tremendous attention because of their unique physical/chemical properties and wide range of applications in energy storage, catalysis, electronics, optoelectronics, and photonics. However, MXenes and their derivatives have many inherent limitations in terms of energy storage applications. In order to further improve their performance for practical application, the nanoengineering of these 2D materials is extensively investigated. In this Review, the latest research and progress on 2D MXene-based nanostructures is introduced and discussed, focusing on their preparation methods, properties, and applications for energy storage such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, and supercapacitors. Finally, the critical challenges and perspectives required to be addressed for the future development of these 2D MXene-based materials for energy storage applications are presented.

Synthesis and characterization of metal-organic framework/biomass-derived CoSe/C@C hierarchical structures with excellent sodium storage performance

Metal selenide has attracted much attention for use in rechargeable batteries due to its excellent conductivity and considerable capacity. However, it is still necessary to achieve a long cycle life and excellent Na+ storage performance to enable its practical application. Volume expansion and poor stability of selenide during operation also hinder its industrial applications. As metal-organic frameworks and aerogels possess porous structures, carbon materials derived from them can effectively reduce the volume expansion of selenide, resulting in improving cycling stability and enhancing Na+ storage. In this work, CoSe/C@C composites with a hierarchical structure were successfully prepared by freeze-drying and in situ selenization as anode materials. The CoSe/C@C composites exhibited superior cycling stability (a capacity of 332.3 mA h g-1) and capacity retention (63.1% compared to the second cycle) at 200 mA g-1, after 500 cycles. CoSe/C@C also exhibited a high rate performance of 403.4 mA h g-1 at 2 A g-1. Moreover, thanks to the high capacitance contribution and some redox reactions during cycling, the CoSe/C@C electrode possesses outstanding rate capability.

CoSe@N-Doped Carbon Nanotubes as a Potassium-Ion Battery Anode with High Initial Coulombic Efficiency and Superior Capacity Retention

Potassium-ion batteries (KIBs) have gained significant interest in recent years from the battery research community because potassium is an earth-abundant and redox-active metal, thus having the potential to replace lithium-ion batteries for sustainable energy storage. However, the current development of KIBs is critically challenged by the lack of competitive electrode materials that can reversibly store large amounts of K⁺ and electrolyte systems that are compatible with the electrode materials. Here, we report that cobalt monochalcogenide (CoSe) nanoparticles confined in N-doped carbon nanotubes (CoSe@NCNTs) can be used as a K⁺-storing electrode. The CoSe@NCNT composite exhibits a high initial Columbic efficiency (95%), decent capacity (435 mAh g^-1 at 0.1 A g^-1), and stability (282 mAh g^-1 2.0 A g^-1 after 500 cycles) in a 1 M KPF₆-DME electrolyte with K as the anode over the voltage range from 0.01 to 3.0 V. A full KIB cell consisting of this anode and a Prussian blue cathode also shows excellent electrochemical performance (228 mAh g^-1 at 0.5 A g^-1 after 200 cycles). We show that the NCNT shell is effective not only in providing high electronic conductivity for fast charge transfer but also in accommodating the volume changes during cycling. We also provide experimental and theoretical evidence that KPF₆ in the electrolyte plays a catalytic role in promoting the formation of a polymer-like film on the CoSe surface during the initial activation process, and this amorphous film is of critical importance in preventing the dissolution of polyselenide intermediates into the electrolyte, stabilizing the Co⁰/K₂Se interface, and realizing the reversibility of Co⁰/K₂Se conversion.

Co-Construction of Sulfur Vacancies and Heterojunctions in Tungsten Disulfide to Induce Fast Electronic/Ionic Diffusion Kinetics for Sodium-Ion Batteries

Engineering novel electrode materials with unique architectures has a significant impact on tuning the structural/electrochemical properties for boosting the performance of secondary battery systems. Herein, starting from well-organized WS₂ nanorods, an ingenious design of a one-step method is proposed to prepare a bimetallic sulfide composite with a coaxial carbon coating layer, simply enabled by ZIF-8 introduction. Rich sulfur vacancies and WS₂ /ZnS heterojunctions can be simultaneously developed, that significantly improve ionic and electronic diffusion kinetics. In addition, a homogeneous carbon protective layer around the surface of the composite guarantees an outstanding structural stability, a reversible capacity of 170.8 mAh g^-1 after 5000 cycles at a high rate of 5 A g^-1 . A great potential in practical application is also exhibited, where a full cell based on the WS_{2- x} /ZnS@C anode and the P2-Na_2/3 Ni_1/3 Mn_1/3 O₂ cathode can maintain a reversible capacity of 89.4 mAh g^-1 after 500 cycles at 1 A g^-1 . Moreover, the underlying electrochemical Na storage mechanisms are illustrated in detail by theoretical calculations, electrochemical kinetic analysis, and operando X-ray diffraction characterization.

Recent Advances on Mixed Metal Sulfides for Advanced Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have drawn enormous attention in the past few years from both academic and industrial battery communities in view of the fascinating advantages of rich abundance and low cost of sodium resources. Among various electrode materials, mixed metal sulfides (MMSs) stand out as promising negative electrode materials for SIBs considering their superior structural and compositional advantages, such as decent electrochemical reversibility, high electronic conductivity, and rich redox reactions. Here, a summary of some recent developments in the rational design and synthesis of various kinds of MMSs with tailorable architectures, structural/compositional complexity, controllable morphologies, and enhanced electrochemical properties is presented. The effect of structural engineering and compositional design of MMSs on the sodium storage properties is highlighted. It is anticipated that further innovative works on the material design of advanced electrodes for batteries can be inspired.

Cucurbit[6]uril-Derived Nitrogen-Doped Hierarchical Porous Carbon Confined in Graphene Network for Potassium-Ion Hybrid Capacitors

Potassium-ion hybrid capacitors (PIHCs) have attracted tremendous attention because their energy density is comparable to that of lithium-ion batteries, whose power density and cyclability are similar to those of supercapacitors. Herein, a pomegranate-like graphene-confined cucurbit[6]uril-derived nitrogen-doped carbon (CBC@G) with ultra-high nitrogen-doping level (15.5 at%) and unique supermesopore-macropores interconnected graphene network is synthesized. The carbonization mechanism of cucurbit[6]uril is verified by an in situ TG-IR technology. In a K half-cell configuration, CBC@G anode demonstrates a superior reversible capacity (349.1 mA h g-1 at 0.1 C) as well as outstanding rate capability and cyclability. Moreover, systematic in situ/ex situ characterizations, and theory calculations are carried out to reveal the origin of the superior electrochemical performances of CBC@G. Consequently, PIHCs constructed with CBC@G anode and KOH-activated cucurbit[6]uril-derived nitrogen-doped carbon cathode demonstrate ultra-high energy/power density (172 Wh kg-1/22 kW kg-1) and extraordinary cyclability (81.5% capacity retention for 5000 cycles at 5 A g-1). This work opens up a new application field for cucurbit[6]uril and provides an alternative avenue for the exploitation of high-performance PIHCs.

Large Interlayer Spacing of Few-Layered Cobalt-Tin-Based Sulfide Providing Superior Sodium Storage

Mixed transition metal sulfides (MTMSs) have been regarded as a potential anode material for sodium-ion batteries (SIBs) due to their high reversible specific capacity. Herein, nanoflower-like few-layered cobalt-tin-based sulfide (F-CoSnS) with a large interlayer spacing is synthesized via a facile route for superior sodium storage. The growth mechanism of this unique F-CoSnS is systematically studied. Such distinctive nanostructured engineering synergistically combines a broad interlayer spacing (∼ 0.85 nm), the functionalities of few (2-3) layers, and the introduction of heterogeneous metal atoms, reducing the ion diffusion energy barrier for high-efficiency intercalation/deintercalation of Na⁺ ions, as revealed by density functional theory (DFT) calculations. With further incorporation of a three-dimensional (3D) conductive network, the F-CoSnS@C electrode shows a large sodium storage capacity (493.4 mAh g^-1 at 50 mA g^-1), remarkable rate capability (316.1 mAh g^-1 at 1600 mA g^-1), and superior cycling stability (450 mAh g^-1 at 50 mA g^-1 with 91.2% capacity retention, 0.044% fading rate per cycle, and approximately 100% Coulombic efficiency after 200 cycles). This work demonstrates that the few-layered ternary MTMSs are highly applicable for the development of advanced SIB anode materials with high performance.

Phase Engineering of Iron-Cobalt Sulfides for Zn-Air and Na-Ion Batteries

Rechargeable batteries are promising platforms for sustainable development of energy conversion and storage technologies. Highly efficient multifunctional electrodes based on bimetallic sulfides for rechargeable batteries are extremely desirable but still challenging to tailor with controllable phase and structure. Here, we report a colloidal strategy to fabricate FeCo-based bimetallic sulfides on reduced graphene oxide (rGO), which are expected to display highly efficient oxygen electrocatalysis and sodium storage performances. Specifically, as-screened FeCo₈S₈ nanosheets (NSs) on rGO originating from suitable tailoring of the Co₉S₈ matrix with Fe at the atomic level exhibited a very low potential difference (0.77 V) at 10 mA cm^-2 and negligible voltage loss after 200 cycles as an air electrode for Zn-air batteries. For Na-ion batteries, FeCo₈S₈ NS/rGO demonstrated a superior high-rate capability (188 mAh g^-1 at 20 A g^-1) with long-term cycling stability. The bifunctional electrocatalytic property and sodium storage performance are attributed to not only the synergistic effect of Fe/Co but also the optimized catalytic activity and ion transport ability by the in situ rGO hybrid. This work demonstrates the potential applications of FeCo-based bimetallic sulfides as efficient electrode materials for both rechargeable Zn-air and Na-ion batteries.

State-of-the-Art Electrode Materials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) were investigated as recently as in the seventies. However, they have been overshadowed for decades, due to the success of lithium-ion batteries that demonstrated higher energy densities and longer cycle lives. Since then, the witness a re-emergence of the SIBs and renewed interest evidenced by an exponential increase of the publications devoted to them (about 9000 publications in 2019, more than 6000 in the first six months this year). This huge effort in research has led and is leading to an important and constant progress in the performance of the SIBs, which have conquered an industrial market and are now commercialized. This progress concerns all the elements of the batteries. We have already recently reviewed the salts and electrolytes, including solid electrolytes to build all-solid-state SIBs. The present review is then devoted to the electrode materials. For anodes, they include carbons, metal chalcogenide-based materials, intercalation-based and conversion reaction compounds (transition metal oxides and sulfides), intermetallic compounds serving as functional alloying elements. For cathodes, layered oxide materials, polyionic compounds, sulfates, pyrophosphates and Prussian blue analogs are reviewed. The electrode structuring is also discussed, as it impacts, importantly, the electrochemical performance. Attention is focused on the progress made in the last five years to report the state-of-the-art in the performance of the SIBs and justify the efforts of research.

Urchin-Like Fe3 Se4 Hierarchitectures: A Novel Pseudocapacitive Sodium-Ion Storage Anode with Prominent Rate and Cycling Properties

Transition metal chalcogenides have received great attention as promising anode candidates for sodium-ion batteries (SIBs). However, the undesirable cyclic life and inferior rate capability still restrict their practical applications. The design of micro-nano hierarchitectures is considered as a possible strategy to facilitate the electrochemical reaction kinetics and strengthen the electrode structure stability upon repeated Na⁺ insertion/extraction. Herein, urchin-like Fe₃ Se₄ hierarchitectures are successfully prepared and developed as a novel anode material for SIBs. Impressively, the as-prepared urchin-like Fe₃ Se₄ can present an ultrahigh rate capacity of 200.2 mAh g^-1 at 30 A g^-1 and a prominent capacity retention of 99.9% over 1000 cycles at 1 A g^-1 , meanwhile, a respectable initial coulombic efficiency of ≈100% is achieved. Through the conjunct study of in situ X-ray diffraction, ex situ X-ray absorption near-edge structure spectroscopy, as well as cyclic voltammetry curves, it is intriguing to reveal that the phase transformation from monoclinic to amorphous structure accompanied by the pseudocapacitive Na⁺ storage behavior accounts for the superior electrochemical performance. When paired with the Na₃ V₂ (PO₄ )₃ cathode materials, the assembled full cell enables high energy density and decent cyclic stability, demonstrating potential practical feasibility of the present urchin-like Fe₃ Se₄ anode.

Cream roll-inspired advanced MnS/C composite for sodium-ion batteries: encapsulating MnS cream into hollow N,S-co-doped carbon rolls

With advantages of high theoretical capacity and low cost, manganese sulfide (MnS) has become a potential electrode material for sodium-ion batteries (SIBs). However, complicated preparations and limited cycle life still hinder its application. Inspired by cream rolls in our daily life, a MnS/N,S-co-doped carbon tube (MnS/NSCT) composite with a 3D cross-linked tubular structure is prepared via an ultra-simple and low-cost method in this work. As the anode for SIBs, the cream roll-like MnS/NSCT composite has delivered the best electrochemical performance to date (the highest capacity of 550.6 mA h g^-1 at 100 mA g^-1, the highest capacity of 447.0 mA h g^-1 after 1400 cycles at 1000 mA g^-1, and the best rate performance of 319.8 mA h g^-1 at 10 000 mA g^-1). Besides, according to several in situ and ex situ techniques, the sodium storage mechanism of MnS/NSCTs is mainly from a conversion reaction, and the superior electrochemical performance of MnS/NSCTs is mainly attributed to the unique cream roll-like structure. More importantly, this simple method may be feasible for other anode materials, which will greatly promote the development of SIBs.

Rationally Designed Three-Layered Cu2 S@Carbon@MoS2 Hierarchical Nanoboxes for Efficient Sodium Storage

Hybrid materials, integrating the merits of individual components, are ideal structures for efficient sodium storage. However, the construction of hybrid structures with decent physical/electrochemical properties is still challenging. Now, the elaborate design and synthesis of hierarchical nanoboxes composed of three-layered Cu₂ S@carbon@MoS₂ as anode materials for sodium-ion batteries is reported. Through a facile multistep template-engaged strategy, ultrathin MoS₂ nanosheets are grown on nitrogen-doped carbon-coated Cu₂ S nanoboxes to realize the Cu₂ S@carbon@MoS₂ configuration. The design shortens the diffusion path of electrons/Na⁺ ions, accommodates the volume change of electrodes during cycling, enhances the electric conductivity of the hybrids, and offers abundant active sites for sodium uptake. By virtue of these advantages, these three-layered Cu₂ S@carbon@MoS₂ hierarchical nanoboxes show excellent electrochemical properties in terms of decent rate capability and stable cycle life.

Nanostructured metal chalcogenides confined in hollow structures for promoting energy storage

The engineering of progressive nanostructures with subtle construction and abundant active sites is a key factor for the advance of highly efficient energy storage devices. Nanostructured metal chalcogenides confined in hollow structures possess abundant electroactive sites, more ions and electron pathways, and high local conductivity, as well as large interior free space in a quasi-closed structure, thus showing promising prospects for boosting energy-related applications. This review focuses on the most recent progress in the creation of diverse confined hollow metal chalcogenides (CHMCs), and their electrochemical applications. Particularly, by highlighting certain typical examples from these studies, a deep understanding of the formation mechanism of confined hollow structures and the decisive role of microstructure engineering in related performances are discussed and analyzed, aiming at prompting the nanoscale engineering and conceptual design of some advanced confined metal chalcogenide nanostructures. This will appeal to not only the chemistry-, energy-, and materials-related fields, but also environmental protection and nanotechnology, thus opening up new opportunities for applications of CHMCs in various fields, such as catalysis, adsorption and separation, and energy conversion and storage.

Ultrafine Co1-xS Attached to Porous Interconnected Carbon Skeleton for Sodium-Ion Batteries

Carbon-based materials are effective carriers of metal sulfides because of their good volume stability and chemical stability, which can reduce volume expansion of materials and can also inhibit the interfacial reaction. In this study, Co_1-xS incorporated into three-dimensional porous biomass carbon skeleton were synthesized by a template method. The three-dimensional porous carbon with large surface area is favorable for the electrolyte infiltration. The uniform distribution of Co_1-xS nanoparticles results in a high reversible electrochemical reaction. The well-designed Co_1-xS/three-dimensional porous carbon structure exhibits outstanding performance when used as an anode for sodium-ion batteries (SIBs). The results show that the transition mental sulfide/three-dimensional porous carbon structure has broad application prospects in SIBs.

Engineering Unique Ball-In-Ball Structured (Ni0.33Co0.67)9S8@C Nanospheres for Advanced Sodium Storage

Constructing hollow architectures based on metal sulfides is of great interest for high-performance electrode materials for sodium-ion batteries because of their intriguing properties and various applications. However, the relatively low volumetric density and high fragile structure are the obstacles blocking the development of hollow-structured electrode materials. In this work, ball-in-ball structured (Ni_0.33Co_0.67)₉S₈@C nanospheres have been synthesized by using NiCo-glycerate as the precursor via solvothermal reaction, which was followed by a carbon coating treatment. In this structural design, hollow cavities are generated between the inner and outer balls to effectively accommodate the volume changes of the metal sulfides in the processes of charging/discharging, whereas the uniform carbon coating can increase the electrical conductivity and maintain the structural stability during repeated cycling. The Rietveld refinement, in situ X-ray diffraction, and ex situ X-ray photoelectron spectroscopy analyses provide evidence for an enlarged lattice parameter, weaker Co-S and Ni-S bondings, and a synergistic effect in (Ni_0.33Co_0.67)₉S₈@C toward boosting the conversion reaction and reversible formation of sulfur in the fully charged state, with sulfur trapped within the composite to additionally account for the superior cycling stability of this material. Capacitive behavior has been verified to dominate the electrochemical reaction, enabling fast charge-transport kinetics. Impressively, the double structural protection combined with the free hollow space and complete carbon layer endows the (Ni_0.33Co_0.67)₉S₈@C nanospheres with good electrochemical performance, featuring high cyclability and good rate capability.

In Situ Formation of Co9S8 Nanoclusters in Sulfur-Doped Carbon Foam as a Sustainable and High-Rate Sodium-Ion Anode

Transition-metal sulfides hold great promise as anode materials for sodium-ion batteries due to the high theoretical capacity and excellent redox reversibility based on multielectron conversion reactions. In this work, an elaborate composite, cobalt sulfide nanoclusters embedded in honeycomb-like sulfur-doped carbon foam (Co₉S₈@S-CF), is prepared via a facile sulfur-assisting calcination strategy, which tactfully induces the co-occurrence of in situ pore-forming, sulfidation, sulfur doping, and carbonization. Notably, sulfur-doped carbon foam (S-CF) possesses abundant voids, which are subject to construction of three-dimensional ionic/electronic pathways, leading to high sodium-ion accessibility and ultrafast sodium-ion/electron transportation toward Co₉S₈ nanoclusters. When worked as an anode in sodium-ion batteries, it delivers a remarkable capacity of 373 mA h g^-1 over 1000 cycles at 0.25 C, achieving superior capacity retention of 80%. Furthermore, this anode could achieve unprecedented rate capability with a reversible capacity of 180 mA h g^-1 at 50 C (20 A g^-1), which significantly precedes those reported previously.

Galvanic Replacement Synthesis of Highly Uniform Sb Nanotubes: Reaction Mechanism and Enhanced Sodium Storage Performance

One-dimensional nanotubes are very useful for achieving excellent performance in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) due to the fact that tubular structures can effectively alleviate the structural strain and shorten the ion diffusion length during repeated cycling. In this work, we report a Cu₂Sb-mediated growth strategy to controllably fabricate highly uniform Sb nanotubes (NTs), as well as Cu@Cu₂Sb and Cu₂Sb@Sb composite NTs, via a facile galvanic replacement reaction using Cu nanowires (NWs) as sacrificial templates. Benefiting from their structural merits, the Sb NTs manifest excellent sodium storage performance with superior rate performance (286 mAh g^-1 at 10 A g^-1) and extraordinary cycling stability (342 mAh g^-1 after 6000 cycles at 1 A g^-1). Furthermore, a full cell with Sb NTs as anode and Na₃(VOPO₄)₂F as cathode exhibits a high energy density (252 Wh kg^-1) and high output voltage (2.7 V), revealing their significant application promise in the next-generation SIBs.

Synthesis of CuS@CoS2 Double-Shelled Nanoboxes with Enhanced Sodium Storage Properties

Metal sulfides have received considerable attention for efficient sodium storage owing to their high capacity and decent redox reversibility. However, the poor rate capability and fast capacity decay greatly hinder their practical application in sodium-ion batteries. Herein, an elegant multi-step templating strategy has been developed to rationally synthesize hierarchical double-shelled nanoboxes with the CoS₂ nanosheet-constructed outer shell supported on the CuS inner shell. Their structure and composition enable these hierarchical CuS@CoS₂ nanoboxes to show boosted electrochemical properties with high capacity, outstanding rate capability, and long cycle life.

Graphene-Encapsulated CuP2: A Promising Anode Material with High Reversible Capacity and Superior Rate-Performance for Sodium-Ion Batteries

Metal polyphosphides are regarded as the ideal anode candidates for sodium storage because of their high theoretical capacity, reasonable potential, and abundant resource alternative. However, most of them suffer from irreversibility problems, as reflected by their low reversible capacity, inferior Coulombic efficiency (CE), low rate capability, and poor cycling stability. In this work, we systematically compare the electrochemical behavior of a variety of polyphosphides bulks, discovering that the CuP₂ bulks have higher initial reversible capacity (416 mAh g^-1 at 0.1 A g^-1) and CE (74%) compared to the FeP₂, CoP₃, and NiP₂ bulks, which is related to the unique crystal structure of CuP₂. The CuP₂ electrode is optimized by the rational design of encapsulating CuP₂ nanoparticles into three-dimensional graphene networks (CuP₂@GNs), leading to excellent electrochemical performance. In the carbonate electrolyte, the CuP₂@GNs electrode can deliver the reversible capacities of up to 804, 736, 685, 621, and 508 mAh g^-1 at 0.1, 0.5, 1, 2, and 5 A g^-1, respectively, along with a first CE of 66%. The reversible capacity can be up to 737 mAh g^-1 at 0.1 A g^-1 with a first CE of 83% in the ether electrolyte. These excellent performance demonstrates that CuP₂@GNs could be a promising anode material for sodium-ion batteries.

Microporous Battery Electrodes from Molecular Cluster Precursors

Developing novel energy storage materials is critical to many renewable energy technologies. In this work, we report on the synthesis and electrochemical properties of materials composed of porous cobalt selenide microspheres prepared from molecular cluster precursors. The cobalt selenide microspheres excel as Na⁺ ion battery electrode materials, with a specific capacity of ∼550 mA h/g and excellent cycling stability of 85% over 100 cycles, and perform equally well as Li⁺ ion battery electrodes with a specific capacity of ∼600 mA h/g and cycling stability of 80% over 100 cycles. Materials which reversibly store large amounts of Na⁺ ions are uncommon, and these performances represent significant advances in the field. More broadly, this work establishes metal chalcogenide molecular clusters as valuable precursors for creating new, tunable energy storage materials.

New Insights into the Electrochemistry Superiority of Liquid Na-K Alloy in Metal Batteries

The significant issues with alkali metal batteries arise from their poor electrochemical properties and safety problems, limiting their applications. Herein, TiO₂ nanoparticles embedded into N-doped porous carbon truncated ocatahedra (TiO₂ ⊂NPCTO) are engineered as a cathode material with different metal anodes, including solid Na or K and liquid Na-K alloy. Electrochemical performance and kinetics are systematically analyzed, with the aim to determine detailed electrochemistry. By using a galvanostatic intermittent titration technique, TiO₂ ⊂NPCTO/NaK shows faster diffusion of metal ions in insertion and extraction processes than that of Na-ions and K-ions in solid Na and K. The lower reaction resistance of liquid Na-K alloy electrode is also examined. The higher b-value of TiO₂ ⊂NPCTO/NaK confirms that the reaction kinetics are promoted by the surface-induced capacitive behavior, favorable for high rate performance. This superiority highly pertains to the distinct liquid-liquid junction between the electrolyte and electrode, and the prohibition of metal dendrite growth, substantiated by symmetric cell testing, which provides a robust and homogeneous interface more stable than the traditional solid-liquid one. Hence, the liquid Na-K alloy-based battery exhibits to better cyclablity with higher capacity, rate capability, and initial coulombic efficiency than solid Na and K batteries.