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Recent Tactics and Advances in the Application of Metal Sulfides as High‐Performance Anode Materials for Rechargeable Sodium‐Ion Batteries

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The successful development of post-lithium technologies depends on two key elements: performance and economy. Because sodium-ion batteries (SIBs) can potentially satisfy both requirements, they are widely considered the most promising replacement for lithium-ion batteries (LIBs) due to the similarity between the electrochemical processes and the abundance of sodium-based resources. Among various SIB anode materials, metal sulfides are most extensively studied as materials for high-performance electrodes due to the versatility of their synthesis procedure, utilization potential, and high sodiation capacity. Herein, some of the most effective strategies aimed at effectively alleviating the performance shortcomings of these materials from the materials engineering/design perspective are summarized. In terms of facilitating ion transport in SIBs, which represents one of the most critical aspects of their performance, a specific family of strategies related to a particular operational mechanism is considered rather than categorizing based-on individual sulfide materials. In the foreseeable future, the development of highly functional SIBs electrode materials and utilization of metal sulfides will become highly relevant due to their stability and performance characteristics. Therefore, it is anticipated that this review will guide further research and facilitate the realization of various applications of sulfide-based high-performance rechargeable batteries.
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2006761 (1 of 33)
Recent Tactics and Advances in the Application of Metal
Sulfides as High-Performance Anode Materials for
Rechargeable Sodium-Ion Batteries
Yew Von Lim, Xue Liang Li, and Hui Ying Yang*
The successful development of post-lithium technologies depends on two
key elements: performance and economy. Because sodium-ion batteries
(SIBs) can potentially satisfy both requirements, they are widely considered
the most promising replacement for lithium-ion batteries (LIBs) due to
the similarity between the electrochemical processes and the abundance
of sodium-based resources. Among various SIB anode materials, metal
sulfides are most extensively studied as materials for high-performance
electrodes due to the versatility of their synthesis procedure, utilization
potential, and high sodiation capacity. Herein, some of the most eective
strategies aimed at eectively alleviating the performance shortcomings
of these materials from the materials engineering/design perspective are
summarized. In terms of facilitating ion transport in SIBs, which represents
one of the most critical aspects of their performance, a specific family of
strategies related to a particular operational mechanism is considered
rather than categorizing based-on individual sulfide materials. In the
foreseeable future, the development of highly functional SIBs electrode
materials and utilization of metal sulfides will become highly relevant due
to their stability and performance characteristics. Therefore, it is antici-
pated that this review will guide further research and facilitate the realiza-
tion of various applications of sulfide-based high-performance rechargeable
DOI: 10.1002/adfm.202006761
Dr. Y. V. Lim, X. L. Li, Prof. H. Y. Yang
Singapore University of Technology and Design
Pillar of Engineering Product and Development
8 Somapah Road, Singapore 687372, Singapore
The ORCID identification number(s) for the author(s) of this article
can be found under
ever, the main issue related and common
to all these sources (which have a tran-
sient demand) is the necessity to store
the generated energy using inexpensive,
highly ecient, and safe devices. Energy
storage systems (ESS) such as lithium-
ion batteries (LIBs) are well-developed
and commonly used in various applica-
tions ranging from small-sized personal
mobile devices to medium-sized vehicles
(including hybrids, electrical vehicles, and
mopeds) with considerable commercial
success. However, the grid-scale energy
storage applications of these systems
require cost-eective and performance
characteristics, which are lacked by LIBs.[8]
To answer these concerns, sodium-ion
batteries (SIBs) emerged as a more eli-
gible alternative to LIBs.[9–11] In terms
of the material costs, the advantages of
sodium-based technologies over lithium-
based ones are indisputable due to the
widespread availability and abundance of
sodium-based resources, which are less
susceptible to price fluctuations. In terms
of research eorts and related costs, the
general guidelines for developing high-
performance SIB electrode materials are
based and leveraged on the current achievements in LIBs due
to the correspondence of electrochemical and kinetic properties
of lithium (Li+) and sodium (Na+) ions. In summary, SIBs rep-
resent the only feasible post-lithium technology that possesses
necessary cost and performance characteristics. However,
to establish SIBs as a commercially viable option, extensive
research studies must be performed to enhance their perfor-
mance by optimizing various aspects, including the eective
design of electrode materials and composition of electrolyte
Transition metal sulfides (TMS) have recently attracted sig-
nificant interest from researchers due to a wide range of poten-
tial applications. The latter include energy storage materials for
high-performance supercapacitors, LIBs, and fuel cells.[17–20]
Chhowalla etal. demonstrated a high potential of using metallic
1T–MoS2, a widely studied open-structure layered metal sulfide,
as an active material for supercapacitors with a capacitance
ranging from 400 to 700 F cm3 in aqueous electrolytes.[21] As
LIBs, A high-capacity SnS2 anode with extremely stable perfor-
mance has been studied as early as in the 1970s.[22] Recently, a
1. Introduction
In recent years, significant research eorts have been empha-
sized on developing sustainable energy resources due to envi-
ronmental concerns, the price volatility caused by political
uncertainty, and potential depletion of fossil fuels.[1] Feasible
alternatives such as solar, wind, and hydroelectric power
sources have various shortcomings, including low solar power
eciency[2–4] as well as the ecological and social disruptions
of hydroelectric dams[5] and wind farms, respectively.[6,7] How-
Adv. Funct. Mater. 2021, 31, 2006761
... Moreover, the integration of biomass-derived porous carbons with nanostructured metal sulfides can enhance the activity of metal sulfides and improve electrical conductivity [33]. Such a combination between active component and conductive substrate can reduce internal resistance and achieve excellent cycling stability [34,35]. For example, Song et al. prepared N-doped carbon/bimetallic sulfide and oxide composites via a heating treatment, which exhibited a high specific capacitance of 2883 F g −1 at 1 A g −1 [36]. ...
The rational design and preparation of cathode and anode materials with high capacitance within both positive and negative potential windows for hybrid supercapacitors remains a great challenge. Herein, a hybrid supercapacitor with ultrahigh energy density is assembled with biomass-derived iron/cobalt disulfides immobilized on porous carbon (FeS2/CoS2@KC) and N, S co-doped porous carbon (NSKC) as cathode and anode materials. These two electrode materials are prepared by a facile impregnation and pyrolysis method. FeS2/CoS2@KC-800 cathode material exhibits excellent electrochemical performance with a superior specific capacitance of 3480.47 F g-1 at 0.5 A g-1 and high capacitance retention of 60.35% at 15 A g-1. NSKC-800 anode material delivers a high specific capacitance of 268.75 F g-1 at 0.5 A g-1. Remarkably, the assembled hybrid supercapacitor outputs an ultrahigh energy density of 200.20 Wh kg-1 at a power density of 463.19 W kg-1. Moreover, it also possesses remarkable cycling stability with improved capacitance retention of 94.79% after 10000 cycles at 5 A g-1. This work demonstrates that kelp is a promising precursor to construct high-performance electrode materials for energy storage applications.
Design hybrid metal sulfides-based anode materials is one of the most effective approaches to improve the performance of sodium-ion batteries (SIBs). However, owing to the huge volume expansion, the capacity of sulfide-based anode will decay significantly after repeated charge/discharge processes. Herein, we reported the successful demonstration of anode material based on concaved NiS2@CoS2 nanocube (NCSC) via a chemical etching strategy, which was derived from etching and sulfidation of Ni-Co coordination polymers (NiCoCP) precursor. The obtained NCSC anode materials deliver a high specific sodium storage capacity of 848 mAh g⁻¹ at 0.1 A g⁻¹ and a stable cyclability of 572 mAh g⁻¹ at 5 A g⁻¹ after 830 cycles. This special etching strategy exploit a novel way for the design and preparation of high-performance anode materials for SIBs.
Transition metal silicates with the intrinsic low electronic conductivity and large volume variation are prohibited by its poor cycling stability. Herein, amorphous carbon coating zinc silicate flower-like structure is successfully synthesized via facile hydrothermal method. The composite shortens the diffusion path of lithium/sodium ions and enhances the electronic conductivity. The carbon coated flower-like structure bestows the composite a high reversible capacity, cycling stability and good rate performance. Even at 1A g⁻¹, it still retains the capacity of 544.7mAh g⁻¹ after 1000 cycles for lithium ion batteries. It also exhibits good sodium storage, delivering a capacity of 294.7mAh g⁻¹ after 50 cycles at 0.05A g⁻¹.
Carbon-coated metal chalcogenide composites have been demonstrated as one type of promising anode material for sodium-ion batteries (SIBs). However, combining carbon materials with micronanoparticles of metal chalcogenide always involve complicated processes, such as polymer coating, carbonization, and sulfidation/selenization. To address this issue, herein, we reported a series of carbon-coated FexSey@CN (FexSey = FeSe2, Fe3Se4, Fe7Se8) composites prepared via the thermodynamic transformation of a crystalline organic hybrid iron selenide [Fe(phen)2](Se4) (phen = 1,10-phenanthroline). By pyrolyzing the bulk crystals of [Fe(phen)2](Se4) at different temperatures, FexSey microrods were formed in situ, where the nitrogen-doped carbon layers were coated on the surface of the microrods. Moreover, all the as-prepared FexSey@CN composites exhibited excellent sodium-ion storage capabilities as anode materials in SIBs. This work proves that crystalline organic hybrid metal chalcogenides can be used as a novel material system for the in situ formation of carbon-coated metal chalcogenide composites, which could have great potential in the application of electrochemical energy storage.
Iron sulfide (Fe7S8) with high theoretical capacity and abundant natural resource is an attractive anode candidate in sodium-ion batteries (SIBs). However, its abnormal capacity variation in ether-based electrolytes is inexplicable. Herein, N,S co-doped carbon-coated Fe7S8 (Fe7S8@NS-C) is constructed. As an anode for SIBs, the Na-storage capacity of Fe7S8@NS-C increases significantly from 503.9 to 565.8 mAh g–1 at 1 A g–1 after 120 cycles. Comprehensive characterizations demonstrate this capacity growth not only originates from the reduced FeSx particle size, but also from the Cu-triggered phase transition to form Cu5FeS4 and CuSx. Subsequently, the unstable Cu5FeS4 is converted to CuSx and FeSx, and the resultant capacity maintains relatively stable. Remarkably, Cu2O and Cu⁰ gradually appear as the cycle number increases, which may result from the side reactions of Cu⁺ with some electrolyte components. The constant Cu-related phase transition accelerates the corrosion of Cu foil, which weakens the adhesion of active materials on it and induces a capacity attenuation after ∼550 cycles. This work is helpful to understand the capacity variation of Fe7S8 anode during sodiation/desodiation processes in ether-based systems, which is of great significance for the design and application of metal sulfide materials in electrochemical energy storage.
Transition metal sulfides have found wide applications as promising catalysts and electrocatalysts. Herein, hollow Co9S8 nanotubes were prepared through hydrothermal method, on which CuS nanosheets were grown at low temperature, and hollow Co9S8@CuS heterostructure nanocomposite was synthesized. The prepared hollow Co9S8 nanotubes possess high specific surface area and efficient charge transfer ability, offering an ideal substrate for the growth of CuS nanosheets. Furthermore, the hollow structure of the synthesized Co9S8@CuS can accelerate mass transfer and provide more reaction sites with the specific area of 36.79 m²/g, and the heterostructure between Co9S8 and CuS enhanced their synergistic effect on the conductivity and electrocatalytic activities. For analytical application, the synthesized Co9S8@CuS nanocomposite was applied for the determination of glucose and H2O2, with the charge transfer rate constants of 3.89 and 1.94 s⁻¹, respectively. Under optimal conditions, the Co9S8@CuS-modified glassy carbon electrode exhibits wide linear ranges of 0.03–13 mM and 0.05–14 mM with detection limits of 5.64 μM and 6.06 μM for the oxidation of glucose and the reduction of H2O2, respectively. Additionally, real sample analyses demonstrate satisfying recoveries of 96.43 % and 101.65 % to glucose and H2O2, respectively, indicating its potential to quantitatively analyze the real samples.
As anode materials of electrochemical energy storage system, metal sulfides with high theoretical capacities suffer from issues of materials smashing and deactivation due to huge volume change, resulting in the inferior cycle stability. In this paper, a new strategy of adding sulfur powder into the electrospinning precursor instead of employing sulfur powder during the sulfurizing treatment is proposed to prepare Fe9S10 composites (CNF@G-Fe9S10-1). In those composites, most of Fe9S10 particles are embedded in the graphene-carbon fibers with multiple protection. As anodes for potassium-ion batteries, CNF@G-Fe9S10-1 display higher rate capacities and more excellent stability (103.2 mAh·g−1 at 1000 mA·g−1 after 892 cycles) than Fe9S10 composites synthesized by the traditional method. In addition, as anodes for potassium-ion hybrid capacitors, they also deliver high capacities of 102.8 mAh·g−1 at 1000 mA·g−1 after 100 cycles. The morphology characterization evidences indicate that the surface and integrity of CNF@G-Fe9S10-1 are more smooth and complete than the Fe9S10 composites fabricated using a common method without sulfur power in electrospinning precursor. The excellent stability and high capacity of CNF@G-Fe9S10-1 can be attributed to nearly full-wrapped structure of Fe9S10 in the carbon matrix arising from the new strategy. Owing to the formation of the structure, Fe9S10 particles are protected from the pulverization, and the structure stability of hybrid carbon fibers is enhanced. This study may provide a new strategy for the controllable synthesis of metal sulfide-CNFs and their application for high stability energy storage.Graphical abstract
Sodium-ion batteries (SIBs) have drawn remarkable attention due to their low cost and intrinsically inexhaustible sodium sources. In the past decades, it has aroused significant interest in building promising negative...
Hybrid-structured coupling metal dichalcogenides with carbon materials serve as prospective anode materials for lithium-ion batteries (LIBs) due to their high electrical conductivity, rich active sites, and Li⁺ diffusion path for Li⁺ storage. In the present work, graphene-wrapped ZnS−MoS2@carbon composites (ZnS−MoS2/[email protected]) are synthesized via high-temperature mixing during the hydrothermal and carbonation processes. The as-prepared ZnS−MoS2/[email protected] composites display alleviated volume change in the electrochemical process, increased Li⁺ diffusion speed, and improved conductivity, which are caused by the synergic effect of phase boundaries and hierarchical construction. Therefore, the ZnS−MoS2/[email protected] composites show superior lithium storage capacity and structure stability, and possess ultrastable cycle (581.0 mAh g⁻¹ after 500 cycles at 1 A g⁻¹) and good rate performance (310.7 mAh g⁻¹ at 5 A g⁻¹). This work confirms that anode materials with a hybrid structure can be rationally engineered for high-performance LIBs with cycle durability and good rate capability.
The fabrication and assembly of electrodes is very important for the manufacture of batteries. Here, we demonstrate a 3D printing technique for the construction of functional electrodes (including anode, cathode, and semi-solid electrolyte) for zinc-manganese batteries. The printed anode consists of many zinc microspheres, which allow for a high degree of zinc utilization. The printed cathode has a layered porous structure with a high surface area, giving the electrode surface activity and a fast diffusion channel for the electrochemical reaction. The printed semi-solid electrolyte has designed ion channels that facilitate rapid ion transport. Benefiting from these advantages, the assembled zinc-manganese ion battery achieves high energy density and better cycling performance (without zinc dendrites). The reasons behind these properties and their respective characteristics are well explored and clarified. This work smartly combines direct ink writing technology and light-curing printing technology to achieve the first fully 3D printed battery, which could revolutionize battery manufacturing in the future.
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High‐nickel LiNi1−x −y Mnx Coy O2 (NMC) and LiNi1−x −y Cox Aly O2 (NCA) are the cathode materials of choice for next‐generation high‐energy lithium‐ion batteries. Both NMC and NCA contain cobalt, an expensive and scarce metal generally believed to be essential for their electrochemical performance. Herein, a high‐Ni LiNi1−x −y Mnx Aly O2 (NMA) cathode of desirable electrochemical properties is demonstrated benchmarked against NMC, NCA, and Al–Mg‐codoped NMC (NMCAM) of identical Ni content (89 mol%) synthesized in‐house. Despite a slightly lower specific capacity, high‐Ni NMA operates at a higher voltage by ≈40 mV and shows no compromise in rate capability relative to NMC and NCA. In pouch cells paired with graphite, high‐Ni NMA outperforms both NMC and NCA and only slightly trails NMCAM and a commercial cathode after 1000 deep cycles. Further, the superior thermal stability of NMA to NMC, NCA, and NMCAM is shown using differential scanning calorimetry. Considering the flexibility in compositional tuning and immediate synthesis scalability of high‐Ni NMA very similar to NCA and NMC, this study opens a new space for cathode material development for next‐generation high‐energy, cobalt‐free Li‐ion batteries.
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The high usage for new energy has been promoting the next-generation energy storage systems (ESS). As promising alternatives to lithium ion batteries (LIBs), sodium ion batteries (SIBs) have caused extensive research interest owing to the high natural Na abundance of 2.4 wt.% (vs. 0.0017 wt.% for Li) in the earth's crust and the low cost of it. The development of high-performance electrode materials has been challenging due to the increase in the feasibility of SIBs technology. In the past years, bimetallic sulfides (BMSs) with high theoretical capacity and outstanding redox reversibility have shown great promise as high performance anode materials for SIBs. Herein, the recent advancements of BMSs as anode for SIBs are reported, and the electrochemical mechanism of these electrodes are systematically investigated. In addition, the current issues, challenges, and perspectives are highlighted to address the extensive understanding of the associated electrochemical process, aiming to provide an insightful outlook for possible directions of anode materials for SIBs.
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Lithium-ion batteries have aided the portable electronics revolution for nearly three decades. They are now enabling vehicle electrification and beginning to enter the utility industry. The emergence and dominance of lithium-ion batteries are due to their higher energy density compared to other rechargeable battery systems, enabled by the design and development of high-energy density electrode materials. Basic science research, involving solid-state chemistry and physics, has been at the center of this endeavor, particularly during the 1970s and 1980s. With the award of the 2019 Nobel Prize in Chemistry to the development of lithium-ion batteries, it is enlightening to look back at the evolution of the cathode chemistry that made the modern lithium-ion technology feasible. This review article provides a reflection on how fundamental studies have facilitated the discovery, optimization, and rational design of three major categories of oxide cathodes for lithium-ion batteries, and a personal perspective on the future of this important area.
Molybdenum disulfide (MoS2) has become a potential anode material for sodium-ion batteries (SIBs) by showing decent cell performance but it suffers poor electronic conductivity and large volume expansion during sodiation. Here we design a nanocomposite with hollow nitrogen doped carbon and polypyrrole modified MoS2 for improving the performance for SIBs. The designed nanocomposite shows a much-improved electronic conductivity and the design of the architecture provides sufficient channels for mass transport and accommodates large volume change. This [email protected]2@PPy anode delivers a high specific capacity of 713 mAh g⁻¹ at 0.1 A g⁻¹ for 100 cycles, and an excellent rate capacity of 294 mAh g⁻¹ at 5 A g⁻¹ for 500 cycles. This specific architecture of [email protected]2@PPy could guide the future design of the electrode material in SIBs and its superior electrochemical performance indicates the great potential application for SIBs.
Long-term cycling stability and high-rate capability have been the major challenges of sodium-ion batteries (SIBs) due to the uncontrollable electrode breathing including huge volume swelling/shrinking and serious ionic/electronic disconnection. Herein an efficient anode material consisting of mesoporous iron-sulfide (Fe0.95S1.05) combined with carbon/graphene double encapsulation (Fe0.95S1.05@C-rGO) is developed to effectively regulate the electrode breathing and realize durable and fast sodium storage. The mesoporous structure combined with double-carbon protection provides complete ionic/electronic circuits and robust structures that enable fast and durable electron/Na⁺ access to each of Fe0.95S1.05 nanocrystal. In situ transmission electron microscopy measurement reveals the structural evolution with reversible mesopores disappearance/recovery and small volume swelling/shrinking upon the sodiation/desodiation. As a consequence, the Fe0.95S1.05@C-rGO electrode delivers a high specific capacity (567.6 mAh g⁻¹ at 100 mA g⁻¹), excellent rate performance (323.5 mAh g⁻¹ at 5000 mA g⁻¹) and ultralong cycle life (more than 1700 cycles with 0.015% capacity decay per cycle). In situ X-ray diffraction and selected area electron diffraction patterns unveil that the Fe0.95S1.05@C-rGO electrode is based on a reversible conversion reaction. Moreover, a Fe0.95S1.05@C-rGO||Na3V2(PO4)3/C full battery is demonstrated, which delivers stable cycling (482.8 mAh g⁻¹ at 500 mAh g⁻¹) and excellent rate capability (445.9 mAh g⁻¹ at 5000 mA g⁻¹).
Sodium-ion batteries are increasingly becoming important in the energy storage field owing to their low cost and high natural abundance of sodium. Cobalt-based sulfide materials have been extensively studied as anode materials owing to their remarkable Na storage capability. Nevertheless, the application of cobalt-based sulfides is hampered by their serious capacity degradation and unsatisfactory cycling stability due to severe structural changes during cycling. Therefore, it is important to comprehensively summarize advances in the understanding and modification of cobalt-based sulfides from various perspectives. In the present review, recent advances on various cobalt-based sulfides, such as CoS, CoS2, Co3S4, Co9S8, NiCo2S4, CuCo2S4, and SnCoS4, are outlined with particular attention paid to strategies that improve their sodium storage performance. First, the mechanisms of charge storage are introduced. Subsequently, the key barriers to their extensive application and corresponding strategies for designing high-performance cobalt-based sulfide anode materials are discussed. Finally, key developments are summarized and future research directions are proposed based on recent advancements, aiming to offer possible fascinating strategies for the future promotion of cobalt-based sulfides as anode materials applied in sodium-ion batteries.
In the light of increasing energy demand and environmental pollution, it is urgently required to find a clean and renewable energy source. In these years, photocatalysis that uses solar energy for either fuel production, such as hydrogen evolution and hydrocarbon production, or environmental pollutant degradation, has shown great potential to achieve this goal. Among the various photocatalysts, covalent organic frameworks (COFs) are very attractive due to their excellent structural regularity, robust framework, inherent porosity and good activity. Thus, many studies have been carried out to investigate the photocatalytic performance of COFs and COF-based photocatalysts. In this critical review, the recent progress and advances of COF photocatalysts are thoroughly presented. Furthermore, diverse linkers between COF building blocks such as boron-containing connections and nitrogen-containing connections are summarised and compared. The morphologies of COFs and several commonly used strategies pertaining to photocatalytic activity are also discussed. Following this, the applications of COF-based photocatalysts are detailed including photocatalytic hydrogen evolution, CO2 conversion and degradation of environmental contaminants. Finally, a summary and perspective on the opportunities and challenges for the future development of COF and COF-based photocatalysts are given.
Monitoring carbon dioxide (CO2) levels is extremely important in a wide range of applications. Although metal oxide-based chemoresistive sensors have emerged as a promising approach for CO2 detection, the development of efficient CO2 sensors at low temperature remains a challenge. Herein, we report a low-temperature hollow nanostructured CeO2-based sensor for CO2 detection. We monitor the changes in the electrical resistance after CO2 pulses in a relative humidity of 70% and show the high performance of the sensor at 100 °C. The yolk-shell nanospheres have not only 2 times higher sensitivity but also significantly increased stability and reversibility, faster response times, and greater CO2 adsorption capacity than commercial ceria nanoparticles. The improvements in the CO2 sensing performance are attributed to hollow and porous structure of the yolk-shell nanoparticles, allowing for enhanced gas diffusion and high specific surface area. We present an easy strategy to enhance the electrical and sensing properties of metal oxides at a low operating temperature that is desirable for practical applications of CO2 sensors.
Constructing heterojunction and introducing interfacial interaction by designing ideal structures have the inherent advantages of optimizing electronic structure and macroscopic mechanical property. An exquisite hierarchical heterogeneous of bimetal sulfide Sb2S3@FeS2 hollow nanorods embedded into nitrogen-doped carbon matrix is fabricated by a concise two-steps of solvothermal method. The FeS2 interlayer bulges in-situ grow on the interface of hollow Sb2S3 nanorods within the nitrogen-doped graphene matrix, forming a delicate heterostructure. Such a well-designed architecture affords rapid Na⁺ diffusion and improves charge transfer at the heterointerfaces. Meanwhile, the strongly synergistic coupling interaction among the interior Sb2S3, interlayer FeS2, and external nitrogen-doped carbon matrix creates a steady nanostructure, which extremely accelerates the electronic/ion transport and effectively alleviates the volume expansion upon long cyclic process. As a result, the composite, as an anode material for sodium-ion batteries, exhibits superior rate capability of 537.9 mAh g⁻¹ at 10 A g⁻¹, excellent cyclic stability with 85.7 % capacity retention after 1000 cycles at 5 A g⁻¹. Based on the density functional theory (DFT) calculation, the existing constructing heterojunction in this composite can not only optimize the electronic structure to enhance the conductivity, but also favor the Na2S adsorption energy to accelerate the reaction kinetics. The outstanding electrochemical performance sheds light on the strategy by rational designing of hierarchical heterogeneous nanostructure for energy storage applications.
Herein, the core-shell structured N-doped carbon coated Fe7S8 nano-aggregates (Fe7S8@NC) were controllably prepared via a simple three-step synthesis strategy. The appropriate thickness of N-doped carbon layer outside Fe7S8 nano-aggregates can not only inhibit the particle pulverization induced by the big volume changes of Fe7S8, but can increase the electron transfer efficiency. The hierarchical Fe7S8 nano-aggregates composed of some primary nanoparticles can accelerate the lithium or sodium diffusion kinetics. As anode materials for Li-ion batteries (LIBs), the well-designed Fe7S8@NC nanocomposites exhibit outstanding lithium storage performance, which is better than that of pure Fe7S8, Fe3O4@NC and Fe7S8@C. Among these nanocomposites, the N-doped carbon coated Fe7S8 with carbon content of 26.87 wt.% shows a high reversible specific capacity of 833 mAh·g−1 after 1,000 cycles at a high current density of 2 A·g−1. The above electrode also shows excellent high rate sodium storage performance. The experimental and theoretical analyses indicate that the outstanding electrochemical performance could be attributed to the synergistic effect of hierarchical Fe7S8 nanostructure and conductive N-doped carbon layer. The quantitative kinetic analysis indicates that the charge storage of Fe7S8@NC electrode is a combination of diffusion-controlled battery behavior and surface-induced capacitance behavior.