Metastable Marcasite-FeS2 as a New Anode Material for Lithium Ion Batteries: CNFs-Improved Lithiation/Delithiation Reversibility and Li-Storage Properties

Powering the Future by Iron Sulfide Type Material (FexSy) Based Electrochemical Materials for Water Splitting and Energy Storage Applications: A Review

Water electrolysis is among the recent alternatives for generating clean fuels (hydrogen). It is an efficient way to produce pure hydrogen at a rapid pace with no unwanted by-products. Effective and cheap water-splitting electrocatalysts with enhanced activity, specificity, and stability are currently widely studied. In this regard, noble metal-free transition metal-based catalysts are of high interest. Iron sulfide (FeS) is one of the essential electrocatalysts for water splitting because of its unique structural and electrochemical features. This article discusses the significance of FeS and its nanocomposites as efficient electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and overall water splitting. FeS and its nanocomposites have been studied also for energy storage in the form of electrode materials in supercapacitors and lithium- (LIBs) and sodium-ion batteries (SIBs). The structural and electrochemical characteristics of FeS and its nanocomposites, as well as the synthesis processes, are discussed in this work. This discussion correlates these features with the requirements for electrocatalysts in overall water splitting and its associated reactions. As a result, this study provides a road map for researchers seeking economically viable, environmentally friendly, and efficient electrochemical materials in the fields of green energy production and storage.

Review of Transition Metal Chalcogenides and Halides as Electrode Materials for Thermal Batteries and Secondary Energy Storage Systems

Transition metal chalcogenides and halides (TMCs and TMHs) have been extensively used and reported as electrode materials in diverse primary and secondary batteries. This review summarizes the suitability of TMCs and TMHs as electrode materials focusing on thermal batteries (utilized for defense applications) and energy storage systems like mono- and multivalent rechargeable batteries. The report also identifies the specific physicochemical properties that need to be achieved for the same materials to be employed as cathode materials in thermal batteries and anode materials in monovalent rechargeable systems. For example, thermal stability of the materials plays a crucial role in delivering the performance of the thermal battery system, whereas the electrical conductivity and layered structure of similar materials play a vital role in enhancing the electrochemical performance of the mono- and multivalent rechargeable batteries. It can be summarized that nonlayered CoS2, FeS2, NiS2, and WS2 were found to be ideal as cathode materials for thermal batteries primarily due to their better thermal stability, whereas the layered structures of these materials with a coating of carbon allotrope (CNT, graphene, rGO) were found to be suitable as anode materials for monovalent alkali metal ion rechargeable batteries. On the other hand, vanadium, titanium, molybdenum, tin, and antimony based chalcogenides were found to be suitable as cathode materials for multivalent rechargeable batteries due to the high oxidation state of cathode materials which resists the stronger field produced during the interaction of di- and trivalent ions with the cathode material facilitating higher energy density with minimal structural and volume changes at a high rate of discharge.

Phase Control in the Synthesis of Iron Sulfides

The identity and repeating arrangement of atoms determine the properties of all solids. Even combinations of two atoms can have multiple crystal structures of varying stoichiometries and symmetries with vastly different electronic and chemical behaviors. The conditions of existing bottom-up routes for achieving one phase over another are serendipitous, and the links among precursor reactivity, decomposition mechanism, temperature, and time are elusive. Our studies take a systematic approach to understanding the role that the precursor kinetic decomposition has in the synthesis of iron sulfides, isolating it from other mechanistic factors. The data suggest that phase determination in binary solids can be logically predicted through the consideration of the anion stacking and thermodynamic relationships between phases. Mapping these relationships allows for the rational synthetic targeting of metastable crystalline phases.

Seven-Coordinated High-Pressure Phase of CrSb2 and Experimental Equation of State of MSb2 (M = Cr, Fe, Ru, Os)

The MSb₂ compounds with M = Cr, Fe, Ru, and Os have been investigated under high pressures by synchrotron powder X-ray diffraction. All compounds, except CrSb₂, were found to retain the marcasite structure up to the highest pressures (more than 50 GPa). In contrast, we found that CrSb₂ has a structural phase transition around 10 GPa to a metastable, MoP₂-type structure with Cr coordinated to seven Sb atoms. In addition, we compared ambient temperature compression with laser-heating experiments and found that laser-heating at pressures below and above this phase transition results in the known CuAl₂-type structure. Density functional theory calculations show that this tetragonal structure is the most stable in the whole pressure interval. However, a crossing of the marcasite's and MoP₂-like structure's enthalpies occurs between 5 and 7.5 GPa, which is in good agreement with the experimental data. The phase transition to the MoP₂-type structure observed in this work opens up for discovering other compounds with this new transition pathway from the marcasite structure.

Recent Configurational Advances for Solid-State Lithium Batteries Featuring Conversion-Type Cathodes

Solid-state lithium metal batteries offer superior energy density, longer lifespan, and enhanced safety compared to traditional liquid-electrolyte batteries. Their development has the potential to revolutionize battery technology, including the creation of electric vehicles with extended ranges and smaller more efficient portable devices. The employment of metallic lithium as the negative electrode allows the use of Li-free positive electrode materials, expanding the range of cathode choices and increasing the diversity of solid-state battery design options. In this review, we present recent developments in the configuration of solid-state lithium batteries with conversion-type cathodes, which cannot be paired with conventional graphite or advanced silicon anodes due to the lack of active lithium. Recent advancements in electrode and cell configuration have resulted in significant improvements in solid-state batteries with chalcogen, chalcogenide, and halide cathodes, including improved energy density, better rate capability, longer cycle life, and other notable benefits. To fully leverage the benefits of lithium metal anodes in solid-state batteries, high-capacity conversion-type cathodes are necessary. While challenges remain in optimizing the interface between solid-state electrolytes and conversion-type cathodes, this area of research presents significant opportunities for the development of improved battery systems and will require continued efforts to overcome these challenges.

Designing of trimetallic-phase ternary metal sulfides coupled with N/S doped carbon protector for superior and safe Li/Na storage

Traditional transition metal sulfides (TMSs) have shown favorable potentials in energy storage. Nevertheless, its further usage is plagued by the issues of particle breakage and large volume change. In this work, the nanostructured ternary TMSs coupled with N/S doped carbon protector (NiCoFe-S@NSC) is delicately designed via compositional regulation and spatial structure protection strategies. As lithium ion batteries anode, this electrode gives an impressive capacity of 995.7 mAh/g after running 1000 cycles at 1 A/g. More importantly, NiCoFe-S@NSC electrode still shows a discharge capacity of 221.94 mAh/g after running 20,000 cycles at 10 A/g, reflecting an extremely-low capacity decay rate of 0.0377 ‰ per cycle. As sodium ion batteries anode, a high initial discharge capacity of 896.4 mA h g^-1 can be found. Even after running 400 cycles at 5 A/g, the electrode still displays a reversible capacity of 334.5 mAh/g with outstanding coulombic efficiency above 98.0 %. Impressively, LiNi_xCo_yMn_1-x-yO₂//NiCoFe-S@NSC full cell gives incipient discharge/charge capacities of 186.89/240.18 mAh/g. Moreover, the discharge capacities for the following 100 cycles remain above 150 mAh/g. Thermal runaway tests also demonstrate the higher thermal safety of cells with NiCoFe-S@NSC electrode, accompanying with the promoted activation energy.

Sheet-Like Stacking SnS2/rGO Heterostructures as Ultrastable Anodes for Lithium-Ion Batteries

SnS₂-based materials have attracted considerable attention in energy storage and conversion owing to their high lithium activity and theoretical capacity. However, the practical application is severely limited by the low coulombic efficiency and short cycle life due to irreversible side reactions, low conductivity, and serious pulverization in the discharge/charge process. In this study, sheet-like stacking SnS₂/reduced graphene oxide (rGO) heterostructures were developed using a facile solvothermal method. It was found that the composites between SnS₂ nanoplates and rGO nanosheets are closely coupled through van der Waals interactions, providing efficient electron/ion paths to ensure high electrical conductivity and sufficient buffer space to alleviate volume expansion. Therefore, the SnS₂/rGO heterostructure anode can obtain a high capacity of 840 mA h g^-1 after 120 cycles at a current density of 200 mA g^-1 and maintain a capacity of 450 mA h g^-1 after 1000 cycles at 1000 mA g^-1. In situ X-ray diffraction tests showed that SnS₂/rGO undergoes typical initial intercalation, conversion, and subsequent alloying reactions during the first discharge, and most of the reactions are dealloying/alloying in the subsequent cycles. The galvanostatic intermittent titration technique showed that the diffusion of lithium ions in the SnS₂/rGO heterostructures is faster in the intercalation and conversion reactions than in the alloying reactions. These observations help to clarify the reaction mechanism and ion diffusion behavior in the SnS₂ anode materials, thus providing valuable insights for improving the energy efficiency of lithium-ion batteries.

A novel "caterpillar with eggs" mesostructured iron sulfide as an anode for a Li-ion battery displaying stable electrochemical performance

Emerging anodes are important for high energy-density lithium-ion batteries. Here, we present a mesostructured FeS₂ comprising nanoparticles embedded in a nanoneedle-assembled nanotube to form a novel "caterpillar with eggs" (CWE) structure. The voids alleviated the volumetric change upon charge-discharge; the nanoneedles-assembled shell provided rapid transport pathways for ions and electrons. The FeS₂ anode exhibited a high capacity of 805.1 mA h g^-1 after 500 cycles at 2 A g^-1. When cycling at -10 °C and 45 °C, the anode provided capacities of 754.5 and 744.4 mA h g^-1 after 100 cycles at 1 A g^-1, respectively. This good electrochemical performance will enable our special design to find broad applications for developing high-performance energy-storage systems.

Kinetic 2D Crystals via Topochemical Approach

The designing of novel materials is a fascinating and innovative pathway in materials science. Particularly, novel layered compounds have tremendous influence in various research fields. Advanced fundamental studies covering various aspects, including reactants and synthetic methods, are required to obtain novel layered materials with unique physical and chemical properties. Among the promising synthetic techniques, topochemical approaches have afforded the platform for widening the extent of novel 2D materials. Notably, the synthesis of binary layered materials is considered as a major scientific breakthrough after the synthesis of graphene as they exhibit a wide spectrum of material properties with varied potential applicability. In this review, a comprehensive overview of the progress in the development of metastable layered compounds is presented. The various metastable layered compounds synthesized from layered ternary bulk materials through topochemical approaches are listed, followed by the descriptions of their mechanisms, structural analyses, characterizations, and potential applications. Finally, an essential research direction concerning the synthesis of new materials is indicated, wherein the possible application of topochemical approaches in unprecedented areas is explored.

Synthetic control over polymorph formation in the d-band semiconductor system FeS2

Pyrite, also known as fool's gold is the thermodynamic stable polymorph of FeS2. It is widely considered as a promising d-band semiconductor for various applications due to its intriguing physical properties. Marcasite is the other naturally occurring polymorph of FeS2. Measurements on natural crystals have shown that it has similarly promising electronic, mechanical, and optical properties as pyrite. However, it has been only scarcely investigated so far, because the laboratory-based synthesis of phase-pure samples or high quality marcasite single crystal has been a challenge until now. Here, we report the targeted phase formation via hydrothermal synthesis of marcasite and pyrite. The formation condition and phase purity of the FeS2 polymorphs are systematically studied in the form of a comprehensive synthesis map. We, furthermore, report on a detailed analysis of marcasite single crystal growth by a space-separated hydrothermal synthesis. We observe that single phase product of marcasite forms only on the surface under the involvement of H2S and sulphur vapor. The availability of high-quality crystals of marcasite allows us to measure the fundamental physical properties, including an allowed direct optical bandgap of 0.76 eV, temperature independent diamagnetism, an electronic transport gap of 0.11 eV, and a room-temperature carrier concentration of 4.14 × 1018 cm-3. X-ray absorption/emission spectroscopy are employed to measure the band gap of the two FeS2 phases. We find marcasite has a band gap of 0.73 eV, while pyrite has a band gap of 0.87 eV. Our results indicate that marcasite - that is now synthetically available in a straightforward fashion - is as equally promising as pyrite as candidate for various semiconductor applications based on earth abundant elements.

Sandwich-like SnS2/graphene multilayers for efficient lithium/sodium storage

2D materials have attracted extensive attention in energy storage and conversion due to their excellent electrochemical performances. Herein, we report utilization of monolayer SnS₂ sheets within SnS₂/graphene multilayers for efficient lithium and sodium storage. SnS₂/graphene multilayers are synthesized through a solution-phase direct assembly method by electrostatic interaction between monolayer SnS₂ and PDDA (polydimethyl diallyl ammonium chloride)-graphene nanosheets. It has been shown that the SnS₂/graphene multilayer electrode has a large pseudocapacity contribution for enhanced lithium and sodium storage. Typical batteries deliver a stable reversible capacity of ∼160 mA h g^-1 at 2 A g^-1 after 2000 cycles for lithium and a stable reversible capacity of ∼142 mA h g^-1 at 1 A g^-1 after 1000 cycles for sodium. The excellent electrochemical performances of SnS₂/graphene multilayers are attributed to the synergistic effect between the monolayer SnS₂ sheets and the PDDA-graphene nanosheets. The multilayer structure assembled by different monolayer nanosheets is promising for the further development of 2D materials for energy storage and conversion.

Study of the Lithium Storage Mechanism of N-Doped Carbon-Modified Cu2 S Electrodes for Lithium-Ion Batteries

Owing to their high specific capacity and abundant reserve, Cu_xS compounds are promising electrode materials for lithium‐ion batteries (LIBs). Carbon compositing could stabilize the Cu_xS structure and repress capacity fading during the electrochemical cycling, but the corresponding Li⁺ storage mechanism and stabilization effect should be further clarified. In this study, nanoscale Cu₂S was synthesized by CuS co‐precipitation and thermal reduction with polyelectrolytes. High‐temperature synchrotron radiation diffraction was used to monitor the thermal reduction process. During the first cycle, the conversion mechanism upon lithium storage in the Cu₂S/carbon was elucidated by operando synchrotron radiation diffraction and in situ X‐ray absorption spectroscopy. The N‐doped carbon‐composited Cu₂S (Cu₂S/C) exhibits an initial discharge capacity of 425 mAh g⁻¹ at 0.1 A g⁻¹, with a higher, long‐term capacity of 523 mAh g⁻¹ at 0.1 A g⁻¹ after 200 cycles; in contrast, the bare CuS electrode exhibits 123 mAh g⁻¹ after 200 cycles. Multiple‐scan cyclic voltammetry proves that extra Li⁺ storage can mainly be ascribed to the contribution of the capacitive storage.

A Polymorphic FeS2 Cathode Enabled by Copper Current Collector Induced Displacement Redox Mechanism

In this contribution, we fabricated a composite consisting of two polymorphs of FeS₂, pyrite (P-FeS₂) and marcasite (M-FeS₂), for high-performance Li-FeS₂ battery. A series of electrochemical, microscopic, and spectroscopic characterizations indicate that the introduction of metastable M-FeS₂ into P-FeS₂ enables the four-electron reduction between FeS₂ and lithium to generate Fe and Li₂S, providing a high specific capacity of 894 mAh/g with specific energy over 1300 Wh/kg. Moreover, it is verified that the electrochemical irreversibility of this composite toward lithium storage is mainly rooted in the shuttle effect, caused by the elemental sulfur which is inevitably produced during the oxidation process of Li₂S and Fe. To tackle this issue, copper (Cu) current collector is adopted to chemically immobilize the soluble lithium polysulfides and fundamentally alter the reaction pathway. It is shown that compared with Fe, Li₂S prefers to react with Cu current collector to generate Cu₂S through the thermodynamically facile displacement reaction mechanism benefiting from the similar lattice framework between Cu₂S and Li₂S. Such displacement reaction without lattice reconstruction renders the composite superior rate capability (∼730 mAh/g@2 A/g) and long lifespan (89.7% capacity retention after 3200 cycles). Present work allows for the fabrication of high-performance electrodes based on metal chalcogenides.

Ultrasmall FeS2 Nanoparticles-Decorated Carbon Spheres with Laser-Mediated Ferrous Ion Release for Antibacterial Therapy

Recent progress in nanotechnology and the ancient use of sulfur in treating dermatological disorders have promoted the development of nano-sulfides for antimicrobial applications. However, the variable valences and abundant forms of nano-sulfides have complicated investigations on their antibacterial activity. Here, carbon nanospheres (CNSs) with decoration of ultrasmall FeS₂ nanoparticles (CNSs@FeS₂ ) is synthesized, and their antibacterial ability and mechanism are explored. The CNSs@FeS₂ released Fe²⁺ and sulfur ions simultaneously through dissolution and disproportionation. In vitro study indicated that the released Fe²⁺ killed bacteria by increasing the oxidative state of bacterial surfaces and intracellular molecules. Importantly, the released sulfur exhibited a protective effect on Fe²⁺ , ensuring the stable existence of Fe²⁺ to continuously combat bacteria. Moreover, the carbon shells of CNSs@FeS₂ not only prevented the aggregation of FeS₂ but also accelerated the release of Fe²⁺ through photothermal effects to achieve synergistic hyperthermia/Fe²⁺ therapy. In vivo experiments indicated that treatment with CNSs@FeS₂ resulted in a marked reduction in bacterial number and improvement in survival in an acute peritonitis mouse model, and antibacterial wound experiments demonstrated high efficacy of CNSs@FeS₂ -enabled synergistic hyperthermia/Fe²⁺ therapy. Thus, this study clarifies the antibacterial mechanism of FeS₂ and offers a synergetic therapeutic platform with laser-mediated Fe²⁺ release for antibacterial applications.

Pseudocapacitive Lithium Storage of Cauliflower-Like CoFe2 O4 for Low-Temperature Battery Operation

Binary transition-metal oxides (BTMOs) with hierarchical micro-nano-structures have attracted great interest as potential anode materials for lithium-ion batteries (LIBs). Herein, we report the fabrication of hierarchical cauliflower-like CoFe₂ O₄ (cl-CoFe₂ O₄ ) via a facile room-temperature co-precipitation method followed by post-synthetic annealing. The obtained cauliflower structure is constructed by the assembly of microrods, which themselves are composed of small nanoparticles. Such hierarchical micro-nano-structure can promote fast ion transport and stable electrode-electrolyte interfaces. As a result, the cl-CoFe₂ O₄ can deliver a high specific capacity (1019.9 mAh g^-1 at 0.1 A g^-1 ), excellent rate capability (626.0 mAh g^-1 at 5 A g^-1 ), and good cyclability (675.4 mAh g^-1 at 4 A g^-1 for over 400 cycles) as an anode material for LIBs. Even at low temperatures of 0 °C and -25 °C, the cl-CoFe₂ O₄ anode can deliver high capacities of 907.5 and 664.5 mAh g^-1 at 100 mA g^-1 , respectively, indicating its wide operating temperature. More importantly, the full-cell assembled with a commercial LiFePO₄ cathode exhibits a high rate performance (214.2 mAh g^-1 at 5000 mA g^-1 ) and an impressive cycling performance (612.7 mAh g^-1 over 140 cycles at 300 mA g^-1 ) in the voltage range of 0.5-3.6 V. Kinetic analysis reveals that the electrochemical performance of cl-CoFe₂ O₄ is dominated by pseudocapacitive behavior, leading to fast Li⁺ insertion/extraction and good cycling life.

Production of Quasi-2D Platelets of Nonlayered Iron Pyrite (FeS2) by Liquid-Phase Exfoliation for High Performance Battery Electrodes

Over the past 15 years, two-dimensional (2D) materials have been studied and exploited for many applications. In many cases, 2D materials are formed by the exfoliation of layered crystals such as transition-metal disulfides. However, it has recently become clear that it is possible to exfoliate nonlayered materials so long as they have a nonisotropic bonding arrangement. Here, we report the synthesis of 2D-platelets from the earth-abundant, nonlayered metal sulfide, iron pyrite (FeS₂), using liquid-phase exfoliation. The resultant 2D platelets exhibit the same crystal structure as bulk pyrite but are surface passivated with a density of 14 × 10¹⁸ groups/m². They form stable suspensions in common solvents and can be size-selected and liquid processed. Although the platelets have relatively low aspect ratios (∼5), this is in line with the anisotropic cleavage energy of bulk FeS₂. We observe size-dependent changes to optical properties leading to spectroscopic metrics that can be used to estimate the dimensions of platelets. These platelets can be used to produce lithium ion battery anodes with capacities approaching 1000 mAh/g.

MoO2 coated few layers of MoS2 and FeS2 nanoflower decorated S-doped graphene interoverlapped network for high-energy asymmetric supercapacitor

Herein, the ultra-thin layer MoS₂ coverd MoO₂ nanocrystal arraying on sulfur-doped graphene framework (MoS₂-MoO₂/3DSG) is obtained via a simple hydrothermal procedure accompanied with high temperature annealing. Sodium thiosulfate and ethanethiol are used as sulfur sources to form three-dimensional sulfur doped graphene (3DSG) in the hydrothermal process. Importantly, MoO₂ nano-particles are uniformly loaded on MoS₂ nanosheets and 3DSG via in-situ collaborative technology. As a result, the stable conductive network take full use of the characteristics of high specific capacitance of MoO₂ nanoparticles, convenient ion transport channel of two-dimensional MoS₂ nanoflakes and efficient charge transfer and cross-linked 3DSG to improve the electrochemical activity and enhance the dynamics of electrons / ions, which is up to 1150.37 F g^-1 specific capacitance and maintains 94.6% of the original capacitance after 10,000 cycles. Also, FeS₂ nanoflowers in situ loading on 3DSG (FeS₂/3DSG) with enhanced the overall performance of the device are fabricated. The asymmetric supercapacitor with the positive electrode of MoS₂-MoO₂/3DSG and the negative electrode of FeS₂/3DSG can work efficiently and stably under the voltage of 1.7 V, and provide energy density of 87.38 Wh kg^-1 at the power density of 683.94 Wkg^-1, displaying an outstanding application prospect for energy storage.

Unraveling the Beneficial Microstructure Evolution in Pyrite for Boosted Lithium Storage Performance

Pyrite FeS₂ as a high-capacity electrode material for lithium-ion batteries (LIBs) is hindered by its unstable cycling performance owing to the large volume change and irreversible phase segregation from coarsening of Fe. Here, the beneficial microstructure evolution in MoS₂ -modified FeS₂ is unraveled during the cycling process; the microstructure evolution is responsible for its significantly boosted lithium storage performance, making it suitable for use as an anode for LIBs. Specifically, the FeS₂ /MoS₂ displays a long cycle life with a capacity retention of 116 % after 600 cycles at 0.5 A g^-1 , which is the best among the reported FeS₂ -based materials so far. A series of electrochemical tests and structural characterizations substantially revealed that the introduced MoS₂ in FeS₂ experiences an irreversible electrochemical reaction and thus the in situ formed metallic Mo could act as the conductive buffer layer to accelerate the dynamics of Li⁺ diffusion and electron transport. More importantly, it can guarantee the highly reversible conversion in lithiated FeS₂ by preventing Fe coarsening. This work provides a fundamental understanding and an effective strategy towards the microstructure evolution for boosting lithium storage performances for other metal sulfide-based materials.

Boosting the lithium-ion and sodium-ion storage performances of pyrite by regulating the energy barrier of ion transport

Pyrite (FeS2) is a functional material of great importance for lithium/sodium ion batteries (LIBs/SIBs), but its sluggish dynamics greatly hinder its high performance. Here, we demonstrate an effective strategy of regulating the energy barrier of ion transport to significantly enhance the sluggish dynamics of FeS2 by Co doping. Compared to pristine FeS2, a series of Co-doped FeS2 shows enhanced alkali metal ion storage performance and most typically, the optimized Fe0.7Co0.3S2 sample displays high reversible capacities, of 1170 mA h g-1 for LIBs and 650 mA h g-1 for SIBs at a current density of 0.1 A g-1 as well as super long-life cycling stability for SIBs (1200 cycles at 5 A g-1). The evidently enhanced performances of Fe0.7Co0.3S2 for LIBs/SIBs can be attributed to its significantly decreased activation energy of ion transport, thus leading to greatly accelerated ion transport dynamics. Furthermore, galvanostatic intermittent titration technique (GITT) experiments also support this important regulation effect of Co doping on the ion transport dynamics of FeS2. The excellent ion transport dynamics induce a strong pseudo-capacitance behavior in both SIBs and LIBs, and their pseudo-capacitance contributions are more than 90% at 1.0 mV s-1. This work provides a new perspective to improve the alkali metal ion storage performance by optimizing the ion transport dynamics.

In-situ synthesis of Fe7S8 nanocrystals decorated on N, S-codoped carbon nanotubes as anode material for high-performance lithium-ion batteries

Fe₇S₈ has emerged as an attractive anode material for lithium-ion batteries (LIBs) due to its outstanding features such as low cost, high theoretical capacity, as well as environmental benignity. However, the rapid capacity fading derived from the tremendous volume change during the charging/discharging process hinders its practical application. Nanostructure engineering and the combination with carbonaceous material are essential to address this issue. In this work, Fe₇S₈ nanocrystals decorated on N, S-codoped carbon nanotubes (Fe₇S₈-NSC) were synthesized through a facile one-step pyrolysis of Fe-containing polypyrrole (PPy) nanotubes with sulphur powders under nitrogen atmosphere. When evaluated as anode of LIBs, Fe₇S₈-NSC demonstrates excellent cycling stability (718.8 mAh g^-1 at 100 mA g^-1 after 100 cycles) and superior rate ability (290.8 mAh g^-1 at 2000 mA g^-1). Moreover, Fe₇S₈-NSC shows a typical specific capacity recovery phenomenon, an extraordinary capacity of 744.4 mAh g^-1 at 2000 mA g^-1 after 1000 cycles can be achieved, which outperforms most of the Fe₇S₈-based anode materials reported before. The Fe₇S₈-NSC should be a promising anode material for high-performance LIBs.

Lithium-Ion-Based Electrochemical Energy Storage in a Layered Vanadium Formate Coordination Polymer

A vanadium formate (VF) coordination polymer and its composite with partially reduced graphene oxide (prGO), namely VF-prGO, can be applied as anode materials for Li-ion based electrochemical energy storage (EcES) systems in the potential range of 0-3 V (vs Li⁺ /Li). This study shows that a reversible capacity of 329 mAh g^-1 at a current density of 50 mA g^-1 after 50 cycles can be realized for VF along with a high rate capability. The composite exhibits even a higher capacity of 504 mAh g^-1 at 50 mA g^-1 . A good capacity retention is observed even after 140 cycles for both VF and the composite. An ex-situ X-ray photoelectron spectroscopy study indicates the involvement of V³⁺ /V⁴⁺ redox couple in the charge storage mechanism. A significant contribution of this reversible capacity is attributed to the pseudocapacitive behavior of the system.

Highly pseudocapacitive metal-organic framework derived carbon skeleton supported Fe-Ti-O nanotablets as an anode material for efficient lithium storage

A facile and effective method to fabricate highly pseudocapacitive electrodes of Fe-Ti-O@C has been proposed here. In this strategy, FeOOH crystals were firstly grown uniformly on the surface of Ti-based MOF (MIL-125) tablet substrates through a solution immersion method, and then converted to uniform carbon supported Fe-Ti-O composites by calcination under argon. The obtained Fe-Ti-O@C composites were first utilized as an efficient anode for lithium ion batteries with a high reversible capacity of 988 mA h g^-1 after 160 cycles at 200 mA g^-1. Such a superior lithium storage performance may be due to the synergistic effect of the Fe₃O₄ nanoparticles with a high capacity, FeTiO₃ nanocomposites with a nearly stable structure during the Li⁺ insertion/removal process, and the conductive carbon skeleton with a large surface area and porous structure. This work represents an important step forward in the fabrication of MOF-derived hybrids and enables transition metal oxides (TMOs) to have potential applications in energy storage systems.

Constructing heterostructured FeS2/CuS nanospheres as high rate performance lithium ion battery anodes

Heterostructured porous FeS₂/CuS nanospheres exhibit enhanced reaction kinetics, excellent rate capability and desirable long-term cycling stability performance.

Fast-Charging High-Energy Battery-Supercapacitor Hybrid: Anodic Reduced Graphene Oxide-Vanadium(IV) Oxide Sheet-on-Sheet Heterostructure

The battery-supercapacitor hybrid (BSH) device has potential applications in energy storage and can be a remedy for low-power batteries and low-energy supercapacitors. Although several studies have investigated electrode materials (particularly for a battery-type anode material) and design for BSHs, the energy density and power density are insufficient (far from the levels required for practical applications). Herein, a hierarchical vanadium(IV) oxide on reduced graphene oxide (rGO@VO₂) heterostructure as an anode and activated carbon on carbon cloth (AC@CC) as a cathode are proposed for fabricating an advanced BSH. The mixed valency of V ions inside the as-prepared VO₂ matrix (V³⁺ and V⁴⁺) facilitates redox reactions at a low potential, giving rise to rGO@VO₂ as a typical anode with a working potential of 0.01-3 V (vs Li/Li⁺). The sheet-on-sheet heterostructured rGO@VO₂ yields a high specific capacity of 1214 mAh g^-1 at 0.1 A g^-1 after 120 cycles, with a high rate capability and stability. The rGO@VO₂//AC@CC BSH device exhibits a maximum gravimetric energy density of 126.7 Wh kg^-1 and a maximum gravimetric power density of ∼10 000 W kg^-1 within a working voltage range of 1-4 V. Moreover, it exhibits fast charging times of 5 and 834 s with energy densities of 15.6 and 82 Wh kg ^-1, respectively.

Boosting High Energy Density Lithium-Ion Storage via the Rational Design of an FeS-Incorporated Sulfurized Polyacrylonitrile Fiber Hybrid Cathode

In order to satisfy the escalating energy demands, it is inevitable to improve the energy density of current Li-ion batteries. As the development of high-capacity cathode materials is of paramount significance compared to anode materials, here we have designed for the first time a unique synergistic hybrid cathode material with enhanced specific capacity, incorporating cost-effective iron sulfide (FeS) nanoparticles in a sulfurized polyacrylonitrile (SPAN) nanofiber matrix through a rational in situ synthesis strategy. Previous reports on FeS cathodes are scarce and consist of an amorphous carbon matrix to accommodate the volume changes encountered during the cycling process. However, this inactive buffering matrix eventually increases the weight of the cell, reducing the overall energy density. By the rational design of this hybrid composite cathode, we ensure that the presence of covalently bonded sulfur in SPAN guarantees high sulfur utilization, while effectively buffering the volume changes in FeS. Meanwhile, FeS can compensate for the conductivity issues in the SPAN, thereby realizing a synergistically driven dual-active cathode material improving the overall energy density of the composite. Simultaneous in situ generation of FeS nanoparticles within the SPAN fiber matrix was carried out via electrospinning followed by a one-step heating procedure. The developed hybrid cathode material displays enhanced lithium-ion storage, retaining 688.6 mA h g_{(FeS@SPAN composite)}^-1 at the end of 500 cycles at 1 A g^-1 even within a narrow voltage range of 1-3.0 V. A high discharge energy density > 900 W h kg_{(FeS@SPAN composite)}^-1, much higher than the theoretical energy density of the commercial LiCoO₂ cathode, was also achieved, revealing the promising prospects of this hybrid cathode material for high energy density applications.

Hierarchically porous nanosheets-constructed 3D carbon network for ultrahigh-capacity supercapacitor and battery anode

An advanced hierarchically porous nanosheets-constructed three-dimensional (3D) carbon material (HPNSC) is prepared by using low-cost agricultural waste-nelumbium seed-pods as the precursor, and potassium hydroxide (KOH) as the activator. The as-prepared HPNSC material has a hierarchically porous nanosheets-constructed structure with 3D carbon nanosheet network morphology, which can enable fast and efficient transfer of Li⁺/Na⁺/H⁺ during charge-discharge process. The assembled HPNSC//HPNSC symmetric supercapacitors exhibit an improved energy density of 41.3 W h kg^-1 with a power density of 180 W kg^-1 in 1 mol l^-1 Na₂SO₄ electrolyte. The energy density can still be maintained at 16.3 W h kg^-1 even if the power density is increased to 9000 W kg^-1. When acting as the reversible electrode for lithium ion batteries, this HPNSC material can achieve a high specific capacity of 1246 mA h g^-1 at 0.1 A g^-1. Moreover, sodium ion battery with HPNSC electrode exhibits excellent cycling performance of 161.8 mA h g^-1 maintained even after being cycled 3350 times. The electrochemical performances clearly indicate that the HPNSC developed in this work is a very promising energy storage electrode material, and can further provide new insights for designing and developing highly porous materials for energy storage in other fields.

Ultrathin carbon-coated FeS2 nanooctahedra for sodium storage with long cycling stability

Porous ultrathin carbon-encapsulated FeS₂@C nanooctahedra synthesized by a facile solvothermal and carbon-coating-annealing-pickling strategy exhibit a superior performance for sodium-ion storage.

Asynchronous reactions of “self-matrix” dual-crystals effectively accommodating volume expansion/shrinkage of electrode materials with enhanced sodium storage

The dual-crystal FeS₂ shows a better tolerance towards large volume changes because of the asynchronous reaction.

Amorphous iron sulfide nanowires as an efficient adsorbent for toxic dye effluents remediation

Environmental and health concerns arising from the toxicity of organic dye effluents is still the issue of the twenty-first century. In that regard, this study presents iron sulfide (FeS₂) for its use in environmental remediation application. Amorphous phase FeS₂ nanowires were synthesized by PVP-assisted solvothermal reaction and were characterized using XRD, XPS, BET, FE-SEM, and EDS techniques. The amorphous phase FeS₂ is attractive from material synthesis point of view as its synthesis does not require delicate control over the process parameters, unlike the crystalline phase. The 1-D nanowire FeS₂ had a high surface-to-volume ratio with negative zeta potential within a wide pH range. Having those surface and microstructural properties, these nanowires exhibited excellent adsorption property towards model organic dyes, Congo red (anionic), and methylene blue (cationic), with theoretical adsorption capacity of 118.86 and 48.82 mg g^-1, respectively. Adsorption kinetics and isotherm models were implemented to study the adsorption processes at different adsorption conditions (pH, adsorbent loading, initial adsorbate concentration). The pH dependence of the adsorption and FT-IR analysis evidenced the prevalence of both physisorption and chemisorption during the adsorption of Congo red. Recyclability test proved the excellent performance of this amorphous FeS₂ nanowire adsorbent for three consecutive cycles. Considering its ease of synthesis, excellent adsorption property, and cyclic performance, the as-prepared adsorbent could be a promising material for dye effluents treatment.

Tetranuclear cobalt(ii)-isonicotinic acid frameworks: selective CO2 capture, magnetic properties, and derived "Co3O4" exhibiting high performance in lithium ion batteries

Two new 3D cobalt metal-organic frameworks (MOFs), [Co4(CH3COO)(in)5(μ3-OH)2]·2H2O (1) and [Co4(SO4)2(in)4(DMF)2]·3DMF (2) (Hin = isonicotinic acid), have been prepared through the anion template method. Compound 1 consists of rare odd-number connected (9-connected) cubane-like SBUs, while compound 2 consists of 8-connected high-symmetry square-planar clusters. Magnetic studies indicate that compound 1 exhibits spin-canting antiferromagnetic ordering, while compound 2 shows antiferromagnetic behavior. At 273 K and 1 bar, compound 1 exhibits a high CO2 selectivity over CH4 and a significant CO2 uptake of 13.6 wt%, which is higher than that of 2 (8.5 wt%). Furthermore, compound 1 was then transformed into ultrasmall Co3O4 nanoparticles via simple but effective annealing treatment. Electrochemical measurements show that the Co3O4 nanospheres derived from compound 1 exhibited high and stable lithium storage properties (1100 mA h g-1 after 100 cycles at 200 mA g-1) and excellent rate capabilities.

Porous MXene Frameworks Support Pyrite Nanodots toward High-Rate Pseudocapacitive Li/Na-Ion Storage

Presented are the novel Ti₃C₂ T _x MXene-based nanohybrid that decorated by pyrite nanodots on its surface (denoted as FeS₂@MXene). The nanohybrid was obtained by the one-step sulfurization of self-assembled iron hydroxide@MXene precursor. When used for Li/Na-ion storage, the FeS₂@MXene nanohybrid present excellent rate capabilities. Particularly, for Li-ion storage, an elevated reversible specific capacity of 762 mAh g^-1 at 10 A g^-1 after 1000 cycles was achieved. And for Na-ion storage, the FeS₂@MXene nanohybrid also delivering a reversible specific capacity of 563 mAh g^-1 after 100 cycles at a current density of 0.1 A g^-1.

Rational design of metal organic framework-derived FeS2 hollow nanocages@reduced graphene oxide for K-ion storage

K-ion batteries (KIBs) have become one of the promising alternatives to lithium ion batteries. In this work, we are the first to utilize reduced graphene oxide (RGO) wrapped metal organic framework-derived FeS2 hollow nanocages (FeS2@RGO) as an anode for KIBs. Owing to the synergistic effect from FeS2 nanocages and RGO shells, our FeS2@RGO sample exhibited superior electrochemical performance. Such FeS2@RGO electrodes demonstrate a high capacity of 264 mA h g-1 after 50 cycles at 50 mA g-1 and 123 mA h g-1 after 420 cycles even at a large current density of 500 mA g-1. More importantly, we also explain the electrochemical reaction process about FeS2 and believe that these results would open the door for a novel class of long cycling performance anode materials in the KIB field.

MnWO4 nanoparticles as advanced anodes for lithium-ion batteries: F-doped enhanced lithiation/delithiation reversibility and Li-storage properties

F-Doped MnWO4 nano-particles were synthesized by a one-pot hydrothermal reaction. When evaluated as an electrode material for a Li ion battery, the F-doped nano-MnWO4 delivers a theoretical capacity of 708 mA h g-1 and a long cycle life, as demonstrated by more than 85% capacity retention when cycled for 150 cycles.

A novel bismuth-based anode material with a stable alloying process by the space confinement of an in situ conversion reaction for a rechargeable magnesium ion battery

Due to the space confinement of in situ conversion, the BiOF electrode shows superior magnesium storage performance.