Vine-like MoS2 anode materials self-assembled from 1-D nanofibers for high capacity sodium rechargeable batteries

Molecular modulation strategies for two-dimensional transition metal dichalcogenide-based high-performance electrodes for metal-ion batteries

In the past few decades, great efforts have been made to develop advanced transition metal dichalcogenide (TMD) materials as metal-ion battery electrodes. However, due to existing conversion reactions, they still suffer from structural aggregation and restacking, unsatisfactory cycling reversibility, and limited ion storage dynamics during electrochemical cycling. To address these issues, extensive research has focused on molecular modulation strategies to optimize the physical and chemical properties of TMDs, including phase engineering, defect engineering, interlayer spacing expansion, heteroatom doping, alloy engineering, and bond modulation. A timely summary of these strategies can help deepen the understanding of their basic mechanisms and serve as a reference for future research. This review provides a comprehensive summary of recent advances in molecular modulation strategies for TMDs. A series of challenges and opportunities in the research field are also outlined. The basic mechanisms of different modulation strategies and their specific influences on the electrochemical performance of TMDs are highlighted.

Homologous Heterostructured NiS/NiS2 @C Hollow Ultrathin Microspheres with Interfacial Electron Redistribution for High-Performance Sodium Storage

Nickel sulfides with high theoretical capacity are considered as promising anode materials for sodium-ion batteries (SIBs); however, their intrinsic poor electric conductivity, large volume change during charging/discharging, and easy sulfur dissolution result in inferior electrochemical performance for sodium storage. Herein, a hierarchical hollow microsphere is assembled from heterostructured NiS/NiS2 nanoparticles confined by in situ carbon layer (H-NiS/NiS2 @C) via regulating the sulfidation temperature of the precursor Ni-MOFs. The morphology of ultrathin hollow spherical shells and confinement of in situ carbon layer to active materials provide rich channels for ion/electron transfer and alleviate the effects of volume change and agglomeration of the material. Consequently, the as-prepared H-NiS/NiS2 @C exhibit superb electrochemical properties, satisfactory initial specific capacity of 953.0 mA h g-1 at 0.1 A g-1 , excellent rate capability of 509.9 mA h g-1 at 2 A g-1 , and superior longtime cycling life with 433.4 mA h g-1 after 4500 cycles at 10 A g-1 . Density functional theory calculation shows that heterogenous interfaces with electron redistribution lead to charge transfer from NiS to NiS2 , and thus favor interfacial electron transport and reduce ion-diffusion barrier. This work provides an innovative idea for the synthesis of homologous heterostructures for high-efficiency SIB electrode materials.

Reduced Graphene-Oxide-Encapsulated MoS2/Carbon Nanofiber Composite Electrode for High-Performance Na-Ion Batteries

Sodium-ion batteries (SIBs) have been increasingly studied due to sodium (Na) being an inexpensive ionic resource (Na) and their battery chemistry being similar to that of current lithium-ion batteries (LIBs). However, SIBs have faced substantial challenges in developing high-performance anode materials that can reversibly store Na⁺ in the host structure. To address these challenges, molybdenum sulfide (MoS₂)-based active materials have been considered as promising anodes, owing to the two-dimensional layered structure of MoS₂ for stably (de)inserting Na⁺. Nevertheless, intrinsic issues of MoS₂—such as low electronic conductivity and the loss of active S elements after a conversion reaction—have limited the viability of MoS₂ in practical SIBs. Here, we report MoS₂ embedded in carbon nanofibers encapsulated with a reduced graphene oxide (MoS₂@CNFs@rGO) composite for SIB anodes. The MoS₂@CNFs@rGO delivered a high capacity of 345.8 mAh g⁻¹ at a current density of 100 mA g⁻¹ for 90 cycles. The CNFs and rGO were synergistically taken into account for providing rapid pathways for electrons and preventing the dissolution of S sources during repetitive conversion reactions. This work offers a new point of view to realize MoS₂-based anode materials in practical SIBs.

Controllable Insertion Mechanism of Expanded Graphite Anodes Employing Conversion Reaction Pillars for Sodium-Ion Batteries

Controlling the structural and reaction characteristics of carbonaceous anode materials is essential to realizing alternative alkali-ion batteries. In this study, we report on expanded graphite material employing MoS_x conversion reaction pillars (EG-MoS_x) inserted into the interlayers and assess them as potential anode candidates for Na-ion batteries. We succeed in a tailored control of the insertion characteristics between one-phase reaction and two-phase reaction by modifying the crystal structure of EG-MoS_x under different thermal treatment conditions. EG-MoS_x-900 anode with an enlarged interlayer of ∼5.38 Å delivers an exceptionally high capacity of 501 mAh g^-1. We successfully solve the irreversible capacity issues of the expanded graphite materials by forming chemical preformation of the solid electrolyte interface (SEI) layer on the electrode surface, thereby significantly increasing coulombic efficiencies of thermally tuned EG-MoS_x (52.20 → 97.25%). We elucidate the electrochemical mechanism and structural properties of the EG-MoS_x anode materials by ex situ characterizations. Inserting active sulfide pillars enables us to overcome the performance limitations of existing Na-ion battery technologies, and we expect that this strategy will be applied to realize another family of alkali-ion batteries.

Hierarchically Designed Nitrogen-Doped MoS2/Silicon Oxycarbide Nanoscale Heterostructure as High-Performance Sodium-Ion Battery Anode

Molybedenum disulfide (MoS₂) is regarded as a promising anode material for next-generation sodium-ion batteries (SIBs) owing to its high theoretical capacity. However, its low conductivity, large volume changes, and undesirable phase transformation hinder its practical applications. In this study, we synthesize a hierarchically designed core-shell heterostructure based on nitrogen-doped MoS₂/C and silicon oxycarbide (SiOC) (N-MoS₂/C@SiOC) via the facile pyrolysis of a suspension of an N-MoS₂/polyfurfural precursor in silicone oil. The in situ nitrogen doping in a two-dimensional MoS₂ structure with carbon incorporation leads to the enlargement of the interlayer spacing and enhancement of the electronic conductivity and mechanical stability, which allows the facile, highly reversible insertion and extraction of sodium ions upon cycling. Further, the nanoscale SiOC shell with surface capacitive reactivity provides a conductive pathway, preventing unfavorable side reactions at the electrode/electrolyte interface and acting as a structure-reinforcing buffer against severe volume expansion issues. As a result, the N-MoS₂/C@SiOC composite exhibits high reversible capacity (540.7 mAh g^-1), high-capacity retention (>100% after 200 cycles), and excellent rate capability up to 10 A g^-1. The simple hierarchical core-shell design strategy developed in this study allows for the fabrication of high-performance metal sulfide anodes as well as other high-capacity anode materials for energy storage applications.

Super-Expansion of Assembled Reduced Graphene Oxide Interlayers by Segregation of Al Nanoparticle Pillars for High-Capacity Na-Ion Battery Anodes

The applicability of Na-ion batteries is contingent on breakthroughs in alternative electrode materials that have high capacities and which are economically viable. Unfortunately, conventional graphite anodes for Li-ion battery systems do not allow Na-ion accommodation into their interlayer space owing to the large ionic radius and low stabilizing energy of Na in graphite. Here, we suggest a promising strategy for significantly increasing Na capacity by expanding the axial slab space of graphite. We successfully synthesized reconstructed graphite materials via self-assembly of negative graphite oxide (GO) flakes and Al cation (positive) pillars and by subsequent chemical reaction of the obtained Al-GO materials. Al pillars, atomically distributed in graphite interlayers, can extend the slab space by up to ∼7 Å, which is a 2-fold interlayer distance of pristine graphite. An exceptionally high capacity of 780 mAh/g is demonstrated for reconstructed graphite anodes with Al pillars, compared with rGO materials (210 mAh/g). We investigated the electrochemical reaction mechanism and structural changes associated with discharge and charge to emphasize the benefit of using reconstructed graphite as anodes in Na-ion batteries. Our strategy of modifying the interlayer distance by introducing metallic pillars between the layers can help address the low capacity of carbonaceous anodes.

Unveiling a bimetallic FeCo-coupled MoS2 composite for enhanced energy storage

Sodium and potassium-ion batteries are promising for energy storage owing to their source abundance and low cost; however, most active materials still suffer from sluggish kinetics, huge volume variations, and poor conductivity and cycle stability. It remains a great challenge to explore appropriate electrode materials for scaled practical applications. Herein, mesoporous FeCo-incorporated MoS₂ nanosheets encapsulated into a porous carbon framework (FeCo@C@MoS₂) are smartly designed, artistically fabricated and evaluated for sodium and potassium storage. The FeCo@C@MoS₂ electrode displays high reversible capacities of 380 mA h g^-1 and 147 mA h g^-1 at 500 mA g^-1 for sodium and potassium storage, respectively. FeCo derived from a Prussian blue analogue promotes fast reaction kinetics of Na⁺/K⁺ transport, introduces the formation of a stable solid electrolyte interphase layer (SEI) in both the interior and exterior of the cube-like porous nanostructure and controls the Na⁺/K⁺ fluxes, suppressing the growth of metal dendrites. The porous carbon framework with large interstitial voids can effectively buffer volume variations and mitigate mechanical stress, contributing significantly to alleviate strain intensification on the surface layer between MoS₂ and FeCo during repeated plating/stripping processes. Density functional theoretical calculations (DFT) further confirm that the synthesized nanostructure shows an intensified electron state, elevated anti-stress ability, high-quality SEI film and preferable Na⁺/K⁺ adsorption energies. This in-depth investigation of the electrochemical performance and the extended energy storage mechanism based on metal alloy/sulfide nanostructures for sodium and potassium storage provides guidance for the smart design of heterojunctions for remarkable energy storage.

SiOC functionalization of MoS2 as a means to improve stability as sodium-ion battery anode

The development of feasible, scalable, and environmentally-safe electrode materials that provide stable cycling performance are critical for success of beyond lithium rechargeable batteries and supercapacitors. With respect to the sodium-ion battery (SIB) anodes constituting of transition metal dichalcogenides such as molybdenum disulfide (MoS₂), poor cycle stability and fast capacity degradation, due to low electronic conductivity and dissolution of chemical species in the electrolyte, hinders use of these promising layered materials as SIB anodes. Herein we report chemical functionalization in MoS₂ nanosheets with polymer-derived silicon oxycarbide or SiOC with the aim to preserve MoS₂ from dissolution in the SIB organic electrolyte, without compromising its role in sodiation and desodiation processes. Our results suggest that a MoS₂-SiOC composite electrode is effective in bringing improved cycle stability to sodium-ion cycling over neat MoS₂ even after 100 cycles.

Controllable Design of MoS2 Nanosheets Grown on Nitrogen-Doped Branched TiO2 /C Nanofibers: Toward Enhanced Sodium Storage Performance Induced by Pseudocapacitance Behavior

In this work, expanded MoS₂ nanosheets grown on nitrogen-doped branched TiO₂ /C nanofibers (NBT/C@MoS₂ NFs) are prepared through electrospinning and hydrothermal treatment method as anode materials for sodium-ion batteries (SIBs). The continuous 1D branched TiO₂ /C nanofibers provide a large surface area to grow expanded MoS₂ nanosheets and enhance the electronic conductivity and cycling stability of the electrode. The large surface area and doping of nitrogen can facilitate the transfer of both Na⁺ ions and electrons. With the merits of these unique design and extrinsic pseudocapacitance behavior, the NBT/C@MoS₂ NFs can deliver ultralong cycle stability of 448.2 mA h g^-1 at 200 mA g^-1 after 600 cycles. Even at a high rate of 2000 mA g^-1 , a reversible capacity of 258.3 mA h g^-1 can still be achieved. The kinetic analysis demonstrates that pseudocapacitive contribution is the major factor to achieve excellent rate performance. The rational design and excellent electrochemical performance endow the NBT/C@MoS₂ NFs with potentials as promising anode materials for SIBs.

Reduced Graphene Oxides Decorated NiSe Nanoparticles as High Performance Electrodes for Na/Li Storage

A facile, one-pot hydrothermal method was used to synthesize Nickel selenide (NiSe) nanoparticles decorated with reduced graphene oxide nanosheets (rGO), denoted as NiSe/rGO. The NiSe/rGO exhibits good electrochemical performance when tested as anodes for Na-ion batteries (SIBs) and Li-ion batteries (LIBs). An initial reversible capacity of 423 mA h g^-1 is achieved for SIBs with excellent cyclability (378 mA h g^-1 for 50th cycle at 0.05 A g^-1). As anode for LIBs, it delivers a remarkable reversible specific capacity of 1125 mA h g^-1 at 0.05 A g^-1. The enhanced electrochemical performance of NiSe/rGO nanocomposites can be ascribed to the synergic effects between NiSe nanoparticles and rGO, which provide high conductivity and large specific surface area, indicating NiSe/rGO as very promising Na/Li storage materials.

Hierarchical Nanostructured NiS/MoS2/C Composite Hollow Spheres for High Performance Sodium-Ion Storage Performance

Development of high performance electrode materials for sodium-ion batteries has been given a lot of attention in recent years but challenges remain. Herein, we have successfully synthesized the first NiS/MoS₂/C composite hollow spheres (NMSCHSs) via a facile hard template method combined with calcined sulfidation process. Owing to its unique hierarchical nanostructure with NiS nanoparticles embedded in shell wrapped with MoS₂ nanosheets, the NMSCHS-based anode electrodes exhibit superior rate capability and cycling stability, with a specific discharge capacity of 516 mAh g^-1 and 98.5% retention after 60 cycles at a current density of 0.1 A g^-1 and a discharge capacity of 398 mAh g^-1 even at 5 A g^-1.

Conversion of MoS2 to a Ternary MoS2- xSe x Alloy for High-Performance Sodium-Ion Batteries

MoS₂ has attracted tremendous attention as an anode for Na-ion batteries (NIBs) owing to its high specific capacity and layered graphite-like structure. Herein, MoS₂ is converted to a ternary MoS_{2- x}Se _x alloy through the selenizing process in order to boost the electrochemical performance for Na-ion batteries. Conversion of MoS₂ to MoS_{2- x}Se _x expands interlayer spacing, improves electronic conductivity, and creates more defects. The expanded interlayer spacing decreases Na⁺ diffusion resistance and facilitates Na⁺ fast transfer. The integrated graphene as a conductive network offers effective pathway for electron migration and maintains structural stability of electrodes during cycles. The ternary MoS_1.2Se_0.8/graphene (MoS_1.2Se_0.8/G) electrode demonstrates an extremely high reversible capacity of 509 mA h g^-1 after 200 cycles at 0.1 A g^-1 (capacity retention of 109%) as an anode for sodium-ion batteries. Even at 2 A g^-1 and after 700 cycles, the MoS_1.2Se_0.8/G electrode also displays a relatively high reversible capacity of 178 mA h g^-1. Full cells assembled with Na₃V₂(PO₄)₂F₃ cathodes and MoS_1.2Se_0.8/G anodes reveal high charge/discharge capacities. This work demonstrates that the ternary MoS_{2- x}Se _x alloy could be a potential anode material for Na-ion storage.

Na3V2(PO4)3: an advanced cathode for sodium-ion batteries

Sodium-ion batteries (SIBs) are considered to be the most promising electrochemical energy storage devices for large-scale grid and electric vehicle applications due to the advantages of resource abundance and cost-effectiveness. The electrochemical performance of SIBs largely relies on the intrinsic chemical properties of the cathodic materials. Among the various cathodes, rhombohedral Na3V2(PO4)3 (NVP), a typical sodium super ionic conductor (NASICON) compound, is very popular owing to its high Na+ mobility and firm structural stability. However, the relatively low electronic conductivity makes the theoretical capacity of NVP cathodes unviable even at low rates, not to mention the high rate of charging/discharging. This is a major drawback of NVPs, limiting their future large-scale applications. Herein, a comprehensive review of the recent progresses made in NVP fabrication has been presented, mainly including the strategies of developing NVP/carbon hybrid materials and elemental doping to improve the electronic conductivity of NVP cathodes and designing 3D porous architectures to enhance Na-ion transportation. Moreover, the application of NVP cathodic materials in Na-ion full batteries is summarized, too. Finally, some remarks are made on the challenges and perspectives for the future development of NVP cathodes.

Nanoflower-like N-doped C/CoS2 as high-performance anode materials for Na-ion batteries

Novel nanoflower-like N-doped C/CoS2 spheres assembled from 2D wrinkled CoS2 nanosheets were synthesized through a facile one-pot solvothermal method followed by sulfurization. Ascribed to the optimized 3D nanostructure and rational surface engineering, the unique hierarchical structure of the nanoflower-like C/CoS2 composites showed an excellent sodium ion storage capacity accompanied by high specific capacity, superior rate performance and long-term cycling stability. Specifically, the conductive interconnected wrinkled nanosheets create a number of mesoporous structures and thus can greatly release the mechanical stress caused by Na+ insertion/extraction. Besides, it was observed from the experiments that many extra defect vacancies and Na+ storage sites are introduced by the nitrogen doping process. It was also observed that the crosslinked 2D nanosheets can effectively reduce the diffusion lengths of sodium ions and electrons, resulting in an outstanding rate performance (>700 mA h g-1 at 1 A g-1 and 458 mA h g-1 at even 10 A g-1) and extraordinary cycling stability (698 mA h g-1 at 1 A g-1 after 500 cycles). The results provide a facile approach to fabricate promising anode materials for high-performance sodium-ion batteries (SIBs).

Sodium-ion batteries: present and future

Energy production and storage technologies have attracted a great deal of attention for day-to-day applications. In recent decades, advances in lithium-ion battery (LIB) technology have improved living conditions around the globe. LIBs are used in most mobile electronic devices as well as in zero-emission electronic vehicles. However, there are increasing concerns regarding load leveling of renewable energy sources and the smart grid as well as the sustainability of lithium sources due to their limited availability and consequent expected price increase. Therefore, whether LIBs alone can satisfy the rising demand for small- and/or mid-to-large-format energy storage applications remains unclear. To mitigate these issues, recent research has focused on alternative energy storage systems. Sodium-ion batteries (SIBs) are considered as the best candidate power sources because sodium is widely available and exhibits similar chemistry to that of LIBs; therefore, SIBs are promising next-generation alternatives. Recently, sodiated layer transition metal oxides, phosphates and organic compounds have been introduced as cathode materials for SIBs. Simultaneously, recent developments have been facilitated by the use of select carbonaceous materials, transition metal oxides (or sulfides), and intermetallic and organic compounds as anodes for SIBs. Apart from electrode materials, suitable electrolytes, additives, and binders are equally important for the development of practical SIBs. Despite developments in electrode materials and other components, there remain several challenges, including cell design and electrode balancing, in the application of sodium ion cells. In this article, we summarize and discuss current research on materials and propose future directions for SIBs. This will provide important insights into scientific and practical issues in the development of SIBs.

1D Nanomaterials: Design, Synthesis, and Applications in Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have received extensive attention as ideal candidates for large-scale energy storage systems (ESSs) owing to the rich resources and low cost of sodium (Na). However, the larger size of Na⁺ and the less negative redox potential of Na⁺ /Na result in low energy densities, short cycling life, and the sluggish kinetics of SIBs. Therefore, it is necessary to develop appropriate Na storage electrode materials with the capability to host larger Na⁺ and fast ion diffusion kinetics. 1D materials such as nanofibers, nanotubes, nanorods, and nanowires, are generally considered to be high-capacity and stable electrode materials, due to their uniform structure, orientated electronic and ionic transport, and strong tolerance to stress change. Here, the synthesis of 1D nanomaterials and their applications in SIBs are reviewed. In addition, the prospects of 1D nanomaterials on energy conversion and storage as well as the development and application orientation of SIBs are presented.

Advances and Challenges in Metal Sulfides/Selenides for Next-Generation Rechargeable Sodium-Ion Batteries

Rechargeable sodium-ion batteries (SIBs), as the most promising alternative to commercial lithium-ion batteries, have received tremendous attention during the last decade. Among all the anode materials for SIBs, metal sulfides/selenides (MXs) have shown inspiring results because of their versatile material species and high theoretical capacity. They suffer from large volume expansion, however, which leads to bad cycling performance. Thus, methods such as carbon modification, nanosize design, electrolyte optimization, and cut-off voltage control are used to obtain enhanced performance. Here, recent progress on MXs is summarized in terms of arranging the crystal structure, synthesis methods, electrochemical performance, mechanisms, and kinetics. Challenges are presented and effective ways to solve the problems are proposed, and a perspective for future material design is also given. It is hoped that light is shed on the development of MXs to help finally find applications for next-generation rechargeable batteries.

MoS2@rGO Nanoflakes as High Performance Anode Materials in Sodium Ion Batteries

A simple one-pot hydrothermal method is developed for fabrication of MoS2@rGO nanoflakes using the economical MoO3 as the molybdenum source. Benefiting from the unique nanoarchitecture, high MoS2 loading (90.3 wt%) and the expanded interlayer spacing, the as-prepared MoS2@rGO nanoflakes exhibit greatly enhanced sodium storage performances including a high reversible specific capacity of 441 mAh g-1 at a current density of 0.2 A g-1, high rate capability, and excellent capacity retention of 93.2% after 300 cycles.

Porous One-Dimensional Nanomaterials: Design, Fabrication and Applications in Electrochemical Energy Storage

Electrochemical energy storage technology is of critical importance for portable electronics, transportation and large-scale energy storage systems. There is a growing demand for energy storage devices with high energy and high power densities, long-term stability, safety and low cost. To achieve these requirements, novel design structures and high performance electrode materials are needed. Porous 1D nanomaterials which combine the advantages of 1D nanoarchitectures and porous structures have had a significant impact in the field of electrochemical energy storage. This review presents an overview of porous 1D nanostructure research, from the synthesis by bottom-up and top-down approaches with rational and controllable structures, to several important electrochemical energy storage applications including lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, lithium-oxygen batteries and supercapacitors. Highlights of porous 1D nanostructures are described throughout the review and directions for future research in the field are discussed at the end.

A review of recent progress in molybdenum disulfide-based supercapacitors and batteries

This article reviews the recent progress in molybdenum disulfide-based supercapacitors and batteries.

Lamellar MoSe2 nanosheets embedded with MoO2 nanoparticles: novel hybrid nanostructures promoted excellent performances for lithium ion batteries

A carbon-free nanocomposite consisting of MoO₂ nanoparticles embedded between MoSe₂ nanosheets, named MoO₂@MoSe₂, has been synthesized and demonstrated excellent electrochemical properties for lithium ion batteries. In such a composite, MoSe₂ nanosheets provide a flexible substrate for MoO₂ nanoparticles; while MoO₂ nanoparticles act as spacers to retain the desired active surface to electrolyte and also introduce metallic conduction. In addition, the heterojunctions at the interface between MoSe₂ and MoO₂ introduce a self-built electric field to promote the lithiation/delithiation process. As a result, such lamellar composite has a long cycling stability with a reversible capacity of 520.4 mA h g^-1 at a current density of 2000 mA g^-1 after 400 cycles and excellent rate performance, which are attributed to the synergistic combination of the two components in nanoscale.

Dimensional Effects of MoS2 Nanoplates Embedded in Carbon Nanofibers for Bifunctional Li and Na Insertion and Conversion Reactions

Controlling structural and morphological features of molybdenum disulfide (MoS₂) nanoplates determines anode reaction performance for Li-ion and Na-ion batteries. In this work, we investigate dimensional effects of MoS₂ nanoplates randomly embedded in twisted mesoporous carbon nanofibers (MoS₂@MCNFs) on Li and Na storage properties. Considering dimensions of the MoS₂ nanoplates (e.g., interlayer, lateral distance, and slabs of stacking in number), we controlled thermolysis temperature to synthesize the MoS₂ nanoplates with different geometry and optimize them in the hybrid anode for delivering high performance. The MoS₂@MCNFs electrode exhibits reversible Li and Na capacities greater than 1000 cycles even at high current density of 1.0 A g^-1 (1221.94 mAh g^-1 with capacity retention of 95.6% for Li-ion batteries and 447.29 mAh g^-1 with capacity retention of 87.11% for Na-ion batteries). We elucidated the insertion, conversion, and interfacial reaction characteristics of the thermosensitive MoS₂ nanoplates in the MCNFs, especially associated with a reversible capacity. Our study will hint at rational design of the nanostructured MoS₂ electrodes and focus on significance of their dimensional effects on anode performance.

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

Peapod-like carbon-encapsulated cobalt chalcogenide nanowires are designed and synthesized by a facile method. The nanowires show excellent electrochemical performance for sodium storage, suggesting that chalcogenides, especially selenides, have potential as advanced anodes for sodium-ion batteries.

Ultrafine Nb2O5 Nanocrystal Coating on Reduced Graphene Oxide as Anode Material for High Performance Sodium Ion Battery

Ultrafine niobium oxide nanocrystals/reduced graphene oxide (Nb2O5 NCs/rGO) was demonstrated as a promising anode material for sodium ion battery with high rate performance and high cycle durability. Nb2O5 NCs/rGO was synthesized by controllable hydrolysis of niobium ethoxide and followed by heat treatment at 450 °C in flowing forming gas. Transmission electron microscopy images showed that Nb2O5 NCs with average particle size of 3 nm were uniformly deposited on rGO sheets and voids among Nb2O5 NCs existed. The architecture of ultrafine Nb2O5 NCs anchored on a highly conductive rGO network can not only enhance charge transfer and buffer the volume change during sodiation/desodiation process but also provide more active surface area for sodium ion storage, resulting in superior rate and cycle performance. Ex situ XPS analysis revealed that the sodium ion storage mechanism in Nb2O5 could be accompanied by Nb(5+)/Nb(4+) redox reaction and the ultrafine Nb2O5 NCs provide more surface area to accomplish the redox reaction.

Solution-Processed Two-Dimensional Metal Dichalcogenide-Based Nanomaterials for Energy Storage and Conversion

The development of renewable energy storage and conversion devices is one of the most promising ways to address the current energy crisis, along with the global environmental concern. The exploration of suitable active materials is the key factor for the construction of highly efficient, highly stable, low-cost and environmentally friendly energy storage and conversion devices. The ability to prepare two-dimensional (2D) metal dichalcogenide (MDC) nanosheets and their functional composites in high yield and large scale via various solution-based methods in recent years has inspired great research interests in their utilization for renewable energy storage and conversion applications. Here, we will summarize the recent advances of solution-processed 2D MDCs and their hybrid nanomaterials for energy storage and conversion applications, including rechargeable batteries, supercapacitors, electrocatalytic hydrogen generation and solar cells. Moreover, based on the current progress, we will also give some personal insights on the existing challenges and future research directions in this promising field.

Heterogeneous WSx/WO₃ Thorn-Bush Nanofiber Electrodes for Sodium-Ion Batteries

Heterogeneous electrode materials with hierarchical architectures promise to enable considerable improvement in future energy storage devices. In this study, we report on a tailored synthetic strategy used to create heterogeneous tungsten sulfide/oxide core-shell nanofiber materials with vertically and randomly aligned thorn-bush features, and we evaluate them as potential anode materials for high-performance Na-ion batteries. The WSx (2 ≤ x ≤ 3, amorphous WS3 and crystalline WS2) nanofiber is successfully prepared by electrospinning and subsequent calcination in a reducing atmosphere. To prevent capacity degradation of the WSx anodes originating from sulfur dissolution, a facile post-thermal treatment in air is applied to form an oxide passivation surface. Interestingly, WO3 thorn bundles are randomly grown on the nanofiber stem, resulting from the surface conversion. We elucidate the evolving morphological and structural features of the nanofibers during post-thermal treatment. The heterogeneous thorn-bush nanofiber electrodes deliver a high second discharge capacity of 791 mAh g(-1) and improved cycle performance for 100 cycles compared to the pristine WSx nanofiber. We show that this hierarchical design is effective in reducing sulfur dissolution, as shown by cycling analysis with counter Na electrodes.

First Introduction of NiSe2 to Anode Material for Sodium-Ion Batteries: A Hybrid of Graphene-Wrapped NiSe2/C Porous Nanofiber

The first-ever study of nickel selenide materials as efficient anode materials for Na-ion rechargeable batteries is conducted using the electrospinning process. NiSe₂-reduced graphene oxide (rGO)-C composite nanofibers are successfully prepared via electrospinning and a subsequent selenization process. The electrospun nanofibers giving rise to these porous-structured composite nanofibers with optimum amount of amorphous C are obtained from the polystyrene to polyacrylonitrile ratio of 1/4. These composite nanofibers also consist of uniformly distributed single-crystalline NiSe₂ nanocrystals that have a mean size of 27 nm. In contrast, the densely structured bare NiSe₂ nanofibers formed via selenization of the pure NiO nanofibers consist of large crystallites. The initial discharge capacities of the NiSe₂-rGO-C composite and bare NiSe₂ nanofibers at a current density of 200 mA g⁻¹ are 717 and 755 mA h g⁻¹, respectively. However, the respective 100^th-cycle discharge capacities of the former and latter are 468 and 35 mA h g⁻¹. Electrochemical impedance spectroscopy measurements reveal the structural stability of the composite nanofibers during repeated Na-ion insertion and extraction processes. The excellent Na-ion storage properties of these nanofibers are attributed to this structural stability.

Sodium-Ion Storage Properties of FeS-Reduced Graphene Oxide Composite Powder with a Crumpled Structure

The sodium-ion storage properties of FeS-reduced graphene oxide (rGO) and Fe3O4 -rGO composite powders with crumpled structures have been studied. The Fe3 O4 -rGO composite powder, prepared by one-pot spray pyrolysis, could be transformed to an FeS-rGO composite powder through a simple sulfidation treatment. The mean size of the Fe3O4 nanocrystals in the Fe3O4 -rGO composite powder was 4.4 nm. After sulfidation, FeS nanocrystals of size several hundred nanometers were confined within the crumpled structure of the rGO matrix. The initial discharge capacities of the FeS-rGO and Fe3O4 -rGO composite powders were 740 and 442 mA h g(-1), and their initial charge capacities were 530 and 165 mA h g(-1), respectively. The discharge capacities of the FeS-rGO and Fe3O4 -rGO composite powders at the 50th cycle were 547 and 150 mA h g(-1), respectively. The FeS-rGO composite powder showed superior sodium-ion storage performance compared to the Fe3O4 -rGO composite powder.