Mechanistic Insight into the Stability of HfO2 -Coated MoS2 Nanosheet Anodes for Sodium Ion Batteries

MoO3@MoS2 Core-Shell Structured Hybrid Anode Materials for Lithium-Ion Batteries

We explore a phase engineering strategy to improve the electrochemical performance of transition metal sulfides (TMSs) in anode materials for lithium-ion batteries (LIBs). A one-pot hydrothermal approach has been employed to synthesize MoS₂ nanostructures. MoS₂ and MoO₃ phases can be readily controlled by straightforward calcination in the (200–300) °C temperature range. An optimized temperature of 250 °C yields a phase-engineered MoO₃@MoS₂ hybrid, while 200 and 300 °C produce single MoS₂ and MoO₃ phases. When tested in LIBs anode, the optimized MoO₃@MoS₂ hybrid outperforms the pristine MoS₂ and MoO₃ counterparts. With above 99% Coulombic efficiency (CE), the hybrid anode retains its capacity of 564 mAh g⁻¹ after 100 cycles, and maintains a capacity of 278 mAh g⁻¹ at 700 mA g⁻¹ current density. These favorable characteristics are attributed to the formation of MoO₃ passivation surface layer on MoS₂ and reactive interfaces between the two phases, which facilitate the Li-ion insertion/extraction, successively improving MoO₃@MoS₂ anode performance.

Injectable Hydrogel Based on Defect-Rich Multi-Nanozymes for Diabetic Wound Healing via an Oxygen Self-Supplying Cascade Reaction

Diabetic wound healing remains challenging owing to the risk for bacterial infection, hypoxia, excessive glucose levels, and oxidative stress. Glucose-activated cascade reactions can consume glucose and eradicate bacteria, avoiding the direct use of hydrogen peroxide (H₂ O₂ ) and wound pH restriction on peroxidase-like activity. However, the anoxic microenvironment in diabetic wounds impedes the cascade reaction due to the oxygen (O₂ ) dependence of glucose oxidation. Herein, defect-rich molybdenum disulfide nanosheets loaded with bovine serum albumin-modified gold nanoparticle (MoS₂ @Au@BSA NSs) heterostructures are designed and anchored onto injectable hydrogels to promote diabetic wound healing through an O₂ self-supplying cascade reaction. BSA decoration decreases the particle size of Au, increasing the activity of multiple enzymes. Glucose oxidase-like Au catalyzes the oxidation of glucose into gluconic acid and H₂ O₂ , which is transformed into a hydroxyl radical (•OH) catalyzed by peroxidase-like MoS₂ @Au@BSA to eradicate bacteria. When the wound pH reaches an alkalescent condition, MoS₂ @Au@BSA mimicks superoxide dismutase to transform superoxide anions into O₂ and H₂ O₂ , and decomposes endogenous and exogenous H₂ O₂ into O₂ via catalase-like mechanisms, reducing oxidative stress, alleviating hypoxia, and facilitating glucose oxidation. The MoS₂ @Au@BSA nanozyme-anchored injectable hydrogel, composed of oxidized dextran and glycol chitosan crosslinked through a Schiff base, significantly accelerates diabetic wound healing.

Solid-State Synthesis of Layered MoS2 Nanosheets with Graphene for Sodium-Ion Batteries

Sodium-ion batteries have potential as energy-storage devices owing to an abundant source with low cost. However, most electrode materials still suffer from poor conductivity, sluggish kinetics, and huge volume variation. It is still challenging to explore apt electrode materials for sodium-ion battery applications to avoid the pulverization of electrodes induced by reversible intercalation of large sodium ions. Herein, we report a single-step facile, scalable, low-cost, and high-yield approach to prepare a hybrid material; i.e., MoS2 with graphene (MoS2-G). Due to the space-confined effect, thin-layered MoS2 nanosheets with a loose stacking feature are anchored with the graphene sheets. The semienclosed hybrid architecture of the electrode enhances the integrity and stability during the intercalation of Na+ ions. Particularly, during galvanostatic study the assembled Na-ion cell delivered a specific capacity of 420 mAhg−1 at 50 mAg−1, and 172 mAhg−1 at current density 200 mAg−1 after 200 cycles. The MoS2-G hybrid excels in performance due to residual oxygen groups in graphene, which improves the electronic conductivity and decreases the Na+ diffusion barrier during electrochemical reaction, in comparison with a pristine one.

A hafnium oxide-coated dendrite-free zinc anode for rechargeable aqueous zinc-ion batteries

In aqueous zinc-ion batteries, metallic zinc is widely used as an anode because of its non-toxicity, environmental benignity, low cost, high abundance and theoretical capacity. However, growth of zinc dendrites, corrosion of zinc anode, passivation, and occurrence of side reactions during continuous charge-discharge cycling hinder development of zinc-ion batteries. In this study, a simple strategy involving application of a HfO₂ coating was used to guide uniform deposition of Zn²⁺ to suppress formation of zinc dendrites. The HfO₂-coated zinc anode improves electrochemical performance compared with bare Zn anode. Therefore, for zinc-zinc symmetric cells, zinc anode with HfO₂ coating (48 mV) shows lower voltage hysteresis than that of bare Zn anode (63 mV) at a current density of 0.4 mA cm^-2. Moreover, cell with HfO₂ coating also shows good cycling performance in Zn-MnO₂ full cells. At a constant current density of 1.0 A g^-1, discharge capacity of bare Zn-MnO₂ full cell is only 37.9 mAh g^-1 after 500 cycles, while that of Zn@HfO₂-MnO₂ full cell is up to 78.3 mAh g^-1. This good electrochemical performance may be the result of confinement effect and reduction of side reactions. Overall, a simple and beneficial strategy for future development of rechargeable aqueous zinc-ion batteries is provided.

Boosting potassium-storage performance via the functional design of a heterostructured Bi2S3@RGO composite

Potassium-ion batteries (PIBs) are considered a promising alternative to lithium-ion batteries (LIBs) for next-generation energy storage due to the abundance and competitive cost of potassium resources. However, the excavation and the development of proper electrodes for PIBs are still confronted with great challenges. Herein, a self-assembled bismuth sulfide microsphere wrapped with reduced graphene oxide was fabricated to form a heterostructured Bi2S3@RGO composite via a visible-light-assisted method and served as the anode for PIBs. The as-prepared Bi2S3@RGO composite presented a high reversible specific capacity of 538 mA h g-1 at 0.2 A g-1 and superior rate capability of 237 mA h g-1 at a high current density of 2 A g-1 after 300 cycles. In particular, the high capacity could be ascribed to the synergistic effect of the conversion and alloying reactions during the electrochemical processes, which was validated by ex situ X-ray diffraction. The fabrication of a unique heterostructure combining the self-assembled Bi2S3 microspheres and flexible RGO boosted the facile charge transfer, leading to the enhanced cyclic stability and rate performance.

Transition Metal Dichalcogenide (TMD) Membranes with Ultrasmall Nanosheets for Ultrafast Molecule Separation

Two-dimensional (2D) transition metal dichalcogenide membranes have entered the spotlight for nanofiltration application owing to the novel mass transport properties in nanochannels. However, further improving the water permeability with high molecular separation rate simultaneously is challenging. In this work, to achieve ultrafast molecule separation, MoS₂ and WS₂ nanosheets with ultrasmall lateral size (<100 nm) are fabricated by sucrose-assisted mechanochemical exfoliation. Ultrasmall nanosheets in the membranes cut down average length of water-transporting paths and create more nanochannels and nanocapillaries for water molecules to pass through membranes. The water flux of these kinds of MoS₂ and WS₂ membranes are significantly enhanced to 918 and 828 L/m² h bar, respectively, which is four and two times higher than those of previously reported MoS₂ and WS₂ membranes with larger lateral size nanosheets. In addition, MoS₂ and WS₂ membranes display excellent rejection performance for rhodamine B and Evans blue with a high rejection rate (∼99%). This study provides a promising method to improve the performance of 2D laminar membranes for nanofiltration application by using ultrasmall 2D nanosheets.

Origin of the Superior Electrochemical Performance of Amorphous-Phase Conversion-Reaction-Based Electrode Materials for Na-Ion Batteries: Formation of a Bicontinuous Metal Network

The realization of conversion type electrode materials in Na-ion batteries (NIBs) has been hindered due to the nucleation property of the active material. During the sodiation, the transition metal (TM) cations reduce to the metallic state, and the respective anions react with the sodium ions. As a result, the metal particles are surrounded by the matrix of the insulating sodium compound, resulting in loss of electrical contact among the TM particles. Here, an amorphous molybdenum sulfide (a-MoS_x) electrode is made highly reversible by suppressing TM particle growth via elongating the cation diffusion pathway. Because of the long distance among Mo atoms in a-MoS_x, the growth of Mo nuclei is limited. This leads to more frequent nucleation and formation of smaller particles (3-5 nm in diameter). Since the smaller particles have a larger surface area than the bigger particles, the electrical contacts among Mo particles are clearly retained. The a-MoS_x anode for NIBs demonstrates a high capacity and excellent cycling retention. This work establishes that the amorphous structure enhances the reversibility and cycling stability of conversion-reaction-based electrodes by elongating the diffusion pathway of the metal ions.

Single-Atom Catalytic Materials for Advanced Battery Systems

Advanced battery systems with high energy density have attracted enormous research enthusiasm with potential for portable electronics, electrical vehicles, and grid-scale systems. To enhance the performance of conversion-type batteries, various catalytic materials are developed, including metals and transition-metal dichalcogenides (TMDs). Metals are highly conductive with catalytic effects, but bulk structures with low surface area result in low atom utilization, and high chemical reactivity induces unfavorable dendrite effects. TMDs present chemical adsorption with active species and catalytic activity promotes conversion processes, suppressing shuttle effect and improving energy density. But they suffer from inferior conductivity compared with metal, and limited sites mainly concentrate on edges and defects. Single-atom materials with atomic sizes, good conductivity, and individual sites are promising candidates for advanced batteries because of a large atom utilization, unsaturated coordination, and unique electronic structure. Single-atom sites with high activity chemically trap intermediates to suppress shuttle effects and facilitate electron transfer and redox reactions for achieving high capacity, rate capability, and conversion efficiency. Herein, single-atom catalytic electrodes design for advanced battery systems is addressed. Major challenges and promising strategies concerning electrochemical reactions, theoretical model, and in situ characterization are discussed to shed light on future research of single-atom material-based energy systems.

Fibrous Network of C@MoS2 Nanocapsule-Decorated Cotton Linters Interconnected by Bacterial Cellulose for Lithium- and Sodium-Ion Batteries

To protect the structure of MoS₂ from collapse, a strong skeleton is expected to help maintain the integrity. In this study, cotton linters burdened with hollow C@MoS₂ nanocapsules are added into nutrient medium for the growth of a bacterial cellulose membrane. Benefitting from good conductivity and structural integrity, the resultant fibrous membrane anode gives reversible capacities of 559 and 155 mAh g^-1 for Li-ion batteries and Na-ion batteries after 100 cycles, respectively. The structural transformation and component evolution in lithiation-delithiation and sodiation-desodiation was elucidated by in situ Raman spectroscopy. After sodiation, the Na₂ S did not transform back into MoS₂ but was more likely converted into elemental sulfur during the conversion reaction. Layered semiconducting transition metal chalcogenides, such as molybdenum disulfide (MoS₂ ), feature open 2 D ion-transport channels amenable to receive various guest ions with high theoretical capacities.^[2] One serious challenge curtailing the applicability of such materials is their volume changes during discharge-charge processes.^{[3, 4]} However, particular morphologies of MoS₂ are proposed to improve the specific capacity.^[5,6,7] Many works have focused on core-shell and hollow MoS₂ micro- and nanostructures, and the results validate the advantages of shortening the lithium-ion diffusion distance and enhancing specific capacity.^[8,9] Unfortunately, the issue of inferior capacity stability is not resolved, because the structure is not effectively protected and is prone to collapse.

Understanding Phase Stability of Metallic 1T-MoS2 Anodes for Sodium-Ion Batteries

We discuss metallic 1T-MoS2 as an anode material for sodium-ion batteries (SIBs). In situ Raman is used to investigate the stability of metallic MoS2 during the charging and discharging processes. Parallel first-principles computations are used to gain insight into the experimental observations, including the measured conductivities and the high capacity of the anode.

3D ordered mesoporous TiO2@CMK-3 nanostructure for sodium-ion batteries with long-term and high-rate performance

Sodium ion battery is abundant in resources and costs low, making it very competitive in the large-scale energy storage devices. The anatase TiO₂ electrode material with insertion/extraction mechanism shows stable cycling performance, which is more in line with the technical requirements of large-scale energy storage batteries. To improve the electrical conductivity and stability of the TiO₂ electrode materials, we have synthesized anatase TiO₂ and CMK-3 composite. TiO₂ nanoparticles were deposited on the surface of CMK-3 by hydrothermal reaction, and the anode material of the SIBs with 3D network structure was prepared. With the CMK-3, the structure stability, conductivity and reaction kinetics of TiO₂@CMK-3 composite is improved. The electrochemical behavior is dominated by pseudocapacitance, which gives the material excellent high-rate performance. It delivers a reversible specific capacity of 186.3 mA h g^-1 after 100 cycles at the current density of 50 mA g^-1, 124.5 mA h g^-1 after 500 long-term cycles, meanwhile it shows an outstanding rate performance, a reversible specific capacity of 105.9 mA h g^-1 at 1600 mA g^-1, 177.3 mA h g^-1 when the current density drops to 50 mA g^-1.

Aqueous Zinc-Ion Storage in MoS2 by Tuning the Intercalation Energy

Aqueous Zn-ion batteries present low-cost, safe, and high-energy battery technology but suffer from the lack of suitable cathode materials because of the sluggish intercalation kinetics associated with the large size of hydrated zinc ions. Herein we report an effective and general strategy to transform inactive intercalation hosts into efficient Zn²⁺ storage materials through intercalation energy tuning. Using MoS₂ as a model system, we show both experimentally and theoretically that even hosts with an originally poor Zn²⁺ diffusivity can allow fast Zn²⁺ diffusion. Through simple interlayer spacing and hydrophilicity engineering that can be experimentally achieved by oxygen incorporation, the Zn²⁺ diffusivity is boosted by 3 orders of magnitude, effectively enabling the otherwise barely active MoS₂ to achieve a high capacity of 232 mAh g^-1, which is 10 times that of its pristine form. The strategy developed in our work can be generally applied for enhancing the ion storage capacity of metal chalcogenides and other layered materials, making them promising cathodes for challenging multivalent ion batteries.

Bio-inspired synthesis of mesoporous HfO2 nanoframes as reactors for piezotronic polymerization and Suzuki coupling reactions

Complex nanostructures with high compositional and structural tailorability are highly desired in order to meet the material needs in the rapid development of nanoscience and nanotechnology. Therefore, the synthetic technique is of essential importance but currently still suffers from many challenges. Herein, we elaborately explore and demonstrate the flexibility of the anisotropic metallo-organic compound (dihafnium dichloride, Cp2HfCl2) for the fabrication of inorganic architectures by mimicking the assembly behaviors in biomolecules. The open and discrete architectures of mesoporous HfO2 nanoframes were constructed via the self-assembly of precursor with acetone as solvent and ammonia as the basic source, but without any addition of auxiliary organic molecules, like surfactants, DAN or peptides. In addition, the nanostructures (hollow spheres, solid spheres, yolk-shells, aggregations and defect-rich nanoparticles) of HfO2 assemblies can be well manipulated by simply modulating the synthesis parameters. The marked difference in the chemical bonds by the different ligands resulted in discrepant hydrolysis and then specific directional bonds for the diversity of the resultant HfO2 assemblies. Interestingly, the HfO2 nanoframe exhibits enhanced piezoelectricity, and can be used as a microelectrode reactor to trigger the pseudo-electrochemical aniline polymerization reaction by introducing ultrasonic excitation to renew the surface charges. Moreover, as compared with nanoparticle catalysts, the palladium (Pd) loaded nanoframe reactor exhibits obvious enhanced catalytic performance for classical Suzuki coupling, benefiting from the structural advantages of the HfO2 frame. Our findings here can be expected to offer new perspectives to find suitable materials by understanding the analogy between materials chemistry and biomolecule chemistry.

Bundled Defect-Rich MoS2 for a High-Rate and Long-Life Sodium-Ion Battery: Achieving 3D Diffusion of Sodium Ion by Vacancies to Improve Kinetics

Molybdenum disulfide (MoS₂ ), a 2D-layered compound, is regarded as a promising anode for sodium-ion batteries (SIBs) due to its attractive theoretical capacity and low cost. The main challenges associated with MoS₂ are the low rate capability suffering from the sluggish kinetics of Na⁺ intercalation and the poor cycling stability owning to the stack of MoS₂ sheets. In this work, a unique architecture of bundled defect-rich MoS₂ (BD-MoS₂ ) that consists of MoS₂ with large vacancies bundled by ultrathin MoO₃ is achieved via a facile quenching process. When employed as anode for a SIB, the BD-MoS₂ electrode exhibits an ultrafast charge/discharge due to the pseudocapacitive-controlled Na⁺ storage mechanism in it. Further experimental and theoretical calculations show that Na⁺ is able to cross the MoS₂ layer by vacancies, not only limited to diffusion along the layer, thus realizing a 3D Na⁺ diffusion with faster kinetics. Meanwhile, the bundling architecture reduces the stack of sheets with a superior cycle life illustrating the highly reversible capacities of 350 and 272 mAh g^-1 at 2 and 5 A g^-1 after 1000 cycles.

Synthesis of Grain-like MoS2 for High-Performance Sodium-Ion Batteries

MoS₂ is a promising anode material for sodium-ion batteries (SIBs) due to its attractive theoretical capacity and low cost. MoS₂ generally presents a sheet-like structure based on its (002) lattice plane; however, such a structure tends to result in agglomeration and stacking of the sheets that cannot accommodate volume expansion, resulting in poor cyclability. Herein, grain-like MoS₂ particulates (G-MoS₂ ) are synthesized by sulfiding MoO₃ in highly concentrated sulfur vapor, which results in epitaxial growth of MoS₂ in (002), (100), and (110) lattice planes, with the product consisting of MoS₂ particulates of about 300 nm coated with few-layered MoS₂ nanosheets. The unique G-MoS₂ architecture ensures good dispersion and sufficient distance to accommodate volume expansion during sodiation/desodiation, which effectively prevents stacking of MoS₂ , maintaining structural stability. When employed as the working electrode for SIB, G-MoS₂ delivers a high reversible capacity of 324 mAh g^-1 at 0.5 A g^-1 , retaining 312 mAh g^-1 over 300 cycles with an average coulombic efficiency of 99.8 %. Even when G-MoS₂ is cycled at a high current density (2.0 A g^-1 ), the retained capacity is 175 mAh g^-1 after 400 cycles. Comparison with literature reveals that these capacities are among the more promising reversible values reported for pure MoS₂ .

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.

Few-layered MoS2/C with expanding d-spacing as a high-performance anode for sodium-ion batteries

Sodium-ion batteries (SIBs) show great potential as alternative energy storage devices for next generation energy storage systems due to the deficiency of lithium resources. MoS₂ is a promising anode material for SIBs due to its high theoretical sodium storage capability and large interspace for accommodating sodium ions with a larger ionic radius than lithium ions. However, bulk MoS₂ exhibits a sluggish kinetics for the intercalation-deintercalation of sodium ions and large volume expansion, which result in poor cyclability and rate performance. In this study, we designed few-layered MoS₂/C nanoflowers with expanded interspacing of MoS₂-MoS₂ planes using polyvinyl alcohol (PVA) as an intercalating reagent and a carbon precursor. Due to the unique nanostructure and larger interlayer spacing, the MoS₂/C nanoflower electrode achieves a high reversible specific capacity of 400 mA h g^-1 after 300 cycles at 500 mA g^-1 for sodium-ion batteries (SIBs), showing a good cycling stability. The improved electrochemical performance suggests that the MoS₂/C composite is a promising anode material for sodium ion storage.

Two-Dimensional SnO Anodes with a Tunable Number of Atomic Layers for Sodium Ion Batteries

We have systematically changed the number of atomic layers stacked in 2D SnO nanosheet anodes and studied their sodium ion battery (SIB) performance. The results indicate that as the number of atomic SnO layers in a sheet decreases, both the capacity and cycling stability of the Na ion battery improve. The thinnest SnO nanosheet anodes (two to six SnO monolayers) exhibited the best performance. Specifically, an initial discharge and charge capacity of 1072 and 848 mAh g^-1 were observed, respectively, at 0.1 A g^-1. In addition, an impressive reversible capacity of 665 mAh g^-1 after 100 cycles at 0.1 A g^-1 and 452 mAh g^-1 after 1000 cycles at a high current density of 1.0 A g^-1 was observed, with excellent rate performance. As the average number of atomic layers in the anode sheets increased, the battery performance degraded significantly. For example, for the anode sheets with 10-20 atomic layers, only a reversible capacity of 389 mAh g^-1 could be obtained after 100 cycles at 0.1 A g^-1. Density functional theory calculations coupled with experimental results were used to elucidate the sodiation mechanism of the SnO nanosheets. This systematic study of monolayer-dependent physical and electrochemical properties of 2D anodes shows a promising pathway to engineering and mitigating volume changes in 2D anode materials for sodium ion batteries. It also demonstrates that ultrathin SnO nanosheets are promising SIB anode materials with high specific capacity, stable cyclability, and excellent rate performance.

MoS2-Based Nanocomposites for Electrochemical Energy Storage

Typical layered transition-metal chalcogenide materials, in particular layered molybdenum disulfide (MoS2) nanocomposites, have attracted increasing attention in recent years due to their excellent chemical and physical properties in various research fieldsHere, a general overview of synthetic MoS2 based nanocomposites via different preparation approaches and their applications in energy storage devices (Li-ion battery, Na-ion battery, and supercapacitor) is presented. The relationship between morphologies and the electrochemical performances of MoS2-based nanocomposites in the three typical and promising rechargeable systems is also discussed. Finally, perspectives on major challenges and opportunities faced by MoS2-based materials to address the practical problems of MoS2-based materials are presented.

High Temperature Carbonized Grass as a High Performance Sodium Ion Battery Anode

Hard carbon is currently considered the most promising anode candidate for room temperature sodium ion batteries because of its relatively high capacity, low cost, and good scalability. In this work, switchgrass as a biomass example was carbonized under an ultrahigh temperature, 2050 °C, induced by Joule heating to create hard carbon anodes for sodium ion batteries. Switchgrass derived carbon materials intrinsically inherit its three-dimensional porous hierarchical architecture, with an average interlayer spacing of 0.376 nm. The larger interlayer spacing than that of graphite allows for the significant Na ion storage performance. Compared to the sample carbonized under 1000 °C, switchgrass derived carbon at 2050 °C induced an improved initial Coulombic efficiency. Additionally, excellent rate capability and superior cycling performance are demonstrated for the switchgrass derived carbon due to the unique high temperature treatment.

ALD TiO2-Coated Flower-like MoS2 Nanosheets on Carbon Cloth as Sodium Ion Battery Anode with Enhanced Cycling Stability and Rate Capability

We report the fabrication of 3D flower-like MoS₂ nanosheets arrays on carbon cloth as a binder-free anode for sodium ion battery. Ultrathin and conformal TiO₂ layers are used to modify the surface of MoS₂ by atomic layer deposition. The electrochemical performance measurements demonstrate that the ALD TiO₂ layer can improve the cycling stability and rate capability of MoS₂. The MoS₂ nanosheets with 0.5-nm TiO₂ coating electrode show the highest initial discharge capacity of 1392 mA h g^-1 at 200 mA g^-1, which is increased by 53% compared with that of bare MoS₂. After 150 cycles, the capacity retention rate of the TiO₂-coated MoS₂ achieves 75.8% of its second cycle's capacity at 200 mA h g^-1 in contrast to that of 59% of pure MoS₂. Furthermore, the mechanism behind the experimental results is revealed by ex situ scanning electron microscope (SEM), X-ray powder diffraction (XRD), and electrochemical impedance spectroscopy (EIS) characterizations, which confirms that the ultrathin TiO₂ modifications can prevent the structural degradation and the formation of SEI film of MoS₂ electrode.

Al2O3coated metal sulfides: one-pot synthesis and enhanced lithium storage stability via localized in situ conversion reactions

Al₂O₃coated Ni₃S₄nanoparticles have been designed to promote thein situconversion of Ni₃S₄, by confining the formed polysulfides within the Al₂O₃layer; these nanoparticles exhibit a high reversible capacity of 651.6 mA h g⁻¹at 500 mA g⁻¹, even after 400 cycles.

Electrospinning Synthesis of Mesoporous MnCoNiOx@Double-Carbon Nanofibers for Sodium-Ion Battery Anodes with Pseudocapacitive Behavior and Long Cycle Life

In this work, MnCoNiO_x (denoted as MCNO) nanocrystals (with a size of less than 30 nm) finely encapsulated in double-carbon (DC, including reduced graphene oxide and amorphous carbon derived by polymer) composite nanofibers (MCNO@DC) were successfully synthesized via an electrospinning method followed by a sintering treatment. The as-obtained MCNO@DC nanofibers present superior sodium storage performance and retain an especially high specific capacity of 230 mAh g^-1 with a large capacity retention of about 96% at 0.1 A g^-1 after 500 cycles and a specific capacity of 107 mAh g^-1 with capacity retention of about 89% at 1 A g^-1 after 6500 cycles. The outstanding cycle characteristic is mainly due to the tiny MCNO nanoparticles, which shorten the ion migration distance, and the three-dimensional DC framework, which remarkably promotes the electronic transfer and efficiently limits the volume expansion during the progress of insertion and extraction of Na⁺ ions. Moreover, nitrogen doped in carbon is able to improve the electrochemical capability as well. Finally, kinetic analysis of the redox reactions is used to verify the pseudocapacitive mechanism in charge storage and the feasibility of using MCNO@DC composite nanofibers as an anode for sodium-ion batteries with the above-mentioned behavior.

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.

Synergetic Effect of Yolk-Shell Structure and Uniform Mixing of SnS-MoS₂ Nanocrystals for Improved Na-Ion Storage Capabilities

Mixed metal sulfide composite microspheres with a yolk-shell structure for sodium-ion batteries are studied. Tin-molybdenum oxide yolk-shell microspheres prepared by a one-pot spray pyrolysis process transform into yolk-shell SnS-MoS2 composite microspheres. The discharge capacities of the yolk-shell and dense-structured SnS-MoS2 composite microspheres for the 100th cycle are 396 and 207 mA h g(-1), and their capacity retentions measured from the second cycle are 89 and 47%, respectively. The yolk-shell SnS-MoS2 composite microspheres with high structural stability during repeated sodium insertion and desertion processes have low charge-transfer resistance even after long-term cycling. The synergetic effect of the yolk-shell structure and uniform mixing of the SnS and MoS2 nanocrystals result in the excellent sodium-ion storage properties of the yolk-shell SnS-MoS2 composite microspheres by improving their structural stability during cycling.

Tungsten diselenide (WSe2) as a high capacity, low overpotential conversion electrode for sodium ion batteries

Tungsten diselenide (WSe₂) is demonstrated as an efficient electrode for sodium ion batteries for the first time.