Improved Electrochemical Performance of NTs-WS2@C Nanocomposites for Lithium-Ion and Sodium-Ion Batteries

Confining WS2 hierarchical structures into carbon core-shells for enhanced sodium storage

The growing demand for clean energy has heightened interest in sodium-ion batteries (SIBs) as promising candidates for large-scale energy storage. However, the sluggish reaction kinetics and significant volumetric changes in anode materials present challenges to the electrochemical performance of SIBs. This work introduces a hierarchical structure where WS2 is confined between an inner hard carbon core and an outer nitrogen-doped carbon shell, forming HC@WS2@NCs core-shell structures as anodes for SIBs. The inner hard carbon core and outer nitrogen-doped carbon shell anchor WS2, enhancing its structural integrity. The highly conductive carbon materials accelerate electron transport during charge/discharge, while the rationally constructed interfaces between carbon and WS2 regulate the interfacial energy barrier and electric field distribution, improving ion transport. This synergistic interaction results in superior electrochemical performance: the HC@WS2@NCs anode delivers a high capacity of 370 mAh g-1 at 0.2 A/g after 200 cycles and retains261 mAh g-1 at 2 A/g after 2000 cycles. In a full battery with a Na3V2(PO4)3 cathode, the Na3V2(PO4)3//HC@WS2@NC full-cell achieves an impressive initial capacity of 220 mAh g-1 at 1 A/g. This work provides a strategic approach for the systematic development of WS2-based anode materials for SIBs.

Al2O3-Induced Phase Conversion Regulation of WS2 Anode Enhances the Lithium Storage Reversibility

WS2 is an attractive anode in alkali metal ion batteries (AMIBs) due to its 2D-layered structure and high theoretical capacity. However, the shuttle effect of sulfur and the spontaneous growth of W nanoparticles are key issues that limit the alkali-ion accommodation ability. Now, it is still a great challenge to achieve in situ control of the microstructure evolution paths in enclosed batteries for extending the cycling reversibility/lifespan. Herein, the phase conversion paths of both film- and powder-type WS2 anodes are investigated in lithium-ion batteries. It is found that the reversible conversion mechanism is beneficial for alleviating the shuttle effect through strong W-LixSy bonding. Also, once the size of the phase-converted W/WS2 redox pair exceeds ∼10 nm inside the anode layer, the Li+ storage ability will severely decay due to uncontrollable W precipitation. To maintain high reversibility, amorphous Al2O3 is introduced upon pristine WS2. After initializing the battery test, the particle size of the W/WS2 redox pair is in situ modulated within the range of ∼3-5 nm because of the refinement effect of gradually pulverized Al2O3. Thus, the decay suppression effect lasting over 750-1400 cycles is obtained with enhanced W ↔ WS2 conversion efficiency and good capacity retention. This is expected to promote the optimization of Mo-group sulfides/selenides/tellurides toward AMIBs.

WS2 Nanotube Transistor for Photodetection and Optoelectronic Memory Applications

Nanotube and nanowire transistors hold great promises for future electronic and optoelectronic devices owing to their downscaling possibilities. In this work, a single multi-walled tungsten disulfide (WS2) nanotube is utilized as the channel of a back-gated field-effect transistor. The device exhibits a p-type behavior in ambient conditions, with a hole mobility µp ≈  1.4 cm2V-1s-1 and a subthreshold swing SS ≈ 10 V dec-1. Current-voltage characterization at different temperatures reveals that the device presents two slightly different asymmetric Schottky barriers at drain and source contacts. Self-powered photoconduction driven by the photovoltaic effect is demonstrated, and a photoresponsivity R ≈ 10 mAW-1 at 2 V drain bias and room temperature. Moreover, the transistor is tested for data storage applications. A two-state memory is reported, where positive and negative gate pulses drive the switching between two different current states, separated by a window of 130%. Finally, gate and light pulses are combined to demonstrate an optoelectronic memory with four well-separated states. The results herein presented are promising for data storage, Boolean logic, and neural network applications.

3D-engineered WO3 microspheres assembled by 2D nanosheets with superior sodium storage capacity

Because of the inadequate sodium storage capacity of graphite, the exploration of high-performance SIB anodes is a crucial step forward. Herein, we report the hydrothermally synthesized self-assembled interconnected nanosheets of WO3 microspheres possessing admirable sodium storage in terms of cycling stability and acceptable rate capability. Benefitting from the interconnected nature of the nanosheets with a hollow interior, the WO3 microspheres exhibited a high sodiation capacity of 431 mA h g-1 at 100 mA g-1 and an excellent rate performance of 60 mA h g-1 at 500 mA g-1 with an impressive coulombic efficiency of around 99%. Importantly, even after continuous cycling with increasing current densities, a specific capacity as high as 220 mA h g-1 could be recovered at a current density of 50 mA g-1, suggesting excellent sodium storage reversibility.

Construction of WS2/NC@C nanoflake composites as performance-enhanced anodes for sodium-ion batteries

The development of layered metal sulfides with stable structure and accessible active sites is of great importance for sodium-ion batteries (SIBs). Herein, a simple liquid-mixing method is elaborately designed to immobilize WS2 nanoflakes on N-doped carbon (NC), then further coat carbon to produce WS2/NC@C. In the formation process of this composite, the presence of NC not only avoids the overlap and improves the dispersion of WS2 nanoflakes, but also creates a connection network for charge transfer, where the wrapped carbon provides a stable chemical and electrochemical reaction interface. Thus, the composite of WS2/NC@C exhibits the desired Na+ storage capacity as anticipated. The reversible capacity reaches the high value of 369.8 mA h g-1 at 0.2 A g-1 after 200 cycles, while excellent rate performances and cycle life are also acquired in that capacity values of 256.7 and 219.6 mA h g-1 at 1 and 5 A g-1 are preserved after 1000 cycles, respectively. In addition, the assembled sodium-ion hybrid capacitors (SIHCs, AC//WS2/NC@C) exhibit an energy/power density of 68 W h kg-1 at 64 W kg-1, and capacity retention of 82.9% at 1 A g-1 after 2000 cycles. The study provides insight into developing layered metal sulfides with eminent performance of Na+ storage.

Addressing Irreversibility and Structural Distortion in WS2 Inorganic Fullerene-Like Nanoparticles: Effects of Voltage Cutoff Experiments in Beyond Li+-Ion Storage Applications

Large interlayer spacing beneficially allows Na+- and K+-ion storage in transition-metal dichalcogenide (TMD)-based electrodes, but side reactions and volume change, which pulverize the TMD crystalline structure, are persistent challenges for the utilization of these materials in next-generation devices. This study first determines whether irreversibility due to structural distortion, which results in poor cycling stability, is also apparent in the case of inorganic fullerene-like (IF) tungsten disulfide (WS2) nanocages (WS2IF). To address these problems, this study proposes upper and lower voltage cutoff experiments to limit specific reactions in Na+/WS2IF and K+/WS2IF half-cells. Three-dimensional (3D) differential capacity curves and derived surface plots highlight the continuation of reversible reactions when a high upper cutoff technique is applied, thereby indirectly suggesting restricted structural dissolution. This resulted in improved capacity retention with stable performance and a higher Coulombic efficiency, laying the ground for the use of TMD-based materials beyond Li+-ion storage devices.

WS2 nanosheets vertically grown on Ti3C2 as superior anodes for lithium-ion batteries

Tungsten disulfide (WS2) is considered as a promising anode material for high-performance lithium-ion batteries (LIBs) result from its inherent characteristics such as high theoretical capacity, large interlayer spacing and weak interlayer Van der Waals force. Nevertheless, WS2 has the drawbacks of easy agglomeration, severe volume expansion and high Li+ migration barrier, which lead to rapid capacity degradation and imperfect rate ability. In this work, a novel two-dimensional (2D) hierarchical composite (Ti3C2/WS2) consisting of WS2 nanosheets vertically grown on titanium carbide (Ti3C2) nanosheets is prepared. Thanks to this distinctive hierarchical structure and synergy between WS2 and Ti3C2, the Ti3C2/WS2 composite demonstrates exceptional electrochemical performance in LIBs. In addition, we investigate the effect of the mass proportion of WS2 in Ti3C2/WS2 composite on the electrochemical performance, and find that the optimal mass ratio of WS2 is 60%. As expected, the optimal electrode exhibits a high specific capacity (650 mAh/g at 0.1 A/g after 100 cycles) and ultra-long cycle stability (400 mAh/g at 1.0 A/g after 5000 cycles).

Silane functionalization of WS2 nanotubes for interaction with poly(lactic acid)

Functionalisation of nanofillers is required for the promotion of strong interfacial interactions with polymers and is essential as a route for the preparation of (nano)composites with superior mechanical properties. Tungsten disulphide nanotubes (WS₂ NTs) were functionalized using (3-aminopropyl) triethoxysilane (APTES) for preparation of composites with poly(lactic acid) (PLA). The WS₂ NTs : APTES ratios used were 1 : 1, 1 : 2 and 1 : 4 WS₂ NTs : APTES. The APTES formed siloxane networks bound to the NTs via surface oxygen and carbon moieties adsorbed on the WS₂ NTs surface, detected by X-ray photoelectron spectroscopy (XPS) studies and chemical mapping using energy dispersive X-ray spectroscopy in the scanning transmission electron microscope (STEM-EDS). The successful silane modification of the WS₂ NTs was clearly evident with both significant peak shifting by as much as 60 cm^-1 for Si-O-Si vibrations (FTIR) and peak broadening of the A_1g band in the Raman spectra of the WS₂ NTs. The evolution of new bands was also observed and are associated with Si-CH₂-CH₂ and, symmetric and assymetric -NH³⁺ deformation modes (FTIR). Further evidence for functionalization was obtained from zeta potential measurements as there was a change in surface charge from negative for pure WS₂ NTs to positive for APTES modified WS₂ NTs. Additionally, the thermal stability of APTES was shifted to much higher temperatures as it was bound to the WS₂ NTs. The APTES modified WS₂ NTs were organophilic and readily dispersed in PLA, while presence of the pendant amine and hydroxyl groups resulted in strong interfacial interactions with the polymer matrix. The inclusion of as little as 0.5 wt% WS₂ NTs modified with 2.0 wt% APTES resulted in an increase of 600% in both the elongation at break (a measure of ductility) and the tensile toughness relative to neat PLA, without impacting the stiffness or strength of the polymer.

WS2 Nanotube-Embedded SiOC Fibermat Electrodes for Sodium-Ion Batteries

Layered transition metal dichalcogenides (TMDs) such as tungsten disulfide (WS₂) are promising materials for a wide range of applications, including charge storage in batteries and supercapacitors. Nevertheless, TMD-based electrodes suffer from bottlenecks such as capacity fading at high current densities, voltage hysteresis during the conversion reaction, and polysulfide dissolution. To tame such adverse phenomena, we fabricate composites with WS₂ nanotubes. Herein, we report on the superior electrochemical performance of ceramic composite fibers comprising WS₂ nanotubes (WS₂NTs) embedded in a chemically robust molecular polymer-derived ceramic matrix of silicon-oxycarbide (SiOC). Such a heterogeneous fiber structure was obtained via electrospinning of WS₂NT/preceramic polymer solution followed by pyrolysis at elevated temperatures. The electrode capacity fading in WS₂NTs was curbed by the synergistic effect between WS₂NT and SiOC. As a result, the composite electrode exhibits high initial capacity of 454 mAh g^-1 and the capacity retention approximately 2-3 times higher than that of the neat WS₂NT electrode.

A Novel Hierarchical Structure of SnCu2Se4/d-Ti3C2Tx/NPC for a Lithium/Sodium Ion Battery and Hybrid Capacitor with Long-Term Cycling Stabilities

To alleviate kinetics imbalance and capacity insufficiency simultaneously, a novel hierarchical structure (SnCu₂Se₄/d-Ti₃C₂T_x/NPC) composed of delaminated Ti₃C₂T_x, SnCu₂Se₄ nanoparticles, and N-doped porous carbon layers is designed as a battery-type anode for lithium/sodium ion hybrid capacitor (LIC/SIC). The combination of SnCu₂Se₄ nanoparticles with high specific capacity, d-Ti₃C₂T_x with accelerated ion diffusion path, and NPC with enhanced electronic conductivity makes the SnCu₂Se₄/d-Ti₃C₂T_x/NPC composite possess excellent cycling stabilities in half-cell lithium-ion and sodium-ion batteries (LIB and SIB), with capacities of 114 mAh g^-1 after 6000 cycles at 10 A g^-1 for LIB and 296 mAh g^-1 after 900 cycles at 1.0 A g^-1 for SIB. The rate performance is also outstanding, with recovered capacity of 738 mAh g^-1 at 0.1 A g^-1 after cycles at current densities up to 50 A g^-1 for LIB. Subsequently, LIC and SIC based on the SnCu₂Se₄/d-Ti₃C₂T_x/NPC anode and activated carbon cathode exhibit high energy densities of 147.9 and 158.6 Wh kg^-1 at a power density of 100 W kg^-1, respectively. They also possess distinctive long lifespans with capacity retentions of 78 and 81% after 10,000 cycles at 1.0 A g^-1, respectively, demonstrating the feasibility of SnCu₂Se₄/d-Ti₃C₂T_x/NPC toward energy devices requiring high energy density, power density, and long-term stability.