Enhanced Kinetics over VS4 Microspheres with Multidimensional Na+ Transfer Channels for High-Rate Na-Ion Battery Anodes

Highly efficient and conductive in-situ assembled VS4-VO2 on reduced Graphene-oxide as advanced cathode materials for thermal batteries

Thermal batteries are a type of thermally activated reserve batteries, where the cathode material significantly influences the operating voltage and specific capacity of the battery. In this work, VS4-VO2 has been synthesized through the hydrothermal method and used as the cathode material for thermal batteries. Firstly, the material with the VS4 crystallinity is obtained at 170 °C and the mass percentages of VS4/VO2 are 63.1 % and 36.9 %, respectively. The formation mechanism of VS4-VO2 has been proposed based on in-situ ultraviolet (UV) spectrum, which shows that the hydrolysis product S2- under alkaline conditions promotes the formation of VS4. To further improve the conductivity of the material, the reduced graphene oxide (rGO) has been introduced into VS4-VO2 nanomaterials. When applied in thermal batteries, the rGO-VS4-VO2 composite exhibits a voltage plateau of approximately 2.4 V and a discharging specific capacity of 327 mAh/g with the cut-off voltage of 1.5 V at 50 mA and 350°C, which are higher than those of VS4-VO2. Furthermore, the discharge mechanisms of rGO-VS4-VO2 in thermal batteries have been analyzed, which indicates that VS4-VO2 involves two processes of phase transformation, including the intercalation process and conversion process. The results confirm rGO-VS4-VO2 as a promising cathode material for thermal batteries.

Cobalt-Mediated Defect Engineering Endows High Reversible Amorphous VS4 Anode for Advanced Sodium-Ion Storage

Metal sulfides are promising anode materials for sodium-ion batteries (SIBs) due to their structural diversity and high theoretical capacity, but the severe capacity decay and inferior rate capability caused by poor structural stability and sluggish kinetics impede their practical applications. Herein, a cobalt-doped amorphous VS4 wrapped by reduced graphene oxide (i.e., Co0.5-VS4/rGO) is developed through a Co-induced defect engineering strategy to boost the kinetics performances. The as-prepared Co0.5-VS4/rGO demonstrates excellent rate capacities over 10 A g-1 and superior cycling stability at 5 A g-1 over 1600 cycles, which is attributed to the defects formed by Co doping, the formed amorphous structure and the robust rGO substrate. The great features of Co0.5-VS4/rGO anode are further confirmed in sodium-ion capacitors when the active carbon cathode is used. Additionally, the relationships between metal doping, the derived defects, the amorphous structure, and the sodium storage of VS4 are uncovered. This work provides deep insights into preparing amorphous functional materials and also probes the potential applications of metal sulfide-based electrode materials for advanced batteries.

Morphology Engineering of VS4 Microspheres as High-Performance Cathodes for Hybrid Mg2+/Li+ Batteries

V-based sulfides are considered as potential cathode materials for Mg2+/Li+ hybrid ion batteries (MLIBs) due to their high theoretical specific capacities, unique crystal structure, and flexible valence adjustability. However, the formation of irreversible polysulfides, poor cycling performance, and severe structural collapse at high current densities impede their further development. Herein, VS4 microspheres with various controllable nanoarchitectures were successfully constructed via a facile solvothermal method by adjusting the amount of hydrochloric acid and were used as cathode materials for MLIBs. The VS4 microsphere self-assembled by bundles of paralleled-nanorods and some intersected-nanorods (VS4@NC-5) exhibits an outstanding initial discharge capacity of 805.4 mAh g-1 at 50 mA g-1 that is maintained at 259.1 mAh g-1 after 70 cycles. Moreover, the VS4@NC-5 cathode can deliver a superior rate capability (146.1 mAh g-1 at 2000 mA g-1) and ultralong cycling life (134.5 mAh g-1 at 2000 mA g-1 after 2000 cycles). The extraordinary electrochemical performance of VS4@NC-5 could be attributed to its special multi-hierarchical microsphere structure and the formation of N-doped carbon layers and V-C bonds, resulting in unobstructed ion diffusion channels, multidimensional electron transfer pathways, and enhancements of electrical conductivity and structure stability. Furthermore, the electrochemical reaction mechanism and phase conversion behavior of the VS4@NC-5 cathode at various states are investigated by a series of ex situ characterization methods. The VS4 well-designed through morphological engineering in this work can pave a way to explore more sulfides with high-rate performance and long cycling stability for energy storage devices.

Structure Engineering of Vanadium Tetrasulfides for High-Capacity and High-Rate Sodium Storage

Structure engineering of electrode materials can significantly improve the life cycle and rate capability of the sodium-ion battery (SIB), yet remains a challenging task due to the lack of an effective synthetic strategy. Herein, the microstructure of VS₄ hollow spheres is successfully engineered through a facile hydrothermal method. The hollow VS₄ microspheres possess rich porosity and are covered with 2D ultrathin nanosheets on the surface. The finite element simulation (FES) reveals that such heterostructures can effectively relieve the stress induced by the sodiation and thereby enhance the structural integrity. The SIB with the hollow VS₄ microspheres as anode displays impressively high specific capacity, excellent stability upon ultra-long cycling, and extraordinary rate capacity, e.g., a reversible capacity of ≈378 mA h g^-1 at ultra-high 10 A g^-1 , while retaining 73.2% capacity after 1000 cycles. The Na storage mechanism is also elucidated through in situ/ex situ characterizations. Moreover, the hollow VS₄ microspheres demonstrate reliable rate performance at a low temperature of -40 °C (e.g., the capacity is ≈163 mA h g^-1 at 2 A g^-1 ). This work provides novel insights toward high-performance SIBs.

Active Sulfur-Host Material VS4 with Surface Defect Engineering: Intercalation-Conversion Hybrid Cathode Boosting Electrochemical Performance of Li-S Batteries

Transition-metal sulfides as late-model electrocatalysts usually remain inactive in lithium-sulfur (Li-S) batteries in spite of their advantages to accelerate the rapid conversion of lithium polysulfides (LiPSs). Herein, a series of cobalt-doped vanadium tetrasulfide/reduced graphene oxide (x%Co-VS₄/rGO) composites with an ultrathin layered structure as an active sulfur-host material are prepared by a one-pot hydrothermal method. The well-designed two-dimensional ultrathin 3%Co-VS₄/rGO with heteroatom architecture defects (defect of Co-doping and defect of S-vacancies) can significantly improve the adsorption ability on LiPSs, the electrocatalytic activity in the Li₂S potentiostatic deposition, and the active sulfur reduction/oxidation conversion reactions and greatly boost the electrochemical performances of Li-S batteries. On the one hand, the ultrathin 3%Co-VS₄/rGO possesses good conductivity inheriting from rGO which contributes to the capacity of internal redox reactions on lithiation from VS₄. On the other hand, the hybrid architectures provide strong adsorption and excellent electrocatalytic ability on LiPSs, which benefit from the surface defects caused by heteroatom doping. The S@3%Co-VS₄/rGO cathode displays a high specific capacity of 1332.6 mA h g^-1 at 0.2 C and a low-capacity decay of only 0.05% per cycle over 1000 cycles at 3 C with a primary capacity of 633.1 mA h g^-1. Furthermore, when the sulfur loading (single-side coating) reaches 4.48 mg cm^-2, it still can deliver 756.2 mA h g^-1 after the 100th cycle at 0.2 C with 89.5% capacity retention. In addition, the in situ X-ray diffraction test reveals that the sulfur conversion mechanism is the processes of α-S₈ → Li₂S → β-S₈ (first cycle) and then β-S₈ ↔ Li₂S during the subsequent cycles. The designing strategy with heteroatom doping and self-intercalation capacity adopted in this work would provide novel inspiration for fabricating advanced sulfur-host materials to achieve excellent electrochemical capability in Li-S batteries.

Vanadium Tetrasulfide for Next-Generation Rechargeable Batteries: Advances and Challenges

Alkali metal-ion batteries (SIBs and PIBs) and multivalent metal-ion batteries (ZIBs, MIBs, and AIBs), among the next-generation rechargeable batteries, are deemed appealing alternatives to lithium-ion batteries (LIBs) because of their cost competitiveness. Improving the electrochemical properties of electrode materials can greatly accelerate the pace of development in battery systems to cover the increasing demands of realistic applications. Vanadium tetrasulfide (VS₄ ) is known as a prospective electrode material due to its unique one-dimensional atomic chain structure with a large chain spacing, weak interactions between adjacent chains, and high sulfur content. This review summarizes the synthetic strategies and recent advances of VS₄ as cathodes/anodes for rechargeable batteries. Meanwhile, we describe the structural characteristics and electrochemical properties of VS₄ . And we describe in detail its specific applications in batteries such as SIBs, PIBs, ZIBs, MIBs, and AIBs as well as modification strategies. Finally, the opportunities and challenges of VS₄ in the domain of energy research are described.

Facile self-assembly of carbon-free vanadium sulfide nanosheet for stable and high-rate lithium-ion storage

Metal sulfides are recognized as potential candidates for the anode materials of lithium ion batteries (LIBs) because of their high theoretical capacity. However, the low reaction kinetics of metal sulfides leads to their poor cycle life and rate performance, which limits their practical application in the field of energy storage. In this work, we synthesized a self-assembled carbon-free vanadium sulfide (V₃S₄) nanosheet via a facile and efficient method. The unique mesoporous nanostructure of V₃S₄ can not only accelerate the migration of ions/electrons, but also alleviate the volume expansion during the lithium ion insertion/extraction process. When used as the anode material of LIBs, the carbon-free V₃S₄ electrode exhibits remarkable electrochemical performance with ultra-high charge capacity (1099.3 mAh g^-1 at 0.1 A g^-1), superior rate capability (668.8 mAh g^-1 at 2 A g^-1 and 588.8 mAh g^-1 at 5 A g^-1) and impressive cycling ability (369.6 mAh g^-1 after 200 cycles at 10 A g ^-1), which is very competitive compared with those of most metal sulfides-based anode materials reported so far. The strategy in this work provides inspiration for the rational design of advanced nanostructured electrode materials for energy storage devices.

Poplar flower-like nitrogen-doped carbon nanotube@VS4 composites with excellent sodium storage performance

As a new anode material for sodium-ion batteries (SIBs), VS₄ shows impressive energy storage potential due to its unique one-dimensional parallel chain structure, large chain spacing and high sulfur content.