Defect-Engineered VS2 Electrocatalysts for Lithium-Sulfur Batteries

Vanadium-Doped Molybdenum Diselenide Accelerates Sulfur Redox Kinetics in Lithium-Sulfur Batteries

The persistent shuttle effect of polysulfides and slow liquid-solid redox kinetics remain major obstacles to the practical application of Lithium-Sulfur (Li─S) batteries. In this study, a vanadium-doped molybdenum diselenide catalyst designed to address these challenges are presented. Experimental analysis and theoretical calculations reveal that V doping slightly disrupts the 2D growth of MoSe2, creating structural defects and abundant edge-active sites. These active sites enhance polysulfide adsorption, facilitate efficient catalytic conversion, and promote the utilization of S species. Additionally, electron redistribution induced by V dopants improves electronic conductivity and accelerates redox kinetics. As a result, Li─S batteries using V0.1Mo0.9Se2 as a catalyst deliver a high discharge capacity of 1467.3 mA h g-1 at 0.1 C and maintain a capacity of 651.9 mA h g-1 after 1000 cycles at 1 C, with an ultralow decay rate of 0.036% per cycle. Under high sulfur loading (5.5 mg cm-2), the batteries exhibit a specific capacity of 803.9 mA h g-1 after 100 cycles and a decay rate of only 0.11% per cycle. This study demonstrates that V doping effectively activates inert MoSe2, providing a promising strategy for designing high-performance sulfur cathode catalysts and advancing the development of next-generation Li─S batteries.

Linking D-Band Center Modulation with Rapid Reversible Sulfur Conversion Kinetics via Structural Engineering of VS₂

The rapid catalytic conversion toward polysulfides is considered to be an advantageous approach to boost the reaction kinetics and inhibit the shuttle effect in lithium-sulfur (Li─S) batteries. However, the prediction of high catalytic activity Li─S catalysts has become challenging given the carelessness in the relationship between important electronic characteristics of catalysts and catalytic activity. Herein, the relationships between the D-band regulation of catalysts with reaction kinetics toward polysulfides are described. Through the combination of experimental and theoretical analysis, the opportune upward shift of the D-band center results in a favorable interaction with polysulfides, controlling the adsorption behavior of polysulfides. In addition, the electron regulation achieved by moderately moving up the D-band center further reduces the reaction energy barrier through hybridization with polysulfides. Based on this, a composite catalyst Mo doped VS2/rGO as a host material is proposed, which provides impressive long-term cycling stability and superior rate performance. This fundamental knowledge of the inherent connection between the D-band center of the catalyst and the reaction Kinetics of polysulfides offers a rationale for the development of the Li─S catalyst and the modification of its activity.

Vanadium doped in-plane 1T-2H molybdenum disulfide heterostructure as efficient electrocatalyst for lithium-sulfur batteries

The active electronic states in 1T-MoS2 are highly desirable for catalyzing polysulfides conversion. However, stable 1T-MoS2 is difficult to produce using common approaches. Herein, V uniformly doped in-plane 1T-2H heterostructured MoS2 nanosheets (V-MoS2) are prepared by a facile hydrothermal method with a polyoxometalate precursor containing periodic Mo and V atomic arrangement. The doping of V induces the phase transition from semiconducting 2H-MoS2 to metallic 1T-MoS2 and stabilizes the resulted 1T phase. Importantly, the incorporation of V not only modifies the surface electronic property of MoS2, enhancing the active site density, but also improves the adsorption of polysulfides and the catalytic efficiency for sulfur redox reactions. With these advantages, the Li-S batteries using V-MoS2 electrocatalyst achieve accelerated reaction kinetics and superior electrochemical performance. When the S loading of the cathode is 5.41 mg cm-2, a favorable discharge capacity of 4.98 mAh cm-2 is obtained with satisfying cycle stability. This work provides an efficient atomic engineering approach for the design of high performance electrocatalyst for Li-S batteries.

In Situ Electrochemical Evolution of Amorphous Metallic Borides Enabling Long Cycling Room-/Subzero-Temperature Sodium-Sulfur Batteries

Room temperature sodium-sulfur batteries (RT Na-S) have garnered significant attention for their high energy density and cost-effectiveness, positioning them as a promising alternative to lithium-ion batteries. However, they encounter challenges such as the dissolution of sodium polysulfides and sluggish kinetics. Introducing high-activity electrocatalysts and enhancing the density of active sites represents an efficient strategy to enhance reaction kinetics. Here, an amorphous Ni-B material that undergoes electrochemical evolution to generate the NiSx phase within an operational sodium-sulfur battery, contrasting with the crystalline NiB counterpart is fabricated. Electrochemical cycling facilitated the establishment of an interface between the amorphous Ni-B and NiSx, leading to heightened catalytic activity and improved reaction kinetics. Consequently, batteries utilizing the amorphous Ni-B showcased a notable initial specific capacity of 1487 mAh g-1 at 0.2 A g-1, exhibiting exceptional performance under high current densities of 5 A g-1, in low-temperature conditions (-10 °C), with high sulfur loading, and in pouch cell configurations.

Cobalt Ditelluride Meets Tellurium Vacancy: An Efficient Catalyst as a Multifunctional Polysulfide Mediator toward Robust Lithium-Sulfur Batteries

The commercialization of lithium-sulfur batteries (LSBs) faces significant challenges due to persistent issues, such as the shuttle effect of lithium polysulfides (LiPSs) and the slow kinetics of cathodic reactions. To address these limitations, this study proposes a vacancy-engineered cobalt ditelluride catalyst (v-CoTe2) supported on nitrogen-doped carbon as a sulfur host at the cathode. Density functional theory calculations and experimental results indicate that the electron configuration modulation of v-CoTe2 enhances the chemical affinity and catalytic activity toward LiPS. Specifically, v-CoTe2 can strongly interact with PSs through multisite coordination, effectively facilitating the kinetics of the LiPS redox reaction. Furthermore, the introduction of Te vacancies generates a large number of spin-polarized electrons, further enhancing the reaction kinetics of LiPS. As a result, the v-CoTe2@S cathode demonstrates high initial capacity and excellent cyclic stability, maintaining 80.4% capacity after 500 cycles at a high current rate of 3 C. Even under a high sulfur load of 6.7 mg cm-2, a high areal capacity of 6.1 mA h cm-2 is retained after 50 cycles. These findings highlight the significant potential of Te vacancies in CoTe2 as a sulfur host material for LSBs.

High-Entropy Transition Metal Phosphorus Trichalcogenides for Rapid Sodium Ion Diffusion

High-entropy strategies are regarded as a powerful means to enhance performance in energy storage fields. The improved properties are invariably ascribed to entropy stabilization or synergistic cocktail effect. Therefore, the manifested properties in such multicomponent materials are usually unpredictable. Elucidating the precise correlations between atomic structures and properties remains a challenge in high-entropy materials (HEMs). Herein, atomic-resolution scanning transmission electron microscopy annular dark field (STEM-ADF) imaging and four dimensions (4D)-STEM are combined to directly visualize atomic-scale structural and electric information in high-entropy FeMnNiVZnPS3. Aperiodic stacking is found in FeMnNiVZnPS3 accompanied by high-density strain soliton boundaries (SSBs). Theoretical calculation suggests that the formation of such structures is attributed to the imbalanced stress of distinct metal-sulfur bonds in FeMnNiVZnPS3. Interestingly, the electric field concentrates along the two sides of SSBs and gradually diminishes toward the two-dimensional (2D) plane to generate a unique electric field gradient, strongly promoting the ion-diffusion rate. Accordingly, high-entropy FeMnNiVZnPS3 demonstrates superior ion-diffusion coefficients of 10-9.7-10-8.3 cm2 s-1 and high-rate performance (311.5 mAh g-1 at 30 A g-1). This work provides an alternative way for the atomic-scale understanding and design of sophisticated HEMs, paving the way for property engineering in multi-component materials.

Effective Bidirectional Mott-Schottky Catalysts Derived from Spent LiFePO4 Cathodes for Robust Lithium-Sulfur Batteries

It is deemed as a tough yet profound project to comprehensively cope with a range of detrimental problems of lithium-sulfur batteries (LSBs), mainly pertaining to the shuttle effect of lithium polysulfides (LiPSs) and sluggish sulfur conversion. Herein, a Co2P-Fe2P@N-doped carbon (Co2P-Fe2P@NC) Mott-Schottky catalyst is introduced to enable bidirectionally stimulated sulfur conversion. This catalyst is prepared by simple carbothermal reduction of spent LiFePO4 cathode and LiCoO2. The experimental and theoretical calculation results indicate that thanks to unique surface/interface properties derived from the Mott-Schottky effect, full anchoring of LiPSs, mediated Li2S nucleation/dissolution, and bidirectionally expedited "solid⇌liquid⇌solid" kinetics can be harvested. Consequently, the S/Co2P-Fe2P@NC manifests high reversible capacity (1569.9 mAh g-1), superb rate response (808.9 mAh g-1 at 3C), and stable cycling (a low decay rate of 0.06% within 600 cycles at 3C). Moreover, desirable capacity (5.35 mAh cm-2) and cycle stability are still available under high sulfur loadings (4-5 mg cm-2) and lean electrolyte (8 µL mg-1) conditions. Furthermore, the as-proposed universal synthetic route can be extended to the preparation of other catalysts such as Mn2P-Fe2P@NC from spent LiFePO4 and MnO2. This work unlocks the potential of carbothermal reduction phosphating to synthesize bidirectional catalysts for robust LSBs.

3D printing of layered vanadium disulfide for water-in-salt electrolyte zinc-ion batteries

Miniaturized aqueous zinc ion batteries are attractive energy storage devices for wearable electronics, owing to their safety and low cost. Layered vanadium disulfide (VS2) has demonstrated competitive charge storage capability for aqueous zinc ion batteries, as a result of its multivalent states and large interlayer spacing. However, VS2 electrodes are affected by quick oxide conversion, and they present predefined geometries and aspect ratios, which hinders their integration in wearables devices. Here, we demonstrate the formulation of a suitable ink for extrusion-based 3D printing (direct ink writing) based on micro flowers of layered VS2 obtained using a scalable hydrothermal process. 3D printed architectures of arbitrary design present electrochemically active, porous and micron-sized struts with tuneable mass loading. These were used as cathodes for aqueous zinc-ion battery electrodes. The 3D printed VS2 cathodes were assembled with carbon/zinc foil anodes to form full cells of zinc-ion, demonstrating a capacity of ∼1.98 mA h cm-2 with an operating voltage of 1.5 V. Upon cycling a capacity retention of around 65% was achieved after ∼100 cycles. The choice of the electrolyte (a water-in-salt electrolyte) and the design of the pre-processing of the 3D printed cathode ensured improved stability against dissolution and swift oxidation, notorious challenges for VS2 in an aqueous environment. This works paves the way towards programmable manufacturing of miniaturized aqueous batteries and the materials processing approach can be applied to different materials and battery systems to improve stability.

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.