Desolvation Synergy of Multiple H/Li-Bonds on an Iron-Dextran-Based Catalyst Stimulates Lithium-Sulfur Cascade Catalysis

In situ construction of 3D 1T-VS2/V2C heterostructures for enhanced polysulfide trapping and catalytic conversion in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries represent a promising next-generation energy storage solution, yet their performance is hindered by the insulating nature of sulfur and the detrimental shuttle effect. This study presents the in-situ synthesis of metal-phase 1T-VS2 as a modified separator material on a two-dimensional Mxene substrate V2C (VSC). The synergistic effect of strong adsorption by V2C and highly conductive catalysis provided by 1T-VS2 significantly enhances the transport of ions and electrons between lithium polysulfide and the interface. The combinations of experimental data and density functional theory (DFT) indicate that 1T-VS2, which is characterized by its high density of defective active sites and high conductivity, not only effectively improves the adsorption of lithium polysulfides, but also dramatically lowers the redox energy barrier of Li2S, thereby accelerating the chemical reaction kinetics. As a result, the Li-S cells assembled by the VSC-modified separator exhibit an impressive initial capacity of 1131 mAh/g at 1 C with a capacity decay rate of only 0.05% per cycle. In addition, even after 100 cycles and at a high sulfur loading of 5.6 mg cm-2, the cells maintain a discharge capacity of 817 mAh/g. Impressively, the VSC continues to deliver excellent cycling and rate performance even when the environmental temperature is reduced to 0 °C. These findings offer valuable insights into the potential for the advancement of highly practical Li-S batteries.

A Review of Advances in Heterostructured Catalysts for Li-S Batteries: Structural Design and Mechanism Analysis

Lithium-sulfur (Li-S) batteries, acclaimed for their high energy density, cost-effectiveness, and environmental benefits, are widely considered as a leading candidate for the next-generation energy storage systems. However, their commercialization is impeded by critical challenges, such as the shuttle effect of lithium polysulfides and sluggish reaction kinetics. These issues can be effectively mitigated through the design of heterojunction catalysts. Despite the remarkable advancements in this field, a comprehensive elucidation of the underlying mechanisms and structure-performance relationships of heterojunction catalysts in sulfur electrocatalysis systems remains conspicuously absent. Here, it is expounded upon the mechanisms underlying heterostructure engineering in Li-S batteries and the latest advancements in heterostructure catalysts guided by these multifarious mechanisms are examined. Furthermore, it illuminates groundbreaking paradigms in heterostructure design, encompassing the realms of composition, structure, function, and application. Finally, the research trends and future development directions for the novel heterojunction materials are extensively deliberated. This study not only provides a comprehensive and profound understanding of heterostructure catalysts in Li-S batteries but also facilitates the exploration of new electrocatalyst systems.

A Universal Electronic Structure Modulation Strategy: Is Strong Adsorption Always Correlated with High Catalysis?

Unveiling the inherent link between polysulfide adsorption and catalytic activity is key to achieving optimal performance in Lithium-sulfur (Li-S) batteries. Current research on the sulfur reaction process mainly relies on the strong adsorption of catalysts to confine lithium polysulfides (LiPSs) to the cathode side, effectively suppressing the shuttle effect of polysulfides. However, is strong adsorption always correlated with high catalysis? The inherent relationship between adsorption and catalytic activity remains unclear, limiting the in-depth exploration and rational design of catalysts. Herein, the correlation between "d-band center-adsorption strength-catalytic activity" in porous carbon nanofiber catalysts embedded with different transition metals (M-PCNF-3, M = Fe, Co, Ni, Cu) is systematically investigated, combining the d-band center theory and the Sabatier principle. Theoretical calculations and experimental analysis results indicate that Co-PCNF-3 electrocatalyst with appropriate d-band center positions exhibits moderate adsorption capability and the highest catalytic conversion activity for LiPSs, validating the Sabatier relationship in Li-S battery electrocatalysts. These findings provide indispensable guidelines for the rational design of more durable cathode catalysts for Li-S batteries.

Amorphous FeSnOx Nanosheets with Hierarchical Vacancies for Room-Temperature Sodium-Sulfur Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries, noted for their low material costs and high energy density, are emerging as a promising alternative to lithium-ion batteries (LIBs) in various applications including power grids and standalone renewable energy systems. These batteries are commonly assembled with glass fiber membranes, which face significant challenges like the dissolution of polysulfides, sluggish sulfur conversion kinetics, and the growth of Na dendrites. Here, we develop an amorphous two-dimensional (2D) iron tin oxide (A-FeSnOx) nanosheet with hierarchical vacancies, including abundant oxygen vacancies (Ovs) and nano-sized perforations, that can be assembled into a multifunctional layer overlaying commercial separators for RT Na-S batteries. The Ovs offer strong adsorption and abundant catalytic sites for polysulfides, while the defect concentration is finely tuned to elucidate the polysulfides conversion mechanisms. The nano-sized perforations aid in regulating Na ions transport, resulting in uniform Na deposition. Moreover, the strategic addition of trace amounts of Ti3C2 (MXene) forms an amorphous/crystalline (A/C) interface that significantly improves the mechanical properties of the separator and suppresses dendrite growth. As a result, the task-specific layer achieves ultra-light (~0.1 mg cm-2), ultra-thin (~200 nm), and ultra-robust (modulus=4.9 GPa) characteristics. Consequently, the RT Na-S battery maintained a high capacity of 610.3 mAh g-1 and an average Coulombic efficiency of 99.9 % after 400 cycles at 0.5 C.

Intricate Ionic Behaviors in High-Performance Self-Powered Hydrothermal Chemical Generator Using Water and Iron (III) Gate

Utilizing the ionic flux to generate voltage output has been confirmed as an effective way to meet the requirements of clean energy sources. Different from ionic thermoelectric (i-TE) and hydrovoltaic devices, a new hydrothermal chemical generator is designed by amorphous FeCl3 particles dispersing in MWCNT and unique ferric chloride or water gate. In the presence of gate, the special ion behaviors enable the cell to present a constant voltage of 0.60 V lasting for over 96 h without temperature difference. Combining the differences of cation concentration, humidity and temperature between the right and left side of sample, the maximum short-circuit current and power output can be obtained to 168.46 µA and 28.11 µW, respectively. The generator also can utilize the low-grade heat to produce electricity wherein Seebeck coefficient is 6.79 mV K-1. The emerged hydrothermal chemical generator offers a novel approach to utilize the low-grade heat, water and salt solution resources, which provides a simple, sustainable and low-cost strategy to realize energy supply.

Achieving High-Performance Lithium-Sulfur Batteries by Modulating Li+ Desolvation Barrier with Liquid Crystal Polymers

Lithium-sulfur (Li-S) batteries offer high theoretical capacity but are hindered by poor rate capability and cycling stability due to sluggish Li2S precipitation kinetics. Here a sulfonate-group-rich liquid crystal polymer (poly-2,2'-disulfonyl-4,4'-benzidine terephthalamide, PBDT) is designed and fabricated to accelerate Li2S precipitation by promoting the desolvation of Li+ from electrolyte. PBDT-modified separators are employed to assemble Li-S batteries, which deliver a remarkable rate capacity (761 mAh g-1 at 4 C) and cycling stability (500 cycles with an average decay rate of 0.088% per cycle at 0.5 C). A PBDT-based pouch cell even delivers an exceptional capacity of ≈1400 mAh g-1 and an areal capacity of ≈11 mAh cm-2 under lean-electrolyte and high-sulfur-loading condition, demonstrating promise for practical applications. Results of Raman spectra, molecular dynamic (MD) and density functional theory (DFT) calculations reveal that the abundant anionic sulfonate groups of PBDT aid in Li+ desolvation by attenuating Li+-solvent interactions and lowering the desolvation energy barrier. Plus, the polysulfide adsorption/catalysis is also excluded via electrostatic repulsion. This work elucidates the critical impact of Li+ desolvation on Li-S batteries and provides a new design direction for advanced Li-S batteries.

Catalyzing Desolvation at Cathode-Electrolyte Interface Enabling High-Performance Magnesium-Ion Batteries

Magnesium ion batteries (MIBs) are expected to be the promising candidates in the post-lithium-ion era with high safety, low cost and almost dendrite-free nature. However, the sluggish diffusion kinetics and strong solvation capability of the strongly polarized Mg2+ are seriously limiting the specific capacity and lifespan of MIBs. In this work, catalytic desolvation is introduced into MIBs for the first time by modifying vanadium pentoxide (V2O5) with molybdenum disulfide quantum dots (MQDs), and it is demonstrated via density function theory (DFT) calculations that MQDs can effectively lower the desolvation energy barrier of Mg2+, and therefore catalyze the dissociation of Mg2+-1,2-Dimethoxyethane (Mg2+-DME) bonds and release free electrolyte cations, finally contributing to a fast diffusion kinetics within the cathode. Meanwhile, the local interlayer expansion can also increase the layer spacing of V2O5 and speed up the magnesiation/demagnesiation kinetics. Benefiting from the structural configuration, MIBs exhibit superb reversible capacity (≈300 mAh g-1 at 50 mA g-1) and unparalleled cycling stability (15 000 cycles at 2 A g-1 with a capacity of ≈70 mAh g-1). This approach based on catalytic reactions to regulate the desolvation behavior of the whole interface provides a new idea and reference for the development of high-performance MIBs.

Juice Vesicles Bioreactors Technology for Constructing Advanced Carbon-Based Energy Storage

The construction of high-quality carbon-based energy materials through biotechnology has always been an eager goal of the scientific community. Herein, juice vesicles bioreactors (JVBs) bio-technology based on hesperidium (e.g., pomelo, waxberry, oranges) is first reported for preparation of carbon-based composites with controllable components, adjustable morphologies, and sizes. JVBs serve as miniature reaction vessels that enable sophisticated confined chemical reactions to take place, ultimately resulting in the formations of complex carbon composites. The newly developed approach is highly versatile and can be compatible with a wide range of materials including metals, alloys, and metal compounds. The growth and self-assembly mechanisms of carbon composites via JVBs are explained. For illustration, NiCo alloy nanoparticles are successfully in situ implanted into pomelo vesicles crosslinked carbon (PCC) by JVBs, and their applications as sulfur/carbon cathodes for lithium-sulfur batteries are explored. The well-designed PCC/NiCo-S electrode exhibits superior high-rate properties and enhanced long-term stability. Synergistic reinforcement mechanisms on transportation of ions/electrons of interface reactions and catalytic conversion of lithium polysulfides arising from metal alloy and carbon architecture are proposed with the aid of DFT calculations. The research provides a novel biosynthetic route to rational design and fabrication of carbon composites for advanced energy storage.

Molecular-Level Interfacial Chemistry Regulation of MXene Enables Energy Storage beyond Theoretical Limit

Ti3C2Tx MXene often suffers from poor lithium storage behaviors due to its electrochemically unfavorable OH terminations. Herein, we propose molecular-level interfacial chemistry regulation of Ti3C2Tx MXene with phytic acid (PA) to directly activate its OH terminations. Through constructing hydrogen bonds (H-bonds) between oxygen atoms of PA and OH terminations on Ti3C2Tx surface, interfacial charge distribution of Ti3C2Tx has been effectively regulated, thereby enabling sufficient ion-storage sites and expediting ion transport kinetics for high-performance energy storage. The results show that Li ions preferably bind to H-bond acceptors (oxygen atoms from PA), and the flexibility of H-bonds therefore renders their interactions with adsorbed Li ions chemically "tunable", thus alleviating undesirable localized geometric changes of the OH terminations. Meanwhile the H-bond-induced microscopic dipoles can act as directional Li-ion pumps to expedite ion diffusion kinetics with lower energy barrier. As a result, the as-designed Ti3C2Tx/PA achieves a 2.4-fold capacity enhancement compared with pristine Ti3C2Tx (even beyond theoretical capacity), superior long-term cyclability (220.0 mAh g-1 after 2000 cycles at 2.0 A g-1), and broad temperature adaptability (-20 to 50 °C). This work offers a promising interface engineering strategy to regulate microenvironments of inherent terminations for breaking through the energy storage performance of MXenes.

Multimodal Engineering of Catalytic Interfaces Confers Multi-Site Metal-Organic Framework for Internal Preconcentration and Accelerating Redox Kinetics in Lithium-Sulfur Batteries

The development of highly efficient catalysts to address the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) in lithium-sulfur batteries (LSBs) remains a formidable challenge. In this study, a series of multi-site catalytic metal-organic frameworks (MSC-MOFs) were elaborated through multimodal molecular engineering to regulate both the reactant diffusion and catalysis processes. MSC-MOFs were crafted with nanocages featuring collaborative specific adsorption/catalytic interfaces formed by exposed mixed-valence metal sites and surrounding adsorption sites. This design facilitates internal preconcentration, a coadsorption mechanism, and continuous efficient catalytic conversion toward polysulfides concurrently. Leveraging these attributes, LSBs with an MSC-MOF-Ti catalytic interlayer demonstrated a 62 % improvement in discharge capacity and cycling stability. This resulted in achieving a high areal capacity (11.57 mAh cm-2 ) at a high sulfur loading (9.32 mg cm-2 ) under lean electrolyte conditions, along with a pouch cell exhibiting an ultra-high gravimetric energy density of 350.8 Wh kg-1 . Lastly, this work introduces a universal strategy for the development of a new class of efficient catalytic MOFs, promoting SRR and suppressing the shuttle effect at the molecular level. The findings shed light on the design of advanced porous catalytic materials for application in high-energy LSBs.

Engineering Strategies for Suppressing the Shuttle Effect in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are supposed to be one of the most potential next-generation batteries owing to their high theoretical capacity and low cost. Nevertheless, the shuttle effect of firm multi-step two-electron reaction between sulfur and lithium in liquid electrolyte makes the capacity much smaller than the theoretical value. Many methods were proposed for inhibiting the shuttle effect of polysulfide, improving corresponding redox kinetics and enhancing the integral performance of Li-S batteries. Here, we will comprehensively and systematically summarize the strategies for inhibiting the shuttle effect from all components of Li-S batteries. First, the electrochemical principles/mechanism and origin of the shuttle effect are described in detail. Moreover, the efficient strategies, including boosting the sulfur conversion rate of sulfur, confining sulfur or lithium polysulfides (LPS) within cathode host, confining LPS in the shield layer, and preventing LPS from contacting the anode, will be discussed to suppress the shuttle effect. Then, recent advances in inhibition of shuttle effect in cathode, electrolyte, separator, and anode with the aforementioned strategies have been summarized to direct the further design of efficient materials for Li-S batteries. Finally, we present prospects for inhibition of the LPS shuttle and potential development directions in Li-S batteries.

Enhancing Electron Conductivity and Electron Density of Single Atom Based Core-Shell Nanoboxes for High Redox Activity in Lithium Sulfur Batteries

Herein, an integrated structure of single Fe atom doped core-shell carbon nanoboxes wrapped by self-growing carbon nanotubes (CNTs) is designed. Within the nanoboxes, the single Fe atom doped hollow cores are bonded to the shells via the carbon needles, which act as the highways for the electron transport between cores and shells. Moreover, the single Fe atom doped nanobox shells is further wrapped and connected by self-growing carbon nanotubes. Simultaneously, the needles and carbon nanotubes act as the highways for electron transport, which can improve the overall electron conductivity and electron density within the nanoboxes. Finite element analysis verifies the unique structure including both internal and external connections realize the integration of active sites in nano scale, and results in significant increase in electron transfer and the catalytic performance of Fe-N4 sites in both Li2 Sn lithiation and Li2 S delithiation. The Li-S batteries with the double-shelled single atom catalyst delivered the specific capacity of 702.2 mAh g-1 after 550 cycles at 1.0 C. The regional structure design and evaluation method provide a new strategy for the further development of single atom catalysts for more electrochemical processes.

A "Catalysis-Immobilization-Deposition" Stepwise Strategy toward Dynamic Equilibrium of Polysulfides Conversion and Diffusion in Lithium-Sulfur Batteries

Stepwise electrocatalysis can remarkably accelerate the kinetics of two consecutive reactions in sulfur electrochemistry. However, the significant difference between the catalysis and diffusion rates of polysulfides results in persistent shuttling in the stepwise electrocatalysts. Here, a stepwise electrocatalytic strategy of catalysis-immobilization-deposition is proposed for achieving the consistency of diffusion and catalysis of polysulfides. Accordingly, a sandwich-like stepwise electrocatalyst is designed, which is composed of Co nanoparticles (Co-NP), mesoporous SiO₂ , and iron single atom (Fe-SA) (denoted as Co-NP@SiO₂ @Fe-SA), serving as catalysis core, immobilization interlayer, and deposition shell, respectively. Benefitting from the dynamic equilibrium between production and consumption of polysulfides achieved by the spatial synergistic effect of the triple sites, the S/Co-NP@SiO₂ @Fe-SA cathode delivers a high reversible capacity of 731 mAh g^-1 over 500 cycles at 1 C with a small capacity decay of 0.039% per cycle. Moreover, a high areal capacity of 3.8 mAh cm^-2 at a sulfur loading of 4.5 mg cm^-2 is achieved with a low electrolyte/sulfur ratio of 5.9. This work sheds light on a new host design concept with high catalytic activity, stability, and selectivity to enable high performance lithium-sulfur batteries.

Synthesis of the Ni2P-Co Mott-Schottky Junction as an Electrocatalyst to Boost Sulfur Conversion Kinetics and Application in Separator Modification in Li-S Batteries

To overcome the shuttling effect and sluggish conversion kinetics of polysulfides, a large number of catalysts have been designed for lithium-sulfur (Li-S) batteries. Herein, a Mott-Schottky junction catalyst composed of Co nanoparticles and Ni₂P was designed to improve polysulfide kinetics. Our investigations reveal the rearrangement of charges at the Schottky junction interface and the construction of the built-in electric field are crucial for lowering the activation energy of the dissolved Li₂S_n reduction and Li₂S nucleation reaction. Furthermore, a series of experimental and electrochemical tests were performed to demonstrate that the Schottky catalytic effect enhanced the synergistic catalytic effect. With a Ni₂P-Co@CNT catalyst, the battery exhibits an initial specific capacity of 874 mAh g^-1 at a rate of 4.0 C, and the decay rate per cycle is 0.049% in 700 cycles. Meanwhile, the battery shows 0.118% decay rate per cycle at 0.5 C in 100 cycles at a high sulfur loading of 10 mg cm^-2. The Schottky heterojunction structure proposed here has been shown to have a good catalytic effect on the reduction of Li₂S_n and nucleation of Li₂S, which provides a profound guidance for efficient and rational catalyst design.