Regulating Polysulfide Diffusion and Deposition via Rational Design of Core-Shell Active Materials in Li-S Batteries

V-Doped CoSe2 Nanowire Catalysts in a 3D-Structured Electrode for Durable Li-S Pouch Cells

Lithium-sulfur (Li-S) batteries have high theoretical energy density and are regarded as a promising candidate for next-generation energy storage systems. However, their practical applications are hindered by the slow kinetics of sulfur conversion and polysulfide shuttling. In particular, large-scale pouch cells show much poor cyclability. Here, we develop a high-efficiency catalyst of V-doped CoSe2 by studying the binary CoSe2-VSe2 system and confirming its effectiveness in accelerating polysulfide conversion. The coin cell tests reveal an initial capacity of 1414 mAh g-1 at 0.1 C and 1049 mAh g-1 at 1 C and demonstrate 1000 times cyclability with a decaying rate of 0.05% per cycle. Furthermore, the assembly and construction of pouch cells were optimized with monolithic three-dimensional (3D) electrodes and a multistacking strategy. Specifically, a 3D metallic scaffold (3MS) was developed to host V-doped CoSe2 nanowires and sulfur. In addition, Janus microspheres of C@TiO2 were synthesized to capture polar polysulfides with their polar part of TiO2 and adsorb nonpolar sulfur with their nonpolar part of carbon. By integrating with 3MS, C@TiO2 microspheres can block all ion channels of 3MS and only allow Li ions in and out. These integral designs and monolithic structures enable multistacking pouch cells with high cyclability. A high-loading pouch cell was demonstrated with a total capacity of 700 mAh. The cell can be cycled for 70 times with a capacity retention of 65.7%. In brief, this work provides an integral strategy of catalyst design and overall 3D assembly for practical Li-S batteries in a large pouch cell format.

Fe3O4-doped mesoporous carbon cathode with a plumber's nightmare structure for high-performance Li-S batteries

Shuttling of lithium polysulfides and slow redox kinetics seriously limit the rate and cycling performance of lithium-sulfur batteries. In this study, Fe3O4-dopped carbon cubosomes with a plumber's nightmare structure (SP-Fe3O4-C) are prepared as sulfur hosts to construct cathodes with high rate capability and long cycling life for Li-S batteries. Their three-dimensional continuous mesochannels and carbon frameworks, along with the uniformly distributed Fe3O4 particles, enable smooth mass/electron transport, strong polysulfides capture capability, and fast catalytic conversion of the sulfur species. Impressively, the SP-Fe3O4-C cathode exhibits top-level comprehensive performance, with high specific capacity (1303.4 mAh g-1 at 0.2 C), high rate capability (691.8 mAh gFe3O41 at 5 C), and long cycling life (over 1200 cycles). This study demonstrates a unique structure for high-performance Li-S batteries and opens a distinctive avenue for developing multifunctional electrode materials for next-generation energy storage devices.

Architecting the Microenvironment Skeleton of Active Materials in High-Capacity Electrodes by Self-Assembled Nano-Building Blocks

In analogy to the cell microenvironment in biology, understanding and controlling the active-material microenvironment (ME@AM) microstructures in battery electrodes is essential to the successes of energy storage devices. However, this is extremely difficult for especially high-capacity active materials (AMs) like sulfur, due to the poor controlling on the electrode microstructures. To conquer this challenge, here, a semi-dry strategy based on self-assembled nano-building blocks is reported to construct nest-like robust ME@AM skeleton in a solvent-and-stress-less way. To do that, poly(vinylidene difluoride) nanoparticle binder is coated onto carbon-nanofibers (NB@CNF) via the nanostorm technology developed in the lab, to form self-assembled nano-building blocks in the dry slurry. After compressed into an electrode prototype, the self-assembled dry-slurry is then bonded by in-situ nanobinder solvation. With this strategy, mechanically strong thick sulfur electrodes are successfully fabricated without cracking and exhibit high capacity and good C-rate performance even at a high AM loading (25.0 mg cm-2 by 90 wt% in the whole electrode). This study may not only bring a promising solution to dry manufacturing of batteries, but also uncover the ME@AM structuring mechanism with nano-binder for guiding the design and control on electrode microstructures.

The electrochemistry of stable sulfur isotopes versus lithium

Sulfur in nature consists of two abundant stable isotopes, with two more neutrons in the heavy one (34S) than in the light one (32S). The two isotopes show similar physicochemical properties and are usually considered an integral system for chemical research in various fields. In this work, a model study based on a Li-S battery was performed to reveal the variation between the electrochemical properties of the two S isotopes. Provided with the same octatomic ring structure, the cyclo-34S8 molecules form stronger S-S bonds than cyclo-32S8 and are more prone to react with Li. The soluble Li polysulfides generated by the Li-34S conversion reaction show a stronger cation-solvent interaction yet a weaker cation-anion interaction than the 32S-based counterparts, which facilitates quick solvation of polysulfides yet hinders their migration from the cathode to the anode. Consequently, the Li-34S cell shows improved cathode reaction kinetics at the solid-liquid interface and inhibited shuttle of polysulfides through the electrolyte so that it demonstrates better cycling performance than the Li-32S cell. Based on the varied shuttle kinetics of the isotopic-S-based polysulfides, an electrochemical separation method for 34S/32S isotope is proposed, which enables a notably higher separation factor than the conventional separation methods via chemical exchange or distillation and brings opportunities to low-cost manufacture, utilization, and research of heavy chalcogen isotopes.

Rational Design of High-Loading Electrodes with Superior Performances Toward Practical Application for Energy Storage Devices

High-loading electrodes play a crucial role in designing practical high-energy batteries as they reduce the proportion of non-active materials, such as current separators, collectors, and battery packaging components. This design approach not only enhances battery performance but also facilitates faster processing and assembly, ultimately leading to reduced production costs. Despite the existing strategies to improve rechargeable battery performance, which mainly focus on novel electrode materials and high-performance electrolyte, most reported high electrochemical performances are achieved with low loading of active materials (<2 mg cm-2). Such low loading, however, fails to meet application requirements. Moreover, when attempting to scale up the loading of active materials, significant challenges are identified, including sluggish ion diffusion and electron conduction kinetics, volume expansion, high reaction barriers, and limitations associated with conventional electrode preparation processes. Unfortunately, these issues are often overlooked. In this review, the mechanisms responsible for the decay in the electrochemical performance of high-loading electrodes are thoroughly discussed. Additionally, efficient solutions, such as doping and structural design, are summarized to address these challenges. Drawing from the current achievements, this review proposes future directions for development and identifies technological challenges that must be tackled to facilitate the commercialization of high-energy-density rechargeable batteries.

Sulfur Migration Enhanced Proton-Coupled Electron Transfer for Efficient CO2 Desorption with Core-Shelled C@Mn3O4

Transforming hazardous species into active sites by ingenious material design was a promising and positive strategy to improve catalytic reactions in industrial applications. To synergistically address the issue of sluggish CO2 desorption kinetics and SO2-poisoning solvent of amine scrubbing, we propose a novel method for preparing a high-performance core-shell C@Mn3O4 catalyst for heterogeneous sulfur migration and in situ reconstruction to active -SO3H groups, and thus inducing an enhanced proton-coupled electron transfer (PCET) effect for CO2 desorption. As anticipated, the rate of CO2 desorption increases significantly, by 255%, when SO2 is introduced. On a bench scale, dynamic CO2 capture experiments reveal that the catalytic regeneration heat duty of SO2-poisoned solvent experiences a 32% reduction compared to the blank case, while the durability of the catalyst is confirmed. Thus, the enhanced PCET of C@Mn3O4, facilitated by sulfur migration and simultaneous transformation, effectively improves the SO2 resistance and regeneration efficiency of amine solvents, providing a novel route for pursuing cost-effective CO2 capture with an amine solvent.

Encapsulating Sulfur into a Gel-Derived Nitrogen-Doped Mesoporous and Microporous Carbon Sponge for High-Performance Lithium-Sulfur Batteries

The practical application of Li-S batteries (LSBs) has long been impeded by the inefficient utilization of sulfur and slow kinetics. Utilizing conductive carbonaceous frameworks as a host scaffold presents an efficient and cost-effective approach to enhance sulfur utilization for redox reactions in LSBs. However, the interaction of pure carbon materials with lithium polysulfide intermediates (LiPSs) is limited to weak van der Waals forces. Hence, the development of an economical method for synthesizing heteroatom-doped carbon materials for sulfur fixation is of paramount importance. In this study, we introduce a hierarchical porous nitrogen-doped carbon sponge (NPCS) with an exceptionally high BET surface area of 3182.2 m2 g-1, achieved through a facile template-assisted polymerization method. The incorporation of inorganic salts, free radical polymerization, and deuteric freeze-drying techniques facilitates the formation of hierarchical pores within the NPCS. After sulfur fixation, the resulting S/NPCS electrode demonstrates remarkable electrochemical performance in LSBs. Specifically, it achieves an 80% sulfur utilization rate, maintains a high reversible specific capacity of 400 mA h g-1 even after 600 cycles at a demanding current density of 5.0 A g-1, and exhibits superior rate capability. It is believed that this work will inspire the rational design of cost-effective carbon-based electrodes for high-performance LSBs.

Polysulfides in Magnesium-Sulfur Batteries

Mg-S batteries hold great promise as a potential alternative to Li-based technologies. Their further development hinges on solving a few key challenges, including the lower capacity and poorer cycling performance when compared to Li counterparts. At the heart of the issues is the lack of knowledge on polysulfide chemical behaviors in the Mg-S battery environment. In this Review, a comprehensive overview of the current understanding of polysulfide behaviors in Mg-S batteries is provided. First, a systematic summary of experimental and computational techniques for polysulfide characterization is provided. Next, conversion pathways for Mg polysulfide species within the battery environment are discussed, highlighting the important role of polysulfide solubility in determining reaction kinetics and overall battery performance. The focus then shifts to the negative effects of polysulfide shuttling on Mg-S batteries. The authors outline various strategies for achieving an optimal balance between polysulfide solubility and shuttling, including the use of electrolyte additives, polysulfide-trapping materials, and dual-functional catalysts. Based on the current understanding, the directions for further advancing knowledge of Mg polysulfide chemistry are identified, emphasizing the integration of experiment with computation as a powerful approach to accelerate the development of Mg-S battery technology.

Anion receptor and heavy metal-free redox mediator decorated separator for lithium-sulfur batteries

The adsorption-catalysis synergy for accelerated conversion of polysulfides is critical toward the electrochemical stability of lithium-sulfur battery (LSB). Herein, a non-metallic polymer network with anion receptor units, trifluoromethanesulfonyl (CF3SO2-) substituted aza-ether, was in-situ integrated on PE separator, working as an efficient host for anchoring lithium thiophosphates (LPS) as redox mediators and polysulfides through Lewis acid-base interaction. The anchored LPS on the modified PE separator displayed a robust chemical adsorption ability towards polysulfides through the formation of SS bond. Meanwhile, LPS decreased the energy barrier of Li2S nucleation and promoted redox reaction kinetics. The battery with LPS decorated separator revealed a long cycling lifespan with a per cycle decay of 0.056 % after 600 cycles, and a competitive initial capacity of 889.1 mAh/g when the of sulfur cathode increased to 3 mg cm-2. This work developed a new design strategy to promote the utilization of lithium phosphorus sulfide compounds in LSB.

Synergizing Spatial Confinement and Dual-Metal Catalysis to Boost Sulfur Kinetics in Lithium-Sulfur Batteries

Sluggish kinetics and parasitic shuttling reactions severely impede lithium-sulfur (Li-S) battery operation; resolving these issues can enhance the capacity retention and cyclability of Li-S cells. Therefore, an effective strategy featuring core-shell-structured Co/Ni bimetal-doped metal-organic framework (MOF)/sulfur nanoparticles is reported herein for addressing these problems; this approach offers unprecedented spatial confinement and abundant catalytic sites by encapsulating sulfur within an ordered architecture. The protective shells exhibit long-term stability, ion screening, high lithium-polysulfide adsorption capability, and decent multistep catalytic conversion. Additionally, the delocalized electrons of the MOF endow the cathodes with superior electron/lithium-ion transfer ability. Via multiple physicochemical and theoretical analysis, the resulting synergistic interactions are proved to significantly promote interfacial charge-transfer kinetics, facilitate sulfur conversion dynamics, and inhibit shuttling. The assembled Li-S batteries deliver a stable, highly reversible capacity with marginal decay (0.075% per cycle) for 400 cycles at 0.2 C, a pouch-cell areal capacity of 3.8 mAh cm-2 for 200 cycles under a high sulfur loading, as well as remarkably improved pouch-cell performance.

Vanadium Intercalation into Niobium Disulfide to Enhance the Catalytic Activity for Lithium-Sulfur Batteries

Despite their high specific energy and great promise for next-generation energy storage, lithium-sulfur (Li-S) batteries suffer from polysulfide shuttling, slow redox kinetics, and poor cyclability. Catalysts are needed to accelerate polysulfide conversion and suppress the shuttling effect. However, a lack of structure-activity relationships hinders the rational development of efficient catalysts. Herein, we studied the Nb-V-S system and proposed a V-intercalated NbS₂ (Nb₃VS₆) catalyst for high-efficiency Li-S batteries. Structural analysis and modeling revealed that undercoordinated sulfur anions of [VS₆] octahedra on the surface of Nb₃VS₆ may break the catalytic inertness of the basal planes, which are usually the primary exposed surfaces of many 2D layered disulfides. Using Nb₃VS₆ as the catalyst, the resultant Li-S batteries delivered high capacities of 1541 mAh g^-1 at 0.1 C and 1037 mAh g^-1 at 2 C and could retain 73.2% of the initial capacity after 1000 cycles. Such an intercalation-induced high activity offers an alternative approach to building better Li-S catalysts.

Mass Production of Customizable Core-Shell Active Materials in Seconds by Nano-Vapor Deposition for Advancing Lithium Sulfur Battery

Rational design and scalable production of core-shell sulfur-rich active materials is vital for not only the practical success of future metal-sulfur batteries but also for a deep insight into the core-shell design for sulfur-based electrochemistry. However, this is a big challenge mainly due to the lack of efficient strategy for realizing precisely controlled core-shell structures. Herein, by harnessing the frictional heating and dispersion capability of the nanostorm technology developed in the authors' laboratory, it is surprisingly found that sulfur-rich active particles can be coated with on-demand shell nanomaterials in seconds. To understand the process, a micro-adhesion guided nano-vapor deposition (MAG-NVD) working mechanism is proposed. Enabled by this technology, customizable nano-shell is realized in a super-efficient and solvent-free way. Further, the different roles of shell characteristics in affecting the sulfur-cathode electrochemical performance are discovered and clarified. Last, large-scale production of calendaring-compatible cathode with the optimized core-shell active materials is demonstrated, and a Li-S pouch-cell with 453 Wh kg^-1 @0.65 Ah is also reported. The proposed nano-vapor deposition may provide an attractive alternative to the well-known physical and chemical vapor deposition technologies.

Manipulating Li2 S Redox Kinetics and Lithium Dendrites by Core-Shell Catalysts under High Sulfur Loading and Lean-Electrolyte Conditions

For practical lithium-sulfur batteries (LSBs), the high sulfur loading and lean-electrolyte are necessary conditions to achieve the high energy density. However, such extreme conditions will cause serious battery performance fading, due to the uncontrolled deposition of Li2 S and lithium dendrite growth. Herein, the tiny Co nanoparticles embedded N-doped carbon@Co9 S8 core-shell material (CoNC@Co9 S8 NC) is designed to address these challenges. The Co9 S8 NC-shell effectively captures lithium polysulfides (LiPSs) and electrolyte, and suppresses the lithium dendrite growth. The CoNC-core not only improves electronic conductivity, but also promotes Li+ diffusion as well as accelerates Li2 S deposition/decomposition. Consequently, the cell with CoNC@Co9 S8 NC modified separator delivers a high specific capacity of 700 mAh g-1 with a low-capacity decay rate of 0.035% per cycle at 1.0 C after 750 cycles under a sulfur loading of 3.2 mg cm-2 and a E/S ratio of 12 µL mg-1 , and a high initial areal capacity of 9.6 mAh cm-2 under a high sulfur loading of 8.8 mg cm-2 and a low E/S ratio of 4.5 µL mg-1 . Besides, the CoNC@Co9 S8 NC exhibits an ultralow overpotential fluctuation of 11 mV at a current density of 0.5 mA cm-2 after 1000 h during a continuous Li plating/striping process.

Conductive Polymer Coated Layered Double Hydroxide as a Novel Sulfur Reservoir for Flexible Lithium-Sulfur Batteries

Lithium-sulfur battery (LSB) is widely regarded as the most promising next-generation energy storage system owing to its high theoretical capacity and low cost. However, the practical application of LSBs is mainly hampered by the low electronic conductivity of the sulfur cathode and the notorious "shuttle effect", which lead to high voltage polarization, severe over-charge behavior, and rapid capacity decay. To address these issues, a novel sulfur reservoir is synthesized by coating polypyrrole (PPy) thin film on hollow layered double hydroxide (LDH) (PPy@LDH). After compositing with sulfur, such PPy@LDH-S cathode shows a multi-functional effect to reserve lithium polysulfides (LiPSs). In addition, the unique architecture provides sufficient inner space to encapsulate the volume expansion and enhances the reaction kinetics of sulfur-based redox chemistry. Theoretical calculations have illustrated that the PPy@LDH has shown stronger chemical adsorption capability for LiPSs than those of porous carbon and LDH, preventing the shuttling of LiPSs and enhancing the nucleation affinity of liquid-solid conversion. As a result, the PPy@LDH-S electrode delivers a stable cycling performance and a superior rate capability. Flexible battery has demonstrated this PPy@LDH-S electrode can work properly with treatments of bending, folding, and even twisting, paving the way for wearable devices and flexible electronics.

P-P Orbital Interaction Enables Single-Crystalline Semimetallic β-MoTe2 Nanosheets as Efficient Electrocatalysts for Lithium-Sulfur Batteries

The practical implementation of lithium-sulfur batteries (LSBs) has been impeded by the sluggish redox kinetics of lithium polysulfides (LiPSs) and shuttle effect of soluble LiPSs during charge/discharge. It is desirable to exploit materials combining superior electrical conductivity with excellent catalytic activity for use as electrocatalysts in LSBs. Herein, we report the employment of chemical vapor transport (CVT) method followed by an electrochemical intercalation process to fabricate high-quality single-crystalline semimetallic β-MoTe₂ nanosheets, which are utilized to manipulate the LiPSs conversion kinetics. The first-principles calculations prove that β-MoTe₂ could lower the Gibbs free-energy barrier for Li₂S₂ transformation to Li₂S. The wavefunction analysis demonstrates that the p-p orbital interaction between Te p and S p orbitals accounts for the strong electronic interaction between the β-MoTe₂ surface and Li₂S₂/Li₂S, making bonding and electron transfer more efficient. As a result, a β-MoTe₂/CNT@S-based LSB cell can deliver an excellent cycling performance with a low capacity fade rate of 0.11% per cycle over 300 cycles at 1C. Our work might not only provide a universal route to prepare high-quality single-crystalline transition-metal dichalcogenides (TMDs) nanosheets for use as electrocatalysts in LSBs, but also suggest a different viewpoint for the rational design of LiPSs conversion electrocatalysts.

FeCoNi Ternary Nano-Alloys Embedded in a Nitrogen-Doped Porous Carbon Matrix with Enhanced Electrocatalysis for Stable Lithium-Sulfur Batteries

The application of composite materials that combine the advantages of carbonaceous material and metal alloy proves to be a valid method for improving the performance of lithium-sulfur batteries (LSBs). Herein iron-cobalt-nickel (FeCoNi) ternary alloy nanoparticles (FNC) that spread on nitrogen-doped carbon (NC) are obtained by a strategy of low-temperature sol-gel followed by annealing at 800 °C under an argon/hydrogen atmosphere. Benefiting from the synergistic effect of different components of FNC and the conductive network provided by the NC, not only can the "shuttle effect" of lithium polysulfides (LiPS) be suppressed, but also the conversion of LiPS, the diffusion of Li⁺, and the deposition of Li₂S can be accelerated. Taking advantage of those merits, the batteries assembled with an FNC@NC-modified polypropylene (PP) separator (FNC@NC//PP) can deliver a high reversible specific capacity of 1325 mAh g^-1 at 0.2 C and maintain 950 mAh g^-1 after 200 cycles, and they can also achieve a low capacity fading rate of 0.06% per cycle over 500 cycles at 1 C. More impressively, even under harsh test conditions (the ratio of electrolyte to sulfur (E/S) = 6 μL mg^-1 and sulfur loading = 4.7 mg cm^-2 and E/S = 10 μL mg^-1 and sulfur loading = 5.9 mg cm^-2), the area capacity of batteries is still much higher than 4 mAh cm^-2.

High-Performance Flexible Sulfur Cathodes with Robust Electrode Skeletons Built by a Hierarchical Self-Assembling Slurry

The electrochemical performance of lithium-sulfur batteries is fundamentally determined by the structural and mechanical stability of their composite sulfur cathodes. However, the development of cost-effective strategies for realizing robust hierarchical composite electrode structures remains highly challenging due to uncontrollable interactions among the components. The present work addresses this issue by proposing a type of self-assembling electrode slurry based on a well-designed two-component (polyacrylonitrile and polyvinylpyrrolidone) polar binder system with carbon nanotubes that forms hierarchical porous structures via optimized water-vapor-induced phase separation. The electrode skeleton is a highly robust and flexible electron-conductive network, and the porous structure provides hierarchical ion-transport channels with strong polysulfide trapping capability. Composite sulfur cathodes prepared with a sulfur loading of 4.53 mg cm-2 realize a very stable specific capacity of 485 mAh g-1 at a current density of 3.74 mA cm-2 after 1000 cycles. Meanwhile, a composite sulfur cathode with a high sulfur loading of 14.5 mg cm-2 in a lithium-sulfur pouch cell provides good flexibility and delivers a high capacity of 600 mAh g-1 at a current density of 0.72 mA cm-2 for 78 cycles.