Suppressing the Shuttle Effect and Dendrite Growth in Lithium-Sulfur Batteries

Synergistic electrochemical catalysis by high-entropy metal phosphide in lithium-sulfur batteries

The shuttle effect and sluggish redox kinetics of polysulfides have hindered the development of lithium-sulfur batteries (LSBs) as premier energy storage devices. To address these issues, a high-entropy metal phosphide (NiCoMnFeCrP) was synthesized using the sol-gel method. NiCoMnFeCrP, with its rich metal species, exhibits strong synergistic effects and provides numerous catalytic active sites for the conversion of polysulfides. These active sites, possessing significant polarity, can bond with polysulfides. In situ ultraviolet-visible were conducted to monitor the dynamic changes in species and concentrations of polysulfides, validating the ability of NiCoMnFeCrP to facilitate the conversion of polysulfides. The batteries with the NiCoMnFeCrP catalyst as functional separators exhibited minimal capacity decay rates of 0.04 % and 0.23 % after 100 cycles at 0 °C and 60 °C, respectively. This indicates that the NiCoMnFeCrP catalyst possesses good thermal stability. Meanwhile, its area capacity can reach 4.78 mAh cm-2 at a high sulfur load of 4.54 mg cm-2. In conclusion, NiCoMnFeCrP achieves the objective of mitigating the shuttle effect and accelerating the kinetics of the redox reaction, thereby facilitating the commercialization of LSBs.

One-Pot Hydrothermal-Derived rGO/MXene/Sulfur Composite Aerogels as Free-Standing Cathodes in Lithium-Sulfur Batteries

The confinement and high utilization of sulfur in the cathodes is critical for improved cycling performance of lithium-sulfur batteries. In this case one-pot hydrothermal strategy is developed to produce rGO/MXene/sulfur composite aerogels where sulfur is in situ trapped in the 3D rGO/MXene conductive skeleton. The optimized composite aerogels as free-standing cathodes delivery a specific capacity of 951 mAhg-1 after 100 cycles at 0.2 C with a low fading rate of 0.062 % per cycle. The excellent cycling performance is correlated with highly oxidized MXene and in situ formed sulfate/thiosulfate complex layer in the long-term cycles.

Neuron-Like Silicone Nanofilaments@Montmorillonite Nanofillers of PEO-Based Solid-State Electrolytes for Lithium Metal Batteries with Wide Operation Temperature

Poly(ethylene oxide) (PEO)-based composite solid electrolytes (CSEs) are promising to accelerate commercialization of solid-state lithium metal batteries (SSLMBs). Nonetheless, this is hindered by the CSEs' limited ion conductivity at room temperature. Here, we propose design, synthesis, and application of the bioinspired neuron-like nanofillers for PEO-based CSEs. The neuron-like superhydrophobic nanofillers are synthesized by controllably grafting silicone nanofilaments onto montmorillonite nanosheets. Compared to various reported fillers, the nanofillers can greatly improve ionic conductivity (4.9×10-4 S cm-1, 30 °C), Li+ transference number (0.63), oxidation stability (5.3 V) and mechanical properties of the PEO-based CSEs because of the following facts. The distinctive neuron-like structure and the resulting synaptic-like connections establish numerous long-distance continuous channels over various directions in the PEO-based CSEs for fast and uniform Li+ transport. Consequently, the assembled SSLMBs with the CSEs and LiFePO4 or NCM811 cathodes display superior cycling stability over a wide temperature range of 50 °C to 0 °C. Surprisingly, the pouch batteries with the large-scale prepared CSEs kept working after being repeatedly bent, folded, cut or even punched in air. We believe that design of neuron-like nanofillers is a viable approach to produce CSEs with high room temperature ionic conductivity for SSLMBs.

Dependence of Interlayer or Sulfur Host on Hollow Framework of Lithium-Sulfur Battery

Lithium-sulfur batteries are recognized as the next generation of high-specific energy secondary batteries owing to their satisfactory theoretical specific capacity and energy density. However, their commercial application is greatly limited by a series of problems, including disordered migration behavior, sluggish redox kinetics, and the serious shuttle effect of lithium polysulfides. One of the most efficient approaches to physically limit the shuttle effect is the rational design of a hollow framework as sulfur host. However, the influence of the hollow structure on the interlayers has not been clearly reported. In this study, the Mo2C/C catalysts with hollow(H-Mo2C/C) and solid(S-Mo2C/C) frameworks are rationally designed to explore the dependence of the hollow structure on the interlayer or sulfur host. In contrast to the physical limitations of the hollow framework as host, the hollow structure of the interlayer inhibited lithium-ion diffusion, resulting in poor electrochemical properties at high current densities. Based on the superiority of the various frameworks, the H-Mo2C/C@S | S-Mo2C/C@PP | Li cells are assembled and displayed excellent electrochemical performance. This work re-examines the design requirements and principles of catalyst frameworks in different battery units.

Design of High-Performance Formyl-Functionalized COF Aerogels as Quasi-Solid Lithium Battery Electrolyte by a Solvent Substitution Strategy

Covalent organic framework (COF) aerogels with functional groups offer exceptional processability and functionality for various applications. These hierarchical porous materials combine the advantages of COFs with the benefits of aerogels, overcoming the limitations of conventional insoluble and nonfusible COF powders. However, achieving both high crystallinity and shape retention remains a challenge for functionalized COF aerogels. In this work, we develop a novel and general solvent substitution method for the one-step synthesis of formyl-functionalized COF aerogels without harsh vacuum conditions. These aerogels exhibit excellent processing capabilities, superior mechanical strength, and enhanced functionality. As a proof-of-concept, they were used in adsorption and lithium metal battery applications, significantly maximizing the structural advantages of COFs, e.g.: (i) the hierarchical porous structure is fully wetted by the electrolyte to form continuous transport channels; (ii) the polar groups, which are easier to be acquired, help in desolvation and transfer of Li+; (iii) the regular pore structures stabilize deposition of Li+ and inhibit the growth of lithium dendrites. These combined benefits contribute to a lighter battery with improved energy density and enhanced safety.

Bismuth oxychloride nanosheets anchored aramid separator with sponge-like structure for improved lithium-ion battery performance

Functional modification of inorganic particles is an effective approach to tackle the issue of Li+ transport and the lithium dendrites formation in lithium-ion batteries (LIBs). In this study, PMIA/BiOCl composite separators are prepared by nonsolvent induce phase separation (NIPS) method using P-type semiconductor bismuth oxychloride (BiOCl) functionalized poly (m-phenylene isophthalamide) (PMIA) separators. Compared with the polypropylene (PP) separator, PMIA has superior thermal stability and the addition of BiOCl further enhances its flame retardancy. And the prepared PMIA/BiOCl separator presents improved porosity (66.47 %), enhanced electrolyte uptake rate (863 %) and higher ionic conductivity (0.49 mS∙cm-1). Besides, the incorporation of BiOCl can anchor PF6- to the three-dimensional network skeleton of the PMIA/BiOCl separators, enabling the desolvation of Li+ and selectively facilitating Li+ transport (the Li+ transfer number is 0.79). Moreover, the uniform porous structure of the PMIA/BiOCl separators and the efficient transport of Li+ uniformly deposite Li+, and minimize the growth of lithium dendrites. Batteries assembled with PMIA/BiOCl separators have a discharge specific capacity of 124.4 mAh∙g-1 and capacity retention of 96.7 % after 200 cycles at 0.2C. Therefore, this work provides an effective route in the design strategy of separators for LIBs.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

Electrospun MoS2-CNTs-PVA/PVA Hybrid Separator for High-Performance Li/FeS2 Batteries

As a promising candidate for high-energy-density rechargeable lithium metal batteries, Li/FeS2 batteries still suffer from the large volume change and severe shuttle effect of lithium polysulfides during cycling. To improve the electrochemical performance, great efforts have been made to modify FeS2 cathodes by constructing various nanocomposites. However, energy density is sacrificed, and these materials are not applicable at a large scale. Herein, we report that the electrochemical performance of commercial FeS2 can be greatly enhanced with the application of a double-layer MoS2-CNTs-PVA (MCP)/PVA separator fabricated by electrospinning. The assembled Li/FeS2 batteries can still deliver a high discharge capacity of 400 mAh/g after 200 cycles at a current density of 0.5 C. The improved cycling stability can be attributed to the strong affinity towards lithium polysulfides (LiPSs) of the hydroxyl-rich PVA matrix and the unique double-layer structure, in which the bottom layer acts as an electrical insulation layer and the top layer coupled with MoS2/CNTs provides catalytic sites for LiPS conversion.

Toward Stimulating the Chemistry Process for Garnet Electrolyte-Based Molten Li-S Batteries: Modulation of the End-Product in the Cathode with High Loading

Due to their low self-discharge rate, no intermediate product dissolution in the cathode, and easy recycle of electrode materials, solid electrolyte-based molten lithium sulfur batteries can be one of the highly anticipated advanced electrochemical chemistry technologies for grid-scale energy storage. However, the actual energy density and reversibility of them still face severe challenges for low active materials loading and the inherent low conductivity of sulfur and its end-products. In this work, with the iodide modulation effect, small size (∼5 nm for the primary particles) and low relative crystallinity discharge end-products in the sulfur cathode can be formed, contributing to the immense specific capacity and reversibility. As validated by theoretical calculations, iodide ions in the homogeneous molten composite cathode display a profound comprehensive effect on the chemical reaction and cycling stability. As a result, high sulfur loading (over 80 mg cm-2) with a significant utilization rate can be achieved, corresponding to a single Li-S cell of 1.39 Ah and a volumetric energy density of 528.5 Wh L-1 based on the overall cell volume; simultaneously, a prominent cycling stability during 300 cycles along with an impressive reversibility is obtained.

Constructing Cooperative Interface via Bi-Functional COF for Facilitating the Sulfur Conversion and Li+ Dynamics

Lithium-sulfur (Li-S) batteries stand out for their high theoretical specific capacity and cost-effectiveness. However, the practical implementation of Li-S batteries is hindered by issues such as the shuttle effect, tardy redox kinetics, and dendrite growth. Herein, an appealingly designed covalent organic framework (COF) with bi-functional active sites of cyanide groups and polysulfide chains (COF-CN-S) is developed as cooperative functional promoters to simultaneously address dendrites and shuttle effect issues. Combining in situ techniques and theoretical calculations, it can be demonstrated that the unique chemical architecture of COF-CN-S is capable of performing the following functions: 1) The COF-CN-S delivers significantly enhanced Li+ transport capability due to abundant ion-hopping sites (cyano-groups); 2) it functions as a selective ion sieve by regulating the dynamic behavior of polysulfide anions and Li+ , thus inhibiting shuttle effect and dendrite growth; 3) by acting as a redox mediator, the COF-CN-S can effectively control the electrochemical behavior of polysulfides and enhance their conversion kinetics. Based on the above advantages, the COF-CN-S endows Li-S batteries with excellent performance. This study highlights the significance of interface modification and offers novel insights into the rational design of organic materials in the Li-S realm.

Co/Mon Invigorated Bilateral Kinetics Modulation for Advanced Lithium-Sulfur Batteries

Sluggish sulfur redox kinetics and Li-dendrite growth are the main bottlenecks for lithium-sulfur (Li-S) batteries. Separator modification serves as a dual-purpose approach to address both of these challenges. In this study, the Co/MoN composite is rationally designed and applied as the modifier to modulate the electrochemical kinetics on both sides of the sulfur cathode and lithium anode. Benefiting from its adsorption-catalysis function, the decorated separators (Co/MoN@PP) not only effectively inhibit polysulfides (LiPSs) shuttle and accelerate their electrochemical conversion but also boost Li+ flux, realizing uniform Li plating/stripping. The accelerated LiPSs conversion kinetics and excellent sulfur redox reversibility triggered by Co/MoN modified separators are evidenced by performance, in-situ Raman detection and theoretical calculations. The batteries with Co/MoN@PP achieve a high initial discharge capacity of 1570 mAh g-1 at 0.2 C with a low decay rate of 0.39%, uniform Li+ transportation at 1 mA cm-2 over 800 h. Moreover, the areal capacity of 4.62 mAh cm-2 is achieved under high mass loadings of 4.92 mg cm-2 . This study provides a feasible strategy for the rational utilization of the synergistic effect of composite with multifunctional microdomains to solve the problems of Li anode and S cathode toward long-cycling Li-S batteries.

Fe3 C/nanocarbon-Enabled Lithium Dendrite Mitigation in Lithium-Sulfur batteries

Lithium dendrite-induced short circuits and material loss are two major obstacles to the commercialization of lithium-sulfur (Li-S) batteries. Here, a nanocarbon composite consisting of cotton-derived Fe3 C-encapsulated multiwalled carbon nanotubes (Fe3 C-MWCNTs) and graphene effectively traps polysulfides to suppress lithium dendrite growth is reported. Machine learning combined with molecular dynamics (MD) simulations unveils a new polysulfide-induced lithium dendrite formation mechanism: the migration of polysulfides away from the anode drags out lithium protrusions through localized lattice distortion of the lithium anode and traps lithium ions in the surrounding electrolyte, leading to lithium dendrite formation. The Li-S battery, constructed using the composite of cotton-derived Fe3 C-MWCNTs and graphene that serves as both the sulfur host and the anode interlayer, exhibits exceptional cycling stability, impressive capacity retention, and effective mitigation of lithium dendrite formation. The findings offer valuable strategies to prevent lithium dendrite formation and enhance understanding of lithium dendrite growth in Li-S batteries.

Breaking the Barrier: Strategies for Mitigating Shuttle Effect in Lithium-Sulfur Batteries Using Advanced Separators

Lithium-sulfur (Li-S) batteries are considered one of the most promising energy storage systems due to their high theoretical capacity, high theoretical capacity density, and low cost. However, challenges such as poor conductivity of sulfur (S) elements in active materials, the "shuttle effect" caused by lithium polysulfide, and the growth of lithium dendrites impede the commercial development of Li-S batteries. As a crucial component of the battery, the separator plays a vital role in mitigating the shuttle effect caused by polysulfide. Traditional polypropylene, polyethylene, and polyimide separators are constrained by their inherent limitations, rendering them unsuitable for direct application in lithium-sulfur batteries. Therefore, there is an urgent need for the development of novel separators. This review summarizes the applications of different separator preparation methods and separator modification methods in lithium-sulfur batteries and analyzes their electrochemical performance.

Design principles for 2D transition metal dichalcogenides toward lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are regarded as a promising candidate for next-generation energy storage systems owing to their remarkable energy density, resource availability, and environmental benignity. Nevertheless, severe shuttling effect, sluggish redox kinetics, large volumetric expansion, and uncontrollable dendrite growth hamper the practical applications. To address these intractable issues, two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged expeditiously as an essential material strategy. Herein, this review emphasizes the development and application of 2D TMDs in Li-S batteries. It starts with introducing the fundamentals of Li-S batteries and common synthetic routes of TMDs, followed by summarizing the employment of pristine, hybrid, and defective TMDs in the realm of expediting sulfur chemistry and stabilizing lithium anode. Finally, the development roadmap and possible research directions of TMDs are proposed to offer guidance for the future design of high-performance Li-S batteries.

Unlocking Liquid Sulfur Chemistry for Fast-Charging Lithium-Sulfur Batteries

A recent study of liquid sulfur produced in an electrochemical cell has prompted further investigation into regulating Li-S oxidation chemistry. In this research, we examined the liquid-to-solid sulfur transition dynamics by visually observing the electrochemical generation of sulfur on a graphene-based substrate. We investigated the charging of polysulfides at various current densities and discovered a quantitative correlation between the size and number density of liquid sulfur droplets and the applied current. However, the areal capacities exhibited less sensitivity. This observation offers valuable insights for designing fast-charging sulfur cathodes. By incorporating liquid sulfur into Li-S batteries with a high sulfur loading of 4.2 mg cm-2, the capacity retention can reach ∼100%, even when increasing the rate from 0.1 to 3 C. This study contributes to a better understanding of the kinetics involved in the liquid-solid sulfur growth in Li-S chemistry and presents viable strategies for optimizing fast-charging operations.

Defect-engineered Sulfur Vacancy Modified NiCo2 S4-x Nanosheet Anchoring Polysulfide for Improved Lithium Sulfur Batteries

The low conductivity of sulfur and the shuttle effect of lithium polysulfides (LiPSs) are the two intrinsic obstacles that limit the application of lithium-sulfur batteries (LSBs). Herein, a sulfur vacancy introduced NiCo2 S4 nanosheet array grown on carbon nanofiber (CNF) membrane (NiCo2 S4-x /CNF) is proposed to serve as a self-supporting and binder-free interlayer in LSBs. The conductive CNF skeleton with a non-woven structure can effectively reduce the resistance of the cathode and accommodate volume expansion during charge-discharge process. The bonding between CNF matrix and NiCo2 S4 nanosheet is enhanced by in situ growth, ensuring fast electron transfer. Besides, the sulfur vacancies in NiCo2 S4 enhance the chemisorption of LiPSs, and the highly active sites at vacancies can accelerate the LiPSs conversion kinetics. LSB paired with NiCo2 S4-x /CNF interlayer achieved improved stability in 500 cycles at 0.2 C and long life of 3000 cycles at 3 C. More importantly, a high areal capacity of 9.69 mAh cm-2 is achieved with a sulfur loading of 10.8 mg cm-2 and a low electrolyte to sulfur (E/S) ratio of 4.8. This work provides insight into the sulfur vacancy in catalysis design for LiPSs conversion and demonstrates a promising direction for electronic defect engineering in material design for LSBs.

Modulating d-Band Electronic Structures of Molybdenum Disulfide via p/n Doping to Boost Polysulfide Conversion in Lithium-Sulfur Batteries

Polysulfide shuttle effect and sluggish sulfur reaction kinetics severely impede the cycling stability and sulfur utilization of lithium-sulfur (Li-S) batteries. Modulating d-band electronic structures of molybdenum disulfide electrocatalysts via p/n doping is promising to boost polysulfide conversion and suppress polysulfide migration in lithium-sulfur batteries. Herein, p-type V-doped MoS2 (V-MoS2 ) and n-type Mn-doped MoS2 (Mn-MoS2 ) catalysts are well-designed. Experimental results and theoretical analyses reveal that both of them significantly increase the binding energy of polysulfides on the catalysts' surface and accelerate the sluggish conversion kinetics of sulfur species. Particularly, the p-type V-MoS2 catalyst exhibits a more obvious bidirectional catalytic effect. Electronic structure analysis further demonstrates that the superior anchoring and electrocatalytic activities are originated from the upward shift of the d-band center and the optimized electronic structure induced by duplex metal coupling. As a result, the Li-S batteries with V-MoS2 modified separator exhibit a high initial capacity of 1607.2 mAh g-1 at 0.2 C and excellent rate and cycling performance. Moreover, even at a high sulfur loading of 6.84 mg cm-2 , a favorable initial areal capacity of 8.98 mAh cm-2 is achieved at 0.1 C. This work may bring widespread attention to atomic engineering in catalyst design for high-performance Li-S batteries.

Two-dimensional materials for high density, safe and robust metal anodes batteries

With a high specific capacity and low electrochemical potentials, metal anode batteries that use lithium, sodium and zinc metal anodes, have gained great research interest in recent years, as a potential candidate for high-energy-density storage systems. However, the uncontainable dendrite growth during the repeated charging process, deteriorates the battery performance, reduces the battery life and more importantly, raises safety concerns. With their unique properties, two-dimensional (2D) materials, can be used to modify various components in metal batteries, eventually mitigating the dendrite growth, enhancing the cycling stability and rate capability, thus leading to safe and robust metal anodes. In this paper, we review the recent advances of 2D materials and summarize current research progress of using 2D materials in the applications of (i) anode design, (ii) separator engineering, and (iii) electrolyte modifications by guiding metal ion nucleation, increasing ion conductivity, homogenizing the electric field and ion flux, and enhancing the mechanical strength for safe metal anodes. The 2D material modifications provide the ultimate solution for obtaining dendrite-free metal anodes, realizes the high energy storage application, and indicates the importance of 2D materials development. Finally, in-depth understandings of subsequent metal growth are lacking due to research limitations, while more advanced characterizations are welcome for investigating the metal deposition mechanism. The more facile and simplified preparation of 2D materials possess great prospects in high energy density metal anode batteries, and thus fulfils the development of EVs.

In Situ 1D Carbon Chain-Mail Catalyst Assembly for Stable Lithium-Sulfur Full Batteries

The main obstacles for the commercial application of Lithium-Sulfur (Li-S) full batteries are the large volume change during charging/discharging process, the shuttle effect of lithium polysulfide (LiPS), sluggish redox kinetics, and the indisciplinable dendritic Li growth. Especially the overused of metal Li leads to the low utilization of active Li, which seriously drags down the actual energy density of Li-S batteries. Herein, an efficient design of dual-functional CoSe electrocatalyst encapsulated in carbon chain-mail (CoSe@CCM) is employed as the host both for the cathode and anode regulation simultaneously. The carbon chain-mail constituted by carbon encapsulated layer cross-linking with carbon nanofibers protects CoSe from the corrosion of chemical reaction environment, ensuring the high activity of CoSe during the long-term cycles. The Li-S full battery using this carbon chain-mail catalyst with a lower negative/positive electrode capacity ratio (N/P < 2) displays a high areal capacity of 9.68 mAh cm-2 over 150 cycles at a higher sulfur loading of 10.67 mg cm-2 . Additionally, a pouch cell is stable for 80 cycles at a sulfur loading of 77.6 mg, showing the practicality feasibility of this design.

Recent Progress for Concurrent Realization of Shuttle-Inhibition and Dendrite-Free Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have become one of the most promising new-generation energy storage systems owing to their ultrahigh energy density (2600 Wh kg-1 ), cost-effectiveness, and environmental friendliness. Nevertheless, their practical applications are seriously impeded by the shuttle effect of soluble lithium polysulfides (LiPSs), and the uncontrolled dendrite growth of metallic Li, which result in rapid capacity fading and battery safety problems. A systematic and comprehensive review of the cooperative combination effect and tackling the fundamental problems in terms of cathode and anode synchronously is still lacking. Herein, for the first time, the strategies for inhibiting shuttle behavior and dendrite-free Li-S batteries simultaneously are summarized and classified into three parts, including "two-in-one" S-cathode and Li-anode host materials toward Li-S full cell, "two birds with one stone" modified functional separators, and tailoring electrolyte for stabilizing sulfur and lithium electrodes. This review also emphasizes the fundamental Li-S chemistry mechanism and catalyst principles for improving electrochemical performance; advanced characterization technologies to monitor real-time LiPS evolution are also discussed in detail. The problems, perspectives, and challenges with respect to inhibiting the shuttle effect and dendrite growth issues as well as the practical application of Li-S batteries are also proposed.

Self-Templated Formation of Carbon Nanotubes Interpenetrating Ordered Microporous Carbon Nanospheres for High-Performance Li-S Batteries

Lithium-sulfur (Li-S) batteries are known as a prospective new generation of battery systems owing to their high energy density, low cost, non-toxicity, and environmental friendliness. Nevertheless, several issues remain in the practical application of Li-S batteries, such as low sulfur usage, poor rate performance, and poor cycle stability. Ordered microporous carbon materials and carbon nanotubes (CNTs) can effectively limit the diffusion of polysulfides (LiPSs) and have high electrical conductivity, respectively. Here, inspired by the evaporation of zinc at high temperatures, we constructed CNTs interpenetrating ordered microporous carbon nanospheres (CNTs/OMC NSs) by high-temperature calcination and used them as a sulfur host material. With the benefit from the excellent electrical conductivity of CNTs and OMC achieving uniform sulfur dispersion and effectively limiting LiPS dissolution, the S@CNTs/OMC NS cathodes show outstanding cycling stability (initial discharge capacity of 879 mAh g^-1 at 0.5 C, maintained at 629 mAh g^-1 for 500 cycles) and excellent rate performance (521 mAh g^-1 at 5.0 C). Furthermore, the current study can serve as a significant reference for the synthesis of CNTs that interpenetrate various materials.

Highly stable lithium sulfur batteries enhanced by flocculation and solidification of soluble polysulfides in routine ether electrolyte

Lithium-sulfur batteries (LSBs) are among the most promising next-generation high energy density energy-storage systems. However, practical application has been hindered by fundamental problems, especially shuttling by the higher-order polysulfides (PSs) and slow redox kinetics. Herein, a novel electrolyte-based strategy is proposed by adding an ultrasmall amount of the low-cost and commercially available cationic antistatic agent octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate (SN) into a routine ether electrolyte. Due to the strong cation-anion interaction and bridge-bonding with SN, rapid flocculation of the soluble polysulfide intermediates into solid-state polysulfide-SN sediments is found, which significantly inhibited the adverse shuttling effect. Moreover, a catalytic effect was also demonstrated for conversion of the polysulfide-SN intermediates, which enhanced the redox kinetics of Li-S batteries. Encouragingly, for cells with only 0.1 % added SN, an initial specific capacity of 783.6 mAh/g and a retained specific capacity of 565.7 mAh/g were found at 2C after 200 cycles, which corresponded to an ultralow capacity decay rate of only 0.014 % per cycle. This work may provide a simple and promising regulation strategy for preparing highly stable Li-S batteries.

Challenges and Solutions for Low-Temperature Lithium-Sulfur Batteries: A Review

The lithium-sulfur (Li-S) battery is considered to be one of the attractive candidates for breaking the limit of specific energy of lithium-ion batteries and has the potential to conquer the related energy storage market due to its advantages of low-cost, high-energy density, high theoretical specific energy, and environmental friendliness issues. However, the substantial decrease in the performance of Li-S batteries at low temperatures has presented a major barrier to extensive application. To this end, we have introduced the underlying mechanism of Li-S batteries in detail, and further concentrated on the challenges and progress of Li-S batteries working at low temperatures in this review. Additionally, the strategies to improve the low-temperature performance of Li-S batteries have also been summarized from the four perspectives, such as electrolyte, cathode, anode, and diaphragm. This review will provide a critical insight into enhancing the feasibility of Li-S batteries in low-temperature environments and facilitating their commercialization.

Ultrathin Carbon-Shell-Encapsulated Cobalt Nanoparticles with Balanced Activity and Stability for Lithium-Sulfur Batteries

High-performance metal-based catalysts are pursued to improve the sluggish reaction kinetics in lithium-sulfur batteries. However, it is challenging to achieve high catalytic activity and stability simultaneously due to the inevitable passivation of the highly active metal nanoparticles by lithium polysulfides (LiPSs). Herein, we show a design with well-balanced activity and stability to solve the above problem, that is, the cobalt (Co) nanoparticles (NPs) encapsulated with ultrathin carbon shells prepared by the one-step pyrolysis of ZIF-67. With an ultrathin carbon coating (∼1 nm), the direct exposure of Co NPs to LiPSs is avoided, but it allows the fast electron transfer from the highly active Co NPs to LiPSs for their conversion to the solid products, ensuring the efficient suppression of shuttling in long cycling. As a result, the sulfur cathode with such a catalyst exhibited good cycling stability (0.073% capacity fading over 500 cycles) and high sulfur utilization (638 mAh g^-1 after 180 cycles under a high sulfur mass loading of 7.37 mg cm^-2 and a low electrolyte/sulfur ratio of 5 μL mg^-1). This work provides insights into the rational design of a protection layer on a metal-based catalyst to engineer both high catalytic activity and stability toward high-energy and long-life Li-S batteries.

Tin disulfide embedded on porous carbon spheres for accelerating polysulfide conversion kinetics toward lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered promising candidates for next-generation advanced energy storage systems due to their high theoretical capacity, low cost and environmental friendliness. However, the severe shuttle effect and weak redox reaction severely restrict the practical application of Li-S batteries. Herein, a functional catalytic material of tin disulfide on porous carbon spheres (SnS₂@CS) is designed as a sulfur host and separator modifier for lithium-sulfur batteries. SnS₂@CS with high electrical conductivity, high specific surface area and abundant active sites can not only effectively improve the electrochemical activity but also accelerate the capture/diffusion of polysulfides. Theoretical calculations and in situ Raman also demonstrate that SnS₂@CS can efficiently adsorb and catalyse the rapid conversion of polysulfides. Based on these advantages, the SnS₂@CS-based Li-S battery delivers an excellent reversible capacity of 868 mAh/g at 0.5C (capacity retention of 96 %), a high rate capability of 852 mAh/g at 2C, and a durable cycle life with an ultralow capacity decay rate of 0.029 % per cycle over 1000 cycles at 2C. This work combines the design of sulfur electrodes and the modification of separators, which provides an idea for practical applications of Li-S batteries in the future.

Suppressing Local Dendrite Hotspots via Current Density Redistribution Using a Superlithiophilic Membrane for Stable Lithium Metal Anode

Li metal anode is considered as one of the most desirable candidates for next-generation battery due to its lowest electrochemical potential and high theoretical capacity. However, undesirable dendrite growth severely exacerbates the interfacial stability, thus damaging battery performance and bringing safety concerns. Here, an efficient strategy is proposed to stabilize Li metal anode by digesting dendrites sprout using a 3D flexible superlithiophilic membrane consisting of poly(vinylidene fluoride) (PVDF) and ZnCl₂ composite nanofibers (PZEM) as a protective layer. Both the experimental studies and theoretical calculations show the origin of superlithiophilicity ascribed to a strong interaction between ZnCl₂ and PVDF to form the ZnF bonds. The multifield physics calculation implies effective removal of local dendrite hotspots by PZEM via a more homogeneous Li⁺ flux. The PZEM-covered Li anode (PZEM@Li) exhibits superior Li deposition/stripping performance in a symmetric cell over 1100 cycles at a high current density of 5 mA cm^-2 . When paired with LiFePO₄ (LFP), PZEM@Li|LFP full cell remains stable over 1000 cycles at 2 C with a degradation rate of 0.0083% per cycle. This work offers a new route for efficient protection of Li metal anode for practical applications.

Brominated flame retardants coated separators for high-safety lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have become highly promising next-generation secondary lithium batteries owing to their high theoretical energy density and abundance of sulfur. Nevertheless, the large-scale application of LSBs is still restricted by the shuttle effect of lithium polysulfide (LiPSs) and the potential fire hazard caused by flammable electrolytes. Herein, three electrolyte-insoluble brominated flame retardants (BFRs) are selected and coated on both sides of commercial polypropylene separators by a facile slurry coating method. The effects of the three BFRs on the safety and electrochemical properties of LSBs are characterized and compared. The coating modification separators greatly improves the flame retardancy of LSBs through radical elimination mechanism. The self-extinguishing time of the electrolyte is reduced from 0.66 s/mg to 0.20 s/mg. Moreover, it is demonstrated that the oxygen (O)-containing BFRs exert a significant adsorption capacity and are more advantageous than O-free BFRs in LSBs. In addition, octabromoether (BDDP) coated separator is more effective in trapping LiPSs than decabromodiphenyl ether (DBDPO) due to higher O content, which can mitigate the shuttle effect and enhance the cycle and rate performance of LSBs. This simple coating strategy for separators with BFRs offers a strongly competitive option for the large-scale production of high-safety LSBs.

Zwitterionic Separator Featured with Superdesolvating Properties for High Performance Lithium-Sulfur Batteries

Lithium-sulfur chemistry has greatly expanded the boundaries of lithium batteries, but the persistent parasitic reaction of soluble sulfur intermediates with lithium anode remains a primary challenge. Understanding and regulating the solvation structures of lithium ions (Li+) and polysulfides (LiPSs) are critical to addressing the above issues. Herein, inspired by the natural superhydrophilic resistance to contamination, we developed a zwitterionic nanoparticles (ZWP) separator capable of modulating the solvated of Li+ and LiPSs. The dense solvated layer induced by ZWP effectively prevents the movement of LiPSs without compromising Li+ transport. Moreover, the high electrolyte affinity of the ZWP effectively results in minimizing the deposition of LiPSs on the separator. Furthermore, the structure of the solvated Li+ and LiPSs is also unveiled by molecular simulation and nuclear magnetic resonance (NMR). In addition, in situ UV setup proved the ZWP separator can effectively suppress the shuttle of LiPSs. The restricted space formed by the tightly packed ZWP stabilizes the lithium deposition and regulates dendrite growth. Consequently, the performance of lithium-sulfur batteries is significantly improved and good cycle stability is maintained even at high sulfur loadings (5 mg cm-2). This contribution provides a new insight into the rational design of lithium-sulfur battery separators.

Dual-Functional Hosts for Polysulfides Conversion and Lithium Plating/Stripping towards Lithium-Sulfur Full Cells

The practical application of lithium-sulfur (Li-S) batteries is greatly hindered by the shuttle effect of dissolved polysulfides in the sulfur cathode and the severe dendritic growth in the lithium anode. Adopting one type of effective host with dual-functions including both inhibiting polysulfide dissolution and regulating Li plating/stripping, is recently an emerging research highlight in Li-S battery. This review focuses on such dual-functional hosts and systematically summarizes the recent research progress and application scenarios. Firstly, this review briefly describes the stubborn issues in Li-S battery operations and the sophisticated counter measurements over the challenges by dual-functional behaviors. Then, the latest advances on dual-functional hosts for both cathode and anode in Li-S full cells are catalogued as species, including metal chalcogenides, metal carbides, metal nitrides, heterostuctures, and the possible mechanisms during the process. Besides, we also outlined the theoretical calculation tools for the dual-functional host based on the first principles. Finally, several sound perspectives are also rationally proposed for fundamental research and practical development as guidelines.

A Ni-MOF derived graphene oxide combined Ni3S2-Ni/C composite and its use in the separator coating for lithium sulfur batteries

Lithium-sulfur batteries (LSBs) are widely regarded as reliable novel secondary batteries due to their low price and high capacity. Nevertheless, the notorious "shuttle effect" limits the commercialization of LSBs. In order to solve this problem, we fabricated a Ni₃S₂-Ni/C composite through carbonization, vulcanization and hydrothermal reactions by using a Ni-MOF precursor and applied it as a separator modification layer to enhance the electrochemical properties of LSBs. To further increase the conductivity of the material, a small amount of GO was added during the experiment. The prepared material was also used as separator modified coating material to optimize the electrochemical performance of LSBs. The as prepared Ni₃S₂-Ni/C(GO) composite shows good conductivity and has a superior porous structure and abundant active sites. Lithium polysulfides (LPs) can be physically confined and chemically adsorbed, what is more, the Ni and Ni₃S₂ active sites enable fast conversion of LPs which further optimizes the rate performance. From the cycle performance measurement, the initial discharge specific capacity of the Ni₃S₂-Ni/C(GO) modified separator battery is found to be 1263.4, 1181.5, 1090.6, and 840.3 mA h g^-1 at 0.05, 0.1, 0.3 and 0.5C, respectively. After 400 charge/discharge cycles at 0.5C, the capacity remains at 483.6mA h g^-1 with a capacity retention ratio of 57.56%.

Defect-Rich Single Atom Catalyst Enhanced Polysulfide Conversion Kinetics to Upgrade Performance of Li-S Batteries

Lithium-sulfur (Li-S) batteries have attracted considerable attention owing to their extremely high energy densities. However, the application of Li-S batteries has been limited by low sulfur utilization, poor cycle stability, and low rate capability. Accelerating the rapid transformation of polysulfides is an effective approach for addressing these obstacles. In this study, a defect-rich single-atom catalytic material (Fe-N4/DCS) is designed. The abundantly defective environment is favorable for the uniform dispersion and stable existence of single-atom Fe, which not only improves the utilization of single-atom Fe but also efficiently adsorbs polysulfides and catalyzes the rapid transformation of polysulfides. To fully exploit the catalytic activity, catalytic materials are used to modify the routine separator (Fe-N₄ /DCS/PP). Density functional theory and in situ Raman spectroscopy are used to demonstrate that Fe-N₄ /DCS can effectively inhibit the shuttling of polysulfides and accelerate the redox reaction. Consequently, the Li-S battery with the modified separator achieves an ultralong cycle life (a capacity decay rate of only 0.03% per cycle at a current of 2 C after 800 cycles), and an excellent rate capability (894 mAh g^-1 at 3 C). Even at a high sulfur loading of 5.51 mg cm^-2 at 0.2 C, the reversible areal capacity still reaches 5.4 mAh cm^-2 .

Self-Supporting Multicomponent Hierarchical Network Aerogel as Sulfur Anchoring-Catalytic Medium for Highly Stable Lithium-Sulfur Battery

The low utilization rate of active materials, shuttle effect of lithium polysulfides (LiPSs), and slow reaction kinetics lead to the extremely low efficiency and poor high current cycle stability of lithium sulfur batteries (Li-S batteries). In this paper, a self-supporting multicomponent hierarchical network aerogel is proposed as the modified cathode (S/GO@MX@VS₄ ). It consists of graphene (GO) and MXene nanosheets (MX) loaded with VS₄ nanoparticles. The experimental results and first-principles calculations show that the GO@MX@VS₄ aerogel has strong adsorption and reversible conversion effects on LiPSs. It can not only inhibit the shuttle effect and improve the utilization rate of active substances by keeping the chain crystal structure of VS₄ , but also promote the reversibility and kinetics of the reaction by accelerating the liquid-solid transformation in the reduction process and the decomposition of insoluble Li₂ S in the oxidation process. The GO@MX@VS₄ aerogel modified cathode with a multicomponent synergy exhibits the capacity ratios (Q₁ /Q₂ ) at different discharge stages is close to the theoretical value (1:2.8), and the capacity decay per cycle is 0.019% in 1200 cycles at 5C. Also, a high areal capacity of 6.90 mAh cm^-2 is provided even at high sulfur loading (7.39 mg cm^-2 ) and low electrolyte/sulfur ratio (E/S, 8.0 µL mg^-1 ).

Poly(ether imide) Porous Membrane Developed by a Scalable Method for High-Performance Lithium-Sulfur Batteries: Combined Theoretical and Experimental Study

Lithium-sulfur (Li-S) batteries are one of the emerging candidates for energy storage systems due to their high theoretical energy density and the abundance/nontoxicity/low cost of sulfur. Compared with conventional lithium-ion batteries, multiple new challenges have been brought into this advanced battery system, such as polysulfide shuttling in conventional polyolefin separators and undesired lithium dendrite formation of the Li metal anode. These issues severely affect the cell performance and impede their practical applications. Herein, we develop a poly(ether imide) (PEI)-based membrane with a sponge-like pore morphology as the separator for the Li-S battery by a simplified phase inversion method. This new separator can not only alleviate the new challenges in Li-S batteries but also exhibit excellent ion conductivity, better thermal stability, and higher mechanical strength compared to those of the conventional polypropylene (PP) separator. A combined experimental and theoretical study indicates that the sponge-like morphology of the PEI membrane and its good wettability toward the electrolyte can facilitate uniform ion transportation and suppress dendrite growth. Meanwhile, the PEI molecules exhibit a strong interaction with polysulfides and avoid their shuttling effectively. As a result, the PEI-based Li-S battery shows a much better performance from various aspects (capacity, rate capability, and cycling stability) than that of the PP-based Li-S battery, especially at high charge/discharge current densities and high sulfur loadings. Since the developed PEI membrane can be easily scaled up, this work may accelerate the practical applications of Li-S batteries from the point of separators.

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.

In Situ Separator Modification with an N-Rich Conjugated Microporous Polymer for the Effective Suppression of Polysulfide Shuttle and Li Dendrite Growth

Lithium-sulfur (Li-S) batteries are very promising high-energy-density electrochemical energy storage devices, but suffer from serious Li polysulfide (LiPS) shuttle and uncontrollable Li dendrite growth. Here, we show in situ polyolefin separator modification with an N-rich conjugated microporous polymer (NCMP) for advanced Li-S battery. In situ polymerization generates an ultrathin NCMP coating on the whole external surface and the internal surface of the separator, which is substantially different from the conventional approaches with thick coatings only on the external surface. The NCMP coating with abundant N-containing groups (-NH₂ and -N═), uniform nanopores (12.294 Å), and π-conjugated structure can simultaneously inhibit LiPS shuttle and regulate uniform nucleation and growth of Li dendrites. Consequently, the NCMP-based separator endows the Li-S battery with significantly enhanced cycling stability at high S loading (5.4 mg cm^-2), lean electrolyte (E/S = 6.3 μL mg^-1), and limited Li excess (50 μm).

Serrated lithium fluoride nanofibers-woven interlayer enables uniform lithium deposition for lithium-metal batteries

The uncontrollable formation of Li dendrites has become the biggest obstacle to the practical application of Li-metal anodes in high-energy rechargeable Li batteries. Herein, a unique LiF interlayer woven by millimeter-level, single-crystal and serrated LiF nanofibers (NFs) was designed to enable dendrite-free and highly efficient Li-metal deposition. This high-conductivity LiF interlayer can increase the Li+ transference number and induce the formation of 'LiF-NFs-rich' solid-electrolyte interface (SEI). In the 'LiF-NFs-rich' SEI, the ultra-long LiF nanofibers provide a continuously interfacial Li+ transport path. Moreover, the formed Li-LiF interface between Li-metal and SEI film renders low Li nucleation and high Li+ migration energy barriers, leading to uniform Li plating and stripping processes. As a result, steady charge-discharge in a Li//Li symmetrical cell for 1600 h under 4 mAh cm-2 and 400 stable cycles under a high area capacity of 5.65 mAh cm-2 in a high-loading Li//rGO-S cell at 17.9 mA cm-2 could be achieved. The free-standing LiF-NFs interlayer exhibits superior advantages for commercial Li batteries and displays significant potential for expanding the applications in solid Li batteries.

Multi-Dimensional Composite Frame as Bifunctional Catalytic Medium for Ultra-Fast Charging Lithium-Sulfur Battery

The shuttle effect of soluble lithium polysulfides (LiPSs) between electrodes and slow reaction kinetics lead to extreme inefficiency and poor high current cycling stability, which limits the commercial application of Li-S batteries. Herein, the multi-dimensional composite frame has been proposed as the modified separator (MCCoS/PP) of Li-S battery, which is composed of CoS₂ nanoparticles on alkali-treated MXene nanosheets and carbon nanotubes. Both experiments and theoretical calculations show that bifunctional catalytic activity can be achieved on the MCCoS/PP separator. It can not only promote the liquid-solid conversion in the reduction process, but also accelerate the decomposition of insoluble Li₂S in the oxidation process. In addition, LiPSs shuttle effect has been inhibited without a decrease in lithium-ion transference numbers. Simultaneously, the MCCoS/PP separator with good LiPSs adsorption capability arouses redistribution and fixing of active substances, which is also beneficial to the rate performance and cycling stability. The Li-S batteries with the MCCoS/PP separator have a specific capacity of 368.6 mAh g^-1 at 20C, and the capacity decay per cycle is only 0.033% in 1000 cycles at 7C. Also, high area capacity (6.34 mAh cm^-2) with a high sulfur loading (7.7 mg cm^-2) and a low electrolyte/sulfur ratio (7.5 μL mg^-1) is achieved.

Recent advances in dendrite-free lithium metal anodes for high-performance batteries

With the merits of high energy density, light weight, and low electrode potential, lithium metal anodes (LMAs) have lately sparked worldwide attention in the field of batteries. However, their low Coulombic efficiency, tremendous volume expansion, and serious dendrite growth make lithium metal batteries (LMBs) unsuitable for a wide variety of applications. Moreover, when lithium dendrite crosses the electrolyte and reaches the cathode material, it may cause short circuit and safety issues for batteries. Herein, to accelerate the development of LMBs, we give a brief summary of the dendrite growth mechanisms in both liquid and solid systems of electrolytes. In particular, various modification approaches to dendrite-free lithium metal batteries are discussed. Furthermore, advanced in situ characterization techniques for the real-time observation of lithium dendrite growth are presented. To address the application issues, various potential research routes for improving the performance of LMBs are provided as well.

Ion sieve membrane: Homogenizing Li+ flux and restricting polysulfides migration enables long life and highly stable Li-S battery

Limited by the notorious Li dendrites growth and serious polysulfide shuttle effect, the development of lithium-sulfur (Li-S) batteries is stagnant. Herein, a multifunctional separator composed of Cu-based metal-organic framework (Cu-MOF) and Li-Nafion was proposed to address the above intractable issues. The Cu-MOF with homogeneous porous structure and abundant Lewis acidic sites not only promotes uniform Li⁺ flux, but also exhibits a strong chemical interaction with polysulfides to inhibit the shuttle effect. Moreover, the narrow pore size distribution in the Cu-MOF and negatively charged gap endowed by the -SO₃^- groups both act as ion sieve to facilitate the passage of Li⁺ and restrict the migration of polysulfide anions, synergistically mitigating the dendritic Li growth and polysulfides shuttling. As a result, the symmetric cell with MOF/Nafion separator achieves ultralong cycling stability (1000 h) and ultralow overpotential of 20 mV at a current density of 1.0 mA cm^-2. Importantly, in the assembled Li-S full battery, the modified PP separator presents the superior cycle stability with capacity retention of 90% after 300 cycles at 0.5 C. Current outcomes open up a new route to design functional separators with ion permselective for realizing the dendrite-free and high-performance Li-S battery.

Hydroxylated Multi-Walled Carbon Nanotubes Covalently Modified with Tris(hydroxypropyl) Phosphine as a Functional Interlayer for Advanced Lithium-Sulfur Batteries

We have successfully constructed a new type of intercalation membrane material by covalently grafting organic tris(hydroxypropyl)phosphine (THPP) molecules onto hydroxylated multi-walled carbon nanotubes (CNT-OH) as a functional interlayer for the advanced LSBs. The as-assembled interlayer has been demonstrated to be responsible for the fast conversion kinetics of polysulfides, the inhibition of polysulfide shuttle effect, as well as the formation of a stable solid electrolyte interphase(SEI) layer. By means of spectroscopic and electrochemical analysis, we further found THPP plays a key role in accelerating the conversion of polysulfides into low-ordered lithium sulfides and suppressing the loss of polysulfides, thus rendering the as-designed lithium-sulfur battery in this work a high capacity, excellent rate performance and long-term stability. Even at low temperatures, the capacity decay rate was only 0.036 % per cycle for 1700 cycles.

Balancing Electrolyte Donicity and Cathode Adsorption Capacity for High-Performance LiS Batteries

LiS batteries with high theoretical capacity are attracting attention as next-generation energy storage systems. Much effort has been devoted to the introduction of cathode materials with strong adsorption to sulfide species, but it is presented that this selection should be refined in the application of high donicity electrolytes. The oxides with different adsorption capacities are explored while controlling the electrolyte donicity, confirming the trade-off effect between the donicity and the adsorption capacity for sulfur conversion. Specifically, a cathode substrate containing oxide nanoparticles of MgO, NiO, Fe₂ O₃ , Co₃ O₄ , and V₂ O₅ is prepared with spectra in adsorption capacity as well as low and high donicity electrolytes by controlling the concentration of LiNO₃ salt. Strong adsorbent oxides such as Co₃ O₄ and V₂ O₅ cause competitive adsorption of electrolyte salts in high donicity electrolytes, resulting in poor cell performance. High cell performance is achieved on weakly adsorbing oxides of MgO or NiO with high donicity electrolytes; the MgO-containing cathode cell delivers a high discharge capacity of 1394 mAh g^-1 at 0.2 C. It is believed that understanding the interactions between electrolytes and adsorbent substrates will be the cornerstone of high-performance LiS batteries.

Phase-Field Investigation of Lithium Electrodeposition at Different Applied Overpotentials and Operating Temperatures

Li metal is an exciting anode for high-energy Li-ion batteries and other future battery technologies due to its high energy density and low redox potential. Despite their high promise, the commercialization of Li-metal-based batteries has been hampered due to the formation of dendrites that lead to mechanical instability, energy loss, and eventual internal short circuits. In recent years, the mechanism of dendrite formation and the strategies to suppress their growth have been studied intensely. However, the effect of applied overpotential and operating temperature on dendrite formation and their growth rate remains to be fully understood. Here, we elucidate the correlation between the applied overpotential and operating temperature to the dendrite height and tortuosity of the Li-metal surface during electrodeposition using phase-field model simulations. We identify an optimal operating temperature of a half-cell consisting of a Li metal anode and 1 M LiPF₆ in EC/DMC (1/1), which increases gradually as the magnitude of the overpotential increases. The investigation reveals that the temperature dependence identified in the simulations and experiments often disagree because they are primarily conducted under galvanostatic and potentiostatic conditions, respectively. The temperature increase under potentiostatic conditions increases the induced current while it decreases the induced overpotential under galvanostatic conditions. Therefore, the analysis and comparison of temperature-dependent characteristics must be carried out with care.

Design Rules of a Sulfur Redox Electrocatalyst for Lithium-Sulfur Batteries

Seeking an electrochemical catalyst to accelerate the liquid-to-solid conversion of soluble lithium polysulfides to insoluble products is crucial to inhibit the shuttle effect in lithium-sulfur (Li-S) batteries and thus increase their practical energy density. Mn-based mullite (SmMn₂ O₅ ) is used as a model catalyst for the sulfur redox reaction to show how the design rules involving lattice matching and 3d-orbital selection improve catalyst performance. Theoretical simulation shows that the positions of Mn and O active sites on the (001) surface are a good match with those of Li and S atoms in polysulfides, resulting in their tight anchoring to each other. Fundamentally, dz² and dx² -y² around the Fermi level are found to be crucial for strongly coupling with the p-orbitals of the polysulfides and thus decreasing the redox overpotential. Following the theoretical calculation, SmMn₂ O₅ catalyst is synthesized and used as an interlayer in a Li-S battery. The resulted battery has a high cycling stability over 1500 cycles at 0.5 C and more promisingly a high areal capacity of 7.5 mAh cm^-2 is achieved with a sulfur loading of ≈5.6 mg cm^-2 under the condition of a low electrolyte/sulfur (E/S) value ≈4.6 µL mg^-1 .

Review of Multifunctional Separators: Stabilizing the Cathode and the Anode for Alkali (Li, Na, and K) Metal-Sulfur and Selenium Batteries

Alkali metal batteries based on lithium, sodium, and potassium anodes and sulfur-based cathodes are regarded as key for next-generation energy storage due to their high theoretical energy and potential cost effectiveness. However, metal-sulfur batteries remain challenged by several factors, including polysulfides' (PSs) dissolution, sluggish sulfur redox kinetics at the cathode, and metallic dendrite growth at the anode. Functional separators and interlayers are an innovative approach to remedying these drawbacks. Here we critically review the state-of-the-art in separators/interlayers for cathode and anode protection, covering the Li-S and the emerging Na-S and K-S systems. The approaches for improving electrochemical performance may be categorized as one or a combination of the following: Immobilization of polysulfides (cathode); catalyzing sulfur redox kinetics (cathode); introduction of protective layers to serve as an artificial solid electrolyte interphase (SEI) (anode); and combined improvement in electrolyte wetting and homogenization of ion flux (anode and cathode). It is demonstrated that while the advances in Li-S are relatively mature, less progress has been made with Na-S and K-S due to the more challenging redox chemistry at the cathode and increased electrochemical instability at the anode. Throughout these sections there is a complementary discussion of functional separators for emerging alkali metal systems based on metal-selenium and the metal-selenium sulfide. The focus then shifts to interlayers and artificial SEI/cathode electrolyte interphase (CEI) layers employed to stabilize solid-state electrolytes (SSEs) in metal-sulfur solid-state batteries (SSBs). The discussion of SSEs focuses on inorganic electrolytes based on Li- and Na-based oxides and sulfides but also touches on some hybrid systems with an inorganic matrix and a minority polymer phase. The review then moves to practical considerations for functional separators, including scaleup issues and Li-S technoeconomics. The review concludes with an outlook section, where we discuss emerging mechanics, spectroscopy, and advanced electron microscopy (e.g. cryo-transmission electron microscopy (cryo-TEM) and cryo-focused ion beam (cryo-FIB))-based approaches for analysis of functional separator structure-battery electrochemical performance interrelations. Throughout the review we identify the outstanding open scientific and technological questions while providing recommendations for future research topics.