A High-Efficiency CoSe Electrocatalyst with Hierarchical Porous Polyhedron Nanoarchitecture for Accelerating Polysulfides Conversion in Li-S Batteries

Leveraging doping strategies and interface engineering to enhance catalytic transformation of lithium polysulfides for high-performance lithium-sulfur batteries

The commercialization of lithium-sulfur (Li-S) batteries has faced challenges due to the shuttle effect of soluble intermediate polysulfides and the sluggish kinetics of sulfur redox reactions. In this study, a synergistic catalyst medium was developed as a high-performance sulfur cathode material for Li-S batteries. Termed A/R-TiO2@ Ni-N-MXene, this sulfur cathode material features an in-situ derived anatase-rutile homojunction of TiO2 nanoparticles on Ni-N dual-atom-doped MXene nanosheets. Using in-situ transmission electron microscopy (TEM) technique, we observed the growth process of the homojunction for the first time confirming that homojunctions facilitated charge transfer, while dual-atom doping offered abundant active sites for anchoring and converting soluble polysulfides. Theoretical calculations and experiments showed that these synergistic effects effectively mitigated the shuttle effect, leading to improved cycling performance of Li-S batteries. After 500 cycles at a 1C rate, Li-S batteries using A/R-TiO2@Ni-N-MXene as cathode materials exhibited stable and highly reversible capacity with a capacity decay of only 0.056 % per cycle. Even after 150 cycles at a 0.1C rate, a high-capacity retention rate of 62.8 % was achieved. Additionally, efficient sulfur utilization was observed, with 1280.76 mA h/g at 0.1C, 694.24 mA h/g at 1C, alongside a sulfur loading of 1.5-2 mg/cm2. The effective strategy based on homojunctions showcases promise for designing high-performance Li-S batteries.

Electron-Spin Regulation Driving Heterointerface Electron Distribution and Phase Transition toward Ultrafast and Durable Sodium Storage

Phase engineering is an effective strategy for modulating the electronic structure and electron transfer mobility of cobalt selenide (CoSe2) with remarkable sodium storage. Nevertheless, it remains challenging to improve fast-charging and cycling performance. Herein, a heterointerface coupling induces phase transformation from cubic CoSe2 to orthorhombic CoSe2 accompanied by the formation of MoSe2 to construct a CoSe2/MoSe2 heterostructure decorated with N-doped carbon layer on a 3D graphene foam (CoSe2/MoSe2@NC/GF). The incorporated Mo cations in the bridged o-CoSe2/MoSe2 not only act an electron donor to regulate charge-spin configurations with more active electronic states but also trigger the upshift of d/p band centers and a decreased ∆d-p band center gap, which greatly enhances ion adsorption capability and lowers the ion diffusion barrier. As expected, the CoSe2/MoSe2@NC/GF anode demonstrates a high-rate capability of 447 mAh g-1 at 2 A g-1 and an excellent cyclability of 298 mAh g-1 at 1 A g-1 over 1000 cycles. The work deepens the understanding of the elaborate construction of heterostructured electrodes for high-performance SIBs.

P-doped RuSe2 on Porous N-Doped Carbon Matrix as Catalysts for Accelerated Sulfur Redox Reactions

Monocomponent catalysts exhibit the limited catalytic conversion of polysulfides due to their intrinsic electronic structure, but their catalytic activity can be improved by introducing heteroatoms to regulate its electronic structure. However, the rational selection principles of doping elements remain unclear. Here, we are guided by theoretical calculations to select the suitable doping elements based on the balanced relationship between the adsorption strength of lithium polysulfides (LiPSs) and catalytic activity of lithium sulfide. We apply the screening method to develop a new catalyst of phosphorus doped RuSe2, manifesting the further enhanced conductivity compared with original RuSe2, facilitating charge transfer and further modulating the d-band center of RuSe2, thereby augmenting its effectiveness in interacting with LiPSs. Consequently, the assembled cell exhibits an areal capacity of 7.7 mAh cm-2, even under high sulfur loading of 8.0 mg cm-2 and a lean electrolyte condition (5.0 μL mg-1). This rational screening strategy offers a robust solution for the design of advanced catalysts in the field of lithium-sulfur batteries and potentially other domains as well.

High-Entropy Metal Nitride Embedded in Concave Porous Carbon Enabling Polysulfide Conversion in Lithium-Sulfur Batteries

The practical implementation of lithium-sulfur batteries is severely hindered by the rapid capacity fading due to the solubility of the intermediate lithium polysulfides (LiPSs) and the sluggish redox kinetics. Herein, high-entropy metal nitride nanocrystals (HEMN) embedded within nitrogen-doped concave porous carbon (N-CPC) polyhedra are rationally designed as a sulfur host via a facile zeolitic imidazolate framework (ZIF)-driven adsorption-nitridation process toward this challenge. The configuration of high-entropy with incorporated metal manganese (Mn) and chromium (Cr) will optimize the d-band center of active sites with more electrons occupied in antibonding orbitals, thus promoting the adsorption and catalytic conversion of LiPSs. While the concave porous carbon not only accommodates the volume change upon the cycling processes but also physically confines and exposes active sites for accelerated sulfur redox reactions. As a result, the resultant HEMN/N-CPC composites-based sulfur cathode can deliver a high specific capacity of 1274 mAh g-1 at 0.2 C and a low capacity decay rate of 0.044% after 1000 cycles at 1 C. Moreover, upon sulfur loading of 5.0 mg cm-2, the areal capacity of 5.0 mAh cm-2 can still be achieved. The present work may provide a new avenue for the design of high-performance cathodes in Li-S batteries.

A Review on Architecting Rationally Designed Metal-Organic Frameworks for the Next-Generation Li-S Batteries

The modern era demands the development of energy storage devices with high energy density and power density. There is no doubt that lithium‒sulfur batteries (Li‒S) claim high theoretical energy density and have attracted great attention from researchers, but fundamental exploration and practical applications cannot converge to utilize their maximum potential. The design parameters of Li-S batteries involve various complex mechanisms, and their obliviousness has resulted in failure at the commercial level. This article presents a review on rationally designed metal-organic frameworks (MOFs) for improving next-generation Li-S batteries. The use of MOFs in Li-S batteries is of great interest because of their large surface area, porous structure, and selective permeability for ions. The working principles of Li-S batteries, the commercialization of Li-S batteries, and the use of MOFs as electrodes, electrolytes, and separators are critically examined. Finally, designed strategies (host structure, binder improvement, separator modification, lithium metal protection, and electrolyte optimization) are developed to increase the performance of Li-S batteries.

Multifunctional TiN-MXene-Co@CNTs Networks as Sulfur/Lithium Host for High-Areal-Capacity Lithium-Sulfur Batteries

The inevitable shuttling and slow redox kinetics of lithium polysulfides (LiPSs) as well as the uncontrolled growth of Li dendrites have strongly limited the practical applications of lithium-sulfur batteries (LSBs). To address these issues, we have innovatively constructed the carbon nanotubes (CNTs) encapsulated Co nanoparticles in situ grown on TiN-MXene nanosheets, denoted as TiN-MXene-Co@CNTs, which could serve simultaneously as both sulfur/Li host to kill "three birds with one stone" to (1) efficiently capture soluble LiPSs and expedite their redox conversion, (2) accelerate nucleation/decomposition of solid Li2S, and (3) induce homogeneous Li deposition. Benefiting from the synergistic effects, the TiN-MXene-Co@CNTs/S cathode with a sulfur loading of 2.5 mg cm-2 could show a high reversible specific capacity of 1129.1 mAh g-1 after 100 cycles at 0.1 C, and ultralong cycle life over 1000 cycles at 1.0 C. More importantly, it even achieves a high areal capacity of 6.3 mAh cm-2 after 50 cycles under a sulfur loading as high as 8.9 mg cm-2 and a low E/S ratio of 5.0 μL mg-1. Besides, TiN-MXene-Co@CNTs as Li host could deliver a stable Li plating/striping behavior over 1000 h.

Precisely Designed Ultra-Small CoP Nanoparticles-Decorated Hollow Carbon Nanospheres as Highly Efficient Host in Lithium-Sulfur Batteries

Designing porous carbon materials with metal phosphides as host materials holds promise for enhancing the cyclability and durability of lithium-sulfur (Li-S) batteries by mitigating sulfur poisoning and exhibiting high electrocatalytic activity. Nevertheless, it is urgent to precisely control the size of metal phosphides to further optimize the polysulfide conversion reaction kinetics of Li-S batteries. Herein, a subtlety regulation strategy was proposed to obtain ultra-small CoP nanoparticles-decorated hollow carbon nanospheres (CoP@C) by using spherical polyelectrolyte brush (SPB) as the template with stabilizing assistance from polydopamine coating, which also works as carbon source. Leveraging the electrostatic interaction between SPB and Co2+, ultra-small Co particles with sizes measuring 5.5±2.6 nm were endowed after calcination. Subsequently, through a gas-solid phosphating process, these Co particles were converted into CoP nanoparticles with significantly finer sizes (7.1±3.1 nm) compared to state-of-the-art approaches. By uniformly distributing the electrocatalyst nanoparticles on hollow carbon nanospheres, CoP@C facilitated the acceleration of Li-ion diffusion and enhanced the conversion reaction kinetics of polysulfides through adsorption-diffusion synergy. As a result, Li-S batteries utilizing the CoP@C/S cathode demonstrated an initial specific discharge capacity of 850.0 mAh g-1 at 1.0 C, with a low-capacity decay rate of 0.03 % per cycle.

Regulating Electron Filling and Orbital Occupancy of Anti-Bonding States of Transition Metal Nitride Heterojunction for High Areal Capacity Lithium-Sulfur Full Batteries

The commercialization of lithium-sulfur (Li-S) battery is seriously hindered by the shuttle behavior of lithium (Li) polysulfide, slow conversion kinetics, and Li dendrite growth. Herein, a novel hierarchical p-type iron nitride and n-type vanadium nitride (p-Fe2N/n-VN) heterostructure with optimal electronic structure, confined in vesicle-like N-doped nanofibers (p-Fe2N/n-VN⊂PNCF), is meticulously constructed to work as "one stone two birds" dual-functional hosts for both the sulfur cathode and Li anode. As demonstrated, the d-band center of high-spin Fe atom captures more electrons from V atom to realize more π* and moderate σ* bond electron filling and orbital occupation; thus, allowing moderate adsorption intensity for polysulfides and more effective d-p orbital hybridization to improve reaction kinetics. Meanwhile, this unique structure can dynamically balance the deposition and transport of Li on the anode; thereby, more effectively inhibiting Li dendrite growth and promoting the formation of a uniform solid electrolyte interface. The as-assembled Li-S full batteries exhibit the conspicuous capacities and ultralong cycling lifespan over 2000 cycles at 5.0 C. Even at a higher S loading (20 mg cm-2) and lean electrolyte (2.5 µL mg-1), the full cells can still achieve an ultrahigh areal capacity of 16.1 mAh cm-2 after 500 cycles at 0.1 C.

Metal Organic Frameworks as Polysulfide Reaction Modulators for Lithium Sulfur Batteries: Advances and Perspectives

Currently, lithium sulfur (Li-S) battery with high theoretical energy density has attracted great research interest. However, the diffusion and loss process of intermediate lithium polysulfide during charge-discharge hindered the application of the Li-S battery in modern life. To overcome this issue, metal organic frameworks (MOFs) and their composites have been regarded as effective additions to restrain the LiPS diffusion process for Li-S battery. Benefiting from the unique structure with rich active sites to adsorb LiPS and accelerate the LiPS redox, the Li-S batteries with MOFs modified exhibit superior electrochemical performance. Considering the rapid development of MOFs in Li-S battery, this review summarizes the recent studies of MOFs and their composites as the sulfur host materials, functional interlayer, separator coating layer, and separator/solid electrolyte for Li-S batteries in detail. In addition, the promising design strategies of functional MOF materials are proposed to improve the electrochemical performance of Li-S battery.

2D Ultrathin Titanium Nitride Nanosheets as Separator Coatings for Li-S Batteries

Transition metal nitrides (TMNs) are affirmed to be an appealing candidate for boosting the performance of lithium-sulfur (Li-S) batteries due to their excellent conductivity, strong interaction with sulfur species, and the effective catalytic ability for conversion of polysulfides. However, the traditional bulk TMNs are difficult to achieve large active surface area and fast transport channels for electrons/ions simultaneously. Here, a 2D ultrathin geometry of titanium nitride (TiN) is realized by a facile topochemical conversion strategy, which can not only serve as an interconnected conductive platform but also expose abundant catalytic active sites. The ultrathin TiN nanosheets are coated on a commercial separator, serving as a multifunctional interlayer in Li-S batteries for hindering the polysulfide shuttle effect by strong capture and fast conversion of polysulfides, achieving a high initial capacity of 1357 mAh g-1 at 0.1 C and demonstrating a low capacity decay of only 0.046% per cycle over 1000 cycles at 1 C.

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.

Effects of O, S, and P in transition-metal compounds on the adsorption and catalytic ability of sulfur cathodes in lithium-sulfur batteries

Transition-metal compounds (TMCs) have recently become promising candidates as lithium-sulfur (Li-S) battery cathode materials because they have unique adsorption and catalytic properties. However, the relationship between the anionic species and performance has not been sufficiently revealed. Herein, using FeCoNiX (X = O, S, and P) compounds as examples, we systematically studied the effects of the anion composition of FeCoNiX compounds on the adsorption and catalytic abilities of sulfur cathodes in Li-S batteries. Adsorption tests and density functional theory calculations showed that the adsorption ability toward lithium polysulfides follows the order: FeCoNiP > FeCoNiO > FeCoNiS, while in situ ultraviolet-visible spectroscopy and cyclic voltammetry revealed that the catalytic ability for lithium polysulfide conversion follows the order: FeCoNiP > FeCoNiS > FeCoNiO. These results indicate that FeCoNiP is an excellent polysulfide immobilizer and catalyst that restricts shuttling and improves reaction kinetics. Electrochemical tests further demonstrated that the FeCoNiP cathode delivered superior cycling performance to FeCoNiO or FeCoNiS. In addition, the battery performance order is consistent with that of catalytic ability, which suggests that catalytic ability plays a key influencing role in batteries. This study provides new insight into the use of O-, S-, and P-doped TMCs as functional sulfur carriers.

Synergistic Effect of In2O3/NC-Co3O4 Interface on Enhancing the Redox Conversion of Polysulfides for High-Performance Li-S Cathode Materials at Low Temperatures

Lithium-sulfur (Li-S) batteries are considered as a promising energy storage technology due to their high energy density; however, the shuttling effect and sluggish redox kinetics of lithium polysulfides (LiPSs) severely deteriorate the electrochemical performance of Li-S batteries. Herein, we report a novel configuration wherein In2O3 and Co3O4 are incorporated into N-doped porous carbon as a sulfur host material (In2O3@NC-Co3O4) using metal-organic framework-based materials to synergistically tune the catalytic abilities of different metal oxides for different reaction stages of LiPSs, achieving a rapid redox conversion of LiPSs. In particular, the introduction of N-doped carbon improved the electron transport of the materials. The polar interface of In2O3 and Co3O4 anchors both long- and short-chain LiPSs and catalyzes long-chain and short-chain LiPSs, respectively, even at low temperatures. Consequently, the Li-S battery with In2O3@NC-Co3O4 cathode materials delivered an excellent discharge capacity of 1042.4 mAh g-1 at 1 C and a high capacity retention of 85.1% after 500 cycles. Impressively, the In2O3@NC-Co3O4 cathode displays superior performances at high current density and low temperature due to the enhanced redox kinetics, delivering 756 mAh g-1 at 2 C (room temperature) and 755 mAh g-1 at 0.1 C (-20 °C).

Alveoli-Inspired Carbon Cathodes with Interconnected Porous Structure and Asymmetric Coordinated Vanadium Sites for Superior Li-S Batteries

Accelerating sulfur conversion catalysis to alleviate the shuttle effect has become a novel paradigm for effective Li-S batteries. Although nitrogen-coordinated metal single-atom (M-N4) catalysts have been investigated, further optimizing its utilization rate and catalytic activities is urgently needed for practical applications. Inspired by the natural alveoli tissue with interconnected structure and well-distributed enzyme catalytic sites on the wall for the simultaneously fast diffusion and in situ catalytic conversion of substrates, here, we proposed the controllable synthesis of bioinspired carbon cathode with interconnected porous structure and asymmetric coordinated V-S1N3 sites for efficient and stable Li-S batteries. The enzyme-mimetic V-S1N3 shows asymmetric electronic distribution and high tunability, therefore enhancing in situ polysulfide conversion activities. Experimental and theoretical results reveal that the high charge asymmetry degree and large atom radius of S in V-S1N3 result in sloping adsorption for polysulfide, thereby exhibiting low thermodynamic energy barriers and long-range stability (0.076 % decay over 600 cycles).

Anchoring Active Li Metal in Oriented Channel by In Situ Formed Nucleation Sites Enabling Durable Lithium-Metal Batteries

Lithium metal is the ultimate anode material for pursuing the increased energy density of rechargeable batteries. However, fatal dendrites growth and huge volume change seriously hinder the practical application of lithium metal batteries (LMBs). In this work, a lithium host that preinstalled CoSe nanoparticles on vertical carbon vascular tissues (VCVT/CoSe) is designed and fabricated to resolve these issues, which provides sufficient Li plating space with a robust framework, enabling dendrite-free Li deposition. Their inherent N sites coupled with the in situ formed lithiophilic Co sites loaded at the interface of VCVT not only anchor the initial Li nucleation seeds but also accelerate the Li+ transport kinetics. Meanwhile, the Li2Se originated from the CoSe conversion contributes to constructing a stable solid-electrolyte interphase with high ionic conductivity. This optimized Li/VCVT/CoSe composite anode exhibits a prominent long-term cycling stability over 3000 h with a high areal capacity of 10 mAh cm-2. When paired with a commercial nickel-rich LiNi0.83Co0.12Mn0.05O2 cathode, the full-cell presents substantially enhanced cycling performance with 81.7% capacity retention after 300 cycles at 0.2 C. Thus, this work reveals the critical role of guiding Li deposition behavior to maintain homogeneous Li morphology and pave the way to stable LMBs.

Rapid Growth of Bi2Se3 Nanodots on MXene Nanosheets at Room Temperature for Promoting Sulfur Redox Kinetics

Li-S batteries are hampered by problems with their cathodes and anodes simultaneously. The improvement of Li-S batteries needs to consider both the anode and cathode. Herein, a Bi2Se3@MXene composite is prepared for the first time by rapidly growing Bi2Se3 nanodots on two-dimensional (2D) MXene nanosheets at room temperature through simply adding high-reactive hydroxyethylthioselenide in Bi3+/MXene aqueous solution. Bi2Se3@MXene exhibits a 2D structure due to the template effect of 2D MXene. Bi2Se3@MXene can not only facilitate the conversion of lithium polysulfides (LiPSs) but also inhibit their shuttling in the S cathode due to its catalytic effect and adsorption force with LiPSs. Bi2Se3@MXene can also be used as an interfacial lithiophilic layer to inhibit Li dendrite growth in the Li metal anode. Theoretical calculations reveal that Bi2Se3 nanodots in Bi2Se3@MXene can effectively boost the adsorption ability with LiPSs, and the MXene in Bi2Se3@MXene can accelerate the electron transport. Under the bidirectional regulation of Bi2Se3@MXene in the Li metal anode and S cathode, the Li-S battery shows an enhanced electrochemical performance.

Spontaneous Built-In Electric Field in C3N4-CoSe2 Modified Multifunctional Separator with Accelerating Sulfur Evolution Kinetics and Li Deposition for Lithium-Sulfur Batteries

The discovery of the heterostructures that is combining two materials with different properties has brought new opportunities for the development of lithium sulfur batteries (LSBs). Here, C3N4-CoSe2 composite is elaborately designed and used as a functional coating on the LSBs separator. The abundant chemisorption sites of C3N4-CoSe2 form chemical bonding with polysulfides, provides suitable adsorption energy for lithium polysulfides (LiPSs). More importantly, the spontaneously formed internal electric field accelerates the charge flow in the C3N4-CoSe2 interface, thus facilitating the transport of LiPSs and electrons and promoting the bidirectional conversion of sulfur. Meanwhile, the lithiophilic C3N4-CoSe2 sample with catalytic activity can effectively regulate the uniform distribution of lithium when Li+ penetrates the separator, avoiding the formation of lithium dendrites in the lithium (Li) metal anode. Therefore, LSBs based on C3N4-CoSe2 functionalized membranes exhibit a stable long cycle life at 1C (with capacity decay of 0.0819% per cycle) and a large areal capacity of 10.30 mAh cm-2 at 0.1C (sulfur load: 8.26 mg cm-2, lean electrolyte 5.4 µL mgs -1). Even under high-temperature conditions of 60 °C, a capacity retention rate of 81.8% after 100 cycles at 1 C current density is maintained.

Fundamentally Manipulating the Electronic Structure of Polar Bifunctional Catalysts for Lithium-Sulfur Batteries: Heterojunction Design versus Doping Engineering

Heterogeneous structures and doping strategies have been intensively used to manipulate the catalytic conversion of polysulfides to enhance reaction kinetics and suppress the shuttle effect in lithium-sulfur (Li-S) batteries. However, understanding how to select suitable strategies for engineering the electronic structure of polar catalysts is lacking. Here, a comparative investigation between heterogeneous structures and doping strategies is conducted to assess their impact on the modulation of the electronic structures and their effectiveness in catalyzing the conversion of polysulfides. These findings reveal that Co0.125Zn0.875Se, with metal-cation dopants, exhibits superior performance compared to CoSe2/ZnSe heterogeneous structures. The incorporation of low Co2+ dopants induces the subtle lattice strain in Co0.125Zn0.875Se, resulting in the increased exposure of active sites. As a result, Co0.125Zn0.875Se demonstrates enhanced electron accumulation on surface Se sites, improved charge carrier mobility, and optimized both p-band and d-band centers. The Li-S cells employing Co0.125Zn0.875Se catalyst demonstrate significantly improved capacity (1261.3 mAh g-1 at 0.5 C) and cycle stability (0.048% capacity delay rate within 1000 cycles at 2 C). This study provides valuable guidance for the modulation of the electronic structure of typical polar catalysts, serving as a design directive to tailor the catalytic activity of advanced Li-S catalysts.

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.

Cubic CoSe2@carbon as polysulfides adsorption-catalytic mediator for fast redox kinetics and advanced stability lithium-sulfur batteries

Although lithium-sulfur batteries (LSBs) are an attractive next-generation rechargeable battery with high theoretical energy density (2600 Wh kg-1) and specific capacity (1675 mA h g-1), the shuttle of soluble lithium polysulfides (LiPSs) is still the protruding obstacle to accelerate the redox reaction of LSBs. Here, cubic cobalt diselenide@carbon (CoSe2@C) derived from zeolite imidazole framework-67 (ZIF-67) was employed as the functional coating of polypropylene (PP) separator to efficiently adsorb and catalyze polysulfides, inhibit "shuttle effect" and improve the electrochemical reaction kinetics of LSBs. The CoSe2@C offers larger mesopore proportion of 77.19 % and abundant active sites to ensure space as a secondary reaction region, and infiltration of electrolyte and rapid transport of Li+. The involved adsorption and catalysis effect are discussed by static adsorption experiment, XPS, and Li2S nucleation kinetics analysis. The results show that CoSe2@C exhibits strong adsorption effect and catalytic activity on LiPSs, and CoSe2@C/PP cells display fast Li+ diffusion and improved redox kinetics (high Li2S nucleation peak current of 0.27 mA and deposition capacity of 148.46 mA h g-1). Ascribe to these advantages, the CoSe2@C/PP cell provides an initial discharge specific capacity of 1335.01 mA h g-1 at 0.1 C and a fine reversible capacity at 5.0 C, and achieves stable and durable lifespan with an average capacity decay rate of 0.12 % over 400 cycles at 0.5 C. This work could promote the practical application of metal selenides in the key components and devices for LSBs.

Interfacial "Double-Terminal Binding Sites" Catalysts Synergistically Boosting the Electrocatalytic Li2S Redox for Durable Lithium-Sulfur Batteries

Catalytic conversion of polysulfides emerges as a promising approach to improve the kinetics and mitigate polysulfide shuttling in lithium-sulfur (Li-S) batteries, especially under conditions of high sulfur loading and lean electrolyte. Herein, we present a separator architecture that incorporates double-terminal binding (DTB) sites within a nitrogen-doped carbon framework, consisting of polar Co0.85Se and Co clusters (Co/Co0.85Se@NC), to enhance the durability of Li-S batteries. The uniformly dispersed clusters of polar Co0.85Se and Co offer abundant active sites for lithium polysulfides (LiPSs), enabling efficient LiPS conversion while also serving as anchors through a combination of chemical interactions. Density functional theory calculations, along with in situ Raman and X-ray diffraction characterizations, reveal that the DTB effect strengthens the binding energy to polysulfides and lowers the energy barriers of polysulfide redox reactions. Li-S batteries utilizing the Co/Co0.85Se@NC-modified separator demonstrate exceptional cycling stability (0.042% per cycle over 1000 cycles at 2 C) and rate capability (849 mAh g-1 at 3 C), as well as deliver an impressive areal capacity of 10.0 mAh cm-2 even in challenging conditions with a high sulfur loading (10.7 mg cm-2) and lean electrolyte environments (5.8 μL mg-1). The DTB site strategy offers valuable insights into the development of high-performance Li-S batteries.

Exquisitely constructing hierarchical carbon nanoarchitectures decorated with sulfides for high-performance Li-S batteries

The sluggish reaction kinetics and notorious shuttle effect of polysulfides significantly hinder the practical application of lithium-sulfur batteries (LSBs). Therefore, polysulfides are anchored and their conversion reactions are catalyzed to enhance the performance of LSBs. Herein, an exquisite hierarchical carbon nanoarchitecture decorated with sulfides is designed and introduced into LSBs. Systematic experiments show that the nanoarchitecture not only enables rapid electron/ion migration but also functions as an active catalyst to increase polysulfide conversion, thus effectively reducing the shuttle effect. As a result, LSBs with the nanoarchitecture modified separator exhibited outstanding rate capacity (724.9 mA h g-1 at 5C), low self-discharge capacity loss (4.1% capacity loss after 72 h), and exceptional reversible capacity (1518.3 mA h g-1 at 0.1C and 25.6% capacity loss after 100 cycles). Through the design of a multifunctional separator, this study offers an effective way to minimize the shuttle effect and speed up redox conversion. The strategy of constructing nanoarchitectures provides an innovative route for hierarchical heterocatalyst design for LSBs.

Ultra-Dispersed α-MoC1-x Embedded in a Plum-Like N-Doped Carbon Framework as a Synergistic Adsorption-Electrocatalysis Interlayer for High-Performance Li-S Batteries

The shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) severely hinder the scalable application of lithium-sulfurr (Li-S) batteries. Herein, the highly dispersed α-phase molybdenum carbide nano-crystallites embedded in a porous nitrogen-doped carbon framework (α-MoC1-x @NCF) are developed via a simple metal-organic frameworks (MOFs) assisted strategy and proposed as the multifunctional separator interlayer for Li-S batteries. The inlaid MoC1-x nanocrystals and in situ doped nitrogen atoms provide a strong chemisorption and outstanding electrocatalytic conversion toward LiPSs, whereas the unique plum-like carbon framework with hierarchical porosity enables fast electron/Li+ transfer and can physically suppress LiPSs shuttling. Benefiting from the synergistic trapping-catalyzing effect of the MoC1-x @NCF interlayer toward LiPSs, the assembled Li-S battery achieves high discharge capacities (1588.1 mAh g-1 at 0.1 C), impressive rate capability (655.8 mAh g-1 at 4.0 C) and ultra-stable lifespan (a low capacity decay of 0.059% per cycle over 650 cycles at 1.0 C). Even at an elevated sulfur loading (6.0 mg cm-2 ) and lean electrolyte (E/S is ≈5.8 µL mg-1 ), the battery can still achieve a superb areal capacity of 5.2 mAh cm-2 . This work affords an effective design strategy for the construction of muti-functional interlayer in advanced Li-S batteries.

Ion/Electron Co-Conductive Triple-Phase Interface Enabling Fast Redox Reaction Kinetics in Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are promising next-generation energy storage systems because of their high energy densities and high theoretical specific capacities. However, most catalysts in the LSBs are based on carbon materials, which can only improve the conductivity and are unable to accelerate lithium-ion transport. Therefore, it would be worthwhile to develop a catalytic electrode exhibiting both ion and electron conductivity. Herein, a triple-phase interface using lithium lanthanum titanate/carbon (LLTO/C) nanofibers to construct ion/electron co-conductive materials was used to afford enhanced adsorption of lithium polysulfides (LiPSs), high conductivity, and fast ion transport in working LSBs. The triple-phase interface accelerates the kinetics of the soluble LiPSs and promotes uniform Li2S precipitation/dissolution. Additionally, the LLTO/C nanofibers decrease the reaction barrier of the LiPSs, significantly improving the conversion of LiPSs to Li2S and promoting rapid conversion. Specifically, the LLTO promotes ion transport owing to its high ionic conductivity, and the carbon enhances the conductivity to improve the utilization rate of sulfur. Therefore, the LSBs with LLTO/C functional separators deliver stable life cycles, high rates, and good electrocatalytic activities. This strategy is greatly important for designing ion/electron conductivity and interface engineering, providing novel insight for the development of the LSBs.

Synergistic design of a semi-hollow core-shell structure and a metal-organic framework-derived Co/Zn selenide coated with MXene for high-performance lithium-sulfur batteries

Lithium-sulfur batteries have garnered significant interest as potential energy storage systems for the future, owing to their remarkable theoretical specific capacity (1675 mA h g-1) and energy density (2600 W h kg-1). However, their development has been severely impeded by several challenges, including the low intrinsic conductivity of sulfur, volume expansion issues, and the polysulfide shuttle effect. To address these issues, polar metal compounds with nanostructures featuring hollow shells and catalytic functions have emerged as promising materials for designing advanced lithium-sulfur batteries. In this study, bimetallic selenides with varying degrees of hollowness are synthesized using a tannic acid etching and selenization strategy. By comparing the electrochemical characteristics of composite electrodes with different degrees of hollowness, an optimal semi-hollow core-shell structure is identified, implying that reasonable structural designing of metal compounds carries immense importance in improving electrochemical reactions. Moreover, the appropriate degree of hollowness effectively mitigates volume expansion issues associated with the sulfur cathode. Consequently, bimetallic selenides with a hollow core-shell structure coated with conductive MXene material exhibit superior electrochemical performance. The synergistic effect achieved through the judicious design of the hollow core-shell structure and the utilization of polar metal compounds has proved instrumental in enhancing the redox kinetics of lithium-sulfur batteries. As such, this research presents a novel avenue for the development of high-performance lithium-sulfur batteries.

Palygorskite-Derived Ternary Fluoride with 2D Ion Transport Channels for Ampere Hour-Scale Li-S Pouch Cell with High Energy Density

Although various excellent electrocatalysts/adsorbents have made notable progress as sulfur cathode hosts on the lithium-sulfur (Li-S) coin-cell level, high energy density (WG ) of the practical Li-S pouch cells is still limited by inefficient Li-ion transport in the thick sulfur cathode under low electrolyte/sulfur (E/S) and negative/positive (N/P) ratios, which aggravates the shuttle effect and sluggish redox kinetics. Here a new ternary fluoride MgAlF5 ·2H2 O with ultrafast ion conduction-strong polysulfides capture integration is developed. MgAlF5 ·2H2 O has an inverse Weberite-type crystal framework, in which the corner-sharing [AlF6 ]-[MgF4 (H2 O)2 ] octahedra units extend to form two-dimensional Li-ion transport channels along the [100] and [010] directions, respectively. Applied as the cathode sulfur host, the MgAlF5 ·2H2 O lithiated by LiTFSI (lithium salt in Li-S electrolyte) acts as a fast ionic conductor to ensure efficient Li-ion transport to accelerate the redox kinetics under high S loadings and low E/S and N/P. Meanwhile, the strong polar MgAlF5 ·2H2 O captures polysulfides by chemisorption to suppress the shuttle effect. Therefore, a 1.97 A h-level Li-S pouch cell achieves a high WG of 386 Wh kg-1 . This work develops a new-type ionic conductor, and provides unique insights and new hosts for designing practical Li-S pouch cells.

Investigation of the Chemisorption-Catalysis Behavior of Sulfur Species on the Electrocatalysts Designed by Co-regulation Strategy of Anions and Cations

Li-S batteries possess high energy density and have been one of the most promising energy storage systems. For sulfur cathodes, the electrochemical performance is still seriously hindered by the polysulfide shuttling and sluggish conversion kinetics. It has been demonstrated to be one effective strategy to address the above issues via designing electrocatalysts with robust affinity and catalytic capacity towards polysulfides. However, it is still a great challenge to rapidly and economically discover high-performance electrocatalysts. Herein, using density functional theory calculation, we studied the chemisorption-catalysis behavior of sulfur species on a series of electrocatalysts (MCo2 X4 , M=Co, Zn, Cu, Ni, Fe, and Mn, X=O, S, and Se) to assess the effect of the anions and cations co-regulation on their electronic structure, chemisorption behavior, and catalytic property. FeCo2 Se4 and CuCo2 Se4 combined appropriate chemisorption with superior electronic conductivity and sulfur reduction catalytic capacity have been predicted as novel electrocatalysts for high-performance Li-S batteries. This study gives theoretical guidance for rapid discovery of high-efficient electrocatalyst to boost the electrochemical performance of sulfur cathodes.

Accelerating S↔Li2 S Reactions in Li-S Batteries through Activation of S/Li2 S with a Bifunctional Semiquinone Catalyst

The reaction rate bottleneck during interconversion between insulating S8 (S) and Li2 S fundamentally leads to incomplete conversion and restricted lifespan of Li-S battery, especially under high S loading and lean electrolyte conditions. Herein, we demonstrate a new catalytic chemistry: soluble semiquinone, 2-tertbutyl-semianthraquinone lithium (Li+ TBAQ⋅- ), as both e- /Li+ donor and acceptor for simultaneous S reduction and Li2 S oxidation. The efficient activation of S and Li2 S by Li+ TBAQ⋅- in the initial discharging/charging state maximizes the amount of soluble lithium polysulfide, thereby substantially improve the rate of solid-liquid-solid reaction by promoting long-range electron transfer. With in situ Raman spectra and theoretical calculations, we reveal that the activation of S/Li2 S is the rate-limiting step for effective S utilization under high S loading and low E/S ratio. Beyond that, the S activation ratio is firstly proposed as an accurate indicator to quantitatively evaluate the reaction rate. As a result, the Li-S batteries with Li+ TBAQ⋅- deliver superior cycling performance and over 5 times higher S utilization ratio at high S loading of 7.0 mg cm-2 and a current rate of 1 C compared to those without Li+ TBAQ⋅- . We hope this study contributes to the fundamental understanding of S redox chemical and inspires the design of efficient catalysis for advanced Li-S batteries.

Stable Lithium-Sulfur Batteries Ensured by GeS2 and α-S8 Lattice Matching During the Charge Process

The charge process of lithium-sulfur batteries (LSBs) is a process in which molecular polarity decreases and the volume shrinks gradually, which is the process most likely to cause lithium polysulfides (LiPSs) loss and interfacial collapse. In this work, GeS2 is utilized, whose (111) lattice plane exactly matches with the (113) lattice of α-S8 , to solve these problems. GeS2 can regulate the interconversion-deposition behavior of S-species during the charge process. Soluble LiPSs can be spontaneously adsorbed on the GeS2 surface, then obtain electrons and eventually convert to α-S8 molecules. More importantly, the α-S8 molecules will crystallize uniformly along the (111) lattice plane of GeS2 to maintain a stable cathode-electrolyte interface. Therefore, outstanding charge/discharge LSBs are successfully accomplished.

Beaded CoSe2-C Nanofibers for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are regarded as highly promising energy storage devices due to their high theoretical specific capacity and high energy density. Nevertheless, the commercial application of Li-S batteries is still restricted by poor electrochemical performance. Herein, beaded nanofibers (BNFs) consisting of carbon and CoSe2 nanoparticles (CoSe2/C BNFs) were prepared by electrospinning combined with carbonization and selenization. Benefitting from the synergistic effect of physical adsorption and chemical catalysis, the CoSe2/C BNFs can effectively inhibit the shuttle effect of lithium polysulfides and improve the rate performance and cycle stability of Li-S batteries. The three-dimensional conductive network provides a fast electron and ion transport pathway as well as sufficient space for alleviating the volume change. CoSe2 can not only effectively adsorb the lithium polysulfides but also accelerate their conversion reaction. The CoSe2/C BNFs-S cathode has a high reversible discharge specific capacity of 919.2 mAh g-1 at 0.1 C and presents excellent cycle stability with a low-capacity decay rate of 0.05% per cycle for 600 cycles at 1 C. The combination of the beaded carbon nanofibers and polar metal selenides sheds light on designing high-performance sulfur-based cathodes.

High Crystallinity 2D π-d Conjugated Conductive Metal-Organic Framework for Boosting Polysulfide Conversion in Lithium-Sulfur Batteries

The catalytic performance of metal-organic frameworks (MOFs) in Li-S batteries is significantly hindered by unsuitable pore size, low conductivity, and large steric contact hindrance between the catalytic site and lithium polysulfide (LPSs). Herein, the smallest π-conjugated hexaaminobenzene (HAB) as linker and Ni(II) ions as skeletal node are in situ assembled into high crystallinity Ni-HAB 2D conductive MOFs with dense Ni-N4 units via dsp2 hybridization on the surface of carbon nanotube (CNT), fabricating Ni-HAB@CNT as separator modified layer in Li-S batteries. As-obtained unique π-d conjugated Ni-HAB nanostructure features ordered micropores with suitable pore size (≈8 Å) induced by HAB ligands, which can cooperate with dense Ni-N4 chemisorption sites to effectively suppress the shuttle effect. Meanwhile, the conversion kinetics of LPSs is significantly accelerated owing to the small steric contact hindrance and increased delocalized electron density endued by the planar tetracoordinate structure. Consequently, the Li-S battery with Ni-HAB@CNT modified separator achieves an areal capacity of 6.29 mAh cm-2 at high sulfur loading of 6.5 mg cm-2 under electrolyte/sulfur ratio of 5 µL mg-1 . Moreover, Li-S single-electrode pouch cells with modified separators deliver a high reversible capacity of 791 mAh g-1 after 50 cycles at 0.1 C with electrolyte/sulfur ratio of 6 µL mg-1 .

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.

Boosting Lean Electrolyte Lithium-Sulfur Battery Performance with Transition Metals: A Comprehensive Review

Lithium-sulfur (Li-S) batteries have received widespread attention, and lean electrolyte Li-S batteries have attracted additional interest because of their higher energy densities. This review systematically analyzes the effect of the electrolyte-to-sulfur (E/S) ratios on battery energy density and the challenges for sulfur reduction reactions (SRR) under lean electrolyte conditions. Accordingly, we review the use of various polar transition metal sulfur hosts as corresponding solutions to facilitate SRR kinetics at low E/S ratios (< 10 µL mg-1), and the strengths and limitations of different transition metal compounds are presented and discussed from a fundamental perspective. Subsequently, three promising strategies for sulfur hosts that act as anchors and catalysts are proposed to boost lean electrolyte Li-S battery performance. Finally, an outlook is provided to guide future research on high energy density Li-S batteries.

Two-birds with one stone: Improving both cathode and anode electrochemical performances via two-dimensional Te-CoTe2/rGO ultrathin nanosheets as sulfur hosts in lithium-sulfur batteries

A Te-doped CoTe₂ film could be grown in situ on reduced graphene oxide (rGO) to develop a Te-CoTe₂/rGO composite with an ultrathin layered structure, which has multiple protective effects on both the sulfur positive electrode and lithium negative electrode in lithium sulfur (Li-S) batteries. The Te-CoTe₂/rGO composite as a sulfur host not only shows a strong adsorbing ability for lithium polysulfides (LiPSs) but can also accelerate the conversion reaction of active material sulfur during the charging/discharging process. More importantly, this host can turn the shuttle effect from an unfavorable factor to a favorable factor, which could improve the electrochemical performance of the lithium anode with uniform lithium plating/stripping resulting from the intermediate polytellurosulfide species (Li₂Te_xS_y), which could be generated on the cathode surface via Te reacting with soluble Li₂S_n (4 ≤ n ≤ 8). As a result, the S@Te-CoTe₂/rGO cathode shows a discharge capacity of 970.0 mA h g^-1 in the first cycle at 1 C and retains a high capacity of 545.5 mA h g^-1 after 1000 cycles, corresponding to a low capacity decay rate of only 0.043% per cycle. In addition, in situ X-ray diffraction (XRD) and in situ Raman were used to explore the sulfur conversion process. This study not only demonstrates that a two-dimensional (2D) ultrathin Te-CoTe₂/rGO composite is successfully developed with multiple effects on Li-S batteries but also opens a new pathway for designing unique sulfur hosts to promote the electrochemical performance of Li-S batteries.

A Rational Design of a CoS2-CoSe2 Heterostructure for the Catalytic Conversion of Polysulfides in Lithium-Sulfur Batteries

Lithium-sulfur batteries are anticipated to be the next generation of energy storage devices because of their high theoretical specific capacity. However, the polysulfide shuttle effect of lithium-sulfur batteries restricts their commercial application. The fundamental reason for this is the sluggish reaction kinetics between polysulfide and lithium sulfide, which causes soluble polysulfide to dissolve into the electrolyte, leading to a shuttle effect and a difficult conversion reaction. Catalytic conversion is considered to be a promising strategy to alleviate the shuttle effect. In this paper, a CoS₂-CoSe₂ heterostructure with high conductivity and catalytic performance was prepared by in situ sulfurization of CoSe₂ nanoribbon. By optimizing the coordination environment and electronic structure of Co, a highly efficient CoS₂-CoSe₂ catalyst was obtained, to promote the conversion of lithium polysulfides to lithium sulfide. By using the modified separator with CoS₂-CoSe₂ and graphene, the battery exhibited excellent rate and cycle performance. The capacity remained at 721 mAh g^-1 after 350 cycles, at a current density of 0.5 C. This work provides an effective strategy to enhance the catalytic performance of two-dimensional transition-metal selenides by heterostructure engineering.

Aqueous Zinc Batteries with Ultra-Fast Redox Kinetics and High Iodine Utilization Enabled by Iron Single Atom Catalysts

Rechargeable aqueous zinc iodine (ZnǀǀI2) batteries have been promising energy storage technologies due to low-cost position and constitutional safety of zinc anode, iodine cathode and aqueous electrolytes. Whereas, on one hand, the low-fraction utilization of electrochemically inert host causes severe shuttle of soluble polyiodides, deficient iodine utilization and sluggish reaction kinetics. On the other hand, the usage of high mass polar electrocatalysts occupies mass and volume of electrode materials and sacrifices device-level energy density. Here, we propose a "confinement-catalysis" host composed of Fe single atom catalyst embedding inside ordered mesoporous carbon host, which can effectively confine and catalytically convert I2/I- couple and polyiodide intermediates. Consequently, the cathode enables the high capacity of 188.2 mAh g-1 at 0.3 A g-1, excellent rate capability with a capacity of 139.6 mAh g-1 delivered at high current density of 15 A g-1 and ultra-long cyclic stability over 50,000 cycles with 80.5% initial capacity retained under high iodine loading of 76.72 wt%. Furthermore, the electrocatalytic host can also accelerate the [Formula: see text] conversion. The greatly improved electrochemical performance originates from the modulation of physicochemical confinement and the decrease of energy barrier for reversible I-/I2 and I2/I+ couples, and polyiodide intermediates conversions.

Polycrystal Li2ZnTi3O8/C anode with lotus seedpod structure for high-performance lithium storage

Lotus-seedpod structured Li₂ZnTi₃O₈/C (P-LZTO) microspheres obtained by the molten salt method are reported for the first time. The received phase-pure Li₂ZnTi₃O₈ nanoparticles are inserted into the carbon matrix homogeneously to form a Lotus-seedpod structure, as confirmed by the morphological and structural measurements. As the anode for lithium-ion batteries, the P-LZTO material demonstrates excellent electrochemical performance with a high rate capacity of 193.2 mAh g^-1 at 5 A g^-1 and long-term cyclic stability up to 300 cycles at 1 A g^-1. After even 300 cyclings, the P-LZTO particles can maintain their morphological and structural integrity. The superior electrochemical performances have arisen from the unique structure where the polycrystalline structure is beneficial for shorting the lithium-ion diffusion path, while the well-encapsulated carbon matrix can not only enhance the electronic conductivity of the composite but also alleviate the stress anisotropy during lithiation/delithiation process, leading to well-preserved particles.

Rough Endoplasmic Reticulum Inspired Polystyrene-Brush-Based Superhigh Sulfur Content Cathodes Enable Lithium-Sulfur Cells with High Mass and Capacity Loading

The development of highly sophisticated biomimetic models is significant yet remains challenging in the electrochemical energy storage field. Lithium-sulfur (Li-S) cells with high sulfur content and high-sulfur-loading cathodes are urgently required to meet the fast-growing demand for electronic devices. Nevertheless, such cathode materials generally suffer from large sulfur agglomeration, nonporous structure, and insufficient conductivity, leading to rapid capacity decay and low sulfur utilization. Herein, inspired by rough endoplasmic reticulum, a 2D polystyrene (PS)-brush-based (G-g-PS) superhigh-sulfur-content (96 wt%) composite(G-g-sPS@S) is fabricated via the vulcanization reaction. The vulcanized PS side-chains and their S₈ composites on the nanosheet surface can efficiently provide sulfur species, and the intersheet interstitial pores can provide rapid mass-transfer channels for redox reactions of sulfur species. Furthermore, the highly sulfophilic vulcanized PS side-chains are able to effectively inhibit the shuttle effect of polysulfides and regulate their redox process. With these merits, the cells with G-g-sPS@S cathodes exhibit an ultralow decay rate of 0.02% per cycle over 400 cycles at 2 C and deliver a superior areal capacity of 12.6 mAh cm^-2 even with a high sulfur loading of 10.5 mg cm^-2 .

Dual-Conductive CoSe2 @TiSe2 -C Heterostructures Promoting Overall Sulfur Redox Kinetics under High Sulfur Loading and Lean Electrolyte

Although lithium-sulfur batteries (LSBs) possess a high theoretical specific capacity and energy density, the inherent problems including sluggish sulfur conversion kinetics and the shuttling of soluble lithium polysulfides (LiPSs) have severely hindered the development of LSBs. Herein, cobalt selenide (CoSe₂ ) polyhedrons anchored on few-layer TiSe₂ -C nanosheets derived from Ti₃ C₂ T_x MXenes (CoSe₂ @TiSe₂ -C) are reported for the first time. The dual-conductive CoSe₂ @TiSe₂ -C heterostructures can accelerate the conversion reaction from liquid LiPSs to solid Li₂ S and promote Li₂ S dissociation process through high conductivity and lowered reaction energy barriers for promoting overall sulfur redox kinetics, especially under high sulfur loadings and lean electrolyte. Electrochemical analysis and density functional theory calculation results clearly reveal the catalytic mechanisms of the CoSe₂ @TiSe₂ -C heterostructures from the electronic structure and atomic level. As a result, the cell with CoSe₂ @TiSe₂ -C interlayer maintains a superior cycling performance with 842.4 mAh g^-1  and a low-capacity decay of 0.031% per cycle over 800 cycles at 1.0 C under a sulfur loading of 2.5 mg cm^-2 . More encouragingly, it with a high sulfur loading of ≈7.0 mg cm^-2  still harvests a high areal capacity of ≈6.25 mAh cm^-2  under lean electrolyte (electrolyte/sulfur, E/S ≈ 4.5 µL mg^-1 ) after 50 cycles at 0.05 C.

CrP Nanocatalyst within Porous MOF Architecture to Accelerate Polysulfide Conversion in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries demonstrate great potential for next-generation electrochemical energy storage systems because of their high specific energy and low-cost materials. However, the shuttling behavior and slow kinetics of intermediate polysulfide (PS) conversion pose a major obstacle to the practical application of Li-S batteries. Herein, CrP within a porous nanopolyhedron architecture derived from a metal-organic framework (CrP@MOF) is developed as a highly efficient nanocatalyst and S host to address these issues. Theoretical and experimental analyses demonstrate that CrP@MOF has a remarkable binding strength to trap soluble PS species. In addition, CrP@MOF shows abundant active sites to catalyze the PS conversion, accelerate Li-ion diffusion, and induce the precipitation/decomposition of Li₂S. As a result, the CrP@MOF-containing Li-S batteries demonstrate over 67% capacity retention over 1000 cycles at 1 C, ∼100% Coulombic efficiency, and high rate capability (674.6 mAh g^-1 at 4 C). In brief, CrP nanocatalysts accelerate the PS conversion and improve the overall performance of Li-S batteries.

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.

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.

High Energy Density Lithium-Sulfur Batteries Based on Carbonaceous Two-Dimensional Additive Cathodes

The increasing demand for electrical energy storage makes it essential to explore alternative battery chemistries that overcome the energy-density limitations of the current state-of-the-art lithium-ion batteries. In this scenario, lithium-sulfur batteries (LSBs) stand out due to the low cost, high theoretical capacity, and sustainability of sulfur. However, this battery technology presents several intrinsic limitations that need to be addressed in order to definitively achieve its commercialization. Herein, we report the fruitfulness of three different formulations using well-selected functional carbonaceous additives for sulfur cathode development, an in-house synthesized graphene-based porous carbon (ResFArGO), and a mixture of commercially available conductive carbons (CAs), as a facile and scalable strategy for the development of high-performing LSBs. The additives clearly improve the electrochemical properties of the sulfur electrodes due to an electronic conductivity enhancement, leading to an outstanding C-rate response with a remarkable capacity of 2 mA h cm^-2 at 1C and superb capacities of 4.3, 4.0, and 3.6 mA h cm^-2 at C/10 for ResFArGO₁₀, ResFArGO₅, and CAs, respectively. Moreover, in the case of ResFArGO, the presence of oxygen functional groups enables the development of compact high sulfur loading cathodes (>4 mg_S cm^-2) with a great ability to trap the soluble lithium polysulfides. Notably, the scalability of our system was further demonstrated by the assembly of prototype pouch cells delivering excellent capacities of 90 mA h (ResFArGO₁₀ cell) and 70 mA h (ResFArGO₅ and CAs cell) at C/10.

Dual-Functional Lithiophilic/Sulfiphilic Binary-Metal Selenide Quantum Dots Toward High-Performance Li-S Full Batteries

The commercial viability of lithium-sulfur batteries is still challenged by the notorious lithium polysulfides (LiPSs) shuttle effect on the sulfur cathode and uncontrollable Li dendrites growth on the Li anode. Herein, a bi-service host with Co-Fe binary-metal selenide quantum dots embedded in three-dimensional inverse opal structured nitrogen-doped carbon skeleton (3DIO FCSe-QDs@NC) is elaborately designed for both sulfur cathode and Li metal anode. The highly dispersed FCSe-QDs with superb adsorptive-catalytic properties can effectively immobilize the soluble LiPSs and improve diffusion-conversion kinetics to mitigate the polysulfide-shutting behaviors. Simultaneously, the 3D-ordered porous networks integrated with abundant lithophilic sites can accomplish uniform Li deposition and homogeneous Li-ion flux for suppressing the growth of dendrites. Taking advantage of these merits, the assembled Li-S full batteries with 3DIO FCSe-QDs@NC host exhibit excellent rate performance and stable cycling ability (a low decay rate of 0.014% over 2,000 cycles at 2C). Remarkably, a promising areal capacity of 8.41 mAh cm-2 can be achieved at the sulfur loading up to 8.50 mg cm-2 with an ultra-low electrolyte/sulfur ratio of 4.1 μL mg-1. This work paves the bi-serve host design from systematic experimental and theoretical analysis, which provides a viable avenue to solve the challenges of both sulfur and Li electrodes for practical Li-S full batteries.

Revealing the Selective Bifunctional Electrocatalytic Sites via In Situ Irradiated X-Ray Photoelectron Spectroscopy for Lithium-Sulfur Battery

The electrocatalysts are widely applied in lithium-sulfur (Li-S) batteries to selectively accelerate the redox kinetics behavior of Li2 S, in which bifunctional active sites are established, thereby improving the electrochemical performance of the battery. Considering that the Li-S battery is a complex closed "black box" system, the internal redox reaction routes and active sites cannot be directly observed and monitored especially due to the distribution of potential active-site structures and their dynamic reconstruction. Empirical evidence demonstrates that traditional electrochemical test methods and theoretical calculations only probe the net result of multi-factors on an average and whole scale. Herein, based on the amorphous TiO2- x @Ni selective bifunctional model catalyst, these limitations are overcome by developing a system that couples the light field and in situ irradiated X-ray photoelectron spectroscopy to synergistically convert the "black box" battery into a "see-through" battery for direct observation of the charge transportation, thus revealing that amorphous TiO2- x and Ni nanoparticle as the oxidation and reduction sites selectively promote the decomposition and nucleation of Li2 S, respectively. This work provides a universal method to achieve a deeper mechanistic understanding of bidirectional sulfur electrochemistry.

A rational design of titanium-based heterostructures as electrocatalyst for boosted conversion kinetics of polysulfides in Li-S batteries

Lithium-sulfur batteries have great potential for next-generation electrochemical storage systems owing to their high theoretical specific energy and cost-effectiveness. However, the shuttle effect of soluble polysulfides and sluggish multi-electron sulfur redox reactions has severely impeded the implementation of lithium-sulfur batteries. Herein, we prepared a new type of Ti₃C₂-TiO₂ heterostructure sandwich nanosheet confined within polydopamine derived N-doped porous carbon. The highly polar heterostructures sandwich nanosheet with a high specific surface area can strongly absorb polysulfides, restraining their outward diffusion into the electrolyte. Abundant boundary defects constructed by new types of heterostructures reduce the overpotential of nucleation and improve the nucleation/conversion redox kinetics of Li₂S. The Ti₃C₂-TiO₂@NC/S cathode exhibited discharge capacities of 1363, and 801 mAh g^-1 at the first and 100th cycles at 0.5C, respectively, and retained an ultralow capacity fade rate of 0.076% per cycle over 500cycles at 1.0C. This study provides a potential avenue for constructing heterostructure materials for electrochemical energy storage and catalysis.

Interface Engineering Toward Expedited Li2 S Deposition in Lithium-Sulfur Batteries: A Critical Review

Lithium-sulfur batteries (LSBs) with superior energy density are among the most promising candidates of next-generation energy storage techniques. As the key step contributing to 75% of the overall capacity, Li₂ S deposition remains a formidable challenge for LSBs applications because of its sluggish kinetics. The severe kinetic issue originates from the huge interfacial impedances, indicative of the interface-dominated nature of Li₂ S deposition. Accordingly, increasing efforts have been devoted to interface engineering for efficient Li₂ S deposition, which has attained inspiring success to date. However, a systematic overview and in-depth understanding of this critical field are still absent. In this review, the principles of interface-controlled Li₂ S precipitation are presented, clarifying the pivotal roles of electrolyte-substrate and electrolyte-Li₂ S interfaces in regulating Li₂ S depositing behavior. For the optimization of the electrolyte-substrate interface, efforts on the design of substrates including metal compounds, functionalized carbons, and organic compounds are systematically summarized. Regarding the regulation of electrolyte-Li₂ S interface, the progress of applying polysulfides catholytes, redox mediators, and high-donicity/polarity electrolytes is overviewed in detail. Finally, the challenges and possible solutions aiming at optimizing Li₂ S deposition are given for further development of practical LSBs. This review would inspire more insightful works and, more importantly, may enlighten other electrochemical areas concerning heterogeneous deposition processes.