High-Entropy Alloys to Activate the Sulfur Cathode for Lithium-Sulfur Batteries

Sulfur element possesses an ultrahigh theoretical specific capacity,while the utilization of sulfur in the whole cathode is lower obviously owing to the sluggish kinetics of sulfur and discharged products,limiting the enhancement on energy density of lithium-sulfur batteries.Herein,for the first time,Fe_(0.24)Co_(0.26)Ni_(0.10)Cu_(0.15)Mn_(0.25)high-entropy alloy is introduced as the core catalytic host to activate the electrochemical performance of the sulfur cathode for lithium-sulfur batteries.It is manifested that Fe_(0.24)Co_(0.26)Ni_(0.10)Cu_(0.15)Mn_(0.25)high-entropy alloy nanocrystallites distributed on nitrogen-doped carbon exhibit high electrocatalytic activity toward the conversion of solid sulfur to solid discharged products across soluble intermediate lithium polysulfides.In particular,benefiting from the accelerated kinetics by high-entropy alloy nanocrystallites and synergistic adsorption by nitrogen-doped carbon,the cathode exhibits high reversible capacity of 1079.5 mAh g_(-cathode)^(-1)(high utilization of 89.4%)with the whole cathode as active material,instead of sulfur element.Moreover,under both lean electrolyte(3μmg^(-1))and ultrahigh sulfur loading(27.0 mg cm^(-2))condition,the high discharge capacity of 868.2 mAh g_(-cathode)^(-1)can be still achieved for the sulfur cathode.This strategy opens up a new path to explore catalytic host materials for enhancing the utilization of sulfur in the whole cathode for lithium-sulfur batteries.

Dry electrode technology for scalable and flexible high-energy sulfur cathodes in all-solid-state lithium-sulfur batteries

All-solid-state lithium-sulfur batteries(ASSLSBs)employing sulfide solid electrolytes are one of the most promising next-generation energy storage systems due to their potential for higher energy density and safety.However,scalable fabrication of sheet-type sulfur cathodes with high sulfur loading and excellent performances remains challenging.In this work,sheet-type freestanding sulfur cathodes with high sulfur loading were fabricated by dry electrode technology.The unique fibrous morphologies of polytetrafluoroethylene(PTFE)binders in dry electrodes not only provides excellent mechanical properties but also uncompromised ionic/electronic conductance.Even employed with thickened dry cathodes with high sulfur loading of 2 mg cm^(-2),ASSLSBs still exhibit outstanding rate performance and cycle stability.Moreover,the all-solid-state lithium-sulfur monolayer pouch cells(9.2 m Ah)were also demonstrated and exhibited excellent safety under a harsh test situation.This work verifies the potential of dry electrode technology in the scalable fabrication of thickened sulfur cathodes and will promote the practical applications of ASSLSBs.

A hydrophilic poly(methyl vinyl ether-alt-maleic acid) polymer as a green, universal, and dual-functional binder for high-performance silicon anode and sulfur cathode

Binders could play crucial or even decisive roles in the fabrication of low-cost, stable and high-capacity electrodes. This is especially the case for the silicon (Si) anodes and sulfur (S) cathodes that undergo large volume change and active material loss in lithium-ion batteries during prolonged cycles. Herein, a hydrophilic polymer poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) was explored as a dual-functional aqueous binder for the preparation of high-performance silicon anode and sulfur cathode. Benefiting from the dual functions of PMVEMA, i.e., the excellent dispersion ability and strong binding forces, the as-prepared electrodes exhibit improved capacity, rate capability and long-term cycling performance. In particular, the as-prepared Si electrode delivers a high initial discharge capacity of 1346.5 mAh g^(−1) at a high rate of 8.4 A/g and maintains 834.5 mAh g^(−1) after 300 cycles at 4.2 A/g, while the as-prepared S cathode exhibits enhanced cycling performance with high remaining discharge capacities of 663.4 mAh g^(−1) after 100 cycles at 0.2 C and 487.07 mAh g^(−1) after 300 cycles at 1 C, respectively. These encouraging results suggest that PMVEMA could be a universal binder to facilitate the green manufacture of both anode and cathode for high-capacity energy storage systems.

A multi-functional binder for high loading sulfur cathode

Lithium sulfur(Li-S)batteries are the promising power sources,but their commercialization is significantly impeded by poor energy-storage functions at high sulfur loading.Here we report that such an issue can be effectively addressed by using a mussel-inspired binder comprised of chitosan grafted with catecholic moiety for sulfur cathodes.The resulting sulfur cathodes possess a high loading up to 12.2 mg cm-2 but also exhibit one of the best electrochemical properties among their counterparts.The excellent performances are attributed to the strong adhesion of the binder to sulfur particles,conducting agent,current collector,and polysulfide.The versatile adhesion effectively increases the sulfur loading,depresses the shuttle effect,and alleviates mechanical pulverization during cycling processes.The present investigation offers a new insight into high performance sulfur cathodes through a bio-adhesion viewpoint.

Metal phosphides and borides as the catalytic host of sulfur cathode for lithium–sulfur batteries

Lithium−sulfur batteries are one of the most competitive high-energy batteries due to their high theoretical energy density of _(2)600 W·h·kg^(−1).However,their commercialization is limited by poor cycle stability mainly due to the low intrinsic electrical conductivity of sulfur and its discharged products(Li_(2)S_(2)/Li_(2)S),the sluggish reaction kinetics of sulfur cathode,and the“shuttle effect”of soluble intermediate lithi-um polysulfides in ether-based electrolyte.To address these challenges,catalytic hosts have recently been introduced in sulfur cathodes to en-hance the conversion of soluble polysulfides to the final solid products and thus prevent the dissolution and loss of active-sulfur material.In this review,we summarize the recent progress on the use of metal phosphides and borides of different dimensions as the catalytic host of sulfur cathodes and demonstrate the catalytic conversion mechanism of sulfur cathodes with the help of metal phosphides and borides for high-en-ergy and long-life lithium-sulfur batteries.Finally,future outlooks are proposed on developing advanced catalytic host materials to improve battery performance.

A functional hyperbranched binder enabling ultra-stable sulfur cathode for high-performance lithium-sulfur battery

Binders are of vital importance in stabilizing the cathodes to enhance the cycling stability of lithiumsulfur(Li-S) batteries. However, conventional binders are typically confronted with the drawback of inability for adsorbing lithium polysulfide(Li PS), thus resulting in severe active material losing and rapid capacity fading. Herein, a novel water-soluble hyperbranched poly(amidoamine)(HPAA) binder with controllable hyperbranched molecular structure and abundant amino end groups for Li-S battery is designed and fabricated, which can improve efficient adsorption for Li PS and stability of the sulfur cathodes. Besides, the strong intermolecular hydrogen bonds in HPAA binder can contribute to the structural stability of S cathode and integration of the conductive paths. Therefore, the Li-S battery with this functional binder exhibits excellent cycle performance with a capacity retention of 91% after 200 cycles at 0.1 C.Even at a high sulfur loading of 5.3 mg cm-2, a specific capacity of 601 mA h g-1 can also be achieved.Density functional theory(DFT) calculation further demonstrates that the enhanced electrochemical stability derives from the high binding energy between amino groups and LiP S and the wide electrochemical window(6.87 e V) of HPAA molecule. Based on the above all, this functional polymer will lighten a new species of binders for eco-friendly sulfur cathodes and significantly promote the practical applications of high-performance Li-S batteries.

Synthesis and application of single-atom catalysts in sulfur cathode for high-performance lithium–sulfur batteries

Lithium–sulfur(Li-S)batteries are regarded as one of the most promising energy storage devices because of their low cost,high energy density,and environmental friendliness.However,Li-S batteries suffer from sluggish reaction kinetics and serious“shuttle effect”of lithium polysulfides(LiPSs),which causes rapid decay of battery capacity and prevent their practical application.To address these problems,introducing single-atom catalysts(SACs)is an effective method to improve the electrochemical performance of Li-S batteries,due to their high catalytic efficiency and definite active sites for LiPSs.In this paper,we summarized the latest developments in enhancing the electrochemical performance of cathode for Li-S batteries through introducing different SACs.Furthermore,we briefly introduced the catalytic mechanism of SACs and discussed the strategies of synthesizing SACs,including the spatial confinement strategy and the coordination design strategy.Finally,the challenges and prospects in this field are proposed.We believe that this review would help to design and fabricate high-performance Li-S batteries via introducing SACs and boost their practical application.

Concurrent hetero-/homo-geneous electrocatalysts to bi-phasically mediate sulfur species for lithium-sulfur batteries

Expediting redox kinetics of sulfur species on conductive scaffolds with limited charge accessible surface is considered as an imperative approach to realize energy-dense and power-intensive lithium-sulfur(Li-S)batteries.In this work,the concept of concurrent hetero-/homo-geneous electrocatalysts is proposed to simultaneously mediate liquid-solid conversion of lithium polysulfides(LiPSs)and solid lithium disulfide/sulfide(Li_(2)S_(2)/Li_(2)S)propagation,the latter of which suffers from sluggish reduction kinetics due to buried conductive scaffold surface by extensive deposition of Li_(2)S_(2)/Li_(2)S.The selected model material to verify this concept is a two-in-one catalyst:carbon nanotube(CNT)scaffold supported iron-cobalt(Fe-Co)alloy nanoparticles and partially carbonized selenium(C-Se)component.The Fe-Co alloy serves as a heterogeneous electrocatalyst to seed Li_(2)S_(2)/Li_(2)S through sulphifilic active sites,while the C-Se sustainably releases soluble lithium polyselenides and functions as a homogeneous electrocatalyst to propagate Li_(2)S_(2)/Li_(2)S via solution pathways.Such bi-phasic mediation of the sulfur species benefits reduction kinetics of LiPS conversion,especially for the massive Li_(2)S_(2)/Li_(2)S growth scenario by affording an additional solution directed route in case of conductive surface being largely buried.This strategy endows the Li-S batteries with improved cycling stability(836 mA h g^(-1)after 180 cycles),rate capability(547 mA h g^(-1)at 4 C)and high sulfur loading superiority(2.96 mA h cm^(-2)at 2.4 mg cm^(-2)).This work hopes to enlighten the employment of bi-phasic electrocatalysts to dictate liquid-solid transformation of intermediates for conversion chemistry batteries.

Biomass-derived porous carbon with single-atomic cobalt toward high-performance aqueous zinc-sulfur batteries at room temperature

Aqueous zinc-sulfur batteries at room temperature hold great potential for next-generation energy storage technology due to their low cost,safety and high energy density.However,slow reaction kinetics and high activation energy at the sulfur cathode pose great challenges for the practical applications.Herein,biomass-derived carbon with single-atomic cobalt sites(MMPC-Co)is synthesized as the cathode in Zn-S batteries.The catalysis of single-atom Co sites greatly promotes the transform of cathode electrolyte interface(CEI)on the cathode surface,while offering accelerated charge transfer rate for high conversion reversibility and large electrochemical surface area(ECSA)for high electrocatalytic current.Furthermore,the rich pore structure not only physically limits sulfur loss,but also accelerates the transport of zinc ions.In addition,the large pore volume of MMPC-Co is able to relieve the stress effect caused by the volume expansion of Zn S during charge/discharge cycles,thereby maintaining the stability of electrode structure.Consequently,the sulfur cathode maintains a high specific capacity of 729.96 m A h g^(-1)after 500 cycles at4 A g^(-1),which is much better than most cathode materials reported in the literature.This work provides new insights into the design and development of room-temperature aqueous Zn-S batteries.

Cathode host engineering for non-lithium(Na,K and Mg)sulfur/selenium batteries:A state-of-the-art review

Sulfur and selenium have been paid more and more attention in energy storage systems because of their high theoretical specific gravimetric and volumetric capacities.With the increasing scarcity of lithium resources,secondary batteries made of sulfur and selenium coupled with other alkali metal/alkaline earth metals(e.g.Na,K,Mg)are expected to play a vital role in future production and human life.Due to the volume expansion,poor conductivity and shuttle effect,the structure design of cathode,as one of the important roles in metal-S/Se batteries,has always been a hot and difficult point.In the review,various host materials of S and Se are clarified and discussed.Typically,carbonaceous materials are the most widely used hosts,while polar materials are becoming more and more popular in metal-S/Se batteries.Through a comprehensive overview,it is hoped that previous research experiences can provide further reference and guidance for the sustainable development of metal-S/Se batteries.

A high-loading and cycle-stable solid-phase conversion sulfur cathode using edible fungus slag-derived microporous carbon as sulfur host

Developing a high sulfur(S)-loading cathode with high capacity utilization and long term cyclability is a key challenge for commercial implementation of Li-S battery technology.To overcome this challenge,we propose a solid-phase conversion sulfur cathode by using an edible fungus slag-derived porous carbon(CFS)as sulfur host to fabricate the S/CFS composite and meanwhile,utilizing the vinyl carbonate(VC)as co-solvent of the ether-based electrolyte to in-situ form a protective layer on the S/CFS composite surface through its nucleophilic reaction with the freshly generated lithium polysulfides(LiPSs)at the very beginning of initial discharge,thus isolating the interior sulfur from the outer electrolyte and inhibiting the further generation of soluble LiPSs.Benefitting from the ultrahigh specific surface area of>3,000 m^(2)·g^(−1),ideal pore size of<4 nm,and large pore volume of>2.0 cm^(3)·g^(−1)of the CFS host matrix,the S/CFS cathode even with a high S-loading of 80 wt.%(based on the weight of S/CFS composite)can still operate in a solid-phase conversion manner in the VC-ether co-solvent electrolyte to exhibit a high reversible capacity of 1,557 mAh·g^(−1),a high rate capability with 50%remaining capacity at 2 A·g^(−1)and a high cycling efficiency of 99.9%over 500 cycles.The results presented in this work suggest that a combined action of solid-phase conversion electrochemistry and nanoarchitectured host structure may provide a new path for the design and development of practical lithium-sulfur batteries.

Recent progress of flexible sulfur cathode based on carbon host for lithium-sulfur batteries

With the emergence and development of wearable devices,the novel ene rgy storage systems with flexible feature and high energy density are urgently needed.As we all know,for next generation high energystorage systems,lithium-sulfur(Li-S) batteries with a high theoretical capacity are regarded as one of the most promising candidates.In addition,the flexible Li-S batteries have received more and more attention.The determined factor in the flexible Li-S batteries is how to design the foldable electrodes including both anode and cathode.As for the flexible sulfur cathode,it could be obtained by integrating the electroactive sulfur with a flexible substrate,generally.In recent years,the flexible cathode of Li-S batteries have made considerable progress,however there are also many huge challenges needing to overcome,such as low content of sulfur,fast decrease of capacity and short cycle life.In this paper,the current develop status of flexible cathodes of Li-S batteries have been summarized,and the future trend also be pointed out.

Constructing high gravimetric and volumetric capacity sulfur cathode with LiCoO_(2)nanofibers as carbon-free sulfur host for lithium-sulfur battery

Although the gravimetric energy density of lithium-sulfur battery is very encouraging,the volumetric energy density still remains a challenge for the practical application.To achieve the high volumetric energy density of battery,much attention should be paid to the sulfur cathode.Herein,we introduce heavy lithium cobalt oxide(LiCoO_(2))nanofibers as sulfur host to enhance the volumetric capacity of cathode,maintaining the high gravimetric capacity simutaneously.With the high tap density of 2.26 g cm^(−3),LiCoO_(2)nanofibers can be used to fabricate a really compact sulfur cathode,with a density and porosity of 0.85 g cm^(−3)and 61.2%,respectively.More importantly,LiCoO2 nanofibers could act as an efficient electrocatalyst for enhancing the redox kinetics of sulfur species,ensuring the cathode electroactivity and alleviating the shuttle effect of polysulfides.Therefore,a balance between compact structure and high electrochemical activity is obtained for the sulfur cathode.At the sulfur loading of 5.1 mg cm^(−2),high volumetric and gravimetric capacities of 724 mA h cm^(−3)cathode and 848 mA h g^(−1)cathode could be achieved based on the cathode volume and weight,respectively.Moreover,with this efficient S/LiCoO_(2)cathode,the lithium corrosion by polysulfides is supressed,leading to a more stable lithium anode.

Designing principles of advanced sulfur cathodes toward practical lithium-sulfur batteries

As one of the most promising candidates for next-generation energy storage systems,lithium-sulfur(Li-S)batteries have gained wide attention owing to their ultrahigh theoretical energy density and low cost.Nevertheless,their road to commercial application is still full of thorns due to the inherent sluggish redox kinetics and severe polysulfides shuttle.Incorporating sulfur cathodes with adsorbents/catalysts has been proposed to be an effective strategy to address the foregoing challenges,whereas the complexity of sulfur cathodes resulting from the intricate design parameters greatly influences the corresponding energy density,which has been frequently ignored.In this review,the recent progress in design strategies of advanced sulfur cathodes is summarized and the significance of compatible regulation among sulfur active materials,tailored hosts,and elaborate cathode configuration is clarified,aiming to bridge the gap between fundamental research and practical application of Li-S batteries.The representative strategies classified by sulfur encapsulation,host architecture,and cathode configuration are first highlighted to illustrate their synergetic contribution to the electrochemical performance improvement.Feasible integration principles are also proposed to guide the practical design of advanced sulfur cathodes.Finally,prospects and future directions are provided to realize high energy density and long-life Li-S batteries.

Harnessing the unique features of MXenes for sulfur cathodes

Lithium-sulfur(Li-S)battery,as an emerging rechargeable energy-storage system,sparks intensive research enthusiasm owing to its high theoretical energy density.However,the sulfur cathode undergoes the low coulombic efficiency,poor rate and cycling performance,caused by the polysulfides shuttle,low conductivity and sluggish redox kinetics.To address the above issues,various hybrid sulfur cathodes are developed based on two-dimensional(2D)materials.Recently,2D transition metal carbides and nitrides(MXenes)are receiving intensive interest as matrix materials for sulfur cathodes owing to their favorable properties,such as superior electrical conductivity,abundant active sites and adjustable surface functional groups.In this review,we mainly summarize the development of novel hybrid sulfur cathodes by taking advantage of unique properties of MXenes.The different roles MXenes played in sulfur cathodes,including facilitating the electron transfer,tuning the adsorption of polysulfides and catalyzing polysulfides conversion,are well discussed.Finally,we propose the future strategies on the rational design of MXene-based sulfur cathodes with high performances.

Sulfide-Based All-Solid-State Lithium-Sulfur Batteries:Challenges and Perspectives

Lithium-sulfur batteries with liquid electrolytes have been obstructed by severe shuttle effects and intrinsic safety concerns.Introducing inorganic solid-state electrolytes into lithium-sulfur systems is believed as an effective approach to eliminate these issues without sacrificing the high-energy density,which determines sulfidebased all-solid-state lithium-sulfur batteries.However,the lack of design principles for high-performance composite sulfur cathodes limits their further application.The sulfur cathode regulation should take several factors including the intrinsic insulation of sulfur,well-designed conductive networks,integrated sulfur-electrolyte interfaces,and porous structure for volume expansion,and the correlation between these factors into account.Here,we summarize the challenges of regulating composite sulfur cathodes with respect to ionic/electronic diffusions and put forward the corresponding solutions for obtaining stable positive electrodes.In the last section,we also outlook the future research pathways of architecture sulfur cathode to guide the develop high-performance all-solid-state lithium-sulfur batteries.

High area-capacity Mg batteries enabled by sulfur/copper integrated cathode design

Rechargeable Mg batteries potentially display lower cost and competitive energy density compared with their Li-ion counterparts.However,the practical implementation of high area-capacity cathodes still remains a formidably challenging task.This work presents the sulfur/copper integrated cathodes fabricated by the conventional blade-coating process and slurry-dipping method.The sulfur/copper foil integrated cathodes deliver a high area-capacity of 2.6 mAh cm^(-2)after 40 cycles,while the sulfur/copperfoam integrated cathode exhibits an ultrahigh area-capacity of 35.4 mAh cm^(-2),corresponding to 743.1 Wh L^(-1)at the electrode level(1.5 times higher than the LiCoO_(2)-graphite system).The in-situ formed copper sulfide intermediates with sufficient cation defects can act as functional intermediates to regulate the sulfur electrochemistry during the first discharge process.The subsequent cycles are operated by the reversible displacement reaction between Mg-ions and copper sulfide active substances.In particular,the copper ions prefer to extrude along the[001]direction in copper sulfides lattice and simultaneously the rock-salt MgS crystals are generated.Besides,the nonuniform surface topography of the cycled Mgmetal anode,caused by the spatial inhomogeneity in current distribution,is demonstrated to lead to the battery performance degradation for high area-capacity Mg batteries.

Recent Advances and Applications Toward Emerging Lithium–Sulfur Batteries:Working Principles and Opportunities

Lithium–sulfur(Li-S)batteries have been considered as promising candidates for large-scale high energy density devices due to the potentially high energy density,low cost,and more pronounced ecological compatibility.However,the complex Li-S conversion reactions,unsatisfactory battery performance,and unsafe metallic Li anode restrict the development of Li-S batteries to achieve commercialization.This review mainly focuses on three aspects which are the remaining challenges,recent advances,and applications in Li-S batteries.Firstly,this review portrays Li-S conversion chemistry involving the multi-step and multi-electron reaction mechanism,as well as the remaining challenges.Then,the scientific strategies and very recent advances of the cathode,electrolyte,lithium anode,and other constituent parts of Li-S batteries are detailly summed up,as well as their advantages and limitations.For the sake of promoting the Li-S batteries practicalization,next section is primarily concerned with problems,the corresponding solutions,and application scenarios of practical pouch cells.Finally,the important findings as guidelines and some future directions as trends for developing emerging Li-S batteries are briefly summarized.

Status and perspectives of hierarchical porous carbon materials in terms of high-performance lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries,although a promising candidate of next-generation energy storage devices,are hindered by some bottlenecks in their roadmap toward commercialization.The key challenges include solving the issues such as low utilization of active materials,poor cyclic stability,poor rate performance,and unsatisfactory Coulombic efficiency due to the inherent poor electrical and ionic conductivity of sulfur and its discharged products(e.g.,Li2S2 and Li_(2)S),dissolution and migration of polysulfide ions in the electrolyte,unstable solid electrolyte interphase and dendritic growth on an odes,and volume change in both cathodes and anodes.Owing to the high specific surface area,pore volume,low density,good chemical stability,and particularly multimodal pore sizes,hierarchical porous carbon(HPC)mate rials have received considerable attention for circumventing the above pro blems in Li-S batteries.Herein,recent progress made in the synthetic methods and deployment of HPC materials for various components including sulfur cathodes,separators and interlayers,and lithium anodes in Li-S batteries is presented and summarized.More importantly,the correlation between the structures(pore volume,specific surface area,degree of pores,and heteroatom-doping)of HPC and the electrochemical performances of Li-S batteries is elaborated.Finally,a discussion on the challenges and future perspectives associated with HPCs for Li-S batteries is provided.

Polar, catalytic, and conductive CoSe2/C frameworks for performance enhanced S cathode in Li–S batteries

Lithium-sulfur battery(Li-S)is considered as one of the new-generation rechargeable batteries with high performance because of its extremely high theoretical capacity,energy density,environmental harmony and low cost.However,low electrical and ionic conductivity of sulfur,safety concerns and parasitic reaction generated by the dissolved polysulfide species in electrolyte hinder the commercialization of Li-S battery.Herein,we report a polyhedral porous structure comprising of carbon coating metal selenide nanoparticles(CoSe2/C),which could not only host sulfur for Li-S battery owing to its porous and conductive structure,but also mitigate the shuttle phenomenon by polysulfides adsorption and catalytic acceleration of redox kinetics.As a result,a performance enhanced CoSe2/C-S electrode for Li-S battery is achieved.