Stepped Channels Integrated Lithium–Sulfur Separator via Photoinduced Multidimensional Fabrication of Metal–Organic Frameworks

Pristine MOF Materials for Separator Application in Lithium-Sulfur Battery

Lithium-sulfur (Li-S) batteries have attracted significant attention in the realm of electronic energy storage and conversion owing to their remarkable theoretical energy density and cost-effectiveness. However, Li-S batteries continue to face significant challenges, primarily the severe polysulfides shuttle effect and sluggish sulfur redox kinetics, which are inherent obstacles to their practical application. Metal-organic frameworks (MOFs), known for their porous structure, high adsorption capacity, structural flexibility, and easy synthesis, have emerged as ideal materials for separator modification. Efficient polysulfides interception/conversion ability and rapid lithium-ion conduction enabled by MOFs modified layers are demonstrated in Li-S batteries. In this perspective, the objective is to present an overview of recent advancements in utilizing pristine MOF materials as modification layers for separators in Li-S batteries. The mechanisms behind the enhanced electrochemical performance resulting from each design strategy are explained. The viewpoints and crucial challenges requiring resolution are also concluded for pristine MOFs separator in Li-S batteries. Moreover, some promising materials and concepts based on MOFs are proposed to enhance electrochemical performance and investigate polysulfides adsorption/conversion mechanisms. These efforts are expected to contribute to the future advancement of MOFs in advanced Li-S batteries.

Porous Organic Framework Materials (MOF, COF, and HOF) as the Multifunctional Separator for Rechargeable Lithium Metal Batteries

The separator is an important component in batteries, with the primary function of separating the positive and negative electrodes and allowing the free passage of ions. Porous organic framework materials have a stable connection structure, large specific surface area, and ordered pores, which are natural places to store electrolytes. And these materials with specific functions can be designed according to the needs of researchers. The performance of porous organic framework-based separators used in rechargeable lithium metal batteries is much better than that of polyethylene/propylene separators. In this paper, the three most classic organic framework materials (MOF, COF, and HOF) are analyzed and summarized. The applications of MOF, COF, and HOF separators in lithium-sulfur batteries, lithium metal anode, and solid electrolytes are reviewed. Meanwhile, the research progress of these three materials in different fields is discussed based on time. Finally, in the conclusion, the problems encountered by MOF, COF, and HOF in different fields as well as their future research priorities are presented. This review will provide theoretical guidance for the design of porous framework materials with specific functions and further stimulate researchers to conduct research on porous framework materials.

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.

Size Effect for Inhibiting Polysulfides Shuttle in Lithium-Sulfur Batteries

It is undeniable that the dissolution of polysulfides is beneficial in speeding up the conversion rate of sulfur in electrochemical reactions. But it also brings the bothersome "shuttle effect". Therefore, if polysulfides can be retained on the cathode side, the efficient utilization of the polysulfides can be guaranteed to achieve the excellent performance of lithium-sulfur batteries. Based on this idea, considerable methods have been developed to inhibit the shuttling of polysulfides. It is necessary to emphasize that no matter which method is used, the solvation mechanism, and existence forms of polysulfides are essential to analyze. Especially, it is important to clarify the sizes of different forms of polysulfides when using the size effect to inhibit the shuttling of polysulfides. In this review, a comprehensive summary and in-depth discussion of the solvation mechanism, the existing forms of polysulfides, and the influencing factors affecting polysulfides species are presented. Meanwhile, the size of diverse polysulfide species is sorted out for the first time. Depending on the size of polysulfides, tactics of using size effect in cathode, separator, and interlayer parts are elaborated. Finally, a design idea of materials pore size is proposed to satisfy the use of size effect to inhibit polysulfides shuttle.

A Keggin Al13 -Montmorillonite Modified Separator Retards the Polysulfide Shuttling and Accelerates Li-Ion Transfer in Li-S Batteries

The commercialization of Li-S batteries as a promising energy system is terribly impeded by the issues of the shuttle effect and Li dendrite. Keggin Al13 -pillared montmorillonite (AlMMT), used as the modified film of the separator together with super-P and poly (vinylidene fluoride) (PVDF), has a good chemical affinity to lithium polysulfide (LiPS) to retard the polysulfide shuttling, excellent electrolyte wettability, and a stable structure, which can improve the rate capability and cycling stability of Li-S batteries. Density function theory (DFT) calculations reveal the strong adsorption ability of AlMMT for LiPS. Consequently, the modified film allows Li-S batteries to reach 902 mAh g-1 at 0.2C after 200 cycles and 625 mAh g-1 at 1C after 1000 cycles. More importantly, a high reversible areal capacity of 4.04 mAh cm-2 can be realized under a high sulfur loading of 6.10 mg cm-2 . Combining the merits of rich resources of montmorillonite, prominent performance, simple operation and cost-effectiveness together, this work exploits a new route for viable Li-S batteries for applications.

Coordination-Driven Heterochiral Self-Assembly: Construction of Cd(II) Coordination Polymers with Sorption Behaviors for Iodine and Dyes

A racemic bispyridyl ligand (L) was synthesized via a Schiff base condensation reaction. Four Cd(II) complexes, {[CdL2Cl2]·2DMF}n (1), [CdLI2]n (2), {[CdL2Br2]·4H2O}n (3), and {[CdL2(H2O)2](NO3)2·2CH3OH·8H2O}n (4), were synthesized and further characterized based on this ligand. Single-crystal structures show that the coordination-driven assembly of the bispyridyl ligand with Cd(II) salts bearing different counteranions can lead to multidimensional coordination polymers via a heterochiral self-discrimination process. Complex 1 exists as a one-dimensional (1D) looped chain polymer, and complex 2 exists as a 1D zigzag chain polymer. Complex 3 is a 2D grid coordination polymer, and complex 4 exists as a 3D framework polymer. Furthermore, the iodine sorption capacities of the four complexes were investigated in the solution of n-hexane and water as well as in the iodine steam. The dye sorption behaviors were investigated in water, which showed that complex 2 exhibited good adsorption for crystal violet (CV), while complex 4 had good adsorption capability toward direct yellow 4 (DY).

Co-based MOF heterogeneous catalyst for the efficient degradation of organic dye via peroxymonosulfate activation

In this study, a new cobalt-based metal-organic framework (JLNU-500), [Co2(OH)(PBA)(AIP)]·3DMA·0.75H2O (4-(pyridin-4-yl) benzoic acid (HPBA), 5-aminoisophthalic acid (H2AIP) and N,N-dimethylacetamide (DMA)), was fabricated using a solvothermal method. JLNU-500 has 3D network architecture with 1D nanopore channels. The prepared JLNU-500 can activate peroxymonosulfate (PMS) for Rhodamine B (RhB) dye decolorization. Interestingly, catalyst JLNU-500 exhibited high efficiency for PMS activation, and nearly 100% (above 99.8%) removal of RhB with a high concentration (50.0 mg L-1, 100 mL) was achieved within 6 min. The reaction rate constant of the JLNU-500/PMS system was 1.02 min-1 calculated based on the pseudo-first-order kinetics, which is higher than that of the other reported catalysts. Furthermore, the factors, which could influence PMS activation were also investigated, such as PMS dosage, catalyst dosage, pollutant RhB concentration, reaction temperature and solution pH. More importantly, the radical trapping experiments ferreted out that sulfate (SO4˙-) and hydroxyl (˙OH) radicals were the dominating oxidants in the removal of RhB. Moreover, the possible degradation mechanism was elucidated. This study provides new prospects for fabricating new MOFs that can potentially be employed for high-efficiency catalytic oxidation as heterogeneous catalysts.

Li+ mobility powered by a crystal compound for fast Li-S chemistry

Placing blocking layers between electrodes has shown paramount prospects in suppressing the shuttle effect of Li-S batteries, but the associated ionic transport would be a concurrent obstacle. Herein, we present a Li-based crystal composited with carbon (LiPN2@C) by a one-step annealing of Li+ absorbed melamine polyphosphate, which simultaneously achieves alleviated polysulfide-shuttling and facilitated Li+ transport. As a homologous crystal, LiPN2 with abundant lithiophilic sites makes Li+ transport more efficient and sustainable. With a LiPN2@C-modified separator, the Li2S cathode exhibits a much-lower activation potential of 2.4 V and a high-rate capacity of 519 mA h g-1 at 2C. Impressively, the battery delivers a capacity of 726 mA h g-1 at 0.5C with a low decay rate of 0.25% per cycle during 100 continuous cycles.

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.

Donor-Acceptor Conjugated Microporous Polymer toward Enhanced Redox Kinetics in Lithium-Sulfur Batteries

Conjugated microporous polymers (CMPs) with porous structure and rich polar units are favorable for high-performance lithium-sulfur (Li-S) batteries. However, understanding the role of building blocks in polysulfide catalytic conversion is still limited. In this work, two triazine-based CMPs are constructed by electron-accepting triazine with electron-donating triphenylbenzene (CMP-B) or electron-accepting triphenyltriazine (CMP-T), which can grow on a conductive carbon nanotube (CNT) to serve as separator modifiers for Li-S batteries. CMP-B@CNT features faster ion transportation than the counterpart of CMP-T@CNT. More importantly, compared with acceptor-acceptor (A-A) CMP-T, donor-acceptor (D-A) CMP-B possesses a higher degree of conjugation and a narrower band gap, which are conducive to the electron transfer along the polymer skeleton, thus accelerating the sulfur redox kinetics. Consequently, the CMP-B@CNT functional separator endows Li-S cells with an outstanding initial capacity of 1371 mAh g^-1 at 0.1 C and favorable cycling stability with a capacity degradation rate of 0.048% per cycle at 1 C for 800 cycles. This work provides insight into the rational design of efficient catalysts for advanced Li-S batteries.

Advances of Electroactive Metal-Organic Frameworks

The preparation of electroactive metal-organic frameworks (MOFs) for applications of supercapacitors and batteries has received much attention and remarkable progress during the past few years. MOF-based materials including pristine MOFs, hybrid MOFs or MOF composites, and MOF derivatives are well designed by a combination of organic linkers (e.g., carboxylic acids, conjugated aromatic phenols/thiols, conjugated aromatic amines, and N-heterocyclic donors) and metal salts to construct predictable structures with appropriate properties. This review will focus on construction strategies of pristine MOFs and hybrid MOFs as anodes, cathodes, separators, and electrolytes in supercapacitors and batteries. Descriptions and discussions follow categories of electrochemical double-layer capacitors (EDLCs), pseudocapacitors (PSCs), and hybrid supercapacitors (HSCs) for supercapacitors. In contrast, Li-ion batteries (LIBs), Lithium-sulfur batteries (LSBs), Lithium-oxygen batteries (LOBs), Sodium-ion batteries (SIBs), Sodium-sulfur batteries (SSBs), Zinc-ion batteries (ZIBs), Zinc-air batteries (ZABs), Aluminum-sulfur batteries (ASBs), and others (e.g., LiSe, NiZn, H⁺ , alkaline, organic, and redox flow batteries) are categorized for batteries.

Ir Nanoparticles Anchored on Metal-Organic Frameworks for Efficient Overall Water Splitting under pH-Universal Conditions

The construction of high-activity and low-cost electrocatalysts is critical for efficient hydrogen production by water electrolysis. Herein, we developed an advanced electrocatalyst by anchoring well-dispersed Ir nanoparticles on nickel metal-organic framework (MOF) Ni-NDC (NDC: 2,6-naphthalenedicarboxylic) nanosheets. Benefiting from the strong synergy between Ir and MOF through interfacial Ni-O-Ir bonds, the synthesized Ir@Ni-NDC showed exceptional electrocatalytic performance for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and overall water splitting in a wide pH range, superior to commercial benchmarks and most reported electrocatalysts. Theoretical calculations revealed that the charge redistribution of Ni-O-Ir bridge induced the optimization of H₂ O, OH* and H* adsorption, thus leading to the accelerated electrochemical kinetics for HER and OER. This work provides a new clue to exploit bifunctional electrocatalysts for pH-universal overall water splitting.

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.

Single Zinc Atom Aggregates: Synergetic Interaction to Boost Fast Polysulfide Conversion in Lithium-Sulfur Batteries

Single-atom catalysts (SACs) pave new possibilities to improve the utilization efficiency of sulfur electrodes arising from polysulfide shuttle effects and sluggish kinetics due to their excellent applicability in atomic-scale reaction mechanisms and structure-activity relationships. Herein, nitrogen (N)-anchored SACs on the highly ordered N-doped carbon nanotube arrays are reported as the sulfur host for fast redox conversion in lithium-sulfur (Li-S) batteries. The cube structure of the aligned carbon nanotubes can promote the rapid mass transfer under high sulfur loadings, and abundant single-atom active sites further accelerate the conversion of lithium polysulfides (LiPSs). The synergistic enhancement effect induced by adjacent single atoms with interatomic distances <1 nm further accelerates the rapid multi-step reaction of sulfur at high sulfur loadings. As a result, the obtained Li-S batteries exhibit outstanding cycle stability with a high areal capacity of 5.6 mAh cm^-2 after 100 cycles under a high sulfur loading of 7.2 mg cm^-2 (electrolyte to sulfur ratio is ≈3.7 mL g^-1 ). Even assembled into a pouch cell, it still delivers a high capacity of 953.4 mAh g^-1 after 100 cycles at 0.1 C, contributing to the development of the practically viable Li-S batteries.

Anisotropically Hybridized Porous Crystalline Li-S Battery Separators

Anisotropically hybridized porous crystalline Li-S battery separators based on porous crystalline materials that can meet the multiple functionalities of both anodic and cathodic sides are much desired for Li-S battery yet still challenging in directional design. Here, an anisotropically hybridized separator (CPM) based on an ionic liquid-modified porphyrin-based covalent-organic framework (COF-366-OH-IL) and catalytically active metal-organic framework (Ni₃ (HITP)₂ ) that can integrate the lithium-polysulfides (LiPSs) adsorption/catalytic conversion and ion-conduction sites together to directionally meet the requirements of electrodes is reported. Remarkably, the-obtained separator exhibits an exceptional high Li⁺ transference-number (t_Li+  = 0.8), ultralow polarization-voltage (<30 mV), high initial specific-capacity (921.38 mAh g^-1 at 1 C), and stable cycling-performance, much superior to polypropylene and monolayer-modified separators. Moreover, theoretical calculations confirm the anisotropic effect of CPM on the anodic side (e.g., Li⁺ transfer, LiPSs adsorption, and anode-protection) and cathodic side (e.g., LiPSs adsorption/catalysis). This work might provide a new perspective for separator exploration.

Design of an Internal/External Bicontinuous Conductive Network for High-Performance Asymmetrical Supercapacitors

High-energy density supercapacitors have attracted extensive attention due to their electrode structure design. A synergistic effect related to core-shell structure can improve the energy storage capacity and power density of electrode materials. The Ni-foam (NF) substrate coupled with polypyrrole (PPy) conductive coating can serve as an internal/external bicontinuous conductive network. In this work, the distinctive PPy@FeNi₂S₄@NF and PPy@NiCo₂S₄@NF materials were prepared by a simple two-step hydrothermal synthesis with a subsequent in situ polymerization method. PPy@FeNi₂S₄@NF and PPy@NiCo₂S₄@NF could deliver ultrahigh specific capacitances of 3870.3 and 5771.4 F·g^-1 at 1 A·g^-1 and marvelous cycling capability performances of 81.39% and 93.02% after 5000 cycles. The asymmetric supercapacitors composed of the prepared materials provided a high-energy density of over 47.2 Wh·kg^-1 at 699.9 W·kg^-1 power density and 67.11 Wh·kg^-1 at 800 W·kg^-1 power density. Therefore, the self-assembled core-shell structure can effectively improve the electrochemical performance and will have an effective service in advanced energy-storage devices.

Metal-Organic Frameworks Functionalized Separators for Robust Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are one of the promising energy storage systems, which consist of electrode materials, electrolyte, and separator. The first two have been significantly received ample development, while the prominent role of the separators in manipulating the stability of the electrode has not attracted sufficient attention. In this work, a separator (UiO-66-GF) modified by Zr-based metal organic framework for robust AZIBs is proposed. UiO-66-GF effectively enhances the transport ability of charge carriers and demonstrates preferential orientation of (002) crystal plane, which is favorable for corrosion resistance and dendrite-free zinc deposition. Consequently, Zn|UiO-66-GF-2.2|Zn cells exhibit highly reversible plating/stripping behavior with long cycle life over 1650 h at 2.0 mA cm^-2, and Zn|UiO-66-GF-2.2|MnO₂ cells show excellent long-term stability with capacity retention of 85% after 1000 cycles. The reasonable design and application of multifunctional metal organic frameworks modified separators provide useful guidance for constructing durable AZIBs.

Two-Dimensional Imide-Based Covalent Organic Frameworks with Tailored Pore Functionality as Separators for High-Performance Li-S Batteries

Modifying the separator of lithium-sulfur batteries (LSBs) is considered to be one of the most effective strategies for relieving the notorious polysulfide shuttle effect. Constructing a stable, lightweight, and effective LSB separator is still a big challenge but highly desirable. Herein, a stable and lightweight imide-based covalent organic framework (COF-TpPa) is facilely fabricated on reduced graphene oxide (rGO) through an oxygen-free solvothermal technique. With the directing effect of rGO and changing the side functional group of the monomer, the morphology and the pore tailoring of COF-TpPa can be simultaneously achieved and two-dimensional (2D) COF nanosheets with different functionalities (such as -SO₃H and -Cl) are successfully constructed on rGO films. The specific functional groups inside the COF's pore channels and the narrowed pore size result in efficient absorption and restriction of Li₂S_n for weakening the "shuttle effect". Meanwhile, the 2D COF nanosheets on the rGO is a favorable morphology for better exploiting pores inside the COF materials. As a result, the COF-SO₃H-modified separator, consisting of rGO and COF-TpPa-SO₃H, exhibits a high specific capacity (1163.4 mA h/g at 0.2 C) and a desirable cyclic performance (60.2% retention rate after 1000 cycles at 2.0 C) for LSBs. Our study provides a feasible strategy to rationally design functional COFs and boosts their applications in various energy storage systems.

Metal-Organic Frameworks Functionalized Separators for Lithium-Sulfur Batteries

Lithium sulfur batteries (LSBs) have attracted tremendous attention owing to their high theoretical specific capacity and specific energy. However, their practical applications are hindered by poor cyclic life, mainly caused by polysulfide shuttling. The development of advanced materials to mitigate the polysulfide shuttling effect is urgently demanded. Metal-organic frameworks (MOFs) have been exploited as multifunctional materials for the decoration of separators owing to their high surface area, structural diversity, tunable pore size, and easy tailor ability. In this review, we aim to present the state-of-the-art MOF-based separators for LSBs. Particular attention is paid to the rational design (pore aperture, metal node, functionality, and dimension) of MOFs with enhanced ability for anchoring polysulfides and facilitating Li⁺ transportation. Finally, the challenges and perspectives are provided regarding to the future design MOF-based separators for high-performance LSBs.

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

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

Constructing MIL-101(Cr) membranes on carbon nanotube films as ion-selective interlayers for lithium-sulfur batteries

It is of significant importance to suppress the polysulfide shuttle effect for the commercial application of lithium-sulfur batteries. Herein, continuous MIL-101(Cr) membranes were successfully fabricated on carbon nanotube films utilizing a simplein situgrowth method, aiming at constructing interlayer materials for inhibiting the shuttle effect. Owing to the suitable pore aperture and super electrolyte wettability, the as-developed MIL-101(Cr) membrane can effectively inhibit the shuttle behaviour of polysulfides while allowing the fast transport of Li-ions simultaneously, working as an ionic sieve. Additionally, this MOFs membrane is also helpful in accelerating the polysulfide catalytic conversion. Therefore, the proposed interlayer delivers an extraordinary rate capability, showing a remarkable capacity of 661.9 mAh g^-1under 5 C. Meanwhile, it also exhibits a high initial capacity of 816.1 mAh g^-1at 1 C and an exceptional durability with an extremely low capacity fading of 0.046% per cycle over 500 cycles.

Heterogeneous activation of peroxymonosulfate by stable Co-MOF for the efficient degradation of organic dye pollutants

A new Co-MOF with splendid stability can act as an excellent heterogeneous catalyst to activate peroxymonosulfate, exhibiting highly efficient organic dye degradation in aquatic environments.

MgCo layered double hydroxide-based yolk shell polyhedrons as multifunctional sulfur mediator for lithium-sulfur batteries

The development of efficient sulfur host materials to address the shuttle effect issues of lithium polysulfides (LiPSs) is crucial in the lithium-sulfur (Li-S) batteries but still challenging. In the present study, a novel yolk shell structured MgCo-LDH/ZIF-67 composite is designed as Li-S battery cathode. In this composite, the shell layer is MgCo layered double hydroxide constructed by partially etching ZIF-67 nanoparticle by Mg²⁺, and the core is the unreacted ZIF-67 particle. The unique yolk shell structure not only provides abundant pores for sulfur accommodation, but also facilitates the electrolyte penetration and ion transport. The ZIF-67 core exhibits strong polar adsorption to LiPSs through the Lewis acid-base interactions, and the micropores/mesoporous can further trap LiPSs. Meanwhile, the MgCo-LDH shell exposes enough sulfur-philic sites for enhancing chemisorption and catalyzes LiPSs conversion. As a result, when MgCo-LDH/ZIF-67 is used as sulfur host in the cathode, the cell achieves a high discharge capacity of 1121 mAh g^-1at 0.2 C, and an areal capacity of 5.0 mAh cm^-2under high sulfur loading of 5.8 mg cm^-2. The S/MgCo-LDH/ZIF-67 electrode holds a promising potential for the development of Li-S batteries.

A novel free-standing metal organic frameworks-derived cobalt sulfide polyhedron array for shuttle effect suppressive lithium-sulfur batteries

Metal-organic-frameworks-derived nanostructures have received broad attention for secondary batteries. However, many strategies focus on the preparation of dispersive materials, which need complicated steps and some additives for making electrodes of batteries. Here, we develop a novel free-standing Co₉S₈polyhedron array derived from ZIF-67, which grows on a three-dimensional carbon cloth for lithium-sulfur (Li-S) battery. The polar Co₉S₈provides strong chemical binding to immobilize polysulfides, which enables efficiently suppressing of the shuttle effect. The free-standing S@Co₉S₈polyhedron array-based cathode exhibits ultrahigh capacity of 1079 mAh g^-1after cycling 100 times at 0.1 C, and long cycling life of 500 cycles at 1 C, recoverable rate-performance and good temperature tolerance. Furthermore, the adsorption energies towards polysulfides are investigated by using density functional theory calculations, which display a strong binding with polysulfides.

Homogeneous and Fast Li-Ion Transport Enabled by a Novel Metal-Organic-Framework-Based Succinonitrile Electrolyte for Dendrite-Free Li Deposition

Lithium (Li) metal has emerged as a promising electrode material for high-energy-density batteries. However, serious Li dendrite issues during cycling have plagued the safety and cyclability of the batteries, thus limiting the practical application of Li metal batteries. Herein, we prepare a novel metal-organic-framework-based (MOF-based) succinonitrile electrolyte, which enables homogeneous and fast Li-ion (Li+) transport for dendrite-free Li deposition. Given the appropriate aperture size of the MOF skeleton, the targeted electrolyte can allow only small-size Li+ to pass through its pores, which effectively guides uniform Li+ transport. Specially, Li ions are coordinated by the C═N of the MOF framework and the C≡N of succinonitrile, which could accelerate Li+ migration jointly. These characteristics afford an excellent quasi-solid-state electrolyte with a high ionic conductivity of 7.04 × 10-4 S cm-1 at room temperature and a superior Li+ transference number of 0.68. The Li/LiFePO4 battery with the MOF-based succinonitrile electrolyte exhibits dendrite-free Li deposition during the charge process, accompanied by a high capacity retention of 98.9% after 100 cycles at 0.1C.

Rational Design of MOF-Based Materials for Next-Generation Rechargeable Batteries

This review summarizes recent progresses in pristine metal–organic frameworks (MOFs), MOF composites, and their derivatives for next-generation rechargeable batteries including lithium–sulfur batteries, lithium–oxygen batteries, sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, and Zn–air batteries.

The design strategies for MOF-based materials as the electrode, separator, and electrolyte are outlined and discussed.

The challenges and development strategies and of MOF-related materials for battery applications are highlighted.

Metal–organic framework (MOF)-based materials with high porosity, tunable compositions, diverse structures, and versatile functionalities provide great scope for next-generation rechargeable battery applications. Herein, this review summarizes recent advances in pristine MOFs, MOF composites, MOF derivatives, and MOF composite derivatives for high-performance sodium-ion batteries, potassium-ion batteries, Zn-ion batteries, lithium–sulfur batteries, lithium–oxygen batteries, and Zn–air batteries in which the unique roles of MOFs as electrodes, separators, and even electrolyte are highlighted. Furthermore, through the discussion of MOF-based materials in each battery system, the key principles for controllable synthesis of diverse MOF-based materials and electrochemical performance improvement mechanisms are discussed in detail. Finally, the major challenges and perspectives of MOFs are also proposed for next-generation battery applications.

Rational Design and Growth of MOF-on-MOF Heterostructures

Multiporous metal-organic frameworks (MOFs) have emerged as a subclass of highly crystalline inorganic-organic materials, which are endowed with high surface areas, tunable pores, and fascinating nanostructures. Heterostructured MOF-on-MOF composites are recently becoming a research hotspot in the field of chemistry and materials science, which focus on the assembly of two or more different homogeneous or heterogeneous MOFs with various structures and morphologies. Compared with one single MOF, the dual MOF-on-MOF composites exhibit unprecedented tunability, hierarchical nanostructure, synergistic effect, and enhanced performance. Due to the difference of inorganic metals and organic ligands, the lattice parameters in a, b, and c directions in the single crystal cells could bring about subtle or large structural difference. It will result in the composite material with distinct growth methods to obtain secondary MOF grown from the initial MOF. In this review, the authors wish to mainly outline the latest synthetic strategies of heterostructured MOF-on-MOFs and their derivatives, including ordered epitaxial growth, random epitaxial growth, etc., which show the tutorial guidelines for the further development of various MOF-on-MOFs.

Progress and Prospect of Organic Electrocatalysts in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries featured by ultra-high energy density and cost-efficiency are considered the most promising candidate for the next-generation energy storage system. However, their pragmatic applications confront several non-negligible drawbacks that mainly originate from the reaction and transformation of sulfur intermediates. Grasping and catalyzing these sulfur species motivated the research topics in this field. In this regard, carbon dopants with metal/metal-free atoms together with transition-metal complex, as traditional lithium polysulfide (LiPS) propellers, exhibited significant electrochemical performance promotions. Nevertheless, only the surface atoms of these host-accelerators can possibly be used as active sites. In sharp contrast, organic materials with a tunable structure and composition can be dispersed as individual molecules on the surface of substrates that may be more efficient electrocatalysts. The well-defined molecular structures also contribute to elucidate the involved surface-binding mechanisms. Inspired by these perceptions, organic electrocatalysts have achieved a great progress in recent decades. This review focuses on the organic electrocatalysts used in each part of Li-S batteries and discusses the structure-activity relationship between the introduced organic molecules and LiPSs. Ultimately, the future developments and prospects of organic electrocatalysts in Li-S batteries are also discussed.