Spherical Macroporous Carbon Nanotube Particles with Ultrahigh Sulfur Loading for Lithium-Sulfur Battery Cathodes

Pinpointing the Cl Coordination Effect on Mn-N3-Cl Moiety Toward Boosting Reaction Kinetics and Suppressing Shuttle Effect in Li-S Batteries

Single atom catalysts (SACs) are highly favored in Li-S batteries due to their excellent performance in promoting the conversion of lithium polysulfides (LiPSs) and inhibiting their shuttling. However, the intricate and interrelated microstructures pose a challenge in deciphering the correlation between the chemical environment surrounding the active site and its catalytic activity. Here, a novel SAC featuring a distinctive Mn-N3-Cl moiety anchored on B, N co-doped carbon nanotubes (MnN3Cl@BNC) is synthesized. Subsequently, the selective removal of the Cl ligands while inheriting other microstructures is performed to elucidate the effect of Cl coordination on catalytic activity. The Cl coordination effectively enhances the electron cloud density of the Mn-N3-Cl moiety, reducing the band gap and increasing the adsorption capacity and redox kinetics of LiPSs. As a modified separator for Li-S batteries, MnN3Cl@BNC exhibits high capacities of 1384.1 and 743 mAh g-1 at 0.1 and 3C, with a decay rate of only 0.06% per cycle over 700 cycles at 1 C, which is much better than that of MnN3OH@BNC. This study reveals that Cl coordination positively contributes to improving the catalytic activity of the Mn-N3-Cl moiety, providing a fresh perspective for the design of high-performance SACs.

Developing Cathode Films for Practical All-Solid-State Lithium-Sulfur Batteries

The development of all-solid-state lithium-sulfur batteries (ASSLSBs) toward large-scale electrochemical energy storage is driven by the higher specific energies and lower cost in comparison with the state-of-the-art Li-ion batteries. Yet, insufficient mechanistic understanding and quantitative parameters of the key components in sulfur-based cathode hinders the advancement of the ASSLSB technologies. This review offers a comprehensive analysis of electrode parameters, including specific capacity, voltage, S mass loading and S content toward establishing the specific energy (Wh kg-1) and energy density (Wh L-1) of the ASSLSBs. Additionally, this work critically evaluates the progress in enhancing lithium ion and electron percolation and mitigating electrochemical-mechanical degradation in sulfur-based cathodes. Last, a critical outlook on potential future research directions is provided to guide the rational design of high-performance sulfur-based cathodes toward practical ASSLSBs.

Structural Engineering of Carbon Host Derived from Organic Pigment toward Physicochemically Confinement and Efficient Conversion of Polysulfide for Lithium-Sulfur Batteries

Lithium-Sulfur Batteries (LSBs) have attracted significant attention as promising next-generation energy storage systems. However, the commercial viability of LSBs have been hindered due to lithium polysulfides (LiPSs) shuttle effect, resulting in poor cycling stability and low sulfur utilization. To address this issue, herein, the study prepares a sulfur host consisting of micro/mesopore-enriched activated carbonaceous materials with ultrahigh surface area using organic pigment via facile one-step activation. By varying the proportion of chemical agent, the pore size and volume of the activated carbonaceous materials are manipulated and their capabilities on the mitigation of LiPSs shuttle effect are investigated. Through the electrochemical measurements and spectroscopic analysis, it is verified that structural engineering of carbon hosts plays a pivotal role in effective physical confinement of LiPSs, leading to the mitigation of LiPSs shuttle effect and sulfur utilization. Additionally, nitrogen and oxygen-containing functional groups originated from PR show electrocatalytic activation sites, facilitating LiPSs conversion kinetics. The approach can reveal that rational design of carbon microstructures can improve trapping and suppression of LiPSs and shuttle effect, enhancing electrochemical performance of LSBs.

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

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

Ultralight Electrolyte with Protective Encapsulation Solvation Structure Enables Hybrid Sulfur-Based Primary Batteries Exceeding 660 Wh/kg

An electrochemical couple of lithium and sulfur possesses the highest theoretical energy density (>2600 Wh/kg) at the material level. However, disappointingly, it is out of place in primary batteries due to its low accessible energy density at the cell level (≤500 Wh/kg) and poor storage performance. Herein, a low-density methyl tert-butyl ether was tailored for an ultralight electrolyte (0.837 g/mL) with a protective encapsulation solvation structure which reduced electrolyte weight (23.1%), increased the utilization of capacity (38.1%), and simultaneously forfended self-discharge. Furthermore, active fluorinated graphite partially replaced inactive carbon to construct a hybrid sulfur-based cathode to bring the potential energy density into full play. Our demonstrated pouch cell achieved an incredible energy density of 661 Wh/kg with a negligible self-discharge rate based on the above innovations. Our work is anticipated to provide a new direction to realize the practicality of lithium-sulfur primary batteries.

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

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

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

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

Polyaniline-Coated Porous Vanadium Nitride Microrods for Enhanced Performance of a Lithium-Sulfur Battery

To solve the slow kinetics of polysulfide conversion reaction in Li-S battery, many transition metal nitrides were developed for sulfur hosts. Herein, novel polyaniline-coated porous vanadium nitride (VN) microrods were synthesized via a calcination, washing and polyaniline-coating process, which served as sulfur host for Li-S battery exhibited high electrochemical performance. The porous VN microrods with high specific surface area provided enough interspace to overcome the volume change of the cathode. The outer layer of polyaniline as a conductive shell enhanced the cathode conductivity, effectively blocked the shuttle effect of polysulfides, thus improving the cycling capacity of Li-S battery. The cathode exhibited an initial capacity of 1007 mAh g^-1 at 0.5 A g^-1, and the reversible capacity remained at 735 mAh g^-1 over 150 cycles.

Comparison of Cell-based and Nanoparticle-based Therapeutics in Treating Atherosclerosis

Today, cardiovascular diseases are among the biggest public health threats worldwide. Atherosclerosis, a chronic inflammatory disease with complex aetiology and pathogenesis, predispose many of these conditions, including the high mortality rate-causing ischaemic heart disease and stroke. Nevertheless, despite the alarming prevalence and absolute death rate, established treatments for atherosclerosis are unsatisfactory in terms of efficacy, safety, and patient acceptance. The rapid advancement of technologies in healthcare research has paved new treatment approaches, namely cell-based and nanoparticle-based therapies, to overcome the limitations of conventional therapeutics. This paper examines the different facets of each approach, discusses their principles, strengths, and weaknesses, analyses the main targeted pathways and their contradictions, provides insights on current trends as well as highlights any unique mechanisms taken in recent years to combat the progression of atherosclerosis.

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

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

Regulated Li2 S Deposition toward Rapid Kinetics Li-S Batteries by a Separator Modified by CeO2 -Decorated Porous Carbon Nanostructure

Although the high-energy-density lithium sulfur (Li-S) battery has been considered one of the most promising next-generation energy storage technology, the practical applications have been plagued by the sluggish reaction kinetics and the shuttle effect of lithium polysulfides intermediates. Here, to address the above issues, the authors report a novel separator modified by CeO₂ -decorated porous carbon nanostructure (CeO₂ /KB/PP). Benefiting from the strong polar surface and large specific surface area, (CeO₂ -doped Ketjen Black) delivers efficient chemical adsorption toward lithium polysulfides. Moreover, rich oxygen vacancies of CeO₂ provide abundant active sites to expedite lithium polysulfides conversion and regulate deposition and nucleation of Li₂ S. Taking advantage of these merits, the battery with the CeO₂ /KB/PP separator exhibits remarkable electrochemical performance, including low-capacity decay of only 0.06% per cycle over 1000 cycles at 2 C and superior rate capability of 627 mAh g^-1 at 3 C. Even with a high sulfur loading of 6.6 mg cm^-2 , the battery can achieve a high areal capacity of 3.6 mAh cm^-2 after 100 cycles. This work provides a new application of rare-earth-based materials to facilitate Li-S batteries.

The Critical Role of Carbon Nanotubes in Bridging Academic Research to Commercialization of Lithium Batteries

Rechargeable lithium batteries have been intensively explored due to their potential to deliver a high energy and stable cycling performance. Yet considerable achievements have been reported on battery performance in lab-based research, a broad gap from fundamental research to their industrial application needs to be filled. The significant advances in the field of carbon nanotubes over the past decades make it a promising candidate to bridge such a gap. Nevertheless, a systematic and profound understanding of its roles in Li batteries is lacking. In this review, we discuss the critical role of carbon nanotube in developing several lithium techniques such as Li-ion, Li-sulfur, and Li-air cells. The focus is laid on the elevation of device capacity, energy, and cyclic life to meet the practical demand. We hope this paper, together with other recently-proposed guiding principles, will pave the way for the massive application of carbon nanotube-based lithium batteries.

Electrochemical Performance of Carbon-Rich Silicon Carbonitride Ceramic as Support for Sulfur Cathode in Lithium Sulfur Battery

As a promising matrix material for anchoring sulfur in the cathode for lithium-sulfur (Li-S) batteries, porous conducting supports have gained much attention. In this work, sulfur-containing C-rich SiCN composites are processed from silicon carbonitride (SiCN) ceramics, synthesized at temperatures from 800 to 1100 °C. To embed sulfur in the porous SiCN matrix, an easy and scalable procedure, denoted as melting-diffusion method, is applied. Accordingly, sulfur is infiltrated under solvothermal conditions at 155 °C into pores of carbon-rich silicon carbonitride (C-rich SiCN). The impact of the initial porosity and microstructure of the SiCN ceramics on the electrochemical performance of the synthesized SiCN-sulfur (SiCN-S) composites is analysed and discussed. A combination of the mesoporous character of SiCN and presence of a disordered free carbon phase makes the electrochemical performance of the SiCN matrix obtained at 900 °C superior to that of SiCN synthesized at lower and higher temperatures. A capacity value of more than 195 mAh/g over 50 cycles at a high sulfur content of 66 wt.% is achieved.

Foldable batteries: from materials to devices

Wearable electronics is a growing field that has important applications in advanced human-integrated systems with high performance and mechanical deformability, especially foldable characteristics. Although foldable electronics such as rollable TVs (LG signature OLED R) or foldable smartphones (Samsung Galaxy Z fold/flip series) have been successfully established in the market, these devices are still powered by rigid and stiff batteries. Therefore, to realize fully wearable devices, it is necessary to develop state-of-the-art foldable batteries with high performance and safety in dynamic deformation states. In this review, we cover the recent progress in developing materials and system designs for foldable batteries. The Materials section is divided into three sections aimed at helping researchers choose suitable materials for their systems. Several foldable battery systems are discussed and the combination of innovative materials and system design that yields successful devices is considered. Furthermore, the basic analysis process of electrochemical and mechanical properties is provided as a guide for researchers interested in the evaluation of foldable battery systems. The current challenges facing the practical application of foldable batteries are briefly discussed. This review will help researchers to understand various aspects (from material preparation to battery configuration) of foldable batteries and provide a brief guideline for evaluating the performance of these batteries.

Customized Structure Design and Functional Mechanism Analysis of Carbon Spheres for Advanced Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are attracting much attention due to their high theoretical energy density and are considered to be the predominant competitors for next-generation energy storage systems. The practical commercial application of LSBs is mainly hindered by the severe "shuttle effect" of the lithium polysulfides (LiPSs) and the serious damage of lithium dendrites. Various carbon materials with different characteristics have played an important role in overcoming the above-mentioned problems. Carbon spheres (CSs) are extensively explored to enhance the performance of LSBs owing to their superior structures. The review presents the state-of-the-art advances of CSs for advanced high-energy LSBs, including their preparation strategies and applications in inhibiting the "shuttle effect" of the LiPSs and protecting lithium anodes. The unique restriction effect of CSs on LiPSs is explained from three working mechanisms: physical confinement, chemical interaction, and catalytic conversion. From the perspective of interfacial engineering and 3D structure designing, the protective effect of CSs on the lithium anode is also analyzed. Not only does this review article contain a summary of CSs in LSBs, but also future directions and prospects are discussed. The systematic discussions and suggested directions can enlighten thoughts in the reasonable design of CSs for LSBs in near future.

Novel functional separator with self-assembled MnO2 layer via a simple and fast method in lithium-sulfur battery

Modifying separator with metal oxides has been considered as a strong strategy to inhibit the shuttling of soluble polysulfide in the lithium-sulfur battery (Li-S battery). Manganesedioxide (MnO₂), one kind of transition metal oxide, is widely applied to decorate the PP (Polypropylene) separator. However, the fabrication by physical coating is always multistep and complicated. Here, we design a simple and fast method to chemically decorate separator. Based on the oxidizing property of acidic KMnO₄ solution, the PP separator was oxidized and an ultrathin self-assembled MnO₂ layer was directly constructed on one side of separator, by immersing in acidic KMnO₄ solution for only 1 h. The self-assembled MnO₂ layer has the synergistic effect of adsorption and catalytic conversion on polysulfides, which can effectively inhibit the shuttle effect. It can also help battery to maintain excellent electrochemical kinetics in the electrochemical cycle and maintain the effective recycling of active substances. As a result, the shuttling of polysulfide is greatly prohibited by this novel functional separator, and cycling stability is outstandingly improved, with a low-capacity decaying of 0.058% after 500 cycles at 0.5C. The rapid and simple modification method proposed in this study has a certain reference value for the future large-scale application of lithium-sulfur battery.

Organosulfur polymer-based cathode materials for rechargeable batteries

Organosulfur polymer cathode materials have shown promising electrochemical performances in rechargeable batteries. This review covers recent developments of the polymer cathodes and the remaining challenges and future prospects are discussed.

Novel melamine-based porous organic polymers: synthesis, characterizations, morphology modifications, and their applications in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have been considered to be one of the most promising energy storage devices in the next generation. However, the insulating properties of sulfur and the shuttle effect of soluble lithium polysulfides (LiPSs) seriously hinder the practical application of Li-S batteries. In this paper, a novel porous organic polymer (HUT3) was prepared based on the polycondensation between melamine and 1,4-phenylene diisocyanate. The micro morphology of HUT3 was improved byin situgrowth on different mass fractions of rGO (5%, 10%, 15%), and the obtained HUT3-rGO composites were employed as sulfur carriers in Li-S batteries with promoted the sulfur loading ratio and lithium-ion mobility. Attributed to the synergistic effect of the chemisorption of polar groups and the physical constraints of HUT3 structure, HUT3-rGO/S electrodes exhibits excellent capacity and cyclability performance. For instance, HUT3-10rGO/S electrode exhibits a high initial specific capacity of 950 mAh g^-1at 0.2 C and retains a high capacity of 707 mAh g^-1after 500 cycles at 1 C. This work emphasizes the importance of the rational design of the chemical structure and opens up a simple way for the development of cathode materials suitable for high-performance Li-S batteries.

Toward High-Performance Lithium-Sulfur Batteries: Efficient Anchoring and Catalytic Conversion of Polysulfides Using P-Doped Carbon Foam

Rational design of the sulfur cathode structure enables effective adsorption of polysulfides and accelerates the sulfur reduction reaction, which is of great significance to the practical application of lithium-sulfur batteries. Here, P-doped carbon foam (PCF) as a sulfur host for the lithium-sulfur battery cathode was successfully synthesized by a facile strategy. The tailored hierarchical pore structure combined with P doping not only facilitates Li⁺ diffusion but also enhances the adsorption and accelerates the catalytic conversion of lithium polysulfides, thus significantly improving lithium storage performance of the PCF/S cathode.

Nitrogen/oxygen codoped hierarchical porous Carbons/Selenium cathode with excellent lithium and sodium storage behavior

A nitrogen/oxygen codoped carbon derived from sweet potato (SPC) with interconnected micro-mesopores is applied to encapsulate selenium composite (SPC/Se) with a high Se loading (74.3%). As a cathode for advanced Li-Se and Na-Se batteries, the SPC/Se exhibits superior electrochemical behavior in low-cost carbonate electrolyte. Including the hierarchically porous structure of SPC and the chemical bonding between Se and carbon, the strong binding energy between SPC and Li₂Se/Na₂Se is also proved by DFT method, which results in the effective mitigation of shuttle reaction and volume change for SPC/Se cathode. For Li-Se batteries, the SPC/Se composite shows the initial specific charge capacity of 668 mAh g^-1 with a high initial coulombic efficiency of 78%, and maintains a stable reversible capacity of 587 mAh g^-1 after 1000 cycles with a weak capacity decay of 0.082% at 0.2C. It still retains a reversible specific capacity of 375 mAh g^-1 even at 20C. For Na-Se battery, the SPC/Se composite displays the initial specific charge capacity of 671 mAh g^-1 at 0.2C and maintains a reversible specific capacity of 412 mAh g^-1 after 500 cycles with a capacity retention of 61.4%. When the current density increases to 20C, it still delivers a high reversible specific capacity of 420 mAh g^-1. Finally, the transformation mechanism of Se molecule is illustrated detailedly in (de)lithi/sodiation process.

Confined Thermolysis for Oriented N-Doped Carbon Supported Pd toward Stable Catalytic and Energy Storage Applications

Carbon-based nanomaterials have been widely utilized in catalysis and energy-related fields due to their fascinating properties. However, the controllable synthesis of porous carbon with refined morphology is still a formidable challenge due to inevitable aggregation/fusion of resulted carbon particles during the high-temperature synthetic process. Herein, a hierarchically oriented carbon-structured (fiber-like) composite is fabricated by simultaneously taking advantage of a confined pyrolysis strategy and disparate bond environments within metal-organic frameworks (MOFs). In the resultant composite, the oriented carbon provides a fast mass (molecule/ion/electron) transfer efficiency; the doping-N atoms can anchor or act as active sites; the mesoporous SiO₂ (mSiO₂ ) shell not only effectively prevents the derived carbon or active metal nanoparticles (NPs) from aggregation or leaching, but also acts as a "polysulfide reservoir" in the Li-S batteries to suppress the "shuttle" effect. Benefiting from these advantages, the synthesized composite Pd@NDHPC@mSiO₂ (NDHPC means N-doped hierarchically porous carbon) exhibits extremely high catalytic activity and stability toward the one-pot Knoevenagel condensation-hydrogenation reaction. Furthermore, the oriented NDHPC@mSiO₂ manifests a boosted capacity and cycling stability in Li-S batteries compared to the counterpart that directly pyrolyzes without silica protection. This report provides an effective strategy of fabricating hierarchically oriented carbon composites for catalysis and energy storage applications.

Applications of Carbon in Rechargeable Electrochemical Power Sources: A Review

Rechargeable power sources are an essential element of large-scale energy systems based on renewable energy sources. One of the major challenges in rechargeable battery research is the development of electrode materials with good performance and low cost. Carbon-based materials have a wide range of properties, high electrical conductivity, and overall stability during cycling, making them suitable materials for batteries, including stationary and large-scale systems. This review summarizes the latest progress on materials based on elemental carbon for modern rechargeable electrochemical power sources, such as commonly used lead–acid and lithium-ion batteries. Use of carbon in promising technologies (lithium–sulfur, sodium-ion batteries, and supercapacitors) is also described. Carbon is a key element leading to more efficient energy storage in these power sources. The applications, modifications, possible bio-sources, and basic properties of carbon materials, as well as recent developments, are described in detail. Carbon materials presented in the review include nanomaterials (e.g., nanotubes, graphene) and composite materials with metals and their compounds.

2D conductive MOFs with sufficient redox sites: reduced graphene oxide/Cu-benzenehexathiolate composites as high capacity anode materials for lithium-ion batteries

As a superconductive metal-organic framework (MOF) material, Cu-BHT (BHT: benzenehexathiol) can exhibit outstanding electrochemical properties owing to the potential redox reactions of the cuprous ions, sulfur species and benzene rings of Cu-BHT, but its compact texture limits the specific capacity of Cu-BHT. To improve the dense feature of Cu-BHT, rGO/Cu-BHT (rGO: reduced graphene oxide) composite materials are fabricated via a facile route and they exhibit applicable conductivities, improved lithium ion diffusion kinetics compared to pristine Cu-BHT, and sufficient redox sites. The rGO/Cu-BHT composite materials maximize the potential capacity of Cu-BHT, and the rGO/Cu-BHT 1 : 1 material achieves outstanding reversible specific capacities of 1190.4, 1230.8, 1131.4, and 898.7 mA h g-1, at current densities of 100, 200, 500, and 1000 mA g-1, respectively, superior to those of pristine Cu-BHT and rGO. These results present the promising future of 2D conductive MOFs as functional materials for energy storage, based on the regulation of electronic conductivity, redox sites, and lithium ion diffusion kinetics.

Hierarchical Nanoreactor with Multiple Adsorption and Catalytic Sites for Robust Lithium-Sulfur Batteries

Developing high-performance cathode host materials is fundamental to solve the low utilization of sulfur, the sluggish redox kinetics, and the lithium polysulfide (LiPS) shuttle effect in lithium-sulfur batteries (LSBs). Here, a multifunctional Ag/VN@Co/NCNT nanocomposite with multiple adsorption and catalytic sites within hierarchical nanoreactors is reported as a robust sulfur host for LSB cathodes. In this hierarchical nanoreactor, heterostructured Ag/VN nanorods serve as a highly conductive backbone structure and provide internal catalytic and adsorption sites for LiPS conversion. Interconnected nitrogen-doped carbon nanotubes (NCNTs), in situ grown from the Ag/VN surface, greatly improve the overall specific surface area for sulfur dispersion and accommodate volume changes in the reaction process. Owing to their high LiPS adsorption ability, outer Co nanoparticles at the top of the NCNTs catch escaped LiPS, thus effectively suppressing the shuttle effect and enhancing kinetics. Benefiting from the multiple adsorption and catalytic sites of the developed hierarchical nanoreactors, Ag/VN@Co/NCNTs@S cathodes display outstanding electrochemical performances, including a superior rate performance of 609.7 mAh g^-1 at 4 C and a good stability with a capacity decay of 0.018% per cycle after 2000 cycles at 2 C. These properties demonstrate the exceptional potential of Ag/VN@Co/NCNTs@S nanocomposites and approach LSBs closer to their real-world application.

The Electrostatic Attraction and Catalytic Effect Enabled by Ionic-Covalent Organic Nanosheets on MXene for Separator Modification of Lithium-Sulfur Batteries

It is of great significance to mediate the redox kinetics and shuttle effect of polysulfides in pursuit of high-energy-density and long-life lithium-sulfur (Li-S) batteries. Herein, a new strategy is proposed based on the electrostatic attraction and catalytic effect of polysulfides for the modification of the polypropylene (PP) separator. Guanidinium-based ionic-covalent organic nanosheets (iCON) on the surface of Ti₃ C₂ is presented as a coating layer for the PP separator. The synergetic effects of Ti₃ C₂ and iCON provide new platforms to suppress the shuttle effect of polysulfides, expedite the redox kinetics of sulfur species, and promote efficient conversion of the intercepted polysulfides. The functional separator endows carbon nanotube/sulfur cathodes with excellent electrochemical performance. The average capacity decay per cycle within 2000 cycles at 2 C is as low as 0.006%. The separator is even effective in the case of sulfur content of 90 wt% and sulfur loading of 7.6 mg cm^-2 ; the reversible capacity, areal capacity, and volumetric capacity at 0.1 C are as high as 1186 mA h g^-1 , 9.01 mA h cm^-2 , and 1201 mA h cm^-3 , respectively. This work provides a promising approach toward separator modification for the development of high-performance Li-S batteries.

Prussian blue analogs derived Fe-Ni-P@nitrogen-doped carbon composites as sulfur host for high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have drawn a lot of attention owing to the high theoretical capacity of 1675 mAh g^-1, environmental friendliness and relative abundance of sulfur. Nevertheless, the severe dissolution and migration of lithium polysulfides (LiPSs) and poor conductivity of sulfur greatly hinder the practical application of Li-S batteries. In this work, Fe-Ni-P@nitrogen-doped carbon (named as Fe-Ni-P@NC) derived from Fe-Ni Prussian blue analog (Fe-Ni PBA) was used as highly efficient sulfur host for Li-S batteries. The Fe-Ni-P particles not only enhance the adsorption of LiPSs but also effectively promote the conversion of LiPSs. In addition, the CN^- of PBAs can readily generate nitrogen-doped carbon during pyrolysis, which can improve the conductivity of composites. Due to these advantages, Li-S batteries using S@Fe-Ni-P@NC composites cathodes exhibited good electrochemical performance with outstanding rate capability and stable cycling over 500 cycles with a lower capacity fading rate of 0.08% per cycle at 1 C.

A Novel Synthesizing Strategy of 3D Cose2 Porous Hollow Flowers for High Performance Lithium–Sulfur Batteries

Redox kinetics of lithium polysulfides (LiPSs) conversion and poor electrical conductivity of sulfur during the charge-discharge process greatly inhibit the commercialization of high-performance lithium–sulfur (Li–S) batteries. Herein, we synthesized CoSe2 porous hollow flowers (CoSe2-PHF) by etching and further selenizing layered double hydroxide, which combined the high catalytic activity of transition metal compound and high electrical conductivity of selenium. The obtained CoSe2-PHF can efficiently accelerate the catalytic conversion of LiPSs, expedite the electron transport, and improve utilization of active sulfur during the charge-discharge process. As a result, with CoSe2-PHF/S-based cathodes, the Li–S batteries exhibited a reversible specific capacity of 955.8 mAh g−1 at 0.1 C and 766.0 mAh g−1 at 0.5 C, along with a relatively small capacity decay rate of 0.070% per cycle within 400 cycles at 1 C. Even at the high rate of 3 C, the specific capacity of 542.9 mAh g−1can be maintained. This work enriches the way to prepare porous composites with high catalytic activity and electrical conductivity as sulfur hosts for high-rate, long-cycle rechargeable Li–S batteries.

Enhancing Polysulfide Confinement and Electrochemical Kinetics by Amorphous Cobalt Phosphide for Highly Efficient Lithium-Sulfur Batteries

The application of lithium-sulfur (Li-S) batteries is severely hampered by the shuttle effect and sluggish redox kinetics. Herein, amorphous cobalt phosphide grown on a reduced graphene oxide-multiwalled carbon nanotube (rGO-CNT-CoP(A)) is designed as the sulfur host to conquer the above bottlenecks. The differences between amorphous cobalt phosphide (CoP) and crystalline CoP on the surface adsorption as well as conversion of lithium polysulfides (LiPSs) are investigated by systematical experiments and density-functional theory (DFT) calculations. Specifically, the amorphous CoP not only strengthens the chemical adsorption to LiPSs but also greatly accelerates liquid-phase conversions of LiPSs as well as the nucleation and growth of Li₂S. DFT calculation reveals that the amorphous CoP possesses higher binding energies and lower diffusion energy barriers for LiPSs. In addition, the amorphous CoP features reduced energy gap and the increased electronic concentrations of adsorbed LiPSs near Fermi level. These characteristics contribute to the enhanced chemisorption ability and the accelerated redox kinetics. Simultaneously, the prepared S/rGO-CNT-CoP(A) electrode delivers an impressive initial capacity of 872 mAh g^-1 at 2 C and 617 mAh g^-1 can be obtained after 200 cycles, exhibiting excellent cycling stability. Especially, it achieves outstanding electrochemical performance even under high sulfur loading (5.3 mg cm^-2) and lean electrolyte (E/S = 7 μL_E mg^-1_S) conditions. This work exploits the application potential for amorphous materials and contributes to the development of highly efficient Li-S batteries.

Efficient Catalytic Conversion of Polysulfides by Biomimetic Design of "Branch-Leaf" Electrode for High-Energy Sodium-Sulfur Batteries

Rechargeable room temperature sodium-sulfur (RT Na-S) batteries are seriously limited by low sulfur utilization and sluggish electrochemical reaction activity of polysulfide intermediates. Herein, a 3D "branch-leaf" biomimetic design proposed for high performance Na-S batteries, where the leaves constructed from Co nanoparticles on carbon nanofibers (CNF) are fully to expose the active sites of Co. The CNF network acts as conductive "branches" to ensure adequate electron and electrolyte supply for the Co leaves. As an effective electrocatalytic battery system, the 3D "branch-leaf" conductive network with abundant active sites and voids can effectively trap polysulfides and provide plentiful electron/ions pathways for electrochemical reaction. DFT calculation reveals that the Co nanoparticles can induce the formation of a unique Co-S-Na molecular layer on the Co surface, which can enable a fast reduction reaction of the polysulfides. Therefore, the prepared "branch-leaf" CNF-L@Co/S electrode exhibits a high initial specific capacity of 1201 mAh g^-1 at 0.1 C and superior rate performance.

Two-dimensional imine-based covalent–organic-framework derived nitrogen-doped porous carbon nanosheets for high-performance lithium–sulfur batteries

COF-derived nitrogen-doped porous carbon nanosheets with S loading achieve high capacities and good long-cycling performance for lithium–sulfur batteries.

Precise Synthesis of Fe-N2 Sites with High Activity and Stability for Long-Life Lithium-Sulfur Batteries

Precisely tuning the coordination environment of the metal center and further maximizing the activity of transition metal-nitrogen carbon (M-NC) catalysts for high-performance lithium-sulfur batteries are greatly desired. Herein, we construct an Fe-NC material with uniform and stable Fe-N₂ coordination structure. The theoretical and experimental results indicate that the unsaturated Fe-N₂ center can act as a multifunctional site for anchoring lithium polysulfides (LiPSs), accelerating the redox conversion of LiPSs and reducing the reaction energy barrier of Li₂S decomposition. Consequently, the batteries based on a porous carbon nitride supported Fe-N₂ site (Fe-N₂/CN) host exhibit excellent cycling performance with a capacity decay of 0.011% per cycle at 2 C after 2000 cycles. This work deepens the understanding of the relationship between electronic structure of M-NC sites and the catalysis effect for the conversion of LiPSs. This strategy also provides a potent guidance for the further application of M-NC materials in advanced lithium-sulfur batteries.

Three-Dimensionally Ordered Macroporous ZnO Framework as Dual-Functional Sulfur Host for High-Efficiency Lithium-Sulfur Batteries

A three-dimensionally ordered macroporous ZnO (3DOM ZnO) framework was synthesized by a template method to serve as a sulfur host for lithium-sulfur batteries. The unique 3DOM structure along with an increased active surface area promotes faster and better electrolyte penetration accelerating ion/mass transfer. Moreover, ZnO as a polar metal oxide has a strong adsorption capacity for polysulfides, which makes the 3DOM ZnO framework an ideal immobilization agent and catalyst to inhibit the polysulfides shuttle effect and promote the redox reactions kinetics. As a result of the stated advantages, the S/3DOM ZnO composite delivered a high initial capacity of 1110 mAh g^-1 and maintained a capacity of 991 mAh g^-1 after 100 cycles at 0.2 C as a cathode in a lithium-sulfur battery. Even at a high C-rate of 3 C, the S/3DOM ZnO composite still provided a high capacity of 651 mAh g^-1, as well as a high areal capacity (4.47 mAh cm^-2) under high loading (5 mg cm^-2).

Carbon/Sulfur Aerogel with Adequate Mesoporous Channels as Robust Polysulfide Confinement Matrix for Highly Stable Lithium-Sulfur Battery

The ability to restrict the shuttle of lithium polysulfide (LiPS_n) and improve the utilization efficiency of sulfur represents an important endeavor toward practical application of lithium-sulfur (Li-S) batteries. Herein, we report the crafting of a robust 3D graphene-wrapped, nitrogen-doped, highly mesoporous carbon/sulfur (G-NHMC/S) hierarchical aerogel as an effective polysulfide confinement matrix for a highly stable Li-S battery. Rich polar sites of NHMC firmly anchor LiPS_n on the matrix surface. Porous NHMC provides ample space for accommodating sulfur and cushioning its volume expansion. Moreover, graphene wrapped on NHMC/S not only physically hinders the LiPS_n shuttle but also interconnects the isolated NHMC/S, thus increasing electron transfer rate. Taken together, triple confinement of G-NHMC/S aerogel synergistically retains the soluble LiPS_n and displays a specific capacity of 1322 mAh g^-1 and 1000-cycle life. As such, rationally designed 3D carbon/sulfur aerogel affords a unique platform to impart high energy density and stable electrodes for energy storage devices.