The Regulating Role of Carbon Nanotubes and Graphene in Lithium-Ion and Lithium-Sulfur Batteries

Molybdenum Boride as an Efficient Catalyst for Polysulfide Redox to Enable High-Energy-Density Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries, despite having high theoretical specific energy, possess many practical challenges, including lithium polysulfide (LiPS) shuttling. To address the issues, here, hydrophilic molybdenum boride (MoB) nanoparticles are presented as an efficient catalytic additive for sulfur cathodes. The high conductivity and rich catalytically active sites of MoB nanoparticles allow for a fast kinetics of LiPS redox in high-sulfur-loading electrodes (6.1 mg cm^-2 ). Besides, the hydrophilic properties and good wettability toward electrolyte of MoB can facilitate electrolyte penetration and LiPS redox, guaranteeing a high utilization of sulfur under a lean-electrolyte condition. Therefore, the cells with MoB achieve impressive electrochemical performance, including a high capacity (1253 mA h g^-1 ) and ultralong lifespan (1000 cycles) with a low capacity fade rate of 0.03% per cycle. Also, pouch cells fabricated with the MoB additive deliver an ultrahigh discharge capacity of 947 mA h g^-1 , corresponding to a low electrolyte-to-capacity ratio of about 4.8 µL (mA h)^-1 , and remain stable over 55 cycles under practically necessary conditions with a low electrolyte-to-sulfur ratio of 4.5 µL mg^-1 .

True Meaning of Pseudocapacitors and Their Performance Metrics: Asymmetric versus Hybrid Supercapacitors

The development of pseudocapacitive materials for energy-oriented applications has stimulated considerable interest in recent years due to their high energy-storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery-like to the pseudocapacitive-like behavior. As a result, it becomes challenging to distinguish "pseudocapacitive" and "battery" materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery-type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid-state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state-of-the-art progress in the engineering of active materials is summarized, which will guide for the development of real-pseudocapacitive energy storage systems.

Three-dimensional hierarchical ZnCo2O4@C3N4-B nanoflowers as high-performance anode materials for lithium-ion batteries

ZnCo2O4 has become one of the most widely used anode materials due to its good specific capacity, cost-efficiency, high thermal stability and environmental benignity. However, its poor conductivity and cycle stability have limited its practical application in lithium-ion batteries. To overcome these issues, we constructed a 3D nanoflower composite material (ZnCo2O4@C3N4-B) by combining ZnCo2O4 as a framework and B-doped g-C3N4 (g-C3N4-B) as a new carbon source material via a simple hydrothermal method. ZnCo2O4@C3N4-B exhibited exceptional specific capacitance of 919.76 mA h g-1 after 500 cycles at 0.2 A g-1 and a long-term capacity retention of 97.8% after 1000 cycles at 2 A g-1. The high reversible capacity, long cycling life and good rate performance could be attributed to the 3D interconnected architecture and doping of g-C3N4-B. This work provides a simple and general strategy to design high-performance anode materials for lithium-ion batteries to meet the needs of practical applications.

3D Graphene Materials: From Understanding to Design and Synthesis Control

Carbon materials, with their diverse allotropes, have played significant roles in our daily life and the development of material science. Following 0D C₆₀ and 1D carbon nanotube, 2D graphene materials, with their distinctively fascinating properties, have been receiving tremendous attention since 2004. To fulfill the efficient utilization of 2D graphene sheets in applications such as energy storage and conversion, electrochemical catalysis, and environmental remediation, 3D structures constructed by graphene sheets have been attempted over the past decade, giving birth to a new generation of graphene materials called 3D graphene materials. This review starts with the definition, classifications, brief history, and basic synthesis chemistries of 3D graphene materials. Then a critical discussion on the design considerations of 3D graphene materials for diverse applications is provided. Subsequently, after emphasizing the importance of normalized property characterization for the 3D structures, approaches for 3D graphene material synthesis from three major types of carbon sources (GO, hydrocarbons and inorganic carbon compounds) based on GO chemistry, hydrocarbon chemistry, and new alkali-metal chemistry, respectively, are comprehensively reviewed with a focus on their synthesis mechanisms, controllable aspects, and scalability. At last, current challenges and future perspectives for the development of 3D graphene materials are addressed.

Layer-Spacing-Enlarged MoS2 Superstructural Nanotubes with Further Enhanced Catalysis and Immobilization for Li-S Batteries

A layer-spacing-enlarged MoS₂ nanotube (LE-MoS₂) consisting of hierarchical superstructural nanosheets (-MoS₂-carbon layer-MoS₂-) was fabricated and served as the sulfur host. The (002) lattice plane of LE-MoS₂ is greatly expanded to 1.04 nm and 67.7% higher than that of the conventional 2H-MoS₂. Benefitting from the layer-spacing-enlarged hierarchical superstructure of LE-MoS₂, the catalytic effect on the S_(s)-Li₂S_x (soluble, x > 6)-Li₂S_y (soluble, y > 2)-Li₂S_(s) phase transformation kinetics and immobilizing effect on the soluble Li₂S_y in Li-S batteries are both further enhanced and demonstrated by in situ X-ray adsorption near-edge structure spectroscopy and first-principles calculations. The formation of hierarchical superstructural nanosheets was carefully investigated by customized synchrotron vacuum ultraviolet photoionization mass spectrometry.

Asymmetric Modification of Carbon Nanotube Arrays with Thermoresponsive Hydrogel for Controlled Delivery

In this work, bipolar electrochemistry is used to perform wireless indirect electrodeposition of two different polymer coatings on both sides of carbon nanotube arrays. Using a thermoresponsive hydrogel on one side and an inert insoluble polymer on the other side, it is possible to generate, in a single step, a nanoporous reservoir with Janus character closed on one side by a thermoresponsive membrane. The thermoresponsive polymer, poly(N-isopropylacrylamide) (pNIPAM), is generated by the local reduction of persulfate ions, which initiates radical polymerization of NIPAM. Electrophoretic paint (EP) is chosen as an inert polymer. It is deposited by precipitation because of a local decrease in pH during water oxidation. Both polymers can be deposited simultaneously on opposite sides of the bipolar electrode during the application of the electric field, yielding a double-modified Janus object. Moreover, the length and thickness of the polymer layers can be controlled by varying the electric field and the deposition time. This concept is applied to vertically aligned carbon nanotube arrays (VACNTs), trapped inside an anodic aluminum oxide membrane, which can further be used as a smart reservoir for chemical storage and release. A fluorescent dye is loaded in the VACNTs and its release is studied as a function of temperature. Low temperature, when the hydrogel layer is in the swollen state, allows diffusion of the molecule. Dye release occurs on the hydrogel-modified side of the VACNTs. At high temperatures, when the hydrogel layer is in the collapsed state, dye release is blocked because of the impermeability of the pNIPAM layer. This concept paves the way toward the design of advanced devices in the fields of drug storage and directed delivery.

Toward High-Energy-Density Lithium Metal Batteries: Opportunities and Challenges for Solid Organic Electrolytes

With increasing demands for safe, high capacity energy storage to support personal electronics, newer devices such as unmanned aerial vehicles, as well as the commercialization of electric vehicles, current energy storage technologies are facing increased challenges. Although alternative batteries have been intensively investigated, lithium (Li) batteries are still recognized as the preferred energy storage solution for the consumer electronics markets and next generation automobiles. However, the commercialized Li batteries still have disadvantages, such as low capacities, potential safety issues, and unfavorable cycling life. Therefore, the design and development of electromaterials toward high-energy-density, long-life-span Li batteries with improved safety is a focus for researchers in the field of energy materials. Herein, recent advances in the development of novel organic electrolytes are summarized toward solid-state Li batteries with higher energy density and improved safety. On the basis of new insights into ionic conduction and design principles of organic-based solid-state electrolytes, specific strategies toward developing these electrolytes for Li metal anodes, high-energy-density cathode materials (e.g., high voltage materials), as well as the optimization of cathode formulations are outlined. Finally, prospects for next generation solid-state electrolytes are also proposed.

Enhancing the Charge Transportation Ability of Yolk-Shell Structure for High-Rate Sodium and Potassium Storage

The microstructure of large-capacity anodes is of great importance in determining the performance of sodium- and potassium-ion batteries. Yolk-shell nanostructures promise excellent structural stability but suffer from insufficient charge transfer rate during cycles. Herein, we tackle this challenge by constructing a single-walled carbon nanotube (SWNT) internally bridged yolk-shell structure, inside which SWNTs cover the surface of the yolk and connect the yolk and shell, for better electron/ion transportation. Combining the merits of both yolk-shell structure and conductive SWNT channels, the as-prepared Fe_1-xS/SWNT@C composite manifests high reversible capacity and ultralong cycling stability up to 8700 cycles. Moreover, it displays the best rate capability (317 mA h g^-1 at 20 A g^-1 for Na⁺ and 236 mA h g^-1 at 10 A g^-1 for K⁺) among the reported yolk-shell structures and iron-sulfide-based anodes thus far. The kinetic analysis and density functional theory calculations further reveal that the Fe_1-xS/SWNT heterointerface can effectively enhance the reversibility of K⁺ storage and decrease the K⁺ diffusion energy barrier, leading to excellent pseudocapacitive behavior and fast ion transportation for outstanding rate capability.

MnO2/rGO/CNTs Framework as a Sulfur Host for High-Performance Li-S Batteries

Lithium-sulfur batteries are very promising next-generation energy storage batteries due to their high theoretical specific capacity. However, the shuttle effect of lithium-sulfur batteries is one of the important bottlenecks that limits its rapid development. Herein, physical and chemical dual adsorption of lithium polysulfides are achieved by designing a novel framework structure consisting of MnO2, reduced graphene oxide (rGO), and carbon nanotubes (CNTs). The framework-structure composite of MnO2/rGO/CNTs is prepared by a simple hydrothermal method. The framework exhibits a uniform and abundant mesoporous structure (concentrating in ~12 nm). MnO2 is an α phase structure and the α-MnO2 also has a significant effect on the adsorption of lithium polysulfides. The rGO and CNTs provide a good physical adsorption interaction and good electronic conductivity for the dissolved polysulfides. As a result, the MnO2/rGO/CNTs/S cathode delivered a high initial capacity of 1201 mAh g-1 at 0.2 C. The average capacities were 916 mAh g-1, 736 mAh g-1, and 547 mAh g-1 at the current densities of 0.5 C, 1 C, and 2 C, respectively. In addition, when tested at 0.5 C, the MnO2/rGO/CNTs/S exhibited a high initial capacity of 1010 mAh g-1 and achieved 780 mAh g-1 after 200 cycles, with a low capacity decay rate of 0.11% per cycle. This framework-structure composite provides a simple way to improve the electrochemical performance of Li-S batteries.

Undercooling-directed NaCl crystallization: an approach towards nanocavity-linked graphene networks for fast lithium and sodium storage

Despite the crystallization of inorganic salt is being technologically related to the fabrication of salt-templated materials, the two key steps, nucleation and crystal growth, still lack the kinetic control to enable precise design of salt scaffolds. Here, we study how the undercooling degree controls the construction of salt scaffolds by kinetically manipulating the nucleation and growth rates in a NaCl-F127-rhodanine system. An effective approach based on undercooling-directed NaCl crystallization is further proposed to tailor the morphology and structure of the carbon materials. Under different undercooling conditions (liquid nitrogen, -55 °C and -25 °C freezing), the salt scaffold can be tuned as spheroidal particles, ellipsoidal nanocrystal aggregates and cubic nanocrystals with round corners, respectively. Correspondingly, hollow carbon nanospheres, nanocavity-linked graphene networks (CGN) and graphene nanosheets (GNS) can be fabricated through a salt template method, respectively. The Li⁺ and Na⁺ storage mechanisms of 3D CGN and 2D GNS are discussed, focusing on the ion diffusion kinetics. The enhanced Li⁺ diffusion kinetics in the 3D interconnected network endows CGN with better rate performance than GNS as lithium-ion battery anode material, and Na⁺ adsorption dominates the Na⁺ storage in CGN as sodium-ion battery anode material. Our findings provide a general idea for the construction crystallization-induced architectures and offer valuable insights to achieve fast Li⁺/Na⁺ storage by boosting the ion diffusion kinetics.

Sandwich-Structured Ordered Mesoporous Polydopamine/MXene Hybrids as High-Performance Anodes for Lithium-Ion Batteries

Organic polymers have attracted significant interest as electrodes for energy storage devices because of their advantages, including molecular flexibility, cost-effectiveness, and environmentally friendly nature. Nevertheless, the real implementation of polymer-based electrodes is restricted by their poor stability, low capacity, and slow electron-transfer/ion diffusion kinetics. In this work, a sandwich-structured composite of ordered mesoporous polydopamine (OMPDA)/Ti₃C₂T_x has been fabricated by in situ polymerization of dopamine on the surface of Ti₃C₂T_x via employing the PS-b-PEO block polymer as a soft template. The OMPDA layers with vertically oriented, accessible nanopores (∼20 nm) provide a continuous pore channel for ion diffusion, while the Ti₃C₂T_x layers guarantee a fast electron-transfer path. The OMPDA/Ti₃C₂T_x composite anode exhibits high reversible capacity, good rate performance, and excellent cyclability for lithium-ion batteries. The in situ transmission electron microscopy analysis reveals that the OMPDA in the composite only shows a small volume expansion and almost preserves the initial morphology during lithiation. Moreover, these in situ experiments also demonstrate the generation of a stable and ultrathin solid electrolyte interphase layer surrounding the active material, which acts as an electrode protective film during cycling. This study demonstrates the method to develop polymer-based electrodes for high-performance rechargeable batteries.

Biomimetic carbon nanotubes for neurological disease therapeutics as inherent medication

Nowadays, nanotechnology is revolutionizing the approaches to different fields from manufacture to health. Carbon nanotubes (CNTs) as promising candidates in nanomedicine have great potentials in developing novel entities for central nervous system pathologies, due to their excellent physicochemical properties and ability to interface with neurons and neuronal circuits. However, most of the studies mainly focused on the drug delivery and bioimaging applications of CNTs, while neglect their application prospects as therapeutic drugs themselves. At present, the relevant reviews are not available yet. Herein we summarized the latest advances on the biomedical and therapeutic applications of CNTs in vitro and in vivo for neurological diseases treatments as inherent therapeutic drugs. The biological mechanisms of CNTs-mediated bio-medical effects and potential toxicity of CNTs were also intensely discussed. It is expected that CNTs will exploit further neurological applications on disease therapy in the near future.

Designing ionic channels in novel carbons for electrochemical energy storage

Tremendous efforts have been dedicated to developing high-performance energy storage devices based on the micro- or nano-manipulation of novel carbon electrodes, as certain nanocarbons are perceived to have advantages such as high specific surface areas, superior electric conductivities, excellent mechanical properties and so on. In typical electrochemical electrodes, ions are intercalated/deintercalated into/from the bulk (for batteries) or adsorbed/desorbed on/from the surface (for electrochemical capacitors). Fast ionic transport, significantly determined by ionic channels in active electrodes or supporting materials, is a prerequisite for the efficient energy storage with carbons. In this report, we summarize recent design strategies for ionic channels in novel carbons and give comments on the promising features based on those carbons towards tailorable ionic channels.

Prussian blue coated with reduced graphene oxide as high-performance cathode for lithium–Sulfur batteries

Lithium–sulfur (Li–S) batteries with their outstanding theoretical energy density are strongly considered to take over the post-lithium ion battery era; however, they are limited by sluggish reaction kinetics and the severe shuttling of soluble lithium polysulfides. Prussian blue analogues (PBs) have demonstrated their efficiency in hindering the shuttle effects as host materials of sulfur; unfortunately, they show an inferior electronic conductivity, exhibiting considerable lifespan but poor rate performance. Herein, we rationally designed a PB@reduced graphene oxide as the host material for sulfur (S@PB@rGO) hybrids via a facile liquid diffusion and physical absorption method, in which the sulfur was integrated into Na₂Co[Fe(CN)₆] and rGO framework. When employed as a cathode, the as-prepared hybrid exhibited excellent rate ability (719 mA h g⁻¹ at 1C) and cycle stability (918 mA h g⁻¹ at 0.5C after 100 cycles). The improved electrochemical performance was attributed to the synergetic effect of PB and conductive rGO, which not only enhanced the physisorption of polysulfides but also provided a conductive skeleton to ensure rapid charge transfer kinetics, achieving high energy/power outputs and considerable lifespan simultaneously. This study may offer a new method manufacturing high performance Li–S batteries.

Lithium–sulfur batteries with high theoretical energy density are strongly considered to take over the post-lithium ion battery era; however, they are limited by sluggish reaction kinetics and the severe shuttling of soluble lithium polysulfides.

Preparation and Carbon-Dependent Supercapacitive Behaviour of Nanohybrid Materials between Polyoxometalate and Porous Carbon Derived from Zeolitic Templates

An electrochemical cell combining the energy storage characteristics of the chemical redox reaction and a physical capacitor effect presents advantages including high energy and power densities, and long durability. In this study, we prepared nanohybrid materials between polyoxometalate (POM) and porous carbon, which have different porous structures and pore sizes, using different zeolitic templates. The POM molecules were loaded inside the porous carbon, and these POM/carbon nanohybrid materials were used as cathode active materials for lithium–ion batteries (LIBs). The performance of these molecular cluster batteries (MCBs) was significantly dependent on the porous carbon. Operando X-ray absorption fine structure (XAFS) and ⁷Li solid-state nuclear magnetic resonance (NMR) measurements of the POM/carbon-MCBs revealed that three-dimensional porous carbon with high surface areas can improve the performance. The results highlight the remarkable performance of porous carbon with a three-dimensionally-linked pore network structure as an additive for supercapacitors to realise high-performance energy storage devices.

In situ encapsulation of Co-based nanoparticles into nitrogen-doped carbon nanotubes-modified reduced graphene oxide as an air cathode for high-performance Zn-air batteries

Exploring highly efficient catalysts for the oxygen reduction/evolution reaction (ORR/OER) is very important in rechargeable Zn-air batteries. N-doped carbon coupled with transition metal-based species are among the most promising cathode catalysts for Zn-air batteries. However, the aggregation of metal-based sites during the synthetic/cycling process is a serious drawback of these catalysts. Herein, in situ encapsulation of ultra-small Co/Co4N nanoparticles into N-doping carbon nanotubes (N-CNTs) anchored on reduced GO (Co/Co4N@N-CNTs/rGO) has been achieved through pyrolyzing a core-shell-structured ZIF-8@ZIF-67-modified GO (ZIF-8@ZIF-67/GO) precursor; the nanoparticles have been further applied as a bifunctional catalyst in Zn-air batteries. Benefitting from its uniform dispersion of Co-based particles, close contact of Co/Co4N species and N-CNTs, and high N content, Co/Co4N@N-CNTs/rGO shows outstanding catalytic activity/stability towards ORR and OER. Moreover, Zn volatilization and rGO introduction in Co/Co4N@N-CNTs/rGO can effectively promote the reactions of Zn-air cells. Hence, the Co/Co4N@N-CNTs/rGO-based conventional Zn-air battery exhibits a fantastic specific capacity of 783 mA h gZn-1, a continuous discharge platform over 6 days, a high-power density of ∼200 mW cm-2 and an ultra-long cycling life of 440 h with a small overpotential of ∼0.8 V. Moreover, a flexible Co/Co4N@N-CNTs/rGO-based Zn-air cell was also designed and revealed outstanding mechanical flexibility and good electrochemical performance, which suggests its potential application prospects in wearable electronic devices.

Carbon-Coated Yttria Hollow Spheres as Both Sulfur Immobilizer and Catalyst of Polysulfides Conversion in Lithium-Sulfur Batteries

Li-S battery has tremendous application prospect on account of the high theoretical specific capacity and large energy density, while its large-scale application is impeded by the severe shuttle effect and the slow electrochemical kinetics of polysulfides conversion. Herein, the Lewis acidic yttria hollow spheres (YHS) are rationally designed as both sulfur immobilizer and catalyst of polysulfides conversion for the advanced Li-S batteries. It can be known that the Lewis acidic yttria can effectively capture the Lewis basic polysulfides and thus mitigate the shuttle effect of Li-S battery; besides, yttria shows the enhanced catalytic effect for the kinetics of interconversion reaction from polysulfides to Li₂S. As a result, either as a sulfur host or as the separator coating, yttria plays a vital part in realizing the high specific discharge capacity and good cycle stability for Li-S battery. In particular, Li-S battery with YHS@C/S cathode and YHS/CNT-0.6- modified separator (2.1 mg cm^-2 active material loading) shows a good specific discharge capacity of 912.5 mAh g^-1 at 0.5C. Even after 200 steady cycles, the discharge specific capacity can keep as 842.3 mAh g^-1, and the capacity decay rate is only 0.038% per cycle. When active material areal loading is increased to 4.24 mg cm^-2, it still maintains a considerable areal capacity of 3.79 mAh cm^-2. In consequence, the synergy of polysulfides confinement and catalytic conversion reaction provides a meaningful exploration for achieving the high performance of Li-S batteries.

Designing a Multifunctional Separator for High-Performance Li-S Batteries at Elevated Temperature

The practical applications of lithium-sulfur (Li-S) batteries are seriously limited by the undesirable polysulfide shuttling and lithium dendrite growth. Herein, a multifunctional membrane is designed and prepared by coating a lithiated Nafion (Li@Nafion) layer and an Al₂ O₃ layer on the two sides of a routine polymer membrane (polypropylene/polyethylene/polypropylene, PEP). The Li@Nafion layer faced to the sulfur cathode builds a "polysulfide-phobic" surface to restrain the shuttle effect via Coulomb repulsion, while the Al₂ O₃ layer with a uniform porous structure aids in regulating homogeneous Li⁺ fluxes to achieve stable Li electrodeposition. As a result, the Li//Li symmetric cell with a Li@Nafion/PEP/Al₂ O₃ (LNPA) separator realizes stable Li plating/striping even after 1000 h at a high current density (5 mA cm^-2 ). Moreover, the Li-S batteries incorporating LNPA separators not only can achieve excellent outstanding cyclic stability at an ultrahigh sulfur loading (7.6 mg cm^-2 ), but also exhibit impressive electrochemical performance at an elevated temperature (60 °C). The rational design of the LNPA separator presents new insights to develop high-performance Li-S batteries.

Advanced Lithium Metal-Carbon Nanotube Composite Anode for High-Performance Lithium-Oxygen Batteries

The low Coulombic efficiency and hazardous dendrite growth hinder the adoption of lithium anode in high-energy density batteries. Herein, we report a lithium metal-carbon nanotube (Li-CNT) composite as an alternative to the long-term untamed lithium electrode to address the critical issues associated with the lithium anode in Li-O₂ batteries, where the lithium metal is impregnated in a porous carbon nanotube microsphere matrix (CNTm) and surface-passivated with a self-assembled monolayer of octadecylphosphonic acid as a tailor-designed solid electrolyte interphase (SEI). The high specific surface area of the Li-CNT composite reduces the local current density and thus suppresses the lithium dendrite formation upon cycling. Moreover, the tailor-designed SEI effectively separates the Li-CNT composite from the electrolyte solution and prevents the latter's further decomposition. When the Li-CNT composite anode is coupled with another CNTm-based O₂ cathode, the reversibility and cycle life of the resultant Li-O₂ batteries are drastically elevated.

Key Aspects of Lithium Metal Anodes for Lithium Metal Batteries

Rechargeable batteries are considered promising replacements for environmentally hazardous fossil fuel-based energy technologies. High-energy lithium-metal batteries have received tremendous attention for use in portable electronic devices and electric vehicles. However, the low Coulombic efficiency, short life cycle, huge volume expansion, uncontrolled dendrite growth, and endless interfacial reactions of the metallic lithium anode are major obstacles in their commercialization. Extensive research efforts have been devoted to address these issues and significant progress has been made by tuning electrolyte chemistry, designing electrode frameworks, discovering nanotechnology-based solutions, etc. This Review aims to provide a conceptual understanding of the current issues involved in using a lithium metal anode and to unveil its electrochemistry. The most recent advancements in lithium metal battery technology are outlined and suggestions for future research to develop a safe and stable lithium anode are presented.

Current Status and Future Prospects of Metal-Sulfur Batteries

Lithium-sulfur batteries are a major focus of academic and industrial energy-storage research due to their high theoretical energy density and the use of low-cost materials. The high energy density results from the conversion mechanism that lithium-sulfur cells utilize. The sulfur cathode, being naturally abundant and environmentally friendly, makes lithium-sulfur batteries a potential next-generation energy-storage technology. The current state of the research indicates that lithium-sulfur cells are now at the point of transitioning from laboratory-scale devices to a more practical energy-storage application. Based on similar electrochemical conversion reactions, the low-cost sulfur cathode can be coupled with a wide range of metallic anodes, such as sodium, potassium, magnesium, calcium, and aluminum. These new "metal-sulfur" systems exhibit great potential in either lowering the production cost or producing high energy density. Inspired by the rapid development of lithium-sulfur batteries and the prospect of metal-sulfur cells, here, over 450 research articles are summarized to analyze the research progress and explore the electrochemical characteristics, cell-assembly parameters, cell-testing conditions, and materials design. In addition to highlighting the current research progress, the possible future areas of research which are needed to bring conversion-type lithium-sulfur and other metal-sulfur batteries into the market are also discussed.

π-Concave Hosts for Curved Carbon Nanomaterials

Carbon nanomaterials have been at the forefront of nanotechnology since its inception. At the heart of this research are the curved carbon nanomaterial families: fullerenes and carbon nanotubes. While both have incredible properties that have been capitalized upon in a wide variety of applications, there is an aspect that is not commonly exploited by nanoscientists and organic chemists alike: the interaction of curved carbon nanomaterials with curved organic small molecules. By taking advantage of these interactions, new avenues are opened for the use of fullerenes and carbon nanotubes.

Enhanced Roles of Carbon Architectures in High-Performance Lithium-Ion Batteries

Lithium-ion batteries (LIBs), which are high-energy-density and low-safety-risk secondary batteries, are underpinned to the rise in electrochemical energy storage devices that satisfy the urgent demands of the global energy storage market. With the aim of achieving high energy density and fast-charging performance, the exploitation of simple and low-cost approaches for the production of high capacity, high density, high mass loading, and kinetically ion-accessible electrodes that maximize charge storage and transport in LIBs, is a critical need. Toward the construction of high-performance electrodes, carbons are promisingly used in the enhanced roles of active materials, electrochemical reaction frameworks for high-capacity noncarbons, and lightweight current collectors. Here, we review recent advances in the carbon engineering of electrodes for excellent electrochemical performance and structural stability, which is enabled by assembled carbon architectures that guarantee sufficient charge delivery and volume fluctuation buffering inside the electrode during cycling. Some specific feasible assembly methods, synergism between structural design components of carbon assemblies, and electrochemical performance enhancement are highlighted. The precise design of carbon cages by the assembly of graphene units is potentially useful for the controlled preparation of high-capacity carbon-caged noncarbon anodes with volumetric capacities over 2100 mAh cm^-3. Finally, insights are given on the prospects and challenges for designing carbon architectures for practical LIBs that simultaneously provide high energy densities (both gravimetric and volumetric) and high rate performance.

An N-doped porous carbon/MXene composite as a sulfur host for lithium–sulfur batteries

The sulfur content of the composite can reach 80%, and the composite has multiple adsorption for polysulfides.