Sulfur Vapor-Infiltrated 3D Carbon Nanotube Foam for Binder-Free High Areal Capacity Lithium-Sulfur Battery Composite Cathodes

New Emerging Fast Charging Microscale Electrode Materials

Fast charging lithium (Li)-ion batteries are intensively pursued for next-generation energy storage devices, whose electrochemical performance is largely determined by their constituent electrode materials. While nanosizing of electrode materials enhances high-rate capability in academic research, it presents practical limitations like volumetric packing density and high synthetic cost. As an alternative to nanosizing, microscale electrode materials cannot only effectively overcome the limitations of the nanosizing strategy but also satisfy the requirement of fast-charging batteries. Therefore, this review summarizes the new emerging microscale electrode materials for fast charging from the commercialization perspective. First, the fundamental theory of electronic/ionic motion in both individual active particles and the whole electrode is proposed. Then, based on these theories, the corresponding optimization strategies are summarized toward fast-charging microscale electrode materials. In addition, advanced functional design to tackle the mechanical degradation problems related to next generation high capacity alloy- and conversion-type electrode materials (Li, S, Si et al.) for achieving fast charging and stable cycling batteries. Finally, general conclusions and the future perspective on the potential research directions of microscale electrode materials are proposed. It is anticipated that this review will provide the basic guidelines for both fundamental research and practical applications of fast-charging batteries.

Aqueous heterocoagulation-driven assembly of graphene oxide and polycation-coated sulfur particles for nanocomposite Li-S battery cathodes

HYPOTHESIS

Reduced graphene oxide (rGO/polycation/sulfur) composites are promising cathode materials for Li-S battery applications because homogeneously dispersed sulfur nano/micro clusters in suitable carbon hosts enable remarkable cycle life for Li-S battery cells. New, benign and economic synthesis methods based only on aqueous colloidal dispersions are demanded for achieving high dispersity grade of sulfur within the carbon host. Colloidal interactions leading to heteroaggregation between carbonaceous lamellae and polycation-modified sulphur nanoparticles at ambient conditions in water are foreseen to afford nanocomposite cathodes, which maintain excellent electrochemical performance.

EXPERIMENTS

Hydrophilic sulfur nanoparticles (SNPs) were coated by low doses of polycation (PDDA) until reaching the isoelectric point (IEP), and in high dose to achieve charge reversal. Streaming potential titrations were performed to reveal appropriate mass ratios of PPDA, SNP and GO. Positively charged SNPs formed stable heteroaggregated structures with GO, and were employed to fabricate rGO/polycation/sulphur cathodes.

FINDINGS

Charge reversal characteristics of SNPs, polycation and GO were characterized quantitatively and mass ratios of PDDA to SNP beyond IEP were found to mediate attractive interactions leading to rapid heteroaggregation between SNPs and GO and also alleviate lithium polysulfide migration. The composite cathode showed an initial discharge capacity of 522 mAhg-1 at 0.2C rate with an excellent capacity retention of 91.4 % and coulombic efficiency of 98.5% after 100 charge-discharge cycles.

Freestanding carbon nanofoam papers with tunable porosity as lithium-sulfur battery cathodes

To reach energy density demands greater than 3 mA h cm-2 for practical applications, the electrode structure of lithium-sulfur batteries must undergo an architectural redesign. Freestanding carbon nanofoam papers derived from resorcinol-formaldehyde aerogels provide a three-dimensional conductive mesoporous network while facilitating electrolyte transport. Vapor-phase sulfur infiltration fully penetrates >100 μm thick electrodes and conformally coats the carbon aerogel surface providing areal capacities up to 4.1 mA h cm-2 at sulfur loadings of 6.4 mg cm-2. Electrode performance can be optimized for energy density or power density by tuning sulfur loading, pore size, and electrode thickness.

Caffeic Acid-Zinc Basic Salt/Chitosan Nanohybrid Possesses Controlled Release Properties and Exhibits In Vivo Anti-Inflammatory Activities

Caffeic acid (CA) exhibits a myriad of biological activities including cardioprotective action, antioxidant, antitumor, anti-inflammatory, and antimicrobial properties. On the other hand, CA presents low water solubility and poor bioavailability, which have limited its use for therapeutic applications. The objective of this study was to develop a nanohybrid of zinc basic salts (ZBS) and chitosan (Ch) containing CA (ZBS-CA/Ch) and evaluate its anti-edematogenic and antioxidant activity in dextran and carrageenan-induced paw edema model. The samples were obtained by coprecipitation method and characterized by X-ray diffraction, Fourier transform infrared (FT-IR), scanning electron microscope (SEM) and UV-visible spectroscopy. The release of caffeate anions from ZBS-CA and ZBS-CA/Ch is pH-dependent and is explained by a pseudo-second order kinetics model, with a linear correlation coefficient of R² ≥ 0.99 at pH 4.8 and 7.4. The in vivo pharmacological assays showed excellent anti-edematogenic and antioxidant action of the ZBS-CA/Ch nanoparticle with slowly releases of caffeate anions in the tissue, leading to a prolongation of CA-induced anti-edematogenic and anti-inflammatory activities, as well as improving its inhibition or sequestration antioxidant action toward reactive species. Overall, this study highlighted the importance of ZBS-CA/Ch as an optimal drug carrier.

Efficient Regulation of Polysulfides by Anatase/Bronze TiO2 Heterostructure/Polypyrrole Composites for High-Performance Lithium-Sulfur Batteries

Despite having ultra-high theoretical specific capacity and theoretical energy density, lithium-sulfur (Li-S) batteries suffer from their low Coulombic efficiency and poor lifespan, and the commercial application of Li-S batteries is seriously hampered by the severe "shuttle effect" of lithium polysulfides (LiPSs) and the large volume expansion ratio of the sulfur electrode during cycling. Designing functional hosts for sulfur cathodes is one of the most effective ways to immobilize the LiPSs and improve the electrochemical performance of a Li-S battery. In this work, a polypyrrole (PPy)-coated anatase/bronze TiO₂ (TAB) heterostructure was successfully prepared and used as a sulfur host. Results showed that the porous TAB could physically adsorb and chemically interact with LiPSs during charging and discharging processes, inhibiting the LiPSs' shuttle effect, and the TAB's heterostructure and PPy conductive layer are conducive to the rapid transport of Li⁺ and improve the conductivity of the electrode. By benefitting from these merits, Li-S batteries with TAB@S/PPy electrodes could deliver a high initial capacity of 1250.4 mAh g^-1 at 0.1 C and show an excellent cycling stability (the average capacity decay rate was 0.042% per cycle after 1000 cycles at 1 C). This work brings a new idea for the design of functional sulfur cathodes for high-performance Li-S battery.

Areal Density Control of Liquid-Supported Carbon Nanotube Thin Films

Carbon nanotube (CNT) films have extensive applications due to their excellent electrical, mechanical, and thermal properties. A grand challenge is controlling areal density of CNT films to accommodate various applications. Here, a method based on the Marangoni effect is used to fabricate liquid-supported CNT films with tunable areal density, scalable area, and transferability to arbitrary substrates. By adjusting the viscosity and surface tension of the base liquid media, the Marangoni flow area of surfactant-assisted single-walled CNT (SWCNT) dispersion on the surface of base media was controllable and sparse or dense SWCNT films can be easily obtained. The thickness of the films is controlled by changing the concentration of the SWCNT dispersion. These SWCNT-based transparent-conductive films have widely controllable transmittance and conductivity and exhibit great photoelectric properties (T ∼ 82.4%, R_s ∼ 407 Ω/sq).

Material Design and Energy Storage Mechanism of Mn-Based Cathodes for Aqueous Zinc-Ion Batteries

Mn-based cathodes have been widely explored for aqueous zinc-ion batteries (ZIBs), by virtue of their high theoretical capacity and low cost. However, Mn-based cathodes suffer from poor rate capability and cycling performance. Researchers have presented various approaches to address these issues. Therefore, these endeavors scattered in various directions (e. g., designing electrode structures, defect engineering and optimizing electrolytes) are necessary to be connected through a systematic review. Hence, we comprehensively overview Mn-based cathode materials for ZIBs from the aspects of phase compositions, electrochemical behaviors and energy storage mechanisms, and try to build internal relations between these factors. Modification strategies of Mn-based cathodes are then introduced. Furthermore, this review also provides some new perspectives on future efforts toward high-energy and long-life Mn-based cathodes for ZIBs.

LiNi0.6Co0.2Mn0.2O2 Cathodes Coated with Dual-Conductive Polymers for High-Rate and Long-Life Solid-State Lithium Batteries

High-energy density and safe solid lithium batteries call for cathodes with high capacity and good kinetic properties. In this work, LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathodes are coated with the ionic-electronic dual-conductive polymers composed of poly(ethylene glycol) (PEG)-doped polyaniline (PANI). Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, and thermogravimetric analysis reveal that the dual-conductive polymers are homogeneously coated on the surfaces of NCM622 cathodes with a thickness of approximately 10 nm. The solid-state lithium batteries consisting of the NCM622 cathodes coated with PANI-PEG show a specific capacity of 158 mA h g^-1 and a retention rate of 88% after 100 cycles at the rate of 0.1 C and room temperature, which are superior to the discharge capacity of 153 mA h g^-1 and capacity retention of 59% after 100 cycles for the batteries with the pristine NCM622 cathodes. Moreover, the cells with the coated cathodes display a better rate performance of 84 mA h g^-1 at 1 C than those with the uncoated ones which show a rate performance of 11 mA h g^-1 at 1 C.

Ni3FeN functionalized carbon nanofibers boosting polysulfide conversion for Li–S chemistry

Limiting the shuttle effect of polysulfides is an important means to realizing high energy density lithium–sulfur batteries (Li–S).

Lithiated Sulfur-Incorporated, Polymeric Cathode for Durable Lithium-Sulfur Batteries with Promoted Redox Kinetics

Even though lithium-sulfur (Li-S) batteries have made much progress in terms of the delivered specific capacity and cycling stability by the encapsulation of sulfur within conductive carbon matrixes or polar materials, challenges such as low active sulfur utilization and unacceptable Coulombic efficiency are still hindering their commercial use. Herein, a lithium-rich conjugated sulfur-incorporated, polymeric material based on poly(Li₂S₆-r-1,3-diisopropenylbenzene) (DIB) is developed as a cathode material for high rate and stable Li-S batteries. Motivated by extra Li⁺ ions affording fast Li⁺ redox kinetics across the conjugated aromatic backbones, the Li-rich sulfur-based copolymer exhibits high delivery capacities (934 mAh g^-1 at 120 cycles), impressive rate capabilities (727 mAh g^-1 even under a current of 2 A g^-1), and long electrochemical cycling performance over 500 cycles. Moreover, by use of the elastic nature and thermoplastic properties of the sulfur-incorporated, polymeric material, a prototype of a flexible Li-S pouch cell is constructed by using a poly(Li₂S₆-r-DIB) copolymer cathode and paired with the flexible carbon cloth/Si/Li anode, which exhibits stable electrochemical performance (658 mAh g^-1 after 100 cycles) and operational capability even under folding at various angle (30°, 60°, 90°, 120°, 150°, 180°). This work extends the molecular-design approach to obtaining a high-performance organosulfur cathode material by introducing extra Li⁺ ions to promote redox kinetics, which provides valuable guidance for the development of high-performance Li-S batteries for practical applications.

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.

Revamping Lithium-Sulfur Batteries for High Cell-Level Energy Density by Synergistic Utilization of Polysulfide Additives and Artificial Solid-Electrolyte Interphase Layers

Despite the high theoretical capacity of lithium-sulfur (Li-S) batteries, a high cell-level energy density and a long cycling life are barely achieved, mainly due to the large electrolyte-to-sulfur ratio, polysulfide (PS) shuttle causing the loss of active sulfur, and the formation of passivation layers on the Li anode. To raise the energy density, holding PS in the cathode has been the most popular approach. Still, it has failed, particularly, when the sulfur loading is high enough to have energy densities similar to those of commercial Li-ion batteries. Here, a practical approach of achieving high "cell-level" energy densities is attempted using lithium PS (LPS)-containing electrolytes instead of a pure electrolyte, reducing the electrolyte-to-sulfur ratio and PS diffusion out of the cathode due to concentration differences. Meanwhile, the persistent problems including PS passivation and Li dendrites are suppressed using Li₂ S-phobic artificial solid-electrolyte interphase (A-SEI) layers on Li metal. The synergistic effects from the LPS additives and A-SEI result in a superior cell-level volumetric energy density of 650 Wh L^-1 as well as large cumulative energy densities considering cycling life. This approach provides an important stepping stone to realize commercial Li-S batteries rivaling the current Li-ion batteries.

New Covalent Triazine Framework Rich in Nitrogen and Oxygen as a Host Material for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have been widely considered as the next-generation energy storage system but hindered by the soluble polysulfide intermediate-induced shuttle effect. Doping heteroatoms was confirmed to enhance the affinity of polysulfide and the carbon host, release the shuttle effect, and improve the battery performance. To enhance the Lewis acidity and reinforce the interaction between polysulfide and the carbon skeleton, a novel covalent triazine framework (CTFO) was designed and fabricated by copolymerizing 2,4,6-triphenoxy-s-triazine and 2,4,6-trichloro-1,3,5-triazine through Friedel-Crafts alkylation. Polymerization led to triazine substitution on the para-position of the phenoxy groups of 2,4,6-triphenoxy-triazine and produced two-dimensional three-connected honeycomb nanosheets. These nanosheets were confirmed to exhibit packing in the AB style through the intralayer π-π interaction to form a three-dimensional layered network with micropores of 0.5 nm. The practical and simulated results manifested the enhanced polysulfide capture capability due to the abundant N and O heteroatoms in CTFO. The unique porous polar network endowed CTFO with improved Li-S battery performance with high Coulombic efficiency, rate capability, and cycling stability. The S@CTFO cathode delivered an initial discharge capacity of 791 mAh g^-1 at 1C and retained a residual capacity of 512 mAh g^-1 after 300 charge-discharge cycles with an attenuation rate of 0.117%. The present results confirmed that multiple heteroatom doping enhances the interaction between the porous polar CTF skeleton and polysulfide intermediates to improve the Li-S battery performance.

Simple and Sustainable Preparation of Cathodes for Li-S Batteries: Regeneration of Granular Activated Carbon from the Odor Control System of a Wastewater Treatment Plant

To obtain a wide variety of green materials, numerous investigations have been undertaken on industrial waste that can act as sustainable resources. The use of hazardous wastes derived from wastewater treatment plants (WWTPs), especially the activated carbon used in odor control systems, is a highly abundant, scalable, and cost-effective strategy. The reuse of waste materials is a key aspect, especially for the sustainable development of emerging energy storage systems, such as lithium-sulfur (Li-S) batteries. Herein, granular active carbons from two WWTP treatment lines were regenerated in air at low temperature and utilized as the sulfur host with micro-/mesoporous framework. The resulting regenerated carbon and sulfur composites were employed as cathodes for Li-S cells. The SL-ACt3@S composite electrode with 60 wt% loaded sulfur exhibited a remarkable initial capacity of 1100 mAh g-1 at C/10 rate and higher than 800 mAh g-1 at C/2. Even at a rate of 1C, it maintained a high capacity of almost 700 mAh g-1 with a capacity retention of 85.4 % after 350 cycles, demonstrating a very low capacity fading of only 0.042 % per cycle. It is essential to note that the coulombic efficiency was always higher than 96 % during all the cycles. In this proposal, the only used source material was expired carbon from WWTP that was obtained with a simple and effective regeneration process. This "trash into treasure" strategy leads to a new way for using hazardous waste material as high-performance and environmentally safe electrodes for advanced Li-S batteries.

Long-life lithium-sulfur batteries with high areal capacity based on coaxial CNTs@TiN-TiO2 sponge

Rational design of heterostructures opens up new opportunities as an ideal catalyst system for lithium polysulfides conversion in lithium-sulfur battery. However, its traditional fabrication process is complex, which makes it difficult to reasonably control the content and distribution of each component. In this work, to rationally design the heterostructure, the atomic layer deposition is utilized to hybridize the TiO₂-TiN heterostructure with the three-dimensional carbon nanotube sponge. Through optimizing the deposited thickness of TiO₂ and TiN layers and adopting the annealing post-treatment, the derived coaxial sponge with uniform TiN-TiO₂ heterostructure exhibits the best catalytic ability. The corresponding lithium-sulfur battery shows enhanced electrochemical performance with high specific capacity of 1289 mAh g⁻¹ at 1 C and capacity retention of 85% after 500 cycles at 2 C. Furthermore, benefiting from the highly porous structure and interconnected conductive pathways from the sponge, its areal capacity reaches up to 21.5 mAh cm⁻².

It is challenging to optimize catalytic heterostructures for lithium sulfur (Li-S) batteries. Here, authors prepare nanometer-scale TiN-TiO₂ heterostructures via atomic layer deposition on carbon nanotube sponge to realize stable Li-S batteries with high areal capacity and improved rate capability.

The Effect of Topology on Phase Behavior under Confinement

This work studies how morphology (i.e., the shape of a structure) and topology (i.e., how different structures are connected) influence wall adsorption and capillary condensation under tight confinement. Numerical simulations based on classical density functional theory (cDFT) are run for a wide variety of geometries using both hard-sphere and Lennard-Jones fluids. These cDFT computations are compared to results obtained using the Minkowski functionals. It is found that the Minkowski functionals can provide a good description of the behavior of Lennard-Jones fluids down to small system sizes. In addition, through decomposition of the free energy, the Minkowski functionals provide a good framework to better understand what are the dominant contributions to the phase behavior of a system. Lastly, while studying the phase envelope shift as a function of the Minkowski functionals it is found that topology has a different effect depending on whether the phase transition under consideration is a continuous or a discrete (first-order) transition.

From Fundamental Understanding to Engineering Design of High-Performance Thick Electrodes for Scalable Energy-Storage Systems

The ever-growing needs for renewable energy demand the pursuit of batteries with higher energy/power output. A thick electrode design is considered as a promising solution for high-energy batteries due to the minimized inactive material ratio at the device level. Most of the current research focuses on pushing the electrode thickness to a maximum limit; however, very few of them thoroughly analyze the effect of electrode thickness on cell-level energy densities as well as the balance between energy and power density. Here, a realistic assessment of the combined effect of electrode thickness with other key design parameters is provided, such as active material fraction and electrode porosity, which affect the cell-level energy/power densities of lithium-LiNi_0.6 Mn_0.2 Co_0.2 O₂ (Li-NMC622) and lithium-sulfur (Li-S) cells as two model battery systems, is provided. Based on the state-of-the-art lithium batteries, key research targets are quantified to achieve 500 Wh kg^-1 /800 Wh L^-1 cell-level energy densities and strategies are elaborated to simultaneously enhance energy/power output. Furthermore, the remaining challenges are highlighted toward realizing scalable high-energy/power energy-storage systems.

Continuous Fly-Through High-Temperature Synthesis of Nanocatalysts

The conventional thermal treatment systems typically feature low ramping/cooling rates, which lead to steep thermal gradients that generate inefficient, nonuniform reaction conditions and result in nanoparticle aggregation. Herein, we demonstrate a continuous fly-through material synthesis approach using a novel high-temperature reactor design based on the emerging thermal-shock technology. By facing two sheets of carbon paper with a small distance apart (1-3 mm), uniform and ultrahigh temperatures can be reached up to 3200 K within 50 ms by simply applying a voltage of 15 V. The raw materials can be continuously fed through the device, allowing the final products to be rapidly collected. As a proof-of-concept demonstration, we synthesized Pt nanocatalysts (∼4 nm) anchored on carbon black via this reactor at ∼1400 K. Furthermore, we find it features excellent electrocatalytic activities toward methanol oxidation reaction. This work offers a highly efficient platform for nanomaterials synthesis at high temperatures.

In situ Construction of Robust Biphasic Surface Layers on Lithium Metal for Lithium-Sulfide Batteries with Long Cycle Life

Lithium-sulfur (Li-S) batteries have potential in high energy density battery systems. However, intermediates of lithium polysulfides (LiPSs) can easily shuttle to the Li anode and react with Li metal to deplete the active materials and cause rapid failure of the battery. A facile solution pretreatment method for Li anodes involving a solution of metal fluorides/dimethylsulfoxide was developed to construct robust biphasic surface layers (BSLs) in situ. The BSLs consist of lithiophilic alloy (Li_x M) and LiF phases on Li metal, which inhibit the shuttle effect and increase the cycle life of Li-S batteries. The BSLs allow Li⁺ transport and they inhibit dendrite growth and shield the Li anodes from corrosive reaction with LiPSs. Li-S batteries containing BSLs-Li anodes demonstrate excellent cycling over 1000 cycles at 1 C and simultaneously maintain a high coulombic efficiency of 98.2 %. Based on our experimental and theoretical results, we propose a strategy for inhibition of the shuttle effect that produces high stability Li-S batteries.

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.

Sb nanosheet modified separator for Li-S batteries with excellent electrochemical performance

An air-stable antimony (Sb) nanosheet modified separator (SbNs/separator) has been prepared by coating exfoliated Sb nanosheets (SbNs) successfully onto a pristine separator through a vacuum infiltration method. The as-prepared Li-S batteries using SbNs/separators exhibit much improved electrochemical performance compared to the ones using commercial separators. The coulombic efficiency (CE) of the Li-S battery using the SbNs/separator after the initial cycle is close to 100% at a current density of 0.1 A g-1, and 660 mA h g-1 capacity retained after 100 cycles. The rate capability of Li-S battery using SbNs/separator delivers a reversible capacity of 425 mA h g-1 when the current density increases to 1 A g-1. The improved electrochemical performance is mainly attributed to the following reasons. Firstly, the combination of physical adsorption and chemical bonding between SbNs and lithium polysulfides (LiPSs), which efficiently inhibits the shuttle phenomena of LiPSs. Secondly, the good electronic conductivity of SbNs improves the utilization of the adsorbed LiPSs, which benefits the capacity release of active materials. Lastly, the fast conversion kinetics of intermediate LiPSs caused by the catalytic effect from SbNs further suppresses the shuttle effect of LiPSs. The SbNs/separators exhibit a great potential for the future high-performance Li-S batteries.

Strategy of Enhancing the Volumetric Energy Density for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries hold the promise of the next generation energy storage system beyond state-of-the-art lithium-ion batteries. Despite the attractive gravimetric energy density (W_G ), the volumetric energy density (W_V ) still remains a great challenge for the practical application, based on the primary requirement of Small and Light for Li-S batteries. This review highlights the importance of cathode density, sulfur content, electroactivity in achieving high energy densities. In the first part, key factors are analyzed in a model on negative/positive ratio, cathode design, and electrolyte/sulfur ratio, orientated toward energy densities of 700 Wh L^-1 /500 Wh kg^-1 . Subsequently, recent progresses on enhancing W_V for coin/pouch cells are reviewed primarily on cathode. Especially, the "Three High One Low" (THOL) (high sulfur fraction, high sulfur loading, high density host, and low electrolyte quantity) is proposed as a feasible strategy for achieving high W_V , taking high W_G into consideration simultaneously. Meanwhile, host materials with desired catalytic activity should be paid more attention for fabricating high performance cathode. In the last part, key engineering technologies on manipulating the cathode porosity/density are discussed, including calendering and dry electrode coating. Finally, a future outlook is provided for enhancing both W_V and W_G of the Li-S batteries.

Molecular to Macroscale Energy Absorption Mechanisms in Biological Body Armour Illuminated by Scanning X-ray Diffraction with In Situ Compression

Determining multiscale, concurrent strain, and deformation mechanisms in hierarchical biological materials is a crucial engineering goal, to understand structural optimization strategies in Nature. However, experimentally characterizing complex strain and displacement fields within a 3D hierarchical composite, in a multiscale full-field manner, is challenging. Here, we determined the in situ strains at the macro-, meso-, and molecular-levels in stomatopod cuticle simultaneously, by exploiting the anisotropy of the 3D fiber diffraction coupled with sample rotation. The results demonstrate the method, using the mineralized 3D α-chitin fiber networks as strain sensors, can capture submicrometer deformation of a single lamella (mesoscale), can extract strain information on multiple constituents concurrently, and shows that α-chitin fiber networks deform elastically while the surrounding matrix deforms plastically before systematic failure under compression. Further, the results demonstrate a molecular-level prestrain gradient in chitin fibers, resulting from different mineralization degrees in the exo- and endo cuticle.

Immobilizing Polysulfide by In Situ Topochemical Oxidation Derivative TiC@Carbon-Included TiO2 Core-Shell Sulfur Hosts for Advanced Lithium-Sulfur Batteries

The performance of lithium-sulfur (Li-S) batteries is greatly hindered by the notorious shuttle effect of lithium polysulfides (LiPSs). To address this issue, in situ topochemical oxidation derivative TiC@carbon-included TiO₂ (TiC@C-TiO₂ ) core-shell composite is designed and proposed as a multifunctional sulfur host, which integrates the merits of conductive TiC core to facilitate the redox reaction kinetics of sulfur species, and porous C-TiO₂ shell to suppress the dissolution and shuttling of LiPSs through chemisorption. A unique dual chemical mediation mechanism is demonstrated for the proposed TiC@C-TiO₂ composite that synergistically entraps LiPSs through thiosulfate/polythionate conversion coupled with strong polar-polar interaction. The morphological characterization reveals that the TiC@C-TiO₂ -based cathode can well regulate the distribution of electrode materials to retard their accumulation inside the electrode, ensuring effective contact between the active materials and electrolyte. Based on its unique function and structure, the cathode delivers an improved capacity of 1256 mAh g^-1 at 0.2C, a remarkable rate capability of 643 mAh g^-1 , and an ultralow capacity decay rate of 0.065% per cycle at 2C over 900 cycles. This work not only demonstrates a dual chemical mediation mechanism to immobilize LiPSs, but also provides a universal strategy to construct multifunctional sulfur hosts for advanced Li-S batteries.

Temperature-Dependent Vapor Infiltration of Sulfur into Highly Porous Hierarchical Three-Dimensional Conductive Carbon Networks for Lithium Ion Battery Applications

Hierarchical, conductive, porous, three-dimensional (3D) carbon networks based on carbon nanotubes are used as a scaffold material for the incorporation of sulfur in the vapor phase to produce carbon nanotube tube/sulfur (CNTT/S) composites for application in lithium ion batteries (LIBs) as a cathode material. The high conductivity of the carbon nanotube-based scaffold material, in combination with vapor infiltration of sulfur, allows for improved utilization of insulating sulfur as the active material in the cathode. When sulfur is evenly distributed throughout the network via vapor infiltration, the carbon scaffold material confines the sulfur, allowing the sulfur to become electrochemically active in the context of an LIB. The electrochemical performance of the sulfur cathode was further investigated as a function of the temperature used for the vapor infiltration of sulfur into the carbon scaffolds (155, 175, and 200 °C) in order to determine the ideal infiltration temperature to maximize sulfur loading and minimize the polysulfide shuttle effect. In addition, the nature of the incorporation of sulfur at the interfaces within the 3D carbon network at the different vapor infiltration temperatures will be investigated via Raman, scanning electron microscopy/energy dispersive X-ray, and X-ray photoelectron spectroscopy. The resulting CNTT/S composites, infiltrated at each temperature, were incorporated into a half-cell using Li metal as a counter electrode and a 0.7 M LiTFSI electrolyte in ether solvents and characterized electrochemically using cyclic voltammetry measurements. The results indicate that the CNTT matrix infiltrated with sulfur at the highest temperature (200 °C) had improved incorporation of sulfur into the carbon network, the best electrochemical performance, and the highest sulfur loading, 8.4 mg/cm2, compared to the CNTT matrices infiltrated at 155 and 175 °C, with sulfur loadings of 4.8 and 6.3 mg/cm2, respectively.

MnO2 nanoflowers grown on a polypropylene separator for use as both a barrier and an accelerator of polysulfides for high-performance Li-S batteries

The separator modification has been considered to be the most effective approach to obtain high-stability lithium-sulfur batteries (LSBs). Therefore, a separator with an ultralight modification layer plays an indispensable role to obtain LSBs with high specific capacity and high energy density. Herein, we report a novel modified separator with an ultrathin and lightweight MnO2 functional layer (500 nm, 0.1 mg cm-2), which was grown in situ on a Celgard-2400 separator (MnO2@PP) via a facile hydrothermal reaction. The MnO2@PP separator effectively suppressed the shuttle of lithium polysulfides (LiPSs) and improved the redox process. In addition, the strong chemical affinity of MnO2 for LiPSs was also verified by first-principles calculations. Benefiting from these advantages, the cell with the MnO2@PP separator delivered a high rate performance of 759 mA h g-1 at 2.5 C and an initial capacity of 825 mA h g-1 with a retention of 684 mA h g-1 after 400 cycles at 1.25 C. Even with a high sulfur loading of 6 mg cm-2, the obtained cell exhibited a reversible capacity of 747 mA h g-1 after 150 cycles.

Complete encapsulation of sulfur through interfacial energy control of sulfur solutions for high-performance Li-S batteries

Complete encapsulation of high-content sulfur into porous carbon or carbon composites is crucial for high-performance Li−S cells. However, the low-to-moderate compatibility of sulfur-dissolved solution with carbon causes difficulty in completely loading sulfur into the porous host. We control the interfacial energy of the sulfur solution by adding a solvent with high compatibility with the carbon surface. The use of NMP improves the infiltration of sulfur solution effectively, resulting in complete sulfur encapsulation. We observe that the control of sulfur loading greatly affects Li−S battery performance. We identify significantly superior cell performance in the complete encapsulation. Our method can also be applied to effectively load active materials for next-generation energy storage devices.

Complete encapsulation of high-content sulfur in porous carbon is crucial for high performance Li−S batteries. To this end, unlike conventional approaches to control the pore of carbon hosts, we demonstrate controlling the interfacial energy of the solution in the process of penetrating the sulfur-dissolved solution. We unveil, experimentally and theoretically, that the interfacial energy with the carbon surface of the sulfur solution is the key to driving complete encapsulation of sulfur. In the infiltration of sulfur solutions with N-methyl-2-pyrrolidone, we achieve complete encapsulation of sulfur, even up to 85 wt %. The sulfur fully encapsulated cathode achieves markedly high volumetric capacity and stable cycle operation in its Li−S battery applications. We achieve a volumetric capacity of 855 mAh/cm³ at 0.2C and a capacity reduction of 0.071% per cycle up to 300 cycles at 1C.

Nanoengineering to achieve high efficiency practical lithium-sulfur batteries

Rapidly increasing markets for electric vehicles (EVs), energy storage for backup support systems and high-power portable electronics demand batteries with higher energy densities and longer cycle lives. Among the various electrochemical energy storage systems, lithium-sulfur (Li-S) batteries have the potential to become the next generation rechargeable batteries because of their high specific energy at low cost. However, the development of practical Li-S batteries for commercial products has been challenged by several obstacles, including unstable cycle life and low sulfur utilization. Only a few studies have considered the importance of low electrolyte and high sulfur loading to improve the overall energy densities of Li-S cells. This article reviews the recent developments of Li-S batteries that can meet the benchmarks of practical parameters and exceed the practical energy density of lithium-ion batteries (LIBs) including areal sulfur loading of at least 4 mg cm^-2, electrolyte to sulfur ratio of less than 10 μL mg^-1, and high cycling stability of over 300 cycles. This review presents the advancements in each component in Li-S batteries, including the enhancement of the electrochemical properties of sulfur cathodes, lithium anodes, or electrolytes. Also identified are several important strategies of nanoengineering and how they address the practical limitations of Li-S batteries to compete against LIBs. Additionally, perspectives on fundamentals, technology, and materials are provided for the development of Li-S batteries based on nanomaterials and nanoengineering so that they can enter the market of high energy density rechargeable storage systems.

Octopus-Inspired Design of Apical NiS2 Nanoparticles Supported on Hierarchical Carbon Composites as an Efficient Host for Lithium Sulfur Batteries with High Sulfur Loading

Developing high-performance Li-S batteries with high sulfur loading is highly desirable for practical application and remains a major challenge. To achieve this goal, the following requirements for designing carbon/metal compound composites need to be met: (i) the carbon materials need to exhibit suitable specific surface area, void structure, and electrical conductivity; (ii) the weight content of the metal compounds should be low; and (iii) the metal compounds need to show a strong adsorption and efficient electrocatalytic function for LiPSs. In this study, inspired by the body structure of an octopus, a new carbon/NiS₂ hierarchical composite is reported, in which the apical NiS₂ nanoparticles (0D) on a 1D carbon nanotubes (CNTs) are supported on a three-dimensional carbon (3DC) framework (3DC-CNTs-NiS₂). The 3DC-CNTs-NiS₂ composite has a high specific surface area (271 m² g^-1), good electrical conductivity, and low NiS₂ content (9.2 wt %), and the apical NiS₂ nanoparticles are capable of adsorption and electrocatalysis toward LiPSs, demonstrated by both electrochemical characterization and theoretical calculation. When used as a cathode host of the Li-S battery, it exhibits an ultra-stable cycling performance with a fade rate of 0.043% per cycle over 1000 cycles; even with a high S loading (6.5 mg cm^-2 with 90 wt % of S), the soft package battery delivers a high area capacity of 5.0 mAh cm^-2 under the E/S ratio of 5 μL_E mg^-1_s. This work provides a new approach to design and fabricate multi-functional S hosts with high S loading.

Built-In Catalysis in Confined Nanoreactors for High-Loading Li-S Batteries

A cathode host with strong sulfur/polysulfide confinement and fast redox kinetics is a challenging demand for high-loading lithium-sulfur batteries. Recently, porous carbon hosts derived from metal-organic frameworks (MOFs) have attracted wide attention due to their unique spatial structure and customizable reaction sites. However, the loading and rate performance of Li-S cells are still restricted by the disordered pore distribution and surface catalysis in these hosts. Here, we propose a concept of built-in catalysis to accelerate lithium polysulfide (LiPSs) conversion in confined nanoreactors, i.e., laterally stacked ordered crevice pores encompassed by MoS₂-decorated carbon thin layers. The functions of S-fixability and LiPS catalysis in these mesoporous cavity reactors benefit from the 2D interface contact between ultrathin catalytic MoS₂ and conductive C pyrolyzed from Al-MOF. The integrated function of adsorption-catalysis-conversion endows the sulfur-infused C@MoS₂ electrode with a high initial capacity of 1240 mAh g^-1 at 0.2 C, long life cycle stability of at least 1000 cycles at 2 C, and high rate endurance up to 20 C. This electrode also exhibits commercial potential in view of considerable capacity release and reversibility under high sulfur loading (6 mg cm^-2 and ∼80 wt %) and lean electrolyte (E/S ratio of 5 μL mg^-1). This study provides a promising design solution of a catalysis-conduction 2D interface in a 3D skeleton for high-loading Li-S batteries.

Enzyme-Free Glucose Biosensors Based on MoS2 Nanocomposites

High-performance glucose biosensors are highly desired for healthcare. To meet these demands, glucose biosensors, particularly enzyme-free glucose biosensors, have received much attention. Two-dimensional materials, e.g., graphene, with high surface area, excellent electrical properties, and good biocompatibility, have been the main focus of biosensor research in the last decade. This review presents the recent progress made in enzyme-free glucose biosensors based on MoS2 nanocomposites. Two different techniques for glucose detections are introduced, with an emphasis on electrochemical glucose biosensors. Challenges and future perspectives of MoS2 nanocomposite glucose biosensors are also discussed.

Flexible 3D carbon cloth as a high-performing electrode for energy storage and conversion

High-performance energy storage and conversion devices with high energy density, power density and long-term cycling life are of great importance in current consumer electronics, portable electronics and electric vehicles. Carbon materials have been widely investigated and utilized in various energy storage and conversion devices due to their excellent conductivity, mechanical and chemical stability, and low cost. Abundant excellent reviews have summarized the most recent progress and future outlooks for most of the current prime carbon materials used in energy storage and conversion devices, such as carbon nanotubes, fullerene, graphene, porous carbon and carbon fibers. However, the significance of three-dimensional (3D) commercial carbon cloth (CC), one of the key carbon materials with outstanding mechanical stability, high conductivity and flexibility, in the energy storage and conversion field, especially in wearable electronics and flexible devices, has not been systematically summarized yet. In this review article, we present a careful investigation of flexible CC in the energy storage and conversion field. We first give a general introduction to the common properties of CC and the roles it has played in energy storage and conversion systems. Then, we meticulously investigate the crucial role of CC in typical electrochemical energy storage systems, including lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries and supercapacitors. Following a description of the wide application potential of CC in electrocatalytic hydrogen evolution, oxygen evolution/reduction, full-water splitting, etc., we will give a brief introduction to the application of CC in the areas of photocatalytically and photoelectrochemically induced solar energy conversion and storage. The review will end with a brief summary of the typical superiorities that CC has in current energy conversion and storage systems, as well as providing some perspectives and outlooks on its future applications in the field. Our main interest will be focused on CC-based flexible devices due to the inherent superiority of CC and the increasing demand for flexible and wearable electronics.

B,N Codoped Graphitic Nanotubes Loaded with Co Nanoparticles as Superior Sulfur Host for Advanced Li-S Batteries

Lithium-sulfur batteries (LSBs) are considered as one of the best candidates for novel rechargeable batteries due to their high energy densities and abundant required materials. However, the poor conductivity and large volume expansion of sulfur and the "shuttle effect" of lithium polysulfides (LPSs) have significantly hindered the development and successful commercialization of LSBs. Bean-like B,N codoped carbon nanotubes loaded with Co nanoparticles (Co@BNTs), which can act as advanced sulfur hosts for the novel LSB cathode, are fabricated. Uniform graphitic nanotubes improve the conductivity of the electrode and load more electroactive sulfur and buffer volume expansion during the electrochemical reaction. In addition, loaded Co nanoparticles and codoped B,N sites can significantly suppress the "shuttle effect" of LPSs with strong chemical interaction. It is established that the Co nanoparticles and codoped B,N can provide more active sites to catalyze the redox reaction of sulfur cathode. This stable Co@BNTs-S cathode displays an exceptional electrochemical performance (1160 mA h g^-1 after 200 cycles at 0.1 C) and outstanding stable cycle performance (1008 mA h g^-1 after 400 cycles at 1.0 C with an extremely low attenuation rate of 0.038% per cycle).

Enhanced Chemical Immobilization and Catalytic Conversion of Polysulfide Intermediates Using Metallic Mo Nanoclusters for High-Performance Li-S Batteries

Rechargeable lithium-sulfur batteries have attracted tremendous scientific attention owing to their high energy density. However, their practical application is greatly hindered by the notorious shuttling of soluble lithium polysulfide (LPS) intermediates with sluggish redox reactions and uncontrolled precipitation behavior. Herein, we report a semiliquid cathode composed of an active LPS solution/carbon nanofiber (CNF) composite layer, capped with a carbon nanotube (CNT) thin film decorated with metallic Mo nanoclusters that regulate the electrochemical redox reactions of LPS. The trace amount (0.05 mg cm^-2) of metallic Mo on the CNT film provides sufficient capturing centers for the chemical immobilization of LPS. Together with physical blocking of LPS by the compact CNT film, free diffusion of LPS is significantly restrained and the self-discharge behavior of the Li-S cell is thus effectively suppressed. Importantly, the metallic Mo nanoclusters enable fast catalytic conversion of LPS and regular deposition of lithium sulfide. As a result, the engineered cathode exhibits a high active sulfur utilization (1401 mAh g^-1 at 0.1 C), stable cycling (500 cycles at 1 C with 0.06% decay per cycle), high rate performance (694 mAh g^-1 at 5 C), and low self-discharge rate (3% after 72 h of rest). Moreover, a high reversible areal capacity of 4.75 mAh cm^-2 is maintained after 100 cycles at 0.2 C for a cathode with a high sulfur loading of 7.64 mg cm^-2. This work provides significant insight into the structural and materials design of an advanced sulfur-based cathode that effectively regulates the electrochemical reactions of sulfur species in high-energy Li-S batteries.

Recent advances in soft functional materials: preparation, functions and applications

Synthetic materials and biomaterials with elastic moduli lower than 10 MPa are generally considered as soft materials. Research studies on soft materials have been boosted due to their intriguing features such as light-weight, low modulus, stretchability, and a diverse range of functions including sensing, actuating, insulating and transporting. They are ideal materials for applications in smart textiles, flexible devices and wearable electronics. On the other hand, benefiting from the advances in materials science and chemistry, novel soft materials with tailored properties and functions could be prepared to fulfil the specific requirements. In this review, the current progress of soft materials, ranging from materials design, preparation and application are critically summarized based on three categories, namely gels, foams and elastomers. The chemical, physical and electrical properties and the applications are elaborated. This review aims to provide a comprehensive overview of soft materials to researchers in different disciplines.

Advanced Li2 S/Si Full Battery Enabled by TiN Polysulfide Immobilizer

Lithium sulfide (Li₂ S) is a promising cathode material with high capacity, which can be paired with nonlithium metal anodes such as silicon or tin so that the safety issues caused by the Li anode can be effectively avoided. However, the Li₂ S full cell suffers from rapid capacity degradation due to the dissolution of intermediate polysulfides. Herein, a Li₂ S/Si full cell is designed with a Li₂ S cathode incorporated by titanium nitride (TiN) polysulfide immobilizer within parallel hollow carbon (PHC). This full cell delivers a high initial reversible capacity of 702 mAh g_Li2S ^-1 (1007 mAh g_sulfur ^-1 ) at 0.5 C rate and excellent cyclability with only 0.4% capacity fade per cycle over 200 cycles. The long cycle stability is ascribed to the strong polysulfide anchor effect of TiN and highly efficient electron/ion transport within the interconnected web-like architecture of PHC. Theoretical calculations, self-discharge measurements, and anode stability experiments further confirm the strong adsorption of polysulfides on the TiN surface. The present work demonstrates that the flexible Li₂ S cathode and paired Si anode can be used to achieve highly efficient Li-S full cells.

Three-dimensional biomass derived hard carbon with reconstructed surface as a free-standing anode for sodium-ion batteries

A three-dimensional free-standing hard carbon (FHC) electrode is synthesized by carbonizing the hemp haulm and employed as anode for sodium-ion batteries directly. A high current charging-discharging process is carried out to reconstruct surface structure of the FHC. Surface reconstructed FHC display a high capacity of 256 mAh/g and enhanced rate ability. With the formation of order surface structure, the plateau capacity increase and more sodium ions can insert into the FHC. This work demonstrates the importance of surface structure for sodium ion diffusion and storage and provide a new strategy to design high-performance anode materials.

Controllable synthesis of mesoporous carbon microspheres with renewable water glass as a template for lithium-sulfur batteries

Mesoporous carbon microspheres (MCMs) were prepared via a spray drying-assisted template method using resorcinol-formaldehyde as the carbon precursor and water glass as the template. The pore structure could be controlled by adjusting the hydrolysis time, hydrolysis temperature, concentration of the water glass and reactant ratio. Water glass could be recycled after use, making this strategy environmentally friendly and cost-effective. MCMs with three-dimensional interconnected networks, high surface area (852-1549 m² g^-1), large pore volume (1.7-2.1 cm³ g^-1) and controllable pore diameter (3.8-15.1 nm) were constructed and have good electrical conductivity and a large volume for sulfur loading. The S/MCM composites with abundant residual nanochannels could not only benefit for the diffusion of electrolyte but also improve the utilization of sulfur and buffer the volume expansion of sulfur. The MCMs with relatively small mesopores manifest a high reversible capacity and rate performance owing to the strong confinement effect of polysulfides. MCM-1 delivered an initial capacity of 888.7 mA h g^-1 under 0.5C with a capacity retention of 700.5 mA h g^-1 after 100 cycles. The good electrochemical performance confirms that mesoporous carbon microspheres can be an excellent host material for sulfur cathodes.