Hierarchical Micro-Nanoclusters of Bimetallic Layered Hydroxide Polyhedrons as Advanced Sulfur Reservoir for High-Performance Lithium-Sulfur Batteries

Juice Vesicles Bioreactors Technology for Constructing Advanced Carbon-Based Energy Storage

The construction of high-quality carbon-based energy materials through biotechnology has always been an eager goal of the scientific community. Herein, juice vesicles bioreactors (JVBs) bio-technology based on hesperidium (e.g., pomelo, waxberry, oranges) is first reported for preparation of carbon-based composites with controllable components, adjustable morphologies, and sizes. JVBs serve as miniature reaction vessels that enable sophisticated confined chemical reactions to take place, ultimately resulting in the formations of complex carbon composites. The newly developed approach is highly versatile and can be compatible with a wide range of materials including metals, alloys, and metal compounds. The growth and self-assembly mechanisms of carbon composites via JVBs are explained. For illustration, NiCo alloy nanoparticles are successfully in situ implanted into pomelo vesicles crosslinked carbon (PCC) by JVBs, and their applications as sulfur/carbon cathodes for lithium-sulfur batteries are explored. The well-designed PCC/NiCo-S electrode exhibits superior high-rate properties and enhanced long-term stability. Synergistic reinforcement mechanisms on transportation of ions/electrons of interface reactions and catalytic conversion of lithium polysulfides arising from metal alloy and carbon architecture are proposed with the aid of DFT calculations. The research provides a novel biosynthetic route to rational design and fabrication of carbon composites for advanced energy storage.

Enhancing supercapacitor electrochemical performance through acetate-ion intercalation in layered nickel-cobalt double hydroxides

Enhancing the performance of layered nickel-cobalt double hydroxides (NiCo-LDH) as electrode materials for supercapacitors represents a promising strategy for optimizing energy storage systems. However, the complexity of the preparation method for electrode materials with enhanced electrochemical performance and the inherent defects of nickel-cobalt LDH remain formidable challenges. In this study, we synthesized acetate-ion-intercalated NiCo-LDH (NCLA) through a simple one-step hydrothermal method. The physical and chemical structural properties and supercapacitor characteristics of the as-prepared NCLA were systematically characterized. The results indicated that the introduction of Ac- engendered a distinctive tetragonal crystal structure in NiCo-LDH, concomitant with a reduced interlayer spacing, thus enhancing structural stability. Electrochemical measurements revealed that NCLA-8 exhibited a specific capacitance of 1032.2 F g-1 at a current density of 1 A g-1 and a high specific capacitance of 922 F g-1 at 10 A g-1, demonstrating a rate performance of 89.3%. Furthermore, NCLA-8 was used to construct the positive electrode of an asymmetric supercapacitor, while the negative electrode was composed of activated carbon. This configuration resulted in an energy density of 67.7 Wh kg-1 at a power density of 800 W kg-1. Remarkably, the asymmetric supercapacitor retained 82.8% of its initial capacitance following 3000 charge-discharge cycles at a current density of 10 A g-1. Thus, this study demonstrates the efficacy of acetate-ion intercalation in enhancing the electrochemical performance of NiCo-LDH, establishing it as a viable electrode material for supercapacitors.

Dual-Confinement Effect of Nanocages@Nanotubes Suppresses Polysulfide Shuttle Effect for High-Performance Lithium-Sulfur Batteries

The shuttle effect of lithium polysulfides (LiPSs) severely hinders the development and commercialization of lithium-sulfur batteries, and the design of high-conductive carbon fiber-host material has become a key solution to suppress the shuttle effect. In this work, a unique Co/CoN-carbon nanocages@TiO2-carbon nanotubes structure (NC@TiO2-CNTs) is constructed using an electrospinning and nitriding process. Lithium-sulfur batteries using NC@TiO2-CNTs as cathode host materials exhibit high sulfur utilization (1527 mAh g-1 at 0.2 C) and can still maintain a discharge capacity of 663 mAh g-1 at a high current density of 5 C, and the capacity loss is only 0.056% per cycle during 500 cycles at 1 C. It is worth noting that even under extreme conditions (sulfur-loading = 90%, surface-loading = 5.0 mg cm-2 (S), and E/S = 6.63 µL mg-1), the lithium-sulfur batteries can still provide a reversible capacity of 4 mAh cm-2. Throughdensity functional theory calculations, it has been found that the Co/CoN heterostructures can adsorb and catalyze LiPSs conversion effectively. Simultaneously, the TiO2 can adsorb LiPSs and transfer Li+ selectively, achieving dual confinement for the shuttle effect of LiPSs (nanocages and nanotubes). The new findings provide a new performance enhancement strategy for the commercialization of lithium-sulfur batteries.

Ultra-Dispersed α-MoC1-x Embedded in a Plum-Like N-Doped Carbon Framework as a Synergistic Adsorption-Electrocatalysis Interlayer for High-Performance Li-S Batteries

The shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) severely hinder the scalable application of lithium-sulfurr (Li-S) batteries. Herein, the highly dispersed α-phase molybdenum carbide nano-crystallites embedded in a porous nitrogen-doped carbon framework (α-MoC1-x @NCF) are developed via a simple metal-organic frameworks (MOFs) assisted strategy and proposed as the multifunctional separator interlayer for Li-S batteries. The inlaid MoC1-x nanocrystals and in situ doped nitrogen atoms provide a strong chemisorption and outstanding electrocatalytic conversion toward LiPSs, whereas the unique plum-like carbon framework with hierarchical porosity enables fast electron/Li+ transfer and can physically suppress LiPSs shuttling. Benefiting from the synergistic trapping-catalyzing effect of the MoC1-x @NCF interlayer toward LiPSs, the assembled Li-S battery achieves high discharge capacities (1588.1 mAh g-1 at 0.1 C), impressive rate capability (655.8 mAh g-1 at 4.0 C) and ultra-stable lifespan (a low capacity decay of 0.059% per cycle over 650 cycles at 1.0 C). Even at an elevated sulfur loading (6.0 mg cm-2 ) and lean electrolyte (E/S is ≈5.8 µL mg-1 ), the battery can still achieve a superb areal capacity of 5.2 mAh cm-2 . This work affords an effective design strategy for the construction of muti-functional interlayer in advanced Li-S batteries.

NiCo-LDH Hollow Nanocage Oxygen Evolution Reaction Promotes Luminol Electrochemiluminescence

Conventional luminol co-reactant electrochemiluminescence (ECL) systems suffer from low stability and accuracy due to factors such as the ease of decomposition of hydrogen peroxide and inefficient generation of reactive oxygen species (ROS) from dissolved oxygen. Inspired by the luminol ECL mechanism mediated by oxygen evolution reaction (OER), the nickel-cobalt layered double hydroxide (NiCo-LDH) hollow nanocages with hollow structure and defect state are used as co-reaction promoters to enhance the ECL emission from the luminol-H2 O system. Thanks to the hollow structure and defect state, NiCo-LDH hollow nanocages show excellent OER catalytic activity, which can stabilize and efficiently produce ROS and enhance the ECL emission. Additionally, mechanistic exploration suggests that the ROS involved in the co-reaction of the luminol-H2 O system are derived from the OER reaction process, and there is a positive correlation between ECL intensity and the OER catalytic activity of the co-reaction promoter. The selection of catalysts with excellent OER catalytic activity is a key factor in improving ECL emission. Finally, a dual-mode immunosensor is constructed for the detection and analysis of alpha-fetoprotein (AFP) based on the promoting effect of NiCo-LDH hollow nanocages on the luminol-H2 O ECL system.

Hybrid Ascharite/Reduced Graphene Oxide with Polysulfide Adsorption Host for Advanced Lithium-Sulfur Batteries

Balancing the adsorption of lithium-polysulfide intermediates on polar host material surfaces and the effect of their electronic conductivity in the subsequent oxidation and reduction kinetics of electrochemical reactions is necessary and remains a challenge. Herein, we have evaluated the role of polarity and conductivity in preparing a series of ascharite/reduced graphene oxide (RGO) aerogels by dispersing strong polar ascharite nanowires of varying mass into the conductive RGO matrix. When severed as Li-S battery cathodes, the optimized S@ascharite/RGO cathode with a sulfur content of 73.8 wt % demonstrates excellent rate performance and cycle stability accompanied by a high-capacity retention for 500 cycles at 1.0 C. Interesting advantages including the enhanced adsorption ability by the formation of the Mg-S and Li bonds, the continuous and quick electron/ion transportations assembled conductive RGO framework, and the effective deposition of Li2S are combined in the ascharite/RGO aerogel hosts. The electrochemical results further demonstrate that the polarity of ascharite components for the S cathode plays a dominant role in the improvement of electrochemical performance, but the absence of a conductive substrate leads to serious capacity attenuation, especially the rate performance. The balanced design protocol provides a universal method for the synthesis of multiple S hosts for high-performance LSBs.

A Review on Engineering Transition Metal Compound Catalysts to Accelerate the Redox Kinetics of Sulfur Cathodes for Lithium-Sulfur Batteries

Engineering transition metal compounds (TMCs) catalysts with excellent adsorption-catalytic ability has been one of the most effective strategies to accelerate the redox kinetics of sulfur cathodes. Herein, this review focuses on engineering TMCs catalysts by cation doping/anion doping/dual doping, bimetallic/bi-anionic TMCs, and TMCs-based heterostructure composites. It is obvious that introducing cations/anions to TMCs or constructing heterostructure can boost adsorption-catalytic capacity by regulating the electronic structure including energy band, d/p-band center, electron filling, and valence state. Moreover, the electronic structure of doped/dual-ionic TMCs are adjusted by inducing ions with different electronegativity, electron filling, and ion radius, resulting in electron redistribution, bonds reconstruction, induced vacancies due to the electronic interaction and changed crystal structure such as lattice spacing and lattice distortion. Different from the aforementioned two strategies, heterostructures are constructed by two types of TMCs with different Fermi energy levels, which causes built-in electric field and electrons transfer through the interface, and induces electron redistribution and arranged local atoms to regulate the electronic structure. Additionally, the lacking studies of the three strategies to comprehensively regulate electronic structure for improving catalytic performance are pointed out. It is believed that this review can guide the design of advanced TMCs catalysts for boosting redox of lithium sulfur batteries.

Dually Sulphophilic Chromium Boride Nanocatalyst Boosting Sulfur Conversion Kinetics Toward High-Performance Lithium-Sulfur Batteries

The sluggish kinetics of sulfur conversions have long been hindering the implementation of fast and efficient sulfur electrochemistry in lithium-sulfur (Li-S) batteries. In this regard, herein the unique chromium boride (CrB) is developed via a well-confined mild-temperature thermal reaction to serve as an advanced sulfur electrocatalyst. Its interstitial-alloy nature features excellent conductivity, while the nano-lamination architecture affords abundant active sites for host-guest interactions. More importantly, the CrB nanocatalyst demonstrates a dual sulphophilicity with simultaneous Cr─S and B─S bondage for establishing strong interactions with the intermediate polysulfides. As a result, significant stabilization and promotion of sulfur redox behavior can be achieved, enabling an excellent Li-S cell cyclability with a minimum capacity fading rate of 0.0176% per cycle over 2000 cycles and a favorable rate capability up to 7 C. Additionally, a high areal capacity of 5.2 mAh cm-2 , and decent cycling and rate performances are still attainable under high sulfur loading and low electrolyte dosage. This work offers a facile approach and instructive insights into metal boride sulfur electrocatalyst, holding a good promise for pursuing high-efficiency sulfur electrochemistry and high-performance Li-S batteries.

Local Built-In Field at the Sub-nanometric Heterointerface Mediates Cascade Electrochemical Conversion of Lithium-sulfur Batteries

Heterogeneous catalytic mediators have been proposed to play a vital role in enhancing the multiorder reaction and nucleation kinetics in multielectron sulfur electrochemistry. However, the predictive design of heterogeneous catalysts is still challenging, owing to the lack of in-depth understanding of interfacial electronic states and electron transfer on cascade reaction in Li-S batteries. Here, a heterogeneous catalytic mediator based on monodispersed titanium carbide sub-nanoclusters embedded in titanium dioxide nanobelts is reported. The tunable catalytic and anchoring effects of the resulting catalyst are achieved by the redistribution of localized electrons caused by the abundant built-in fields in heterointerfaces. Subsequently, the resulting sulfur cathodes deliver an areal capacity of 5.6 mAh cm-2 and excellent stability at 1 C under sulfur loading of 8.0 mg cm-2 . The catalytic mechanism especially on enhancing the multiorder reaction kinetic of polysulfides is further demonstrated via operando time-resolved Raman spectroscopy during the reduction process in conjunction with theoretical analysis.

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.

Enhanced Pseudo-Capacitance Process in Nanoarchitectural Layered Double Hydroxide Nanoarrays Hollow Nanocages for Improved Capacitive Deionization Performance

Layered double hydroxides (LDHs) are perceived as a hopeful capacitive deionization (CDI) faradic electrode for Cl^- insertion due to its tunable composition, excellent anion exchange capacity, and fast redox activity. Nevertheless, the self-stacking and inferior electrical conductivity of the two-dimensional structure of LDH lead to unsatisfactory CDI performance. Herein, the three-dimensional (3D) hollow nanocage structure of CoNi-layered double hydroxide/carbon composites is well designed as a CDI anode by cation etching of the pre-carbonized ZIF-67 template. C/CoNi-LDH has a unique 3D hollow nanocage structure and abundant pore features, which can effectively suppress the self-stacking of LDH sheets and facilitate the transport of ions. Moreover, the introduced amorphous carbon layer can act as a conductive network. When employed as the CDI anode, C/CoNi-LDH exhibited a high Cl^- removal capacity of 60.88 mg g^-1 and a fast Cl^- removal rate of 18.09 mg g^-1 min^-1 at 1.4 V in 1000 mg L^-1 NaCl solution. The mechanism of the Cl^- intercalation pseudo-capacitance reaction of C/CoNi-LDH is revealed by electrochemical kinetic analysis and ex situ characterization. This study provides vital guidance for the design of high-performance electrodes for CDI.

Electrospun CuCoN0.6 coating necklace-like N-doped carbon nanofibers for high performance lithium-sulfur batteries

Freestanding electrodes with high energy density and cycle stability have attracted attention on the development of lithium-sulfur (Li-S) batteries. However, both severe shuttle effect and sluggish conversion kinetics hinder their practical applications. Herein, we employed the electrospinning and subsequent nitridation processes to prepare a necklace-like structure of CuCoN_0.6 nanoparticles anchored on N-doped carbon nanofibers (CuCoN_0.6/NC) as freestanding sulfur host for Li-S batteries. Such bimetallic nitride boosts chemical adsorption and catalytic activity throughout detailed theoretical calculation and experimental electrochemical characterization. The three-dimensional conductive necklace-like framework could provide abundant cavities for realizing high sulfur utilization and alleviating the volume variation, as well as fast lithium-ions diffusion and electron transfer. The Li-S cell with the S@CuCoN_0.6/NC cathode delivers a stable cycling performance with a capacity attenuation rate of 0.076% per cycle after 150cycles at 2.0C and an exceptional capacity retention of 657 mAh g^-1 even at a high sulfur loading of 6.8 mg cm^-2 over 100cycles. The facile and scalable method can help promote the widespread application of fabrics.

Conductive Polymer Coated Layered Double Hydroxide as a Novel Sulfur Reservoir for Flexible Lithium-Sulfur Batteries

Lithium-sulfur battery (LSB) is widely regarded as the most promising next-generation energy storage system owing to its high theoretical capacity and low cost. However, the practical application of LSBs is mainly hampered by the low electronic conductivity of the sulfur cathode and the notorious "shuttle effect", which lead to high voltage polarization, severe over-charge behavior, and rapid capacity decay. To address these issues, a novel sulfur reservoir is synthesized by coating polypyrrole (PPy) thin film on hollow layered double hydroxide (LDH) (PPy@LDH). After compositing with sulfur, such PPy@LDH-S cathode shows a multi-functional effect to reserve lithium polysulfides (LiPSs). In addition, the unique architecture provides sufficient inner space to encapsulate the volume expansion and enhances the reaction kinetics of sulfur-based redox chemistry. Theoretical calculations have illustrated that the PPy@LDH has shown stronger chemical adsorption capability for LiPSs than those of porous carbon and LDH, preventing the shuttling of LiPSs and enhancing the nucleation affinity of liquid-solid conversion. As a result, the PPy@LDH-S electrode delivers a stable cycling performance and a superior rate capability. Flexible battery has demonstrated this PPy@LDH-S electrode can work properly with treatments of bending, folding, and even twisting, paving the way for wearable devices and flexible electronics.

A rational design of titanium-based heterostructures as electrocatalyst for boosted conversion kinetics of polysulfides in Li-S batteries

Lithium-sulfur batteries have great potential for next-generation electrochemical storage systems owing to their high theoretical specific energy and cost-effectiveness. However, the shuttle effect of soluble polysulfides and sluggish multi-electron sulfur redox reactions has severely impeded the implementation of lithium-sulfur batteries. Herein, we prepared a new type of Ti₃C₂-TiO₂ heterostructure sandwich nanosheet confined within polydopamine derived N-doped porous carbon. The highly polar heterostructures sandwich nanosheet with a high specific surface area can strongly absorb polysulfides, restraining their outward diffusion into the electrolyte. Abundant boundary defects constructed by new types of heterostructures reduce the overpotential of nucleation and improve the nucleation/conversion redox kinetics of Li₂S. The Ti₃C₂-TiO₂@NC/S cathode exhibited discharge capacities of 1363, and 801 mAh g^-1 at the first and 100th cycles at 0.5C, respectively, and retained an ultralow capacity fade rate of 0.076% per cycle over 500cycles at 1.0C. This study provides a potential avenue for constructing heterostructure materials for electrochemical energy storage and catalysis.

Interface Engineering Toward Expedited Li2 S Deposition in Lithium-Sulfur Batteries: A Critical Review

Lithium-sulfur batteries (LSBs) with superior energy density are among the most promising candidates of next-generation energy storage techniques. As the key step contributing to 75% of the overall capacity, Li₂ S deposition remains a formidable challenge for LSBs applications because of its sluggish kinetics. The severe kinetic issue originates from the huge interfacial impedances, indicative of the interface-dominated nature of Li₂ S deposition. Accordingly, increasing efforts have been devoted to interface engineering for efficient Li₂ S deposition, which has attained inspiring success to date. However, a systematic overview and in-depth understanding of this critical field are still absent. In this review, the principles of interface-controlled Li₂ S precipitation are presented, clarifying the pivotal roles of electrolyte-substrate and electrolyte-Li₂ S interfaces in regulating Li₂ S depositing behavior. For the optimization of the electrolyte-substrate interface, efforts on the design of substrates including metal compounds, functionalized carbons, and organic compounds are systematically summarized. Regarding the regulation of electrolyte-Li₂ S interface, the progress of applying polysulfides catholytes, redox mediators, and high-donicity/polarity electrolytes is overviewed in detail. Finally, the challenges and possible solutions aiming at optimizing Li₂ S deposition are given for further development of practical LSBs. This review would inspire more insightful works and, more importantly, may enlighten other electrochemical areas concerning heterogeneous deposition processes.

Self-assembled ZnO microspheres coated with carbon dot-doped CoNi LDH wrinkled films as electrochemical sensors for highly sensitive detection of hydrazine

In this study, a 3D surface-folded composite was prepared in situ as a hydrazine sensor by loading a hybrid film of CoNi-layered double hydroxides (LDHs) with nitrogen-doped carbon dots on self-assembled ZnO microspheres. The nanocomposite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), and the electrochemical behavior of the sensors was investigated by cyclic voltammetry (CV), amperometry and electrochemical impedance spectroscopy (EIS). The results showed that ZnO microspheres with nitrogen-doped carbon dots strongly coupled with LDHs can significantly reduce the charge transfer resistance, accelerate the oxidation kinetics of hydrazine, and effectively increase the electrochemically active surface area (ECSA). The sensor achieved ultra-sensitive (13 040 μA mM-1 cm-2 (S/N = 3)) detection of hydrazine in the concentration range of 0.7 μM to 4 mM, exhibited excellent selectivity, reproducibility and high stability, and was successfully applied to the determination of hydrazine in actual environmental water samples and landfill leachate samples.

Flower-Shaped Hollow VOOH Spheres Wrapped by Carbon Nanotubes as the Cathode Electrocatalyst Enable Ultrafast and Long-Lasting Li-S Batteries

Lithium-sulfur batteries (LSBs) have been considered promising candidates for next-generation energy storage devices owing to their high energy density, low price, and environment-friendly characteristics. However, their commercialization has been hindered by the "shuttle effect", which occurs during the charge/discharge cycles and leads to poor cycling performance and low coulombic efficiency. Here, we synthesized flower-shaped hollow VOOH spheres on the carbon nanotube (CNT) network, which were used as the multifunctional sulfur host materials for the first time in LSBs. These VOOH spheres can chemically and physically confine polysulfides as well as catalyze their redox conversion; additionally, their hollow structure can effectively accommodate the volume change during cycling. Moreover, the CNTs among spheres can improve the conductivity of the host material and increase the number of active sites for interfacial reactions. Accordingly, when used as a cathode material, VOOH@CNTs/S composites exhibited a large specific discharge capacity of 1414.63 mAh/g at 0.1 C and excellent cycling stability. At a low current density of 0.5 C, VOOH@CNTs/S exhibited a capacity decay of 0.044% per cycle after 100 cycles. Importantly, at an ultrahigh current density of 5 C, a specific capacity as high as 455.09 mAh/g could be still be delivered after 1000 cycles, corresponding to a superior capacity retention of 90.46% and an ultralow capacity decay of 0.009% per cycle. These findings open up a new material for the practical application of LSBs with ultrafast charge/discharge property and long-lasting cyclic stability.

Carbon Nanotube-Modified Nickel Hydroxide as Cathode Materials for High-Performance Li-S Batteries

The advantages of high energy density and low cost make lithium–sulfur batteries one of the most promising candidates for next-generation energy storage systems. However, the electrical insulativity of sulfur and the serious shuttle effect of lithium polysulfides (LiPSs) still impedes its further development. In this regard, a uniform hollow mesoporous Ni(OH)₂@CNT microsphere was developed to address these issues. The SEM images show the Ni(OH)₂ delivers an average size of about 5 μm, which is composed of nanosheets. The designed Ni(OH)₂@CNT contains transition metal cations and interlayer anions, featuring the unique 3D spheroidal flower structure, decent porosity, and large surface area, which is highly conducive to conversion systems and electrochemical energy storage. As a result, the as-fabricated Li-S battery delivers the reversible capacity of 652 mAh g⁻¹ after 400 cycles, demonstrating excellent capacity retention with a low average capacity loss of only 0.081% per cycle at 1 C. This work has shown that the Ni(OH)₂@CNT sulfur host prepared by hydrothermal embraces delivers strong physical absorption as well as chemical affinity.

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.

Combined enhanced redox kinetics and physiochemical confinement in three-dimensionally ordered macro/mesoporous TiN for highly stable lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with tremendous energy density possess great promise for the next-generation energy storage devices. Even though, the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) seriously restrict practical applications of Li-S batteries. Herein, a three-dimensionally ordered macro/mesoporous TiN (3DOM TiN) nanostructure is established via using poly (methyl methacrylate) PMMA spheres as template. The interconnected macro/mesoporous channels are constructed to effectively alleviate the stacking of composite materials and render a large portion of inherent active sites exposed on the surface region. Moreover, TiN exhibits high electrical conductivity, which efficiently enhances charge-transfer kinetics and guarantees the favorable electrochemical performance of sulfur cathode. More importantly, the as-prepared 3DOM TiN suppresses the shuttle effect and improves the redox kinetics significantly due to strong affinity toward LiPSs. Attributed to these unique features, the S/3DOM TiN electrode achieves an ultrahigh initial discharge capacity of 1187 mAh g^-1at 0.2 C, and stable cycling performance of 552 mAh g^-1over 500 cycles at 1 C. Meanwhile, the discharge capacity retention of 701 mAh g^-1(3.5 mAh cm^-2) can be endowed for the S/3DOM TiN electrode under high sulfur loading of 5 mg cm^-2after 100 cycles at 0.1 C. Therefore, the 3DOM TiN nanostructure electrocatalyst provides a promising path for developing practically useable Li-S batteries.

Semi-Immobilized Molecular Electrocatalysts for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries constitute promising next-generation energy storage devices due to the ultrahigh theoretical energy density of 2600 Wh kg^-1. However, the multiphase sulfur redox reactions with sophisticated homogeneous and heterogeneous electrochemical processes are sluggish in kinetics, thus requiring targeted and high-efficient electrocatalysts. Herein, a semi-immobilized molecular electrocatalyst is designed to tailor the characters of the sulfur redox reactions in working Li-S batteries. Specifically, porphyrin active sites are covalently grafted onto conductive and flexible polypyrrole linkers on graphene current collectors. The electrocatalyst with the semi-immobilized active sites exhibits homogeneous and heterogeneous functions simultaneously, performing enhanced redox kinetics and a regulated phase transition mode. The efficiency of the semi-immobilizing strategy is further verified in practical Li-S batteries that realize superior rate performances and long lifespan as well as a 343 Wh kg^-1 high-energy-density Li-S pouch cell. This contribution not only proposes an efficient semi-immobilizing electrocatalyst design strategy to promote the Li-S battery performances but also inspires electrocatalyst development facing analogous multiphase electrochemical energy processes.

Interspersing Partially Oxidized V2C Nanosheets and Carbon Nanotubes toward Multifunctional Polysulfide Barriers for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have attracted much attention attributed to their high theoretical energy density, whereas the parasitic shuttling behavior of lithium polysulfides (LiPS) hinders this technology from yielding practically competitive performance. Targeting this critical challenge, we develop an advanced polysulfide barrier by modifying the conventional separator with CNTs-interspersed V₂C/V₂O₅ nanosheets to alleviate the shuttle effect. The partial oxidization of V₂C MXene constructs the V₂C/V₂O₅ composite with V₂O₅ nanoparticles uniformly dispersed on few-layered V₂C nanosheets, which synergistically and concurrently improves the sulfur confinement and redox reaction kinetics. Moreover, the interstacking between the 1D CNTs and the 2D V₂C/V₂O₅ not only prevents the agglomeration of nanosheets for efficient exposure of active interfaces but also constructs a robust conductive network for fast charge and mass transfers. The Li-S cells with V₂C/V₂O₅/CNTs-modified separator realize a high initial capacity (1240.4 mAh g^-1 at 0.2 C), decent capacity retention (82.6% over 500 cycles), and favorable areal capacity (5.9 mAh cm^-2) at a raised sulfur loading (6.0 mg cm^-2). This work affords a unique multifunctional separator design toward durable and efficient sulfur electrochemistry, holding great promise for improving the electrochemical properties of Li-S batteries.

Engineering Oversaturated Fe-N5 Multifunctional Catalytic Sites for Durable Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are regarded as a promising next-generation system for advanced energy storage owing to a high theoretical energy density of 2600 Wh kg^-1 . However, the practical implementation of Li-S batteries has been thwarted by the detrimental shuttling behavior of polysulfides, and the sluggish kinetics in electrochemical processes. Herein, a novel single atom (SA) catalyst with oversaturated Fe-N₅ coordination structure (Fe-N₅ -C) is precisely synthesized by an absorption-pyrolysis strategy and introduced as an effective sulfur host material. The experimental characterizations and theoretical calculations reveal synergism between atomically dispersed Fe-N₅ active sites and the unique carbon support. The results exhibit that the sulfur composite cathode built on the Fe-N₅ -C can not only adsorb polysulfides via chemical interaction, but also boost the redox reaction kinetics, thus mitigating the shuttle effect. Meanwhile, the robust three-dimensional nitrogen doped carbon nanofiber with large surface area, and high porosity enables strong physical confinement and fast electron/ion transfer process. Attributed to such unique features, Li-S batteries with S/Fe-N₅ -C composite cathode realize outstanding cyclability and rate capability, as well as high areal capacities under raised sulfur loading, which demonstrates great potential in developing advanced Li-S batteries.

Rational design of a cobalt sulfide nanoparticle-embedded flexible carbon nanofiber membrane electrocatalyst for advanced lithium-sulfur batteries

Both the sluggish redox kinetics and severe polysulfide shuttling behavior hinders the commercialization of lithium-sulfur (Li-S) battery. To solve these obstacles, we design a cobalt sulfide nanoparticle-embedded flexible carbon nanofiber membrane (denoted as CoS₂@NCF) as sulfiphilic functional interlayer materials. The hierarchically porous structure of carbon nanofiber is conducive to immobilizing sulfur species and facilitating lithium-ion penetration. Moreover, electrocatalytic CoS₂nanoparticles can significantly enhance the catalytic effect, achieving favorable adsorption-diffusion-conversion interface of polysulfide. Combined with these synergistic features, the assembled Li-S cell with CoS₂@NCF interlayer exhibited a great discharge capacity of 950.9 mAh g^-1with prolonged cycle lifespan at 1 C (maintained 648.1 mAh g^-1over 500 cycles). This multifunctional interlayer material used in this contribution provides an advanced route for developing high-energy-density Li-S battery.

Oriented Nanosheet-Assembled CoNi-LDH Cages with Efficient Ion Diffusion for Quasi-Solid-State Hybrid Supercapacitors

Fast-charged energy-storage technologies have become important nowadays as they are required by many applications, including automobiles. This inspires the exploitation of hybrid supercapacitors (HSCs) with the advantages of fast charge offered by the capacitor characters and high energy density from the property of battery technology. The challenges lay in the construction of advanced materials with high pseudocapacitive activity. Herein, a metal-organic framework derivative is utilized to address the problems. Specifically, polyhedral CoNi layered double hydroxide (CoNi-LDH_x) cages assembled in the form of nanosheet arrays are prepared from ZIF-67 using a facile ion-exchange approach. Based on the control over the mass ratio of ZIF-67 to Ni salt, the optimal CoNi-LDH₂ is attained. It exhibits ultrahigh capacities ranging from 1031.4 to 667.3 C g^-1 under 1-25 A g^-1, thanks to rich Faradaic active spots and the accelerated kinetics provided by the synergy between nanosheet arrays and the hollow structure. The CoNi-LDH₂-based HSC with the gel electrolyte shares remarkable energy output of 49 Wh kg^-1 and approving cyclability with almost no capacity decay after 12 000 cycles. This is an advancement vs many related studies and can arouse tremendous interests of researchers in solving the main problems of energy storage.

Three-Dimensionally Ordered Macro/Mesoporous Nb2O5/Nb4N5 Heterostructure as Sulfur Host for High-Performance Lithium/Sulfur Batteries

The severe shuttle effect of soluble polysulfides hinders the development of lithium–sulfur batteries. Herein, we develop a three-dimensionally ordered macro/mesoporous (3DOM) Nb₂O₅/Nb₄N₅ heterostructure, which combines the strong adsorption of Nb₂O₅ and remarkable catalysis effect of Nb₄N₅ by the promotion “adsorption-transformation” mechanism in sulfur reaction. Furthermore, the high electrocatalytic activity of Nb₄N₅ facilitates ion/mass transfer during the charge/discharge process. As a result, cells with the S-Nb₂O₅/Nb₄N₅ electrode delivered outstanding cycling stability and higher discharge capacity than its counterparts. Our work demonstrates a new routine for the multifunctional sulfur host design, which offers great potential for commercial high-performance lithium–sulfur batteries.

Nanotechnology for Sulfur Cathodes

The field of lithium-sulfur batteries has benefited enormously from the advances in nanotechnology. At each step of technological improvement, lithium-sulfur batteries have relied upon techniques and methodologies brought upon by nanotechnology. Nanoporous material, heterogeneous nanocomposite, and hierarchical electrode developments have all been well-established as critical milestones for lithium-sulfur batteries. This review will briefly discuss the specific major roles of nanotechnology in lithium-sulfur batteries regarding practically relevant testing conditions in addition to research trends and future directions for electrocatalysis.