Polysulfide Anchoring Mechanism Revealed by Atomic Layer Deposition of V2O5 and Sulfur-Filled Carbon Nanotubes for Lithium-Sulfur Batteries

Design of Coatings for Sulfur-Based Cathode Materials in Lithium-Sulfur Batteries: A review

Lithium-sulfur batteries (LSBs) are considered next-generation energy storage and conversion solutions owing to their high theoretical specific capacity and the high abundance/low-cost of sulfur-based cathode materials. However, LSBs still encounter significant challenges, including the low conductivities of sulfur-based materials, severe volumetric expansion of sulfur during the discharge process, and the persistent "shuttle effect" of polysulfides. In recent years, a tremendous amount of research has been conducted to address the above challenges by developing coating and compositing materials and corresponding fabrication strategies for sulfur-based cathode materials. In this study, the surface coating, compositing materials, and fabrication methodologies of LSB cathodes are comprehensively reviewed in terms of advanced materials, structure/component characterization, functional mechanisms, and performance validation. Some technical challenges are analyzed in detail, and possible future research directions are proposed to overcome the challenges toward practical applications of lithium-sulfur batteries.

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.

A ductile and strong-affinity network binder coupling inorganic oligomers and biopolymers for high-loading lithium-sulfur batteries

Lithium sulfur (Li-S) batteries have become the predominant energy storage devices of the future. However, the reasons why Li-S batteries have not been widely commercialized include the shuttle effect of polysulfides and the volume expansion of sulfur active substances. In this study, a binder with a stretchable 3D reticular structure was induced using inorganic oligomers. Potassium tripolyphosphate (PTP) has been used to powerfully connect the tamarind seed gum (TSG) chain through robust intermolecular forces due to the strong electronegativity of P-O^- groups. With this binder, the volume expansion of sulfur active substances can be well restrained. In addition, a large amount of -OH groups in TSG and P-O^- bonds in PTP can also effectively adsorb polysulfides and inhibit the shuttle effect. Therefore, the S@TSG-PTP electrode shows an improved cycle performance. When the sulfur loading is as high as 4.29 mg cm^-2, the areal specific capacity can reach 3.37 mA h cm^-2 after 70 cycles. This study highlights a new way for the binder design of high-loading sulfur electrodes.

Wide-Temperature-Range Li-S Batteries Enabled by Thiodimolybdate [Mo2S12]2- as a Dual-Function Molecular Catalyst for Polysulfide Redox and Lithium Intercalation

In lithium-sulfur batteries, a serious obstacle is the dissolution and diffusion of long-chain polysulfides, resulting in rapid capacity decay and low Coulombic efficiency. At present, a common practice is designing cathode materials to solve this problem, but this gives rise to reduced gravimetric and volumetric energy densities. Herein, we present a thiodimolybdate [Mo₂S₁₂]^2- cluster as sulfur host material that can effectively confine the shuttling of polysulfides and contribute its own capacity in Li-S cells. Moreover, the [Mo₂S₁₂]^2- cluster as a "bidirectional catalyst" can effectively catalyze polysulfide reduction and lithium sulfide oxidation. We further investigate the catalytic mechanism of [Mo₂S₁₂]^2- clusters by theoretical calculations, in situ spectroscopic techniques, and electrochemical studies. The (NH₄)₂Mo₂S₁₂/S cathodes show good electrochemical performance under a wide range of temperatures. In addition, a pouch cell fabricated with (NH₄)₂Mo₂S₁₂/S cathodes maintains a stable output for more than 50 cycles.

In Situ Synthesis of Organopolysulfides Enabling Spatial and Kinetic Co-Mediation of Sulfur Chemistry

Li-S batteries have been regarded as one of the most promising alternatives of the next-generation Li batteries. However, the dissolution and shuttling of lithium polysulfides lead to low cycle stability and low Coulombic efficiency, which intensively hinder the practical application of Li-S batteries. Herein, we propose a strategy to simultaneously promote the redox kinetics and inhibit the shuttle of lithium polysulfides, through in situ synthesis of insoluble organopolysulfides by adding a special additive. Attractively, the thus-formed insoluble organopolysulfides in the form of nanoparticle aggregates are also capable of adsorbing unconverted lithium polysulfides and hence effectively spatially suppress the shuttle effect. Furthermore, the organopolysulfides served as active redox mediators, showing faster redox kinetics of S chemistry than that of lithium polysulfides. As a result, the Li-S batteries showed impressive capacity, improved rate performance, and long cycling stability even under lean-electrolyte and high sulfur loading conditions.

Precise surface control of cathode materials for stable lithium-ion batteries

The increasing demand for high-energy Li-ion batteries (LIBs) continues to push the development of electrode materials, particularly cathode materials, towards their capacity limits. Despite the enormous success, the stability and reliability of LIBs are becoming a serious concern due to the much-aggravated side reactions between electrode materials and organic electrolytes. How to stabilize the cathode/electrolyte interface is therefore an imperative and urgent task drawing considerable attention from both academia and industry. An active treatment on the surface of cathode materials, usually by introducing an inert protection layer, to diminish their side reaction with electrolytes turns out to be a reasonable and effective strategy. This Feature Article firstly outlines our synthesis efforts for the construction of a uniform surface nanocoating on various cathode materials. Different wet chemical routes have been designed to facilitate the control of growth kinetics of targeted coating species so that a precise surface coating could be achieved with nanometer accuracy. Furthermore, we showed the possibility to transform the outer coating layer into a surface doping effect through surface solid reaction at high temperature. A detailed discussion on the structure-performance relationship of these surface-controlled cathode materials is introduced to probe the stabilization mechanism. Finally, perspectives on the development tendency of high-energy cathodes for stable LIBs are provided.

Large-Pore Ordered Mesoporous Turbostratic Carbon Films Prepared Using Rapid Thermal Annealing for High-Performance Micro-pseudocapacitors

Carbonization by rapid thermal annealing (RTA) of precursor films structured by a brush block copolymer-mediated self-assembly enabled the preparation of large-pore (40 nm) ordered mesoporous carbon (MPC)-based micro-supercapacitors within minutes. The large pore size of the fabricated films facilitates both rapid electrolyte diffusion for carbon-based electric double-layer capacitors and conformal deposition of V₂O₅ without pore blockage for pseudocapacitors. The pores were templated using bottlebrush block copolymers (BBCPs) via cooperative assembly of phenol-formaldehyde resin to produce microphase-segregated carbon precursor films on a variety of substrates. Ultrafast RTA processing (∼50 °C/s) at elevated temperatures (up to 1000 °C) then generated stable, conductive, turbostratic MPC films, resolving a significant bottleneck in rapid fabrication. MPC prepared on stainless steel at 900 °C demonstrated exceptionally high areal and volumetric capacitances of 6.3 mF/cm² and 126 F/cm³ (at 0.8 mA/cm² using 6 M KOH as the electrolyte), respectively, and 91% capacitance retention after 10,000 galvanostatic charge/discharge cycles. Post-RTA conformal V₂O₅ deposition yielded pseudocapacitors with 10-fold increase in energy density (20 μW h cm^-2 μm^-1) without adversely affecting the high power density (450 μW cm^-2 μm^-1). The use of RTA coupled with BBCP templating opens avenues for scalable, rapid fabrication of high-performance carbon-based micro-pseudocapacitors.

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.

Advances in Lithium-Sulfur Batteries: From Academic Research to Commercial Viability

Lithium-ion batteries, which have revolutionized portable electronics over the past three decades, were eventually recognized with the 2019 Nobel Prize in chemistry. As the energy density of current lithium-ion batteries is approaching its limit, developing new battery technologies beyond lithium-ion chemistry is significant for next-generation high energy storage. Lithium-sulfur (Li-S) batteries, which rely on the reversible redox reactions between lithium and sulfur, appears to be a promising energy storage system to take over from the conventional lithium-ion batteries for next-generation energy storage owing to their overwhelming energy density compared to the existing lithium-ion batteries today. Over the past 60 years, especially the past decade, significant academic and commercial progress has been made on Li-S batteries. From the concept of the sulfur cathode first proposed in the 1960s to the current commercial Li-S batteries used in unmanned aircraft, the story of Li-S batteries is full of breakthroughs and back tracing steps. Herein, the development and advancement of Li-S batteries in terms of sulfur-based composite cathode design, separator modification, binder improvement, electrolyte optimization, and lithium metal protection is summarized. An outlook on the future directions and prospects for Li-S batteries is also offered.

Atomic/molecular layer deposition for energy storage and conversion

Energy storage and conversion systems, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting, have played vital roles in the reduction of fossil fuel usage, addressing environmental issues and the development of electric vehicles. The fabrication and surface/interface engineering of electrode materials with refined structures are indispensable for achieving optimal performances for the different energy-related devices. Atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques, the gas-phase thin film deposition processes with self-limiting and saturated surface reactions, have emerged as powerful techniques for surface and interface engineering in energy-related devices due to their exceptional capability of precise thickness control, excellent uniformity and conformity, tunable composition and relatively low deposition temperature. In the past few decades, ALD and MLD have been intensively studied for energy storage and conversion applications with remarkable progress. In this review, we give a comprehensive summary of the development and achievements of ALD and MLD and their applications for energy storage and conversion, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting. Moreover, the fundamental understanding of the mechanisms involved in different devices will be deeply reviewed. Furthermore, the large-scale potential of ALD and MLD techniques is discussed and predicted. Finally, we will provide insightful perspectives on future directions for new material design by ALD and MLD and untapped opportunities in energy storage and conversion.

Vanadium based carbide-oxide heterogeneous V2O5@V2C nanotube arrays for high-rate and long-life lithium-sulfur batteries

Due to their ultra-high theoretical energy density, low cost, and environmental friendliness, lithium-sulfur batteries have become a potentially strong competitor for next-generation energy storage devices. The search for a host material that can effectively anchor sulfur to a cathode to solve the adverse effects of the shuttle effect on batteries has become a research hotspot in the academic world. Here, we propose a three-dimensional heterostructure of V₂O₅ nanotube arrays vertically grown on V₂C-MXenes as a sulfur-supporting host material for the cathode of lithium-sulfur batteries. Through first-principles calculations, we found that V₂O₅@V₂C exhibits an extreme adsorption capacity for polysulfides. Besides, thanks to the excellent catalytic performance of V₂O₅ for oxidation reactions, the conversion reaction potential of polysulfides to Li₂S and Li₂S₂ is significantly reduced, and the shuttle effect of lithium-sulfur batteries is effectively suppressed. Also, the larger specific surface area and tubular structure of the composite host material can increase the sulfur loading of the cathode while ensuring the stability of the electrode structure. The V₂O₅@V₂C/S electrode exhibits higher initial capacity (1173 mA h g^-1 at 0.2C), longer cycle life (1000 cycles with 0.047% decay per period), and higher sulfur loading (8.4 mg cm^-2). We believe that this work can provide a reference for the design of cathode host materials for lithium-sulfur batteries with long cycle life.

A nanostructured porous carbon/MoO2 composite with efficient catalysis in polysulfide conversion for lithium-sulfur batteries

Lithium-sulfur batteries are considered as the next generation of energy storage systems because of their high theoretical specific capacity and energy density. Unfortunately, the sluggish reaction kinetics, weak adsorption toward to lithium polysulfides, and slow lithium ion diffusion impede the smooth electrochemical process, resulting in the lithium-sulfur batteries with the unsatisfactory cycling stability and rate performance. Since it is recognized that polar metal oxides and doped nitrogen in carbon materials have chemical interaction with lithium polysulfides, a nanostructured nitrogen-doped porous carbon/MoO₂ composite is synthesized through a simple hydrothermal method by using graphene oxide nanoribbon and phosphomolybdic acid hydrate as precursors. The porous nanostructure promotes the charge and mass transport, while MoO₂ nanoparticles immobilize lithium polysulfides via strong chemisorption and enhance the redox kinetics of polysulfides owing to the efficient catalytic activity in liquid-solid boundary. Consequently, the as-obtained nanostructured porous carbon/MoO₂-based sulfur cathode exhibits low polarization, high initial discharge capacity (1403 mAh g^-1 at 0.1 C), good rate capabilities (584 mAh g^-1 at 4 C), and impressive cycling performance at 1 C (503 mAh g^-1 after 500 cycles with capacity fade rate of 0.07% per cycle).

Interfacially Polymerized Polyamide Interlayer onto Ozonated Carbon Nanotube Networks for Improved Stability of Sulfur Cathodes

Lithium-sulfur (Li-S) batteries are considered promising energy-storage devices owing to the high specific capacity and low cost of the S cathode. However, they suffer from capacity decay and poor coulombic efficiency arising from the dissolution of long-chain polysulfides and their shuttling. A facile and scalable method was developed to directly coat a thin (≈57.3 nm) and porous polyamide (PA) interlayer onto a S cathode by interfacial polymerization. This PA interlayer prevented the shuttling of polysulfides by creating a physical barrier and, through chemical interactions between the amide functionalities of PA and the polysulfides, allowing access to the S electrode by the Li ions. The resulting PA-coated cathode exhibited approximately 64.2 % capacity retention over 1000 cycles at 1 C with only 0.0358 % decay per cycle and a moderate capacity of 1008 mAh g^-1 at 0.1 C.

2D/1D V2O5 Nanoplates Anchored Carbon Nanofibers as Efficient Separator Interlayer for Highly Stable Lithium-Sulfur Battery

Quick capacity loss due to the polysulfide shuttle effects is a critical challenge for high-performance lithium-sulfur (Li-S) batteries. Herein, a novel 2D/1D V2O5 nanoplates anchored carbon nanofiber (V-CF) interlayer coated on standard polypropylene (PP) separator is constructed, and a stabilization mechanism derived from a quasi-confined cushion space (QCCS) that can flexibly accommodate the polysulfide utilization is demonstrated. The incorporation of the V-CF interlayer ensures stable electron and ion pathway, and significantly enhanced long-term cycling performances are obtained. A Li-S battery assembled with the V-CF membrane exhibited a high initial capacity of 1140.8 mAh·g-1 and a reversed capacitance of 1110.2 mAh·g-1 after 100 cycles at 0.2 C. A high reversible capacity of 887.2 mAh·g-1 is also maintained after 500 cycles at 1 C, reaching an ultra-low decay rate of 0.0093% per cycle. The excellent electrochemical properties, especially the long-term cycling stability, can offer a promising designer protocol for developing highly stable Li-S batteries by introducing well-designed fine architectures to the separator.

Investigating the Electrocatalysis of a Ti3C2/Carbon Hybrid in Polysulfide Conversion of Lithium-Sulfur Batteries

Despite the fact that lithium-sulfur batteries are regarded as promising next-generation rechargeable battery systems owning to high theoretical specific capacity (1675 mA h g^-1) and energy density (2600 W h kg^-1), several issues such as poor electrical conductivity, sluggish redox kinetics, and severe "shuttle effect" in electrodes still hinder their practical application. MXenes, novel two-dimensional materials with high conductivity, regulable interlayer spacing, and abundant functional groups, are widely applied in energy storage and conversion fields. In this work, a Ti₃C₂/carbon hybrid with expanded interlayer spacing is synthesized by one-step heat treatment in molten potassium hydroxide. The subsequent experiments indicate that the as-prepared Ti₃C₂/carbon hybrid can effectively regulate polysulfide redox conversion and has strong chemisorption interaction to polysulfides. Consequently, the Ti₃C₂/carbon-based sulfur cathode boosts the performance in working lithium-sulfur batteries, in terms of an ultrahigh initial discharge capacity (1668 mA h g^-1 at 0.1 C), an excellent rate performance (520 mA h g^-1 at 5 C), and an outstanding capacity retention of 530 mA h g^-1 after 500 cycles at 1 C with a low capacity fade rate of 0.05% per cycle and stable Coulombic efficiency (nearly 99%). The above results indicate that this composite with high catalytic activity is a potential host material for further high-performance lithium-sulfur batteries.

Selective Adsorption and Electrocatalysis of Polysulfides through Hexatomic Nickel Clusters Embedded in N-Doped Graphene toward High-Performance Li-S Batteries

The shuttle effect hinders the practical application of lithium-sulfur (Li-S) batteries due to the poor affinity between a substrate and Li polysulfides (LiPSs) and the sluggish transition of soluble LiPSs to insoluble Li₂S or elemental S. Here, we report that Ni hexatomic clusters embedded in a nitrogen-doped three-dimensional (3D) graphene framework (Ni-N/G) possess stronger interaction with soluble polysulfides than that with insoluble polysulfides. The synthetic electrocatalyst deployed in the sulfur cathode plays a multifunctional role: (i) selectively adsorbing the polysulfides dissolved in the electrolyte, (ii) expediting the sluggish liquid-solid phase transformations at the active sites as electrocatalysts, and (iii) accelerating the kinetics of the electrochemical reaction of multielectron sulfur, thereby inhibiting the dissolution of LiPSs. The constructed S@Ni-N/G cathode delivers an areal capacity of 9.43 mAh cm^-2 at 0.1 C at S loading of 6.8 mg cm^-2, and it exhibits a gravimetric capacity of 1104 mAh g^-1 with a capacity fading rate of 0.045% per cycle over 50 cycles at 0.2 C at S loading of 2.0 mg cm^-2. This work opens a rational approach to achieve the selective adsorption and expediting of polysulfide transition for the performance enhancement of Li-S batteries.

Mesoscale Elucidation of Self-Discharge-Induced Performance Decay in Lithium-Sulfur Batteries

The polysulfide shuttle phenomenon substantially deteriorates the electrochemical performance of lithium-sulfur (Li-S) batteries, resulting in continued self-discharge and capacity fade during cycling. In this study, a mesoscale analysis is presented to explore the mechanisms of self-discharge behavior in the Li-S battery during the resting state. It is found that the self-discharge rate is determined by the sulfur solubility, desorption capability, diffusion kinetics, and reaction rate on the anode surface. Three regimes have been identified: desorption control, diffusion control, and charge transfer control. Correspondingly, strategies are suggested to increase the capacity retention, such as enhancing the binding of sulfur molecules to the host, reducing dissolved sulfur diffusivity, and improving the chemical stability of active materials with a Li metal anode. Furthermore, the use of an interlayer with high diffusion barriers can effectively suppress the self-discharge rate due to the confinement effect.

Synchronous Gains of Areal and Volumetric Capacities in Lithium-Sulfur Batteries Promised by Flower-like Porous Ti3C2T x Matrix

The areal and volumetric capacities are important metrics in practical deployment of advanced energy storage systems with the imposed constraints of device volume and chip area. Conductive carbons are promising sulfur host materials for improving areal capacity in lithium-sulfur (Li-S) batteries, but they face a few congenital deficiencies, such as low tap density and weak polysulfide entrapment ability, resulting in poor volumetric performance. Here, we report one type of cathode system based on flower-like porous Ti₃C₂T _x (FLPT) without the incorporation of any carbon hosts or conductive additives. The resultant FLPT-S electrode synchronously acquires a high areal capacity of 10.04 mAh cm^-2 and ultrahigh volumetric capacity of 2009 mAh cm^-3. Furthermore, ex situ electron paramagnetic resonance and UV-visible spectra have demonstrated that FLPT enables a fast dynamic equilibrium between S₆^2- anion and S₃^•- radical during cycling, which promotes the redox reactions of sulfur species.

Covalent bonding of sulfur nanoparticles to unzipped multiwalled carbon nanotubes for high-performance lithium-sulfur batteries

The use of sulfur as a cathode material for lithium-sulfur (Li-S) batteries has attracted significant attention due to its high theoretical specific capacity (1675 mA h g^-1); however, practicality is hindered by a number of obstacles, including the shuttling effect of polysulfides and the low electrical conductivity of sulfur. Herein, ball milling sulfur with unzipped multiwalled carbon nanotubes (UMWNTs) was found to covalently immobilize sulfur nanoparticles to the UMWNTs and resulted in composites (designated as S@UMWNTs) with high electrical conductivity. The unzipping degree of MWNTs was first controlled to optimize the immobilization of sulfur nanoparticles to UMWNTs and the electrochemical performance of the resulting Li-S batteries. The presence of C-S covalent bonds between the UMWNTs and sulfur nanoparticles was verified using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, and the formation of C-S bonds was ascribed to the reactions between the mechanically-induced sulfur radicals and the functional groups of UMWNTs. As a result, when used as a cathode material for Li-S batteries, the S@UMWNTs exhibited excellent electrochemical performance, including a good long-term cycling stability and low capacity decay (e.g., ca. 0.09% per cycle over 500 charge/discharge cycles at 1 C) due to the suppression of the shuttling effect by the C-S covalent bonds.

Unexpected Effect of Electrode Architecture on High-Performance Lithium-Sulfur Batteries

In the past years, considerable efforts have been devoted to the deliberate synthesis of nanosulfur in various hosts with sophisticated structures to improve the performance of lithium-sulfur batteries (LSBs) and reveal the structure-property relationship. It is taken for granted that these elaborate sulfur nanostructures are well maintained in the ultimate electrode after the traditional mixing and coating method. Herein, we, for the first time, reveal the unexpected sulfur structure deterioration in nanosulfur/graphene composites during the electrode preparation using the traditional method because of the long-term neglected dissolution-recrystallization effect of sulfur in solvents. Consequently, compared with binder-free three-dimensional graphene/sulfur electrodes, the milled graphene/sulfur electrodes exhibit much worse electrochemical performance. On the basis of this, we further propose a facile and universal graphene oxide-assisted assembly method to avoid the dissolution-recrystallization of sulfur, by which binder-free three-dimensional ethylenediamine-functionalized graphene/sulfur (3DEFGS) electrodes have been successfully prepared. The 3DEFGS electrodes with a high areal sulfur loading of ∼6 mg cm^-2 exhibit an ultrahigh initial capacity of 1394 mA h g^-1 at 0.1 C, an excellent rate performance with a capacity of 796 mA h g^-1 at 4 C, and superior long-term cycling stability (885 mA h g^-1 after 500 cycles at 1 C), which are among the best performances achieved by all reported LSB cathodes with high areal sulfur loadings.

Surface Functionalization of Carbon Architecture with Nano-MnO2 for Effective Polysulfide Confinement in Lithium-Sulfur Batteries

Li-S batteries have received tremendous attention owing to their high theoretical capacity (1672 mA h g^-1 ), sulfur abundance, and low cost. However, main systemic issues, associated with polysulfide shuttling and low Coulombic efficiency, hinder the practical use of the sulfur electrode in commercial batteries. Herein, we demonstrate an effective strategy of decorating nano-MnO₂ (less than 10 wt %) onto the sulfur reservoir to capture the out-diffused polysulfides through chemical interaction and thereby improve the electrochemical performance of the sulfur electrode without increasing the mass burden of total battery configuration. Pistachio shell-derived sustainable carbon (PC) was employed as effective sulfur containers owing to its structural characteristics (interconnected macro channels and micropores). With the aids of the structural benefits of the PC scaffold and the uniform decoration of nano-MnO₂ , polysulfide shuttling was significantly suppressed and the cycling performance of the sulfur cathode was dramatically improved over 250 cycles.

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

A carbon host capable of effective and uniform sulfur loading is the key for lithium-sulfur batteries (LSBs). Despite the application of porous carbon materials of various morphologies, the carbon hosts capable of uniformly impregnating highly active sulfur is still challenging. To address this issue, we demonstrate a hierarchical pore-structured CNT particle host containing spherical macropores of several hundred nanometers. The macropore CNT particles (M-CNTPs) are prepared by drying the aerosol droplets in which CNTs and polymer particles are dispersed. The spherical macropore greatly improves the penetration of sulfur into the carbon host in the melt diffusion of sulfur. In addition, the formation of macropores greatly develops the volume of the micropore between CNT strands. As a result, we uniformly impregnate 70 wt % sulfur without sulfur residue. The S-M-CNTP cathode shows a highly reversible capacity of 1343 mA h g^-1 at a current density of 0.2 C even at a high sulfur content of 70 wt %. Upon a 10-fold current density increase, a high capacity retention of 74% is observed. These cathodes have a higher sulfur content than those of conventional CNT hosts but nevertheless exhibit excellent performance. Our CNTPs and pore control technology will advance the commercialization of CNT hosts for LSBs.

A high areal capacity lithium-sulfur battery cathode prepared by site-selective vapor infiltration of hierarchical carbon nanotube arrays

The widespread use of melt infiltration has to date restricted sulfur-carbon cathode architectures to only host materials processed as bulk powders with no site control of sulfur deposits. Here, we combine structurally designed hierarchical carbon nanotube (CNT) arrays with site-selective vapor phase sulfur infiltration to produce thick electrodes with controlled sulfur loading and high areal performance. Our results illustrate the critical role structural hierarchy plays in sustaining electrical connectivity to enable high utilization of the sulfur embedded in thick electrodes with high gravimetric loading. Here, a primary large-diameter CNT population provides robust conductive trunks that branch into a secondary small-diameter and high-surface-area CNT population capable of giving rapid electrical access to coated sulfur. Site-selective vapor phase sulfur infiltration, based on the capillary effect, controllably targets loading of one or both of the CNT populations to facilitate gravimetric loading from 60 wt% to 70 wt% sulfur. With the high areal loading of 6 mg cm^-2, we demonstrate 1092 mA h g_S^-1 and 6.5 mA h cm^-2 and excellent rate performance with >60% capacity retained at 10 times the discharge rate. Overall, our work leverages site control of sulfur incorporation into a host cathode enabled by controlled CNT growth techniques to emphasize the important principle of "quality over quantity" in designing high areal loading strategies with high areal performance and good sulfur utilization.

Cerium Oxide Nanocrystal Embedded Bimodal Micromesoporous Nitrogen-Rich Carbon Nanospheres as Effective Sulfur Host for Lithium-Sulfur Batteries

For developing lithium-sulfur (Li-S) batteries, it is critical to design advanced cathode materials with high sulfur loading/utilization ratios and strong binding interactions with sulfur species to prevent the dissolution of intermediate polysulfides. Here we report an effective sulfur host material prepared by implanting cerium oxide (CeO₂) nanocrystals homogeneously into well-designed bimodal micromesoporous nitrogen-rich carbon (MMNC) nanospheres. With the high conductivity and abundant hierarchical pore structures, MMNC nanospheres can effectively store and entrap sulfur species. Moreover, the inserted polar and electrocatalytically active CeO₂ nanocrystals and high nitrogen content of MMNC can synergistically solve the hurdle of the polysulfide dissolution and furthermore significantly promote stable redox activity. By combining these advantages, CeO₂/MMNC-S cathodes with 1.4 mg cm^-2 sulfur exhibit high reversible capacities (1066 mAh g^-1 at 0.2 C after 200 cycles and 836 mAh g^-1 at 1.0 C after 500 cycles), good rate capability (737 mAh g^-1 at 2.0 C), and high cycle stability (721 mAh g^-1 at 2.0 C after 1000 cycles with a low capacity decay of 0.024% per cycle). Furthermore, a high and stable reversible capacity of 611 mAh g^-1 is achieved after cycling for 200 cycles with higher sulfur loading of 3.4 mg cm^-2.

Highly Conductive Porous Transition Metal Dichalcogenides via Water Steam Etching for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries show significant advantages for next-generation energy storage systems owing to their high energy density and cost effectiveness. The main challenge in the development of long-life and high-performance Li-S batteries is to simultaneously facilitate the redox kinetics of sulfur species and suppress the shuttle effect of polysulfides. In this contribution, we present a general and green water-steam-etched approach for the fabrication of H- and O-incorporated porous TiS₂ (HOPT). The conductivity, porosity, chemisorptive capability, and electrocatalytic activity of HOPT are enhanced significantly when compared with those of raw TiS₂. The synthetic method can be expanded to the fabrication of other highly conductive transition metal dichalcogenides such as porous NbS₂ and CoS₂. The as-obtained HOPT can serve as both a substitute of conductive agents and an additive of interlayer materials. The optimal electrode delivers discharge capacities of 950 mA h g^-1 after 300 cycles at 0.5 C and 374 mA h g^-1 after 1000 cycles at 10 C. Impressively, an unprecedented reversible capacity of 172 mA h g^-1 is achieved after 2500 cycles at 30 C, and the average capacity fading rate per cycle is as low as 0.015%. Importantly, four half-cells based on this electrode in series could drive 60 light-emitting diode indicator modules (the nominal power 3 W) after 20 s of charging. The instantaneous current and power of this device on reaching 275 A g^-1 and 2611 W g^-1, respectively, indicate outstanding high-power discharge performance and potential applications in electric vehicles and other large-scale energy storage systems.

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

Here, we demonstrate a strategy to produce high areal loading and areal capacity sulfur cathodes by using vapor-phase infiltration of low-density carbon nanotube (CNT) foams preformed by solution processing and freeze-drying. Vapor-phase capillary infiltration of sulfur into preformed and binder-free low-density CNT foams leads to a mass loading of ∼79 wt % arising from interior filling and coating of CNTs with sulfur while preserving conductive CNT-CNT junctions that sustain electrical accessibility through the thick foam. Sulfur cathodes are then produced by mechanically compressing these foams into dense composites (ρ > 0.2 g/cm³), revealing specific capacity of 1039 mAh/g_S at 0.1 C, high sulfur areal loading of 19.1 mg/cm², and high areal capacity of 19.3 mAh/cm². This work highlights a technique broadly adaptable to a diverse group of nanostructured building blocks where preformed low-density materials can be vapor infiltrated with sulfur, mechanically compressed, and exhibit simultaneous high areal and gravimetric storage properties. This provides a route for scalable, low-cost, and high-energy density sulfur cathodes based on conventional solid electrode processing routes.