Advances in lithium–sulfur batteries based on multifunctional cathodes and electrolytes

Catalytic Mo2C decorated hollow mesoporous carbon spheres as sulfur host for lithium-sulfur batteries with high sulfur loading

The widespread application of lithium-ion batteries in portable electronics represents how electrical energy storage (EES) technologies can revolutionize human society. The transformation of the EES technologies to large-scale applications, such as electric vehicles and grid storage, depends heavily on the cost-competitiveness, cycle life, safety, and environmental compatibility. Lithium-sulfur (Li-S) batteries are one of the most promising future EES systems due to their high theoretical energy density of 2600 Wh kg-1. The high-capacity sulfur cathode (theoretical capacity: 1675 mAh g-1) has low production cost and high abundance. However, the scientific challenges of Li-S batteries mainly result from the sulfur core. First, the insulating nature of sulfur results in its low electrochemical utilization. Second, the generation of polysulfide intermediates (Li2S x , x = 4 – 8) induces the irreversible polysulfide diffusion from the cathode to the anode. The polysulfide migration leads to active-material loss, lithium-anode degradation, and low charge-discharge efficiency. Third, the conventional cathode configuration may not be able to make the best use of sulfur because of the differences in the battery chemistries between the lithium-insertion-compound oxide cathodes and the conversion-reaction sulfur cathodes. Fourth, the cyclability of Li-S cells faces a significant decline on going from low sulfur loadings (< 2 mg cm-2) to high sulfur loadings. To overcome the challenges of the Li-S technology, this presentation will focus on the development of high-loading structural sulfur cathodes and the activation processes of such structuiral cathodes. A core-shell structural sulfur cathode is designed to investigate the feasibility of holding a high-loading sulfur core within a carbon-shell electrode configuration. This concept aims at utilizing the unique materials chemistry of sulfur rather than restricting it as usual. The formation and diffusion of polysulfides are now in-charge of activating the high-loading sulfur core and bettering the electrochemical utilization of sulfur. The carbon-shell electrode, on the other hand, offers the high-loading sulfur core with fast ion and electron transport and stabilizes the active material within the structural cathode configuration. As a result, the sulfur-carbon core-shell cathode effectively utilizes the stabilized sulfur core within the carbon-shell electrode, demonstrating an overall boost in the electrochemical utilization and polysulfide retention. The core-shell cathodes with high sulfur loadings of 4.0 to 30.0 mg cm-2 exhibit outstanding cycle stability at various cycling rates (0.05C to 0.5C rates). For example, the core-shell cathode with a 4 mg cm-2 sulfur loading exhibits the high electrochemical utilization of sulfur of above 96 % with the stable electrochemical cyclability for over 100 cycles at 0.2C rate. The high-loading core-shell cathodes with 20 and 30 mg cm-2 sulfur loadings attain peak discharge capacities of, respectively, 870 and 780 mAh g-1 at 0.2C rate. Such high electrochemical utilization facilitates a high areal capacity of 17 – 23 mAh cm-2. A comparative analysis of the structural cathodes with increasing sulfur loading provides insights into the development of advanced sulfur cathodes with high electrochemical performance and attracting active-material loading. Our findings indicate that the insulating sulfur core may form within the active-material fillings and thereby reduce the initial active-material utilization. The possible solution presented in this work is to channel the dissolved polysulfides to activate the insulating sulfur clusters. Despite the vast number of publications on Li-S batteries employing regular-loading sulfur cathodes (sulfur loading < 2 mg cm-2), the new challenges including increasing polarization and cell resistance that arise with high-loading sulfur cathodes need to be tackled. In this regard, the findings and the cathode engineering of the core-shell structural cathodes presented here with high sulfur content (50 – 60 wt. %), sulfur loading (4.0 – 30.0 mg cm-2), and sulfur mass (4.0 – 30.0 mg cathode-1) might pave the way for the development of structural cathodes with high sulfur loading.

Toward a practical Li-S battery enabled by synergistic confinement of a nitrogen-enriched porous carbon as a multifunctional interlayer and sulfur-host material

Development of advanced energy-storage systems needs to consider a balance among cost, cycle life, safety, energy, power, and environmental benignity. With these requirements, lithium-sulfur (Li-S) and sodium-sulfur (Na-S) batteries are promising candidates as next-generation energy-storage systems because of the high charge-storage capacity, natural abundance, and environmental friendliness of sulfur. However, the practical utility of Li-S and Na-S cells is hampered by the low electrochemical utilization of sulfur and severe polysulfide diffusion from the cathode to the anode. These drawbacks result in low discharge capacity and poor cycle life. The Li-S and Na-S battery chemistries have several scientific challenges in common. The degradation of both the anode and cathode active materials, as well as the decomposition of the liquid electrolyte, causes a fast capacity fade and low electrochemical utilization of the active material. Unfortunately, the efforts to overcome the persistent problems often result in the incorporation of excessive conductive carbon into the electrode and low sulfur loading per unit area. In fact, it is often easy in the literature to obtain greatly improved performance by using either low sulfur content, low sulfur loading, or low sulfur mass in a cathode. The use of low-sulfur-loading cathodes can defeat the energy-density advantage of sulfur cathodes and the purpose of Li-S and Na-S cells replacing the current lithium-ion technology. Moreover, the traditional cathode configuration borrowed from the commercial insertion-compound cathodes may not allow the pure sulfur cathode to put its unique materials chemistry to good use due to the very different battery chemistries between the solid insertion-compound oxide cathodes and the electrochemical conversion-reaction sulfur cathodes. Recognizing the importance of operating the Li-S and Na-S cells with high-sulfur-loading cathodes for being competitive with the existing lithium-ion technology, this presentation will focus on unique approaches in engineering the sulfur cathodes with high-sulfur loadings and employing solid electrolytes. The cathode engineering presented can lead the way towards employing high-loading cathodes with promising cell performance while the easily-prepared pure sulfur powders are utilized as the active material. The first high-capacity cathode engineering involves a layer-by-layer strategy. This method confines sulfur powders between porous carbon nanofiber (PCN) multi-layers. The layer-by-layer cathode facilitates fast ion and electron transport and traps the soluble polysulfide intermediates within the multilayered electrode configuration. A single-sulfur-layer cathode coupled with two-PCN layers offers a high discharge capacity of 1265 mAh g-1 at C/5 rate with good cyclability. The cathode engineering further facilitates high areal sulfur loading by increasing the number of sulfur layers. For example, a six-sulfur-layer cathode attains a high areal sulfur loading of 11.4 mg cm-2. The high-sulfur-loading cathode delivers a high initial discharge capacity of 995 mA h g-1 at C/10 rate with a corresponding areal capacity of 11.3 mA h cm-2. The second high-capacity cathode engineering involves an edge-encapsulation method. An omurice-type cathode consists of a light-weight multiwall carbon nanotube (MWCNT) thin-film as the omelette cover and the active-material filling as the fried rice. The active-material paste is first dropped onto an aluminum-foil current collector and then covered by the MWCNT thin-film, followed by pressing the edge of the electrode for the favorable edge-encapsulation of the sulfur core. As a result, the polysulfide migration is stabilized within the structural cathode due to the strong tortuosity of MWCNT layer and the edge-encapsulated cathode configuration, benefiting the capacity retention. The omurice-type cathodes exhibit a high discharge capacity (1190 mAh g-1), a long lifespan (500 cycles), and low capacity fade (0.08 % cycle-1). In addition, the structural cathodes with a good balance among high sulfur loading (4.2 – 10.0 mg cm-2), high sulfur content (50 – 60 wt. %), and high sulfur mass (4.2 – 10.0 mg cathode-1) are able to attain a high areal capacity (5.1 – 7.8 mAh cm-2). In addition, polysulfide-trapping interlayers, multi-functional separators, and solid electrolyte membranes developed in our group are integrated with the above advanced structural cathodes for suppressing polysulfide migration and alkali-metal dendrite growth. The integrated cells with high active-material loading exhibit good cyclability.

Towards full demonstration of high areal loading sulfur cathode in lithium–sulfur batteries

Lithium-ion batteries, whose energy density ranges from 100–250 Wh kg-1 and 250–700 Wh L-1, dominate the high-energy-density energy-storage market. However, in addition to the limitations in advancing the material and manufacturing technology, lithium-ion batteries face challenges such as rising material costs and market expectations for lower battery prices. Therefore, the development of next-generation high-energy-density batteries has become urgent. Lithium–sulfur batteries stand out as a promising candidate due to their high energy density and low cathode material costs. Unlike lithium-ion batteries, the electrochemical conversion-type lithium–sulfur batteries could fully convert their chemical energy into electrical energy in theory and would not be limited by the structural constraint of electrode materials, thus resulting in higher electrochemical utilization. By combining with lithium-metal anodes, lithium–sulfur batteries could achieve a high theoretical capacity of 1675 mAh g-1 and a high theoretical energy density of 2500 Wh kg-1. Additionally, the sulfur cathode is free from heavy metals, making it a safer and more eco-friendly material. Thus, these advantages let lithium–sulfur batteries become a promising option for next-generation high-energy-density energy storage technology.However, there are some challenges that hinder the development of lithium–sulfur batteries, including the high resistance of active materials, the sluggish redox conversion, and the irreversible polysulfide diffusion. All of them result in low electrochemical utilization, irreversible capacity loss, poor cycling stability, and insulative deposition of sulfides on electrode surfaces. Furthermore, the significant volume change of the cathode during the solid-liquid-solid conversion exacerbates the instability of electrodes and shortens the lifespan of lithium–sulfur batteries. Thus, it is much more difficult to fabricate the lithium–sulfur batteries with practical parameters, such as high sulfur loading (> 5 mg cm-2) and low electrolyte-to-sulfur ratio (< 5 µL mg-1).To address the above challenges faced by lithium–sulfur batteries, in this study, two optimization methods for cathode are introduced, involving decoration with conductive electrocatalyst and physical optimization of cathode material and structural design. This inner-nickel–outer-carbon shell cathode, featuring structural optimization and electrochemical catalyst modification, utilizes a non-nanoporous carbon nanotubes /carbon nanofiber woven microstructure carbon substrate with inner nickel deposited on the inner surface to encapsulate the high-concentration polysulfide catholyte (Figure 1a). This design enables the encapsulation and trapping of polysulfides while promoting their electrochemical conversion. With this inner-nickel–outer-carbon shell cathode, the assembled lithium–sulfur cells could achieve a high sulfur loading of 12.6−28.2 mg cm-2, a high sulfur content of 61.5−74.4 wt%, and a low electrolyte-to-sulfur ratio of 7−3 μL mg-1 (Figure 1b and 1c). Thus, by these optimizations on the physical structure design, electrochemical additives, and critical parameters of the lithium–sulfur cells, the lithium-sulfur cells could achieve a high areal capacity of 14.91 mAh cm-2, a high energy density of 30.56 mWh cm-2, which exceeded the criteria for powering electric vehicles (2–4 mAh cm-2), and a low electrolyte-to-capacity ratio of 3.87 μL (mAh)-1. Figure 1

High-energy storage technologies have garnered extensive interests in recent decades due to the skyrocketing demand for efficient and affordable energy storage systems in stationary electricity storage, portable electronic devices and transports (such as cars, aircrafts and ships) to relieve climate changes and secure energy sustainability. However, the state-of-art lithium-ion (Li-ion) batteries are unable to meet the exponentially increasing demands in these markets, since they suffer from low energy densities and have limited potential to be further developed. In recent years, other Li metal-based battery systems with higher theoretical energy density are introduced and fully developed, particularly the non-aqueous lithium-sulfur (Li-S) batteries and lithium-air (Li-air) batteries. The Li-S batteries are able to reach a theoretical energy density as high as 2567 Wh kg&lt;sup&gt;-1&lt;/sup&gt;, while Li-air batteries have demonstrated an extraordinary theoretical energy density of 11680 Wh kg&lt;sup&gt;-1&lt;/sup&gt;, both of which are ten times higher than that of the Li-ion batteries. Nevertheless, the widespread applications of these two types of battery systems have been hindered by several critical issues including the shuttle effect of Li-S batteries and poor redox kinetics in air cathode of Li-air batteries. The major goal of this thesis is to address these challenges and propel the place of commercialization of Li-based batteries through a bottom-up positive electrode design. We design a series of bottom-up polar material nanostructures in different dimensions to suppress the diffusion of polysulfides for Li-S batteries, including 0D-boron carbide (B&lt;sub&gt;4&lt;/sub&gt;C) nanoparticles, 2D-layered-molybdenum trioxide (MoO&lt;sub&gt;3&lt;/sub&gt;) nanoflakes and 3D-zinc oxide (ZnO) yolk-shell spheres. These polar materials hold high binding energies towards long-chain polysulfides, and thus exhibit strongly chemical anchoring ability to polysulfides. These properties allow Li-S batteries to exhibit an excellent cycling stability after 3000 cycles (0D-B&lt;sub&gt;4&lt;/sub&gt;C nanoparticles decorated activated cotton fibers), a high areal sulfur loading of 8.0 mg cm&lt;sup&gt;-2&lt;/sup&gt; (2D-layered-MoO&lt;sub&gt;3&lt;/sub&gt; nanoflakes decorated carbon paper), and excellent rate capability and high retention capacity rate (3D-yolk-shell ZnO spheres as sulfur host). Meanwhile, in-situ Raman spectra is carried out to examine the sulfur conversion reactions during the discharge/charge process as well as the chemical bonds formed between polar materials and polysulfides. For Li-air batteries, to obtain more uniform oxygen (O&lt;sub&gt;2&lt;/sub&gt;) /electrolyte distribution and larger electrochemically available surface area within the air electrode, we construct more abundant O&lt;sub&gt;2&lt;/sub&gt; and electrolyte transportation paths by designing a series of bottom-up positive electrodes from 0 to 3D, in the same manner as what we have done in the Li-S batteries, including the 0D-mesoporous ultrafine tantalum pentoxide (Ta&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;) nanoparticles, 1D-paramecium-like ferric oxide (Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;) nanotubes, 0D&amp;1D-ruthenium dioxide (RuO&lt;sub&gt;2&lt;/sub&gt;)-decorated carbonized tubular polypyrrole, and 1D&amp;1D-vanadium pentoxide-nickel dioxide (V&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;-NiO) composite nanowire. Based on these novel electrodes, we enlarge the reversible capacity and cycling lifespan of pure carbon cathodes with low-overpotentials and high rate capability for Li-air batteries in pure oxygen atmosphere and fortify the stable operation of Li-air batteries with carbon-free cathodes in ambient air. Keywords: Bottom-up positive electrode design; Energy storage systems; Li-S batteries; Shuttle effect; Polar materials; in-situ Raman; Li-air batteries; Ambient air operation.

Lithium–sulfur (Li–S) batteries offer a significantly higher theoretical energy density compared to modern lithium-ion batteries. In addition, sulfur – the cathode material in Li–S batteries – is naturally abundant, non-toxic, and cost-effective. These attributes position Li–S batteries as a promising next-generation energy storage technology. However, realizing their commercial viability requires increasing their areal capacity by fabricating sulfur cathodes with elevated areal sulfur loadings (>4 mg cm⁻²).Increasing the areal sulfur loading is inherently linked with an increase in cathode thickness, which negatively impacts microstructure and, consequently, electrochemical performance. At high sulfur loadings, sulfur cathodes experience (i) longer ion and mass transport distances that slow conversion reactions; (ii) mechanical degradation caused by extensive volume variation (>80%) of sulfur upon charge and discharge; and (iii) accelerated electrolyte and anode degradation due to the higher concentration of liquid-phase discharge products. Additionally, significant slurry shrinkage during drying induces cracking and delamination in thick sulfur cathodes, further compromising cell performance. These challenges lead to thickness-dependent electrochemical degradation in Li–S batteries.In recent years, substantial progress has been made toward enabling high-sulfur-loading cathodes. However, most advances have been demonstrated using coin cell formats. For Li–S batteries to become commercially viable, it is essential to transition these advancements to more practical formats, particularly pouch cells. The challenges associated with high-sulfur-loading cathodes are exacerbated in pouch cells due to their larger electrode area. This scale-up intensifies issues such as non-uniform electrolyte wetting, higher interface resistance due to lower external pressure compared to coin cells, complex assembly procedures, and increased resistance from welded tabs. Consequently, sulfur cathodes that exhibit excellent performance in coin cells often display significantly increased resistance and reduced capacity in pouch cell configurations.This talk presents a practical strategy for developing large-area sulfur cathodes capable of supporting high areal sulfur loadings while maintaining low cell resistance in Li–S pouch cells. The approach utilizes a multilayer cathode architecture incorporating two immiscible polymeric binders, each dissolved in a compatible solvent. During electrode fabrication, cathode layers containing identical sulfur and carbon compositions, but different binders are systematically stacked to form a multilayer architecture. This configuration enables high overall sulfur loading while preserving the desired microstructure within each layer and across the entire cathode. The areal sulfur loading of individual layers is optimized in the range of 0.9 to 1.4 mg cm⁻². Our studies have demonstrated that this multilayer design preserves cathode microstructure at high loadings by mitigating cracking and delamination, thereby maintaining electronic conductivity. Additionally, it enhances ion transport by extending ion diffusion pathways across the layered architecture. As a result, the multilayer cathode design significantly reduces overall cell resistance and improves both ion and electron transport. This concept, through its simultaneous enhancement of microstructural integrity and electrochemical performance, offers a promising strategy toward the development of commercially viable, large-format Li–S batteries.

Lithium-sulfur (Li-S) batteries have emerged as one of the most promising next-generation energy storage systems due to their high theoretical energy density and the abundance and low cost of sulfur¹. Despite their potential, significant challenges, such as the lithium polysulfide (LiPS) shuttling effect, poor catalytic activity, and rapid capacity fading, have hindered their practical implementation². Addressing these issues requires advanced interlayer designs capable of suppressing LiPS diffusion while simultaneously enhancing catalytic activity.In this study, an innovative electrospun polyvinylidene fluoride (PVDF) fiber-based interlayer incorporating two different MXene-Transition Metal Oxide (MXene-TMO) composite structures in medium (2–3 mg·cm⁻²) and high (5–6 mg·cm⁻²) sulfur loading cells is presented. The electrospinning process enables the creation of a three-dimensional (3D) interconnected fibrous and porous architecture, providing efficient ion transport pathways and strong physical barriers to LiPS migration, where the PVDF structure develops polar-polar interactions due to its inherent polarity. Moreover, the addition of MXene-TMO structures embedded into the electrospun fibers improves the catalytic conversion of LiPSs. MXene nanoparticles possess high catalytic activity ability, which lowers the energy barriers and promotes the redox reactions of long-chain polysulfides to short-chain polysulfides. On the other hand, TMO structures act as mediators, chemically trapping LiPSs via polar-polar interactions and decreasing the activation energy of long-chain LiPSs³. The deposition of TMOs onto MXene particles also provides a high surface area with numerous polar sites for enhanced LiPS adsorption, immobilization, and conversion⁴. Furthermore, a hot-pressing method was applied to eliminate the gap between the interlayer and electrode during assembly, enhancing compactibility. This process reduced internal resistance and further improved capacity retention.Integration of PVDF/MXene-TMO interlayers significantly reduced capacity decay over extended cycling, improved capacity retention, and enhanced cell reversibility and stability in both sulfur-type cells. Electrochemical test results revealed that, especially for high-sulfur-loaded cells, the charge transfer resistance of polysulfide species on the positive electrode (represented by the second semicircle in the data⁵) was diminished by 94% compared to the reference cell. This suggests that LiPSs were successfully adsorbed via polar-polar interactions and the shuttling effect was mitigated. The adsorption of polysulfides by the interlayers was clearly demonstrated through adsorption tests. Initially, the polysulfide solution exhibited a dark yellowish color. However, upon introducing the PVDF/MXene-TMO-based interlayer, the solution’s color shifted to a pale yellowish-white. Quantitative analysis using UV-VIS spectroscopy revealed that the initial polysulfide concentration of 4 mM was reduced to 1.8 mM following the addition of the PVDF/MXene-TMO interlayers. Moreover, using the Randles-Sevcik equation, the influence of interlayers on the diffusion rate and catalytic conversion of polysulfides was evaluated. The diffusion rate of Li⁺ ions demonstrated a 90% increase. These findings underscore the effectiveness of both polar-polar interactions and enhanced catalytic activity in suppressing the polysulfide shuttle effect. Our findings suggest that these innovative interlayer materials present a promising solution for the development of high-performance and durable Li-S batteries.This research highlights the significant potential of combining PVDF, MXene, and MXene-TMO electrospun fibers with advanced catalytic materials as effective interlayer solutions for Li-S batteries. By leveraging the unique properties of these materials, the polysulfide shuttling effect—one of the most critical challenges in Li-S battery technology—was addressed. The results demonstrate a promising pathway toward developing long-lasting, high-performance Li-S batteries, which are crucial for advanced energy storage applications. This approach not only tackles key issues but also paves the way for the practical implementation of Li-S batteries in energy storage systems.The authors gratefully acknowledge the financial support of The Scientific and Technological Research Council of Türkiye (Grant Number: 121N816) and the Swiss National Science Foundation (Grant Number: IZJFZ2_202476).

Carbon nanofibril composites with high sulfur loading fabricated from nanocellulose for high-performance lithium-sulfur batteries

Conventional lithium-ion batteries are unable to meet the increasing demands for high-energy storage systems, because of their limited theoretical capacity.1 In recent years, intensive attention has been paid to enhancing battery energy storage capability to satisfy the increasing energy demand in modern society and reduce the average energy capacity cost. Among the candidates for next generation high energy storage systems, the lithium sulfur battery is especially attractive because of its high theoretical specific energy (around 2600 W h kg-1) and potential cost reduction. In addition, sulfur is a cost effective and environmentally friendly material due to its abundance and low-toxicity. 2 Despite all of these advantages, the practical application of lithium sulfur batteries to date has been hindered by a series of obstacles, including low active material loading, poor cycle life, and sluggish sulfur conversion kinetics.3 Achieving high mass loading cathode in the traditional 2D planar thick electrode has been challenged. The high distorsion of the traditional planar thick electrodes for ion/electron transfer leads to the limited utilization of active materials and high resistance, which eventually results in restricted energy density and accelerated electrode failure.4 Furthermore, of the electrolyte to pores in the cathode and utilization ratio of active materials. Catalysts such as MnO2 and Co dopants were employed to accelerate the sulfur conversion reaction during the charge and discharge process.5 However, catalysts based on transition metals suffer from poor electronic conductivity. Other catalysts such as transition metal dopants are also limited due to the increased process complexities. . In addition, the severe shuttle effects in Li-S batteries may lead to fast failures of the battery. Constructing a protection layer on the separator for limiting the transmission of soluble polysulfides is considered an effective way to eliminate the shuttle phenomenon. However, the soluble sulfides still can largely dissolve around the cathode side causing the sluggish reaction condition for sulfur conversion.5 To mitigate the issues above, herein we demonstrate a novel sulfur electrode design strategy enabled by additive manufacturing and oxidative vapor deposition (oCVD). Specifically, the electrode is strategically designed into a hierarchal hollow structure via stereolithography technique to increase sulfur usage. The active material concentration loaded to the battery cathode is controlled precisely during 3D printing by adjusting the number of printed layers. Owing to its freedom in geometry and structure, the suggested design is expected to improve the Li ions and electron transport rate considerably, and hence, the battery power density. The printed cathode is sintered at 700 °C at N2 atmosphere to achieve carbonization of the cathode during which intrinsic carbon defects (e.g., pentagon carbon) as catalytic defect sites are in-situ generated on the cathode. The intrinsic carbon defects equipped with adequate electronic conductivity. The sintered 3D cathode is then transferred to the oCVD chamber for depositing a thin PEDOT layer as a protection layer to restrict dissolutions of sulfur compounds in the cathode. Density functional theory calculation reveals the electronic state variance between the structures with and without defects, the structure with defects demonstrates the higher kinetic condition for sulfur conversion. To further identify the favorable reaction dynamic process, the in-situ XRD is used to characterize the transformation between soluble and insoluble polysulfides, which is the main barrier in the charge and discharge process of Li-S batteries. The results show the oCVD coated 3D printed sulfur cathode exhibits a much higher kinetic process for sulfur conversion, which benefits from the highly tailored hierarchal hollow structure and the defects engineering on the cathode. Further, the oCVD coated 3D printed sulfur cathode also demonstrates higher stability during long cycling enabled by the oCVD PEDOT protection layer, which is verified by an absorption energy calculation of polysulfides at PEDOT. Such modeling and analysis help to elucidate the fundamental mechanisms that govern cathode performance and degradation in Li-S batteries. The current study also provides design strategies for the sulfur cathode as well as selection approaches to novel battery systems.

Molten Lithium-Brass/Zinc Chloride System as High-Performance and Low-Cost Battery

Synergistic effect of Co3Fe7 alloy and N-doped hollow carbon spheres with high activity and stability for high-performance lithium-sulfur batteries

Free-standing 3D nitrogen-doped graphene/Co4N aerogels with ultrahigh sulfur loading for high volumetric energy density Li-S batteries

The poor conductivity of sulfur, the shuttle effect and sluggish redox reaction kinetics of lithium polysulfides (LiPSs) are considered the main obstacles to the practical application of Lithium-sulfur (Li-S) batteries. Thus, it is urgent to design multifunctional host materials to eliminate these obstacles. Herein, we designed a hollow flower-like CoTiO3 wrapped by reduced graphene oxide (h-CoTiO3@rGO) as sulfur host materials. The hollow structure of h-CoTiO3@rGO not only endows sufficient space for high sulfur loading, but also physically and chemically confines the shuttle effect of LiPSs through the formation of Co-S chemical bonding. The large specific surface area and excellent electrocatalytic ability of h-CoTiO3@rGO provide amounts of active sites to accelerate the redox reaction of LiPSs. Meanwhile, the conductive reduced graphene oxide (rGO) covered on the surface of CoTiO3 microspheres offers an interconnected conductive network to support the fast electron/ion transfer. Profit from these merits, the battery employing the multifunctional h-CoTiO3@rGO as sulfur host exhibited excellent cycling stability with an ultralow capacity fading of 0.0127 % per cycle after 500 cycles at 1C. Even the battery with high sulfur loading of 5.2 mg/cm2 still delivered a high area capacity of 5.02 mAh/cm2, which was competitive with the commercial Li-ion batteries. Therefore, the competitive capacity and superior cycling stability suggest that the h-CoTiO3@rGO/S cathode is a potential candidate for high-performance Li-S batteries.