High-performance Sulfur Cathode Research Articles

Leveraging doping strategies and interface engineering to enhance catalytic transformation of lithium polysulfides for high-performance lithium-sulfur batteries

The commercialization of lithium-sulfur (Li–S) batteries has faced challenges due to the shuttle effect of soluble intermediate polysulfides and the sluggish kinetics of sulfur redox reactions. In this study, a synergistic catalyst medium was developed as a high-performance sulfur cathode material for Li–S batteries. Termed A/R-TiO2@ Ni-N-MXene, this sulfur cathode material features an in-situ derived anatase–rutile homojunction of TiO2 nanoparticles on Ni-N dual-atom-doped MXene nanosheets. Using in-situ transmission electron microscopy (TEM) technique, we observed the growth process of the homojunction for the first time confirming that homojunctions facilitated charge transfer, while dual-atom doping offered abundant active sites for anchoring and converting soluble polysulfides. Theoretical calculations and experiments showed that these synergistic effects effectively mitigated the shuttle effect, leading to improved cycling performance of Li–S batteries. After 500 cycles at a 1C rate, Li–S batteries using A/R-TiO2@Ni-N-MXene as cathode materials exhibited stable and highly reversible capacity with a capacity decay of only 0.056 % per cycle. Even after 150 cycles at a 0.1C rate, a high-capacity retention rate of 62.8 % was achieved. Additionally, efficient sulfur utilization was observed, with 1280.76 mA h/g at 0.1C, 694.24 mA h/g at 1C, alongside a sulfur loading of 1.5–2 mg/cm2. The effective strategy based on homojunctions showcases promise for designing high-performance Li–S batteries.

Selenium-Doped Sulfurized Polyacrylonitrile Hybrid Cathodes with Ultrahigh Sulfur Content for High-Performance Solid-State Lithium Sulfur Batteries.

The solid-state lithium sulfur battery (SSLSB) is an attractive next-generation energy storage system by reason of its remarkably high energy density and safety. However, the SSLSB still faces critical challenges, such as sluggish reaction kinetics, mismatched interface, and undesirable reversible capacity. Herein, a high-performance SSLSB is reported using sulfurized polyacrylonitrile with rich selenium-doped sulfur (Se/S-S@pPAN) as a cathode and poly(ethylene oxide)/Li7La3Zr1.4Ta0.6O12 (PEO-LLZTO) as an electrolyte. The sulfur content of the cathode up to 60.9 wt % can be achieved by dispersing selenium sulfide (SeSx) species in the sulfurized polyacrylonitrile (S@pPAN) skeleton at a molecular level. Selenium as a eutectic accelerator can be uniformly distributed in the composite through the Se-S bond and can accelerate the reaction kinetics. The PEO-LLZTO hybrid solid-state electrolyte (SSE) displays an attractive electrochemical performance and provides an intimate contact with electrodes. At 60 °C, Se/S-S@pPAN delivers an impressive discharge capacity of 1042 mAh g-1 at 0.1C and 445 mAh g-1 at 1C. Additionally, the LiFePO4 cathodes combined with PEO-LLZTO deliver a high reversible capacity (158.9 mAh g-1, 1C) and an ultralong lifespan (a capacity retention of 80%, 1000 cycles) at 1C. The synergetic design of the high-performance sulfur cathode and the organic/inorganic hybrid electrolyte is crucial for enabling the high-performance SSLSB.

Bioinspired urchin-like murray carbon nanostructure with protection shell for advanced lithium-sulfur batteries

Commercial application of lithium-sulfur (Li-S) batteries is hindered by the insulating nature of sulfur and the dissolution of polysulfides. Here, a bioinspired 3D urchin-like N-doped Murray’s carbon nanostructure (N-MCN) with interconnected micro-meso-macroporous structure and a polydopamine protection shell has been designed as an effective sulfur host for high-performance Li-S batteries. The advanced 3D hierarchically porous framework with the characteristics of the generalized Murray’s law largely improves electrolyte diffusion, facilitates electrons/ions transfer and provides strong chemisorption for active species, leading to the synergistic structural and chemical confinement of polysulfides. As a result, the obtained P@S/N-MCN electrode with high areal sulfur loading demonstrates high capacity at high current densities after long cycles. This work reveals that following the generalized Murray’s law is feasible to design high-performance sulfur cathode materials for potentially practical Li-S battery applications.

Softening and enriching polarity of chitosan backbone as a bifunctional binder for high-performance sulfur cathode

Lithium-sulfur batteries have attracted much attention because of their high energy density; their long-term stability suffers from the shuttle effect of polysulfides and the volume variation of sulfur during charging and discharging process. Herein, by chemically grafting highly flexible and polar poly(N-aryloylglycamide) (PNAGA) segments onto the linear backbone of the naturally abundant, hard and brittle chitosan, a hyper-branched and 3D-linked aqueous binder was prepared, which has stronger binding strength and is more flexible than the pristine chitosan or the commercial PVDF. Moreover, owing to the presence of affluent diamide groups in the PNAGA branches, the grafted binder demonstrates much better ability for capturing polysulfides. When applied in sulfur cathode, the binder is bifunctionally effective, which can suppress the shuttle behaviors of the polysulfides and well maintain the interfacial intimacy, thus enabling excellent long-term cycling stability. After 300 cycles at 0.2 C, the relevant battery still retains 843.1 mAh g − 1, spelling a retention rate 49.4% and 69.6% higher than those using PVDF and the pristine chitosan, respectively; even under a high sulfur loading of 5.2 mg cm−2, the battery can still operate steadily more than 100 cycles at 0.2 C, maintaining a specific capacity above 620.1 mAh g − 1.

The Optimization of a Carbon Paper/MnO2 Composite Current Collector for Manufacturing a High-Performance Li–S Battery Cathode

High theoretical energy density endows lithium–sulfur batteries to be a promising candidate of the secondary batteries. Numerous studies have been implemented relying on exploring efficient host materials or separator modifying layers to solve the problematic shuttling and insufficient conversion of soluble polysulfides, whereas few studies have focused on the modification of the cathode collector. Herein, a high-performance sulfur cathode is manufactured with carbon paper/MnO2 as the cathode collector and liquid lithium polysulfides as the electrode material. The interface of carbon paper/MnO2 is proposed to afford fast electronic transport, strong chemical adsorption, and effective electrocatalysis to confine the diffusion of lithium polysulfides and facilitate their conversion during the charge/discharge process. More importantly, with no conductive additives and binders assisting, the gravimetric energy density of the sulfur cathode could be largely improved. Specifically, lithium–sulfur batteries using carbon paper/MnO2 as a cathode collector could stably circulate for 200 cycles at 0.2 C with a capacity of 664 mAh g−1, which is higher than that of carbon paper as a cathode collector (486 mAh g−1). This work may provide a new perspective to enhance the electrochemical performance of lithium–sulfur batteries by optimizing the cathode collector.

(Digital Presentation) A Design of Nickel/Sulfur Energy-Storage Materials for Electrochemical Lithium-Sulfur Cells

Introduction As one of the next-generation rechargeable battery technologies beyond the lithium-ion chemistry, the lithium-sulfur chemistry enables the low-cost sulfur cathode to generate a high theoretical capacity of 1,675 mAh g-1 (10 times higher capacity than those of lithium-ion battery cathode). It further exhibits a high theoretical energy density of 2,600 Wh kg-1 in lithium-sulfur batteries (2–3 times higher energy density than lithium-ion batteries). However, as reported in recent publications, the development is far from adequate with respect to the high-loading sulfur cathode with high active-material content in building advanced lithium-sulfur batteries with a high energy density. The material challenges result from the use of an insulating sulfur as the active material, which would generate lithium polysulfides that can easily diffuse out from the cathode. The high cathode resistance and fast loss of the active material lead to the poor electrochemical utilization and efficiency of lithium-sulfur battery cathodes. These negative impacts subsequent derive the additional electrochemical challenges. A high amount of conductive and porous substrates is added in the cathode to replace the active material, which results in the limited amount of sulfur in the cathode and further blocks the improvement of designing high-energy-density sulfur cathodes.To address the above-mentioned issues, the research progresses of high-performance sulfur cathodes aim to design functional host for sulfur cathodes with the use of carbon for high conductivity, polymers for high ionic transfer, porous materials for physical polysulfide retention, polar materials for chemical polysulfide adsorption, catalysts for high reaction kinetics, etc. However, metallic materials that naturally have high conductivity, strong polysulfide adsorption capability, and catalytic conversion ability, are rarely reported. This is because metals have the highest density as compared to the aforementioned host materials, which commonly causes an insufficient amount of active material in the cathode and therefore inhibits the design of metal-sulfur nanocomposite in sulfur cathodes.To explore the metal/sulfur nanocomposite as a new research trend in sulfur cathodes, we propose a design for a nickel/sulfur nanocomposite as a novel energy-storage material by the electroless nickel plating method, and discuss its applications in lithium–sulfur battery cathodes. The nickel/sulfur energy-storage material possesses metallic nickel on the surface of the insulating sulfur particles as a result of the reduction of nickel ions during autocatalytic plating. By controlling the synthesis and fabrications conditions, the nickel/sulfur energy-storage material attains adjustable high sulfur contents of 60–95 wt% and adjustable high sulfur loadings of 2–10 mg cm−2 in the resulting cathode. The high-loading cathode with the nickel/sulfur energy-storage material demonstrates high electrochemical utilization and stability, which attains a high areal capacity of 8.2 mA∙h cm−2, an energy density of 17.3 mW∙h cm−2, and a stable cyclability for 100 cycles. Results and Discussion Here, in our presentation, we discuss our novel method for the fabrication of nickel/sulfur energy-storage material as an advanced composite cathode material for exploring battery electrochemistry and battery engineering. We adopt a modified electroless-plating method to synthesize nickel/sulfur energy-storage materials characterized by adjustable high sulfur contents and promising cathode performance. The plated nickel coating provides the nickel/sulfur energy-storage materials with metallic conductivity and polysulfide adsorption ability, which addresses the two major issues of sulfur cathodes.[1,2] Therefore, the nickel/sulfur energy-storage material attains high sulfur contents in the cathode and exhibits a high charge-storage capacity of 1,362 mA∙h g−1 and an excellent cyclability for 100 cycles. Moreover, the nickel/sulfur energy-storage material enables high-loading sulfur cathodes with a sulfur loading of 10 mg cm−2, a high areal capacity of 8.2 mA∙h cm−2, and an energy density of 17.3 mW∙h cm−2. Conclusion In summary, the summary of our nickel/sulfur energy-storage materials presented in this presentation would demonstrate a light-weight metallic nickel coating technique for fast charge transfer and strong polysulfide retention in the sulfur nanocomposites composite sulfur cathode. Moreover, our systematic analysis of the nickel/sulfur energy-storage materials exhibits their achievements in attaining both high electrochemical designs of high sulfur content and loading as well as possessing high energy density and electrochemical stability. References C.-S. Cheng, S.-H. Chung, Chem. Eng. J. 2022, 429, 132257.C.-S. Cheng, S.-H. Chung, Batter. Supercaps 2022, 5, e202100323.

Zirconia-supported cobalt nanoparticles as high-performance sulfur cathode for lithium–sulfur batteries

Lithium–sulfur (Li–S) battery is now a promising technology for energy storage. However, rapid capacity decay due to sulfur dissolution and shutting effect severely limit its commercial development. In this work, a NH2-UIO-66 metal organic framework-derived porous composite (Co-ZrO2@NC) consists of nitrogen-doped carbon (NC) and zirconium oxide (ZrO2) loaded with cobalt nanoparticles was prepared. The porous NC component not only increases the accommodation of sulfur in the cathode, but also benefits the charge transfer in sulfur electrochemistry. The Co and ZrO2 would act as active centers to enhance the adsorption/conversion of lithium polysulfide and improve its electrochemical utilization. When used in sulfur cathode, the Co-ZrO2@NC electrode shows excellent electrochemical performance with an initial specific capacity of 1073 mAh g−1 at a rate of 0.2 C and a reversible capacity of 1015 mAh g−1 after 100 cycles, corresponding to a capacity retention of 94.6%. Furthermore, after 300 cycles at 1.0 C, corresponding to a capacity retention of 75.4%. Moreover, the cell also exhibits good rate performance (640 mAh g−1 at 3.0 C). Even at high sulfur loading of 4.0 mg cm−2, the S/Co-ZrO2@NC cathode is able to deliver an areal specific capacity of 4.8 mAh cm−2.

Ionic liquid modified mesoporous silica (SAB-15) as an effective polysulfide reservoir for high-performance lithium sulfur batteries

To restrict the polysulfide migration effectively, the fabrication of sulfur host material with strong polysulfide adsorption is necessary. Herein, we grafted the cation on SBA-15 surface to achieve the high-efficiency polysulfide reservoir through electrostatic force and the derived Im-SBA-15/CNT hybrid could exhibit a promising application potential as a host material for sulfur cathode owing to the strong polysulfide adsorption of Im-SBA-15 and the successful electron conduction of CNT. As a result, the Im-SBA-15/CNT/S composite delivers a superior electrochemical performance. Even after 350 cycles, Im-SBA-15/CNT/S cathode also could show a capacity of 682.3 mAh/gsulfur with no obvious capacity fading. This work demonstrates a promising polysulfide suppression strategy for high-performance sulfur cathode.

Renewable biomass-derived carbon-based hosts for lithium–sulfur batteries

This review sorts biomass-derived carbon-based hosts out according to their structure and properties, aiming to elucidate the great potential of biomass-derived carbon in achieving high-performance sulfur cathodes.

"First-Cycle Effect" of Trace Li2S in a High-Performance Sulfur Cathode.

Lithium-sulfur battery is one of the most promising choices for next-generation batteries due to its high theoretical energy density and natural abundance. However, the sulfur cathode undergoes a stepwise reduction process and generates multiple soluble polysulfide intermediates; for the further conversion from the dissolved intermediates to the final solid product (Li2S), the surface nucleation barrier limits the speed of the electrochemical precipitation, resulting in serious polysulfide diffusion loss and low sulfur utilization. Herein, the trace Li2S (tLi2S) is modified on the carbon fiber (CF) skeleton as preloaded crystal nuclei to boost the electrokinetics of Li2S deposition in the initial cycle. The trace Li2S decreases the nucleation barrier on the modified electrode (tLi2S@CF), resulting in a high initial capacity of 1423 mAh g-1 for the Li2S6 catholyte (0.2 C), which corresponds to a nearly 100% utilization of Li2S6. Furthermore, the trace Li2S nuclei induce a uniform distribution of the redeposited active materials, and the uniform distribution persists in the following cycles, which benefits the cycle life significantly. The sulfur cathode based on the tLi2S@CF matrix maintains a capacity of 1106 mAh g-1 at 1 C rate after 100 cycles. The strategy can provide a new avenue for the rational design of the sulfur cathode.

Rational design of graphene oxide wrapped porous microspheres as high-performance sulfur cathode in lithium-sulfur batteries

The application of lithium-sulfur batteries (LSBs) encounters many problems including polysulfides shuttling, low sulfur conductivity and poor stability. To address these issues, a porous microsphere-based sulfur cathode, consists of Mg2+ etched ZIF-67 and carbon nanotubes encapsulated with graphene oxide (Mg ZIF-67/CNT@GO), was fabricated. The introduction of CNTs endows the composite with good electrical conductivity, and at the same time the loss of polysulfides is mitigated through its unique porous structure. Moreover, the Mg2+ etched ZIF-67 also provides a large area of active interface, which promotes its trapping with polysulfides and catalytic performance towards polysulfides conversion. Accordingly, the sulfur cathode with Mg ZIF-67/CNT@GO composite delivers good electrochemical performance. The battery exhibits a high capacity retention rate of 87.4% and an areal capacity of 3.35 mAh cm-‍2 under 3.0 mg cm-2 sulfur loading at 0.2 C. In addition, the pouch cell cycled at 0.1 C retains its high capacity of 640.8 mAh g-l after 50 cycles. This work provides a promising sulfur cathode design approach for the implementation of LSBs.

Carbon nanotube-supported polyimide nanoarrays as sulfur host with physical/chemical polysulfide-traps for Li–S batteries

Lithium-sulfur (Li–S) batteries have been regarded as the most promising next-generation energy storage devices due to their large specific capacity and high energy density. However, their practical implementation is still subjected to the insulation of sulfur and discharge products, serious shuttle effect, and large volume expansion of sulfur during the discharge/charge processes. Herein, polyimide nanoarrays functionalized carbon nanotubes (PI@CNT) were proposed as a sulfur host with the incorporation of additional carbon nanotubes (CNTs) conductive networks. The as-preformed polyimide nanoarrays on the surface of CNTs expose sufficient adsorption sites for sulfur loading. PI@CNT chemically bind lithium polysulfides (LiPS) via the polar Li–N bonding interaction and physically confine LiPS in the network. Meanwhile, the intertwined frameworks can bear the volume expansion of sulfur and maintain the electrode integrity. The PI@CNT/CNT/S cathode exhibits the sulfur loading as high as 70 wt% and shows the cycling stability with a capacity retention of 67% after 300 cycles at 1 C. Furthermore, the additional incorporation of CNTs can form continuous electron transfer paths, thereby promoting the rate capability. This work integrated the polar polymer host and conductive networks with robust LiPS trapping and fast conversion, and would propose a new paradigm for designing high-performance sulfur cathodes.

Boron nitride nanosheets wrapped by reduced graphene oxide for promoting polysulfides adsorption in lithium-sulfur batteries

The polysulfides shuttling and slow redox kinetics of sulfur-based cathodes have severely hindered the commercialization of lithium-sulfur (Li-S) batteries. Herein, distinctive three-dimensional microspheres composed of boron nitride (BN) nanosheets and reduced graphene oxide (rGO) were applied to act as efficient sulfur cathode hosts for the first time using in a spray-drying process. Using this construction, the robust microsphere structure could shorten ion diffusion pathways and supply sufficient spaces to alleviate the volumetric expansion of sulfur during lithiation. Besides, the synergistic effect between BN and rGO significantly enhanced polysulfides adsorption capability and accelerated their conversion, verified by the density functional theory (DFT) calculations and adsorption experiments. Consequently, the S-BN@rGO cathode could manifest the high initial capacity (1137 mAh g−1 at 0.2 C) and remarkable cycling/stability performance (572 mAh g−1 at 1 C after 500 cycles). These results shed light on a design concept of high-performance sulfur cathode host materials.

Properties of S-Functionalized Nitrogen-Based MXene (Ti2NS2) as a Hosting Material for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have received extensive attention due to their high theoretical specific capacity and theoretical energy density. However, their commercialization is hindered by the shuttle effect caused by the dissolution of lithium polysulfide. To solve this problem, a method is proposed to improve the performance of Li-S batteries using Ti2N(Ti2NS2) with S-functional groups as the sulfur cathode host material. The calculation results show that due to the mutual attraction between Li and S atoms, Ti2NS2 has the moderate adsorption energies for Li2Sx species, which is more advantageous than Ti2NO2 and can effectively inhibit the shuttle effect. Therefore, Ti2NS2 is a potential cathode host material, which is helpful to improve the performance of Li-S batteries. This work provides a reference for the design of high-performance sulfur cathode materials.

Nickel-plated sulfur nanocomposites for electrochemically stable high-loading sulfur cathodes in a lean-electrolyte lithium-sulfur cell

An electrochemical sulfur cathode is attractive due to its high theoretical charge-storage capacity, low cost, and natural abundance. For practical viability, a high-performance sulfur cathode with a sufficient sulfur loading/content and stable electrochemical utilization must be developed. However, the satisfaction of these two essential requirements has been proven to be in opposition to each other due to the insulating nature of sulfur and the repeated conversion between solid-/liquid-state active materials that damage the electrochemical efficiency and reversibility. To address these problems, in this work we demonstrate the chemical plating of conductive and electrocatalytic nickel onto sulfur particles to form an electroless-nickel-plated sulfur nanocomposite. This cathode material features a lightweight nickel nanoshell on the surface of the sulfur particles, which enables high electrochemical utilization and kinetics with a high charge-storage capacity (1,008 mA∙h g−1) and excellent rate performance (C/20–C/2). The nickel nanoshell chemically traps and catalyzes the liquid-state active material, resulting in stable long-term cyclability for 200 cycles at various rates. These improved electrochemical characteristics are realized by the enhanced battery properties simultaneously reaching up to a high sulfur loading (14 mg cm−2) and a high sulfur content (74 wt%) with a low electrolyte-to-sulfur ratio (7 µL mg−1). With the capability to utilize and stabilize such a high amount of sulfur, the electroless-nickel-plated sulfur cathode demonstrates enhanced areal/gravimetric capacities along with high energy densities (13–28 mW∙h cm−2) that are comparable to those of the current available lithium-ion oxide cathodes (10–14 mW∙h cm−2).

A robust polymeric binder based on complementary multiple hydrogen bonds in lithium-sulfur batteries

The practical application of sulfur cathodes in traditional lithium–sulfur batteries has been hindered by the substantial deterioration of the sulfur electrode due to the polysulfide shuttling effect and the large volume expansion of the electrode during charge/discharge cycling. The resolving of this issue demands for a robust binder to hold the polysulfide/sulfur particles, but without causing severe disintegration of the electrode. A polar polymeric binder with high mechanical strength was designed and synthesized for use in high-performance sulfur cathodes. The complementary multiple hydrogen bonds formed in the polymeric binder significantly enhanced the adhesive strength of the binder, and buffered the dramatic volume expansion of the sulfur cathode during cycling. The strong physical and chemical interactions between the functional groups (e.g. carboxyl and tertiary amine groups) of the binder and the polysulfides effectively mitigated the shuttling effect in the Li–S batteries. As a consequence, the sulfur cathode exhibited excellent electrochemical performance at a high sulfur loading, yielding an initial discharge capacity of 627.8 mA h g−1 with sulfur loading up to 9.610 mg cm−2 at a rate of 0.2C, corresponding to an aerial capacity of 6.03 mA h cm−1. The present work opens a new avenue for constructing a high-performance Li–S battery using a simple and effective binder.

A design of the cathode substrate for high-loading polysulfide cathodes in lean-electrolyte lithium-sulfur cells

High-performance sulfur cathodes characterized by high loading and content of active material and stable electrochemical properties with a lean electrolyte hold the key to realizing lithium-sulfur batteries with a high energy density. In this study, we present high-loading polysulfide cathodes using a series of carbon nanofibers that are generated from the carbonized electrospun nanofibers (CENFs). We fabricate the CENFs with similar porous fibrous skeleton decorating with tunable nanoporosity that allows us to explore the effect of nanoporosity on the electrochemical characteristics of the high-loading polysulfide cathodes. The CENF-polysulfide cathode made with non-nanoporous CENFs attains a high sulfur content of 71 wt% and loading of 14.4 mg cm−2, both of which exceed sulfur cathodes reported in the literature (<60 wt% and <3 mg cm−2). The high-loading CENF-polysulfide cathodes attain high reversible discharge capacities of 802 and 670 mA h g−1, high capacity retention rates of 82% after 200 cycles, and a long shelf life of 3 months at C/20 and C/10 rates, respectively. The cells further demonstrate high areal energy density values of 23.6 and 18.6 mW h cm−2 in a cell with a low electrolyte-to-sulfur ratio of 4 µL mg−1 at C/20 and C/10 rates. Therefore, our results demonstrate that the porous CENFs with limited nanopores prevent the rapid consumption of electrolyte and enable high-loading polysulfide cathodes to maintain high electrochemical efficiency and stability.

In-situ crosslinked binder for high-stability S cathodes with greatly enhanced conduction and polysulfides anchoring

An in-situ crosslinked binder based on a new chlorine-containing anionic copolymer for high-performance lithium-sulfur battery is fabricated. The elaborately constructed and optimized network structure shows excellent adhesion strength and suitable electrolyte swellability that ensuring the electrode integrity during long-term cycling. The abundant electron-donating groups on the polymer networks endow sulfur cathode with high lithium-ion conduction and polysulfide-trapping capacity, promoting the electrochemical kinetics. These effects are proved by cyclic voltammetry tests, UV–Vis absorption spectrum, X-ray photoelectron spectroscopy, and density-functional theory calculation (DFT). Consequently, sulfur cathode with this crosslinked binder exhibits a high initial capacity of 1038.1 mAh g−1 and high capacity retention of 77.4% after 800cycles at 0.5C. After 800cycles at 1.0C, the sulfur cathode holds a discharge capacity of 684.2 mAh g−1 and a capacity decay of only 0.033% per cycle. What’s more, the cathode still gains a discharge capacity exceeding 800 mAh g−1 at the rate of 3C. This work gives an effective method to design functional binder for high-performance sulfur cathode with polysulfide-trapping and ion-transporting features.

3-D Edge-Oriented Electrocatalytic NiCo 2 S 4 Nanoflakes on Vertical Graphene for Li-S Batteries

Polysulfide shuttle effect, causing extremely low Coulombic efficiency and cycling stability, is one of the toughest challenges hindering the development of practical lithium sulfur batteries (LSBs). Introducing catalytic nanostructures to stabilize the otherwise soluble polysulfides and promote their conversion to solids has been proved to be an effective strategy in attacking this problem, but the heavy mass of catalysts often results in a low specific energy of the whole electrode. Herein, by designing and synthesizing a free-standing edge-oriented NiCo 2 S 4 /vertical graphene functionalized carbon nanofiber (NCS/EOG/CNF) thin film as a catalytic overlayer incorporated in the sulfur cathode, the polysulfide shuttle effect is largely alleviated, revealed by the enhanced electrochemical performance measurements and the catalytic function demonstration. Different from other reports, the NiCo 2 S 4 nanosheets synthesized here have a 3-D edge-oriented structure with fully exposed edges and easily accessible in-plane surfaces, thus providing a high density of active sites even with a small mass. The EOG/CNF scaffold further renders the high conductivity in the catalytic structure. Combined, this novel structure, with high sulfur loading and high sulfur fraction, leads to high-performance sulfur cathodes toward a practical LSB technology.

Carbon nanotubes assembled on porous TiO2 matrix doped with Co3O4 as sulfur host for lithium–sulfur batteries

Advanced design and fabrication of high performance sulfur cathodes with improved conductivity and chemical adsorption towards lithium polysulfides (LiPS) are crucial for further development of Li–S batteries. Hence, we designed a TiO2/Co3O4-CNTs composite derived from Ti-MOF (MIL-125) as the host matrix for sulfur cathode. The polar nature of metal oxides (TiO2, Co3O4) creates the adsorptive sites in the composite and leads to an efficient chemical capture of LiPS. The CNTs ensure the contact between S/Li2S and the host material with high conductivity, enhanced charge transfer and fast electrochemical kinetics. At the same time, the CNTs strengthen the stability of the electrode material. Consequently, the as-prepared TiO2/Co3O4-CNTs composite showed excellent electrochemical performance. The cell with S–TiO2/Co3O4-CNTs delivers an initial specific capacity of 1270 mAh g–1 at 0.2 C and high rate performance with a capacity of 603 mAh g–1 at 3 C.