Lithium-sulfur Cathodes Research Articles

Insight into the Impact of Electrolyte on Passivation of Lithium–Sulfur Cathodes

AbstractOne of the remaining challenges for lithium–sulfur batteries toward practical application is early cathode passivation by the insulating discharge product: Li2S. To understand how to best mitigate passivation and minimize related performance loss, a kinetic Monte–Carlo model for Li2S crystal growth from solution is developed. The key mechanisms behind the strongly different natures of Li2S layer growth, structure, and morphology for salts with different (DN) are revealed. LiTFSI electrolyte in dimethyl ether leads to lateral Li2S growth on carbon and fast passivation because it increases the Li2S precipitation‐to‐dissolution probability on carbon relative to Li2S. In contrast, LiBr electrolyte has a higher DN and yields a particle‐like structure due to a significantly higher precipitation‐to‐dissolution probability on Li2S compared to carbon. The resulting large number of Li2S sites further favors particle growth, leading to low passivation. This study is able to identify the key parameters of the electrolyte and substrate material to tune Li2S morphology and growth to pave the way for optimized performance.

Mxene quantum dots decorated reduced graphene oxide networks as multifunctional electrocatalyst for advanced lithium–sulfur batteries

Lithium sulfur (Li-S) battery has shown great potential as an attractive rechargeable energy storage devices, but the shuttle behavior and slow conversion kinetics of the intermediate lithium polysulfides (LiPSs) are the main obstacles to the practical application of Li-S battery. Herein, a simple and scalable spray drying strategy was used to construct conductive polar Ti3C2 MXene quantum dots (QDs)-decorated reduced graphene oxide (rGO) microsphere (rGO@Ti3C2 QDs) as efficient electrocatalyst and absorbent for Li-S battery. Firstly, the DFT results show that Ti3C2 QDs can effectively adsorb and catalyze LiPSs conversion. This ability can be attributed to the Ti3C2 QDs can provide a large number of LiPSs catalytic active sites. In addition, the rGO provides physical LiPSs constraint and a flexible substrate to prevent QDs from aggregating. Moreover, both parts are conductive, effectively improving the electron/charge transfer. Therefore, this unique structure and composition show high LiPSs adsorption and catalysis, while allowing rapid Li+/electron transfer. As a result, the S/rGO@Ti3C2 QDs electrode provides high initial capacity (1185 mAh/g at 0.2C), good rate capability (758 mAh/g at 3C), and excellent long-term cyclability (500 cycles at 1C with low attenuation of 0.07% per cycle), as well as an excellent electrochemical performance even at high sulfur loading. Meanwhile, the Li-S pouch cell based on S/rGO@Ti3C2 QDs also achieved a high initial energy density of 230.9 Wh kg−1. This work may provide a promising strategy to obtain better electrochemical performance by introducing quantum dots into Li-S cathodes.

Application of MXene-Based Materials for Cathode in Lithium-Sulfur Batteries.

The lithium-sulfur (Li-S) batteries have a high theoretical specific capacity of 1675 mAh ⋅ g-1 and have become the most promising high-energy storage system for the next generation batteries technology. However, their applications are hindered by insulated feature and volume expansion of sulfur, as well as the "shuttle effect" of polysulfides. MXenes own metallic conductivity and strong ability of polysulfides adsorption. Besides, their unique two-dimensional (2D) structure, large specific surface area, abundant functional groups, and adjustability are beneficial to overcome the drawbacks of the sulfur cathode. In this review, different mainstream preparation methods and excellent properties of MXenes are summarized. Significant achievements and recent progress of MXene-based cathodes and interlayers applied to Li-S cathodes are concluded later. Finally, the challenges, possible solutions and potential applications of MXenes for Li-S batteries are also presented.

Configuring a O,S-doped carbon substrate as sulfur anchor for Li–S batteries

Configuring a carbon substrate with low surface polarity seems very important and significant for accelerating the cathode electrochemical performances of the Lithium-sulfur batteries, which is widely regarded as one of the most promising candidates for the next-generation green energy suppliers. The corn starch-derived carbon with in-situ multi-elements doping, initially carbonized by 6 mol/L H2SO4 and then calcined in nitrogen atmosphere, is employed to configure sulfur cathode for Lithium–Sulfur batteries in this study. As-received carbon with randomly distributed graphical domains serves as charge carriers diffusion channels during discharging/charging cycles, thus endowing the cathode considerable excellent performances. Specifically, the loading amount of sulfur in cathode is around 60.31 wt% and the effective utilization efficiency of active reagent sulfur in cathode is up to 60 %. On activating the cathode at 0.114 A g−1 at 0, 25 and 40 °C, the initial discharge capacities of the Lithium–Sulfur batteries with corn starch-derived carbon-based composite cathode (with ∼1.3 mg cm−2 sulfur) are 278.6, 1023.7 and 976.1 mAh∙g−1, respectively. Accordingly, more uniform, and thinner solid electrolyte interphase membrane formed under room temperature activation, leaving in the dramatically diminished Rsur value, contributes to the comparable cycling stability and rate performances of as-designed carbon-based sulfur cathode for Lithium–Sulfur Batteries.

A Novel Approach for the Development of a Scalable, High Energy Density, and Long Life Lithium-Sulfur Battery Technology

Rechargeable lithium-sulfur (Li-S) batteries represent one of the most promising “Beyond Li-ion” battery chemistries due to their high theoretical specific energies ~2,500 Wh/kg.1,2 However, Li-S batteries face substantial technical challenges that must be overcome before they become commercially viable.3 One of the major technical challenges is low practical specific capacity and fast performance degradation due to the formation, migration, and shuttling of intermediate lithium polysulfides (PSs). Several strategies have been used to trap the PS species either chemically or physically; however, they either incur increased cost due to the use of expensive catalysts4 or suffer from the reduced battery specific energy due to added inactive weights from the cell design.5,6 We showed previously a novel strategy to address the PS-shuttle issue using a nanolayer polymer modified high surface area carbon (NPC) as a new type of PS-trapping material (Fig. 1a).7,8 When thin films of NPC were coated on sulfur electrodes (NPC-S), we found that our NPC-S based Li-S battery demonstrated a high discharge specific capacity (~1,600 mAh/g) that is nearing sulfur’s theoretical specific capacity (Fig. 1b). We also showed that our molecular dynamics simulation suggested the observed high specific capacity was attributed to NPC’s strong PS trapping capability via dipole-dipole interactions (Fig. 1c).In this presentation, we will show our continued research effort on this novel approach to further stabilize the long-term battery cycle stability and battery product scalability. We believe our novel approach holds a high promise of developing of a scalable, high energy density, and long life Li-S battery technology for many high-energy-density demanding applications. References Zhang, S. S., Journal of Power Sources 2013, 231, 153-162.Manthiram, A.; Fu, Y.; Su, Y.-S., Accounts of Chemical Research 2013, 46 (5), 1125-1134.Chen, Z. X.; Zhao, M.; Hou, L. P.; Zhang, X. Q.; Li, B. Q.; Huang, J. Q., Advanced Materials 2022, 2201555.Hamal, D.; Awadallah, O.; El-Zahab, B., Catalysis in Lithium-Sulfur Cathodes for Improved Performance and Stability. In 242nd The Electrochemical Society Meeting, Atlanta, GA, USA, 2022.Chung, S.-H.; Han, P.; Singhal, R.; Kalra, V.; Manthiram, A., Advanced Energy Materials 2015, 5 (18).Singhal, R.; Chung, S.-H.; Manthiram, A.; Kalra, V., Journal of Materials Chemistry A 2015, 3 (8), 4530-4538.Hasan, W.; Hyynh, K.; Razzaq, A.; Smdani, G.; Shende, R.; Paudel, T.; Xing, W., "Scalable, High Energy Density Lithium-Sulfur Batteries". In NASA Battery Workshop, November 15-17, 2022 , Huntsville, AL, USA, 2022.Hasan, W.; Huynh, K.; Razzaq, A. A.; Sumdani, G.; Shende, R.; Paudel, T.; Xing, W., #A01-0417, “An Effective Polysulfide Trapping Strategy for the Development of a Scalable, High Energy Density Lithium-Sulfur Battery”, 243rd ECS Meeting, Boston, MA, May 28 – June 2, 2023. Acknowledgment This work was supported by the Larry and Linda Pearson Endowed Chair at the Department of Mechanical Engineering, South Dakoda School of Mines and Technology. Figure 1

Zwitterionic Covalent Organic Framework Based Electrostatic Field Electrocatalysts for Durable Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) are one of the most promising candidates for next-generation energy storage systems. To develop long-life LSBs, there is an urgent need to develop functional materials with higher catalytic activity toward polysulfides and reduced dendritic lithium growth. Herein, an electrostatic field electrocatalyst is designed in a zwitterionic covalent organic framework (COF) with a "two birds with one stone" ability for simultaneously overcoming obstacles in the lithium metal anode and sulfur cathode. The synergism between cationic and anionic moieties in the zwitterionic COF creates an electrostatic field for bidirectionally catalyzing S cathode conversion. Besides, the rational design of zwitterionic COF as a separator modification layer allows lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dissociation and fast lithium-ion conduction, which alleviates lithium dendrite growth and thus improves the cycling life of LSBs. This contribution not only pioneers the application of zwitterionic COF in the field of LSBs but also highlights the potential of electrostatic field electrocatalysts.

CoS2/carbon hollow sphere was used as a matrix of the sulfur cathode for lithium–sulfur batteries with enhanced rate and cycling performance

CoS2/carbon hollow sphere was used as a matrix of the sulfur cathode for lithium–sulfur batteries with enhanced rate and cycling performance

High Entropy Sulfide Nanoparticles as Lithium Polysulfide Redox Catalysts.

The polysulfide shuttle contributes to capacity loss in lithium-sulfur batteries, which limits their practical utilization. Materials that catalyze the complex redox reactions responsible for the polysulfide shuttle are emerging, but foundational knowledge that enables catalyst development remains limited with only a small number of catalysts identified. Here, we employ a rigorous electrochemical approach to show quantitatively that the lithium polysulfide redox reaction is catalyzed by nanoparticles of a high entropy sulfide material, Zn0.30Co0.31Cu0.19In0.13Ga0.06S. When 2% by weight of the high entropy sulfide is added to the lithium sulfur cathode composite, the capacity and Coulombic efficiency of the resulting battery are improved at both moderate (0.2 C) and high (1 C) charge/discharge rates. Surface analysis of the high entropy sulfide nanoparticles using X-ray photoelectron spectroscopy provides important insights into how the material evolves during the cycling process. The Zn0.30Co0.31Cu0.19In0.13Ga0.06S nanoparticle catalyst outperformed the constituent metal sulfides, pointing to the role that the high-entropy "cocktail effect" can play in the development of advanced electrocatalytic materials for improved lithium sulfur battery performance.

An Effective Polysulfide Trapping Strategy for the Development of a Scalable, High Energy Density Lithium-Sulfur Battery

Rechargeable lithium-sulfur (Li-S) batteries represent an attractive, “beyond Li-ion”, battery technology because they offer a high specific energy of 2,500 Wh/kg at the material level1 and 550 Wh/kg at the cell level.2 However, Li-S batteries face substantial technical challenges that have thus far prevented the realization of the battery’s tremendous performance potentials.3 One of the major technical challenges is low practical specific capacity and fast performance degradation due to the formation, migration, and shuttling of intermediate lithium polysulfides (PSs). Several strategies have been used to trap the PS species either chemically or physically; however, they either incur increased cost due to the use of expensive catalysts4 or suffer from the reduced battery specific energy due to added inactive weights from the cell design.5,6 We will present a novel strategy to address the PS-shuttle issue using a nanolayer polymer modified high surface area carbon (NPC) as a new type of PS-trapping material.7 When thin films of NPC were coated on sulfur electrodes (NPC-S), we found that our NPC-S based Li-S battery demonstrated a high discharge specific capacity (~1,600 mAh/g) that is nearing sulfur’s theoretical specific capacity. Our molecular dynamics simulation suggests such an excellent performance is attributed to NPC’s strong PS trapping capability via dipole-dipole interactions. We will show that, using a sustainable starting material, our approach is low-cost and economically scalable for the advanced Li-S battery technology. References Zhang, S. S., Journal of Power Sources 2013, 231, 153-162.Manthiram, A.; Fu, Y.; Su, Y.-S., Accounts of Chemical Research 2013, 46 (5), 1125-1134.Chen, Z. X.; Zhao, M.; Hou, L. P.; Zhang, X. Q.; Li, B. Q.; Huang, J. Q., Advanced Materials 2022, 2201555.Hamal, D.; Awadallah, O.; El-Zahab, B., Catalysis in Lithium-Sulfur Cathodes for Improved Performance and Stability. In 242nd The Electrochemical Society Meeting, Atlanta, GA, USA, 2022.Chung, S.-H.; Han, P.; Singhal, R.; Kalra, V.; Manthiram, A., Advanced Energy Materials 2015, 5 (18).Singhal, R.; Chung, S.-H.; Manthiram, A.; Kalra, V., Journal of Materials Chemistry A 2015, 3 (8), 4530-4538.Hasan, W.; Hyynh, K.; Razzaq, A.; Smdani, G.; Shende, R.; Paudel, T.; Xing, W., "Scalable, High Energy Density Lithium-Sulfur Batteries". In NASA Battery Workshop, November 15-17, 2022 , Huntsville, AL, USA, 2022. Acknowledgment This work was supported by the Larry and Linda Pearson Endowed Chair at the Department of Mechanical Engineering, South Dakoda School of Mines and Technology and by the South Dakota Governor’s Research Center for Electrochemical Energy Storage. Figure 1

Integrating an In‐Plane Electron‐Conductive Separator to Enable Short‐Circuit Warning in Lithium–Sulfur Batteries

AbstractLithium–sulfur (Li–S) batteries are one of the most competitive candidates for high‐energy‐density batteries. However, the high energy density and high reactivity of the lithium anode and sulfur cathode make the safety issues of Li–S batteries particularly prominent. Herein, an early warning strategy for the short circuits in Li–S batteries is explored by integrating an in‐plane electron‐conductive separator. The internal short circuits caused by lithium dendrites or manufacturing defects can be quickly and accurately predicted before catastrophic thermal runaway, with enough time to take rescue measures. The separator with high thermal conductivity also facilitates the heat dissipation of the cell, thus reducing the risk of thermal runaway under abuse. The fast and reliable early warning strategy based on the in‐plane electron‐conductive separator builds the Great Wall of active defense against inherently unsafe Li–S batteries.

Cover Feature: High Entropy Oxide (CrMnFeNiMg)3O4 with Large Compositional Space Shows Long‐Term Stability as Cathode in Lithium‐Sulfur Batteries (ChemSusChem 8/2023)

The Cover Feature shows the design of a new (CrMnFeNiMg)3O4 high entropy oxide (HEO) for use in sulfur cathode in lithium–sulfur batteries. The HEO chemically adsorbed the diffusing lithium polysulfides through Li−O and metal−S bonds. The combination of Cr, Mn, Fe, Ni, and Mg metals in a highly stable HEO provides abundant active sites to enhance the adsorption of lithium polysulfides in the cathode. As a result, the HEO-containing sulfur cathode delivers a high and stable charge-storage capacity for a large number of cycles and at high rates. More information can be found in the Research Article by S.-H. Chung et al.

Nickel single atom overcoordinated active sites to accelerate the electrochemical reaction kinetics for Li-S cathode

Porous 2D N-doped carbon electrocatalyst consisting of atomically disperse Ni active centers with Ni-N 4 -O coordinated structure which act as efficient polysulfides traps and highly LiPSs conversion catalysts. Lithium-sulfur (Li-S) batteries with high theoretical energy density are promising advanced energy storage devices. However, shuttling of dissolute lithium polysulfide (LiPSs) and sluggish conversion kinetics impede their applications. Herein, single nickel (Ni) atoms on two-dimensional (2D) nitrogen(N)-doped carbon with Ni-N 4 -O overcoordinated structure (SANi-N 4 -O/NC) are prepared and firstly used as a sulfur host of Li-S batteries. Due to the efficient polysulfides traps and highly LiPSs conversion effect of SANi-N 4 -O/NC, the electrochemical performance of Li-S batteries obviously improved. The batteries can well operate even under high sulfur loading (5.8 mg·cm -2 ) and lean electrolyte (6.1 μL·mg -1 ) condition. Meanwhile, density functional theory (DFT) calculations demonstrate that Ni single atom’s active sites decrease the energy barriers of conversion reactions from Li 2 S 8 to Li 2 S due to the strong interaction between SANi-N 4 -O/NC and LiPSs. Thus, the kinetic conversion of LiPSs was accelerated and the shuttle effect is suppressed on SANi-N 4 -O/NC host. This study provides a new design strategy for a 2D structure with single-atom overcoordinated active sites to facilitate the fast kinetic conversion of LiPSs for Li-S cathode.

Rational design of the cathode catalysts for high performance lithium–sulfur batteries

Lithium–sulfur batteries (LSBs) have received significant interest over the past decade due to their high energy density. Nevertheless, a pivotal challenge facing high-performance LSBs is exploring advanced cathode materials that can efficiently catalyze the conversion of lithium polysulfides (LiPSs) during both the charging and discharging processes. However, the development of catalysts for LSBs is still in its infancy due to the complex physical–chemical reaction mechanisms involved in transforming LiPSs during the cycles. Many up-and-coming strategies have been performed to solve this challenge. In this article, we overview lithium–sulfur storage mechanisms, the technology challenge, and the optimization strategies for designing high-performance catalysts of the lithium–sulfur cathode. Finally, future research directions are proposed for the design of bifunctional catalysts for LSBs.

Construction of Polypyrrole-Coated CoSe2 Composite Material for Lithium-Sulfur Battery.

Lithium-sulfur batteries with high theoretical energy density and cheap cost can meet people's need for efficient energy storage, and have become a focus of the research on lithium-ion batteries. However, owing to their poor conductivity and "shuttle effect", lithium-sulfur batteries are difficult to commercialize. In order to solve this problem, herein a polyhedral hollow structure of cobalt selenide (CoSe2) was synthesized by a simple one-step carbonization and selenization method using metal-organic bone MOFs (ZIF-67) as template and precursor. CoSe2 is coated with conductive polymer polypyrrole (PPy) to settle the matter of poor electroconductibility of the composite and limit the outflow of polysulfide compounds. The prepared CoSe2@PPy-S composite cathode shows reversible capacities of 341 mAh g-1 at 3 C, and good cycle stability with a small capacity attenuation rate of 0.072% per cycle. The structure of CoSe2 can have certain adsorption and conversion effects on polysulfide compounds, increase the conductivity after coating PPy, and further enhance the electrochemical property of lithium-sulfur cathode material.

Catalysis in Lithium-Sulfur Cathodes for Improved Performance and Stability

Among next generation batteries, lithium-sulfur batteries are expected to be first battery to find a commercial route in the next few years. The sulfur cathodes in lithium-sulfur batteries provide both a lower cost and high capacity (1675 mAh/g) in comparison to intercalation cathode materials [1]. Despite these upsides, this conversion reaction type battery suffers from few problems that hinders their adoption. Some of these problems include the sluggish reaction kinetics, low sulfur utilization, rapid capacity loss due to various sulfur loss phenomena, and low Coulombic efficiency [2]. The use of electrocatalysts was shown to significantly boost the polysulfides redox reactions and improves the battery performance [3]. Transition metals, especially platinum group metal (PGM) based catalysts are proven to effectively boost the reaction rate of polysulfides conversion during cycling due to their high electrocatalytic activity [4], [5]. However, catalyst incorporation in conversion reaction batteries systems often would lead to side reactions and strategies on how to incorporate them into the battery system have to be developed.In this work, platinum group metal (PGM) nanocatalysts were implemented in lithium-sulfur cathodes using a process that is tailored to effectively improve catalyst dispersion and to provide controlled catalyst electrolyte contact. The nanocatalysts were loaded in carbon nanotube at variable low contents 0.1 – 5 wt% (Figure 1a) and were used in cathodes with sulfur loading up to 70 wt%. Using standard lithium-sulfur electrolyte based on 1 mol/kg LiTFSI in DOL:DME (v:v = 1:1) with lean electrolyte condition, batteries based on 2032 type coin cells and multilayer pouch cells were studied. The batteries' performance was studied for their impedance growth using electrochemical impedance spectroscopy, the redox performance using cycling voltammetry, and for their sulfur utilization/sulfur loss/Coulombic efficiency using galvanostatic charge-discharge cycling. These cathodes were shown to have improved redox performance in the batteries, improved sulfur utilization, and maintained stable capacity even at high sulfur loadings of 4-5 mg/cm2. Comparison of performance of nanocatalyst-containing batteries versus control batteries show improved first cycle capacity and stabilized capacity retention in the early cycling life of the battery (Figure 1b). Elucidating the underlying phenomena of the stabilization is studied in detail revealing reduced sulfur precipitation and shuttle effects. Higher C-rate performance of up to 1C revealed similar observations of stabilization.

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.

La2NiO4 nanoparticles as a core host of sulfur to enhance cathode volumetric capacity for lithium–sulfur battery

Lithium–sulfur battery is recognized as one of the most promising next-generation energy storage devices. But the volumetric energy density of sulfur cathode is insufficient as compared with the cathodes of the commercial lithium-ion batteries owing to the low tap density of nonpolar and light-weight carbon materials as sulfur hosts. In this work, for the first time, La2NiO4 (LNO) nanoparticles uniformly coated around carbon nanotubes (CNTs) are introduced as the host of sulfur cathode for lithium–sulfur battery. The polarity of LNO delivers the high electrocatalytic activity towards intermediate soluble lithium polysulfides by a strong chemical interaction. Benefiting from the synergistic effect of LNO nanoparticles and CNTs, the [email protected] host accelerates the conversion kinetics of sulfur species. Consequently, the [email protected] composite exhibits improved cycling stability with a slow capacity decay rate (0.088% per cycle) at 1 C for 500 cycles. Importantly, the high tap density of 1.49 g cm−3 for this composite promises a high volumetric capacity of 1486.07 mAh cm−3 at 0.05 C, almost 2.6 times higher than that of the S-CNT composite. This work provides a practicable strategy to improve the cycling stability and high-volumetric capacity of sulfur cathodes.

Novel nitrogen-doped bamboo-structure carbon nanotubes as superior sulfur host for high-performance lithium-sulfur batteries

In this work, nitrogen-doped bamboo-structure carbon nanotubes (BCNTs) with large diameters (ranging from 50 nm to 300 nm), high specific surface area (437.41 m2·g−1) and thin tube wall (less than 8 carbon layers) were prepared as sulfur host for lithium-sulfur (Li-S) batteries. Sulfur nanoparticles (NPs) with diameters of 20–30 nm were in-situ synthesized on the surface of BCNTs by a facile ultrasonic treatment, which can enhance the binding ability between sulfur and carbon, and then improve the utilization of sulfur. It is found that the in-situ synthesized S@BCNTs composite cathode with a high sulfur content of 62.2 wt% exhibits an initial specific capacity of 1008.4 mAh·g−1 at a current density of 0.1 C, and can still maintain a capacity of 383.9 mAh·g−1 after 500 cycles. Careful composition and microstructure analyses reveal that these excellent electrochemical performance can be ascribed to the synergistic effect of conductive nitrogen doping (especially pyridinic-N and pyrrolic-N) and homogeneous sulfur coating on the surface of BCNTs, which contributes to accelerating electron transport, adsorbing polysulfides and alleviating the shuttle effect. As a result, the as-prepared nitrogen-doped BCNTs can be pretty promising cathode materials for Li-S batteries. This work can open up a new possibility for the design of stable Li-S cathodes for high-performance batteries.

Hybridization of Mesoporous Carbon and Iron Oxide for Better Mitigation of Polysulfide Shuttling in Li-S Batteries

With a higher theoretical capacity, lithium-sulfur (Li-S) batteries have been considered as promising candidates for next-generation batteries. Due to the non-conducting nature of sulfur, however, lithium-sulfur batteries tend to exhibit poor performance at a high current rate (C-rate).Here we demonstrate that Fe3O4, synthesized from precursor iron (III) acetylacetonate (AAI), and mesoporous carbon material, Ketjen Black (KB), can be synergistically combined to enhance the electrochemical performance of lithium-sulfur batteries substantially. Instead of adding commercial magnetite particles into Li-S cathodes, iron oxides are synthesized and imbedded into KB from a precursor, AAI, through thermal treatments in air and Ar. The sulfur, then, is incorporated into iron oxides/KB hybrids by melting at an elevated temperature. With air-controlled electrospray as the processing method, sulfur embedded iron oxides/KB, poly(acrylic acid), and rGO sheets are mixed and directly deposited onto the carbon-coated aluminum collector, to employ as the Li-S battery cathode. X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS) studies confirm that Fe3O4 and iron carbide (Fe3C) are synthesized from the precursor, AAI, embedded in mesoporous carbon materials, and reducing the charge transfer resistance of batteries. The rate-capability tests show that systems with KB/Fe3O4 can achieve enhanced performance compared to batteries without iron oxides, especially at high C-rates. With 14 wt % of solid materials as iron oxides and iron carbide, batteries exhibit 750 mAh/g at 2C discharge/charge rates, which is 83% higher compared to systems without iron oxides. However, incorporated via 250 °C for 0.5 hr in air and 850 °C for 2 hr in Ar, the composite of KB/Fe3O4/Fe3C induces irreversible side reactions during the initial charging process, which causes a huge difference in capacity between the first and the second cycle. To achieve an optimal status with improved rate capability and acceptable initial charging time, we modify the thermal treatments and thus increase the proportion of Fe3O4 in the mixture. According to the postmortem analysis, cathodes with iron oxides can interact with soluble polysulfides strongly and alleviate the polysulfide shuttle effect significantly, compared with those without Fe3O4. Such enhanced rate capability by KB/Fe3O4 (synthesized) over KB only or KB/Fe3O4 (commercial) systems suggests that the incorporation of iron oxides can play an important role in improving the electrical conductivity of cathode and mitigating polysulfide shuttle effect. Figure 1

Metal phosphides and borides as the catalytic host of sulfur cathode for lithium–sulfur batteries

Metal phosphides and borides as the catalytic host of sulfur cathode for lithium–sulfur batteries