Rechargeable Lithium-sulfur Batteries Research Articles

Effective Lithium Polysulfides Anchoring on Vanadium Disulfide Facets for Lithium-Sulfur Batteries – A Computational Study

The commercialization of Li-S batteries is hindered by the shuttle effects of lithium polysulfides (LiPS) and the sluggish reaction kinetics. Hence, effectively trapping and promoting the conversion rates of LiPSs is of prime importance1. However, the fundamental kinetics of the electrocatalytic charging and discharging of Li-S batteries and the underlying mechanism have not been sufficiently explored yet.2 Therefore, by taking the 2D transition metal sulfide, VS2 as a model, we conducted a systematic investigation using density functional theory to study the ability of dominant exposed crystal planes of VS2 to trap LiPSs from leaching into electrolyte solvents and to act as an electrocatalyst to increase the Sulfur Reduction Reaction (SRR) kinetics3. To reflect a realistic environment of a battery, the effect of electrolyte solvents on the electrocatalytic activity was further investigated. Our calculations show that VS2 has moderate binding energy toward LiPSs which inhibits LiPS from leaching into electrolytes while fulfilling the key prerequisite to act as an electrocatalyst simultaneously.4 At the discharge, the conversion of S8 to the long chain Li2S8 was facile with a lower energy barrier while the rest of the reactions were sluggish explaining the accumulation of LiPSs. Further, the VS2 (001) facet exhibits excellent electrocatalytic activity for the SRR and Li2S decomposition reaction at charging compared to other dominant crystal planes, which significantly lowers the energy barriers of LiPS conversion during the charging and discharging process, ensuring high-rate performance and longer cycle life4. References Manthiram, A., Fu, Y., Chung, S.-H., Zu, C., & Su, Y.-S. (2014). Rechargeable Lithium–Sulfur Batteries. Chemical Reviews, 114(23), 11751–11787.Abraham, A. M., Thiel, K., Shakouri, M., Xiao, Q., Paterson, A., Schwenzel, J., Ponnurangam, S., & Thangadurai, V. (2022). Ultrahigh Sulfur Loading Tolerant Cathode Architecture with Extended Cycle Life for High Energy Density Lithium–Sulfur Batteries. Advanced Energy Materials, 2201494.Abraham, A. M., Boteju, T., Ponnurangam, S., & Thangadurai, V. (2022). A global design principle for polysulfide electrocatalysis in lithium–sulfur batteries—A computational perspective. Battery Energy, 20220003.Boteju, T., Abraham, A. M., Ponnurangam, S., & Thangadurai, V. (2023). Theoretical Study on the Role of Solvents in Lithium Polysulfide Anchoring on Vanadium Disulfide Facets for Lithium–Sulfur Batteries. The Journal of Physical Chemistry C.

Enhancement of Overall Kinetics by Se-Br Chemistry in Rechargeable Li-S Batteries.

The sluggish kinetics of lithium-sulfur (Li-S) batteries severely impedes the application in extreme conditions. Bridging the sulfur cathode and lithium anode, the electrolyte plays a crucial role in regulating kinetic behaviors of Li-S batteries. Herein, we report a multifunctional electrolyte additive of phenyl selenium bromide (PhSeBr) to simultaneously exert positive influences on both electrodes and the electrolyte. For the cathode, an ideal conversion routine with lower energy barrier can be attained by the redox mediator and homogeneous catalyst derived from PhSeBr, thus improving the reaction kinetics and utilization of sulfur. Meanwhile, the presence of Se-Br bond helps to reconstruct a loose solvation sheath of lithium ions and a robust bilayer SEI with excellent ionic conductivity, which contributes to reducing the de-solvation energy and simultaneously enhancing the interfacial kinetics. The Li-S battery with PhSeBr displays superior long cycling stability with a reversible capacity of 1164.7 mAh g-1 after 300 cycles at 0.5 C rate. And the pouch cell exhibits a maximum capacity of 845.3 mAh and a capacity retention of 94.8 % after 50 cycles. Excellent electrochemical properties are also obtained in extreme conditions of high sulfur loadings and low temperature of -20 °C. This work demonstrates the versatility and practicability of the special additive, striking out an efficient but simple method to design advanced Li-S batteries.

Nonconventional Electrochemical Reactions in Rechargeable Lithium-Sulfur Batteries.

Rechargeable lithium-sulfur (Li-S) batteries are promising for high-energy storage. However, conventional redox reactions involving sulfur (S) and lithium (Li) can lead to unstable intermediates. Over the past decade, many strategies have emerged to address this challenge, enabling nonconventional electrochemical reactions in Li-S batteries. In our Perspective, we provide a brief review of these strategies and highlight their potential benefits. Specifically, our group has pioneered a top-down approach, investigating Li-S reactions at molecular and subatomic levels, as demonstrated in our recent work on stable S isotopes. These insights not only enhance understanding of charge transfer and storage properties but also offer exciting opportunities for advancements in battery materials research.

Pseudo-covalent triazine frameworks for superior Li-S batteries

Rechargeable lithium-sulfur batteries are promising because of exceptional energy density and low cost. However, lithium-sulfur batteries suffer from severe polysulfide shuttle problems and sluggish conversion kinetics, which result in poor electrode reversibility and a limited lifespan. Herein, pseudo-covalent triazine frameworks integrated with conductive Ketjenblack have been desgined as sulfur hosts. The pseudo-covalent triazine frameworks, controllably synthesized via regulating on temperature and ratio between 1,4-dicyanobenzene precursor and ZnCl2, maintain highly porous triazine ring-lining skeleton with amorphous graphitic layers and abundant defects such as pyridine/pyrrole/quaternary-N atoms. Strong immobilization and fast catalytic conversion towards polysulfide are verified and theoretical explanations reveal these reaction sites are mostly occurring around triazine rings groups due to enhanced electron donating ability from N-atoms. Coin-type Li-S cells based on CTF@KB hosts exhibit outstanding rate performances (425.7 mAh/g at 10C) and lifespan (960.5 mAh/g mAh/g after 180 cycles), which are superior than previous reports. Pouch cells stress practicality of pseudo-covalent triazine frameworks (550.6 mAh/g after 60 cycles).

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

Counting d-Orbital Vacancies of Transition-Metal Catalysts for the Sulfur Reduction Reaction.

The electrocatalytic sulfur reduction reaction (SRR) would allow the production of renewable high-capacity rechargeable lithium-sulfur (Li-S) batteries using sustainable and nontoxic elemental sulfur as a cathode material, but its slow reaction rate causes a serious shuttle effect and dramatically reduces the capacity. We found that a catalyst composed of Pd nanoparticles supported by ordered mesoporous carbon (Pd/OMC) had a high reaction rate in the SRR, and a Li-S battery assembled with this catalyst had a low shuttle constant of 0.031 h-1 and a high-rate performance with a specific capacity of 1527 mAh g-1 at 0.1 C which is close to the theoretical value. The high activity of Pd/OMC with a d-orbital vacancy of 0.87 e was predicted from a volcano relationship between the d charge for the metal and the adsorption activation entropy and reaction rate for the SRR by examining Pd, Au, Pt, Rh, and Ru transition-metal nanocatalysts. The strategy of using a single electronic structure descriptor to design high-efficiency SRR catalysts has suggested a way to produce practical Li-S batteries.

Lithiophilic metal oxide-based double gradient anode host design for lithium-sulfur batteries

The development of rechargeable lithium-sulfur (Li-S) batteries is hampered by Li dendrite growth and large volume changes in the anode. To tackle these issues, a novel double gradient anode host material consists of carbon nanofibers (CNFs) embedded ZnO and Co3O4 is developed. In this ZnOCo3O4/CNF composite, the decorated ZnO and Co3O4 forms lithiophilic and Li nucleation overpotential double gradient, which is beneficial for the uniform Li deposition and suppressing the irregular growth of Li dendrites. The 3D network structure of the CNFs substrate improves the electrical conductivity and buffering the stress of volume changes as well. Owing to these features, the ZnOCo3O4/CNF electrode exhibits stable voltage during the 400 h plating/stripping process at current density of 5 mA cm−2 and delivers an area capacity of 5 mAh cm−2. The Li@ZnOCo3O4/CNF||S/CNT battery maintains excellent stability with capacity decay rate of 0.036 % per cycle after 500 cycles at 1 C. The design of gradient anode hosts constructed from bimetallic oxides offers a promising alternative strategy for suppressing the irregular growth of Li dendrites, thereby increasing the cycle life of the batteries.

Mott Schottky heterojunction Co/CoSe2 electrocatalyst: Achieved rapid conversion of polysulfides and Li2S deposition dissolution via built-in electric field interface effect

Rechargeable lithium-sulfur (Li-S) batteries are considered ideal candidates for the next generation of energy storage devices. However, the insulation properties of S and Li2S, as well as the notorious “shuttle effect” of lithium polysulfide, result in severe loss of active sulfur, poor redox kinetics, and rapid capacity decline. To overcome these limitations, this paper designs a self-supporting electrocatalytic electrode based on Co/CoSe2 Mott Schottky heterojunction coated carbon nanofibers (Co/CoSe2@NCNFs), and engineers it for capturing and converting polysulfides. Density functional theory calculations show that the introduction of Co/CoSe2 heterojunction effectively reduces the redox barrier of Li2S. The electron current and electron interaction at the Co/CoSe2 interface induce the redistribution of charge density in the depletion region, thus increasing the chemical reactivity of the metal semiconductor heterojunction interface, which is conducive to the ion/electron transport, polysulfide conversion and Li2S oxidation process. Therefore, the Li-S battery assembled by Co/CoSe2@NCNFs/S electrode exhibited a high initial specific capacity of 1043.3 mAh/g at 1C, and maintained a capacity of 709.9 mAh/g after 1000 cycles, with a capacity decay rate of only 0.032% per cycle. The proposed Mott Schottky heterojunction as an electrocatalyst deepens the promotion of polysulfides and Li2S in long-life Li-S batteries.

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

Parametric optimization of sulfur@graphene composites for aqueous and solid-state rechargeable lithium-sulfur batteries

Lithium‑sulfur batteries have great potential for use in electric vehicles and power grids, but the poor conductivity and volume expansion of sulfur during the lithiation process have hindered their commercialization. One potential solution is to entrap elemental sulfur between graphene parallel sheets, which can improve the conductivity and stability of the battery. This work reports on a parametric study of a method for incorporating sulfur into graphene sheets using ultrasonication and low surface tension solvents. Results show that the method is successful in loading sulfur between graphene sheets, with a maximum of 36.48 wt% sulfur. The resulting nanocomposite material was found to have stable cycling performance over 150 cycles with fast C-regime for aqueous lithium‑sulfur battery making it a promising candidate for use in lithium‑sulfur batteries.But more research is required to optimize S@G-50's performance in all-solid-state systems and address associated challenges to improve cycling performance.

Fast Polysulfide Conversion Catalysis and Reversible Anode Operation by A Single Cathode Modifier in Li-Metal Anode-Free Lithium-Sulfur Batteries.

The two major issues confronting the commercialization of rechargeable lithium-sulfur (Li-S) batteries are the sluggish kinetics of the sulfur electrochemical reactions on the cathode and inadequate lithium deposition/stripping reversibility on the anode. They are commonly mitigated with additives designed specifically for the anode and the cathode individually. Here, we report the use of a single cathode modifier, In2 Se3 , which can effectively catalyse the polysulfide reactions on the cathode, and also improve the reversibility of Li deposition and removal on the anode through a LiInS2 /LiInSe2 containing solid electrolyte interface formed in situ by the Se and In ions dissolved in the electrolyte. The amounts of dissolved Se and In are small relative to the amount of In2 Se3 administered. The benefits of using this single modification approach were verified in Li-metal anode-free Li-S batteries with a Li2 S loading of 4 mg cm-2 and a low electrolyte/Li2 S ratio of 7.5 μL mg-1 . The resulting battery showed 60 % capacity retention after 160 cycles at the 0.2 C rate and an average Coulombic efficiency of 98.27 %, comparing very well with recent studies using separate electrode modifiers.

Observation of high ionic conductivity of polyelectrolyte microgels in salt-free solutions

Here, we report an observation that illustrate the potential of polyelectrolyte microgels in salt-free solutions to display a high ionic conductivity. Laser light scattering and ionic conductivity tests on very dilute aqueous dispersions of the microgels indicate that both small size and swollen state of gel particles play vital roles, which should favor the counterions to freely penetrate and leave gel particles, and thus can contribute to the ion-conducting property. Upon discovering this on microgels that are composed of imidazolium-based poly(ionic liquid), we also illustrate the generality of the finding to single lithium-ion polyelectrolyte microgels that are of more technically relevant features for applications, for instance, as injectable liquid “microgel-in-solution” electrolytes of high conductivity (ca. 8.2 × 10−2 S/m at 25.0 °C for 1.0 × 10−2 g/mL of microgels in a LiNO3-free 1:1 v/v mixture of 1,2-dioxolane and dimethoxymethane) and high lithium-ion transference number (0.87) for use in the rechargeable lithium-sulfur battery.

Structural Transformation in a Sulfurized Polymer Cathode to Enable Long-Life Rechargeable Lithium–Sulfur Batteries

Sulfurized polyacrylonitrile (SPAN) represents a class of sulfur-bonded polymers, which have shown thousands of stable cycles as a cathode in lithium-sulfur batteries. However, the exact molecular structure and its electrochemical reaction mechanism remain unclear. Most significantly, SPAN shows an over 25% 1st cycle irreversible capacity loss before exhibiting perfect reversibility for subsequent cycles. Here, with a SPAN thin-film platform and an array of analytical tools, we show that the SPAN capacity loss is associated with intramolecular dehydrogenation along with the loss of sulfur. This results in an increase in the aromaticity of the structure, which is corroborated by a >100× increase in electronic conductivity. We also discovered that the conductive carbon additive in the cathode is instrumental in driving the reaction to completion. Based on the proposed mechanism, we have developed a synthesis procedure to eliminate more than 50% of the irreversible capacity loss. Our insights into the reaction mechanism provide a blueprint for the design of high-performance sulfurized polymer cathode materials.

Tubular NiCo2S4 hierarchical architectures as sulfur hosts for advanced rechargeable lithium sulfur batteries

Tubular nickel and cobalt bimetal sulfides NiCo2S4 hierarchical architectures were fabricated by a facile solvothermal method and investigated electrochemically as sulfur hosts for lithium sulfur batteries compared to bare sulfur. The results indicated that the single/double-walled tubular NiCo2S4 could be tuned to assemble the hierarchical architectures consisting of the nanoparticles, their electrochemical performances as sulfur hosts for lithium sulfur batteries are exhibited differently with respect to the host morphology and even compared to those of bare sulfur as well. Comparatively, the double-walled tubular NiCo2S4 hierarchical architecture as sulfur host for lithium sulfur batteries delivers a higher initial specific capacity of as high as 1078.9 mAh g−1, and exhibits better cyclability and rate capability, which might be ascribed to even dispersion of sulfur over the electrically conductive double-walled tubular NiCo2S4 hierarchical architecture, thus facilitating the full utilization of sulfur and the fast redox reaction kinetics of lithium polysulfides. In a word, bimetal sulfide NiCo2S4 are promising as sulfur host for the industrial implementation of lithium sulfur batteries, dependent of its optimization on morphology and structure.

Designing a Stable Solid Electrolyte Interphase on Lithium Metal Anodes by Tailoring a Mg Atom Center and the Inner Helmholtz Plane for Lithium–Sulfur Batteries

Arising from the extraordinary theoretical energy density, rechargeable lithium-sulfur (Li-S) batteries have been reputed as one of the most appealing options for next-generation high-performance energy storage and conversion devices. Unfortunately, their industrial implementation has been strongly governed by the formation of Li dendrites caused by the unstable solid electrolyte interphase (SEI) film. Herein, we report a novel electrolyte by introducing the Mg(NO3)2 additive to suppress the growth of Li dendrites, further improving the cycling lifetime of Li-S batteries. On the one hand, Mg2+ can rapidly react with Li atoms to generate Mg atoms, replacing the Li atoms on the top surface of Li metal and forming the Mg center simultaneously. On the other hand, NO3- can be adsorbed in the inner Helmholtz plane and reduced as an inorganic-rich SEI film for stabilizing the Li metal anode when the electrolyte comes in contact with Li metal, effectively mitigating the formation of Li dendrites. Combining the experimental results and theoretical calculations, we confirm that the Mg atom center and the inorganic-rich SEI film are both beneficial for enhancing the electrochemical performance of Li-S batteries. This work provides a new insight into the electrolyte additive and a possible alternative for the design of high-performance Li-S batteries beyond the LiNO3 additive.

A low-cost sulfur-loading material based on the modification of Ketjen Black for rechargeable lithium-sulfur battery

The practical application of lithium-sulfur (Li-S) battery is impeded by some technical hurdles such as short cycle life and poor capability, which is radically caused by the uncontrollable electrochemical reactions at the cathode. In this work, we develop a Ketjen Black carbon-based cathode material, modified with transition metals through the coordination fixing action of 2, 2′-bipyridine and followed with an annealing activation process, to be employed as the sulfur host in a Li-S battery. It is demonstrated that the decoration of Co and Fe on the matrix of carbon can substantially enhance the efficiency for catalytic conversion of polysulfides in Li-S batteries, thus greatly improving the performance, including capacity, rate capability and cycling life. This simple and economic strategy of modifying the commercial Ketjen Black shall accelerate the practical application of Li-S battery.

Electrochemically Stable Rechargeable Lithium-Sulfur Batteries Equipped with an Electrospun Polyacrylonitrile Nanofiber Film.

The high theoretical charge-storage capacity and energy density of lithium-sulfur batteries make them a promising next-generation energy-storage system. However, liquid polysulfides are highly soluble in the electrolytes used in lithium-sulfur batteries, which results in irreversible loss of their active materials and rapid capacity degradation. In this study, we adopt the widely applied electrospinning method to fabricate an electrospun polyacrylonitrile film containing non-nanoporous fibers bearing continuous electrolyte tunnels and demonstrate that this serves as an effective separator in lithium-sulfur batteries. This polyacrylonitrile film exhibits high mechanical strength and supports a stable lithium stripping and plating reaction that persists for 1000 h, thereby protecting a lithium-metal electrode. The polyacrylonitrile film also enables a polysulfide cathode to attain high sulfur loadings (4-16 mg cm-2) and superior performance from C/20 to 1C with a long cycle life (200 cycles). The high reaction capability and stability of the polysulfide cathode result from the high polysulfide retention and smooth lithium-ion diffusion of the polyacrylonitrile film, which endows the lithium-sulfur cells with high areal capacities (7.0-8.6 mA·h cm-2) and energy densities (14.7-18.1 mW·h cm-2).

Achieving balanced behavior between polysulfides adsorption and catalytic conversion from heterostructure Fe3C-Fe3P promotor for high-performance lithium-sulfur batteries

Although rechargeable lithium-sulfur batteries (LSBs) are next generation energy storage devices, severe shuttle effect and sluggish multi-electron redox reactions compromise the practical application of LSBs. To address these issues and enable the manufacture of robust LSBs, here the use of Fe3C-Fe3P heterostructure encapsulated in nitrogen–doped carbon nanotubes (FeCP@NCNT) was synthesized. The tubular geometry of FeCP@NCNT provided buffering void to suppress volume change, and afforded conductive network to expedite the diffusion of Li+, as well as endowed plenteous active sites to absorb and catalyze the transformation of LiPSs during charge–discharge cycles. Experimental data proved that FeCP@NCNT could strengthen the “anchoring of lithium polysulfides (LiPSs)” (by Fe3P) and expedite the “diffusion of intermediate” (by CNT) as well as accelerate the “catalytic phase conversion” (by Fe3C), resulting in balanced “trapping-diffusion-conversion” dynamic process. Notably, FeCP-3 h@NCNT/G/S attained an initial capacity of 1127 mAh/g with a low decay rate of 0.12 % at 1C for 300 cycles Moreover, FeCP-3 h@NCNT/G/S delivered excellent battery performances under high currents of 2 and 5C for 500 cycles. This work felicitously proposed the strategy to fabricate metal carbide-phosphide heterostructure electrocatalyst for high-performance LSBs.

Effect of morphological variation in three-dimensional multiwall carbon nanotubes as the host cathode material for high-performance rechargeable lithium-sulfur batteries.

Lithium-sulfur batteries (LSBs) demonstrate potential as next-generation energy storage systems due to the high theoretical capacity and energy density of the sulfur cathode (1672 mAh g-1 and 2600 W h kg-1, respectively) in addition to the low-cost, natural abundance, and environmentally benign characteristics of sulfur. However, the insulating nature of sulfur requires an efficient conductive and porous host material such as three-dimensional carbon nanotubes (3D CNTs). Identifying parameters that provide high conduction pathways and short diffusion lengths for Li-ions within the CNT structure is essential for a highly efficient CNT-S cathode in a LSB. Herein, the effect of morphological variation in 3D CNTs as a sulfur host material is studied, and parameters that affect the performance of a CNT-S cathode in LSB are investigated. Four different 3D CNTs are synthesized via the chemical vapor deposition (CVD) technique that vary in specific surface area (SSA), CNT diameter, pore sizes, and porosity. The superior 3D CNT-S (CNT-S-50) cathode, which possessed high surface area and porosity as compared to the rest of the 3D CNT-S cathodes, with ∼38 wt% (6.27 mg cm-2) sulfur loading, demonstrated an areal and specific discharge capacity of 8.70 mAh cm-2 and 1387 mAh g-1 at 0.1C, respectively. Results from this work demonstrate that the combination of high surface area and porosity are two crucial parameters in 3D CNTs as an efficient sulfur host material for LSB cathodes.

S-doped Ti3C2F2 MXene as an ideal sulfur cathode host for high-performance rechargeable lithium–sulfur batteries

S-doped Ti3C2F2 MXene offers high conductivity, shuttle effect suppression, fast charge/discharge kinetics, rapid ion/polysulfide diffusion, and serves as a 3D Li2S deposition substrate, making it an ideal sulfur cathode for advanced RLSBs.