Lithium Polysulfide Intermediates Research Articles

High-efficiency Lithium Metal Stabilization and Polysulfide Suppression in Li-S Battery Enabled by Weakly Solvating Solvent.

Lithium-sulfur batteries (LSBs) are considered a highly promising next-generation energy storage technology due to their exceptional energy density and cost-effectiveness. However, the practical use of current LSBs is hindered primarily by issues related to the "shuttle effect" of lithium polysulfide (LiPS) intermediates and the growth of lithium dendrites. In strongly solvating electrolytes, the solvent-derived solid electrolyte interphase (SEI) lacks mechanical strength due to organic components, leading to ineffective lithium dendrite suppression and severe LiPS dissolution and shuttling. In contrast, the weakly solvating electrolyte (WSE) can create an anion-derived SEI layer which can enhance compatibility with lithium metal anode, and restricting LiPS solubility. Herein, a WSE consisting of 0.4м LiTFSI in the mixture of 1,4-dioxane (DX):dimethoxymethane (DMM) is designed to overcome the issues associated with LSB. Surface analyses confirmed the formation of a beneficial SEI layer rich in LiF, enabling homogeneous lithium deposition with an average Coulombic efficiency CE exceeding 99% over 100 cycles. Implementing the low-concentration WSE in Li||SPAN cells yielded an impressive initial specific capacity of 671mAhg-1. This research highlights the advantages of WSE and offers the pathway for cost-effective electrolyte development, enabling the realization of high-performance LSBs.

Metal Organic Frameworks as Polysulfide Reaction Modulators for Lithium Sulfur Batteries: Advances and Perspectives.

Currently, lithium sulfur (Li-S) battery with high theoretical energy density has attracted great research interest. However, the diffusion and loss process of intermediate lithium polysulfide during charge-discharge hindered the application of the Li-S battery in modern life. To overcome this issue, metal organic frameworks (MOFs) and their composites have been regarded as effective additions to restrain the LiPS diffusion process for Li-S battery. Benefiting from the unique structure with rich active sites to adsorb LiPS and accelerate the LiPS redox, the Li-S batteries with MOFs modified exhibit superior electrochemical performance. Considering the rapid development of MOFs in Li-S battery, this review summarizes the recent studies of MOFs and their composites as the sulfur host materials, functional interlayer, separator coating layer, and separator/solid electrolyte for Li-S batteries in detail. In addition, the promising design strategies of functional MOF materials are proposed to improve the electrochemical performance of Li-S battery.

1T-rich MoS2 nanosheets anchored on conductive porous carbon as effective polysulfide promoters for lithium–sulfur batteries

The practical applications of lithium-sulfur (Li-S) batteries have severely been hindered by notorious shuttle effect and sluggish redox kinetics of lithium polysulfide intermediates (LiPSs), which bring about rapid capacity degradation, low coulombic efficiency and poor cycling stability. In this work, 1T-rich MoS2 nanosheets are in-situ developed onto the conductive porous carbon matrix (1T-rich MoS2@PC) as efficient polysulfide promotors for high-performance Li-S batteries. The porous carbon skeleton tightly anchors MoS2 nanosheets to prevent their reaggregation and ensures accessible electrical channels, and at the same time provides a favorable confined space that promotes the generation of 1T-rich MoS2 structure. More importantly, the uniformly distributed metallic 1T-rich MoS2 nanosheets not only affords rich sulfphilic sites and high binding energy for immobilizing LiPSs, but also favors rapid electron transfer and LiPSs conversation kinetics, substantially regulating sulfur chemistry in working cells. Consequently, the Li-S cell assembled with 1T-rich MoS2@PC modified separator delivers a remarkable cycling stability with ultralow capacity decay rate of 0.067 % over 500 cycles at 1C. Encouragingly, under harsh conditions (high sulfur loading of 4.78 mg cm−2 and low E/S ratio of 8 μL mg−1), a favorable electrochemical performance can still be demonstrated. This study highlights the profitable design of 1T-rich MoS2/carbon based electrocatalyst for suppressing shuttle effect and promoting catalytic conversation of LiPSs, and has the potential to be applied to in other energy storage systems.

FeSx/MoS2 heterostructure decorated S-coated hydroxylated carbon nanotubes for boosting catalytic activity and mitigating polysulfide shuttling in lithium-sulfur batteries

Heterostructure was widely study to figure out the inferior shuttle effect of intermediate lithium polysulfides and the sluggish kinetics of sulfur redox reaction in lithium-sulfur batteries (LSBs). However, they have low electrical conductivity and no clear discharge/charge catalytic mechanism as LSBs cathode. Combination of heterostructure and functional carbonaceous is a promising choice. Herein, FeSx/MoS2 heterostructure decorated S-coated hydroxylated carbon nanotubes (FSM/SHC) were successfully designed and the catalytic mechanism of FSM was elucidated by in-/ex- situ electrochemical characterizations. Compared to FeSx/MoS2 heterostructure decorated carbon nanotubes (FSM/C)-based sulfur cathode, the chemical adsorption capacity to anchor intermediate polysulfides and the Li-S conversion reaction kinetics of FSM/SHC has been enhanced ascribed to the introduction of polar bonds and functional groups. As a consequence, FSM/SHC-based sulfur modified cathode delivers a marked sulfur reversion (1280 mAh g−1 after 800 cycles at 0.2C and 1048 mAh g−1 after 300 cycles at 4C) and a high capacity retention of 6 mAh cm−2 over 70 cycles at 0.5C (8 mg cm−2). Moreover,the FSM heterostructuredemonstrates an accelerated electron transfer caused by the valence change of Fe0/Fe3+transition, Mo4+/Mo6+ transition and heterointerface, and thus facilitates the redox reaction kinetics of polysulfide. This work reveals the advantages of multi metal-based heterostructures and functional group modification in LSBs.

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.

Crystalline-amorphous heterostructure on the phosphatized P-CoS2/CNT for augmenting the catalytic conversion kinetics of Li-S batteries

Crystalline-amorphous heterostructure catalyst is employed to conquer the notorious shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) intermediates of lithium-sulfur (Li-S) batteries. Herein, crystalline-amorphous heterostructure on the phosphatized cobalt disulfide/carbon nanotube (designated as P-CoS2/CNT) are served as the functional interlayer for Li-S batteries. Crystalline-amorphous heterostructure of P-CoS2/CNT is composed of high crystalline CoS2 core and amorphous Co(PO3)2 (a-Co(PO3)2) shell along with abundant active Co-O-P bonds. The crystalline CoS2 core and grain boundary defects on the heterostructure can prop up the well-pleasing electron conductivity when a-Co(PO3)2 accelerates the catalytic conversion kinetics of the polysulfides through the comprehensive survey in terms of chemical anchoring capability, nucleation barrier for Li2S, In-situ Raman for monitoring the shuttle case of polysulfides, and the analysis of inactive sulfur species on Li anode. In consequence, the Li-S battery using the P-CoS2/CNT functional separator delivers an outstanding low-capacity decay of only 0.048 % per cycle for 1000 cycles at 2C, and the LiPSs's shuttle effect is efficaciously restrained. Even with a high sulfur loading of 3.6 mg cm−2, the cell still maintains an outstanding areal capacity of 1.75 mAh cm−2 after 200 cycles at 1C. This work develops a scalable crystalline-amorphous heterostructure strategy using the conventional heteroatom modulation in aspire of accurately guiding the high-efficiency electrocatalyst served for the Li-S electrochemistry.

Understanding the synergistic improving adsorbed and catalytic activity of polysulfide by design of oxygen vacancies and Li+ lithiation/delithiation behavior in Titanium Oxide separator

The commercialization of lithium-sulfur (Li-S) battery is hindered by severe shuttle effect and sluggish electrochemical kinetics, which are induced by the high dissolution of intermediate lithium polysulfides (LiPSs) in cathode side. Here, we describe a strategy towards efficient adsorption and conversion of polysulfides by designing a functional TiO2-based separator. The enhanced overall electrochemical performance of cells is highly related to the synergistic effect of mutually transformational of TiO2 and LixTiO2 and the existence of oxygen vacancies (OVs). During the charging and discharging process of Li-S cell, the in-situ formation of LixTiO2 assigned to lithiation of anatase TiO2 plays a pivotal role in reversible adsorption and desorption of LiPSs. In addition, we also discussed the effect of OVs, which can act as active sites to accelerate electrochemical kinetics and exhibit stronger chemical interaction with LiPSs. The synergy of lithiation and delithiation process of TiO2 with OVs not only offers an effective pathway towards the improvement of LiPSs adsorption and catalytic performance but could also inspire new ideas on developing functional metal oxides modified separator for Li-S battery. We anticipate that this work will provide new avenues for Li-S battery commercialization.

Encapsulating Sulfur into a Gel-Derived Nitrogen-Doped Mesoporous and Microporous Carbon Sponge for High-Performance Lithium-Sulfur Batteries.

The practical application of Li-S batteries (LSBs) has long been impeded by the inefficient utilization of sulfur and slow kinetics. Utilizing conductive carbonaceous frameworks as a host scaffold presents an efficient and cost-effective approach to enhance sulfur utilization for redox reactions in LSBs. However, the interaction of pure carbon materials with lithium polysulfide intermediates (LiPSs) is limited to weak van der Waals forces. Hence, the development of an economical method for synthesizing heteroatom-doped carbon materials for sulfur fixation is of paramount importance. In this study, we introduce a hierarchical porous nitrogen-doped carbon sponge (NPCS) with an exceptionally high BET surface area of 3182.2 m2 g-1, achieved through a facile template-assisted polymerization method. The incorporation of inorganic salts, free radical polymerization, and deuteric freeze-drying techniques facilitates the formation of hierarchical pores within the NPCS. After sulfur fixation, the resulting S/NPCS electrode demonstrates remarkable electrochemical performance in LSBs. Specifically, it achieves an 80% sulfur utilization rate, maintains a high reversible specific capacity of 400 mA h g-1 even after 600 cycles at a demanding current density of 5.0 A g-1, and exhibits superior rate capability. It is believed that this work will inspire the rational design of cost-effective carbon-based electrodes for high-performance LSBs.

High-Throughput Screening of Sulfur Reduction Reaction Catalysts Utilizing Electronic Fingerprint Similarity.

The catalytic performance is determined by the electronic structure near the Fermi level. This study presents an effective and simple screening descriptor, i.e., the one-dimensional density of states (1D-DOS) fingerprint similarity, to identify potential catalysts for the sulfur reduction reaction (SRR) in lithium-sulfur batteries. The Δ1D-DOS in relation to the benchmark W2CS2 was calculated. This method effectively distinguishes and identifies 30 potential candidates for the SRR from 420 types of MXenes. Further analysis of the Gibbs free energy profiles reveals that MXene candidates exhibit promising thermodynamic properties for SRR, with the protocol achieving an accuracy rate exceeding 93%. Based on the crystal orbital Hamilton population (COHP) and differential charge analysis, it is confirmed that the Δ1D-DOS could effectively differentiate the interaction between MXenes and lithium polysulfide (LiPS) intermediates. This study underscores the importance of the electronic fingerprint in catalytic performance and thus may pave a new way for future high-throughput material screening for energy storage applications.

Establishing reaction networks in the 16-electron sulfur reduction reaction.

The sulfur reduction reaction (SRR) plays a central role in high-capacity lithium sulfur (Li-S) batteries. The SRR involves an intricate, 16-electron conversion process featuring multiple lithium polysulfide intermediates and reaction branches1-3. Establishing the complex reaction network is essential for rational tailoring of the SRR for improved Li-S batteries, but represents a daunting challenge4-6. Herein we systematically investigate the electrocatalytic SRR to decipher its network using the nitrogen, sulfur, dual-doped holey graphene framework as a model electrode to understand the role of electrocatalysts in acceleration of conversion kinetics. Combining cyclic voltammetry, in situ Raman spectroscopy and density functional theory calculations, we identify and directly profile the key intermediates (S8, Li2S8, Li2S6, Li2S4 and Li2S) at varying potentials and elucidate their conversion pathways. Li2S4 and Li2S6 were predominantly observed, in which Li2S4 represents the key electrochemical intermediate dictating the overall SRR kinetics. Li2S6, generated (consumed) through a comproportionation (disproportionation) reaction, does not directly participate in electrochemical reactions but significantly contributes to the polysulfide shuttling process. We found that the nitrogen, sulfur dual-doped holey graphene framework catalyst could help accelerate polysulfide conversion kinetics, leading to faster depletion of soluble lithium polysulfides at higher potential and hence mitigating the polysulfide shuttling effect and boosting output potential. These results highlight the electrocatalytic approach as a promising strategy for tackling the fundamental challenges regarding Li-S batteries.

Hybrid Ascharite/Reduced Graphene Oxide with Polysulfide Adsorption Host for Advanced Lithium-Sulfur Batteries.

Balancing the adsorption of lithium-polysulfide intermediates on polar host material surfaces and the effect of their electronic conductivity in the subsequent oxidation and reduction kinetics of electrochemical reactions is necessary and remains a challenge. Herein, we have evaluated the role of polarity and conductivity in preparing a series of ascharite/reduced graphene oxide (RGO) aerogels by dispersing strong polar ascharite nanowires of varying mass into the conductive RGO matrix. When severed as Li-S battery cathodes, the optimized S@ascharite/RGO cathode with a sulfur content of 73.8 wt % demonstrates excellent rate performance and cycle stability accompanied by a high-capacity retention for 500 cycles at 1.0 C. Interesting advantages including the enhanced adsorption ability by the formation of the Mg-S and Li bonds, the continuous and quick electron/ion transportations assembled conductive RGO framework, and the effective deposition of Li2S are combined in the ascharite/RGO aerogel hosts. The electrochemical results further demonstrate that the polarity of ascharite components for the S cathode plays a dominant role in the improvement of electrochemical performance, but the absence of a conductive substrate leads to serious capacity attenuation, especially the rate performance. The balanced design protocol provides a universal method for the synthesis of multiple S hosts for high-performance LSBs.

Elevating Lithium-Sulfur Battery Durability through Samarium Oxide/Ketjen Black Modified Separator.

Lithium-sulfur batteries have garnered significant attention as a promising next-generation battery technology due to their potential for high energy density. However, their practical application is hampered by slow reaction kinetics and the shuttle effect of lithium polysulfide intermediates. In this context, the authors introduce a pioneering solution in the form of a novel porous carbon nanostructure modified with samarium oxide, denoted as Sm2O3/KB. The material has a highly polar surface, allowing lithium polysulfide to be chemisorbed efficiently. The unsaturated sites provided by the oxygen vacancies of Sm2O3 promote Li2S nucleation, lowering the reaction energy barrier and accelerating Li2S dissolution. The porous structure of Ketjen Black provides a highly conductive channel for electron transport and effectively traps polysulfides. Meanwhile, the batteries with Sm2O3/KB/PP spacers exhibited remarkable electrochemical performances, including a low-capacity decay rate of only 0.046 % for 1000 cycles at 2 C and an excellent multiplicative performance of 624 mAh g-1 at 3 C. This work opens up a new avenue for the potential use of rare-earth-based materials in lithium-sulfur batteries.

Surface-coated AlF3 nanolayers enable polysulfide confinement within biomass-derived nitrogen-doped hierarchical porous carbon microspheres for improved lithium-sulfur batteries

The electrically insulating and volumetric deformation of sulfur and the shuttle effect of the intermediate lithium polysulfide (LiPSs) have severely hindered the development of lithium-sulfur batteries (LSBs). Herein, a synergistic strategy of hierarchical porous nitrogen-doped carbon microspheres (PNCM) derived from low-cost biomass with surface-coated AlF3 nanolayer as a multifunctional sulfur host (denoted as PNCM@S@AlF3) was developed. The PNCM not only possesses an abundant pore structure, large surface area, and high electrical conductivity but also features an intrinsic N-doped and fluorinated framework, which effectively enhances the physical adsorption and chemical anchoring to LiPSs. In addition, the AlF3 nanolayer protects the open surface of the porous carbon to isolate sulfur species from the electrolyte to reduce irreversible losses while accelerating the redox kinetics of LiPSs through strong polar adsorption and bonding. Hence, the PNCM@S@AlF3 cathode exhibits an initial capacity as high as 1176.2 mAh/g at 0.2C, and the cycling stability and rate capability are superior to that of PNCM@S without AlF3 coating. Impressively, the PNCM@S@AlF3 cathode delivers stable long-term cycling performance at a high rate of 2C, with 95.6% capacity retention after 500 cycles. This work presents a facile, sustainable, and efficient synergistic strategy for developing advanced LSBs.

Theoretical investigation of synergistically boosting the anchoring and electrochemical performance of lithiophilic/sulfiphilic transition metal carbides for lithium-sulfur batteries.

Lithium-sulfur (Li-S) battery is one of the most promising next-generation energy-storage systems with a high energy density and low cost. However, their commercial applications face several challenges, such as the shuttle effect caused by the soluble lithium polysulfide (LiPSs) intermediates and the sluggish sulfur redox reaction. In this article, we systematically investigated the anchoring and electrochemical performance of a series of transition metal carbides (TMCs: TiC, VC, ZrC, NbC, HfC, TaC) as cathode materials for Li-S batteries by theoretical calculations. The lithiophilic/sulfiphilic non-polar (001) surfaces of TMCs can offer moderate binding strength with LiPS intermediates, ensuring good performance of sulfur immobilization. These TMCs can also facilitate lithium diffusion, indicating the good rate performance of Li-S batteries. We also demonstrated that the studied TMCs can be classified into two classes according to their catalytic activity for Li2S decomposition which originated from their different electronic structural features. Furthermore, TiC, ZrC, and HfC exhibited excellent bifunctional electrochemical activity through reducing the Gibbs free energy for sulfur reduction reactions (SRRs) and lowering the barrier for Li2S decomposition which facilitates accelerating electrode kinetics and elevating utilization of sulfur. Our results offer a systematic approach to designing and screening non-polar materials for high-performance Li-S batteries, based on the rational electronic structure and lattice match strategy.

Theoretical study of highly efficient VS2-based single-atom catalysts for lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries have become a research hotspot due to their high energy density. However, they also have certain disadvantages and limitations. To enhance the performance of Li-S batteries, this study focuses on the utilization of transition metal (TM)-embedded vanadium disulfide (VS2) materials as cathode catalysts. Using density functional theory (DFT), comprehensive calculations and atomic-level screening of ten TM atoms were conducted to understand the underlying mechanisms and explore the potential of TM@VS2 catalysts for enhancing battery performance. The computational results indicate that five selected catalysts possess sufficient bonding strength towards high-order lithium polysulfide intermediates by the formation of a significant covalent bond between S atoms in Li2Sn and TM atoms, thereby effectively suppressing the shuttle effect. The Ni@VS2 catalyst can effectively decrease the decomposition energy barrier of Li2S in the charge reaction and can have an optimal Gibbs free energy at the rate-determining step among TM@VS2 catalysts for the discharge reaction. This study elucidates the mechanism of VS2-based transition-metal single-atom catalysts and provides an effective reference for the anchoring of TM atoms on other materials.

Physical and Electrochemical Properties of Transition Metal Oxides with Hollow Structure As Sulfur Host Material for Lithium-Sulfur Batteries

INTRODUCTION Because of its high theoretical energy density, possibly low cost, and environmental friendliness, lithium-sulfur (Li-S) batteries have received a lot of interest. However, the principal disadvantage impeding the success of Li–S batteries lies in the severe leakage and migration of soluble lithium polysulfide intermediates out of cathodes upon cycling caused “shuttle effect”. The loss of active sulfur species incurs significant capacity decay and poor battery lifespans which has prevented it from commercial realization.Several researches have been conducted with an attempt to improve capacity of batteries while maintaining life of the Li-S cellใ including an introduction of nanostructured cathode host materials. Two main approaches have currently been explored a. chemical confinement and b. physical confinement to anchor the lithium poly-sulfide (LiPSs) reaction products durin the charging process. Transition metal oxides such as TiO2 and SnO2 has been studied with a potential material to anchor polysulfides via Lewis acid–base interactions and thus maybe able to chemically confine LiPSs within or on the transition metal oxide. Physical confinement may also be possible by trapping LiPSs within a transition metal oxide host structure e.g. hollow structure and thus help impedes polysulfide dissolution into the electrolyte. In this study, TiO2 and SnO2 are focused to understand the physical and electrochemical properties of sulfur host material with hollow structures. The in situ XAS is also conducted to understand the behavior of the dissolution and migration of long-chain LiPSs intermediates (Li2S x , 4 ≤ x ≤ 8) in the sulfur cathode upon discharge. EXPERIMENTAL The transition metal oxide, TiO2 and SnO2, were successfully synthesized by a templated method. The synthesis process involved four steps, preparation of SiO2 spheres, synthesis of SiO2@transition metal oxide core-shell structure by coating transition metal oxide shell on SiO2 and crystallization by calcination and etching the SiO2@transition metal oxide to form hollow transition metal oxide spheres. Structural properties of the synthesized samples were studied by X-ray diffraction (XRD) using Cu-Kα (λ=1.5418 Å) radiation. Particle morphologies and size of the resulting compounds were observed using a field emission scanning electron microscope. Composite electrodes for electrochemical studies were prepared by doctor blade coating of a slurry compound onto carbon-coated aluminium foil current-collectors. The transition metal oxide and sulfur composite, conductive carbon and PVDF binder were mixed in the ratio of 80:10:10 by weight. Electrochemical characterizations were performed by in 2032 coin cells and Galvanostatic charge-discharge cycling was done between 1.8-3.0 V at 0.1C using a MACCOR Series 4000 at room temperature. RESULTS AND DISCUSSIONS Based on the XRD results, single phase anatase TiO2 and tetragonal SnO2 were both successfully synthesized by the templated method. SEM images (Fig. 1a and 1b) demonstrate that TiO2 and SnO2 are generally spherical structures with nanometer scale dimensions ranging from 250-350 nm and 450-500 nm, respectively. The interior hollow region can be seen clearly in the images of broken spheres. The shelled surface of the synthesized powders is hierarchically made up of interconnected nanocrystals providing a possibly porous structure. Hence, the hierarchically porous and hollow structure has a large surface area for adsorbing the LiPSs distributed in the electrolyte.Fig. 1c shows the charge and discharge voltage profiles of SnO2 and sulfur composite electrode cathode in the first five cycles. Two discharge plateaus were clearly observed, which might be attributed to the two-step sulfur-lithium reaction process. The initial plateau, centered about 2.30 V, was commonly attributed to the reduction of the S8 ring and the formation of S8 2−. The second discharge plateau at 2.10 V was attributed to further reduction of the higher polysulfides (Li2S n , 4 ≤ n ≤ 8) to the lower polysulfides (Li2S n , n ≤ 3). There exhibited two plateaus in the charge process at about 2.25 and 2.35 V, respectively. Electrochemical performance in relations to capacity retention and the in situ XAS to understand the behavior of the dissolution and migration of LiPSs will be discussed in the meeting. Figure 1

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

Synergistic polarization engineering on BaTiO3 bulk and surface for boosting redox kinetics of polysulfides in lithium–sulfur batteries

The notorious shuttle effect of intermediate lithium polysulfides and the sluggish kinetics of sulfur redox reactions restrict the further development of high-energy-density lithium-sulfur (Li–S) batteries. Herein, a strategy of synergistic polarization engineering on ferroelectric barium titanate (BaTiO3) bulk and surface is reported, aiming to collectively improve the adsorption-catalytic ability of ferroelectric BaTiO3 to polysulfides. Differential phase contrast-scanning transmission electron microscopy (DPC-STEM) demonstrates that the introduction of ultrathin heteroepitaxial TiOx surface can give rise to the surface local electric field differing from bulk internal polarization field. Experimental and theoretical results further reveal that synergistic polarization engineering by integrating the enhanced bulk internal polarization field with the surface local electric field can collaboratively realize excellent adsorption-catalytic activity resulting from rapid electrons transfer and optimized active sites. As a result, employing BaTiO3@TiOx modified separator can endow the batteries with favorable rate performance (the discharge specific capacity achieves 710 mAh g−1 at 4 C) and substantial enhancement on cyclic performance (64.5 % capacity retention at 2 C over 500 cycles). Impressively, even at high sulfur loading of 2.5 mg cm−2, the BaTiO3@TiOx-based cell still stabilizes 78 % capacity retention with at 1 C over 150 cycles, showing the practical potential of BaTiO3@TiOx in optimizing catalytic efficiency.

A Catalytic Electrolyte Additive Modulating Molecular Orbital Energy Levels of Lithium Polysulfides for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have ultrahigh theoretical specific capacity, but the practical application is hindered by the severe shuttle effect and the sluggish redox kinetics of the intermediate lithium polysulfides (LiPSs). Effectively enhancing the conversion kinetics of LiPSs is essential for addressing these issues. Herein, the redox kinetics of LiPSs are effectively improved by introducing 6-azauracil (6-AU) molecules to the organic electrolyte to modulate the molecular orbital energy level of LiPSs. The 6-AU as a soluble catalyst can form complexes with LiPSs via Li-O bonds. These complexes are liable to transform because of the elevated HOMO and the reduced LUMO energy levels as compared to the dissociative LiPSs, resulting in small energy gaps (Egap) and exhibiting stronger redox activity. Benefiting from the rapid conversion kinetics, the shuttling effect of LiPSs is alleviated to a great extent, so that sulfur utilization is improved and the lithium electrode is protected. In addition, the introduction of 6-AU modulates the deposition behavior of Li2S and eases the coverage of the cathode surface by the insulating Li2S layer. The Li-S battery containing 6-AU provides superior capacity retention of 853 mAh g-1 after 150 cycles at 0.2 C and shows remarkable high-rate performance and retains a specific discharge capacity of 855 mAh g-1 at 5 C. This study accelerates the kinetics of Li-S batteries by tuning the HOMO and LUMO energy levels of LiPSs, which opens an avenue for designing functional electrolyte additives.

Alleviating the Polysulfide Shuttle Effect by Optimization of 3D Flower-Shaped Vanadium Dioxide for Lithium-Sulfur Batteries

With the rapid development of portable devices and Energy Storage Systems (ESS), secondary batteries with high energy density and high capacity are in great demand. Among various candidates, Lithium-sulfur (Li-S) batteries have been considered for next-generation energy devices given their high theoretical capacity (1675 mAh g<sup>-1</sup>) and energy density (2500 Wh kg<sup>-1</sup>). However, the commercialization of Li-S batteries faces challenges due to sulfur’s low electrical conductivity and the shuttle effect, caused by the dissolution of lithium polysulfide intermediates in the electrolyte during the charge-discharge process. Herein, to resolve these problems, we report the fabrication of a vanadium dioxide (VO<sub>2</sub>) composite via a simple hydrothermal method and optimize the structure of VO<sub>2</sub> for constructing an effective Multi-Walled Carbon Nano Tube (MWCNT) and 3D flower-shaped VO<sub>2</sub> (MWCNT@VO<sub>2</sub>) binary sulfur host by a simple melt diffusion method. In particular, the polar VO<sub>2</sub> composite not only physically absorbs the soluble lithium polysulfides but also has strong chemical bonds with a higher affinity for lithium polysulfides, which act as a catalyst, enhancing electrochemical reversibility. Additionally, MWCNT improves sulfur’s poor electrical conductivity and buffers volume expansion during cycling. The designed S-MWCNT@VO<sub>2</sub> electrode also exhibits better capacity retention and cycling performance than a bare S-MWCNT electrode as a lithium polysulfide reservoir.