Sodium Sulfur Research Articles

Synergistically boosting the anchoring effect and catalytic activity of MXenes as bifunctional electrocatalysts for sodium-sulfur batteries by single-atom catalyst engineering.

MXene based sulfur hosts have attracted enormous attention in room temperature sodium-sulfur (RT Na-S) batteries due to their strong affinity towards soluble sodium polysulfides (NaPSs). However, their electrocatalytic performance needs further improvement. Here, a series of single non-noble transition metal (TM = Fe, Co, Ni, and Cu) atoms anchored on Ti2CS2 (TM@Ti2CS2) were proposed as bifunctional sulfur hosts for Na-S batteries. The results testify that the introduction of TMs dramatically enhanced the chemical interaction between sulfur-containing species and Ti2CS2, which is attributed to the co-formation of TM-S and Na-S covalent bonds. Importantly, compared with pristine Ti2CS2, the sulfur reduction reaction (SRR) is thermodynamically more favorable on TM@Ti2CS2. In addition, the incorporation of Fe, Co, and Ni atoms is also conducive to promoting the dissociation of Na2S. The density of states (DOS) results suggest that TM@Ti2CS2 maintains metallic conductivity during the whole charge and discharge process. Overall, constructing single atom catalysts is an effective strategy to further improve the electrochemical performance of MXene based sulfur hosts for Na-S batteries.

Two-dimensional NiCl2 monolayers as a promising multifunctional anchoring material in sodium–sulfur batteries

By means of DFT computations, we proposed 2D NiCl2 as a promising Na–S anchoring material.

Double design of host and guest synergistically reinforces the Na-ion storage of sulfur cathodes.

Development of room-temperature sodium-sulfur batteries is significantly hampered by the shuttle effect of soluble intermediates and intrinsically sluggish conversion kinetics. In this work, a double design host and guest strategy (i.e., implantation of a polar V2O3 adsorbent into a carbon substrate and selenium doping of a sulfur guest) is proposed to synergistically reinforce the electrochemical properties of sulfur electrodes in sodium ion storage. The V2O3 adsorbent efficiently immobilizes sulfur species via strong polar-polar interactions, while the selenium dopant improves the electronic conductivity of sulfur cathodes and accelerates the redox conversion of sulfur cathodes. The synergistic effect between the V2O3 adsorbent and selenium dopant is shown to inhibit the shuttle effect and improve the redox kinetics, thus realizing greatly enhanced Na-ion storage properties of sulfur cathodes. The as-designed sulfur cathode delivers a superior rate capability of 663 mA h g-1 at 2.0 A g-1 and demonstrates excellent cyclability of 405 mA h g-1 over 700 cycles at 1.0 A g-1.

Strategies to mitigate the shuttle effect in room temperature sodium-sulfur batteries: improving cathode materials.

Room-temperature sodium-sulfur batteries (RT-Na/S batteries) with high reversible capacity (1675 mA h g-1) and excellent energy density (1274 W h kg-1) based on abundant resources of the metal Na have become a research hotspot recently. However, the intermediate product sodium polysulfides (NaPSs) generated during the charge-discharge process are easily dissolved in the ether electrolyte and transferred from the sulfur cathode to the metallic sodium surface, resulting in rapid capacity decay (shuttle effect), which seriously affects the practical application of RT-Na/S batteries. Herein, the mechanism and recent research progress in suppressing the shuttle effect of the sulfur cathode in RT-Na/S batteries are summarized. Strategies such as carbon-based materials physically fixing NaPSs, polar materials absorbing NaPSs to reduce their dissolution, and catalytic materials accelerating the transformation of NaPSs into final products are provided. Challenges and insights into high-performance sulfur electrodes for optimizing RT-Na/S batteries are discussed.

A Review on the Status and Challenges of Cathodes in Room‐Temperature Na‐S Batteries

AbstractThe cathode materials for sodium‐sulfur batteries have attracted great attention since cathode is one of the important components of the sodium‐sulfur battery, and there are cathode materials that have high capacity, non‐toxicity, and cost‐efficiency. Nevertheless, due to their low Coulombic efficiency and proneness to cycling decay, the practical application of the sodium–sulfur battery has always been suppressed. In terms of the responsibility of these problems, the polysulfide shuttle and the sluggish kinetics are the main culprits. To address these issues, impeding the notorious reaction between polysulfide intermediates on the cathode and improve the kinetics reaction on the anode are extremely important. Herein, a comprehensive review is prepared of different approaches to increasing the electrochemical performance and strengthening the stability of cathodes. The influences of various choices and the consequent properties of the cathode in relation to the whole sodium–sulfur battery performance is investigated. Finally, the current research challenges related to cathodes for sodium–sulfur batteries and future perspectives are also discussed.

Advances and challenges in tuning the reversibility & cyclability of room temperature sodium–sulfur and potassium–sulfur batteries with catalytic materials

The high theoretical energy density of room temperature sodium-sulfur and potassium-sulfur batteries (Na–S; 1274 Wh/kg, K–S; 914 Wh/kg; based on the mass of sulfur) due to the multi-electron transfer associated with the unique conversion chemistry of S and the natural abundance of Na, K, and S raw materials make them ideal candidates for large-scale energy storage applications beyond Li batteries. However, achieving good reversibility, cyclability, and active material utilization in Na–S and K–S batteries demands alleviation of the complex polysulfide dissolution and the shuttle phenomena during cycling. Rational employment of catalytic materials is beneficial to address these issues by facilitating effective polysulfide transformation and thereby accelerating the sluggish reaction kinetics. This review focuses on the roles and evolution of catalytic materials in polysulfide adsorption, catalytic conversion, and redox mediation in facilitating high-performing Na–S and K–S batteries. Specifically, the advances in tuning the reversibility and cyclability of Na-S and K–S batteries strategically with catalytic material-incorporated S-host cathodes, separators, and interlayers and the interaction of various catalytic materials with the polysulfide species are discussed in the light of advanced characterization techniques. Lastly, the challenges and the plausible strategies for future research are elucidated.

Three-Dimensional Honeycomb-Like Carbon as Sulfur Host for Sodium-Sulfur Batteries without the Shuttle Effect.

Sodium-sulfur batteries operating at ambient temperature are being extensively studied because of the high theoretical capacity and abundant resources, yet the long-chain polysulfides' shuttle effect causes poor cycling performance of Na-S batteries. We report an annealing/etching method to converse low-cost wheat bran to a 3D honeycomb-like carbon with abundant micropores (WBMC), which is smaller than S8 molecular size (∼0.7 nm). Thus, the microporous structure could only fill small molecular sulfur (S2-4). The micropores made sulfur a one-step reaction without the shuttle effect due to the formed short-chain polysulfides being insoluble. The WBMC@S exhibits an excellent initial capacity (1413 mAh g-1) at 0.2 C, outstanding cycling performance (822 mAh g-1 after 100 cycles at 0.2 C), and high rate performance (483 mAh g-1 at 3.0 C). The electrochemical performance proves that the steric confinement of micropores effectively terminates the shuttle effect.

Atomically Dispersed Dual-Site Cathode with a Record High Sulfur Mass Loading for High-Performance Room-Temperature Sodium-Sulfur Batteries.

Room-temperature sodium-sulfur (RT-Na/S) batteries possess high potential for grid-scale stationary energy storage due to their low cost and high energy density. However, the issues arising from the low S mass loading and poor cycling stability caused by the shuttle effect of polysulfides seriously limit their operating capacity and cycling capability. Herein, sulfur-doped graphene frameworks supporting atomically dispersed 2H-MoS2 and Mo1 (S@MoS2 -Mo1 /SGF) with a record high sulfur mass loading of 80.9wt.% are synthesized as an integrated dual active sites cathode for RT-Na/S batteries. Impressively, the as-prepared S@MoS2 -Mo1 /SGF display unprecedented cyclic stability with a high initial capacity of 1017mAhg-1 at 0.1Ag-1 and a low-capacity fading rate of 0.05% per cycle over 1000cycles. Experimental and computational results including X-ray absorption spectroscopy, in situ synchrotron X-ray diffraction and density-functional theory calculations reveal that atomic-level Mo in this integrated dual-active-site forms a delocalized electron system, which could improve the reactivity of sulfur and reaction reversibility of S and Na, greatly alleviating the shuttle effect. The findings not only provide an effective strategy to fabricate high-performance dual-site cathodes, but also deepen the understanding of their enhancement mechanisms at an atomic level.

Dynamic Multistage Coupling of FeS2/S Enables Ultrahigh Reversible Na–S Batteries

AbstractThe fundamental challenges that coexisted around sulfur cathode energy storage systems, are the severe polysulfide dissolution and low reactivity resulting in poor reversibility and short cycle life, specifically, in inexpensive sodium ion batteries. Herein, the solution‐processed synthesis of ultra‐high intimate contacted FeS2/S architecture is reported and evolution of the dynamic multistage coupling between the FeS2 and S in sodium–sulfur batteries is revealed. Atomic visualization and in situ spectroscopy conclude that: NaxFeS2 (0 <x ≤1) effectively captures sodium polysulfides and promotes the conversion of S8 to Na2S4 to Na2S2/Na2S; simultaneously, the presence of Na2S2/Na2S traps the continuous growth of iron grains during continuously discharging to 0.4 V, thereby boosting the reversibility and high capacity. Moreover, the density functional theory further analyses the unique coupling effect of Na2Sx with different intermediate states of FeS2. The electrode with unique structure and dynamic coupling exhibits outstanding cycle reversibility and extremely long life, which delivers a reversible capacity of 860 mAh g−1 after 1000 cycles with no capacity decay at 0.5 A g−1. Even under a practical areal capacity of 4 mAh cm−2, it still shows pretty‐well cycling stability.

Surface Film Formation from Sodium Polysulfide Decomposition on Sodium-Metal Anode Surface

Room-temperature sodium–sulfur batteries are being considered as an alternative next generation of energy storage devices to replace lithium–sulfur batteries due to lower costs of Na metal while keeping a high theoretical capacity. A comprehensive understanding of polysulfide decomposition mechanisms and passivation film formation on the Na–metal surface has challenged the development of this metal–sulfur chemistry. Here, using first-principles modeling, we study the adsorption of sodium polysulfide (NaPS) molecules on the Na-metal surface and investigate the Na2S film formation from soluble NaPS decomposition in the presence of different electrolyte solvents (i.e., EC, PC, and EC/PC mixture). We find that NaPS molecules strongly interact with the Na-metal surface via Na–S bonds, leading to charge migration from the metal to the adsorbates. Such strong adsorption precedes a complete spontaneous electron-transfer decomposition of NaPS to form an amorphous Na2S film on the anode surface. The reduction reaction mechanisms are identified for each electrolyte, suggesting that polysulfides are completely decomposed in a short time. The energetic properties suggest that the first and second steps in the reaction of NaPS decomposition in the mixture solvent are thermodynamically uphill. The decomposed S atoms from NaPS can insert into the Na slab, leading to Na2S formation. The decomposition of multiple NaPS molecules reveals that the reduction of further NaPS on the surface after the first one is sluggish and incomplete because of the passivating nature of the nascent Na2S film, while NaPS far from the surface remains in the electrolyte phase forming a soluble NaPS cluster dissolved in the solvent.

Variability of sea salt and methanesulfonate in firn cores from northern Victoria Land, Antarctica: Their links to oceanic and atmospheric condition variability in the Ross Sea

The potential ice core proxies of variability in oceanic and atmospheric conditions over the Ross Sea were evaluated. This study examined sea salt sodium (ss–Na+) and biogenic sulfur (methanesulfonate, MS–) records, covering 23 years between 1990 and 2012, from two firn cores drilled on the Styx Glacier plateau (SGP), northern Victoria Land, East Antarctica, to examine the potential links between those records and datasets for various climate variables. The comparison showed that the interannual variability of the ss–Na+ record is closely related to Pacific–South American mode 2 (PSA2) in the Ross Sea sector, exhibiting an increased ss–Na+ flux, owing most likely to more frequent penetration of maritime air masses from the western Ross Sea to the SGP when the winter/spring PSA2 mode becomes more pronounced. The observed MS– record revealed statistically significant positive correlations with the changes in the summertime chlorophyll a concentration in the Ross Sea polynya (RSP) and wind speed in the southern Ross Sea region. This indicates the dominant role of a combination of changes in the summertime primary productivity and wind speed over the RSP in modulating the MS– deposition flux at the SGP. These results highlight the suitability of the ss–Na+ and MS– records from the SGP as proxies for characterizing the dominant patterns of variability in oceanic and atmospheric conditions and their underlying mechanisms on interannual and longer timescales beyond the instrumental limits over the Ross Sea region.

Efficient Control of the Shuttle Effect in Sodium–Sulfur Batteries with Functionalized Nanoporous Graphenes

Efficient Control of the Shuttle Effect in Sodium–Sulfur Batteries with Functionalized Nanoporous Graphenes

Azo-Branched Covalent Organic Framework Thin Films as Active Separators for Superior Sodium-Sulfur Batteries.

Sodium-Sulfur (Na-S) batteries are outstanding for their ultrahigh capacity, energy density, and low cost, but they suffer from rapid cell capacity decay and short lifespan because of serious polysulfide shuttle and sluggish redox kinetics. Herein, we synthesize thin films of covalent organic frameworks (COFs) with azobenzene side groups branched to the pore walls. The azobenzene branches deliver dual functions: (1) narrow the pore size to the sub-nanometer scale thus inhibiting the polysulfide shuttle effect and (2) act as ion-hopping sites thus promoting the Na+ migration. Consequently, the Na-S battery using the COF thin film as the separator exhibits a high capacity of 1295 mA h g-1 at 0.2 C and an extremely low attenuation rate of 0.036% per cycle over 1000 cycles at 1 C. This work highlights the importance of separator design in upgrading Na-S batteries and demonstrates the possibility of functionalizable framework materials in developing high-performance energy storage systems.

Metalized Polyacrylates as Efficient Binder for a Sulfurized Polyacrylonitrile/Polydopamine Active Material in Sulfur Cathodes for Room Temperature Sodium–Sulfur Batteries

Promising binder systems with special chemical and mechanical functions are under extensive exploration to cope with serious volume change and harmful shuttle effect occurring during charge/discharge cycles of a sulfur cathode in sodium–sulfur (Na–S) batteries. In this aspect, sulfurized polyacrylonitrile (SPAN)/polydopamine (PDA) active materials are combined with different metalized polyacrylates (MPAAs) to result in a SPAN/PDA/MPAA binder system with peculiar morphology and superior mechanical and interfacial strengths. As the outer layer of SPAN/PDA/MPAA, MPAA can extend its long chains to interact with cathode components and, moreover, metal ions of MPAA can participate in the beneficial electron transport process. The results suggest that stability and electrochemical performance of the sulfur cathodes depend on the applied metal ions, which become better and better as the valence of metal ions change from mono (Na), di (Ca), and tri (Fe) to tetra (Ti). Cathode derived from SPAN/PDA/titanium polyacrylate (TiPAA) shows the best stability and electrochemical performance, exhibiting a rather high specific capacity of 1438 mAh g–1 at 0.2 C for 100 cycles and 1271 mAh g–1 at 1 C for 300 cycles. Hopefully, this study can provide a foundation on how to use different metal ions to manipulate the electrochemical performance of sulfur cathode in Na–S batteries.

The Future for Room‐Temperature Sodium–Sulfur Batteries: From Persisting Issues to Promising Solutions and Practical Applications

AbstractRoom‐temperature sodium–sulfur (RT‐Na/S) batteries are emerging as promising candidates for stationary energy‐storage systems, due to their high energy density, resource abundance, and environmental benignity. A better understanding of RT‐Na/S batteries in the view of the whole battery components is of essential importance for fundamental research and practical applications. In particular, the components other than sulfur cathodes in preventing the migration of polysulfides and accelerating the reaction kinetics have been greatly overlooked. Such a biased research trend is also adverse to the broader applications for RT‐Na/S batteries, which have long been ignored in previous reviews. Herein, approaches to the historical progress toward practical RT‐Na/S batteries through a “teamwork” perspective are comprehensively summarized, and balanced research trends are encouraged to enable practical RT‐Na/S batteries. In the meantime, the persisting issues, promising solutions, and practical applications of advanced sulfur host design, Na metal anode protection, electrolyte optimization, separator modification, and binder engineering are clearly emphasized. Finally, the device‐scale evaluation in practical parameters and advanced characterization tools are thoroughly provided. This review aims to provide the “teamwork” perspective on the whole‐cell design and fundamental guidelines that can shed light on research directions for practical RT‐Na/S batteries.

Room-Temperature Sodium-Sulfur Batteries: Rules for Catalyst Selection and Electrode Design.

Seeking an optimal catalyst to accelerate conversion reaction kinetics of room-temperature sodium-sulfur (RT Na-S) batteries is crucial for improving their electrochemical performance and promoting the practical applications. Herein, theoretical calculations of interfacial interactions of catalysts and polysulfides in terms of the surface adsorption state, interfacial ions migration, and electronic concentration around the Fermi level are systematically proposed as guiding principles of catalyst selection for RT Na-S batteries. As a case, MoN catalyst is accurately selected from transition metal nitrides with different d orbital electrons, and for experiment, it is introduced into the carbon nanofibers as a dual-functioning host (MoN@CNFs). The MoN@CNFs can effectively anchor polysulfides and accelerate their conversion reaction. In addition, for the sodium anode, the MoN@CNFs can also induce uniform deposition of Na and inhibit dendrite growth, which are supported by in situ characterizations and finite element simulation technique. As a result, the as-prepared RT Na-S battery displays high reversible capacity of 990 mAh g-1 at 0.2 A g-1 after 100 cycles and long lifespan over 1500 cycles at 2 A g-1 . Even with high S loading of 5mg cm-2 , the RT Na-S battery still exhibits a high areal capacity of 2.5 mAh cm-2 .

(Invited) Redox Flow Battery Innovation

Flow battery innovations should offer significant improvements in performance, without compromising the durability / lifetime, and be cost-effective and scalable. The presentation will review some of the progress that has been made to enhance flow battery performance, and will discuss a number of recent innovations that aim to deliver these characteristics. These will include: Magnetic flowable electrodes applied in a polysulfide-iodide flow battery.Using flow through the current feeder to enhance mass transport and enable dendrite free zinc deposition in the zinc-iodide flow battery.Graphene modified membrane for enhanced power density. Flowable electrodes have emerged as a novel concept for high energy density batteries. To date, in most cases the flowable solid phase includes a redox active energy storage material, for example in zinc-nickel, sodium-sulfur, and lithium-sulfur systems [1-3]. In contrast, we have demonstrated the use of a carbon – magnetite nanocomposite which acts as an electrocatalyst but is not redox active [4,5]. This nanomaterial can be dispersed in the electrolyte and circulated through the battery to enhance the performance of a conventional static electrode. The magnetic characteristics of the nanocomposite can also be exploited, by using a magnetic field to assemble a high surface area electrode comprising a percolating network of the nanomaterial on the current feeder. The electrode also can be removed by releasing the magnetic field at the current feeder, and after being washed out of the cell the nanocomposite can be separated in a magnetic field. This enables replacement of the active electrode without the need to dismantle the cell.Zinc-iodide flow batteries offer high energy density due to the high aqueous solubility of the ZnI2. However, the power density that can be achieved is limited by potential for the dendritic growth of zinc deposits, and as zinc metal builds up in the cell the areal capacity is limited. We have found that by drawing some of the electrolyte through the current feeder, improved performance can be obtained [6]. This enables operation at higher power density and the denser uniform deposit should enable increased areal capacity.We attempted to reduce crossover in the all-vanadium redox flow battery by using a graphene modified nafion membrane. However, we found that the addition of the graphene reduced the losses in the battery and enabling a significant increase in the power density and discharge capacity. Currently we are working to optimize and scale up the membrane modification process, and to explore the mechanism of performance enhancement. References G. Zhu et al. (2020) High-energy and high-power Zn–Ni flow batteries with semi-solid electrodes. Sustainable Energy Fuels, 4, 4076-4085.Yang et al. (2018) Sodium–Sulfur Flow Battery for Low-Cost Electrical Storage. Advanced Energy Materials, 11, 1711991.Suo et al. (2015) Carbon cage encapsulating nano-cluster Li2S by ionic liquid polymerization and pyrolysis for high performance Li–S batteries. Nano Energy, 13, 467-473.Rahimi, A.M. Dehkordi, E.P.L. Roberts (2021) Magnetic nanofluidic electrolyte for enhancing the performance of polysulfide/iodide redox flow batteries. Electrochimica Acta, 309, 137687.Rahimi, A.M. Dehkordi, H. Gharibi, E.P.L. Roberts (2021) Novel Magnetic Flowable Electrode for Redox Flow Batteries: A Polysulfide/Iodide Case Study. Ind. Eng. Chem. Res., 60, 824-841.F. ShakeriHosseinabad et al. (2021) Influence of Flow Field Design on Zinc Deposition and Performance in a Zinc-Iodide Flow Battery. ACS Applied Mat. & Interfa

Single-Atom Electrocatalyst for Engineered Cathode Interfaces in Sodium-Sulfur Batteries

The demand for portable rechargeable energy storage devices is ever increasing, especially because of the advent of electric vehicles and widespread usage of portable electronics. The lithium-ion batteries are currently leading the battery market; however, the high-cost and potentially depleting storage of lithium metals are stimulating the search for alternative technologies. Metal-sulfur batteries are deemed to be promising candidates to supplant the ubiquitously used lithium-ion batteries owing to their high energy density, specific capacity, low cost of sulfur, and environmental benignity. Room temperature sodium sulfur batteries (RT Na-S) is a technologically viable alternative candidate which possesses astounding advantages such as low cost (both sodium and sulfur), non–toxicity, natural abundance, and high theoretical energy density (1274 Whkg-1). However, the inevitable problems such as the solubility of higher order polysulfides to the electrolyte, known as shuttle effect, and the slow kinetics of electrochemical conversion reactions of intermediate sodium polysulfides (Na2Sn) significantly impede the practical realization of Na-S batteries. The conventionally used various forms of carbonaceous nanomaterials for cathode design have floundered to overcome the challenges because their nonpolar nature cannot produce adequate anchoring and enhanced polysulfides reaction kinetics. The polar anchoring materials (AM) have exhibited promising performance to improve sulfur chemistry. It is generally understood that catalytic performance is directly connected to the surface area of catalytic particles, and the single-atomic level provides the maximum surface area, resulting in the highest catalytic efficacy. Herein, we use first principles-based density functional theory (DFT) simulations to investigate the interfacial interactions between Na2Sn and novel transition metal (TM) single-atom catalysts (SACs) embedded on nitrogen doped graphene and various lattice sites of transition metal chalcogenides (TMDC) (chalcogenides- and Metal-substitution, Metal-top sites). For example, the pristine and Mo-sub sites of MoS2 are found to be ineffective for efficient confinement of the polysulfides within the cathode material. We demonstrate that SACs on both S-site and Mo-top sites of MoS2 and on nitrogen doped graphene possess strong adsorption strength with the Na2Sn which are superior to the commonly used ether electrolyte solvents, a requisite to prevent shuttle effect. We illustrate the influence of d-band center of SACs as an important descriptor in describing Na2Sn interactions with them. The underlying anchoring mechanism of polysulfide adsorption over AM is examined through Bader charge, charge density difference and projected density of states (PDOS) analysis. We also investigate the effect of SACs in improving the kinetics of sulfur reduction reactions (SRRs) and catalytic decomposition of short-chain polysulfides which are crucial for achieving excellent rate capability and longer cycle life. Overall, the unprecedented insights obtained on the role of SACs in tailoring the polysulfides redox chemistry at the interfaces and their relation to their TM’s d-band center is an important step towards rational design cathode materials for high-performance Na-S batteries, in particular, but metal-chalcogenide batteries, in general.

Rational Electrolyte Design toward Cyclability Remedy for Room‐Temperature Sodium–Sulfur Batteries

AbstractRechargeable room‐temperature sodium–sulfur (RT Na–S) batteries are a promising energy storage technology, owing to the merits of high energy density and low cost. However, their electrochemical performance has been severely hindered by the poor compatibility between the existing electrolytes and the electrodes. Here, we demonstrate that an all‐fluorinated electrolyte, containing 2,2,2‐trifluoro‐N,N‐dimethylacetamide (FDMA) solvent, 1,1,2,2‐tetrafluoroethyl methyl ether (MTFE) anti‐solvent and fluoroethylene carbonate (FEC) additive, can greatly enhance the reversibility and cyclability of RT Na–S batteries. A NaF‐ and Na3N‐rich cathode electrolyte interphase derived from FDMA and FEC enables a “quasi‐solid‐phase” Na–S conversion, eliminating the shuttle of polysulfides. The MTFE not only reduces polysulfide dissolution, but also further stabilizes the Na anode via a tailored solvation structure. The as‐developed RT Na–S batteries deliver a high capacity, long lifespan, and enhanced safety.

Rational Electrolyte Design toward Cyclability Remedy for Room-Temperature Sodium-Sulfur Batteries.

Rechargeable room-temperature sodium-sulfur (RT Na-S) batteries are a promising energy storage technology, owing to the merits of high energy density and low cost. However, their electrochemical performance has been severely hindered by the poor compatibility between the existing electrolytes and the electrodes. Here, we demonstrate that an all-fluorinated electrolyte, containing 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) solvent, 1,1,2,2-tetrafluoroethyl methyl ether (MTFE) anti-solvent and fluoroethylene carbonate (FEC) additive, can greatly enhance the reversibility and cyclability of RT Na-S batteries. A NaF- and Na3 N-rich cathode electrolyte interphase derived from FDMA and FEC enables a "quasi-solid-phase" Na-S conversion, eliminating the shuttle of polysulfides. The MTFE not only reduces polysulfide dissolution, but also further stabilizes the Na anode via a tailored solvation structure. The as-developed RT Na-S batteries deliver a high capacity, long lifespan, and enhanced safety.