Sodium-sulfur Batteries Research Articles

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.

Incorporating TiO2 nanoparticles into the multichannels of electrospun carbon fibers to increase the adsorption of polysulfides in room temperature sodium-sulfur batteries

Incorporating TiO2 nanoparticles into the multichannels of electrospun carbon fibers to increase the adsorption of polysulfides in room temperature sodium-sulfur batteries

Deciphering the interaction mechanism between copper and polysulfides for enhanced performance and cost-efficiency in quasi-sodium-sulfur batteries

Room-temperature Na-S batteries with Al current collectors face the long-standing challenges of poor cycling performance and rate capability due to the serious sodium polysulfides (NaPSs) shuttling and sluggish reaction kinetics. Here, we demonstrate that a high-performance and low-cost quasi-Na-S battery can be realized by using the Cu@carbon nanotube (CNT) cathode host and unconventional Cu current collector (Cu-CC) in an ether electrolyte. Detailed ex-situ characterizations reveal that the Cu@CNT/S was transformed to NaPSs anchoring on Cu7S4 nanocrystals (~11 nm) during the cycling, forming the NaPS@Cu7S4/CNT cathode with robust sulfur immobilization and enhanced Na+ reaction kinetics. Moreover, the chemical interaction between NaPSs and Cu-CC in situ creates a robust Cu-CC/electrode interface with ultra-small resistance (< 4 Ω), greatly improving the electrode stability and charge transfer kinetics. The synergy of efficient NaPSs trapping and favorable Cu/electrode interface endows the quasi-Na-S battery with a moderate discharge plateau (around 1.2~1.75 V), excellent rate capability (396.9 mAh g-1 at 10 A g-1), and ultra-stable cycling performance (nearly no capacity decay over 1190 cycles). These features make it quite suitable for stable and cost-sensitive grid-scale applications.

Single-Atom Vanadium Catalyst Boosting Reaction Kinetics of Polysulfides in Na-S Batteries.

The practical application of the room-temperature sodium-sulfur (RT Na-S) batteries is hindered by the insulated sulfur, the severe shuttle effect of sodium polysulfides, and insufficient polysulfide conversion. Herein, on the basis of first principles calculations, single-atom vanadium anchored on a 3Dnitrogen-doped hierarchical porous carbon matrix (denoted as 3D-PNCV) is designed and fabricated to enhance sulfur reactivity, and adsorption and catalytic conversion performance of sodium polysulfide. The 3D-PNCV host with abundant and active V sites, hierarchical porous structure, high electrical conductivity, and strong chemical adsorption/conversion ability of V-N bonding can immobilize the polysulfides and promote reversibly catalytic conversion of polysulfides toward Na2 S. Therefore, as-fabricated RT Na-S batteries can achieve a high reversible capacity (445mAhg-1 over 800 cycles at 5Ag-1 ) and excellent rate capability (224mAhg-1 at 10Ag-1 ). The electrocatalysis mechanism of sodium polysulfides is further experimentally and theoretically revealed, which provides a new strategy to develop the highly stable RT Na-S batteries.

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.

Orthorhombic Nb2 O5 Decorated Carbon Nanoreactors Enable Bidirectionally Regulated Redox Behaviors in Room-Temperature Na-S Batteries.

Regulating redox kinetics is able to spur the great-leap-forward development of room-temperature sodium-sulfur (RT Na-S) batteries, especially on propelling their Na-ion storage capability. Here, an innovative metal oxide kinetics accelerator, orthorhombic Nb2 O5 Na-ion conductor, is proposed to functionalize porous carbon nanoreactors (CNR) for S cathodes. The Nb2 O5 is shown to chemically immobilize sodium polysulfides via strong affinity. Theoretical and experimental evidence reveals that the Nb2 O5 can bidirectionally regulate redox behaviors of S cathodes, which accelerates reduction conversions from polysulfides to sulfides as well as promotes oxidation reactions from sulfides to S. In situ and ex situ characterization techniques further verify its electrochemical lasting endurance in catalyzing S conversions. The well-designed S cathode demonstrates a high specific capacity of 1377mA h g-1 at 0.1 A g-1 , outstanding rate capability of 405mA h g-1 at 2 A g-1 , and stable cyclability with a capacity retention of 617mA h g-1 over 600 cycles at 0.5 A g-1 . An ultralow capacity decay rate of 0.0193% per cycle is successfully realized, superior to those of current state-of-the-art RT Na-S batteries. This design also suits emerging Na-Se batteries, which contribute to outstanding electrochemical performance as well.

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.

Incorporating TiO2 nanoparticles into the multichannels of electrospun carbon fibers to increase the adsorption of polysulfides in room temperature sodium-sulfur batteries

With the rapid development of electric vehicles and large-scale power grids, lithium-ion batteries inevitably face the problem that their limited energy density and high cost cannot meet the growing demand. Room temperature sodium-sulfur (RT Na-S) batteries, which have the potential to replace lithium-ion batteries, have become a focus of attention. However, the challenging problem of their poor cycling performance cause by the “shuttle effect” of the reaction intermediates (sodium polysulfides) needs to be addressed. We report a method to incorporate TiO2 nano particles into the multichannels of electrospun carbon fibers (TiO2@MCCFs) to stabilize the sulfur compounds and produce high-performance RT Na-S batteries. The TiO2@MCCFs were prepared by electrospinning followed by heat treatment, and were infiltrated by molten sulfur to fabricate S/TiO2@MCCF cathode materials. The addition of the TiO2 nanoparticles increases the affinity of cathode materials for polysulfides and promotes the conversion of polysulfides to lower order products. This was verified by DFT calculations. A S/TiO2@MCCF cathode with a S content of 54% has improved electrochemical rate and cycling performance, with a specific capacity of 445.1 mAh g−1 after 100 cycles at 0.1 A g−1 and a nearly 100% Coulombic efficiency. Even at 2 A g−1, the cathode still has a capacity of 300.5 mAh g−1 after 500 cycles. This work provides a new way to construct high performance RT Na-S battery cathodes.

Selection of energy storage technologies under neutrosophic decision environment

The variability of renewable energy can be addressed by incorporating energy storage technologies (ESTs). Multiple energy storage technologies are available for renewable energy with wide disparity in attributes. Reports regarding the attributes are conflicting and complex, which makes it a multi-attribute decision analysis problem. To address this issue, new decision support tools are needed to aid in selecting ESTs based on their technical, environmental, and economic characteristics. In this study, a neutrosophic data envelopment analysis (NDEA) technique is developed and applied to selection of ESTs considering neutrosophic uncertainty inherent in new technologies. The decision tool systematically evaluates EST options by considering the expert's degree of satisfaction for higher technical performance, degree of dissatisfaction for lower technical performance and degree of indeterminacy for attaining better technical performance. Two case studies adapted from literature are used to illustrate the decision support tool. The first case study, which is used to demonstrate the tool for EST selection, involves the selection of thermal energy storage options. The second case study involves eight ESTs with different mechanisms: supercapacitor, flywheel, compressed air energy storage, pumped hydro energy storage, Li-ion battery, NiCd battery, NaS battery, and Pb-acid battery. The results reveal certain ESTs that are preferred over wide range of expert's perception to uncertainty in terms of dissatisfaction and indeterminacy. For example, Li-ion battery is DEA efficient if the risk tolerance for indeterminacy is greater than 40% and Pb-acid battery is DEA efficient at falsity tolerance greater than 80% and indeterminacy tolerance of less than 5%. These alternatives can be regarded as robust choices. Insights gained from the application of the decision tool can be used for guiding investment decisions in planning of renewable energy systems with energy storage.

Theoretical exploration of the structural evolution of sodium sulfide clusters in Na-S batteries

The nanosized sodium sulfide species greatly enhance the performance of Na-S batteries. However, as a typical ionic compound, the diminished stability with decreasing cluster size has been rarely considered. Numerous theoretical works only simulated the Na-S binary system based on quite small sodium sulfide clusters, with no account of the stability of the sub-nanoscale cluster. Here, by using an advanced structure search algorithm, we built a binary phase diagram of the sodium sulfide clusters (NSCs). The commonly studied monomer model with low sulfur concentrations is indeed energetically unfavorable, especially for the final discharge product, the Na2S monomer. Therefore, the aggregation of monomers should take place to form multimers. According to the energy, charge, and geometry, relatively stable clusters with low sulfur concentrations are located, including (Na2S5)2, (Na2S4)2, (Na2S3)3, (Na2S2)4, and (Na2S)6 clusters. Furthermore, these multimers bind more intensely to four typical models of carbon-based substrates. The B-doped carbon material exhibits outstanding affinity to NSCs, which may facilitate overcoming the shuttle effect in applications. This work represents a significant step toward understanding the evolution mechanism of NSCs that may guide the future development of high-performance Na-S batteries.

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.

Stable all-solid-state sodium-sulfur batteries for low-temperature operation enabled by sodium alloy anode and confined sulfur cathode

All-solid-state sodium-sulfur (Na-S) batteries are promising for stationary energy storage devices because of their low operating temperatures (less than 100 °C), improved safety, and low-cost fabrication. Using Na alloy instead of Na metal as an anode in Na-S batteries can prevent dendrite growth and improve interfacial stability between the anode and solid electrolytes to achieve long-cycling stability. A high-sulfur content cathode possessing high sulfur utilization is also important to enable an energy-dense Na-S battery. In this work, we studied Na-Sb and Na-Sn alloy anodes and demonstrated the superiority of Na3Sb alloy undergoing a stable Na alloying/dealloying process at 0.04 mA cm−2 for over 500 h. Combining the optimized Na3Sb alloy anode with sulfur-carbon composites prepared by the vapor deposition approach, the full cell shows a high sulfur specific capacity and improved rate performance. Moreover, the all-solid-state Na alloy-S battery can deliver a high initial discharge specific capacity of 1377 mAh g−1 and maintain good capacity retention of 70 % after 180 cycles at 60 °C. Post-cycle characterizations show that both the anode and cathode perform a reversible discharge/charge process after the 1st cycle, and the cathode undergoes significantly rearranged distributions of carbon and solid-state electrolytes after 180 cycles due to severe volume change induced by repeated sodiation/desodiation process. Data availabilityData will be made available on request.

Hierarchically porous carbon derived from delignified biomass for high sulfur-loading room-temperature sodium-sulfur batteries

The commercial applications of room-temperature sodium-sulfur battery still suffers from low sulfur utilization and poor reaction kinetics. Here, we develop a novel carbon material with hierarchical pores from camellia oleifera seed cake as the host of sulfur by introducing a delignification process followed by KOH activation. The large specific surface area (1362 m2 g−1) and well-developed porosity produced by the two-step method make it possible to realize high sulfur content (61.9 wt%). By the physical confinement of micropores, the formation of Na2Sx (4 ≤ x ≤ 8) is effectively suppressed to avoid the side reactions. The mesopores and macropores optimize the electrolyte accessibility. The sulfur-loaded carbon cathode delivers a reversible capacity of 702 mAh g−1 after 100 cycles at 0.1 C (1 C = 1675 mAh g−1). Even at 1 C, a reversible capacity of 404 mAh g−1 has been achieved after 300 cycles. This work demonstrates a sustainable cathode with a high sulfur content for the practical application of room-temperature Na–S batteries.

A novel Sb-Zn electrode with ingenious discharge mechanism towards high-energy-density and kinetically accelerated liquid metal battery

Liquid metal battery (LMB) has recently captured intensive attention for large-scale energy storage, originating from its attractive cost-efficiency, robust cyclability, and ultralong service lifetime. Nevertheless, realizing high energy density remains a great challenge. Herein, a novel dual-active Sb-Zn electrode is elaborately designed. A unique lithiation mechanism is demonstrated for the first time in LMB field. A ternary intermetallic compound LiZnSb is preferentially formed with a high discharge plateau at ca. 1.1 V, which is followed by a conversion reaction to Li3Sb and Zn at around 0.8 V and then a consecutive dissolution reaction of lithium in molten Zn, significantly ameliorating the voltage and capacity properties. Meanwhile, part Zn melts regenerate and disperse among discharge product layer, constructing rapid electron/lithium percolating networks in-situ, which accelerates the electrode reaction kinetics. As a result, the Li||Sb-Zn battery exhibits high average discharge voltage of 0.763 V at 100 mA cm−2 and superior rate performance (0.596 V at 1000 mA cm−2). Outstanding energy and power densities (290.6 Wh kg−1 and 239.66 W kg−1) are achieved, remarkably surpassing most reported LMBs and even comparable to Na-S battery. This work showcases an innovative electrochemistry system, opening a new avenue for high-performance LMBs.

Single-Atom Yttrium Engineering Janus Electrode for Rechargeable Na–S Batteries

The development of rechargeable Na-S batteries is very promising, thanks to their considerably high energy density, abundance of elements, and low costs and yet faces the issues of sluggish redox kinetics of S species and the polysulfide shuttle effect as well as Na dendrite growth. Following the theory-guided prediction, the rare-earth metal yttrium (Y)-N4 unit has been screened as a favorable Janus site for the chemical affinity of polysulfides and their electrocatalytic conversion, as well as reversible uniform Na deposition. To this end, we adopt a metal-organic framework (MOF) to prepare a single-atom hybrid with Y single atoms being incorporated into the nitrogen-doped rhombododecahedron carbon host (Y SAs/NC), which features favorable Janus properties of sodiophilicity and sulfiphilicity and thus presents highly desired electrochemical performance when used as a host of the sodium anode and the sulfur cathode of a Na-S full cell. Impressively, the Na-S full cell is capable of delivering a high capacity of 822 mAh g-1 and shows superdurable cyclability (97.5% capacity retention over 1000 cycles at a high current density of 5 A g-1). The proof-of-concept three-dimensional (3D) printed batteries and the Na-S pouch cell validate the potential practical applications of such Na-S batteries, shedding light on the development of promising Na-S full cells for future application in energy storage or power batteries.

Enabling Ambient Sodium Sulfur Batteries

Sodium and Sulfur are attractive energy storage materials because of their reactivity with each other and global abundance. Therefore, the Na-S battery is one of the oldest conceptualized batteries (Ford 1960s). However, the complex, multistep electrochemical reaction between the two has prevented commercial realization. We couple novel ultrafast spectroscopy with optical microscopy to bridge length and time scales of the reaction, to obtain the fundamental information necessary to facilitate a functioning battery (separator, electrolyte, geometry, etc.). With in-situ optical microscopy, we observe polysulfide anions ranging from S8^2- to S3^.- via color changes in the electrolyte during electrochemcial cycling on the order of hours. The observed, soluble species contribute to the reaction complexity and are most commonly blamed for low cell capacity or poor capacity retention. To better understand their interaction with the electrolyte solvent, novel pump/probe, ultrafast lasing is used to observe transient signals indicative of chemical recombination. This allows comparison of the strength of polysulfide interaction with solvent molecules at specific cell voltages and in various electrolyte cocktails. Similar analysis is also used in a symmetric sodium system to isolate plating and stripping phenomenon from the sulfur reaction.

Lychee seed-derived microporous carbon for high-performance sodium-sulfur batteries

Sodium-sulfur (Na–S) batteries are regarded as one of the promising next-generation energy storage systems; while being more cost-effective than lithium-sulfur batteries, Na–S batteries also suffer from the shuttle effect. Different strategies to tackle the long-chain polysulfide product shuttling issue have been proposed, mainly focusing on sulfur product confinement with costly materials and complex methods. Seeking high-performance and low-cost electrode material precursors is of great importance to promoting Na–S battery applications. We present a high specific surface area microporous carbon framework synthesized from degradable biowaste, namely lychee seeds, with a facile room-temperature etching process. Unlike the traditional dissolution-precipitation mechanism, a quasi-solid-state route takes place with the help of micropore (0.48 nm) confinement, preventing the formation of long-chain polysulfides for excellent electrochemical performance. The obtained Na–S battery exhibits an outstanding initial reversible discharge specific capacity of 1395 mAh g−1 at 0.2C and still maintains a high capacity of 518 mAh g−1 after 500 cycles at 1.0C. The lychee seed-derived microporous carbon provides insights into sustainable and scalable host fabrication for high-performance sulfur-based batteries.