Temperature Sodium-sulfur Batteries Research Articles

A highly-efficient electrocatalyst for room temperature sodium-sulfur batteries: assembled nitrogen-doped hollow porous carbon spheres decorated with ultrafine α-MoC1-x nanoparticles

While room-temperature sodium-sulfur (RT Na-S) battery is considered one of the most promising technologies for next-generation energy storage, its commoditization is constrained by the shuttling and sluggish redox kinetics of the sulfur electrode. Herein, a honeycomb-like sulfur electrocatalyst with ultrafine α-MoC1-x nanoparticles uniformly distributed on nitrogen-doped hollow porous carbon spheres (MoC@NHC) is designed and synthesized. Prepared through a template-assisted strategy followed by a self-assembly and pyrolysis process, the interconnected hollow porous structure of MoC@NHC provides not only a microenvironment for confinement of sodium polysulfides (NaPSs) but also sufficient free space for accommodation of volume change during electrochemical cycling. Moreover, the polar α-MoC1-x nanoparticles coupled with N-doped carbon provides strong affinity to NaPSs and promote catalytic conversion of NaPSs, as confirmed by experimental results and theoretical calculations. Owing to the physical and chemical dual confinement effect and the fast conversion kinetics of NaPSs, the S/MoC@NHC-15 cathode demonstrates good rate performances (351.8 mAh g−1 at 10 C) and outstanding cyclability (retaining capacities of 418.4 and 312.6 mAh g−1 after 1000 cycles at 1 and 5 C, respectively). This study introduces a simple and effective method for fabrication of S/MoC@NHC cathode materials for high-performance RT Na-S batteries.

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.

Polydopamine as an interfacial layer to enhance mechanical and adhesive properties of the active materials in a sulfur cathode of sodium-sulfur batteries

Room temperature sodium-sulfur (Na-S) batteries are promising devices for energy storage system, but for practical applications volume expansion and detrimental shuttle effect of the sulfur cathode should be solved. Herein, we introduced a novel sulfur cathode system of using polydopamine (PDA) as an interlayer in between sulfurized polyacrylonitrile (SPAN) active material and pullulan-graft-sodium polyacrylic acid (PuA) binder. Active NH and OH functional groups of PDA interlayer serve as facile hydrogen bonding (H bonding) and/or chemical reaction sites to various functional groups of SPAN and PuA, thus forming an intimately packed SPAN/PDA/PuA composite with sufficient mechanical and interfacial adhesive strengths to survive from the dimensional variation of sulfur cathode during charge/discharge cycling. Moreover, various functional groups of the SPAN/PDA/PuA are capable of absorbing polysulfides to limit the shuttle effect. Sulfur cathode derived from SPAN/PDA/PuA exhibited a high specific capacity of 1340 mAh g−1 after 100 cycles at 0.2 C. Without the PDA interlayer, sulfur cathode derived from SPAN/PuA exhibits a much lower capacity of 790 mAh g−1. The role of PDA in promoting the stability and electrochemical performance of sulfur cathode is thus verified in this study.

A Review on the Construction of Carbon-Based Metal Compound Composite Cathode Materials for Room Temperature Sodium-Sulfur Batteries.

Room temperature sodium-sulfur batteries are one of the most attractive energy storage systems due to their low cost, environmental friendliness, and ultra-high energy density. However, due to the inherent slow redox kinetics and the shuttle of polysulfides, the road of room temperature sodium-sulfur batteries to practical application is still full of difficulties. As a sulfur cathode, which is directly related to battery performance, a lot of research efforts have been devoted to it and many strategies have been proposed to solve the shuttle effect problem of sulfur cathodes. This paper analyzes the existing problems and solutions of sodium-sulfur batteries, mainly discusses and summarizes the research progress of constructing carbon-based cathode materials for sodium-sulfur batteries, and expounds the current research popular from two main directions. That is to construct advanced cathode materials based on two mechanisms of adsorption and electrocatalysis. Finally, the research direction of advanced sodium-sulfur batteries is prospected.

Electrocatalysis in Room Temperature Sodium-Sulfur Batteries: Tunable Pathway of Sulfur Speciation.

Benefiting from the merits of natural abundance, low cost, and ultrahigh theoretical energy density, the room temperature sodium-sulfur (RT NaS) batteries are regarded as one of the promising candidates for the next-generation scalable energy storage devices. However, the uncontrollable sulfur speciation pathways severely hinder its practical applications. Recently, various strategies have been employed to tune the conversion pathways of sulfur, such as physical confinement, chemical inhibition, and electrocatalysis. Herein, the recent advances in electrocatalytic effects manipulate sulfur speciation pathways in advanced RT NaS electrochemistry are reviewed, including the promotion of the nearly full conversion of long-chain polysulfides, short-chain polysulfides, and small sulfur molecules. The underlying catalytic modulation mechanism that fundamentally tunes the electrochemical pathway of sulfur species is comprehensively summarized along with the design strategies for catalytic active centers. Furthermore, the challenge and potential solutions to realize the quasi-solid conversion of sulfur are proposed to accelerate the real application of RT NaS batteries.

Covalent encapsulation of sulfur in a graphene/N-doped carbon host for enhanced sodium-sulfur batteries

Application of emerging room temperature sodium-sulfur (RT Na-S) battery is restrained by the poor conductivity, volume expansion of sulfur cathode and the shuttle effect of soluble polysulfides in electrolytes. Herein, an N-doped two-dimensional (2D) carbon host was derived from the polydopamine coated graphene for sulfur storage. Different from the conventional used melt-diffusion method to integrate sulfur on graphene layer physically, we employed a vapor-infiltration method to realize the homogenous incorporation of sulfur in the graphene-based host via C-Sx-C bond. A polydopamine-derived N-doped carbon layer was further coated on graphene to confine the high-temperature-induced gas-phase sulfur, which effectively increase the covalently bonded sulfur content in the host. Moreover, based on Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) measurement, the C-S bonds are mainly formed beside N-doped carbon, being well explained by the stronger interaction between N-doped carbon and S4 (sulfur vapor) than that of pure carbon from density functional theory (DFT) calculation results. When tested as a cathode for RT Na-S battery, the obtained N-doped graphene/sulfur cathode shows superior cycle stability.

Challenge and Strategies in Room Temperature Sodium-Sulfur Batteries: A Comparison with Lithium-Sulfur Batteries.

Metal-sulfur batteries exhibit great potential as next-generation rechargeable batteries due to the low sulfur cost and high theoretical energy density. Sodium-sulfur (Na-S) batteries present higher feasibility of long-term development than lithium-sulfur (Li-S) batteries in technoeconomic and geopolitical terms. Both lithium and sodium are alkali metal elements with body-centered cubic structures, leading to similar physical and chemical properties and exposing similar issues when employed as the anode in metal-sulfur batteries. Indeed, some inspiration for mechanism researches and strategies in Na-S systems comes from the more mature Li-S systems. However, the dissimilarities in microscopic characteristics determine that Na-S is not a direct Li-S analogue. Herein, the daunting challenges derived by the differences of fundamental characteristics in Na-S and Li-S systems are discussed. And the corresponding strategies in Na-S batteries are reviewed. Finally, general conclusions and perspectives toward the research direction are presented based on the dissimilarities between both systems. This review attempts to provide important insights to facilitate the assimilation of the available knowledge on Li-S systems for accelerating the development of Na-S batteries on the basis of their dissimilarities.

A High-Efficiency Mo2 C Electrocatalyst Promoting the Polysulfide Redox Kinetics for Na-S Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries, as promising next-generation energy storage candidates, are drawing more and more attention due to the high energy density and abundant elements reserved in the earth. However, the native downsides of RT Na-S batteries (i.e., enormous volume changes, the polysulfide shuttle, and the insulation and low reactivity of S) impede their further application. To conquer these challenges, hierarchical porous hollow carbon polyhedrons embedded with uniform Mo2 C nanoparticles are designed deliberately as the host for S. The micro- andmesoporous hollow carbon indeed dramatically enhances the reactivity of the S cathodes andaccommodates the volume changes. Meanwhile, the highly conductive dispersed Mo2 C has a strong chemical adsorption to polysulfides and catalyzes the transformation of polysulfides, which can effectively inhibit the dissolution of polysulfides and accelerate the reaction kinetics. Thus, the as-prepared S cathode can display a high reversible capacity (1098 mAh g-1 at 0.2 A g-1 after 120 cycles) and superior rate performance (483 mAh g-1 at 10.0 A g-1 ). This work provides a new method to boost the performance of RT Na-S batteries.

A flexible, ceramic-rich solid electrolyte for room-temperature sodium-sulfur batteries.

A sodium superionic conductor, Na3Zr2Si2PO12 (NZSP) ceramic, is a promising solid electrolyte (SE) and holds the potential to solve the safety and energy density problems of several sodium-based batteries. In particular, in room temperature sodium-sulfur (RT Na/S) batteries, the use of SEs can solve polysulfide shuttle effects. A significant challenge in the commercialization of NZSP is producing the ceramic in a thin and flexible form. Herein, we report a method to produce a thin (<250 μm thickness) and flexible "polymer in ceramic" type sodium ion conductor film from the erstwhile brittle ceramic film and demonstrate its application in RT Na/S batteries.

Potassium hydroxide activated carbon derived from albumen as an efficient sulfur host for room temperature sodium-sulfur batteries

The room temperature sodium–sulfur (RT/NaS) battery provides a potential energy storage technology with high theoretical capacity and low cost. However, the gap between its practical performance and theoretical expectation confines its comprehensive implementation. In this work, a simple annealing process successfully synthesized a hierarchical micro/mesoporous egg carbon with KOH activation (ECK) from albumen as sulfur hosting for RT/NaS batteries. KOH activation plays a vital role in enhancing conductivity, surface area, and porosity. Elemental sulfur was loaded to the ECK through simple heat evaporation to form an ECK@S composite. Even at the high rate of 1 C, the discharge capacity of the ECK@S electrode reached 473 mAh/g and maintained 202 mAh/g after 800 cycles, representing an outstanding performance. Therefore, preparing micro/mesoporous egg carbon by KOH activation creates a promising electrode material for RT/NaS batteries.

Biomass Based Porous Carbons As Cathode's Component for Room Temperature Sodium Sulfur Battery

Porous carbons originated from microalgae powder, were synthesized using a hydrothermal carbonization followed by the chemical-activation process. Porous carbons are the used as cathode's components with sulfur for Sodium Sulfur (NaS) Batteries. the presence of the carbons in the composites can increase the electrical conductivity and assist the sodium ion transfer in the cell since it can allow the electrolyte to permeate easily. The micropores (<2 nm) of porous carbons are the main sulfur host and help to adsorb the small sulfur molecules , so it can improve the electrochemical performance of carbon-sulfur composites as cathodes for NaS batteries at room temperature. The porous carbons can form more actives site that improves the electrical conductivity and prevent the shuttle effect of polysulfide The composite cathodes can give a high initial discharge capacity of 1267 mAh g−1 at 0.1 C and a superior capacity retention of 267 mAh g−1 after 100 cycles at 1 C. This study suggest that microalgae can be used in the application of the room temperature NaS battery.

Low Temperature Sodium-Sulfur Battery Enabled By Superior Molten Na Wettability

Sodium based batteries are inexpensive and widely available, making it a promising candidate grid energy storage application. Particularly, high temperature molten sodium batteries, such as sodium–sulfur (NaS) and sodium–metal halide (ZEBRA) batteries, have received increasing attentions, where the enormous capacity demand of grid storage will require the natural abundance of raw materials and a reasonable footprint of the facility. NaS batteries use molten sulfur/polysulfides as the cathode material and operate typically at 350 °C.Although operating at higher temperatures, the state-of-art high-temperature NaS batteries offer high system level energy and long-life expectancy (over 10 years) all at a low cost of materials.In fact, conventional high-temperature molten NaS batteries have already been in production and widely implemented as test units for grid storage or for supplementing wind and solar installations. Despite of its longevity and high energy density, NaS battery technology still faces tremendous challenges for further the market penetration due to their safety concerns and high cost. Reducing the operating temperatures of molten NaS batteries would retard the severity of discharge from cell failures and make them safer. Moreover, lower temperatures allow the integration of cost-effective polymer materials as seals, replacing more expensive techniques used for NaS batteries in the past. Improving sodium wetting by engineering the β"-Al2O3 solid-state electrolytes (BASE)-anode interface is one of the most important topics for lowering the operating temperature of NaS battery. In here, we present a new surface treatment method to greatly improve the Na wettability on surface of BASE, and report that the performance of low-temperature (<150 °C) NaS battery is drastically improved in both capacity and stability. Innovations in surface modification boost the interfacial activity of BASE even further at lower operating temperature and make NaS battery more competitive in the upcoming challenges in grid energy storage applications.

Regulating the Deposition of Insoluble Sulfur Species for Room Temperature Sodium-Sulfur Batteries

Regulating the Deposition of Insoluble Sulfur Species for Room Temperature Sodium-Sulfur Batteries

A sodium bis(perfluoropinacol) borate-based electrolyte for stable, high-performance room temperature sodium-sulfur batteries based on sulfurized poly(acrylonitrile)

Sodium bis(perfluoropinacol)borate, NaB[O2C2(CF3)4]2 (Na-PPB), as part of the electrolyte is introduced to room temperature (RT) sodium-sulfur batteries based on a sulfurized poly(acrylonitrile) (Na-SPAN) cathode. Na-PPB was stable under atmospheric conditions for 20 days and showed no sign of degradation. Na-SPAN full cells based on a Na-PPB electrolyte demonstrated excellent oxidation stability against various current collectors and delivers a high discharge capacity of >950 mAh/gsulfur with 100 % coulombic efficiency over 500 cycles.

Sulfur encapsulation into yolk-shell Fe2N@nitrogen doped carbon for ambient-temperature sodium-sulfur battery cathode

Room temperature sodium-sulfur (RT-Na-S) battery represents an advanced energy storage technology because of low cost and large theoretical energy density. However, RT-Na-S battery technology is facing severe challenges such as dissolution of sodium polysulfide, loss of active material on the surface of anode, serious shuttle effect and poor cycle stability. Herein, we synthesis hollow polar iron nitride nanoparticle encased N-doped carbon yolk shell (YS-Fe2N@NC) as sulfur carrier. The synergistic effect of YS-Fe2N@NC as well as wide void can be effectively trap polysulfides and improve the conductivity of sulfur-based cathode. The reversible reaction mechanism of Na-S battery is studied by in/ex-situ characterizations, catalytic behaviour of YS-Fe2N@NC and Density functional theory (DFT) calculations. The as made S/YS-Fe2N@NC composite exhibit promising specific capacity of 1123 mAh g−1 at the rate of 1C for the initial cycle, good rate capability (845 mAh g−1 at 2C) and ultra-stable cycling performance with an ultra-low capacity decay of 0.0724% per cycle. The present work highlights the importance of introducing the Fe2N to catalyse the conversion reactions of polysulfide within NC shell for boosting the RT-Na-S battery in term of high storage capacity, rate capability and stability.

Role of Catalytic Materials on Conversion of Sulfur Species for Room Temperature Sodium–Sulfur Battery

Room temperature sodium–sulfur (RT Na‐S) battery with high theoretical energy density and low cost has spurred tremendous interest, which is recognized as an ideal candidate for large‐scale energy storage applications. However, serious sodium polysulfide shutting and sluggish reaction kinetics lead to rapid capacity decay and poor Coulombic efficiency. Recently, catalytic materials capable of adsorbing and catalyzing the conversion of polysulfides are profiled as a promising method to improve electrochemical performance. In this review, the research progress is summarized that the application of catalytic materials in RT Na‐S battery. For the role of catalyst on the conversion of sulfur species, specific attention is focused on the influence factors of reaction rate during different redox processes. Various catalytic materials based on lightweight and high conductive carbon materials, including heteroatom‐doped carbon, metals and metal compounds, single‐atom and heterostructure, promote the reaction kinetic via lowered energy barrier and accelerated charge transfer. Additionally, the adsorption capacity of the catalytic materials is the key to the catalytic effect. Particular attention to the interaction between polysulfides and sulfur host materials is necessary for the exploration of catalytic mechanism. Lastly, the challenges and outlooks toward the desired design of efficient catalytic materials for RT Na‐S battery are discussed.

Towards high performance room temperature sodium-sulfur batteries: Strategies to avoid shuttle effect

Room temperature sodium-sulfur battery has high theoretical specific energy and low cost, so it has good application prospect. However, due to the disadvantageous reaction between soluble intermediate polysulfides and sodium anode, the capacity drops sharply, which greatly limits its practical application. In recent years, various strategies have been formulated to address the problem of polysulfides dissolution. This perspective article provides an overview of the research progress on research progress of novel cathode materials, multifunctional host, new electrolyte systems and modified separator/interlayer/anode. The challenge and prospect of the advanced strategies to suppress the polysulfides shuttle for long-life and high-efficiency room temperature sodium-sulfur batteries are proposed.

Mechanistic Insights into Interactions of Polysulfides at VS2 Interfaces in Na-S Batteries: A DFT Study.

Room temperature sodium-sulfur (Na-S) batteries, because of their high theoretical energy density and low cost, are considered as a promising candidate for next-generation energy storage devices. However, the practical utilization of the Na-S batteries is greatly hindered by various deleterious factors such as dissolution of sodium polysulfides (Na2Sn) into the electrolyte commonly termed as "shuttle effect," sluggish decomposition of solid Na2S, and poor electronic conductivity of sulfur. To overcome the challenges, we introduced single-layer vanadium disulfide (VS2) as an anchoring material (AM) to immobilize higher-order polysulfides from the dissolution and also to accelerate the otherwise sluggish kinetics of insoluble short-chain polysulfides. We employ density functional theory (DFT) calculations to elucidate the Na2Sn interactions at the VS2 interfaces. We show that the adsorption strengths of various Na2Sn species on the VS2 basal plane are adequate (1.21-4.3 eV) to suppress the shuttle effect, and the structure of Na2Sn are maintained without any decomposition, which is necessary to mitigate capacity fading. The calculated projected density of states (PDOS) reveals that the metallic character of the pristine VS2 is retained even after Na2Sn adsorption. The calculated Gibbs free energy of each elementary sulfur reduction reaction indicates a significant decrement in the free energy barrier due to the catalytic activity of the VS2 surface. Furthermore, VS2 is found to be an excellent catalyst to significantly reduce the oxidative decomposition barrier of Na2S, which facilitates accelerated electrode kinetics and higher utilization of sulfur. Overall, VS2 with strong adsorption behavior, enhanced electronic conductivity, and improved oxidative decomposition kinetics of polysulfides can be considered as an effective AM to prevent the shuttle effect and to improve the performance of Na-S batteries.

Metal-Organic Frameworks-Derived Nitrogen-Doped Porous Carbon Nanocubes with Embedded Co Nanoparticles as Efficient Sulfur Immobilizers for Room Temperature Sodium-Sulfur Batteries.

Room temperature sodium-sulfur (RT Na-S) batteries are considered a promising candidate for energy-storage due to their high energy-density and low-cost. However, the shutting effect of polysulfides and sluggish kinetics of sulfur redox reactions still severely limit their practical implementation. Herein, a new type of 3D hierarchical porous carbonaceous nanocubes is reported as efficient sulfur hosts, composed of carbon nanotubes (CNT) and Co nanoparticles (NPs) uniformly embedded into a nitrogen-doped carbon matrix (NC). Because of the high specific surface area, large degree of graphitization, and the synergetic effects between Co NPs and N-doping, the as-designed CNTs/Co@NC electrodes not only significantly increase polysulfides immobilization, but also efficiently catalyze sulfur redox reactions, as confirmed by experimental results and DFT calculations. When tested in a RT Na-S battery, the S@CNTs/Co@NC-0.25 cathode demonstrates outstanding electrochemical performance, achieving high initial specific capacity of 1200.3mAhg-1 at 0.1C, remarkable rate capability up to 5.0C (474.2mAhg-1 ), and superior cyclic performance of 450.5mAhg-1 (292mAhg-1 ) after 400 cycles at 1.0C (5.0C). The integration of a 3D hierarchical porous architecture with well-dispersed Co NPs of an electro-catalyst provides valuable insights based on structure-adsorption-catalysis engineering for advanced RT Na-S batteries.

Multi-channel sulfurized polyacrylonitrile with hollow structure as cathode for room temperature sodium–sulfur batteries

Sulfurized polyacrylonitrile (SPAN) has been comprehensively studied as a promising electrode material for sodium–sulfur batteries. However, problems such as low capacity and poor cycle stability still exist in room temperature sodium–sulfur batteries (RT-Na/S batteries). Here, a multi-channel sulfurized polyacrylonitrile (MSPAN) with hollow structure prepared by electrospinning technology was combined with polystyrene (PS) acting as a pore-forming agent, which not only provided a larger specific surface area and enlarged contact between electrode and electrolyte, but also limited the shuttling of polysulfides effectively, thereby improving the reversible specific capacity and rate performance of the electrodes. Through comparing the electrochemical performances of MSPAN on different current collectors, it was found that copper foil as the current collector favored the electrochemical performances of the materials. As a result, the MSPAN-2 used as the cathode for RT-Na/S batteries exhibited a high discharge specific capacity of 314.2 mAh g−1 at a current density of 2 ​A ​g−1. The fabrication of MSPAN provides a good example for improving the electrochemical performance of RT-Na/S batteries.