RT Na-S Batteries Research Articles

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.

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.

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.

Oxygen vacancy-mediated amorphous GeOx assisted polysulfide redox kinetics for room-temperature sodium-sulfur batteries

The practical applications of room-temperature sodium-sulfur (RT Na-S) batteries have been greatly hindered by the natural sluggish reaction kinetics of sulfur and the shuttle effect of sodium polysulfide (NaPSs). Herein, oxygen vacancy (OV)-mediated amorphous GeOx/nitrogen doped carbon (donated as GeOx/NC) composites were well designed as sulfur hosts for RT Na–S batteries. Experimental and density functional theory studies show that the introduction of oxygen vacancies on GeOx/NC can effectively immobilize polysulfides and accelerate the redox kinetics of polysulfides. Meanwhile, the micro-and mesoporous framework, acting as a reactor for storing active S, is conducive to alleviating the expansion of S during the charging/discharging process. Consequently, the S@GeOx/NC cathode affords a reversible capacity of 1017 mA h g−1 at 0.1 A g−1 after 100 cycles, outstanding rate capability of 333 mA h g−1 at 10.0 A g−1 and long lifespan cyclability of 385 mAh g−1 at 1 A g−1 after 1200 cycles. This work furnishes a new way for the rational design of metal oxides with oxygen vacancies and boosts the application for RT Na-S batteries.

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.

Effect of specifically-adsorbed polysulfides on the electron transfer kinetics of sodium metal anodes

Room-temperature sodium-sulfur (RT Na-S) batteries hold great promise for large-scale energy storage applications owing to the high energy density and earth-abundance of Na and S. However, the dissolution and migration of sodium polysulfides, uncontrollable Na dendrite growth, and the lack of studies on Na electrodeposition kinetics have hindered the development of these batteries. Herein, we reveal the mechanism of sodium polysulfides on the Na plating/stripping kinetics using a three-electrode system. First, the kinetic behavior deviates from the commonly supposed Butler–Volmer model, which is well described by the Marcus model. In addition, the specific adsorption of polysulfides on the sodium electrode surface is a key factor influencing the kinetics. Higher-order polysulfides (S82− and S62−) exhibit distinct specific adsorption behaviors because of their high adsorption energies compared to lower-order polysulfides (S42− and S22−). The electrostatic effect caused by specific adsorption can accelerate the kinetics, whereas the blocking effect can slow the kinetics. Thus, this competitive relationship enables low concentrations of high-order polysulfides to stimulate kinetics. This implies that a weak shuttle effect is beneficial for obtaining a stable Na deposition in RT Na-S batteries. An in-depth understanding of the Na electrodeposition kinetics provides beneficial clues for future metal sodium/electrolyte interface designs.

Nanostructure Engineering Strategies of Cathode Materials for Room-Temperature Na-S Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries are considered to be a competitive electrochemical energy storage system, due to their advantages in abundant natural reserves, inexpensive materials, and superb theoretical energy density. Nevertheless, RT Na-S batteries suffer from a series of critical challenges, especially on the S cathode side, including the insulating nature of S and its discharge products, volumetric fluctuation of S species during the (de)sodiation process, shuttle effect of soluble sodium polysulfides, and sluggish conversion kinetics. Recent studies have shown that nanostructural designs of S-based materials can greatly contribute to alleviating the aforementioned issues via their unique physicochemical properties and architectural features. In this review, we review frontier advancements in nanostructure engineering strategies of S-based cathode materials for RT Na-S batteries in the past decade. Our emphasis is focused on delicate and highly efficient design strategies of material nanostructures as well as interactions of component-structure-property at a nanosize level. We also present our prospects toward further functional engineering and applications of nanostructured S-based materials in RT Na-S batteries and point out some potential developmental directions.

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.

Mo2 N-W2 N Heterostructures Embedded in Spherical Carbon Superstructure as Highly Efficient Polysulfide Electrocatalysts for Stable Room-Temperature Na-S Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries are highly desirable for a sustainable large-scale energy-storage system due to their high energy density and low cost. Nevertheless, practical applications of RT Na-S batteries are still prevented by the shuttle effect of sodium polysulfides (NaPS), slow reaction kinetics of S, and incomplete conversion process of NaPS. Here, Mo2 N-W2 N heterostructures embedded in a spherical carbon superstructure (Mo2 N-W2 N@PC) are designed to efficiently suppress the "polysulfide shuttle" and promote NaPS redox reactions. The designed Mo2 N-W2 N@PC heterostructure with abundant heterointerfaces, high conductivity, and porosity can facilitate electron/ion diffusion and provide high catalytic activity for efficient NaPS conversion. The obtained Na-S battery delivers high reversible capacity with superior long-term cyclability (517 mAh g-1 at 1 A g-1 after 400 cycles) and unprecedented rate capability (417 mAh g-1 at 2 A g-1 ). Furthermore, the electrocatalysis mechanism is revealed by combining in situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), UV-vis spectra, and precipitation experiments. This work demonstrates a novel heterostructure design strategy that enables high-performance Na-S batteries.

Manipulating the Electronic Structure of Nickel via Alloying with Iron: Toward High-Kinetics Sulfur Cathode for Na–S Batteries

The sluggish conversion kinetics and severe shuttle effect in room-temperature Na-S (RT Na-S) batteries cause knotty issues, such as poor rate performance, fast capacity decay as well as low Coulombic efficiency, which seriously impede their practical application. Therefore, exploiting cost-effective and efficient electrocatalysts for absorbing soluble long-chain sodium polysulfides (NaPSs) and expediting NaPSs conversion is of paramount importance. Herein, catalyst mining is first conducted by density functional theory calculations, which reveal that the alloying of Fe into Ni can tailor the electronic structure, leading to lower reaction energy barrier for polysulfide conversion. Based on this, FeNi3@hollow porous carbon spheres (FeNi3@HC) as a promising sulfur host for RT Na-S batteries are rationally designed and fabricated. As expected, the S@FeNi3@HC cathode exhibits an excellent cycling stability (591 mAh g-1 after 500 cycles at 2 A g-1) and outstanding rate performance (383 mAh g-1 at 5 A g-1). Our work demonstrates an effective strategy (i.e., alloying strategy with a rich electron state) to design superior electrocatalysts for RT 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.

Layered-like structure of TiO2-Ti3C2 Mxene as an efficient sulfur host for room-temperature sodium-sulfur batteries

The ideal sulfur supporting material for room-temperature sodium-sulfur (RT-NaS) batteries would concurrently incorporate adsorption capabilities, and high-electrical conductivity, which are essential for improving cycling stability and crucial for enhancing cycling stability and implementation in large-scale applications. In this work, the layered-like structure of TiO2-Ti3C2 Mxene was prepared by a simple hydrothermal method. The prepared TiO2-Ti3C2 material possesses a better optimal structure, which showed the evenly dispersed TiO2 on the Ti3C2 (Ti3C2). The layered-like structure material combines the decrease of volume expansion and the high conductivity of Ti3C2. After being impregnated with sulfur, a significant specific capacity of 255.196 mA h/g was achieved after 1500 cycles at a 1 C-rate with a low-capacity decay. The layered-like structure of TiO2-Ti3C2 prepared by the hydrothermal method is an auspicious cathode material for RT-NaS batteries.

Dual-porosity carbon derived from waste bamboo char for room-temperature sodium-sulfur batteries using carbonate-based electrolyte

Room-temperature sodium-sulfur (RT Na-S) batteries have recently drawn a great deal of attention owing to their low cost and high theoretical energy density, making them promising energy storage systems. In this study, a dual-porosity carbon (DPC) matrix with oxygen-containing functional groups derived from waste bamboo char was synthesized by a facile chemical activation for RT Na-S batteries. A high initial discharge capacity of 1168 mAh g−1 at 0.1 C and a superior capacity retention of 320 mAh g−1 at 0.5 C over 600 cycles were obtained. The excellent electrochemical performances came from the unique porous structure and oxygen-containing functional groups of DPC. These properties combined physical and chemical methods to anchor polysulfides and further enhance the electrochemical performance. This study has great significance in terms of building a relationship between waste biomass and electrochemical materials, providing low-cost, green, and sustainable development of advanced energy materials in the future.

Ultrastable Sodium-Sulfur Batteries without Polysulfides Formation Using Slit Ultramicropore Carbon Carrier.

The formation of the soluble polysulfides (Na2Sn, 4 ≤ n ≤ 8) causes poor cycling performance for room temperature sodium–sulfur (RT Na–S) batteries. Moreover, the formation of insoluble polysulfides (Na2Sn, 2 ≤ n < 4) can slow down the reaction kinetics and terminate the discharge reaction before it reaches the final product. In this work, coffee residue derived activated ultramicroporous coffee carbon (ACC) material loading with small sulfur molecules (S2–4) as cathode material for RT Na–S batteries is reported. The first principle calculations indicate the space confinement of the slit ultramicropores can effectively suppress the formation of polysulfides (Na2Sn, 2 ≤ n ≤ 8). Combining with in situ UV/vis spectroscopy measurements, one‐step reaction RT Na–S batteries with Na2S as the only and final discharge product without polysulfides formation are demonstrated. As a result, the ultramicroporous carbon loaded with 40 wt% sulfur delivers a high reversible specific capacity of 1492 mAh g−1 at 0.1 C (1 C = 1675 mA g−1). When cycled at 1 C rate, the carbon–sulfur composite electrode exhibits almost no capacity fading after 2000 cycles with 100% coulombic efficiency, revealing excellent cycling stability and reversibility. The superb cycling stability and rate performance demonstrate ultramicropore confinement can be an effective strategy to develop high performance cathode for RT Na–S batteries.

Vanadium carbide nanoparticles incorporation in carbon nanofibers for room-temperature sodium sulfur batteries: Confining, trapping, and catalyzing

Room-temperature sodium-sulfur (RT Na-S) batteries have aroused extensive interest from researchers owing to the high theoretical volumetric energy density, nontoxicity and low-cost. However, poor conductivity of sulfur and high solubility of polysulfides in electrolyte are two major challenges for the practical application of the RT Na-S batteries. Herein, we report a three dimensional self-supported structure with Vanadium carbide (VC) nanoparticles embeddedin carbon nanofibers for RT Na-S batteries. Finally, the VC-CNFs@S electrode displays a reversible capacity of 379 mAh g−1 after 2000 cycles at 0.5C with a high capacity retention of 96.2%. Such outstanding electrochemical property is ascribed to the “confining – trapping – catalyzing” effect of VC-CNFs structure.

Cobalt nanoparticles embedded into free-standing carbon nanofibers as catalyst for room-temperature sodium-sulfur batteries

Room-temperature sodium-sulfur (RT Na-S) batteries are seriously limited because of poor conductivity of sulfur and sluggish reaction kinetics of polysulfide intermediates. Here, we design a free-standing film, constructed from Co nanoparticles onto nitrogen-doped porous carbon nanofibers (Co@NPCNFs), to load sulfur for RT Na-S batteries. Experiment result shows that Co as catalyst can enable the rapid sodium intercalation and fast reduction reaction of the polysulfides during cycling. Hence, the prepared Co@NPCNFs/S cathode exhibits a remarkable capacity of 906 mAh g−1 at 0.1 C and long cycling life up to 800 cycles with a slow capacity decay of 0.038% per cycle at 1 C.

Remedies for Polysulfide Dissolution in Room-Temperature Sodium-Sulfur Batteries.

Rechargeable room-temperature sodium-sulfur (RT-NaS) batteries represent one of the most attractive technologies for future stationary energy storage due to their high energy density and low cost. The S cathodes can react with Na ions via two-electron conversion reactions, thus achieving ultrahigh theoretical capacity (1672 mAh g-1 ) and specific energy (1273 Wh kg-1 ). Unfortunately, the sluggish reaction kinetics of the nonconductive S, severe polysulfide dissolution, and the use of metallic Na are causing enormous challenges for the development of RT-NaS batteries. Fatal polysulfide dissolution is highlighted, important studies toward polysulfide immobilization and conversion are presented, and the reported remedies in terms of intact physical confinement, strong chemical interaction, blocking layers, and optimization of electrolytes are summarized. Future research directions toward practical RT-NaS batteries are summarized.

Sulfur-Based Electrodes that Function via Multielectron Reactions for Room-Temperature Sodium-Ion Storage.

Emerging rechargeable sodium-ion storage systems-sodium-ion and room-temperature sodium-sulfur (RT-NaS) batteries-are gaining extensive research interest as low-cost options for large-scale energy-storage applications. Owing to their abundance, easy accessibility, and unique physical and chemical properties, sulfur-based materials, in particular metal sulfides (MSx ) and elemental sulfur (S), are currently regarded as promising electrode candidates for Na-storage technologies with high capacity and excellent redox reversibility based on multielectron conversion reactions. Here, we present current understanding of Na-storage mechanisms of the S-based electrode materials. Recent progress and strategies for improving electronic conductivity and tolerating volume variations of the MSx anodes in Na-ion batteries are reviewed. In addition, current advances on S cathodes in RT-NaS batteries are presented. We outline a novel emerging concept of integrating MSx electrocatalysts into conventional carbonaceous matrices as effective polarized S hosts in RT-NaS batteries as well. This comprehensive progress report could provide guidance for research toward the development of S-based materials for the future Na-storage techniques.

Sodium-Sulfur Batteries with a Polymer-Coated NASICON-type Sodium-Ion Solid Electrolyte

Summary The shuttling of dissolved sodium polysulfides through conventional porous separators has been a challenging issue with the development of room temperature sodium-sulfur (RT Na-S) batteries. In this study, a NASICON-type Na+-ion solid-electrolyte membrane, Na3Zr2Si2PO12, is used as a polysulfide-shield separator. However, as a general issue with solid-electrolyte batteries, the ionic interface between the Na-metal anode and the Na-ion conduction Na3Zr2Si2PO12 membrane is fairly poor. To address this problem, a critical approach by coating a layer of a polymer that exhibits intrinsic nanoporosity (PIN) onto the Na3Zr2Si2PO12 membrane has been developed. The PIN coating greatly improves the ionic interfacial properties between the Na anode and the Na3Zr2Si2PO12 membrane. RT Na-S batteries with a PIN-coated Na3Zr2Si2PO12 solid-electrolyte separator show enhanced cycle life.

CNF/S Cathodes for RT Na-S Batteries in Carbonate Electrolyte: Understanding the Role of Sulfur Phase and Solid Electrolyte Interphase

Over the last few years, there is growing interest towards safe and stable room temperature sodium-sulfur batteries owing to their high theoretical capacity and energy density of ~1672 mAh/g and 1230 Wh/kg respectively based on the final discharge product of Na2S. However, these Na-S batteries exhibit poor cycling properties mainly due to severe shuttle effect. Sulfur cathodes with various nanostructured carbon have been introduced to achieve long-term cycling. However, that these advances are partially due to the use of a non-carbonate solvent-based ethereal electrolytes, and the additive NaNO3 salt, in which the solubility of polysulfides is reduced or the polysulfide shuttle is passivated. Given the high flammability of ether-based electrolytes, such systems are not practically viable. Moreover, the conversion of sulfur to Na2S/Na2S2 in these reports is unclear. In this work, we have developed free-standing carbon nanofiber/S cathodes for achieving long-term cycling in RT Na-S batteries. The as-prepared CNF/S (~1.08 mg/cm2, 43.8 wt% S) cathodes were used directly as cathodes in 2032 type coin sized RT Na-S cells. The electrochemical tests were performed in EC/PC/FEC based electrolyte against Na/Na+ anode. The cyclic voltammetry and charge discharge results showed a single potential for conversion of sulfur to Na2S. The CNF/S cathodes delivered capacity of ~1229 mAh/g during the first cycle with ~51.1% coulombic efficiency. The capacity of RT Na-S cells was stabilized at ~350 mAh/g after Ist cycle and sustained up to 300 cycles with only ~.03% decay rate per cycle. The postmortem XRD results confirmed the conversion of sulfur to Na2S and vice versa. Further, we performed in situ electrochemical impedance spectroscopy, postmortem XPS and galvanostatic intermittent titration technique (GITT) to understand the underlaying conversion mechanism. The preliminary results showed that the observed single plateau and long term cycling of RT Na-S cells were the convoluted effect of deposited sulfur and stable SEI layer on the cathode side. #RP and AS have contributed equally