Room-temperature Sodium Sulfur Research Articles

Achieving a Quasi‐Solid‐State Conversion of Polysulfides via Building High Efficiency Heterostructure for Room Temperature Na–S Batteries

AbstractThe practical application of room temperature sodium–sulfur (RT Na–S) batteries are prevented by the sulfur insulation, the severe shuttling effect of high‐order sodium polysulfides (Na2Sn, 4 ≤ n ≤ 8), and the sluggish reaction kinetics. Therefore, designing an ideal host material to suppress the polysulfides shuttle process and accelerate the redox reactions of soluble NaPSs to Na2S2/Na2S is of paramount importance for RT Na–S batteries. Here, a quasi‐solid‐state transformation of NaPSs is realized by building high efficiency MoC‐W2C heterostructure in freestanding multichannel carbon nanofibers via electrospinning and calcination methods (MoC‐W2C‐MCNFs). The multichannel carbon nanofibers are interlinked micro‐mesoporous structures that can accommodate volume change of electrode materials and confine the entire redox process of NaPSs (restraining the polysulfides shuttle process). Meanwhile, the MoC‐W2C heterostructure with abundant heterointerfaces can facilitate electron/ion transport and accelerate conversion of NaPSs. Consequently, the S/MoC‐W2C‐MCNFs cathode delivers a high capacity of 640 mAh g−1 after 500 cycles at 0.2 A g−1 and an excellent reversible performance of 200 mAh g−1 after ultralong 3500 cycles at 4 A g−1. What's more, the heterostructure catalytic mechanism (a quasi‐solid‐state transformation) is proposed and confirmed in carbonate electrolyte by combining experimentally and theoretically.

Heterostructured Co/CeO2-Decorating N-Doped Porous Carbon Nanocubes as Efficient Sulfur Hosts with Enhanced Rate Capability and Cycling Durability toward Room-Temperature Na-S Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries have gained significant interest thanks to their satisfactory energy density and abundant earth resources. Nevertheless, practical implementations of RT Na-S batteries are still impeded by serious shuttle effects of sodium polysulfide (NaPS) intermediates, sluggish redox kinetics of cathodes, and poor electronic conductivity from S-species. To solve these problems, heterostructured Co/CeO2-decorating N-doped porous carbon nanocubes (Co/CeO2-NPC) are constructed as a S support, which integrates the strong adsorption and fast conversion of NaPSs, together with superior electronic conductivity. Consequently, the as-synthesized S@Co/CeO2-NPC cathode for RT Na-S batteries exhibits improved rate performance (1275, 561.1, and 485 mAh g-1 at 0.1, 5, and 10 C, respectively) and superior cyclic durability (capacity degeneration of 0.027% per cycle after 1000 cycles at 5 C). Such a S cathode combining a heterostructure interface, hierarchical porous carbon nanocubes, and polar compositions can considerably increase electronic conductivity and promote NaPS adsorption and conversion, achieving superior performance toward RT Na-S batteries.

A Mott-Schottky Heterojunction with Strong Chemisorption and Fast Conversion Effects for Room-Temperature Na-S Batteries.

The practical application of the room-temperature sodium-sulfur (RT Na-S) batteries is currently limited by low reversible capacity and serious capacity decay due to the sluggish reaction kinetics and shuttle effect. It is necessary to design a suitable sulfur host integrated with electrocatalysts to realize effective chemisorption and catalysis of sodium polysulfides (NaPSs). Herein, under the guidance of theoretical calculation, the Mott-Schottky heterojunction with a built-in electric field composed of iron (Fe) and iron disulfide (FeS2) components anchored on a porous carbon matrix (Fe/FeS2-PC) is designed and prepared. The enhanced chemisorption effect of Fe, the fast electrocatalytic effect of FeS2, and the fast transfer effect of the built-in electric field within the Fe/FeS2 heterojunction in the cathode of RT Na-S batteries work together to effectively improve the electrochemical performance. As a result, the Fe/FeS2-PC@S cathode exhibits high reversible capacity (815 mAh g-1 after 150 cycles at 0.2 A g-1) and excellent stability (516 mAh g-1 after 600 cycles at 5 A g-1, with only 0.07% decay per cycle). The design of the Fe/FeS2 heterojunction electrocatalyst provides a new strategy for the development of highly stable RT Na-S batteries.

Defect engineering of a TiO2 anatase/rutile homojunction accelerating sulfur redox kinetics for high-performance Na-S batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries have the drawbacks of the poor shuttle effect of soluble sodium polysulfides (NaPSs) as well as slow sulfur redox kinetics, which result in poor cycling stability and low capacity, seriously affecting their extensive application. Herein, defect engineering is applied to construct rich oxygen vacancies at the interface of a TiO2 anatase/rutile homojunction (OV-TRA) to enhance sulfur affinity and redox reaction kinetics. Combining structural characterizations with electrochemical analysis reveals that OV-TRA well alleviates the shuttle effect of NaPSs and precipitates the deposition and diffusion kinetics of Na2S. Consequently, S/OV-TRA provides excellent electrochemical performance with a reversible capacity of 870 mA h g-1 at 0.1 C after 100 cycles and a long-term cycling capability of 759 mA h g-1 at 1 C after 1000 cycles. This work provides an effective interfacial defect engineering strategy to promote the application of metal oxides in RT Na-S batteries.

Mechanism and Kinetics of Na2Sx (x ≤ 2) Precipitation in Sodium-Sulfur and Sodium/(Oxygen)-Sulfur Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries have attracted ever-increasing attention because of their enhanced energy density and low price. Although the performance of RT Na-S batteries is obtained in many other research, the basic mechanism and kinetics have not involved yet, especially in discharge product growth, which affects electrochemical performance. Meanwhile, designed additional redox activities (in the presence of oxygen) could simultaneously suppress sodium polysulfide shuttling and enhance energy density according to our group reported. However, the kinetic study of the intermediate has not been explored. In this work, we discussed the deposition of low-order sodium polysulfide (Na2Sx, x ≤ 2) in different potentials and types of glyme-solvents in Na-S and Na/(O2)-S system. The results show that the morphology of deposition Na2Sx (x ≤ 2) is affected by interfacial energy barrier controlled by overpotentials and the radius of sodium ions, which produced the precipitation of particle shape rather than film. Potentiostatic experiments show the kinetics are elevated in the presence of oxygen. In addition, the exchange current density of different sodium polysulfides was studied. The high-order sodium polysulfide has a lower exchange current density than that of low-order sodium polysulfide in Na-S system, requiring greater driving force, while transformation of the intermediate from high-order oxy-sulfur to low-order oxy-sulfur species require less impulse in Na/(O2)-S systems. This paper provides new understandings of the deposition mechanism and kinetics of Na2Sx (x ≤ 2) Na-S and Na/(O2)-S system in and to choose the appropriate solvent and potential.

Altering Na-ion solvation to regulate dendrite growth for a reversible and stable room-temperature sodium–sulfur battery

Theoretical calculation reveals that the additive (BiI3) changes the local solvation shell dynamics and improves the Na ion kinetics by reducing binding energy. In addition, the formation of an alloy interphase realizes a dendrite-free deposition.

3D Flower-like Nanospheres Constructed by Transition Metal Telluride Nanosheets as Sulfur Immobilizers for High-Performance Room-Temperature Na-S Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries hold immense promise as next-generation energy storage systems, owing to their exceptionally high theoretical capacity, abundant resources, eco-friendliness, and affordability. Nevertheless, their practical application is impeded by the shuttling effect of sodium polysulfides (NaPSs) and sluggish sulfur redox kinetics. In this study, an advanced strategy by designing 3D flower-like molybdenum telluride (MoTe2) as an efficient catalyst to promote sulfur redox for RT Na-S batteries is presented. The unique 3D flower-like MoTe2 effectively prevents NaPS shuttling and simultaneously offers abundant active catalytic sites facilitating polysulfide redox. Consequently, the obtained MoTe2/S cathode delivers an outstanding initial reversible capacity of 1015mAhg-1 at 0.1C, along with robust cycling stability of retaining 498mAhg-1 at 1C after 500 cycles. In addition, pouch cells are fabricated with the MoTe2 additive to deliver an ultrahigh initial discharge capacity of 890mAhg-1 and remain stable over 40 cycles under practically necessary conditions, demonstrating the potential application in the commercialization of RT Na-S batteries.

Chemically tuned nitrogen-doped sulfur host for a reversible and stable room-temperature sodium-sulfur batteries

The fast transition of long-chain polysulfide to short-chain polysulfide causes a sharp decay in the performance of room-temperature sodium sulfur (RT-Na/S) batteries. The nitrogen-doped sulfur host is identified as effective in slowing the transition process by entrapping the sodium polysulfide. However, precise control over the amount of nitrogen remained a challenge. We report a chemical route to fine-tune nitrogen doping in the sulfur host. The nitrogen content in the sulfur host is identified to vary from 7 to 19 at. % by varying the reaction time from 4 to 12 h. The optimized reaction time of about 8 h results in the highest pyridinic and pyrrolic nitrogen content. In addition to nitrogen doping, the sulfur host with a hierarchical pore structure could be achieved with 8 h of reaction time. The as-developed sulfur host serves as a sulfur cathode and is used to fabricate an RT-Na/S battery. The cell could function stably for over 500 cycles at 1C, with a high Coulombic efficiency of ~99.5 % and a capacity decay of 0.28 mAh g−1 per cycle at 1C. The cell could function reversibly and stably at various C-rates (0.2C – 2C). This study paves a path for the researcher to revisit the design of the sulfur host to construct a stable cathode for RT-Na/S batteries.

Encapsulation of sulfur in MoS2-modified metal-organic framework-derived N, O-codoped carbon host for sodium–sulfur batteries

Room-temperature sodium–sulfur batteries (RT Na-S) are promising energy storage systems with high energy densities and low costs. Nevertheless, drawbacks, including the limited cycle life and sluggish redox kinetics of sodium polysulfides, hinder their implementation. Herein, a heterostructure of MoS2 nanosheets coated on a metal–organic framework (MOF)-derived N, O-codoped flower-like carbon matrix (NOC) was designed as a sulfur host for advanced RT Na-S batteries. The NOC@MoS2 hierarchical host provided a sufficient space to guarantee a high sulfur loading and confinement for the volume expansion of sulfur during the charge/discharge process. According to first-principle calculations, the NOC@MoS2 composite exhibited metallic conductivity because electronic states crossed the Fermi level, which indicates that the introduction of NOC significantly improved the electronic conductivity of MoS2. Furthermore, electron transfer from MoS2 to the O-doped carbon sites was observed owing to the strong electronegativity of O, which can effectively increase the Lewis acidity of MoS2 and weaken the sodium–sulfur bonds in sodium polysulfides after adsorption on the cathode, leading to reductions in the Na2S dissociation energy barrier and Gibbs free energy for the rate-limiting step of the sulfur reduction process. Therefore, with the synthetic effects of MoS2 and N, O-codoped carbon, the obtained cathode exhibited a superior electrochemical performance.

P-doped porous carbon from camellia shell for high-performance room temperature sodium–sulfur batteries

Room-temperature sodium–sulfur batteries are still hampered by severe shuttle effects and sluggish kinetics. Most of the sulfur hosts require high cost and complex synthesis process. Herein, a facile method is proposed to prepare a phosphorous doped porous carbon (CSBP) with abundant defect sites from camellia shell by oxidation pretreatment combined with H3PO4 activation. The pretreatment can introduce pores and adjust the structure of biochar precursor, which facilitates the further activation of H3PO4 and effectively avoids the occurrence of large agglomeration. Profiting from the synergistic effects of physical confinement and doping effect, the prepared CSBP/S cathode delivers a high reversible capacity of 804 mAh g−1 after 100 cycles at 0.1 C and still maintains an outstanding capacity of 458 mAh g−1 after 500 cycles at 0.5 C (1 C = 1675 mA g−1). This work provides new insights into the rational design of the microstructures of carbon hosts for high-performance room temperature sodium–sulfur batteries.

Engineering CoMoO4 in reduced graphene oxide as superior cathode hosts for advanced room-temperature sodium-sulfur batteries

Promising room-temperature sodium-sulfur (RT Na-S) battery systems rely on purposely designed high-performing and low-cost electrode materials. Nevertheless, there are the challenges of irreversible dissolution and slow redox kinetics of NaPSs in the complete discharge of sulfur capacity. Herein, engineered CoMoO4 in reduced graphene oxide (CoMoO4@rGO) is reported as a class of superior cathode hosts for RT Na-S batteries. The CoMoO4@rGO matrix is designed to facilitate the reversible sodiation and desodiation of sulfur, considering the strong chemisorption between sulfur (and short-chain sodium sulfides) and CoMoO4, which alleviates the shuttle effect of sodium sulfides and accelerates the electrochemical reaction rate at RT. The obtained S/CoMoO4@rGO cathode with ∼52% S loading exhibits a high capacity of 520.1 mA h g−1 after 100 cycles at 0.1 A g−1. Moreover, an enhanced long-term performance at high current densities (212.2 mA h g−1 at 4 A g−1 over 1000 cycles) with high Coulombic efficiency (∼100%) is also achieved. This work demonstrates a novel multifunctional additive for RT Na-S battery cathodes, which is expected to promote the long-waited development towards practical applications of RT Na-S batteries.

3D layered structure Ti3C2Tx MXene/Ni(OH)2/C with strong catalytic and adsorption capabilities of polysulfides for high-capacity Sodium–Sulfur battery

The room temperature sodium-sulfur battery has attracted researchers' attention due to its ultra-high energy storage capacity and extremely low cost, but its poor cycling performance and severe dissolution of sodium polysulfide hinder its practical application. Here, we report a stable MXene derived composite sulfur host material based on nickel hydroxide coated with carbon nano network, to achieve the adsorption and conversion of sodium polysulfides. Due to the physical constraints provided by the closed layered structure and the synergistic effect of MXene adsorption and Ni(OH)2catalytic activity, the shuttling effect is effectively suppressed. The ex-situ analysis of electrode after reaction shows that the composite material has strong adsorption on polysulfides. In addition, Ni(OH)2can also accelerate the reaction process from sulfur to sodium sulfide. Therefore, Ti3C2Tx/Ni(OH)2/C/S composite cathode can provide extraordinary reversible capacity 1175.3 mAh/g at 0.22C after 100 cycles and excellent long cycle stability (673.5 mAh/g at 2.2 C with a low decay rate of only 0.032% per cycle over 800 cycles).

Core-Shell Tandem Catalysis Coupled with Interface Engineering For High-Performance Room-Temperature Na-S Batteries.

The sluggish redox kinetics and shuttle effect seriously impede the large application of room-temperature sodium-sulfur (RT Na-S) batteries. Designing effective catalysts into cathode material is a promising approach to overcome the above issues. However, considering the multistep and multiphase transformations of sulfur redox process, it is impractical to achieve the effective catalysis of the entire S8 →Na2 Sx →Na2 S conversion through applying a single catalyst. Herein, this work fabricates a nitrogen-doped core-shell carbon nanosphere integrated with two different catalysts (ZnS-NC@Ni-N4 ), where isolated Ni-N4 sites and ZnS nanocrystals are distributed in the shell and core, respectively. ZnS nanocrystals ensure the rapid reduction of S8 into Na2 Sx (4<x≤8), while Ni-N4 sites realize the efficient conversion of Na2 Sx into Na2 S, bridged by the diffusion of Na2 Sx from the core to shell. Besides, Ni-N4 sites on the shell can also induce an inorganic-rich cathode-electrolyte interface (CEI) on ZnS-NC@Ni-N4 to further inhibit the shuttle effect. As a result, ZnS-NC@Ni-N4 /S cathode exhibits an excellent rate-performance (650 mAh g-1 at 5 A g-1 ) and ultralong cycling stability for 2000 cycles with a low capacity-decay rate of 0.011% per cycle. This work will guide the rational design of multicatalysts for high-performance RT Na-S batteries.

Growing Intact Membrane by Tuning Carbon Down to Ultrasmall 0.37 nm Microporous Structure for Confining Dissolution of Polysulfides Toward High‐Performance Sodium–Sulfur Batteries

Room temperature sodium–sulfur (Na–S) batteries are severely hampered by dissolution of polysulfides into electrolytes. Herein, a facile approach is used to tune a biomass‐derived carbon down to an ultrasmall 0.37 nm microporous structure for the first time as a cathode in sodium–sulfur batteries. This produced an intact uniform Na2S membrane to greatly confine the dissolution of polysulfides while realizing a direct solid phase conversion for complete reduction of sulfur to Na2S, which delivers a sulfur loading of 1 mg cm−2 (50 wt.%), an excellent rate capacity (933 mAh g−1 @ 0.1 A g−1 and 410 mAh g−1 @ 2 A g−1), long cycle performance (0.036% per cycle decay at 1 A g−1 after 1500 cycles), and a high energy density for 373 Wh kg−1 (0.1 A g−1) based on whole electrode weight (active sulfur loading + carbon), ranking the best among all reported plain carbon cathode‐based room temperature sodium–sulfur batteries in terms of the cycle life and rate capacity. It is proposed that the solid Na2S produced in the ultrasmall pores (0.37 nm) can be squeezed out to grow an intact membrane on the electrode surface covering the outlet of the pores and greatly depressing the dissolution effect of polysulfides for the long cycle life. This work provides a green chemistry to recycle wastes for sustainable energies and sheds light on design of a unique pore structure to effectively block the dissolution of polysulfides for high‐performance sodium–sulfur batteries.

Waste coffee grounds-derived carbon: Nanoarchitectured pore-structure regulation for sustainable room-temperature sodium–sulfur batteries

A systematic comparison has been made of three different porous carbon structures derived from waste coffee grounds to investigate the effect of carbon porosity on the electrochemical performance of RT Na–S batteries. The differences in their electrochemical performances were investigated in relation to the pore size distribution and the presence of sulfur molecules (Sn, 2 ≤ n ≤ 8) in the pores. We demonstrated that the hierarchically porous structure resulted in good rate capability and superior cycling stability. In particular, optimized carbon with micro-, meso-, and macroporous structures is beneficial because of its excellent wettability and kinetic accessibility. The optimized carbon structure with an appropriate sulfur content exhibited significantly higher capacity retention and long cycle stability in RT Na–S batteries. In addition, the reaction mechanisms have been investigated in combination with X-ray photoelectron spectroscopy measurements during the discharge process. The study established a relevance between the exact regulation of the pore structure of the carbon materials and their electrochemical performance, and also built a correlation between waste biomass and high-effective energy storage materials, which can inspire the rational design of porous carbon structures for further development of the highly efficient, cost-effective and sustainable RT Na–S batteries.

High performance sulfur/carbon cathode for Na-S battery enabled by electrocatalytic effect of Sn-doped In2S3

Room-temperature sodium-sulfur (RT Na-S) batteries have been attracting enormous interests due to their low-cost, high capacity and environmental benignity. However, the shuttle effect and the sluggish electrochemical reaction activity of sodium polysulfides (NaPSs) seriously restrict their practical application. To solve these issues, we rationally designed an advanced Sn-doped In2S3/S/C cathode for RT Na-S batteries by magnetron sputtering in this work, which exhibited a high reversible capacity (1663.5 mAh g−1 at 0.1 A g−1) and excellent cycling performance (902.9 mAh g−1 after 50 cycles). The in situ electrochemical impedance spectroscopy indicated that the Sn-doped In2S3 coating can accelerate charge-transfer kinetics and facilitate the diffusion of Na+. Furthermore, theoretical calculation revealed that doping of Sn into In2S3 can reduce the energy band gap, thus accelerating the electron transfer and promoting the electrochemical conversion of active species. It is demonstrated that adjusting the electronic structure is a reliable method to improve the electrocatalytic effect of catalyst and significantly improve the performance of S cathode in RT Na-S batteries.

Toward Complete Transformation of Sodium Polysulfides by Regulating the Second-Shell Coordinating Environment of Atomically Dispersed Fe.

Room temperature sodium-sulfur (RT Na-S) batteries are highly competitive as potential energy storage devices. Nevertheless, their actually achieved reversible capacities are far below the theoretical value due to incomplete transformation of polysulfides. Herein, atomically dispersed Fe-N/S active center by regulating the second-shell coordinating environment of Fe single atom is proposed. The Fe-N4S2 coordination structure with enhanced local electronic concentration around the Fermi level is revealed via synchrotron radiation X-ray absorption spectroscopy (XAS) and theoretical calculations, which can not only significantly promote the transformation kinetics of polysulfides, but induce uniform Na deposition for dendrite-free Na anode. As a result, the obtained S cathode delivers a high initial reversible capacity of 1590 mAh g-1, nearly the theoretical value. This work opens up a new avenue to facilitate the complete transformation of polysulfides for RT Na-S batteries.

Advances in Strategic Inhibition of Polysulfide Shuttle in Room-Temperature Sodium-Sulfur Batteries via Electrode and Interface Engineering

Room-temperature sodium-sulfur batteries (RT-NaSBs) with high theoretical energy density and low cost are ideal candidates for next-generation stationary and large-scale energy storage. However, the dissolution of sodium polysulfide (NaPS) intermediates and their migration to the anode side give rise to the shuttle phenomenon that impedes the reaction kinetics leading to rapid capacity decay, poor coulombic efficiency, and severe loss of active material. Inhibiting the generation of long-chain NaPS or facilitating their adsorption via physical and chemical polysulfide trapping mechanisms is vital to enhancing the electrochemical performance of RT-NaSBs. This review provides a brief account of the polysulfide inhibition strategies employed in RT-NaSBs via physical and chemical adsorption processes via the electrode and interfacial engineering. Specifically, the sulfur immobilization and polysulfide trapping achieved by electrode engineering strategies and the interfacial engineering of the separator, functional interlayer, and electrolytes are discussed in detail in light of recent advances in RT-NaSBs. Additionally, the benefits of engineering the highly reactive Na anode interface in improving the stability of RT-NaSBs are also elucidated. Lastly, the future perspectives on designing high-performance RT-NaSBs for practical applications are briefly outlined.

Polar Electrocatalysts for Preventing Polysulfide Migration and Accelerating Redox Kinetics in Room‐Temperature Sodium–Sulfur Batteries

Due to the high theoretical energy density, low cost, and rich abundance of sodium and sulfur, room-temperature sodium-sulfur (RT Na-S) batteries are investigated as the promising energy storage system. However, the inherent insulation of the S8 , the dissolution and shuttle of the intermediate sodium polysulfides (NaPSs), and especially the sluggish conversion kinetics, restrict the commercial application of the RT Na-S batteries. To address these issues, various catalysts are developed to immobilize the soluble NaPSs and accelerate the conversion kinetics. Among them, the polar catalysts display impressive performance. Polar catalysts not only can significantly accelerate (or alter) the redox process, but also can adsorb polar NaPSs through polar-polar interaction because of their intrinsic polarity, thus inhibiting the notorious shuttle effect. Herein, the recent advances in the electrocatalytic effect of polar catalysts on the manipulation of S speciation pathways in RT Na-S batteries are reviewed. Furthermore, challenges and research directions to realize rapid and reversible sulfur conversion are put forward to promote the practical application of RT Na-S batteries.

Co4N embedded nitrogen doped carbon with 2D/3D hybrid structure as sulfur host for room-temperature sodium-sulfur batteries

Room temperature sodium-sulfur (RT Na-S) batteries demonstrate a high theoretical energy density, but their practical application is limited by the sodium polysulfides (NaPSs) shuttling and slow redox kinetics. Herein, we report the design of the dimensional hybrid structure of 2D ZIF-67 nanosheets and 3D ZIF-67 polyhedron on the surface of carbon fiber by a pseudomorphic replication approach. After pyrolysis in ammonia, a hybrid structure composed of 2D N-doped carbon nanosheets and 3D N-doped carbon nano-polyhedrons embedded with Co4N nanoparticles (denoted as 2D/3D Co4N-NC@CC) is designed as a sulfur host for RT Na-S battery. The complex structure of 2D/3D composite guarantees abundant adsorption and catalytic sites, accelerating electrons/mass transport abilities compared with single 2D or 3D structure, in which Co4N can effectively catalyze the conversion of NaPSs and inhibit “shuttling effect”. Consequently, the RT Na-S cell with 2D/3D Co4N-NC@CC cathode exhibits extra-high discharge capacity of 466 mAh g−1 at 3.0 C and an outstanding long-term cycling stability (592 mAh g−1 at 1.0 C after 1000 cycles). The hybrid 2D/3D Co4N-NC@CC with excellent electrochemical performance represents a potential candidate for developing advanced RT Na-S batteries and other energy storage systems.