Room-temperature Sodium-sulfur Batteries Research Articles

A Highly Dispersed Cobalt Electrocatalyst with Electron-Deficient Centers Induced by Boron toward Enhanced Adsorption and Electrocatalysis for Room-Temperature Sodium-Sulfur Batteries.

As vitally prospective candidates for next-generation energy storage systems, room-temperature sodium-sulfur (RT-Na/S) batteries continue to face obstacles in practical implementation due to the severe shuttle effect of sodium polysulfides and sluggish S conversion kinetics. Herein, the study proposes a novel approach involving the design of a B, N co-doped carbon nanotube loaded with highly dispersed and electron-deficient cobalt (Co@BNC) as a highly conductive host for S, aiming to enhance adsorption and catalyze redox reactions. Crucially, the pivotal roles of the carbon substrate in prompting the electrocatalytic activity of Co are elucidated. The experiments and density functional theory (DFT) calculations both demonstrate that after B doping, stronger chemical adsorption toward polysulfides (NaPSs), lower polarization, faster S conversion kinetics, and more complete S transformation are achieved. Therefore, the as-assembled RT-Na/S batteries with S/Co@BNC deliver a high reversible capacity of 626 mAh g-1 over 100 cycles at 0.1 C and excellent durability (416 mAh g-1 over 600 cycles at 0.5 C). Even at 2 C, the capacity retention remains at 61.8%, exhibiting an outstanding rate performance. This work offers a systematic way to develop a novel Co electrocatalyst for RT-Na/S batteries, which can also be effectively applied to other transition metallic electrocatalysts.

Linearly Interlinked Fe-Nx -Fe Single Atoms Catalyze High-Rate Sodium-Sulfur Batteries.

Linearly interlinked single atoms offer unprecedented physiochemical properties, but their synthesis for practical applications still poses significant challenges. Herein, linearly interlinked iron single-atom catalysts that are loaded onto interconnected carbon channels as cathodic sulfur hosts for room-temperature sodium-sulfur batteries are presented. The interlinked iron single-atom exhibits unique metallic iron bonds that facilitate the transfer of electrons to the sulfur cathode, thereby accelerating the reaction kinetics. Additionally, the columnated and interlinked carbon channels ensure rapid Na+ diffusion kinetics to support high-rate battery reactions. By combining the iron atomic chains and the topological carbon channels, the resulting sulfur cathodes demonstrate effective high-rate conversion performance while maintaining excellent stability. Remarkably, even after 5000 cycles at a current density of 10 A g-1 , the Na-S battery retains a capacity of 325 mAh g-1 . This work can open a new avenue in the design of catalysts and carbon ionic channels, paving the way to achieve sustainable and high-performance energy devices.

Tailoring Na+ Solvation Environment and Electrode-Electrolyte Interphases with Sn(OTf)2 Additive in Non-flammable Phosphate Electrolytes towards Safe and Efficient Na-S Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries are promising for low-cost and large-scale energy storage applications. However, these batteries are plagued by safety concerns due to the highly flammable nature of conventional electrolytes. Although non-flammable electrolytes eliminate the risk of fire, they often result in compromised battery performance due to poor compatibility with sodium metal anode and sulfur cathode. Herein, we develop an additive of tin trifluoromethanesulfonate (Sn(OTf)2 ) in non-flammable phosphate electrolytes to improve the cycling stability of RT Na-S batteries via modulating the Na+ solvation environment and interface chemistry. The additive reduces the Na+ desolvation energy and enhances the electrolyte stability. Moreover, it facilitates the construction of Na-Sn alloy-based anode solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). These interphases help to suppress the growth of Na dendrites and the dissolution/shuttling of sodium polysulfides (NaPSs), resulting in improved reversible capacity. Specifically, the Na-S battery with the designed electrolyte boosts the capacity from 322 to 906 mAh g-1 at 0.5 A g-1 . This study provides valuable insights for the development of safe and high-performance electrolytes in RT Na-S batteries.

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.

Battery Technologies in Electrochemical Energy Storage

Electrochemical energy storage technologies play a pivotal role in stabilizing renewable energy sources, ensuring a consistent power supply, and reducing our reliance on fossil fuels. In this article, three electrochemical energy storage technologies—lithium-ion batteries, sodium-sulfur batteries, and flow batteries—are analyzed and contrasted with an emphasis on their hopeful futures. Lithium-ion batteries operate by shuttling lithium ions between cathodes and anodes through an electrolyte, offering high energy density, rechargeability, stable voltage, long cycle life, and low self-discharging rate, making them versatile for a variety of uses, such as grid-scale power storage. However, cost, recycling challenges, and safety concerns have led to ongoing research into solid-state lithium-ion batteries for enhanced performance and safety. Sodium-sulfur batteries, while operating at high temperatures, provide high energy density and reliability, making them suitable for grid-level energy storage and backup power applications. Considering their shortages, researchers are exploring room-temperature sodium-sulfur batteries as a possible alternative with improved safety and cost-effectiveness for various energy storage applications, such as grid integration and electric vehicles. Flow batteries, with their separate electrolyte reservoirs, offer scalability and prolonged lifespan, making them ideal for grid-level energy storage and renewable energy integration. However, they have lower energy density and efficiency compared to some other battery types, requiring ongoing research to address these limitations and enhance their competitiveness in the energy storage market. Compared with sodium-sulfur batteries and flow batteries, lithium-ion batteries hold a dominant position due to their versatility, ongoing research advancements, and extensive infrastructure support.

Strategies to Stabilize the Sodium metal anode for High-energy Room-temperature Sodium-Sulfur Batteries

Room temperature sodium-sulfur batteries possess higher specific energy and improved inherent safety compared to their high-temperature analogs used in stationary grid storage. The viability of room temperature sodium batteries depends critically on the mechanical and ionic transport properties of the solid electrolyte interphase. Solid electrolyte interphases address a number of concomitant challenges, including large volume change, low ionic conductivity, rapid dendrite growth, and high chemical reactivity, which limit the viability of sodium anodes. In this presentation, novel strategies to stabilize the sodium metal anode are discussed that enable a high-rate cycling of sodium anodes. A solid-vapor growth approach is developed to fabricate a variety of artificial interphases directly on the surface of the sodium metal anode. As a result, the metal anode could be cycled for over 600 cycles at relatively higher currents. A room-temperature sodium-sulfur cell comprising modified sodium metal anode and sulfur cathode could be cycled for over 500 cycles with minimal capacity decay per cycle.

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.

Polysulfide regulation by defect-modulated Ta3N5−x electrocatalyst toward superior room-temperature sodium-sulfur batteries

Resolving low sulfur reaction activity and severe polysulfide dissolution remains challenging in metal-sulfur batteries. Motivated by a theoretical prediction, herein, we strategically propose nitrogen-vacancy tantalum nitride (Ta3N5−x) impregnated inside the interconnected nanopores of nitrogen-decorated carbon matrix as a new electrocatalyst for regulating sulfur redox reactions in room-temperature sodium-sulfur batteries. Through a pore-constriction mechanism, the nitrogen vacancies are controllably constructed during the nucleation of Ta3N5−x. The defect manipulation on the local environment enables well-regulated Ta 5d-orbital energy level, not only modulating band structure toward enhanced intrinsic conductivity of Ta-based materials, but also promoting polysulfide stabilization and achieving bifunctional catalytic capability toward completely reversible polysulfide conversion. Moreover, the interconnected continuous Ta3N5−x-in-pore structure facilitates electron and sodium-ion transport and accommodates volume expansion of sulfur species while suppressing their shuttle behavior. Due to these attributes, the as-developed Ta3N5−x-based electrode achieves superior rate capability of 730 mAh g−1 at 3.35 A g−1, long-term cycling stability over 2000 cycles, and high areal capacity over 6 mAh cm−2 under high sulfur loading of 6.2 mg cm−2. This work not only presents a new sulfur electrocatalyst candidate for metal-sulfur batteries, but also sheds light on the controllable material design of defect structure in hopes of inspiring new ideas and directions for future research.

Intercalation-type catalyst for non-aqueous room temperature sodium-sulfur batteries

Ambient-temperature sodium-sulfur (Na-S) batteries are potential attractive alternatives to lithium-ion batteries owing to their high theoretical specific energy of 1,274 Wh kg−1 based on the mass of Na2S and abundant sulfur resources. However, their practical viability is impeded by sodium polysulfide shuttling. Here, we report an intercalation-conversion hybrid positive electrode material by coupling the intercalation-type catalyst, MoTe2, with the conversion-type active material, sulfur. In addition, MoTe2 nanosheets vertically grown on graphene flakes offer abundant active catalytic sites, further boosting the catalytic activity for sulfur redox. When used as a composite positive electrode and assembled in a coin cell with excess Na, a discharge capacity of 1,081 mA h gs−1 based on the mass of S with a capacity fade rate of 0.05% per cycle over 350 cycles at 0.1 C rate in a voltage range of 0.8 to 2.8 V is realized under a high sulfur loading of 3.5 mg cm−2 and a lean electrolyte condition with an electrolyte-to-sulfur ratio of 7 μL mg−1. A fundamental understanding of the electrocatalysis of MoTe2 is further revealed by in-situ synchrotron-based operando X-ray diffraction and ex-situ time-of-flight secondary ion mass spectrometry.

Enhanced conversion kinetics by constructing boron and nitrogen co-doped porous carbon with sulfurophilic and sodiophilic sites in room-temperature sodium-sulfur batteries

Enhanced conversion kinetics by constructing boron and nitrogen co-doped porous carbon with sulfurophilic and sodiophilic sites in room-temperature sodium-sulfur batteries

Covalent sulfur confined in mesoporous hollow carbon spheres for effective kinetic regulation of room-temperature sodium-sulfur batteries

Room-temperature sodium-sulfur batteries have attracted extensive attention as a cost-effective and high theoretical energy density next-generation energy storage systems. However, the insulating nature of sulfur, the sluggish reactivity of sulfur with sodium, and severe dissolution of polysulfide are the main challenges of this technology. Here, we propose a covalent sulfur bond breakage mechanism by bonding of sulfur chain onto the inner cavity of the sulfydryl-functionalized mesoporous hollow carbon spheres (MHCS) to efficiently promote the generation of short-chain sodium polysulfide and accelerate polysulfide redox kinetics. The covalent sulfur confined MHCS (S@MHCS) cathode delivers an unprecedented rate capability (250 mAh g−1 at 5 C) and exhibits excellent long-term cycling stability over 1000 cycles at 1 C with a high cathode loading of 5 mg cm−2. Moreover, the associated electrochemical reaction mechanism is also revealed by ex-situ X-ray photoelectron spectroscopy and theoretical calculation. This work introduces a novel sulfur cathode design to enhance the performance of room-temperature sodium-sulfur 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.

Revealing the binding mechanism of redox intermediates in sodium–sulfur batteries by two-dimensional Janus monolayers

Ultrahigh theoretical energy density and naturally abundant electrode materials (i.e., sodium and sulfur) have rendered room-temperature sodium-sulfur batteries (Na-SBs) to be the emerging alternative for the large-scale applications. Nevertheless, rapid capacity decay caused by the shuttle effect, poor electrical conductivity of sulfur, and sluggish electrochemistry pose major obstacles to achieving commercial viability. Herein, we have proposed a new functionality of Janus-type transition metal dichalcogenides (TMDs) as cathode hosting materials to resolve the mentioned hindrances. Based on density functional theory (DFT), this work reports the interfacial interactions of sodium polysulfides (Na2Sn) and a series of Janus MSX (M = Mo, W and X = Se, Te), electronic properties, and the crucial parameters of the electrochemical reaction. Among MSX, we find that MoSTe binds with Na2Snvia chemical Na–S bonds causing the strongest binding energies (−1.18 to −2.48 eV) which are greater than do the electrolytes (−0.20 to −0.98 eV), thus effectively alleviating the shuttle effect. This immense binding is attributed to the magnified polar nature of MoSTe which intensifies the Na2Sn–MoSTe interaction. Moreover, the charge accumulation in MoSTe as donated by Na2Sn maximizes the electronic conductivity of MoSTe to improve the charge transport during the redox process. Importantly, this material facilitates the overall reversible electrochemical reactions by lowering the energy barriers of conversions among the redox intermediates in the sulfur reduction reaction (SRR), the decomposition barrier of final discharge product Na2S, and diffusion barrier of Na+ ions. Hence, Janus MoSTe offers the manifold benefits for boosting the efficiency of Na-SBs.

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.