Room-temperature Na-S Batteries Research Articles

Sustainable Sulfur-Carbon Hybrids for Efficient Sulfur Redox Conversions in Nanoconfined Spaces.

Nanoconfinement is a promising strategy in chemistry enabling increased reaction rates, enhanced selectivity, and stabilized reactive species. Sulfur's abundance and highly reversible two-electron transfer mechanism have fueled research on sulfur-based electrochemical energy storage. However, the formation of soluble polysulfides, poor reaction kinetics, and low sulfur utilization are current bottlenecks for broader practical application. Herein, a novel strategy is proposed to confine sulfur species in a nanostructured hybrid sulfur-carbon material. A microporous sulfur-rich carbon is produced from sustainable natural precursors via inverse vulcanization and condensation. The material exhibits a unique structure with sulfur anchored to the conductive carbon matrix and physically confined in ultra-micropores. The structure promotes Na+ ion transport through micropores and electron transport through the carbon matrix, while effectively immobilizing sulfur species in the nanoconfined environment, fostering a quasi-solid-state redox reaction with sodium. This translates to ≈99% utilization of the 2e- reduction of sulfur and the highest reported capacity for a room temperature Na-S electrochemical system, with high rate capability, coulombic efficiency, and long-term stability. This study offers an innovative approach toward understanding the key physicochemical properties of sulfurcarbon nanohybrid materials, enabling the development of high-performance cathode materials for room-temperature Na-S batteries with efficient sulfur utilization.

Phosphorus and Nitrogen Dual-Doped Hollow Porous Carbon Spheres toward Enhanced Cycling Stability of Room-Temperature Na-S Batteries.

Development of room-temperature sodium-sulfur (RT Na-S) batteries with satisfactory cycling life and rate capability remains challenging due to the unfavorable electric conductivity from S species, sluggish redox kinetics of S conversion, and serious shuttle effects of sodium polysulfides (NaPSs). To address these issues, a phosphorus and nitrogen dual-doped hollow porous carbon sphere (PN-HPCs) is synthesized as the S hosts, which enhances the electric conductivity, ion diffusion, and conversion of polysulfides. Such a hollow hierarchically porous structure is beneficial to accommodate the volume variations of S species and shorten the ion/electron transfer distances during electrochemical reaction process. As a result, the S@PN-HPCs600 cathode delivers noticeable cycling performance (313 mAh g-1 after 4500 cycles at 5.0 C, and capacity degeneration of only 0.01% per cycle) and rate capability (646.4 mAh g-1@1.0 and 527.5 mAh g-1@3.0 C). This work presents an efficient strategy based on structural confinement and dual-heteroatom doping engineering for long-life RT Na-S batteries.

Promoting Cathodic Kinetics and Anodic Stability in Practical Room-Temperature Sodium-Sulfur Batteries with Bifunctional Electrolytes.

The development of room-temperature (RT) sodium-sulfur (Na-S) batteries is severely hindered due to the slow kinetics of the S cathode and the instability of the Na-metal anode. To overcome this, we introduced a dual-functional electrolyte cosolvent, trifluoromethanesulfonamide (TFMSA). Short-chain Na2Sx (1 ≤ x ≤ 2) can be effectively dissolved due to the strong H-S bond interaction between TFMSA and sulfides, which changes the S conversion process, thereby effectively enhancing the conversion kinetics of the cathode. Meanwhile, TFMSA can generate a stable solid electrolyte interphase on the Na-metal surface to protect it from soluble polysulfide attack. Therefore, the RT Na-S batteries using the ether electrolyte show a high initial discharge capacity of 896.6 mAh g-1 and a capacity retention rate of 73% after 150 cycles at 0.2C, and the pouch cell also demonstrates its practical performance. This work proposes a dual-functional electrolyte cosolvent selection principle to inspire the practical application of high-performance RT Na-S batteries.

Chitin-Derived Hierarchical Meso- and Microporous Carbon Enables High-Rate Sulfur Cathode of Sodium-Sulfur Batteries.

Room temperature Na-S batteries are considered as a promising alternative energy storage system because of their abundant material resources and high theoretical energy density. However, the severe polysulfide shuttle effect and slow reaction kinetics hinder their practical application. Herein, a hierarchical meso- and microporous carbon with nitrogen self-doping (NSPC) is prepared using chitin as the carbon precursor and serves as a novel host to confine the sulfur (S⊂NSPC). An optimized structure of NSPC, including abundant graphite nanocrystals, large pore volume of 1.76 cm3 g-1, and large specific surface area of 2073 m2 g-1 is obtained at the carbonization temperature of 1000 °C. These merits contribute to significantly enhanced charge transfer and ion diffusion of the as-prepared S⊂NSPC-1000 cathode, which exhibits the outstanding sodium storage performance, including high reversible capacities of 1207 mAh g-1 at 0.1 C and 891 mAh g-1 at 2 C and stable cycling with a low capacity decay for 400 cycles at 1 C, among other S⊂NSPC cathodes and previously reported cathodes for Na-S batteries. This cathode can also afford stable cycling at a high sulfur loading.

Nitrogen-doped porous carbon hosted sulfur-rich polymer for room temperature Na-S batteries with superior cycle performances

Room temperature sodium-sulfur (RT Na-S) batteries are one of the most promising energy storage systems with high energy density due to the abundant reserves of sodium and sulfur elements on Earth. As a potential cathode material, sulfur-rich polymers are rarely reported in RT Na-S batteries compared with other metal-sulfur batteries. The unusual occurrence is a result of sulfur-rich polymer cathodes failing in Na-S batteries. To reverse the process, herein, we first illuminate the failure mechanism of sulfur-rich polymer cathodes (S-DIB as an example) in Na-S batteries, which root from the chemical reaction between the polysulfide and the sodium anode. To address this issue, we incorporate nitrogen-doped carbon (NC) into composites with S-DIB to establish ion diffusion pathways and limit polysulfide diffusion. The resulting S-DIB@NC composite demonstrates exceptional cycling performance, achieving a high capacity of 457 mA h g-1 after 1300 cycles. This research constitutes a significant step towards enhancing the viability of sulfur-rich polymers in Na-S batteries and paves the way for their widespread application.

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.

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.

Low-Coordinated Zn-N2 Sites as Bidirectional Atomic Catalysis for Room-Temperature Na-S Batteries.

The rational design of advanced catalysts for sodium-sulfur (Na-S) batteries is important but remains challenging due to the limited understanding of sulfur catalytic mechanisms. Here, we propose an efficient sulfur host consisting of atomic low-coordinated Zn-N2 sites dispersed on N-rich microporous graphene (Zn-N2@NG), which realizes state-of-the-art sodium-storage performance with a high sulfur content of 66 wt %, high-rate capability (467 mA h g-1 at 5 A g-1), and long cycling stability for 6500 cycles with an ultralow capacity decay rate of 0.0062% per cycle. Ex situ methods combined with theoretical calculations demonstrate the superior bidirectional catalysis of Zn-N2 sites on sulfur conversion (S8 ↔ Na2S). Furthermore, in situ transmission electron microscopy was applied to visualize the microscopic S redox evolution under the catalysis of Zn-N2 sites without liquid electrolytes. During the sodiation process, both surface S nanoparticles and S molecules in the mircopores of Zn-N2@NG quickly convert into Na2S nanograins. During the following desodiation process, only a small part of the above Na2S can be oxidized into Na2Sx. These results reveal that, without liquid electrolytes, Na2S is difficult to be decomposed even with the assistance of Zn-N2 sites. This conclusion emphasizes the critical role of liquid electrolytes in the catalytic oxidation of Na2S, which was usually ignored by previous works.

Design and applications of transition metal sulfides in room-temperature Na-S batteries

Room-temperature sodium-sulfur (RT Na-S) batteries have attracted considerable research interests in the past years, due to their advantages in natural resources, materials cost, specific capacity, and energy density etc.; however, they are suffering from various threats from S cathodes, encompassing shuttle effect, low electronic conductivity, volume change, and sluggish kinetics etc. Transition metal sulfides are demonstrated as promising redox regulators to help tackle these key issues as a result of their excellent chemical affinity and/or catalytic ability and improve the overall performance of RT Na-S batteries. Herein, the recent advances in rational design of the mainstream transition metal sulfides for RT Na-S batteries are comprehensively reviewed, including cobalt sulfides, iron sulfides, nickel/zinc sulfides, molybdenum sulfides, and their heterostructures. The emphasis is on fundamental properties of these sulfides, interactions between metal sulfides and polysulfides, materials design strategies and electrochemical performance. Potential developmental directions are also put forward to promote the further progress on RT Na-S batteries.

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

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

A stable anode-free Na-S full cell at room temperature

The extended cycling life of room-temperature Na-S batteries depends predominantly on the excessive Na metal. Inhibiting Na corrosion by soluble Na polysulfides (NaPS) and reducing the usage of Na metal are key challenges to achieve practical Na-S batteries. Herein, an anode-free Na-S full cell is assembled with Na2S@carbon paper cathode prepared by in situ carbon-thermal reduction of Na2SO4, and 3D current collector (3DCC) of carbon nanofibers at the anode side, extraordinarily using Fluoroethylene carbonate (FEC) as electrolyte additive. This Na2S-based 3DCC||Na2S full cell not only provides stoichiometric Na source but also permits FEC to participate in formation of SEI on 3DCC ahead of the production of soluble NaPS during the initial charging, overcoming the incompatibility of FEC in Na-S battery. The polysulfide-resistant SEI guarantees the stable plating/stripping of volume-expansion alleviated Na metal on 3DCC. The as-developed anode-free 3DCC||Na2S full cell demonstrates 500-cycle life at 0.5 C, delivering much higher overall energy density than those using excessive Na metal. This is the first report of rechargeable anode-free Na-S battery with satisfactory cycling durability, representing a significant step toward achieving practical Na-S batteries.

A Fe3N/carbon composite electrocatalyst for effective polysulfides regulation in room-temperature Na-S batteries

The practical application of room-temperature Na-S batteries is hindered by the low sulfur utilization, inadequate rate capability and poor cycling performance. To circumvent these issues, here, we propose an electrocatalyst composite material comprising of N-doped nanocarbon and Fe3N. The multilayered porous network of the carbon accommodates large amounts of sulfur, decreases the detrimental effect of volume expansion, and stabilizes the electrodes structure during cycling. Experimental and theoretical results testify the Fe3N affinity to sodium polysulfides via Na-N and Fe-S bonds, leading to strong adsorption and fast dissociation of sodium polysulfides. With a sulfur content of 85 wt.%, the positive electrode tested at room-temperature in non-aqueous Na metal coin cell configuration delivers a reversible capacity of about 1165 mA h g−1 at 167.5 mA g−1, satisfactory rate capability and stable capacity of about 696 mA h g−1 for 2800 cycles at 8375 mA g−1.

Multi-step Controllable Catalysis Method for the Defense of Sodium Polysulfide Dissolution in Room-Temperature Na–S Batteries

Room-temperature (RT) sodium-sulfur batteries hold great promise for the development of efficient, low-cost, and environmentally friendly energy storage systems. Nevertheless, the dissolution of long-chain polysulfides is a huge obstacle. In this work, a composite cathode which integrates Ni/Co bimetal nanoparticles as the catalyst and carbon spheres with abundant channels as the host is prepared for RT Na-S batteries. Moreover, a valuable strategy to reduce the dissolution of polysulfides by accurately regulating the two-step reaction kinetics of polysulfide transformation (from Na2S to long-chain polysulfides and then from polysulfides to sulfur) is presented. Through adjusting the ratio of Ni and Co, the optimal cathode with a Ni/Co ratio of 1:2 can retard the first conversion of Na2S to polysulfides and simultaneously accelerate the subsequent transformation of polysulfides to sulfur. In this case, the soluble polysulfides can immediately transform to solid sulfur as soon as it appears, thus avoiding the shuttle of polysulfides. The galvanostatic intermittent titration method and in situ Raman are employed to supervise the transformation of polysulfides during the discharge/charge process. As a result, the composite shows excellent performance as the cathode of RT liquid/quasi-solid-state Na-S batteries in terms of specific capacities, rate capability, and cycle stability.

General Synthesis of Single-Atom Catalysts for Hydrogen Evolution Reactions and Room-Temperature Na-S Batteries.

Herein, we report a comprehensive strategy to synthesize a full range of single-atom metals on carbon matrix, including V, Mn, Fe, Co, Ni, Cu, Ge, Mo, Ru, Rh, Pd, Ag, In, Sn, W, Ir, Pt, Pb, and Bi. The extensive applications of various SACs are manifested via their ability to electro-catalyze typical hydrogen evolution reactions (HER) and conversion reactions in novel room-temperature sodium sulfur batteries (RT-Na-S). The enhanced performances for these electrochemical reactions arisen from the ability of different single active atoms on local structures to tune their electronic configuration. Significantly, the electrocatalytic behaviors of diverse SACs, assisted by density functional theory calculations, are systematically revealed by in situ synchrotron X-ray diffraction and in situ transmission electronic microscopy, providing a strategic library for the general synthesis and extensive applications of SACs in energy conversion and storage.

High performance room temperature Na-S batteries based on FCNT modified Co3C-Co nanocubes

High-temperature Sodium-sulfur (Na-S) batteries have been commercial owing to their high energy density. However, their extra safety and cost issues caused by high-temperature inhibits their wide application. Recently, room-temperature Na-S batteries have attracted widespread attention due to the low cost and excellent energy density. Nevertheless, they still suffer from the poor conductivity, sluggish redox kinetics and shuttle effect. Herein, the incorporated polar Co3C-Co with open fluorinated carbon nanotubes arrays encapsulated in porous three-dimensional (3D) framework (FCNT@Co3C-Co) was designed and applied as the sulfur host for Na-S battery. Theoretical and experimental results indicate that the polar and porous FCNT@Co3C-Co possesses the strong interactions with Na+ and S intermediate species (NaPSs), which increases the sulfide utilization and suppresses the shuttle effect by the efficient physisorption/chemisorption and rapid electrocatalytic conversion. Moreover, the synergy of the porous cube-like framework and superior interface property in FCNT@Co3C-Co mitigates the huge volume variations and reduces the energy barrier for Na-S battery. Hence, the FCNT@Co3C-Co based Na-S batteries deliver a high discharge capacity of 1364 mAh g−1 at 0.1 C even with a lean E/S of 5 mL g−1 under a high S loading of 3.2 mg cm−2 and show Coulombic efficiency above 75% after 500 loops under 2 C at room-temperature.

TiO2 nanoparticle dispersed porous gel polymer electrolyte membrane for room temperature Na-S battery

Room temperature sodium-sulfur (Na-S) batteries are promising energy storage devices for meeting increasing energy demands. An electrolyte with reasonably high ionic conductivity (≥10−4 S cm−1) is one of the key requirements for room temperature Na-S batteries. In this work, a sodium ion conducting flexible porous gel polymer electrolyte membrane of TiO2 (Titanium dioxide) dispersed Poly(vinylidene fluoride-hexafluoropropylene) soaked in a liquid electrolyte of NaPF6 (sodium hexafluorophosphate) in EC (ethylene carbonate): PC (Propylene carbonate) has been prepared. The electrolyte is obtained through phase inversion method and shows an ionic conductivity of 1.3 × 10−3 S cm−1. A proto-type Na-S battery has been fabricated and characterized using the prepared electrolyte membrane. The battery shows an open circuit voltage of ∼2.1 V and discharge capacity of 231 mA h g−1. However, battery shows capacity fading during charge-discharge cycle.

Rational construction of rGO/VO2 nanoflowers as sulfur multifunctional hosts for room temperature Na-S batteries

Developing high energy density room-temperature sodium sulfur (RT Na-S) batteries relies on the design of delicate structure that can be efficiently injected sulfur and enhance the cycle life of electrode active material. Herein, a three dimensional (3D) hierarchical cathode substrate with VO2 nanoflowers as catalyst in situ grown on reduced graphene oxide (rGO) for sulfur cathodes are designed and prepared. In this novel structure, the electronic conductivity of sulfur cathode can be greatly improved due to the high electrical conductivity of rGO substrate. More importantly, the catalytic effect of VO2 accelerates the conversion long-chain NaPSs to Na2S2/Na2S, and enhances the cycle capability, which can be validated by experimental data. As a result, the as-obtained rGO/VO2/S composites achieves an initial reversible capacity of 876.4 mA h g−1 at 0.2C. Moreover, the capacity of 156.1 mA h g−1 is demonstrated after long-cycling term of 1000 cycles at 2C and high cycle stability of only 0.07% capacity decay per cycle is exhibited.

Non-flammable electrolyte for dendrite-free sodium-sulfur battery

Room temperature (RT) sodium-sulfur (Na-S) batteries are a promising technology for stationary energy storage thanks to their high energy density of 1274 Wh kg−1 and low cost. However, RT Na-S batteries are hazardous because they use highly volatile and flammable electrolytes. Here, we develop a new nonflammable electrolyte for RT Na-S batteries, consisting of sodium trifluoromethanesulfonimide (NaTFSI) in a mixture of trimethyl phosphate (TMP) and fluoroethylene carbonate (FEC). The nonflammable electrolyte facilitates highly stable and reversible Na plating/stripping during cycles. The dendrite-free Na-S battery with the NaTFSI/TMP+FEC electrolyte delivers a remarkable reversible capacity of 788 ​mAh g−1 after 300 cycles at 1C, corresponding to a negligible capacity decay below 0.04% per cycle. The ab initio molecular dynamics simulations and surface analysis reveal the formation of a NaF-rich solid electrolyte interphase (SEI) film with reduced interfacial resistance thanks to the introduction of FEC into the electrolyte. The formed NaF SEI layer suppresses the growth of Na dendrites on the anode, enhancing the electrochemical performance of the RT Na-S batteries. The new findings reported here will shed new light on dendrite-free RT Na-S batteries by the rational design of nonflammable electrolytes.

Development of low-cost sodium-aqueous polysulfide hybrid batteries

There has been increasing interest in sodium-sulfur (Na-S) batteries as an option for low-cost grid-scale energy storage. However, traditional Na-S batteries operate at high temperatures, raising concerns about long-term maintenance costs and safety. On the other hand, room-temperature Na-S batteries have their own limitations, including Na dendrite formation, polysulfide shuttling, and low utilization of active material. To overcome these issues, we present here a novel low-cost room-temperature sodium-aqueous polysulfide (Na-APS) hybrid battery system with a Na-metal anode, Na+-ion solid electrolyte separator, and an aqueous polysulfide catholyte. The solid electrolyte blocks Na dendrites and polysulfide shuttling while simultaneously protecting the reactive Na metal anode from the aqueous catholyte. The redox kinetics of the APS catholyte is improved with a rational development of a freestanding CuS-CNT catalytic electrode. The improvements with the Na-APS hybrid battery compared to the traditional Na-S battery systems are discussed. The Na-APS hybrid battery displays excellent performance under a 418 mA h g−1 of sulfur capacity-restricted cycling. The battery achieves an energy efficiency of 90% over 100 cycles at 0.5 mA cm−2 current density.

Synthesis of hollow porous carbon microspheres and their application to room-temperature Na-S batteries

A novel electrode material of room-temperature Na-S batteries was designed by hollow porous carbon microspheres (HPCM) derived from metal-organic frameworks (MOFs), which were used as a matrix to form HPCM/S composite by melt-infiltrating method. The electrochemical performance show that the HPCM/S composite as cathode delivered a reversible capacity over 617 mA h g−1 at 0.7C, maintaining over 311 mA h g−1 capacities after 60 cycles. The good electrochemical properties can be attributed to the hollow and porous structure of HPCM, which can host sulfur efficiently and alleviate the volume expansion caused by polysulfide.