Room-temperature Sodium Sulfur Research Articles

Origin of the High Catalytic Activity of MoS2 in Na-S Batteries: Electrochemically Reconstructed Mo Single Atoms.

Room-temperature sodium-sulfur (RT Na-S) batteries with high energy density and low cost are considered promising next-generation electrochemical energy storage systems. However, their practical feasibility is seriously impeded by the shuttle effect of sodium polysulfide (NaPSs) resulting from the sluggish reaction kinetics. Introducing a suitable catalyst to accelerate conversion of NaPSs is the most used strategy to inhibit the shuttle effect. Traditional catalytic approaches often want to avoid the irreversible phase transition of the catalyst at a deep discharge. On the contrary, here, we leverage the intrinsic structural tunability of the MoS2 catalyst in the opposite direction and innovatively propose a voltage modulation strategy for in situ generation of trace Mo single atoms (MoSAC) during the first charge-discharge process, leading to the formation of highly active catalytic phases (MoS2/MoSAC) through the self-reconstruction. Theoretical calculations reveal that the incorporation of MoSAC modulates the electronic structure of the Mo d-band center, which not only effectively promotes the d-p orbital hybridization but also accelerates the catalytic intermediate desorption by the bonding transition, the dynamic single-atom synergistic catalytic mechanism enhances the adsorption response between the metal active site and NaPSs, which significantly improves the sulfur redox reaction (SRR), and the initial capacity of the MoS2/MoSAC/CF@S cell at 0.2 A g-1 is increased by 46.58% compared to that of the MoS2/CF@S cell. The discovery of the MoS2/MoSAC/CF catalyst provides new insights into adjusting the structure and function of transition metal disulfide catalysts at the atomic scale, offering hope for the development of high-specific-energy RT Na-S batteries.

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.

Fluorinated ester additive to regulate nucleation behavior and interfacial chemistry of room temperature sodium-sulfur batteries

Room temperature sodium-sulfur (RT Na-S) batteries are considered as advanced energy storage technology due to their low cost and high theoretical energy density. However, challenges such as the growth of sodium dendrite and dissolution of sodium polysulfides significantly hinder the electrochemical performance. Herein, we developed a propylene carbonate (PC)-based electrolyte with Methyl 2-Fluoroisobutyrate (MFB) as an additive. The ester group in the MFB additive is capable of participating in and reconfiguring the coordination of their Na+ solvated structures, thereby lowering the desolvation barrier and regulating the Na anode’s interfacial reaction and nucleation behavior. The polar C−F bond at the other end helps to reduce the lowest unoccupied molecular orbital (LUMO) energy of the MFB additive, enabling the preferential decomposition of MFB to form the F-rich inorganic phase strong polar solid electrolyte interphase (SEI), contributing to the inhibition of Na dendrite growth, the accumulation of dead Na. In addition, NaF-riched cathode electrolyte interphase (CEI) was also observed on sulfur-based cathode, which can effectively inhibited the shuttle effect. Consequently, the developed RT Na-S battery exhibit excellent electrochemical performance.

Inhibiting Shuttle Effect and Dendrite Growth in Sodium-Sulfur Batteries Enabled by Applying External Acoustic Field.

The room-temperature sodium-sulfur (RT Na-S) battery is a promising alternative to traditional lithium-ion batteries owing to its abundant material availability and high specific energy density. However, the sodium polysulfide shuttle effect and dendritic growth pose significant challenges to their practical applications. In this study, we apply diverse disciplinary backgrounds to introduce a novel method to stimulate polarized BaTiO3 (BTO) nanoparticles on the separator. This approach generates more charges due to the piezoelectric effect under stronger driving forces produced by applying a controllable acoustic field at the outer edge of the cell. The acoustically stimulated BTO attracts more polysulfides, thus reducing the shuttling effect from the cathode to the anode and ultimately enhancing the battery performance. Meanwhile, the acoustic waves create additional streaming flows, improving the uniformity of the sodium ion dispersion, enhancing the sodium ion transport and reducing the possibility of sodium dendrite development. We believe that this work offers a new strategy for the development of high-performance Na-S batteries.

Stable Dendrite-Free Room Temperature Sodium-Sulfur Batteries Enabled by a Novel Sodium Thiotellurate Interface.

The practical application of room-temperature sodium-sulfur (RT Na-S) batteries was severely hindered by inhomogeneous sodium deposition and notorious sodium polysulfides (NaPSs) shuttling. Herein, novel sodium thiotellurate (Na2TeS3) interfaces are constructed both on the cathode and anode for Na-S batteries to simultaneously address the Na dendritic growth and polysulfide shuttling. On the cathode side, a heterostructural sodium sulfide/sodium telluride embedded in a carbon matrix (Na2S/Na2Te@C) was rationally designed through a facile carbothermal reaction, where the Na2TeS3interface will be in-situ chemically obtained. Such an interface provides abundant electron/ion diffusion channels and ensures rich catalytic surfaces toward Na-S redox, which could significantly improve the utilization of active material and alleviate polysulfide shuttling in the cathode. On the anode side, the inevitable formation of soluble polytellurosulfides species will migrate on Na anode surface, finally constructing a compact and smooth solid-electrolyte Na2TeS3 interphase (SEI) layer. Such electrochemical formed Na2TeS3 interface can significantly enhance ionic transport and stabilize Na deposition, thus realizing dendrite-free Na-metal plating/stripping. Benefitting from these advantages, an anode-free cell fabricated with the Na2S/Na2Te@C cathode exhibits an ultrahigh initial discharge capacity of 634 mAh g-1 at 0.1 C, which could pave a new path to design high-performance cathodes for anode-free RT Na-S batteries.

The design of chemisorption and catalysis synergistic defender for efficient room temperature sodium-sulfur batteries

Room temperature sodium-sulfur (RT-Na/S) batteries are a promising candidate for large-scale energy storage systems owing to their low manufacturing cost and high energy density. However, the severe shuttle effects and sluggish reaction kinetics hinder their practical application. Here, a Fe3Se4 nanoparticle anchored three-dimensional nitrogen-doped porous carbon nanosheet was designed as a functional defender to inhibit the shuttle effect and achieve high sulfur utilization. The porous carbon nanosheet builds a fast platform for electron and ion transport and acts as a limiting barrier for polysulfide dissolution and shuttling. Additionally, Fe3Se4 nanoparticles are incorporated to enhance the chemical anchoring and catalytic activity of polysulfides. The ex-situ characterization revealed that the Fe sites can feed electrons to polysulfides, thus facilitating the conversion of long-chain polysulfides to Na2S, resulting in high sulfur availability (323 mAh/g at 2 A/g) and long-term cycle life (72 % capacity retention at 1 A/g for 500 cycles).

Nature-Derived Sulfur Carbons for Highly-Efficient Room Temperature Sodium-Sulfur Energy Storage

In recent years, a growing interest in “beyond-Li-ion“ batteries has caused a speedy development of alternative battery technologies based on other alkali metals. Room temperature sodium sulfur (RT Na-S) batteries are potential candidate for sustainable large-scale energy storage systems. They offer low cost, nontoxicity and natural abundance of both cathode and anode materials combined with high theoretical energy density. However, rapid capacity fading related to the irreversible shuttling of soluble polysulfides, poor reaction kinetics and low sulfur utilisation in the cathode materials significantly limit their practical application.In this work, a microporous sulfur-carbon complex is produced from sustainable natural precursors in a one-pot synthesis via stepwise thermally-induced inverse vulcanisation and condensation. The material exhibits a unique structure, with sulfur chains covalently anchored to the conductive carbon matrix and physically confined in ultra-micropores. An increase in sulfur content in the sulfur-copolymer alters the morphology and chemical composition of the final sulfur-carbon material, enhancing the amount of long-chain sulfur. The combination of optimal microstructure, good electrical conductivity and high content of electrochemically active sulfur translates to an unprecedented ~99% utilisation of sulfur and the highest reported capacity for a room temperature Na-S cathode, along with high rate capability, coulombic efficiency and long-term stability. This study offers an innovative approach towards the understanding of the key chemico-physical properties of the sulfur-carbon composite materials for the development of high-performance cathodes in RT Na-S batteries with an atom-efficient utilisation of sulfur.

Amorphous FeSnOx Nanosheets with Hierarchical Vacancies for Room-Temperature Sodium-Sulfur Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries, noted for their low material costs and high energy density, are emerging as a promising alternative to lithium-ion batteries (LIBs) in various applications including power grids and standalone renewable energy systems. These batteries are commonly assembled with glass fiber membranes, which face significant challenges like the dissolution of polysulfides, sluggish sulfur conversion kinetics, and the growth of Na dendrites. Here, we develop an amorphous two-dimensional (2D) iron tin oxide (A-FeSnOx) nanosheet with hierarchical vacancies, including abundant oxygen vacancies (Ovs) and nano-sized perforations, that can be assembled into a multifunctional layer overlaying commercial separators for RT Na-S batteries. The Ovs offer strong adsorption and abundant catalytic sites for polysulfides, while the defect concentration is finely tuned to elucidate the polysulfides conversion mechanisms. The nano-sized perforations aid in regulating Na ions transport, resulting in uniform Na deposition. Moreover, the strategic addition of trace amounts of Ti3C2 (MXene) forms an amorphous/crystalline (A/C) interface that significantly improves the mechanical properties of the separator and suppresses dendrite growth. As a result, the task-specific layer achieves ultra-light (~0.1 mg cm-2), ultra-thin (~200 nm), and ultra-robust (modulus=4.9 GPa) characteristics. Consequently, the RT Na-S battery maintained a high capacity of 610.3 mAh g-1 and an average Coulombic efficiency of 99.9 % after 400 cycles at 0.5 C.

An Investigation into Electrolytes and Cathodes for Room-Temperature Sodium–Sulfur Batteries

In the pursuit of high energy density batteries beyond lithium, room-temperature (RT) sodium–sulfur (Na-S) batteries are studied, combining sulfur, as a high energy density active cathode material and a sodium anode considered to offer high energy density and very good standard potential. Different liquid electrolyte systems, including three different salts and two different solvents, are investigated in RT Na-S battery cells, on the basis of the solubility of sulfur and sulfides, specific capacity, and cyclability of the cells at different C-rates. Two alternative cathode host materials are explored: A bimodal pore size distribution activated carbon host AC MSC30 and a highly conductive carbon host of hollow particles with porous particle walls. An Na-S cell with a cathode coating with 44 wt% sulfur in the AC MSC30 host and the electrolyte 1M NaFSI in DOL/DME exhibited a specific capacity of 435 mAh/gS but poor cyclability. An Na-S cell with a cathode coating with 44 wt% sulfur in the host of hollow porous particles and the electrolyte 1M NaTFSI in TEGDME exhibited a specific capacity of 688 mAh/gS.

Synergistically promoting the catalytic conversion of polysulfides via in-situ construction of Ni-MnO2 heterostructure on N-doped hollow carbon spheres towards high-performance sodium-sulfur batteries

The room-temperature sodium-sulfur (RT Na-S) battery is considered to be a highly promising electrochemical energy storage device, attributed to its high energy density, rich sulfur reserve, and nontoxicity. However, it is constrained by the polysulfide shuttling and the low intrinsic conductivity of active sulfur. A sacrificial template method has been used to develop hetero-structured Ni-MnO2 embedded in micro/mesoporous hollow carbon spheres (HCS@Ni-MnO2) to overcome these challenges. As evidenced by electrochemical properties and computational results, the construction of hetero-structured Ni-MnO2 provides a strong affinity to polysulfides. Meanwhile, the highly conductive in-situ constructing Ni-MnO2 structure has strong adsorption to soluble sodium polysulfides and effectively improves the catalytic conversion. The micro- and mesoporous hollow carbon sphere improves the reactivity of the sulfur cathodes and physically suppresses polysulfides shuttling. Befitting from the physical and chemical confinement and the fast redox reaction of polysulfides, the as-prepared S/HCS@Ni-MnO2 cathode exhibits a high capacity of 1031.7 mAh g−1 at 0.2 A g−1 after 100 cycles, surpassing the capacities of S/HCS@Ni (820.3 mAh g−1), S/HCS@MnO2 (942.4 mAh g−1) and S/HCS (866.7 mAh g−1). Moreover, the battery with S/HCS@Ni-MnO2 cathode also exhibits excellent cycle life (586.8 mAh g−1 at 5 A g−1 after 1000 cycles) and a high rate performance (553.8 mAh g−1 at 10 A g−1). This study provides an efficient strategy for synthesizing multiple compound hetero-structured materials to facilitate the development of energy storage applications.

Stable room-temperature sodium-sulfur battery enabled by pre-sodium activated carbon cloth anode and nonflammable localized high-concentration electrolyte

Room-temperature (RT) sodium-sulfur (Na–S) battery is a promising energy storage technology with low-cost, high-energy-density and environmental-friendliness. However, the current RT Na–S battery suffers from various problems, such as poor cycling stability and poor electrolyte-electrode compatibility caused by polysulfide shuttling and active Na-metal anode. Here, a nonflammable localized high-concentration electrolyte (LHCE) (sodium bis(trifluoromethanesulfonyl)imide salt, sulfolane solvent and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether diluent in a molar ratio of 1:2:2), and a pre-sodium activated carbon cloth (NaACC) anode, are combined to enable stable and high-safety RT Na–S battery. In LHCE, the shuttle effect of polysulfide is greatly alleviated, a stable anions-derived NaF-rich cathode electrolyte interphase is formed, and a solid-solid conversion mechanism of a solid S8-solid Na2Sn (1 ≤ n ≤ 3) is achieved. Meanwhile, the Na dendrites and side reactions between electrolyte and anode are effectively inhibited by using NaACC anode. Therefore, under the synergistic effect of electrolyte regulation and negative electrode structure optimization, although using a low N/P ratio of 1.7, the RT Na–S battery also delivers a high initial capacity of 1220.8 mAh g−1, good rate capability and stable cycling performance with a high average Coulombic efficiency of 99.1 %. The capacity still remains at 704.5 mAh g−1 after 100 cycles. This innovative combination of LHCE and NaACC anode in Na–S batteries provides a new idea for further achieving stable RT Na–S batteries with long-cycle-life and high-safety.

A Polysulfides‐Defensive, Dendrite‐Suppressed, and Flame‐Retardant Separator with Lean Electrolyte for Room Temperature Sodium–Sulfur Batteries

AbstractThe dissolution/shuttling of sodium polysulfides, coupled with sodium dendrites growth, severely compromises the lifespan and stability of room temperature sodium–sulfur (RT Na–S) batteries. Herein, it proposes employing a functionalized porous ZIF‐based membrane (PZM) to address these two challenges. First, the metal ions embedded within the zeolitic imidazolate framework chemically bind with polysulfide anions, curtailing their detrimental shuttling. Second, the tailored porous structure of the membrane ensures a selective and uniform pathway for sodium ions, significantly reducing non‐uniform deposition and curbing dendritic sodium growth. Third, the intrinsically non‐combustible nature of the ZIF‐based membrane acts as a fortification against thermal outbursts and electrolyte decomposition. Implementing this polysulfide‐resistant, dendrite‐inhibiting and flame‐retardant PZM with a standard S/C cathode leads to the creation of a robust separator with lean electrolyte RT Na–S battery. This configuration may impart a novel perspective for the advancement and enhancement of RT Na–S battery systems.

Accelerating Na2S/Na2S2 conversion kinetics by electrolyte additive with high Na2S/Na2S2 solubility for high-performance room-temperature sodium–sulfur batteries

The development of room-temperature sodium sulfur batteries is severely constrained by the sluggish solid-solid conversion kinetics of Na2S/Na2S2 and the accumulation of “dead Na2S/Na2S2”. Here, we accelerate the conversion kinetics of Na2S/Na2S2 as well as reduce the accumulation of “dead Na2S/Na2S2” by 1-butyl-1-methylpyrrolidine trifluoromethanesulfonate ([P14][OTf]) ionic liquid additive that is compatible with metallic Na and has high Na2S/Na2S2 solubility. The results of three-electrode kinetics tests show a significant enhancement of the apparent redox kinetics of Na2S/Na2S2 through increasing its concentration. During battery cycling, the increase in Na2S/Na2S2 concentration can induce the formation of three-dimensional Na2S deposition and reduce the coverage of the electrode effective electroactive area, thus decreasing the battery polarization, especially at high rates. In addition, high Na2S/Na2S2 solubility can promote the reuse of “dead Na2S/Na2S2” and greatly improve the utilization of active material. At 2C rate, 351 mAh g−1 can be maintained after 800 cycles, and the capacity decay per cycle is 0.046 %. The rate and cycle performance of the battery are greatly improved. Further, a mechanism is proposed for the enhancement of battery performance via overpotential and diffusion theories.

Enhancing Conversion Kinetics through Electron Density Dual-Regulation of Catalysts and Sulfur toward Room-/Subzero-Temperature Na-S Batteries.

Room-temperature sodium-sulfur (RT Na/S) batteries have received increasing attention for the next generation of large-scale energy storage, yet they are hindered by the severe dissolution of polysulfides, sluggish redox kinetic, and incomplete conversion of sodium polysulfides (NaPSs). Herein, the study proposes a dual-modulating strategy of the electronic structure of electrocatalyst and sulfur to accelerate the conversion of NaPSs. The selenium-modulated ZnS nanocrystals with electron rearrangement in hierarchical structured spherical carbon (Se-ZnS/HSC) facilitate Na+ transport and catalyze the conversion between short-chain sulfur and Na2S. And the in situ introduced Se within S can enhance conductivity and form an S─Se bond, suppressing the "polysulfides shuttle". Accordingly, the S@Se-ZnS/HSC cathode exhibits a specific capacity of as high as 1302.5 mAh g-1 at 0.1 A g-1 and ultrahigh-rate capability (676.9 mAh g-1 at 5.0 A g-1). Even at -10 °C, this cathode still delivers a high reversible capacity of 401.2 mAh g-1 at 0.05 A g-1 and 94% of the original capacitance after 50 cycles. This work provides a novel design idea for high-performance Na/S batteries.

Designing Urchin-Like S/SiO2 with Regulated Pores Toward Ultra-Fast Room Temperature Sodium-Sulfur Battery.

Captured by high theoretical capacity and low-cost, Sodium-Sulfur (Na-S) batteries have been deemed as promising energy-storage systems. However, their electrochemical properties, containing both cycling and rate properties, still suffer from the notorious "shuttle effect" of polysulfide. Herein, through the effective regulation of pore sizes, a series of S/SiO2 cathode materials are obtained. Benefitting from the abundant pore channels of SiO2 particles, the sulfur loading is as high as 76.3%. Importantly, a suitable pore size can lead to adequate reaction and rapid diffusion behaviors, resulting in excellent electrochemical performances. Specifically, at 2.0Ag-1, the initial capacity of the as-optimized sample can be up to 1370.6mAhg-1. Surprisingly, even after 1050 cycles, it could achieve a high reversible capacity of 1280.8mAhg-1 with an attenuation rate of 0.089%. At 5.0Ag-1, after 500 cycles, the capacity can still remain ≈ 1132.6mAhg-1 (capacity retention rate, 97.5%). Given this, the work is anticipated to offer an effective strategy for advanced electrodes for Na-S batteries.

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.

A Critical Review on Room-Temperature Sodium-Sulfur Batteries: From Research Advances to Practical Perspectives.

Room-temperature sodium-sulfur (RT-Na/S) batteries are promising alternatives for next-generation energy storage systems with high energy density and high power density. However, some notorious issues are hampering the practical application of RT-Na/S batteries. Besides, the working mechanism of RT-Na/S batteries under practical conditions such as high sulfur loading, lean electrolyte, and low capacity ratio between the negative and positive electrode (N/P ratio), is of essential importance for practical applications, yet the significance of these parameters has long been disregarded. Herein, it is comprehensively reviewed recent advances on Na metal anode, S cathode, electrolyte, and separator engineering for RT-Na/S batteries. The discrepancies between laboratory research and practical conditions are elaborately discussed, endeavors toward practical applications are highlighted, and suggestions for the practical values of the crucial parameters are rationally proposed. Furthermore, an empirical equation to estimate the actual energy density of RT-Na/S pouch cells under practical conditions is rationally proposed for the first time, making it possible to evaluate the gravimetric energy density of the cells under practical conditions. This review aims to reemphasize the vital importance of the crucial parameters for RT-Na/S batteries to bridge the gaps between laboratory research and practical applications.

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.

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.