Sodium Polysulfide Research Articles

Generating Short‐Chain Sulfur Suitable for Efficient Sodium–Sulfur Batteries via Atomic Copper Sites on a N,O‐Codoped Carbon Composite

AbstractSodium–sulfur batteries have attracted attention due to their high energy capacities and low costs, but the dissolution of sodium polysulfides still severely affects their cycle life, limiting their real‐world applications. Herein, a stable sulfur host is reported, based on a N,O‐codoped carbon composite derived from a bimetallic Cu–Zn metal‐organic framework, which ensures high sulfur loading (67 wt%). Most importantly, this composite also includes single‐atom copper catalysts, with a high Cu loading of 8.03 wt%. Solid‐state nuclear magnetic resonance, synchrotron X‐ray absorption spectroscopy, and single‐crystal X‐ray diffraction analysis show that single atoms of Cu are coordinated with two N and two O atoms within the produced composite material. Those copper sites can weaken SS bonds in the S8 ring structure, and thus are able to catalyze the formation of short‐chain sulfur molecules in even larger‐size pores. In addition, Cu atoms facilitate the conversion between the short‐chain sulfur and Na2S. As a result, when the produced sulfur‐loaded carbon framework containing the atomic Cu catalyst is used as a cathode for sodium–sulfur batteries, it exhibits superior capacity of 776 mAh g–1 with a high sulfur utilization (1158 mAh gs–1 normalized with sulfur content) after 100 cycles at 0.1 A g–1, and an excellent rate performance of 483 mAh g–1 (720 mAh gs–1) at 5 A g–1.

A COMPARISON OF THREE-WAY SYNTHESIS AND CHARACTERIZATION OF REDUCED GRAPHENE OXIDE–SULFUR COMPOSITE

Graphite oxide was prepared by improved Hummer’s method. Then the graphene oxide (GO) suspension was obtained through ultrasonication for 1 h. The GO suspension was mixed with sulfur (S) using three different methods (namely sodium polysulfide route, sodium borohydride route, and hydrothermal route) of which two were chemical methods while one was hydrothermal method to make the composite material of reduce GO and sulfur (rGO–S). The electrode of the rGO–S composite was then prepared by making a slurry of active material, carbon black and polyvinylidene fluoride (PVDF). The sample of GO was analyzed using UV–visible and FTIR spectroscopy, while the sample of rGO and S was analyzed using XRD. This confirmed the synthesis of rGO–S for all the three methods. The comparison of all the three methods shows that the chemical methods are time consuming, difficult and toxic while hydrothermal method is easy and friendly.

АДСОРБЦИОННАЯ ОЧИСТКА СТОЧНЫХ ВОД, ОБРАЗУЮЩИХСЯ ПРИ ДЕМЕРКУРИЗАЦИИ РТУТЬЗАГРЯЗНЕННЫХ ПОЧВ

The soils of industrial enterprises operating plants for the production of chlorine and 
 alkali with a mercury cathode are contaminated with mercury. Demercurization of the soil leads to the 
 formation of mercury-containing wastewater. To remove mercury from wastewater, an adsorption 
 method is proposed using a sorbent based on lignin, organochlorine waste, and sodium polysulfide

In Situ TEM Studies of Sodium Polysulfides Electrochemistry in High Temperature Na-S Nanobatteries.

Understanding polysulfide electrochemistry in high temperature sodium-sulfur (HT-Na-S) batteries is crucial for their practical applications. Currently the discharge capacity of commercial HT-Na-S battery achieves only one third of its theoretical capacity due to polysulfides formation, understanding of which is limited due to technical difficulty in direct imaging polysulfides. Herein, in situ transmission electron microscopy implemented with a microelectromechanical systems (MEMS) heating device is used to investigate the electrochemical reactions of HT-Na-S batteries. The formation and evolution of transient polysulfides during cycling are revealed in real-time. Upon discharge, sulfur transforms to long-chain polysulfides, short-chain polysulfides, and finally Na2 S or its mixture with polysulfides, and the process is reversible during charge at high temperatures. Surprisingly, by introducing nanovoids into the sulfur cathode to buffer the large volume change thus preserving the integrity of the electronic/ionic pathways and reducing the diffusion distance of Na+ ions, the sulfur cathode is fully discharged to Na2 S rather than the conventionally observed Na2 S2 at 300°C. Moreover, the electrochemical reaction is swift and highly reversible. The in situ studies provide not only new understanding to the polysulfide electrochemistry, but also critical strategies to boost the capacity and cyclability of HT-Na-S batteries for large-scale energy storage applications.

Metal-N4@Graphene as Multifunctional Anchoring Materials for Na-S Batteries: First-Principles Study.

Developing highly efficient anchoring materials to suppress sodium polysulfides (NaPSs) shuttling is vital for the practical applications of sodium sulfur (Na-S) batteries. Herein, we systematically investigated pristine graphene and metal-N4@graphene (metal = Fe, Co, and Mn) as host materials for sulfur cathode to adsorb NaPSs via first-principles theory calculations. The computing results reveal that Fe-N4@graphene is a fairly promising anchoring material, in which the formed chemical bonds of Fe-S and N-Na ensure the stable adsorption of NaPSs. Furthermore, the doped transition metal iron could not only dramatically enhance the electronic conductivity and the adsorption strength of soluble NaPSs, but also significantly lower the decomposition energies of Na2S and Na2S2 on the surface of Fe-N4@graphene, which could effectively promote the full discharge of Na-S batteries. Our research provides a deep insight into the mechanism of anchoring and electrocatalytic effect of Fe-N4@graphene in sulfur cathode, which would be beneficial for the development of high-performance Na-S batteries.

MOF-Derived CoS2/N-Doped Carbon Composite to Induce Short-Chain Sulfur Molecule Generation for Enhanced Sodium-Sulfur Battery Performance.

Dissolution of intermediate sodium polysulfides (Na2Sx; 4≤x≤8) is a crucial obstacle for the development of room-temperature sodium-sulfur (Na-S) batteries. One promising strategy to avoid this issue is to load short-chain sulfur (S2-4), which could prohibit the generation of soluble polysulfides during the sodiation process. Herein, unlike in the previous reported cases where short-chain sulfur was stored by confinement within a small-pore-size (≤0.5 nm) carbon host, we report a new strategy to generate short-chain sulfur in larger pores (>0.5 nm) by the synergistic catalytic effect of CoS2 and appropriate pore size. Based on density functional theory calculations, we predict that CoS2 can serve as a catalyst to weaken the S-S bond in the S8 ring structure, facilitating the formation of short-chain sulfur molecules. By experimentally tuning the pore size of the CoS2-based hosts and comparing their performances as cathodes in Na-S and Li-S batteries, we conclude that such a catalytic effect depends on the proximity of sulfur to CoS2. This avoids the generation of soluble polysulfides and results in superior electrochemical properties of the composite materials introduced here for Na-S batteries. As a result, the optimized CoS2/N-doped carbon/S electrode showed excellent electrochemical performance with high reversible specific capacities of 488 mA h g-1 (962 mA h g(s)-1) after 100 cycles (0.1 A g-1) and 403 mA h g-1 after 1000 cycles (1 A g-1) with a superior rate performance (262 mA h g-1 at 5.0 A g-1).

Sulfur in Amorphous Silica for an Advanced Room-Temperature Sodium-Sulfur Battery.

The room-temperature (RT) Na/S battery is a promising energy storage system owing to suitable operating temperature, high theoretical energy density, and low cost. However, it has a poor cycle life and low reversible capacity. In this work, we report a long-life RT-Na/S battery with amorphous porous silica as a sulfur host. The sulfur is loaded into amorphous silica by a dipping method; the optimal sulfur loading is up to 73.48 wt %. Molecular dynamics simulation and first-principles calculations suggest that the complex pores, acting as micro-containers and the formation of Na-O chemical bonds between amorphous silica and sodium polysulfide, give the electrodes a strong ability to inhibit sodium polysulfide shuttle. This would give rise to effectively avoiding the loss of active sulfur, corresponding to a superior capacity and an excellent cyclability even at 10 A gsulfur -1 (nearly 100 % coulomb efficiency and high reversible capacity of 955.8 mAh gsulfur -1 after 1460 cycles).

Sulfur in Amorphous Silica for an Advanced Room‐Temperature Sodium–Sulfur Battery

AbstractThe room‐temperature (RT) Na/S battery is a promising energy storage system owing to suitable operating temperature, high theoretical energy density, and low cost. However, it has a poor cycle life and low reversible capacity. In this work, we report a long‐life RT‐Na/S battery with amorphous porous silica as a sulfur host. The sulfur is loaded into amorphous silica by a dipping method; the optimal sulfur loading is up to 73.48 wt %. Molecular dynamics simulation and first‐principles calculations suggest that the complex pores, acting as micro‐containers and the formation of Na‐O chemical bonds between amorphous silica and sodium polysulfide, give the electrodes a strong ability to inhibit sodium polysulfide shuttle. This would give rise to effectively avoiding the loss of active sulfur, corresponding to a superior capacity and an excellent cyclability even at 10 A gsulfur−1 (nearly 100 % coulomb efficiency and high reversible capacity of 955.8 mAh gsulfur−1 after 1460 cycles).

Enabling a Stable Room-Temperature Sodium-Sulfur Battery Cathode by Building Heterostructures in Multichannel Carbon Fibers.

Room-temperature sodium-sulfur (RT Na-S) batteries are widely considered as one of the alternative energy-storage systems with low cost and high energy density. However, the both poor cycle stability and capacity are two critical issues arising from low conversion kinetics and sodium polysulfides (NaPSs) dissolution for sulfur cathodes during the charge/discharge process. Herein, we report a highly stable RT Na-S battery cathode via building heterostructures in multichannel carbon fibers. The TiN-TiO2@MCCFs, fabricated by electrospinning and nitriding techniques, are loaded with the active material S, forming S/TiN-TiO2@MCCFs as the cathode in a RT Na-S battery. At 0.1 A g-1, the cathode produces the capacity of more than 640 mAh g-1 within 100 cycles with a high Coulombic efficiency of nearly 100%. Even at 5 A g-1, the battery still exhibites a capacity of 257.1 mAh g-1 after 1000 cycles. Combining structural and electrochemical analyses with the first-principles calculations reveals that the incorporation of the highly electrocatalytic activity of TiN with the powerful chemisorption of TiO2 well stabilizes S and also alleviates the shuttle effects of polysulfides. This work with simple processes and low cost is expected to promote the further development and application of metal-S batteries.

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.

High‐Capacity and Stable Sodium‐Sulfur Battery Enabled by Confined Electrocatalytic Polysulfides Full Conversion

AbstractThe efficient polysulfide capture and reversible sulfur recovery during reverse charging process are critical to exploiting the full potential of room temperature NaS batteries. Here, based on a core‐shell design strategy, the structural and chemical synergistic manipulation of sodium polysulfides quasi‐solid‐state reversible conversion is proposed. The sulfur is encapsulated in the multi‐pores of 3D interconnected carbon fiber as the core structure. The Fe(CN)64−‐doped polypyrrole film serves as a redox‐active polar shell to lock up polysulfides and promote complete polysulfide conversion. Importantly, the short‐chain Na2S4 polysulfides are reduced to Na2S directly leaving with a small fraction of soluble intermediates as the cation‐transfer medium at the core/shell interface, and freeing up formation of solid Na2S2 incomplete product. Further, the redox mediator with open Fe species electrocatalytically lowers the Na2S oxidation energy barrier and renders the high reversibility of electrodeposited Na2S. The tunable quasi‐solid‐state reversible sulfur conversion under versatile polymer sheath greatly enhances sulfur utilization, affording a remarkable capacity of 1071 mAh g−1 and a stable high capacity of 700 mAh g−1 at 200 mA g−1 after 200 cycles. The confined electrocatalytic effect provides a strategy for tuning electrochemical pathway of sulfur species and guarantees high‐efficiency sulfur electrochemistry.

Effect of Cr-C Coatings on the Corrosion Resistance of 304 Stainless Steel in the Molten Sodium Polysulfide

Effect of Cr-C Coatings on the Corrosion Resistance of 304 Stainless Steel in the Molten Sodium Polysulfide

Superior Anchoring of Sodium Polysulfides to the Polar C2N 2D Material: A Potential Electrode Enhancer in Sodium-Sulfur Batteries.

Despite the high theoretical specific energy in rechargeable sodium–sulfur batteries, the shuttle effect severely hampers its capacity and reversibility, which could be overcome by introducing an anchoring material. We, herein, use first-principles calculations to study the low-cost, easily synthesized, environmentally friendly, and stable two-dimensional polar nitrogenated holey graphene (C2N) and nonpolar polyaniline (C3N) to investigate their performance as anchoring materials and the mechanism behind the binding to identify the best candidate to improve the performance of sodium–sulfur batteries. We gain insight into the interaction, including the lowest-energy configurations, binding energies, binding nature, charge transfer, and electronic properties. Sodium primarily contributes to binding with the nanosheets, which is in accordance with their characteristics as anchoring materials. Sodium polysulfides (NaPSs) and the S8 cluster adsorb at the pores of C2N, where there are six electron lone pairs, one for each N atom. The polar C2N binds the NaPSs much strongly than the nonpolar C3N. In contrast to C3N, the charge population substantially modifies by adsorbing NaPSs on C2N, with a substantial charge transfer from the sulfur atoms. The calculated work function of 6.04 eV for pristine C2N, comparable with the previously reported values, decreases on adsorption of the NaPSs formed from battery discharging. We suggest that the inclusion of C2N into sulfur electrodes could also improve their issue with poor conductivity.

Electrochemical redox kinetic behavior of S8 and Na2Sn (n = 2, 4, 6, 8) on vulcan XC-72R carbon in a flowing-electrolyte system

Many studies have shown that sulfur electrodes in room-temperature sodium–sulfur (RT Na–S) batteries undergo a liquid-phase electrochemical reaction. Moreover, the electrochemical redox kinetic behavior of S8 and sodium polysulfides (Na2S8, Na2S6, Na2S4, and Na2S2) is important in understanding the macroscopic kinetics of sulfur electrodes. In this study, a three-electrode electrochemical test system is built using a two-chamber micro-electrolysis cell with a flowing electrolyte and Nafion membrane. Electrochemical kinetic parameters, such as the onset redox potentials, exchange current densities, reaction orders, and apparent activation energies of the sodium polysulfides during the redox process are obtained from a steady-state polarization curve. The onset redox potentials of S8, Na2S8, Na2S6, Na2S4, and Na2S2 on Vulcan XC-72R carbon are 2.37, 2.23, 2.11, 1.99, and 1.83 V (vs. Na/Na+), respectively. Furthermore, the relationship between the discharge capacity of sodium polysulfides and their onset redox potentials is established. The aforementioned kinetic parameters are vital in elucidating the formation of discharge/charge platforms and sloping regions in an RT Na–S battery. The results of this work provide a basis to further understand the performance of RT Na–S batteries.

Metal chalcogenide hollow polar bipyramid prisms as efficient sulfur hosts for Na-S batteries

Sodium sulfur batteries require efficient sulfur hosts that can capture soluble polysulfides and enable fast reduction kinetics. Herein, we design hollow, polar and catalytic bipyramid prisms of cobalt sulfide as efficient sulfur host for sodium sulfur batteries. Cobalt sulfide has interwoven surfaces with wide internal spaces that can accommodate sodium polysulfides and withstand volumetric expansion. Furthermore, results from in/ex-situ characterization techniques and density functional theory calculations support the significance of the polar and catalytic properties of cobalt sulfide as hosts for soluble sodium polysulfides that reduce the shuttle effect and display excellent electrochemical performance. The polar catalytic bipyramid prisms sulfur@cobalt sulfide composite exhibits a high capacity of 755 mAh g−1 in the second discharge and 675 mAh g−1 after 800 charge/discharge cycles, with an ultralow capacity decay rate of 0.0126 % at a high current density of 0.5 C. Additionally, at a high mass loading of 9.1 mg cm−2, sulfur@cobalt sulfide shows high capacity of 545 mAh g−1 at a current density of 0.5 C. This study demonstrates a hollow, polar, and catalytic sulfur host with a unique structure that can capture sodium polysulfides and speed up the reduction reaction of long chain sodium polysulfides to solid small chain polysulfides, which results in excellent electrochemical performance for sodium-sulfur batteries.

Single-sulfur atom discrimination of polysulfides with a protein nanopore for improved batteries

Research on batteries mostly focuses on electrodes and electrolytes while few activities regard separator membranes. However, they could be used as a toolbox for injecting chemical functionalities to capture unwanted species and enhance battery lifetime. Here, we report the use of biological membranes hosting a nanopore sensor for electrical single molecule detection and use aqueous sodium polysulfides encountered in sulfur-based batteries for proof of concept. By investigating the host-guest interaction between polysulfides of different chain-lengths and cyclodextrins, via combined chemical approaches and molecular docking simulations, and using a selective nanopore sensor inserted into a lipid membrane, we demonstrate that supramolecular polysulfide/cyclodextrin complexes only differing by one sulfur can be discriminated at the single molecule level. Our findings offer innovative perspectives to use nanopores as electrolyte sensors and chemically design membranes capable of selective speciation of parasitic molecules for battery applications and therefore pave the way towards smarter electrochemical storage systems.

On the prospects of using a modified sulfidizer in the processing of oxidized copper ores

In order to improve the efficiency of sulfidization methods for oxidized ores, the problem of reducing the energy intensity of the process must be solved. In this regard, a promising method is the sulfidization of oxidized copper ores using a modified reagent that allows the process to be conducted without heating or any separate equipment. The modified sulfidizing agent designed to improve the efficiency of flotation concentration is produced by the mixing of sodium polysulfide and ammonium sulfate solutions. Comparative flotation experiments were conducted using pre-sulfidized oxidized copper ore containing 1.2 % of total copper, of which 1.08 % (or 90 %) was oxidized copper. The possibility of carrying out the sulfidization process in a flotation cell without forced heating of the reaction mixture has been established. At the same time, the modified reagent exceeds sodium polysulfide in terms of its flotation efficiency by 5 %. The chemical analysis of the processing products for the content of oxidized copper has demonstrated that its mass fraction decreased from 1.08 to 0.63 %. The experimental design method has been used to establish the best application conditions for the modified reagent. These are: the reagent consumption of 2.6 kg/t; slurry agitation with the sulfidizing agent for four minutes; and the collector (potassium butyl xanthate) consumption for the flotation process of 500 g/t. The copper recovery was 69.85 %. A mathematical model was designed for the flotation process with preliminary sulfidization of the oxidized copper ore in the form of a generalized miltifactorial equation.The work was performed with the grant support of the Ministry of Education and Science of the Republic of Kazakhstan (grant No. AP05130143).

Mesoporous Nitrogen-Doped Carbon Nanospheres as Sulfur Matrix and a Novel Chelate-Modified Separator for High-Performance Room-Temperature Na-S Batteries.

Room-temperature sodium-sulfur (RT/Na-S) batteries are considered among the most promising next-generation energy storage and conversion systems because of the earth-abundant reserves of sodium and sulfur. These batteries also possess the advantages of high theoretical gravimetric capacity, high energy density, and low cost. Herein, highly uniform Fe3+ /polyacrylamide nanospheres (FPNs) are fabricated on a large-scale by a facile, low-cost approach. Subsequently, mesoporous nitrogen-doped carbon nanospheres (PNC-Ns), obtained by carbonizing FPNs, are applied as a sulfur matrix to improve the utilization of sulfur, enhance the overall conductivity of the cathode, and inhibit the shuttling of sodium polysulfides (SPSs). In addition, graphene and FPNs are simultaneously coated onto the side of the separator to form a FPNs-graphene-functionalized separator (FPNs-G/separator); here, the mesoporous FPNs effectively anchor and block the SPSs, while the large specific area graphene sheets eliminate the intrinsic mechanical brittleness of the FPNs and improve the overall conductivity of RT/Na-S batteries. When S/PNC-Ns as a cathode and FPNs-G/separator are assembled into an RT/Na-S battery, it delivers a high discharge capacity (639 mAh g-1 at 0.1 C after 400 cycles), stable cycle life (396 mAh g-1 at 0.5 C after 800 cycles), and good rate performance (228 mAh g-1 at 2 C).

ОПРЕДЕЛЕНИЕ ПОЛИСУЛЬФИД-ИОНОВ В ЩЕЛОЧНОЙ СРЕДЕ В УСЛОВИЯХ КАТОДНОЙ ИНВЕРСИОННОЙ ВОЛЬТАМПЕРОМЕТРИИ С РТУТНО-ПЛЕНОЧНЫМ ЭЛЕКТРОДОМ

Актуальность. Полисульфиды щелочных, щелочноземельных металлов и аммония являются компонентами технологических сред в крупнотоннажных производствах (щёлоки в технологии целлюлозы; растворы чернения и воронения; реагенты для производства полисульфидных эластомеров), используются для получения новых функциональных материалов (герметики), играют определяющую роль при функционировании химических источников тока нового поколения. В связи с этим изучение закономерностей протекания электродных процессов с участием полисульфидов является актуальным. Цель: установить условия определения полисульфид-ионов в щелочных растворах с использованием катодной инверсионной вольтамперометрии с ртутно-пленочным электродом. Объекты: растворы полисульфидов натрия Na2S2 и Na2S3, растворы гидроксида натрия. Методы: постоянно- и переменнотоковая катодная инверсионная вольтамперометрия, циклическая вольтамперометрия, накопительный электролиз. Результаты. Предложены эмпирические уравнения для расчета изменения энергии Гиббса образования Sn2–-ионов в водных растворах и их стандартных потенциалов в зависимости от степени полисульфидности в интервале n=1…8. Проведены расчеты равновесных активностей ионно-молекулярных форм в системе Hg–S–H2O при различных значениях рН и потенциалов. Установлены оптимальные условия определения полисульфид-ионов S22– и S32– в щелочной среде (0,1 М NaOH) на ртутно-пленочном электроде с использованием постоянно- и переменнотоковой катодной инверсионной вольтамперометрии: потенциал предэлектролиза –0,5 В (х. с. э.); продолжительность предэлектролиза 1…2 мин; последующая катодная поляризация до Екон= –1,0 В; предварительное деаэрирование растворов азотом. В этих условиях концентрационная зависимость величины максимума катодного тока Iк при Еmax= –0,8…–0,9 В линейна в интервале концентраций полисульфидов 1×10–7…1×10–3 М. Метод может быть использован для определения общего содержания полисульфидов в растворе и для расчета средней степени полисульфидности в ионах Sn2–.

АДСОРБЦИОННАЯ ТЕХНОЛОГИЯ ОЧИСТКИ СТОЧНЫХ ВОД ОТ СОЕДИНЕНИЙ КАДМИЯ

The possibility of using lignin based sorbents for removal of the cadmium compounds from sewage is researched. The sorbents were obtained by polycondensation of chlorlignin, wastewaresepichlorgidrin production and sodium polysulfide. The data about removal of cadmium from model solutions: the pH influence and process kinetic are discussed.