Sulfur Batteries Research Articles

Probing the Effect of Stoichiometric Ratio of Mg(CF3SO3)2/AlCl3 on Optimizing the Electrolyte Performance for Mg Sulfur Battery

The low cost and safety qualify Magnesium (Mg) metal batteries to be one of the utmost post-lithium batteries. Nonetheless, most Mg electrolyte suffers from conditionality and incompatibility with most the cathodes which have hindered the progress of Mg battery applications. Herein, we try to optimize a new electrolyte system based on Mg(CF3SO3)2 dissolved in co-solvent of acetonitrile (ACN) and tetra ethylene glycol dimethyl (TEGDME) via studying the effect of the stoichiometry of Mg(CF3SO3)2 and AlCl3 on the electrical and the electrochemical performance. Interestingly, it is found that the electrolytes with an optimized Mg(CF3SO3)2 /AlCl3 stoichiometric ratio(0.45/0.35) yield are much more efficient reversible deposition and stripping of Mg and lower overpotential. In addition, a dual (polymer/liquid) electrolyte system is used to avoid the direct contact between the Mg anode and the liquid electrolyte to protect the Mg metal anode from passivation and adjust the position of HOMO and LUMO levels of electrode/electrolyte interface relative to the Fermi level. Furthermore, this work uses an unconventional electrode, based silicon carbide, sulfur and barium titanate to demonstrate the performance of Mg batteries. This optimized electrolyte coupled with the unconventional cathode allows high initial specific discharge capacity. The present study offers new approaches for designing high-performance rechargeable magnesium battery.

Ni@Ni3N Embedded on Three-Dimensional Carbon Nanosheets for High-Performance Lithium/Sodium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are recognized as one of the most promising next-generation energy storage devices, but their practical application is greatly limited by several obstacles, such as the highly insulating nature and sluggish redox kinetics of sulfur and the dissolution of lithium polysulfides. Herein, three-dimensional carbon nanosheet frameworks anchored with Ni@Ni3N heterostructure nanoparticles (denoted Ni@Ni3N/CNS) are designed and fabricated by a chemical blowing and thermal nitridation strategy. It is demonstrated that the Ni@Ni3N heterostructure can effectively accelerate polysulfide conversion and promote the chemical trapping of polysulfides. Meanwhile, the carbon nanosheet frameworks of Ni@Ni3N/CNS establish a highly conductive network for fast electron transportation. The cells with Ni@Ni3N heterostructures as the catalyst in the cathode show excellent electrochemical performance, revealing stable cycling over 600 cycles with a low-capacity fading rate of 0.04% per cycle at 0.5 C and high-rate capability (594 mAh g-1 at 3 C). Furthermore, Ni@Ni3N/CNS can also work well in room-temperature sodium-sulfur (RT-Na/S) batteries, delivering a high specific capacity (454 mAh g-1 after 400 cycles at 0.5 C). This work provides a rational way to prepare the metal-metal nitride heterostructures to enhance the performance both of Li-S and RT-Na/S batteries.

Progress and innovation of nanostructured sulfur cathodes and metal-free anodes for room-temperature Na-S batteries.

Rechargeable batteries are a major element in the transition to renewable energie systems, but the current lithium-ion battery technology may face limitations in the future concerning the availability of raw materials and socio-economic insecurities. Sodium–sulfur (Na–S) batteries are a promising alternative energy storage device for small- to large-scale applications driven by more favorable environmental and economic perspectives. However, scientific and technological problems are still hindering a commercial breakthrough of these batteries. This review discusses strategies to remedy some of the current drawbacks such as the polysulfide shuttle effect, catastrophic volume expansion, Na dendrite growth, and slow reaction kinetics by nanostructuring both the sulfur cathode and the Na anode. Moreover, a survey of recent patents on room temperature (RT) Na–S batteries revealed that nanostructured sulfur and sodium electrodes are still in the minority, which suggests that much investigation and innovation is needed until RT Na–S batteries can be commercialized.

Titanium nitride nanocrystals anchored evenly on interconnected carbon nanosheets with effective chemisorption and catalytic effects towards polysulfides for long-life lithium−sulfur batteries

The “shuttle effect” of lithium polysulfides (LiPSs) and sluggish redox reactions limit the application of Li−S batteries. In this study, titanium nitride (TiN) nanocrystals merely and evenly anchored on carbon nanosheets (TiN@CNs) are prepared by heat treating TiO2@CNs in flowing ammonia. TiN nanoparticles do not accumulate in places without CNs, which can alleviate volume expansion in cycling process. CNs with high conductivity and a large specific surface area can accelerate Li+ and electron transportation and accommodate a higher sulfur content. Moreover, TiN nanocrystals can effectively anchor polysulfides and accelerate the redox reaction, which can be explained by the adsorption experiment of LiPSs, X-ray photoelectron spectroscopy, and theoretical calculations. Thus, the TiN@CNs-2/S cathode delivers an initial capacity of 1273 mAh g−1 and remains at 908 mAh g−1 after 100 cycles for 0.5 A g−1. For the long-term cycle performance, the cathode exhibits a slow capacity decay rate of 0.035% per cycle over 1000 cycles at 2 A g−1. This novel structure has potential in the design of advanced performance Li−S batteries.

Regulating polysulfide intermediates by ultrathin Co-Bi nanosheet electrocatalyst in lithium−sulfur batteries

The practical application of lithium–sulfur (Li–S) batteries is hindered by the nonconductivity of sulfur, sluggish reaction kinetics and polysulfide shuttling. The liquid lithium polysulfide intermediates, connecting the Li–S battery electrochemical reaction of sulfur to Li2S, play a decisive role on battery performance. Herein, Co-Bi nanosheets intimately grown on reduced graphene oxides (Co-Bi/rGO) composite has been reported for the first time to regulate the polysulfide intermediates. The Co-Bi could not only chemically trap polysulfides but also propel the acceleration of polysulfide conversion enabled by a lower free energy and decomposition energy barrier in Li–S reaction process. Therefore, the Co-Bi/rGO–S cathode delivers a high capacity of 1334 mAh g–1 at 0.2 C, impressive rate performance up to 8 C, outstanding cycling stability over 500 cycles at 1 C, and remarkable areal capacity of 8.3 mAh cm–2 with a high sulfur mass loading of 9.5 mg cm–2. The chemical binding strength, the Gibbs free energy and the energy barrier for transition state from theoretical calculations give a deep insight of polysulfide regulation by Co-Bi.

Progress and Prospect of Organic Electrocatalysts in Lithium-Sulfur Batteries.

Lithium−sulfur (Li−S) batteries featured by ultra-high energy density and cost-efficiency are considered the most promising candidate for the next-generation energy storage system. However, their pragmatic applications confront several non-negligible drawbacks that mainly originate from the reaction and transformation of sulfur intermediates. Grasping and catalyzing these sulfur species motivated the research topics in this field. In this regard, carbon dopants with metal/metal-free atoms together with transition–metal complex, as traditional lithium polysulfide (LiPS) propellers, exhibited significant electrochemical performance promotions. Nevertheless, only the surface atoms of these host-accelerators can possibly be used as active sites. In sharp contrast, organic materials with a tunable structure and composition can be dispersed as individual molecules on the surface of substrates that may be more efficient electrocatalysts. The well-defined molecular structures also contribute to elucidate the involved surface-binding mechanisms. Inspired by these perceptions, organic electrocatalysts have achieved a great progress in recent decades. This review focuses on the organic electrocatalysts used in each part of Li−S batteries and discusses the structure–activity relationship between the introduced organic molecules and LiPSs. Ultimately, the future developments and prospects of organic electrocatalysts in Li−S batteries are also discussed.

Cathode-Electrolyte Interfacial Processes in Lithium∥Sulfur Batteries under Lean Electrolyte Conditions.

The implementation of a low electrolyte/sulfur (E/S) ratio is essential to achieving high specific energy for lithium∥sulfur (Li∥S) batteries. In reality, however, the lean electrolyte condition results in low achievable capacity and inferior cyclability. In this study, we probe the interfacial processes on the sulfur cathode under the lean electrolyte condition using operando electrochemical impedance spectroscopy (EIS) and a galvanostatic intermittent titration technique (GITT). The operando EIS reveals a significant and rapid increase in the charge-transfer resistance during the transition from high-order polysulfides to low-order ones at a low E/S ratio, which is induced by a kinetic bottleneck at the interphase due to Li-ion mass transfer limitation. The GITT results confirm the kinetic bottleneck by revealing a large discharge overpotential during the transition phase. We further demonstrate that improving the adsorption of dissolved high-order polysulfides, a key step in the interfacial processes, can alleviate the kinetic limitation, thus enhancing the achievable capacity under the lean electrolyte condition.

Magnesium‐Sulfur Batteries: Polyoxometalate Modified Separator for Performance Enhancement of Magnesium–Sulfur Batteries (Adv. Funct. Mater. 26/2021)

In article number 2100868, Zhirong Zhao-Karger and co-workers report the functionalization of a commercial separator with a polyoxovanadate/carbon composite that can effectively suppress the polysulfide shuttle effect in magnesium – sulfur batteries via the chemical interaction between the vanadate and sulfur species. This innovative strategy could be an efficient approach to enhance the performance of metal–sulfur battery systems.

Rational Design and Engineering of One‐Dimensional Hollow Nanostructures for Efficient Electrochemical Energy Storage

AbstractThe unique structural characteristics of one‐dimensional (1D) hollow nanostructures result in intriguing physicochemical properties and wide applications, especially for electrochemical energy storage applications. In this Minireview, we give an overview of recent developments in the rational design and engineering of various kinds of 1D hollow nanostructures with well‐designed architectures, structural/compositional complexity, controllable morphologies, and enhanced electrochemical properties for different kinds of electrochemical energy storage applications (i.e. lithium‐ion batteries, sodium‐ion batteries, lithium‐sulfur batteries, lithium‐selenium sulfur batteries, lithium metal anodes, metal‐air batteries, supercapacitors). We conclude with prospects on some critical challenges and possible future research directions in this field. It is anticipated that further innovative studies on the structural and compositional design of functional 1D nanostructured electrodes for energy storage applications will be stimulated.

Ultra-fast and facile preparation of uniform sulfur/graphene composites with microwave for lithium−sulfur batteries

Lithium−sulfur batteries are one of the most promising energy storage systems due to their high energy density. Many efforts have been made to improve the electrochemical performance of lithium−sulfur batteries. However, the complex and time-consuming preparation process hinders their practical application. In this work, an ultra-fast and facile method has been proposed to prepare the sulfur/graphene composites in a simplified and time-saving preparation process with the assistance of microwave. Microwave is introduced to help sulfur fleetly deposit uniformly on the surface of graphene within just 30 s. Nano-sized sulfur within 30 nm is generated in this ultra-fast process. Lithium−sulfur batteries with as-prepared sulfur/graphene composites exhibit good cycling life with a capacity of 503.5 mAh g−1 at 0.2 C. This method makes it possible for lithium−sulfur batteries to be practical.

Bimetal CoNi Active Sites on Mesoporous Carbon Nanosheets to Kinetically Boost Lithium-Sulfur Batteries.

In order to solve the problem that soluble polysulfide intermediates diffuse between cathode and anode during charging and discharging, which leads to rapid attenuation of battery cycle life, the separator modification materials come into people's sight. Herein, a mesoporous carbon-supported cobalt-nickel bimetal composite (CoNi@MPC) is synthesized and directly coated on the original separator to serve as a secondary collector for lithium-sulfur batteries. CoNi@MPC exhibits multiple Co-Ni active sites, able to catalyze the reactions of soluble polysulfides, specifically accelerating the generation and decomposition of insoluble Li2 S in lithiation and delithiation process testified by the electrochemical results and density functional theory calculation. Relying on the bifunctionality of CoNi@MPC composite, the shuttle effect of lithium polysulfides can be effectively alleviated. Moreover, porous carbon as the conductive scaffold favors the improvement of electronic conductivity. Benefiting from the above advantages, the cell with CoNi@MPC separator indicates significantly enhanced electrochemical performances with excellent cycling life over 500 cycles and superior rate capabilities.

A Protein-Based Janus Separator for Trapping Polysulfides and Regulating Ion Transport in Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are a promising candidate for the next-generation energy storage system, yet their commercialization is primarily hindered by polysulfide shuttling and uncontrollable Li dendrite growth. Here, a protein-based Janus separator was designed and fabricated for suppressing both the shuttle effect and dendrite growth, while facilitating the Li+ transport. The Li metal-protecting layer was a protein/MoS2 nanofabric with high ionic conductivity and good Li+ affinity, thus capable of homogenizing the Li+ flux and facilitating the Li+ transport. The polysulfide-trapping layer was a conductive protein nanofabric enabling strong chemical/electrostatic interactions with polysulfides. Combination of the two layers was achieved by an integrated electrospinning method, yielding a robust and integral Janus separator. As a result, a long-lived symmetric Li|Li cell (>700 h) with stable cycling performance was demonstrated. More significantly, the resulting Li-S battery delivered greatly improved electrochemical performance, including excellent rate capacity and remarkable cycle stability (with a low decay rate of 0.063 % per cycle at 0.5 A g-1 over 500 cycles). This study demonstrates the effectiveness of the Janus separator configurations for simultaneously addressing the shuttle effect and dendrite growth issues of Li-S batteries and broadens the applications of electrospinning in electrochemistry community.

2D TiN@C sheets derived from MXene as highly efficient polysulfides traps and catalysts for lithium−sulfur batteries

Well known for their high energy density, lithium-sulfur (Li-S) batteries face the problem of rapid capacity degradation caused by the polysulfides (LiPSs) shuttling. By modifying the battery separator with specific materials, the shuttle effect can be effectively alleviated. Herein, two-dimensional (2D) TiN@C sheets obtained by in-situ nitridation of MXene (Ti3C2Tx, T means the termination groups, such as -F, -O, and -OH) are designed as the traps and catalysts for LiPSs in Li-S batteries. TiN@C has strong chemical absorptivity of LiPSs and can promote their conversion to Li2S2/Li2S. By mixing with graphene, which servers as a conductive network and physical barrier, a TiN@C/G separator coating is fabricated via a vacuum filtration method. Based on the carbon black/sulfur (CB/S) cathode and TiN@C/G coated separator, the batteries deliver a surprising initial discharge capacity at 0.1 C (1490.2 mAh g−1) and show a extremely low capacity loss over 600 cycles at 1 C (0.047% per cycle). This work shows new views into the design of separator coating using 2D materials for Li-S batteries with high capacity and stability.

Electrochemical Behavior Promotion of Polysulfides by Cobalt Selenide/Carbon Cloth Interlayer in Lithium−Sulfur Batteries

AbstractLithium−sulfur batteries have been regarded as the next generation of competitive batteries because of their high theoretical capacity and energy density. However, the commercial development of lithium−sulfur batteries is restricted by the shuttle action of polysulfides and volumetric expansion of sulfur. Herein, we developed cobalt selenide/carbon cloth composites (CoSe2/CC) as the interlayer. CoSe2 can not only limit the shuttling of polysulfides by Co−S bonds and accelerate the catalytic conversion kinetics of sulfur chemistry, but also increases the electrical conductivity of materials, leading to an excellent cycle stability. As a result, the cell with CoSe2/CC interlayer has a high initial capacity of 1420 mAh g−1 at 0.1 C and keeps high‐capacity retention of 596 mAh g−1 after 500 cycles at 1 C rate (70 %). Subsequent electrochemical tests show that CoSe2/CC enhance the electrochemical behavior of the polysulfides. Therefore, the hierarchical CoSe2/CC composites have promising application potential in lithium−sulfur batteries.

Yolk@Shell Structured MnS@Nitrogen-Doped Carbon as a Sulfur Host and Polysulfide Conversion Booster for Lithium/Sodium Sulfur Batteries

Lithium-sulfur (Li-S) batteries have been regarded as an important candidate for next-generation energy storage devices due to their low cost and high theoretical energy density. However, several factors retard the practical use of Li-S batteries including the slow kinetics of lithium polysulfide (LiPS) transformation as well as the shuttle effect induced by the diffusion of LiPS that damages the cycling stability of Li-S batteries. In this study, a yolk@shell structured MnS@nitrogen-doped carbon (MnS@N-C) is developed as the S host and polysulfide conversion booster, which offers both the physical confinement of S species and accelerated kinetics toward LiPS catalytic conversion. As a result, the developed S/yolk@shell MnS@N-C delivers a higher rate performance compared to S/yolk@shell MnO@N-C and S/N-C and long cycle life with a remaining capacity of 636.1 mAh g–1 after 330 cycles at 0.5C. When equipped with MnS@N-C functional separators, S/yolk@shell MnS@N-C retains a capacity of 504.2 mAh g–1 after 1000 cycles at 1C. In addition, S/yolk@shell MnS@N-C also delivers a decent capacity decay of 0.16% per cycle after 300 cycles at 0.5C in a room-temperature Na-S battery.

A dual-role electrolyte additive for simultaneous polysulfide shuttle inhibition and redox mediation in sulfur batteries

We show that thiourea serves as both a polysulfide shuttle suppressing- and a redox mediating-additive, through an investigation of thiourea redox activity, shuttle current measurements, and study of Li2S activation.

Strong lithium-polysulfide anchoring effect of amorphous carbon for lithium–sulfur batteries

Solving the shuttle effect caused by lithium polysulfide (LPS) dissolution is important in lithium−sulfur batteries. The anchoring of LPSs to carbon combined with sulfur is a method of suppressing the shuttle effect. This first-principles study is the first to report that amorphous carbon offers the best ability to anchor LPSs. The adsorption energies of LPSs on amorphous carbon are at least six times higher than those on graphene and at least two times higher than those on pyridinic-N doped graphene. The LPSs adsorbed on amorphous carbon undergo significant molecular distortion and/or partial dissociation due to the S-to-C electron transfer of 1.2–1.8 e per molecule, as well as the formation of strong bonds between both the Li and S atoms and the sp- and sp2-site C atoms. We propose an amorphous carbon−graphite hybrid anchoring material, because amorphous carbon can strongly capture LPSs and graphite can act as an electron channel.

The Effect of Monomers of Conducting Polymer in the Electrolytes on the Electrochemical Behavior of Lithium−Sulfur Batteries

The recent demand for the energy storage system with a higher energy density has turned the attention to the lithium−sulfur (Li−S) batteries due to its higher gravimetric/volumetric capacities (1672 mAh g-1 and 3467 mAh cm-3, respectively) than the metal oxide-based cathodes (e.g., 148 mAh g-1 and 1363 mAh cm-3 for LiCoO2) [1] However, in the Li−S batteries the intermediate lithium-polysulfides (LiPS) dissolve into the electrolyte followed by their shuttle between Li metal anode and S cathode, which is called the shuttle effect, has led to the performance degradation of Li−S batteries. [2-3] Thus, the strategies that reduce the dissolution of the LiPS from the cathode side, for example forming a chemical/physical protective layer on S cathode, have been mainly studied. [2-3] Among them, adding an additive into the electrolytes that can form a protective layer on S cathode during charge/discharge or pre-treatment has been considered as an effective way because it has achieved the improvement of electrochemical performance by more facile and cost-effective method compared to the ex-situ methods [4]. However, the effect of electrolyte additives and their chemical/physical change during electrochemical treatment (or cycling) on the electrochemical behavior of Li−S batteries have been rarely studied. In particular, the effect of electrochemical variables (current or voltage), which determines the electrochemical behavior of Li−S batteries and consequent electrochemical performance, has been not fully understood, therefore is needed to be delineated in detail.In this work, we employed three monomers (aniline, thiophene, pyrrole) of conducting polymers as an electrolyte additive and evaluated their effect on the electrochemical behavior of Li−S batteries. In particular, the monomers are expected to be electrochemically polymerized into the conducting polymers during battery cycling [4]. Moreover, since the three monomers contain heteroatomic bonds (C−S or C−N) where LiPS can be adsorbed, it might suppress the dissolution of LiPS [4].The galvanostatic charge/discharge test employing four different electrolytes was conducted first to investigate the stability of electrolytes containing monomers and the interaction among the electrolyte composites. (Fig. 1) Both batteries with base electrolyte and base+thiophene electrolyte (Fig. 1a-b), respectively, manifested the typical charge/discharge behavior of Li−S batteries. Meanwhile, the battery with aniline showed the impeded lower plateau reaction (from Li2SX to Li2S2/Li2S, 4≤X≤8) and that with pyrrole showed the absence of higher plateau reaction (from Li2S2/Li2S to Li2SX, 4≤X≤8) at the initial cycles. (Fig. 1c-d) The corresponding overpotential (Ƞ) at the 10th discharge and charge states was smallest in the case of base+thiophene followed by base electrolyte and base+aniline as shown in Fig. 1f. Given that the overpotential at the discharge and charge states respectively represents the resistance of liquid-to-solid and solid-to-liquid reaction, this disparity of overpotential suggests that the different molecular interaction between the electrolyte components/electrodes and monomers leads to different electrochemical behavior of Li−S batteries. [5] The effect of monomers on the solvents’ properties and the electrochemical polymerization mechanism using the monomers will be further studied, to design the highly stable Li−S battery.

Development of Non-Deteriorating Lithium-Sulfur Battery

To resolve energy issues, the demand of large-scaled capacity storage batteries are increasing. Therefore, the realization of lithium-sulfur (Li-S) battery, which is one candidate of the next-generation high-performance innovative battery systems, is strongly desired. In general, lithium metal is used as the negative electrode for Li-S batteries. On the other hand, elemental sulfur (S8) is also used as the positive electrode, and it has high theoretical reversible capacity of 1,672 mAhg-1. However, effect of Li metal negative electrode is unclear due to their chemical properties with charge/discharge process. In this study, we applied Li-doped negative electrode for suppressing the Li-dendrite formation. Therefore, we obtained Li4Ti5O12 (LTO) electrode as stable negative electrode, which is strain-free intercalation material, and high reversible characteristics of battery system are expected.To applying LTO for Li-S batteries, electrochemical doping of Li into LTO is required owing to their lack of carrier ion into LTO. Therefore, at first [Li| electrolyte |LTO] cells were assembled by using disassemble cell, which can be easily taken out cell materials without short circuit into inert atmosphere (e.g., glove box). After takeoff of Li-doping LTO (Li-LTO), lithium (Li-doped) -sulfur battery was fabricated by using SPAN as sulfur positive electrode ([Li-LTO|1M-LiFSI EC/DEC=3/7|SPAN] cell). (SPAN:developed non-degraded S positive electrode). Charge / discharge performance of prepared cells were evaluated.Fig. 1 (a) and (b) shows the charge and discharge profiles and the cycle number dependences of coulombic efficiency for prepared cell at 303K. Although operating voltage and capacity are relatively low, charge and discharge over 2000 cycles were observed. Therefore, this cell has suitable constitution in battery materials. Within 200 cycles, high coulombic efficiencies (about 99.9%) were always observed. Therefore, it suggests the possibility of realizing a non-degraded battery, which has high reversible characteristics by using Li-LTO electrode and SPAN electrode. Figure 1

Bifunctional Additive with Smoothing and Protecting Effects for Stable Lithium Metal Anode

Practical applications of lithium metal anodes are gravely impeded by inhomogeneous lithium deposition, which results in dendrite growth. Electrolyte additives are proven to be effective in improving performance but usually serve only a single function. Herein, nitrofullerene is introduced as a bifunctional additive with a smoothing effect and forms a protective solid electrolyte interphase (SEI) layer on stable lithium metal anodes. By design, nitro-C60 can gather on electrode protuberances via electrostatic interactions and then be reduced to NO2 − and insoluble C60. Next, the C60 anchors on the uneven groove of the lithium surface, resulting in a homogeneous distribution of Li ions. Finally, NO2 – anions can react with metallic Li to build a compact and stable SEI with high ion transport. With a 5 mM nitro-C60 additive, Li−Li symmetric cells show superior cycle stability in both carbonate and ether electrolytes, Li−sulfur batteries with a high cathode loading (10.6 mg cm− 2 , 6 mAh cm− 2) can achieve improved cycle retention of 63.2% over 100 cycles in a carbonate electrolyte, and full cells paired with a high-areal-capacity LiNi0.6Co0.2Mn0.2O2 cathode (3.5 mAh cm− 2) exhibit a significantly enhanced cycle lifespan even under lean electrolyte conditions. This work not only develops a new insight into the application of fullerene but also provides a novel design strategy for electrolyte additives with multiple functions for stable lithium metal anodes. Reference: Jiang, Z.; Zeng, Z.; Yang, C.; Han, Z.; Hu, W.; Lu, J.; Xie, J. Nano Lett. 2019, 19, 8780−8786. Figure 1