Selenium or Tellurium as Eutectic Accelerators for High-Performance Lithium/Sodium–Sulfur Batteries

Materials Design and Mechanistic Understanding of Tellurium and Tellurium-Sulfur Cathodes for Rechargeable Batteries

ConspectusThe market demand for lithium-ion batteries (LIBs) has been proliferating in wide applications, from portable electronics and electric vehicles to renewable energy storage, due to their advantages of high energy density and reliable life cycles. Currently, further development of LIBs is hindered by the limited specific/volumetric capacity and high cost of conventional intercalation-type cathode materials. In this context, sulfur (S) has gained intensive attention as a conversion-type cathode because of its abundance, low cost, and high theoretical capacity (1675 mAh g-1). However, the insulating nature of S causes severe issues of sluggish redox kinetics, low S utilization, and unsatisfactory practical capacity. So far, extensive efforts have been devoted to boosting Li-S redox kinetics and enhancing cycling stability by inhibiting the shuttle effect, including developing functional electrolyte additives, introducing redox catalysts, and tailoring the S cathode structure. Partially substituting S atoms in S8 rings with high-electrical-conductivity elements (e.g., selenium, 1 × 10-3 S m-1) at the molecular level proves to be an effective strategy for tackling the above-mentioned challenges in Li-S batteries. It is noteworthy that tellurium (Te), with remarkable electrical conductivity (2 × 102 S m-1) and high density (6.24 g cm-3), is a promising battery electrode material that can realize fast electron transport and deliver volumetric capacity comparable to that of S or Se. Additionally, Te-S molecular regulation is one facile strategy to reshape Li-S chemistry, accelerate redox kinetics, and manipulate the lithiation/delithiation behaviors. Te is an effective eutectic accelerator that prevents polysulfide dissolution in Li-S batteries under the dissolution-deposition mechanism. Meanwhile, the Li-Te electrochemistry can contribute to reversible capacity in Li-TexSy batteries through Te-Li2Te conversion and enhance the materials utilization of TexSy.This Account highlights state-of-the-art advancements in applying Te or TexSy as high-capacity cathodes for rechargeable batteries. First, battery configuration and reaction pathways in Li-Te batteries are discussed, followed by the introduction of cathode design strategies to improve cathode structure stability. The limitations of this Te-only cathode are outlined in terms of the abundance, cost, and energy density. Second, the role of Te in Li-S chemistry is clarified by the analysis of the crystal structure, electrochemical behaviors, solid electrolyte interphase composition, and energy profiles. Third, recent progresses on quasi-solid-state Li-Te batteries have been introduced, focusing on flexible gel polymer electrolytes with adjustable ionic conductivity. Afterward, advancements in interface engineering by the atomic layer deposition technique in metal-Te batteries are highlighted. Additionally, mechanistic analysis in emerging zinc-TexSy batteries with outstanding areal capacity is demonstrated. Finally, we provide insightful perspectives on the future directions of material design in Te-based energy storage technologies. This Account is expected to deepen the fundamental understanding of metal-Te/TexSy chemistry and offer inspiration for the further development of Te-based high-energy-density rechargeable batteries.

Sulfurized polyacrylonitrile as cathodes for advanced lithium-sulfur batteries: advances in modification strategies

Sulfurized polyacrylonitrile (S@PAN) composites have gathered a lot of interest because of their advantages of high theoretical energy density, excellent cycling stability, and environmental friendliness. Meanwhile, their unique "covalent bonding" mechanism effectively avoids the dissolution and shuttling of polysulfides, and thus they are expected to be the most promising candidate for the cathode material in lithium-sulfur (Li-S) batteries. Over the past five years, S@PAN cathode materials have been widely studied in Li-S batteries, and it is very important to summarize the advances over time for their practical applications. This article reviews the latest progress concerning the modification of S@PAN cathode materials for improving poor electrical conductivity, low sulfur content, and sluggish reaction kinetics, and proposes possible research directions. We hope this review provides valuable insights and references for future research on Li-S batteries.

Alginic acid-functionalized silver nanoparticles: A rapid monitoring tool for detecting the technology-critical element tellurium

The increasing global demand for tellurium, driven by its critical role in alloys, photovoltaic devices, and electronics, has raised concerns about its environmental pollution and neurotoxicity. In response, the potential of alginic acid (AA), a renewable, low-cost, and sustainable biopolymer, was explored for the biosynthesis of ultra-small silver nanoparticles (AgNPs) and their application in the detection of tellurium (Te(IV)). The effect of key synthesis parameters on desired physicochemical properties and yield of AgNPs was established to ensure high specificity and sensitivity towards Te(IV). The purified AgNPs with AA surface ligands were utilized to demonstrate a ratiometric absorbance sensor that exhibits excellent linearity and nanomolar-level affinity. This approach achieved a high correlation coefficient of ∼ 0.982, with a low detection limit of about 22 nM. Further investigations into the effect of pH, ionic strength, and organic molecules were conducted to elucidate detection performance and molecular understanding. The detection mechanism relies on the coordination between Te(IV) ions and the carboxylate groups of AA, which initiates aggregation-induced plasmon coupling in adjacent AgNPs. The capability of this analytical method to monitor Te(IV) in real-world water samples features its rapidity, user-friendliness, and suitability for point-of-care monitoring, making it a promising alternative to more complex techniques.

Quantum Spin Exchange Interactions to Accelerate the Redox Kinetics in Li-S Batteries

Spin-engineering with electrocatalysts have been exploited to suppress the "shuttle effect" in Li-S batteries. Spin selection, spin-dependent electron mobility and spin potentials in activation barriers can be optimized as quantum spin exchange interactions leading to a significant reduction of the electronic repulsions in the orbitals of catalysts. Herein, we anchor the MgPc molecules on fluorinated carbon nanotubes (MgPc@FCNT), which exhibits the single active Mg sites with axial displacement. According to the density functional theory calculations, the electronic spin polarization in MgPc@FCNT not only increases the adsorption energy toward LiPSs intermediates but also facilitates the tunneling process of electron in Li-S batteries. As a result, the MgPc@FCNT provides an initial capacity of 6.1 mAh cm-2 even when the high sulfur loading is 4.5 mg cm-2, and still maintains 5.1 mAh cm-2 after 100 cycles. This work provides a new perspective to extend the main group single-atom catalysts enabling high-performance Li-S batteries.

Phenyl Tellurosulfides as Cathode Materials for Rechargeable Lithium Batteries

Phenyl ditelluride (PDTe) as a cathode material for rechargeable batteries has a low specific capacity (130.9 mAh g-1) due to limited active sites (two). To increase its capacity, additional active species need to be added to the structure of PDTe, like sulfur. Here, phenyl tellurosulfide (PDTeS) and phenyl tellurodisulfide (PDTeS2) can be formed via addition reactions and have specific capacities of 242.8 and 339.6 mAh g-1, respectively. The products are characterized by mass spectrometry and Raman spectroscopy. The Li/PDTeSn (n = 1-2) cells exhibit high material utilization (>85%) and unique redox mechanism. They can be cycled stably for more than 1000 cycles at an areal mass loading of 1.1 mg cm-2 and maintain capacity retentions of >72% after 100 cycles with PDTeSn loading of ∼6 mg cm-2. Moreover, the Li/PDTeS2 cell achieves a specific energy of up to 695 Wh kg-1 even when the electrolyte/PDTeS2 ratio is as low as 2.5 μL mg-1. The successful synthesis and application of PDTeSn prove that they are promising cathode materials for rechargeable lithium batteries.

A Catalytic Electrolyte Additive Modulating Molecular Orbital Energy Levels of Lithium Polysulfides for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have ultrahigh theoretical specific capacity, but the practical application is hindered by the severe shuttle effect and the sluggish redox kinetics of the intermediate lithium polysulfides (LiPSs). Effectively enhancing the conversion kinetics of LiPSs is essential for addressing these issues. Herein, the redox kinetics of LiPSs are effectively improved by introducing 6-azauracil (6-AU) molecules to the organic electrolyte to modulate the molecular orbital energy level of LiPSs. The 6-AU as a soluble catalyst can form complexes with LiPSs via Li-O bonds. These complexes are liable to transform because of the elevated HOMO and the reduced LUMO energy levels as compared to the dissociative LiPSs, resulting in small energy gaps (Egap) and exhibiting stronger redox activity. Benefiting from the rapid conversion kinetics, the shuttling effect of LiPSs is alleviated to a great extent, so that sulfur utilization is improved and the lithium electrode is protected. In addition, the introduction of 6-AU modulates the deposition behavior of Li2S and eases the coverage of the cathode surface by the insulating Li2S layer. The Li-S battery containing 6-AU provides superior capacity retention of 853 mAh g-1 after 150 cycles at 0.2 C and shows remarkable high-rate performance and retains a specific discharge capacity of 855 mAh g-1 at 5 C. This study accelerates the kinetics of Li-S batteries by tuning the HOMO and LUMO energy levels of LiPSs, which opens an avenue for designing functional electrolyte additives.

Manipulating Redox Kinetics using p-n Heterojunction Biservice Matrix as both Cathode Sulfur Immobilizer and Anode Lithium Stabilizer for Practical Lithium-Sulfur Batteries

As an attractive high-energy-density technology, the practical application of lithium-sulfur (Li-S) batteries is severely limited by the notorious dissolution and shuttle effect of lithium polysulfides (LiPS), resulting in sluggish reaction kinetics and uncontrollable dendritic Li growth. Herein, a p-n typed heterostructure consisting of n-type MoS2 nanoflowers embedded with p-type NiO nanoparticles is designed on carbon nanofibers (denoted as NiO-MoS2 @CNFs) as both cathode sulfur immobilizer and anode Li stabilizer for practical Li-S batteries. Such p-n typed heterostructure is proposed to establish the built-in electric field across the heterointerface for facilitated the positive charge to reach the surface of NiO-MoS2 , meanwhile inherits the excellent LiPS adsorption ability of p-type NiO nanoparticles and catalytic ability of n-type MoS2 . As the anode matrix, the implementation of NiO-MoS2 heterostructure can prevent the growth of Li dendrites by enhancing the lithiophilicity and reducing local current density. The obtained Li-S full battery exhibits an ultra-high areal capacity over 7.3 mAh cm-2 , far exceeding that of current commercial Li-ion batteries. Meanwhile, a stable cycling performance can be achieved under low electrolyte/sulfur ratio of 5.8 µL mg-1 and negative/positive capacity ratio of 1. The corresponding pouch cell maintains high energy density of 305 Wh kg-1 and stable cycling performance under various bending angles.

Research on Wide-Temperature Rechargeable Sodium-Sulfur Batteries: Features, Challenges and Solutions

Sodium-sulfur (Na-S) batteries hold great promise for cutting-edge fields due to their high specific capacity, high energy density and high efficiency of charge and discharge. However, Na-S batteries operating at different temperatures possess a particular reaction mechanism; scrutinizing the optimized working conditions toward enhanced intrinsic activity is highly desirable while facing daunting challenges. This review will conduct a dialectical comparative analysis of Na-S batteries. Due to its performance, there are challenges in the aspects of expenditure, potential safety hazards, environmental issues, service life and shuttle effect; thus, we seek solutions in the electrolyte system, catalysts, anode and cathode materials at intermediate and low temperatures (T < 300 °C) as well as high temperatures (300 °C < T < 350 °C). Nevertheless, we also analyze the latest research progress of these two situations in connection with the concept of sustainable development. Finally, the development prospects of this field are summarized and discussed to look forward to the future of Na-S batteries.

Strategies to mitigate the shuttle effect in room temperature sodium-sulfur batteries: improving cathode materials

Room-temperature sodium-sulfur batteries (RT-Na/S batteries) with high reversible capacity (1675 mA h g^-1) and excellent energy density (1274 W h kg^-1) based on abundant resources of the metal Na have become a research hotspot recently. However, the intermediate product sodium polysulfides (NaPSs) generated during the charge-discharge process are easily dissolved in the ether electrolyte and transferred from the sulfur cathode to the metallic sodium surface, resulting in rapid capacity decay (shuttle effect), which seriously affects the practical application of RT-Na/S batteries. Herein, the mechanism and recent research progress in suppressing the shuttle effect of the sulfur cathode in RT-Na/S batteries are summarized. Strategies such as carbon-based materials physically fixing NaPSs, polar materials absorbing NaPSs to reduce their dissolution, and catalytic materials accelerating the transformation of NaPSs into final products are provided. Challenges and insights into high-performance sulfur electrodes for optimizing RT-Na/S batteries are discussed.

Interface Engineering Toward Expedited Li2 S Deposition in Lithium-Sulfur Batteries: A Critical Review

Lithium-sulfur batteries (LSBs) with superior energy density are among the most promising candidates of next-generation energy storage techniques. As the key step contributing to 75% of the overall capacity, Li₂ S deposition remains a formidable challenge for LSBs applications because of its sluggish kinetics. The severe kinetic issue originates from the huge interfacial impedances, indicative of the interface-dominated nature of Li₂ S deposition. Accordingly, increasing efforts have been devoted to interface engineering for efficient Li₂ S deposition, which has attained inspiring success to date. However, a systematic overview and in-depth understanding of this critical field are still absent. In this review, the principles of interface-controlled Li₂ S precipitation are presented, clarifying the pivotal roles of electrolyte-substrate and electrolyte-Li₂ S interfaces in regulating Li₂ S depositing behavior. For the optimization of the electrolyte-substrate interface, efforts on the design of substrates including metal compounds, functionalized carbons, and organic compounds are systematically summarized. Regarding the regulation of electrolyte-Li₂ S interface, the progress of applying polysulfides catholytes, redox mediators, and high-donicity/polarity electrolytes is overviewed in detail. Finally, the challenges and possible solutions aiming at optimizing Li₂ S deposition are given for further development of practical LSBs. This review would inspire more insightful works and, more importantly, may enlighten other electrochemical areas concerning heterogeneous deposition processes.

Synthesis of the Ni2P-Co Mott-Schottky Junction as an Electrocatalyst to Boost Sulfur Conversion Kinetics and Application in Separator Modification in Li-S Batteries

To overcome the shuttling effect and sluggish conversion kinetics of polysulfides, a large number of catalysts have been designed for lithium-sulfur (Li-S) batteries. Herein, a Mott-Schottky junction catalyst composed of Co nanoparticles and Ni₂P was designed to improve polysulfide kinetics. Our investigations reveal the rearrangement of charges at the Schottky junction interface and the construction of the built-in electric field are crucial for lowering the activation energy of the dissolved Li₂S_n reduction and Li₂S nucleation reaction. Furthermore, a series of experimental and electrochemical tests were performed to demonstrate that the Schottky catalytic effect enhanced the synergistic catalytic effect. With a Ni₂P-Co@CNT catalyst, the battery exhibits an initial specific capacity of 874 mAh g^-1 at a rate of 4.0 C, and the decay rate per cycle is 0.049% in 700 cycles. Meanwhile, the battery shows 0.118% decay rate per cycle at 0.5 C in 100 cycles at a high sulfur loading of 10 mg cm^-2. The Schottky heterojunction structure proposed here has been shown to have a good catalytic effect on the reduction of Li₂S_n and nucleation of Li₂S, which provides a profound guidance for efficient and rational catalyst design.

Locally Concentrated Ionic Liquid Electrolyte with Partially Solvating Diluent for Lithium/Sulfurized Polyacrylonitrile Batteries

The development of Li/sulfurized polyacrylonitrile (SPAN) batteries requires electrolytes that can form stable electrolyte/electrode interphases simultaneously on lithium-metal anodes (LMAs) and SPAN cathodes. Herein, a low-flammability locally concentrated ionic liquid electrolyte (LCILE) employing monofluorobenzene (mFBn) as the diluent is proposed for Li/SPAN cells. Unlike non-solvating diluents in other LCILEs, mFBn partially solvates Li⁺ , decreasing the coordination between Li⁺ and bis(fluorosulfonyl)imide (FSI^- ). In turn, this triggers a more substantial decomposition of FSI^- and consequently results in the formation of a solid electrolyte interphase (SEI) rich in inorganic compounds, which enables a remarkable Coulombic efficiency (99.72%) of LMAs. Meanwhile, a protective cathode electrolyte interphase (CEI), derived mainly from FSI^- and organic cations, is generated on the SPAN cathodes, preventing the dissolution of polysulfides. Benefiting from the robust interphases simultaneously formed on both the electrodes, a highly stable cycling of Li/SPAN cells for 250 cycles with a capacity retention of 71% is achieved employing the LCILE and only 80% lithium-metal excess.

A phenyl S-Te bond with unique redox activity in dilute electrolyte of a lithium battery

Phenyl tellurosulfide (PhS-TePh) was used to study the redox activity of the S-Te bond in lithium batteries. PhS-TePh formed a dynamic covalent network during lithiation, which provided a balance between responsiveness and stability to facilitate ion and electron transfer, enabling Li/PhS-TePh cells to achieve stable cycling and excellent rate performance in dilute electrolyte.

Advances in the Development of Single-Atom Catalysts for High-Energy-Density Lithium-Sulfur Batteries

Although lithium-sulfur (Li-S) batteries are promising next-generation energy-storage systems, their practical applications are limited by the growth of Li dendrites and lithium polysulfide shuttling. These problems can be mitigated through the use of single-atom catalysts (SACs), which exhibit the advantages of maximal atom utilization efficiency (≈100%) and unique catalytic properties, thus effectively enhancing the performance of electrode materials in energy-storage devices. This review systematically summarizes the recent progress in SACs intended for use in Li-metal anodes, S cathodes, and separators, briefly introducing the operating principles of Li-S batteries, the action mechanisms of the corresponding SACs, and the fundamentals of SACs activity, and then comprehensively describes the main strategies for SACs synthesis. Subsequently, the applications of SACs and the principles of SACs operation in reinforced Li-S batteries as well as other metal-S batteries are individually illustrated, and the major challenges of SACs usage in Li-S batteries as well as future development directions are presented.

Ion-Selective Covalent Organic Framework Membranes as a Catalytic Polysulfide Trap to Arrest the Redox Shuttle Effect in Lithium-Sulfur Batteries

In the wake of shaping the energy future through materials innovation, lithium-sulfur batteries (LSBs) are top-of-the-line energy storage system attributed to their high theoretical energy density and specific capacity inclusive of low material costs. Despite their strengths, LSBs suffer from the cross-over of soluble polysulfide redox species to the anode, entailing fast capacity fading and inferior cycling stability. Adding to the concern, the insulating character of polysulfides lends to sluggish reaction kinetics. To address these challenges, we construct optimized polysulfide blockers-cum-conversion catalysts by accommodating the battery separator with covalent organic framework@Graphene (COF@G) composites. We settle on a crystalline TAPP-ETTB COF in the interest of its nitrogen-enriched scaffold with a regular pore geometry, providing ample lithiophilic sites for strong chemisorption and catalytic effect to polysulfides. On another front, graphene enables high electron mobility, boosting the sulfur redox kinetics. Consequently, a lithium-sulfur battery with a TAPP-ETTB COF@G-based separator demonstrates a high reversible capacity of 1489.8 mA h g^-1 at 0.2 A g^-1 after the first cycle and good cyclic performance (920 mA h g^-1 after 400 cycles) together with excellent rate performance (827.7 mA h g^-1 at 2 A g^-1). The scope and opportunities to harness the designability and synthetic structural control in crystalline organic materials is a promising domain at the interface of sustainable materials, energy storage, and Li-S chemistry.

Hierarchically porous TiO2@C membrane with oxygen vacancy: A novel platform for enhancing catalytic conversion of polysulfides

In the case of high sulfur loading or high current discharge, constructing sulfur composite cathode by the traditional coating preparation process is difficult to solve the intractable problems of the...

An organodiselenide containing electrolyte enables sulfurized polyacrylonitrile cathodes with fast redox kinetics in Li-S batteries

An organoselenide compound, phenyl diselenide (PDSe), is employed as a soluble electrolyte additive to enhance the kinetics of a sulfurized polyacrylonitrile cathode, in which radical exchange in the solid-liquid interface forms dynamic S-Se bonds. Consequently, the PDSe assisted cathode exhibits enhanced battery performance in both ether and carbonate electrolytes.

Expediting the Conversion of Li2S2 to Li2S Enables High-Performance Li-S Batteries

The solid-solid conversion of Li₂S₂ to Li₂S is a crucial and rate-controlling step that provides one-half of the theoretical capacity of lithium-sulfur (Li-S) batteries. The catalysts in the Li-S batteries are often useless in the solid-solid conversion due to the poor contact interfaces between solid catalysts and insoluble solid Li₂S₂. Considering that ultrafine nanostructured materials have the properties of quantum size effects and unconventional reactivities, we design and synthesize for the pomegranate-like sulfur nanoclusters@nitrogen-doped carbon@nitrogen-doped carbon nanospheres (S@N-C@N-C NSs) with a seed-pulp-peel nanostructure. The ultrafine S@N-C subunits (diameter ≈5 nm) and effects of a spatial structure perfectly realize the rapid conversion of ultrafine Li₂S₂ to Li₂S. The S@N-C@N-C seed-pulp-peel NS cathodes exhibit excellent sulfur utilization, superb rate performance (760 mAh g^-1 at 10.0 C), and an ultralow capacity decay rate of about 0.016% per cycle over 1000 cycles at 4.0 C. The proposed strategy based on ultrafine nanostructured materials can also inform material engineering in related energy storage and conversion fields.

An Emerging Energy Storage System: Advanced Na-Se Batteries

Sodium-selenium (Na-Se) batteries have aroused enormous attention due to the large abundance of the element sodium as well as the high electronic conductivity and volumetric capacity of selenium. In this battery system, some primary advances in electrode materials have been achieved, mainly involving the design of Se-based cathode materials. In this Review, the electrochemical mechanism is discussed, thus revealing the main challenges in Na-Se batteries. Then, the advances in the design of Se-based cathode materials for Na-ion storage are systemically summarized, classified, and discussed, including Se/carbon composite, Se/polar material/carbon composites, and hybrid Se_xS_y alloys. Some potential strategies enabling the improvement of crucial challenges and enhancement of electrochemical performance are also proposed to provide guidelines for the enhancements of Na-ion storage. An outlook for future valuable research directions is proposed to understand more deeply the electrochemical mechanism of Na-Se batteries and promote their further developments in full cell performance and commercialization.