A New Type of Electrolyte System To Suppress Polysulfide Dissolution for Lithium-Sulfur Battery

Extended Battery Compatibility Consideration from an Electrolyte Perspective

The performance of electrochemical batteries is intricately tied to the physicochemical environments established by their employed electrolytes. Traditional battery designs utilizing a single electrolyte often impose identical anodic and cathodic redox conditions, limiting the ability to optimize redox environments for both anode and cathode materials. Consequently, advancements in electrolyte technologies are pivotal for addressing these challenges and fostering the development of next-generation high-performance electrochemical batteries. This review categorizes perspectives on electrolyte technology into three key areas: additives engineering, comprehensive component analysis encompassing solvents and solutes, and the effects of concentration. By summarizing significant studies, the efficacy of electrolyte engineering is highlighted, and the review advocates for further exploration of optimized component combinations. This review primarily focuses on liquid electrolyte technologies, briefly touching upon solid-state electrolytes due to the former greater vulnerability to electrode and electrolyte interfacial effects. The ultimate goal is to generate increased awareness within the battery community regarding the holistic improvement of battery components through optimized combinations.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

Zwitterionic Separator Featured with Superdesolvating Properties for High Performance Lithium-Sulfur Batteries

Lithium-sulfur chemistry has greatly expanded the boundaries of lithium batteries, but the persistent parasitic reaction of soluble sulfur intermediates with lithium anode remains a primary challenge. Understanding and regulating the solvation structures of lithium ions (Li+) and polysulfides (LiPSs) are critical to addressing the above issues. Herein, inspired by the natural superhydrophilic resistance to contamination, we developed a zwitterionic nanoparticles (ZWP) separator capable of modulating the solvated of Li+ and LiPSs. The dense solvated layer induced by ZWP effectively prevents the movement of LiPSs without compromising Li+ transport. Moreover, the high electrolyte affinity of the ZWP effectively results in minimizing the deposition of LiPSs on the separator. Furthermore, the structure of the solvated Li+ and LiPSs is also unveiled by molecular simulation and nuclear magnetic resonance (NMR). In addition, in situ UV setup proved the ZWP separator can effectively suppress the shuttle of LiPSs. The restricted space formed by the tightly packed ZWP stabilizes the lithium deposition and regulates dendrite growth. Consequently, the performance of lithium-sulfur batteries is significantly improved and good cycle stability is maintained even at high sulfur loadings (5 mg cm-2). This contribution provides a new insight into the rational design of lithium-sulfur battery separators.

Fluorinated Multi-Walled Carbon Nanotubes Coated Separator Mitigates Polysulfide Shuttle in Lithium-Sulfur Batteries

Li-S batteries still suffer from two of the major challenges: polysulfide shuttle and low inherent conductivity of sulfur. Here, we report a facile way to develop a bifunctional separator coated with fluorinated multiwalled carbon nanotubes. Mild fluorination does not affect the inherent graphitic structure of carbon nanotubes as shown by transmission electron microscopy. Fluorinated carbon nanotubes show an improved capacity retention by trapping/repelling lithium polysulfides at the cathode, while simultaneously acting as the "second current collector". Moreover, reduced charge-transfer resistance and enhanced electrochemical performance at the cathode-separator interface result in a high gravimetric capacity of around 670 mAh g^-1 at 4C. Unique chemical interactions between fluorine and carbon at the separator and the polysulfides, studied using DFT calculations, establish a new direction of utilizing highly electronegative fluorine moieties and absorption-based porous carbons for mitigation of polysulfide shuttle in Li-S batteries.

Opportunities of Flexible and Portable Electrochemical Devices for Energy Storage: Expanding the Spotlight onto Semi-solid/Solid Electrolytes

The ever-increasing demand for flexible and portable electronics has stimulated research and development in building advanced electrochemical energy devices which are lightweight, ultrathin, small in size, bendable, foldable, knittable, wearable, and/or stretchable. In such flexible and portable devices, semi-solid/solid electrolytes besides anodes and cathodes are the necessary components determining the energy/power performances. By serving as the ion transport channels, such semi-solid/solid electrolytes may be beneficial to resolving the issues of leakage, electrode corrosion, and metal electrode dendrite growth. In this paper, the fundamentals of semi-solid/solid electrolytes (e.g., chemical composition, ionic conductivity, electrochemical window, mechanical strength, thermal stability, and other attractive features), the electrode-electrolyte interfacial properties, and their relationships with the performance of various energy devices (e.g., supercapacitors, secondary ion batteries, metal-sulfur batteries, and metal-air batteries) are comprehensively reviewed in terms of materials synthesis and/or characterization, functional mechanisms, and device assembling for performance validation. The most recent advancements in improving the performance of electrochemical energy devices are summarized with focuses on analyzing the existing technical challenges (e.g., solid electrolyte interphase formation, metal electrode dendrite growth, polysulfide shuttle issue, electrolyte instability in half-open battery structure) and the strategies for overcoming these challenges through modification of semi-solid/solid electrolyte materials. Several possible directions for future research and development are proposed for going beyond existing technological bottlenecks and achieving desirable flexible and portable electrochemical energy devices to fulfill their practical applications. It is expected that this review may provide the readers with a comprehensive cross-technology understanding of the semi-solid/solid electrolytes for facilitating their current and future researches on the flexible and portable electrochemical energy devices.

Self-Assembled Networks for Regulating Lithium Polysulfides in Lithium-Sulfur Batteries

Inhibiting the shuttle effect caused by soluble lithium polysulfides (LiPSs) is of importance for lithium-sulfur (Li-S) batteries. Here, a strategy was developed to construct protective layers by self-assembly networks to regulate the LiPSs. 2,5-Dichloropyridine (25DCP) holds two kinds of functional groups. Among them, the two C-Cl bonds were nucleophilic substituted by S in LiPSs to form long chains. The pyridine N interacted with Li in other LiPSs via Li bonds to form a short chain. As a result, the long chains were cross-linked by the short chain to form an insoluble network. The as-prepared network covered the sulfur electrode interface to suppress the shuttle effect of the subsequently generated LiPSs. Furthermore, 25DCP improved the redox dynamics by changing the energy level and electronic structure of the sulfur species. Therefore, the Li-S batteries with 25DCP exhibited good electrochemical performance. This work provides a feasible strategy for regulating the LiPSs.

Electrostatic Potential-Induced Co-N4 Active Centers in a 2D Conductive Metal-Organic Framework for High-Performance Lithium-Sulfur Batteries

The use of single-atom catalysts is a promising approach to solve the issues of polysulfide shuttle and sluggish conversion chemistry in lithium-sulfur (Li-S) batteries. However, a single-atom catalyst usually contains a low content of active centers because more metal ions lead to generation of aggregation or the formation of nonatomic catalysts. Herein, a 2D conductive metal-organic framework [Co₃(HITP)₂] with abundant and periodic Co-N₄ centers was decorated on carbon fiber paper as a functional interlayer for advanced Li-S batteries. The Co₃(HITP)₂-decorated interlayer exhibits a chemical anchoring effect and facilitates conversion kinetics, thus effectively restraining the polysulfide shuttle effect. Density functional theory calculations demonstrate that the Co-N₄ centers in Co₃(HITP)₂ feature more intense electron density and more negative electrostatic potential distribution than those in the carbon matrix as the single-atom catalyst, thereby promoting the electrochemical performance due to the lower reaction Gibbs free energies and decomposition energy barriers. As a result, the optimized batteries deliver a high rate capacity of over 400 mA h g^-1 at 4 C current and a satisfying capacity decay rate of 0.028% per cycle over 1000 cycles at 1 C. The designed Co₃(HITP)₂-decorated interlayer was used to prepare one of the most advanced Li-S batteries with excellent performance (reversible capacity of 762 mA h g^-1 and 79.6% capacity retention over 500 cycles) under high-temperature conditions, implying its great potential for practical applications.

Unity of Opposites between Soluble and Insoluble Lithium Polysulfides in Lithium-Sulfur Batteries

Rechargeable batteries based on Li-S chemistry show promise as being possible for next-generation energy storage devices because of their ultrahigh capacities and energy densities. Research over the past decade has demonstrated that the morphology of lithium polysulfides (LPSs) in electrolytes (soluble or insoluble) plays a decisive role in battery performance. Early studies have focused mainly on inhibiting the dissolution of LPSs and invested considerable effort to realize this objective. However, in recent years, a completely different view that the dissolution of LPSs during battery discharge/charge should be promoted has emerged. At this critical juncture in the large-scale application of Li-S batteries, it is time to summarize and discuss both sides of the contradiction. Herein, an overview of these two opposite views pertaining to soluble and insoluble LPSs, including their historical environment, classical strategies, advantages, and disadvantages. Finally, the future morphology of LPSs in Li-S batteries is predicted based on a multiangle review of research studies conducted thus far, and the reasoning behind this conjecture is thoroughly discussed.

In Situ Synthesis of Organopolysulfides Enabling Spatial and Kinetic Co-Mediation of Sulfur Chemistry

Li-S batteries have been regarded as one of the most promising alternatives of the next-generation Li batteries. However, the dissolution and shuttling of lithium polysulfides lead to low cycle stability and low Coulombic efficiency, which intensively hinder the practical application of Li-S batteries. Herein, we propose a strategy to simultaneously promote the redox kinetics and inhibit the shuttle of lithium polysulfides, through in situ synthesis of insoluble organopolysulfides by adding a special additive. Attractively, the thus-formed insoluble organopolysulfides in the form of nanoparticle aggregates are also capable of adsorbing unconverted lithium polysulfides and hence effectively spatially suppress the shuttle effect. Furthermore, the organopolysulfides served as active redox mediators, showing faster redox kinetics of S chemistry than that of lithium polysulfides. As a result, the Li-S batteries showed impressive capacity, improved rate performance, and long cycling stability even under lean-electrolyte and high sulfur loading conditions.

Recent Advances and Strategies toward Polysulfides Shuttle Inhibition for High-Performance Li-S Batteries

Lithium-sulfur (Li-S) batteries are regarded as the most promising next-generation energy storage systems due to their high energy density and cost-effectiveness. However, their practical applications are seriously hindered by several inevitable drawbacks, especially the shuttle effects of soluble lithium polysulfides (LiPSs) which lead to rapid capacity decay and short cycling lifespan. This review specifically concentrates on the shuttle path of LiPSs and their interaction with the corresponding cell components along the moving way, systematically retrospect the recent advances and strategies toward polysulfides diffusion suppression. Overall, the strategies for the shuttle effect inhibition can be classified into four parts, including capturing the LiPSs in the sulfur cathode, reducing the dissolution in electrolytes, blocking the shuttle channels by functional separators, and preventing the chemical reaction between LiPSs and Li metal anode. Herein, the fundamental aspect of Li-S batteries is introduced first to give an in-deep understanding of the generation and shuttle effect of LiPSs. Then, the corresponding strategies toward LiPSs shuttle inhibition along the diffusion path are discussed step by step. Finally, general conclusions and perspectives for future research on shuttle issues and practical application of Li-S batteries are proposed.

Manipulating the Conversion Kinetics of Polysulfides by Engineering Oxygen p-Band of Halloysite for Improved Li-S Batteries

Polar oxides are widely used as the cathodes to impede the shuttle effect in lithium-sulfur batteries, but suffer from the sluggish desorption and conversion of polysulfides due to too strong affinity of polysulfides on oxygen sites. Herein, employing halloysite as a model, an approach to overcome these shortcomings is proposed via engineering oxygen p-band center by loading titanium dioxide nanoparticles onto Si-O surface of halloysite. Using density functional theory calculations, it is predicted that electron transfer from titanium dioxide nanoparticles to interfacial O sites results in downshift of p-band center of O sites that promote desorption of polysulfides and the cleavage of Li-S and S-S, accelerating the conversion kinetics of polysulfides. The designed composite cathode material delivers outstanding electrochemical performance in Li-S batteries, outperforming the recently reported similar cathodes. The concept could provide valuable insight into the design of other catalysts for Li-S batteries and beyond.

Rational design of a cobalt sulfide nanoparticle-embedded flexible carbon nanofiber membrane electrocatalyst for advanced lithium-sulfur batteries

Both the sluggish redox kinetics and severe polysulfide shuttling behavior hinders the commercialization of lithium-sulfur (Li-S) battery. To solve these obstacles, we design a cobalt sulfide nanoparticle-embedded flexible carbon nanofiber membrane (denoted as CoS₂@NCF) as sulfiphilic functional interlayer materials. The hierarchically porous structure of carbon nanofiber is conducive to immobilizing sulfur species and facilitating lithium-ion penetration. Moreover, electrocatalytic CoS₂nanoparticles can significantly enhance the catalytic effect, achieving favorable adsorption-diffusion-conversion interface of polysulfide. Combined with these synergistic features, the assembled Li-S cell with CoS₂@NCF interlayer exhibited a great discharge capacity of 950.9 mAh g^-1with prolonged cycle lifespan at 1 C (maintained 648.1 mAh g^-1over 500 cycles). This multifunctional interlayer material used in this contribution provides an advanced route for developing high-energy-density Li-S battery.

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.

Isomeric Organodithiol Additives for Improving Interfacial Chemistry in Rechargeable Li-S Batteries

Lithium-sulfur (Li-S) batteries have a high theoretical specific energy; however, their performance is plagued by the shuttle effect of lithium polysulfides and the instability of the lithium anode interface. Great efforts have been made using electrolyte additives to address the issues. Herein, we report a class of electrolyte additives, i.e., benzenedithiols (BDTs). Among the three isomers of BDTs, 1,4-BDT shows the best effect on the performance improvement of a Li-S battery because it can bond more sulfur atoms than the other two. The functionality of 1,4-BDT on the cathode and anode involves the chemical reactions of thiol groups. The S-S bonds were generated from 1,4-BDT and sulfur through oligomerization, which change the original redox path of sulfur and inhibit the shuttle effect of lithium polysulfides. In addition, 1,4-BDT can form a smooth and stable solid-electrolyte interphase (SEI), which can enable the Li/Li symmetric cell with an ultralow overpotential of 0.08 V at a high current density of 5 mA cm^-2 for over 300 h. The Li-S cell with 1,4-BDT displays the highest cycling stability at a C/5 rate, with an initial capacity of 1548.5 mAh g^-1 and a reversible capacity of 1306.9 mAh g^-1 after 200 cycles. The Li-S pouch cell with 1,4-BDT and 2.8 g of sulfur exhibits an initial capacity of 2640 mAh and a capacity retention rate of 84.2% after 26 cycles at a C/10 rate. This work demonstrates that organodithiol compounds can be used as functional electrolyte additives and provides a new direction to design materials for advanced Li-S batteries.

Artificial dual solid-electrolyte interfaces based on in situ organothiol transformation in lithium sulfur battery

The interfacial instability of the lithium-metal anode and shuttling of lithium polysulfides in lithium-sulfur (Li-S) batteries hinder the commercial application. Herein, we report a bifunctional electrolyte additive, i.e., 1,3,5-benzenetrithiol (BTT), which is used to construct solid-electrolyte interfaces (SEIs) on both electrodes from in situ organothiol transformation. BTT reacts with lithium metal to form lithium 1,3,5-benzenetrithiolate depositing on the anode surface, enabling reversible lithium deposition/stripping. BTT also reacts with sulfur to form an oligomer/polymer SEI covering the cathode surface, reducing the dissolution and shuttling of lithium polysulfides. The Li-S cell with BTT delivers a specific discharge capacity of 1,239 mAh g^-1 (based on sulfur), and high cycling stability of over 300 cycles at 1C rate. A Li-S pouch cell with BTT is also evaluated to prove the concept. This study constructs an ingenious interface reaction based on bond chemistry, aiming to solve the inherent problems of Li-S batteries.

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^-1at 0.2 C. This method makes it possible for lithium-sulfur batteries to be practical.

An Organodiselenide Comediator to Facilitate Sulfur Redox Kinetics in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered as promising next-generation energy storage devices due to their ultrahigh theoretical energy density, where soluble lithium polysulfides are crucial in the Li-S electrochemistry as intrinsic redox mediators. However, the poor mediation capability of the intrinsic polysulfide mediators leads to sluggish redox kinetics, further rendering limited rate performances, low discharge capacity, and rapid capacity decay. Here, an organodiselenide, diphenyl diselenide (DPDSe), is proposed to accelerate the sulfur redox kinetics as a redox comediator. DPDSe spontaneously reacts with lithium polysulfides to generate lithium phenylseleno polysulfides (LiPhSePSs) with improved redox mediation capability. The as-generated LiPhSePSs afford faster sulfur redox kinetics and increase the deposition dimension of lithium sulfide. Consequently, the DPDSe comediator endows Li-S batteries with superb rate performance of 817 mAh g^-1 at 2 C and remarkable cycling stability with limited anode excess. Moreover, Li-S pouch cells with the DPDSe comediator achieve an actual initial energy density of 301 Wh kg^-1 and 30 stable cycles. This work demonstrates a novel redox comediation strategy with an effective organodiselenide comediator to facilitate the sulfur redox kinetics under pouch cell conditions and inspires further exploration in mediating Li-S kinetics for practical high-energy-density batteries.

Nitrogen-doped multi-channel carbon nanofibers incorporated with nickel nanoparticles as a multifunctional modification layer of the separator for ultra stable Li–S batteries

This work provided insight into the mechanism of the reversible conversion of LiPSs and the construction of ultra-stable Li–S batteries.

Strongly trapping soluble lithium polysulfides using polar cysteamine groups for highly stable lithium sulfur batteries

Sulfur has become one of the most promising positive electrode materials for lithium sulfur batteries due to its high theoretical capacity and high energy density (2500 Wh kg^-1). The use of common nonpolar carbon/sulfur composites has proved to be a good way to improve the performance, but they still cannot efficiently trap highly polar lithium polysulfides due to the weak interactions between nonpolar carbon and polar polysulfides. Herein, we report a new strategy of using polar cysteamine groups to trap polar polysulfides, leading to greatly enhanced capacity of ∼920 mAh g^-1 at 1 C with a high Coulombic efficiency of ∼99.1%, and a long cycle life of over 600 cycles with a capacity retention higher than 80%. Importantly, in situ UV/Vis spectroscopy was employed to identify intermediates during cycling, which demonstrates the constructed unique polar cysteamine functionalized carbon nanotubes (CNTs) can greatly reduce the production of polysulfides and suppress the shuttle effect. The broken-bond model of linear polysulfane during cycling was further demonstrated by density functional theory calculations. The present strategy of using polar cysteamine-functionalized CNTs to trap soluble intermediates is promising and has significant potential for the development of highly efficient lithium sulfur batteries.

CO2-Oxidized Ti3C2Tx-MXenes Components for Lithium-Sulfur Batteries: Suppressing the Shuttle Phenomenon through Physical and Chemical Adsorption

Lithium-sulfur (Li-S) batteries are one of the main challenges facing Li-ion technology because the insulating nature of sulfur and the shuttle phenomenon of dissolved lithium polysulfides (LPSs) in liquid electrolytes result in critical problems, including low Coulombic efficiency, loss of active material, and rapid capacity decay. Here, we oxidized delaminated transition metal carbides (MXenes) using CO₂ (Oxi-d-MXenes) and used them as both cathode electrode with sulfur and modified separator coated onto the glass fiber without a conductive material and binder to suppress the diffusion of LPSs. Oxi-d-MXenes annealed at 900 °C using CO₂ gas formed perfectly converted rutile-TiO₂ nanocrystalline particles on their two-dimensional sheets. Li-S batteries fabricated with the Oxi-d-MXenes cathode and the Oxi-d-MXenes-modified separator exhibited high Coulombic efficiency (nearly 99%) and retained a capacity of about 900 mAh g^-1 after 300 cycles at a current density of 1C. These results were attributed to the chemical and physical adsorption between the Oxi-d-MXenes and the LPSs. Our results imply that Oxi-d-MXenes prepared by the CO₂ treatment exhibit physical and electrochemical properties that enhance the performance of Li-S batteries.

Atomic-Scale Dispersed Fe-Based Catalysts Confined on Nitrogen-Doped Graphene for Li-S Batteries: Polysulfides with Enhanced Conversion Efficiency

Lithium-sulfur batteries have been considered as potential electrochemical energy-storage devices owing to their satisfactory theoretical energy density. Nonetheless, the inferior conversion efficiency of polysulfides in essence leads to fast capacity decay during the discharge/charge cycle. In this work, it is successfully demonstrated that the conversion efficiency of lithium polysulfides is remarkably enhanced by employing a well-distributed atomic-scale Fe-based catalyst immobilized on nitrogen-doped graphene (Fe@NG) as a coating of separator in lithium-sulfur batteries. The quantitative electrocatalytic efficiency of the conversion of lithium polysulfides is determined through cyclic voltammetry. It is also proven that the Fe-N_X configuration with highly catalytic activity is quite beneficial for the conversion of lithium polysulfides. In addition, the adsorption and permeation experiments distinctly indicate that the strong anchoring effect, originated from the charge redistribution of N doping into the graphene matrix, inhibits the movement of lithium polysulfides. Thanks to these advantages, if the as-prepared Fe@NG catalyst is combined with polypropylene and applied as a separator (Fe@NG/PP) in Li-S batteries, a high initial capacity (1616 mA h g^-1 at 0.1 C), excellent capacity retention (93 % at 0.2 C, 70 % at 2 C), and superb rate performance (820 mA h g^-1 at 2 C) are achieved.

Boosting High-Performance in Lithium-Sulfur Batteries via Dilute Electrolyte

Polysulfide shuttle effects, active material losses, formation of resistive surface layers, and continuous electrolyte consumption create a major barrier for the lightweight and low-cost lithium-sulfur (Li-S) battery adoption. Tuning electrolyte composition by using additives and most importantly by substantially increasing electrolyte molarity was previously shown to be one of the most effective strategies. Contrarily, little attention has been paid to dilute and super-diluted LiTFSI/DME/DOL/LiNO₃ based-electrolytes, which have been thought to aggravate the polysulfide dissolution and shuttle effects. Here we challenge this conventional wisdom and demonstrate outstanding capabilities of a dilute (0.1 mol L^-1 of LiTFSI in DME/DOL with 1 wt. % LiNO₃) electrolyte to enable better electrode wetting, greatly improved high-rate capability, and stable cycle performance for high sulfur loading cathodes and low electrolyte/sulfur ratio in Li-S cells. Overall, the presented study shines light on the extraordinary ability of such electrolyte systems to suppress short-chain polysulfide dissolution and polysulfide shuttle effects.

A wet-processed, binder-free sulfur cathode integrated with a dual-functional separator for flexible Li-S batteries

Developing flexible, robust and lightweight sulfur cathodes by rationally designing their structures and configurations through a viable and scalable strategy is a critical enabler for fulfilling flexible lithium-sulfur (Li-S) batteries. However, besides the requirements for cathode flexibility, intrinsic limitations from the shuttling of lithium polysulfides and the growth of Li dendrites have restricted the widespread implementations of Li-S batteries. Here, we report a wet-processed strategy by dissolving and recrystallizing S in a suitable solvent to fabricate a flexible, binder-free S cathode. Integrating the resulting S cathode with a dual-functional separator has demonstrated to be able to suppress both the shuttle effect and growth of dendritic Li. The wet-processed strategy not only enables the fabrication of flexible and binder-free S-nanomat cathodes, but also facilitates the deposition of the cathodes on the separators. Meanwhile, a dual-functional separator is fabricated by vapor-phase polymerization of polypyrrole (PPy) coating on both surfaces of the commercial separator, which leads to the reduction of the shuttle effect and the suppression of the growth of dendritic Li simultaneously. As a result, by integrating the S-nanomat and the dual-functional separator, the cathode exhibits exceptional mechanical properties and electrochemical performance. Li-S pouch cells are further demonstrated to show stable cycling performance in the bending state, indicating the feasibility of the integrated S cathode for flexible Li-S batteries.

Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries

This review article summarizes the current trends and provides guidelines towards next-generation rechargeable lithium and lithium-ion battery chemistries.