A Bifunctional Perovskite Promoter for Polysulfide Regulation toward Stable Lithium–Sulfur Batteries

Lithium‐sulfur (Li? S) batteries are strongly considered as the next‐generation rechargeable cells. However, both the shuttle of lithium polysulfides (LiPSs) and sluggish kinetics in random deposition of lithium sulfides (Li₂S) significantly degrade the capacity, rate performance, and cycling life of Li? S cells. Herein, bifunctional Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ perovskite nanoparticles (PrNPs) are proposed as a promoter to immobilize LiPSs and guide the deposition of Li₂S in a Li? S cell. The oxygen vacancy in PrNPs increases the metal reactivity to anchor LiPSs, and co‐existence of lithiophilic (O) and sulfiphilic (Sr) sites in PrNP favor the dual‐bonding (Li? O and Sr? S bonds) to anchor LiPSs. The high catalytic nature of PrNP facilitates the kinetics of LiPS redox reaction. The PrNP with intrinsic LiPS affinity serves as nucleation sites for Li₂S deposition and guides its uniform propagation. Therefore, the bifunctional LiPS promoter in Li? S cell yields high rate performance and ultralow capacity decay rate of 0.062% (a quarter of pristine Li? S cells). The proposed strategy to immobilize LiPSs, promotes the conversion of LiPS, and regulates deposition of Li₂S by an emerging perovskite promoter and is also expected to be applied in other energy conversion and storage devices based on multi‐electron redox reactions.     

Revisiting the Role of Polysulfides in Lithium–Sulfur Batteries

Intermediate polysulfides (S_n, where n = 2–8) play a critical role in both mechanistic understanding and performance improvement of lithium–sulfur batteries. The rational management of polysulfides is of profound significance for high‐efficiency sulfur electrochemistry. Here, the key roles of polysulfides are discussed, with regard to their status, behavior, and their correspondingimpact on the lithium–sulfur system. Two schools of thoughts for polysulfide management are proposed, their advantages and disadvantages are compared, and future developments are discussed.     

Single Nickel Atoms on Nitrogen‐Doped Graphene Enabling Enhanced Kinetics of Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have arousing interest because of their high theoretical energy density. However, they often suffer from sluggish conversion of lithium polysulfides (LiPS) during the charge/discharge process. Single nickel (Ni) atoms on nitrogen‐doped graphene (Ni@NG) with Ni–N₄ structure are prepared and introduced to modify the separators of Li–S batteries. The oxidized Ni sites of the Ni–N₄ structure act as polysulfide traps, efficiently accommodating polysulfide ion electrons by forming strong S_x ^2????Ni? N bonding. Additionally, charge transfer between the LiPS and oxidized Ni sites endows the LiPS on Ni@NG with low free energy and decomposition energy barrier in an electrochemical process, accelerating the kinetic conversion of LiPS during the charge/discharge process. Furthermore, the large binding energy of LiPS on Ni@NG also shows its ability to immobilize the LiPS and further suppresses the undesirable shuttle effect. Therefore, a Li–S battery based on a Ni@NG modified separator exhibits excellent rate performance and stable cycling life with only 0.06% capacity decay per cycle. It affords fresh insights for developing single‐atom catalysts to accelerate the kinetic conversion of LiPS for highly stable Li–S batteries.     

MoS2/Celgard Separator as Efficient Polysulfide Barrier for Long‐Life Lithium–Sulfur Batteries

A high lithium conductive MoS₂/Celgard composite separator is reported as efficient polysulfides barrier in Li–S batteries. Significantly, thanks to the high density of lithium ions on MoS₂ surface, this composite separator shows high lithium conductivity, fast lithium diffusion, and facile lithium transference. When used in Li–S batteries, the separator is proven to be highly efficient for depressing polysulfides shuttle, leading to high and long cycle stability. With 65% of sulfur loading, the device with MoS₂/Celgard separator delivers an initial capacity of 808 mAh g^?1 and a substantial capacity of 401 mAh g^?1 after 600 cycles, corresponding to only 0.083% of capacity decay per cycle that is comparable to the best reported result so far. In addition, the Coulombic efficiency remains more than 99.5% during all 600 cycles, disclosing an efficient ionic sieve preventing polysulfides migration to the anode while having negligible influence on Li⁺ ions transfer across the separator. The strategy demonstrated in this work will open the door toward developing efficient separators with flexible 2D materials beyond graphene for energy‐storage devices.     

Multifunctional Interlayer Based on Molybdenum Diphosphide Catalyst and Carbon Nanotube Film for Lithium–Sulfur Batteries

A multifunctional interlayer, composed of molybdenum diphosphide (MoP₂) nanoparticles and a carbon nanotube (CNT) film, is introduced into a lithium–sulfur (Li–S) battery system to suppress polysulfide migration. Molybdenum diphosphide acts as the catalyst and can capture polysulfides and improve the polysulfide conversion activity during the discharge/charge processes. The CNT film acts as a conductive skeleton to support the MoP₂ nanoparticles and to ensure their uniform distribution. The CNT film physically hinders polysulfide migration, acts as a current collector, and provides abundant electron pathways. The Li–S battery containing the multifunctional MoP₂/CNT interlayer exhibits excellent electrochemical performance. It delivers a reversible specific capacity of 905 mA h g^?1 over 100 cycles at 0.2 C, with a capacity decay of 0.152% per cycle. These results suggest the introduction of the multifunctional CNT/MoP₂ interlayer as an effective and practical method for producing high‐performance Li–S batteries.     

Novel Non‐Carbon Sulfur Hosts Based on Strong Chemisorption for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are considered as promising candidates for energy storage systems owing to their high theoretical capacity and high energy density. The application of Li–S batteries is hindered by several obstacles, however, including the shuttle effect, poor electrical conductivity, and the severe volume expansion of sulfur. The traditional method is to integrate sulfur with carbon materials. But the interaction between polysulfide intermediates and carbon is only weak physical adsorption, which easily leads to the escape of species from the framework (shuttle effect) of the material causing capacity loss. Recently, however, there has been a trend for the introduction of novel non‐carbon materials as sulfur hosts based on the strong chemisorption. This review highlights recent research progress on novel non‐carbon sulfur hosts based on strong chemisorption, in Li–S batteries. In comparison with carbon‐based sulfur hosts, most non‐carbon sulfur hosts have been demonstrated to be polar host materials that could efficiently adsorb polysulfide via strong chemisorption, mitigating their dissolution. The intrinsic mechanism associated with the role of non‐carbon‐based host materials in improving the performance of Li–S batteries is discussed.     

A Combined Ordered Macro‐Mesoporous Architecture Design and Surface Engineering Strategy for High‐Performance Sulfur Immobilizer in Lithium–Sulfur Batteries

The practical application of lithium–sulfur (Li–S) batteries is hindered by the “shuttle” of lithium polysulfides (LiPS) and sluggish Li–S kinetics issues. Herein, a synergistic strategy combining mesoporous architecture design and defect engineering is proposed to synthesize multifunctional defective 3D ordered mesoporous cobalt sulfide (3DOM N‐Co₉S_8?x) to address the shuttling and sluggish reaction kinetics of polysulfide in Li–S batteries. The unique 3DOM design provides abundant voids for sulfur storage and enlarged active interfaces that reduce electron/ion diffusion pathways. Meanwhile, X‐ray absorption spectroscopy shows that the surface defect engineering tunes the CoS₄ tetrahedra to CoS₆ octahedra on Co₉S₈, endowing abundance of S vacancies on the Co₉S₈ octahedral sites. The ever‐increasing S vacancies over the course of electrochemical process further promotes the chemical trapping of LiPS and its conversion kinetics, rendering fast and durable Li–S chemistry. Benefiting from these features, the as‐developed 3DOM N‐Co₉S_8?x/S cathode delivers high areal capacity, superb rate capability, and excellent cyclic stability with ultralow capacity fading rate under raised sulfur loading and low electrolyte content. This design strategy promotes the development of practically viable Li–S batteries and sheds lights on the material engineering in related energy storage application.     

Lithium–Sulfur Batteries: Progress and Prospects

Development of advanced energy‐storage systems for portable devices, electric vehicles, and grid storage must fulfill several requirements: low‐cost, long life, acceptable safety, high energy, high power, and environmental benignity. With these requirements, lithium–sulfur (Li–S) batteries promise great potential to be the next‐generation high‐energy system. However, the practicality of Li–S technology is hindered by technical obstacles, such as short shelf and cycle life and low sulfur content/loading, arising from the shuttling of polysulfide intermediates between the cathode and anode and the poor electronic conductivity of S and the discharge product Li₂S. Much progress has been made during the past five years to circumvent these problems by employing sulfur–carbon or sulfur–polymer composite cathodes, novel cell configurations, and lithium‐metal anode stabilization. This Progress Report highlights recent developments with special attention toward innovation in sulfur‐encapsulation techniques, development of novel materials, and cell‐component design. The scientific understanding and engineering concerns are discussed at the end in every developmental stage. The critical research directions needed and the remaining challenges to be addressed are summarized in the Conclusion.     

Atomic Interlamellar Ion Path in High Sulfur Content Lithium‐Montmorillonite Host Enables High‐Rate and Stable Lithium–Sulfur Battery

Fast lithium ion transport with a high current density is critical for thick sulfur cathodes, stemming mainly from the difficulties in creating effective lithium ion pathways in high sulfur content electrodes. To develop a high‐rate cathode for lithium–sulfur (Li–S) batteries, extenuation of the lithium ion diffusion barrier in thick electrodes is potentially straightforward. Here, a phyllosilicate material with a large interlamellar distance is demonstrated in high‐rate cathodes as high sulfur loading. The interlayer space (≈1.396 nm) incorporated into a low lithium ion diffusion barrier (0.155 eV) significantly facilitates lithium ion diffusion within the entire sulfur cathode, and gives rise to remarkable nearly sulfur loading‐independent cell performances. When combined with 80% sulfur contents, the electrodes achieve a high capacity of 865 mAh g^?1 at 1 mA cm^?2 and a retention of 345 mAh g^?1 at a high discharging/charging rate of 15 mA cm^?2, with a sulfur loading up to 4 mg. This strategy represents a major advance in high‐rate Li–S batteries via the construction of fast ions transfer paths toward real‐life applications, and contributes to the research community for the fundamental mechanism study of loading‐independent electrode systems.     

Yolk–Shelled C@Fe3O4 Nanoboxes as Efficient Sulfur Hosts for High‐Performance Lithium–Sulfur Batteries

Owing to the high theoretical specific capacity (1675 mA h g^?1) and low cost, lithium–sulfur (Li–S) batteries offer advantages for next‐generation energy storage. However, the polysulfide dissolution and low electronic conductivity of sulfur cathodes limit the practical application of Li–S batteries. To address such issues, well‐designed yolk–shelled carbon@Fe₃O₄ (YSC@Fe₃O₄) nanoboxes as highly efficient sulfur hosts for Li–S batteries are reported here. With both physical entrapment by carbon shells and strong chemical interaction with Fe₃O₄ cores, this unique architecture immobilizes the active material and inhibits diffusion of the polysulfide intermediates. Moreover, due to their high conductivity, the carbon shells and the polar Fe₃O₄ cores facilitate fast electron/ion transport and promote continuous reactivation of the active material during the charge/discharge process, resulting in improved electrochemical utilization and reversibility. With these merits, the S/YSC@Fe₃O₄ cathodes support high sulfur content (80 wt%) and loading (5.5 mg cm^?2) and deliver high specific capacity, excellent rate capacity, and long cycling stability. This work provides a new perspective to design a carbon/metal‐oxide‐based yolk–shelled framework as a high sulfur‐loading host for advanced Li–S batteries with superior electrochemical properties.     

Design Principles for Heteroatom‐Doped Nanocarbon to Achieve Strong Anchoring of Polysulfides for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have been intensively concerned to fulfill the urgent demands of high capacity energy storage. One of the major unsolved issues is the complex diffusion of lithium polysulfide intermediates, which in combination with the subsequent paradox reactions is known as the shuttle effect. Nanocarbon with homogeneous nonpolar surface served as scaffolding materials in sulfur cathode basically cannot afford a sufficient binding and confining effect to maintain lithium polysulfides within the cathode. Herein, a systematical density functional theory calculation of various heteroatoms‐doped nanocarbon materials is conducted to elaborate the mechanism and guide the future screening and rational design of Li–S cathode for better performance. It is proved that the chemical modification using N or O dopant significantly enhances the interaction between the carbon hosts and the polysulfide guests via dipole–dipole electrostatic interaction and thereby effectively prevents shuttle of polysulfides, allowing high capacity and high coulombic efficiency. By contrast, the introduction of B, F, S, P, and Cl monodopants into carbon matrix is unsatisfactory. To achieve the strong‐couple effect toward Li₂S_x, the principles for rational design of doped carbon scaffolds in Li–S batteries to achieve a strong electrostatic dipole–dipole interaction are proposed. An implicit volcano plot is obtained to describe the dependence of binding energies on electronegativity of dopants. Moreover, the codoping strategy is predicted to achieve even stronger interfacial interaction to trap lithium polysulfides.