Programmed Design of a Lithium-Sulfur Battery Cathode by Integrating Functional Units

Electrochemical Investigations of Sulfur-Decorated Organic Materials as Cathodes for Alkali Batteries

Alkali metal-sulfur batteries (particularly, lithium/sodium- sulfur (Li/Na-S)) have attracted much attention because of their high energy density, the natural abundance of sulfur, and environmental friendliness. However, Li/Na-S batteries still face big challenges, such as limited cycle life, poor conductivity, large volume changes, and the "shuttle effect" caused by the high solubility of Li/Na-polysulfides. Herein, novel organosulfur-containing materials, i.e., bis(4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)disulfide (BiTEMPS-OH) and 2,4-thiophene/arene copolymer (TAC) are proposed as cathode materials for Li and Na batteries. BiTEMPS-OH shows an initial discharge/charge capacity of 353/192 mAh g-1 and a capacity of 62 mAh g-1 after 200 cycles at 100 mA g-1 in ether-based Li-ion electrolyte. Meanwhile, TAC has an initial discharge/charge capacity of 270/248 mAh g-1 and better cycling performance (106 mAh g-1 after 200 cycles) than BiTEMPS-OH in the same electrolyte. However, the rate capability of TAC is limited by the slow diffusion of Li-ions. Both materials show inferior electrochemical performances in Na battery cells compared to the Li analogs. X-ray powder diffraction reveals that BiTEMPS-OH loses its crystalline structure permanently upon cycling in Li battery cells. X-ray photoelectron spectroscopy demonstrates the cleavage and partially reversible formation of S-S bonds in BiTEMPS-OH and the formation/decomposition of thick solid electrolyte interphase on the electrode surface of TAC.

Breaking Barriers to High-Practical Li-S Batteries with Isotropic Binary Sulfiphilic Electrocatalyst: Creating a Virtuous Cycle for Favorable Polysulfides Redox Environments

Investigations into lithium-sulfur batteries (LSBs) has focused primarily on the initial conversion of lithium polysulfides (LiPSs) to Li2 S2 . However, the subsequent solid-solid reaction from Li2 S2 to Li2 S and the Li2 S decomposition process should be equally prioritized. Creating a virtuous cycle by balancing all three chemical reaction processes is crucial for realizing practical LSBs. Herein, amorphous Ni3 B in synergy with carbon nanotubes (aNi3 B@CNTs) is proposed to implement the consecutive catalysis of S8(solid) → LiPSs(liquid) → Li2 S(solid) →LiPSs(liquid) . Systematic theoretical simulations and experimental analyses reveal that aNi3 B@CNTs with an isotropic structure and abundant active sites can ensure rapid LiPSs adsorption-catalysis as well as uniform Li2 S precipitation. The uniform Li2 S deposition in synergy with catalysis of aNi3 B enables instant/complete oxidation of Li2 S to LiPSs. The produced LiPSs are again rapidly and uniformly adsorbed for the next sulfur evolution process, thus creating a virtuous cycle for sulfur species conversion. Accordingly, the aNi3 B@CNTs-based cell presents remarkable rate capability, long-term cycle life, and superior cyclic stability, even under high sulfur loading and extreme temperature environments. This study proposes the significance of creating a virtuous cycle for sulfur species conversion to realize practical LSBs.

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.

High-Performance Aqueous Zinc-Ion Battery Based on an Al0.35 Mn2.52 O4 Cathode: A Design Strategy from Defect Engineering and Atomic Composition Tuning

Rechargeable zinc-ion batteries (ZIBs), which adopt mild aqueous electrolytes with high power density and safety, have received significant interest. As the most widely used cathode material for ZIBs, manganese-based oxide has poor rate performance owing to its low electronic conductivity and slow ion diffusion kinetics. In this study, using the synergistic regulation strategy of defect engineering and atomic composition tuning, a mesoporous Al_0.35 Mn_2.52 O₄ with an ultrahigh surface area (up to 82 m² g^-1 ) is fabricated through Al substitution in the Mn₃ O₄ , followed by an Al-selective leaching process. During the entire process, numerous defects are obtained in the spinel structure by removing ≈30% of the Al cations. Al substitution can improve the material conductivity, while cation defects can weaken the electrostatic effect and promote ion diffusion ability. Therefore, the Al_0.35 Mn_2.52 O₄ cathode of ZIBs exhibits a high reversible capacity of 302 mAh g^-1 at a current density of 100 mA g^-1 . Furthermore, the reversible capacity remains at 147 mAh g^-1 after 1000 cycles at a current density of 1500 mA g^-1 . This synergistic regulation of atomic composition tuning and defect engineering provides a new perspective for improving the performance of electrode materials in ZIBs.

Polymers in Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) hold great promise as one of the next-generation power supplies for portable electronics and electric vehicles due to their ultrahigh energy density, cost effectiveness, and environmental benignity. However, their practical application has been impeded owing to the electronic insulation of sulfur and its intermediates, serious shuttle effect, large volume variation, and uncontrollable formation of lithium dendrites. Over the past decades, many pioneering strategies have been developed to address these issues via improving electrodes, electrolytes, separators and binders. Remarkably, polymers can be readily applied to all these aspects due to their structural designability, functional versatility, superior chemical stability and processability. Moreover, their lightweight and rich resource characteristics enable the production of LSBs with high-volume energy density at low cost. Surprisingly, there have been few reviews on development of polymers in LSBs. Herein, breakthroughs and future perspectives of emerging polymers in LSBs are scrutinized. Significant attention is centered on recent implementation of polymers in each component of LSBs with an emphasis on intrinsic mechanisms underlying their specific functions. The review offers a comprehensive overview of state-of-the-art polymers for LSBs, provides in-depth insights into addressing key challenges, and affords important resources for researchers working on electrochemical energy systems.

Lithium-Sulfur Battery Cathode Design: Tailoring Metal-Based Nanostructures for Robust Polysulfide Adsorption and Catalytic Conversion

Lithium-sulfur (Li-S) batteries have a high specific energy capacity and density of 1675 mAh g^-1 and 2670 Wh kg^-1 , respectively, rendering them among the most promising successors for lithium-ion batteries. However, there are myriads of obstacles in the practical application and commercialization of Li-S batteries, including the low conductivity of sulfur and its discharge products (Li₂ S/Li₂ S₂ ), volume expansion of sulfur electrode, and the polysulfide shuttle effect. Hence, immense attention has been devoted to rectifying these issues, of which the application of metal-based compounds (i.e., transition metal, metal phosphides, sulfides, oxides, carbides, nitrides, phosphosulfides, MXenes, hydroxides, and metal-organic frameworks) as sulfur hosts is profiled as a fascinating strategy to hinder the polysulfide shuttle effect stemming from the polar-polar interactions between the metal compounds and polysulfides. This review encompasses the fundamental electrochemical principles of Li-S batteries and insights into the interactions between the metal-based compounds and the polysulfides, with emphasis on the intimate structure-activity relationship corroborated with theoretical calculations. Additionally, the integration of conductive carbon-based materials to ameliorate the existing adsorptive abilities of the metal-based compound is systematically discussed. Lastly, the challenges and prospects toward the smart design of catalysts for the future development of practical Li-S batteries are presented.

Organic Dye-Derived N, S Co-Doped Porous Carbon Hosts for Effective Lithium Polysulfide Confinement in Lithium-Sulfur Batteries

Lithium–sulfur batteries are considered as attractive candidates for next-generation energy storage systems originating from their high theoretical capacity and energy density. However, the severe shuttling of behavior caused by the dissolution of lithium polysulfide intermediates during cycling remains a challenge for practical applications. Herein, porous carbon materials co-doped with nitrogen and sulfur atoms were prepared through a facile hydrothermal reaction of graphene oxide and methylene blue to obtain a suitable host structure for regulating the lithium polysulfide shuttling behavior. Experimental results demonstrated that the abundant heteroatom-containing moieties in the carbon frameworks not only generated favorable active sites for capturing lithium polysulfide but also enhanced redox reaction kinetics of lithium polysulfide intermediates. Consequently, the corresponding sulfur composite electrodes exhibited excellent rate performance and cycling stability along with high Columbic efficiency. This work highlights the approach for the preparation of nitrogen and sulfur co-doped carbon materials derived from organic dye compounds for high performance energy storage systems.

Efficient Polysulfide Trapping and Conversion on N-Doped CoTe2 via Enhanced Dual-Anchoring Effect

Polysulfide shuttling and sluggish sulfur redox kinetics hinder the cyclability and rate capability of lithium-sulfur (Li-S) batteries. The intrinsic redox kinetics of sulfur cathodes strongly depends on the interaction between catalysts and sulfur species. Herein, N-doped CoTe₂ is proposed as an effective dual-anchoring electrocatalyst, which can simultaneously bind Li and S atoms in lithium polysulfides via ionic Te-Li/N-Li bonding and coordinate covalent Co-S bonding. The incorporated N not only serves as enhanced lithiophilic site, but also an agent to improve the sulfiphilicity of the Co site as revealed by a series of experimental and computational results. Benefiting from these superiorities, the use of N-doped CoTe₂ as a catalytic interlayer enables efficient operation of Li-S batteries in terms of impressive rate capability of 758 mAh g^-1 at 4 C and very low capacity decay of 0.021% per cycle over 1000 cycles. The material and strategy demonstrated in this work may open the door toward developing more advanced Li-S electrocatalysts.

Advances in Lithium-Sulfur Batteries: From Academic Research to Commercial Viability

Lithium-ion batteries, which have revolutionized portable electronics over the past three decades, were eventually recognized with the 2019 Nobel Prize in chemistry. As the energy density of current lithium-ion batteries is approaching its limit, developing new battery technologies beyond lithium-ion chemistry is significant for next-generation high energy storage. Lithium-sulfur (Li-S) batteries, which rely on the reversible redox reactions between lithium and sulfur, appears to be a promising energy storage system to take over from the conventional lithium-ion batteries for next-generation energy storage owing to their overwhelming energy density compared to the existing lithium-ion batteries today. Over the past 60 years, especially the past decade, significant academic and commercial progress has been made on Li-S batteries. From the concept of the sulfur cathode first proposed in the 1960s to the current commercial Li-S batteries used in unmanned aircraft, the story of Li-S batteries is full of breakthroughs and back tracing steps. Herein, the development and advancement of Li-S batteries in terms of sulfur-based composite cathode design, separator modification, binder improvement, electrolyte optimization, and lithium metal protection is summarized. An outlook on the future directions and prospects for Li-S batteries is also offered.

Porous NiCo2S4 Nanoneedle Arrays with Highly Efficient Electrocatalysis Anchored on Carbon Cloths as Self-Supported Hosts for High-Loading Li-S Batteries

Lithium-sulfur (Li-S) batteries have attracted all-time attention because of their supernormal high energy density and low cost, whereas they are still plagued by the severe polysulfide shuttling and sluggish sulfur redox reaction kinetics. Moreover, poor sulfur electrochemical utilization and rapid capacity degradation are top concerns in the high-loading Li-S batteries, which severely hinder their practical applications. Herein, a completely novel porous nanoneedle array NiCo₂S₄ electrocatalyst grown on a nitrogen-sulfur-doped carbon cloth (NSCC) (NiCo₂S₄@NSCC) is constructed as a 3D self-supported sulfur host for high-loading Li-S batteries, in which the highest sulfur loading reaches 4.9 mg cm^-2. The as-prepared NiCo₂S₄@NSCC with a typical sulfur loading of around 2.0 mg cm^-2 provides a high discharge capacity of 1223 mA h g^-1 at 0.2 C and long-term cycle stability with a low capacity decay of 0.046% per cycle over 500 cycles at 1 C. Additionally, NiCo₂S₄@NSCC/S with a high sulfur loading of 4.9 mg cm^-2 delivers an excellent reversible areal capacity of 4.4 mA h cm^-2 g over 50 cycles. Noting that such superior electrochemical performance of NiCo₂S₄@NSCC/S with high-loading sulfur is mainly attributed to high electronic conductivity and the abundant porous structure of NSCC to transport electrons and ions fastly and accommodate sulfur as well as robust absorbability and the outstanding catalytic effect of NiCo₂S₄ to accelerate the capture and conversion of the polysulfide intermediate. Predictably, this work can provide a guideline to efficiently and rationally design the structure of metal-based compounds with catalytic functions for various applications.

Enhanced Polysulfide Regulation via Porous Catalytic V2O3/V8C7 Heterostructures Derived from Metal-Organic Frameworks toward High-Performance Li-S Batteries

The development of Li-S batteries is largely impeded by the complicated shuttle effect of lithium polysulfides (LiPSs) and sluggish reaction kinetics. In addition, the low mass loading/utilization of sulfur is another key factor that makes Li-S batteries difficult to commercialize. Here, a porous catalytic V₂O₃/V₈C₇@carbon composite derived from MIL-47 (V) featuring heterostructures is reported to be an efficient polysulfide regulator in Li-S batteries, achieving a substantial increase in sulfur loading while still effectively suppressing the shuttle effect and enhancing kinetics. Systematic mechanism analyses suggest that the LiPSs strongly adsorbed on the V₂O₃ surface can be rapidly transferred to the V₈C₇ surface through the built-in interface for subsequent reversible conversion by an efficient catalytic effect, realizing enhanced regulation of LiPSs from capture to conversion. In addition, the porous structure provides sufficient sulfur storage space, enabling the heterostructures to exert full efficacy with a high sulfur loading. Thus, this S-V₂O₃/V₈C₇@carbon@graphene cathode exhibits prominent rate performance (587.6 mAh g^-1 at 5 C) and a long lifespan (1000 cycles, 0.017% decay per cycle). It can still deliver superior electrochemical performance even with a sulfur loading of 8.1 mg cm^-2. These heterostructures can be further applied in pouch cells and produce stable output at different folding angles (0-180°). More crucially, the cells could retain 4.3 mAh cm^-2 even after 150 cycles, which is higher than that of commercial lithium-ion batteries (LIBs). This strategy for solving the shuttle effect under high sulfur loading provides a promising solution for the further development of high-performance Li-S batteries.