Strategy of Enhancing the Volumetric Energy Density for Lithium-Sulfur Batteries

Cutting-Edge Progress in Aqueous Zn-S Batteries: Innovations in Cathodes, Electrolytes, and Mediators

Rechargeable aqueous zinc-sulfur batteries (AZSBs) are emerging as prominent candidates for next-generation energy storage devices owing to their affordability, non-toxicity, environmental friendliness, non-flammability, and use of earth-abundant electrodes and aqueous electrolytes. However, AZSBs currently face challenges in achieving satisfied electrochemical performance due to slow kinetic reactions and limited stability. Therefore, further research and improvement efforts are crucial for advancing AZSBs technology. In this comprehensive review, it is delved into the primary mechanisms governing AZSBs, assess recent advancements in the field, and analyse pivotal modifications made to electrodes and electrolytes to enhance AZSBs performance. This includes the development of novel host materials for sulfur (S) cathodes, which are capable of supporting higher S loading capacities and the refinement of electrolyte compositions to improve ionic conductivity and stability. Moreover, the potential applications of AZSBs across various energy platforms and evaluate their market viability based on recent scholarly contributions is explored. By doing so, this review provides a visionary outlook on future research directions for AZSBs, driving continuous advancements in stable AZSBs technology and deepening the understanding of their charge-discharge dynamics. The insights presented in this review signify a significant step toward a sustainable energy future powered by renewable sources.

N-Vacancy Enriched Porous BN Fibers for Enhanced Polysulfides Adsorption and Conversion in High-Performance Lithium-Sulfur Batteries

Severe shuttle effect of soluble polysulfides and sluggish redox kinetics have been thought of as the critical issues hindering the extensive applications of lithium-sulfur batteries (LSBs). Herein, one-dimensional boron nitride (1D BN) fibers with abundant pores and sufficient N-vacancy defects were synthesized using a thermal crystallization following a pre-condensation step. The 1D structure of BN facilitates unblocked ions diffusion pathways during charge/discharge cycles. The embedded pores within the polar BN strengthen the immobilization of polysulfides via both physical confinement and chemical interaction. Moreover, the highly exposed active surface area and intentionally created N-vacancy sites substantially promote reaction kinetics by lowering the energy barriers of the rate-limiting steps. After incorporating with conductive carbon networks and elemental S, the as-prepared S/Nv-BN@CBC cathode of LSBs deliver an initial discharge capacity of up to 1347 mAh g-1 at 200 mA g-1, while maintaining a low decay rate of 0.03 % per cycle over 1000 cycles at 1600 mA g-1. This work offers an effective strategy to mitigate the shuttle effect and highlights the significant potential of defect-engineered BN in accelerating the reaction kinetics of LSBs.

Progresses and Perspectives of Carbon-Free Metal Compounds-Modified Separators for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) have the advantages of high theoretical specific capacity, excellent energy density, abundant elemental sulfur reserves. However, the LSBs is mainly limited by shuttling of lithium polysulfides (LiPSs), slow reaction kinetics of sulfur cathode. For solving the above problems, by developing high-performance battery separators, the reversible capacity, Coulombic efficiency (CE) and cycle life of LSBs can be effectively enhanced. Carbon-free based metal compounds are expected to be highly efficient separator modifiers for a new generation of high-performance LSBs by virtue of superior chemical adsorption capacity, strong catalytic properties and excellent lithophilicity to a certain extent. They can give play to the synergistic effect of their "adsorption-catalysis" sites to accelerate the redox kinetics of LiPSs, and their good lithophilicity can accelerate the Li+ transport kinetics, thus showing more remarkable electrochemical performances. However, a comprehensive summary of carbon-free metal compounds-modified separators for LSBs is still lacking. Here, this review systematically summarizes the researching progresses and performance characteristics of carbon-free-based metal compounds modified materials for separators of LSBs, and summarizes the corresponding mechanisms of using carbon-based separators to enhance the performance of LSBs. Finally, the review also looks forward to the prospects of LSBs using carbon-free metal compounds separators.

Integrated Design for Discrete Sulfur@Polymer Nanoreactor with Tandem Connection as Lithium-Sulfur Battery Cathodes

Apart from electrode material modification, architecture design and optimization are important approaches for improving lithium-sulfur battery performance. Herein, an integrated structure with tandem connection is constructed by confining nanosulfur (NS) in conductive poly(3,4-ethylenedioxythiophene) (PEDOT) reaction chambers, forming an interface of discrete independent nanoreactor units bonded onto carbon nanotubes (noted as CNT/NS@PEDOT). The unique spatial confinement and concentration gradients of sulfur@PEDOT nanoreactors (SP-NRs) can promote reaction kinetics while facilitating rapid polysulfide transformation and minimizing dissolution and diffusion losses. Meanwhile, overall ultrahigh energy input and output are achieved through tandem connection with carbon nanotubes, isolation with PEDOT coating, and synergistic multiplicative effects among SP-NRs. As a result, it delivers a high initial discharge capacity of 1246 mAh g-1 at 0.1 C and 918 mAh g-1 at 1 C, the low capacity decay rate per lap of 0.011 % is achieved at a current density of 1 C after 1000 cycles. This research emphasizes the innovative structural design to provide a fresh trajectory for the further advancement of high-performance energy storage devices.

In Situ Growth Strategy to Construct "Four-In-One" Separators with Functionalized Polyphosphazene Coatings for Safe and Stable Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are facing many challenges, such as the inadequate conductivity of sulfur, the shuttle effect caused by lithium polysulfide (LiPSs), lithium dendrites, and the flammability, which have hindered their commercial applications. Herein, a "four-in-one" functionalized coating is fabricated on the surface of polypropylene (PP) separator by using a novel flame-retardant namely InC-HCTB to meet these challenges. InC-HCTB is obtained by cultivating polyphosphazene on the surface of carbon nanotubes with an in situ growth strategy. First, this unique architecture fosters an enhanced conductive network, bolstering the bidirectional enhancement of both ionic and electronic conductivities. Furthermore, InC-HCTB effectively inhibits the shuttle effect of LiPSs. LSBs exhibit a remarkable capacity of 1170.7 mA h g-1 at 0.2 C, and the capacity degradation is a mere 0.0436% over 800 cycles at 1 C. Third, InC-HCTB coating serves as an ion migration network, hindering the growth of lithium dendrites. More importantly, InC-HCTB exhibits notable flame retardancy. The radical trapping action in the gas phase and the protective effect of the shielded char layer in the condensed phase are simulated and verified. This facile in situ growth strategy constructs a "four-in-one" functional separator coating, rendering InC-HCTB a promising additive for the large-scale production of safe and stable LSBs.

Bridging the gap between academic research and industrial development in advanced all-solid-state lithium-sulfur batteries

The energy storage and vehicle industries are heavily investing in advancing all-solid-state batteries to overcome critical limitations in existing liquid electrolyte-based lithium-ion batteries, specifically focusing on mitigating fire hazards and improving energy density. All-solid-state lithium-sulfur batteries (ASSLSBs), featuring earth-abundant sulfur cathodes, high-capacity metallic lithium anodes, and non-flammable solid electrolytes, hold significant promise. Despite these appealing advantages, persistent challenges like sluggish sulfur redox kinetics, lithium metal failure, solid electrolyte degradation, and manufacturing complexities hinder their practical use. To facilitate the transition of these technologies to an industrial scale, bridging the gap between fundamental scientific research and applied R&D activities is crucial. Our review will address the inherent challenges in cell chemistries within ASSLSBs, explore advanced characterization techniques, and delve into innovative cell structure designs. Furthermore, we will provide an overview of the recent trends in R&D and investment activities from both academia and industry. Building on the fundamental understandings and significant progress that has been made thus far, our objective is to motivate the battery community to advance ASSLSBs in a practical direction and propel the industrialized process.

Surface-Phosphided Metal Oxide Microspheres as Catalytic Host of Sulfur to Enhance the Performance of Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are one of the most promising high-energy density secondary batteries due to their high theoretical energy density of 2600 Wh kg-1. However, the sluggish kinetics and severe "shuttle effect" of polysulfides are the well-known barriers that hinder their practical applications. A carefully designed catalytic host of sulfur may be an effective strategy that not only accelerates the conversion of polysulfides but also limit their dissolution to mitigate the "shuttle effect." Herein, in situ surface-phosphided Ni0.96Co0.03Mn0.01O (p-NCMO) oxide microspheres are prepared via gas-phase phosphidation as a catalytic host of sulfur. The as-prepared unique heterostructured microspheres, with enriched surface-coated metal phosphide, exhibit superior synergistic effect of catalytic conversion and absorption of the otherwise soluble intermediate polysulfides. Correspondingly, the sulfur cathode exhibits excellent electrochemical performance, including a high initial discharge capacity (1162 mAh gs-1 at 0.1C), long cycling stability (491 mAh gs-1 after 1000 cycles at 1C), and excellent rate performance (565 mAh gs-1 at 5C). Importantly, the newly prepared sulfur cathode shows a high areal capacity of 4.0 mAh cm-2 and long cycle stability under harsh conditions (high sulfur loading of 5.3 mg cm-2 and lean electrolyte/sulfur ratio of 5.8 μL mg-1). This work proposes an effective strategy to develop the catalytic hosts of sulfur for achieving high-performance Li-S batteries via surface phosphidation.

New Emerging Fast Charging Microscale Electrode Materials

Fast charging lithium (Li)-ion batteries are intensively pursued for next-generation energy storage devices, whose electrochemical performance is largely determined by their constituent electrode materials. While nanosizing of electrode materials enhances high-rate capability in academic research, it presents practical limitations like volumetric packing density and high synthetic cost. As an alternative to nanosizing, microscale electrode materials cannot only effectively overcome the limitations of the nanosizing strategy but also satisfy the requirement of fast-charging batteries. Therefore, this review summarizes the new emerging microscale electrode materials for fast charging from the commercialization perspective. First, the fundamental theory of electronic/ionic motion in both individual active particles and the whole electrode is proposed. Then, based on these theories, the corresponding optimization strategies are summarized toward fast-charging microscale electrode materials. In addition, advanced functional design to tackle the mechanical degradation problems related to next generation high capacity alloy- and conversion-type electrode materials (Li, S, Si et al.) for achieving fast charging and stable cycling batteries. Finally, general conclusions and the future perspective on the potential research directions of microscale electrode materials are proposed. It is anticipated that this review will provide the basic guidelines for both fundamental research and practical applications of fast-charging batteries.

Bifunctional Sulfhydryl-Based Polyimides for Highly Active Cathodes of Li-S Batteries

Sulfhydryl-based polyimides were synthesized by the nucleophilic ring-opening reaction of thiolactone monomers (BPDA-T, ODPA-T, BTDA-T) with polyethylenimine (PEI), and they were coated on carbon nanotubes as host materials (BPTP@CNT, ODTP@CNT, and BTTP@CNT) of the sulfur cathode. BPTP@CNT/S, ODTP@CNT/S, and BTTP@CNT/S as cathode materials not only promote the covalent bonding of sulfur and polysulfide with sulfhydryl-based polyimides but also reduce the shuttle effect of soluble polysulfide in the redox process. Moreover, sulfhydryl-based polyimides can help improve the compatibility and interfacial contact between sulfur and conductive carbon while alleviating the volume expansion of the cathode. In addition, the conductive network of carbon nanotubes improves the electronic conductivity of the cathode materials. The BTTP@CNT/S cathode showed superior stability (the initial capacity was 902 mAh g-1 at 1C, and the capacity retention rate was 88.58% after 500 cycles) and the initial capacity could reach 718 mAh g-1 when the sulfur loading was 4.8 mg cm-2 (electrolyte/sulfur ratio: 10 μL mg-1), which fully proves the feasibility of the large-scale application of sulfhydryl-based polyimide materials.

Applications, prospects and challenges of metal borides in lithium sulfur batteries

Although the lithium-sulfur (Li-S) battery has a theoretical capacity of up to 1675 mA h g-1, its practical application is limited owing to some problems, such as the shuttle effect of soluble lithium polysulfides (LiPSs) and the growth of Li dendrites. It has been verified that some transition metal compounds exhibit strong polarity, good chemical adsorption and high electrocatalytic activities, which are beneficial for the rapid conversion of intermediate product in order to effectively inhibit the "shuttle effect". Remarkably, being different from other metal compounds, it is a significant characteristic that both metal and boron atoms of transition metal borides (TMBs) can bind to LiPSs, which have shown great potential in recent years. Here, for the first time, almost all existing studies on TMBs employed in Li-S cells are comprehensively summarized. We firstly clarify special structures and electronic features of metal borides to show their great potential, and then existing strategies to improve the electrochemical properties of TMBs are summarized and discussed in the focus sections, such as carbon-matrix construction, morphology control, heteroatomic doping, heterostructure formation, phase engineering, preparation techniques. Finally, the remaining challenges and perspectives are proposed to point out a direction for realizing high-energy and long-life Li-S batteries.

Multimodal Engineering of Catalytic Interfaces Confers Multi-Site Metal-Organic Framework for Internal Preconcentration and Accelerating Redox Kinetics in Lithium-Sulfur Batteries

The development of highly efficient catalysts to address the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) in lithium-sulfur batteries (LSBs) remains a formidable challenge. In this study, a series of multi-site catalytic metal-organic frameworks (MSC-MOFs) were elaborated through multimodal molecular engineering to regulate both the reactant diffusion and catalysis processes. MSC-MOFs were crafted with nanocages featuring collaborative specific adsorption/catalytic interfaces formed by exposed mixed-valence metal sites and surrounding adsorption sites. This design facilitates internal preconcentration, a coadsorption mechanism, and continuous efficient catalytic conversion toward polysulfides concurrently. Leveraging these attributes, LSBs with an MSC-MOF-Ti catalytic interlayer demonstrated a 62 % improvement in discharge capacity and cycling stability. This resulted in achieving a high areal capacity (11.57 mAh cm-2 ) at a high sulfur loading (9.32 mg cm-2 ) under lean electrolyte conditions, along with a pouch cell exhibiting an ultra-high gravimetric energy density of 350.8 Wh kg-1 . Lastly, this work introduces a universal strategy for the development of a new class of efficient catalytic MOFs, promoting SRR and suppressing the shuttle effect at the molecular level. The findings shed light on the design of advanced porous catalytic materials for application in high-energy LSBs.

Synergistic Interfacial Optimization for High-Sulfur-Content All-Solid-State Lithium-Sulfur Batteries

Improving the sulfur content in the cathode is essential for achieving high-energy-density all-solid-state lithium-sulfur batteries (ASSLSBs). However, the complex multiinterfaces, akin to the short wooden planks that consist of the cask, severely limit the performance of ASSLSBs with high sulfur content. Since singular approaches fail to optimize these interfaces simultaneously, we propose a synergistic approach using a dual-doped sulfide solid electrolyte (Y2S3 and LiI) and an SbSn alloy sulfur host in this work. The incorporation of Y2S3 in the solid electrolyte serves to improve the electrolyte-electrolyte interfaces and enhance the ionic conductivity, while the inclusion of LiI helps stabilize the electrolyte-anode interface and suppress dendrite formation. Meanwhile, the SbSn alloy sulfur host facilitates the transfer of Li+ at the electrolyte-cathode interfaces. Consequently, the solid-solid interfaces are significantly improved, leading to impressive specific capacities in ASSLSBs with high sulfur content (>44% in the cathode composite) at room temperature (1163.5 mAh g-1) and at 60 °C (1408.7 mAh g-1) during the 50th cycle at 0.05C. This work presents a promising strategy for achieving practical high-performance ASSLSBs.

First-principles study of the discharge electrochemical and catalytic performance of the sulfur cathode host Fe0.875M0.125S2 (M = Ti, V)

Lithium-sulfur batteries (LSBs) are one of the most promising energy storage devices with high energy density. However, their application and commercialization are hampered by the slow Li-S redox chemistry. Fe0.875M0.125S2 (M = Ti, V), as the sulfur cathode host, enhances the Li-S redox chemistry. FeS2 with Pa3̄ is transformed into Li2FeS2 with P3̄m1 after discharge. The structure changes and physicochemical properties during Fe0.875M0.125S2 discharge process are further investigated to screen out the sulfur cathode host materials with the best comprehensive properties. The discharge structure of Fe0.875M0.125S2 is verified by the thermodynamic stability of Li-deficient phases, voltage and capacity based on Monte Carlo methods. Fe0.875M0.125S2 with Pa3̄ is transformed into Li2Fe0.875M0.125S2 with P3̄m1 after discharge. Using the first-principles calculations, the physicochemical properties of Li2Fe0.875M0.125S2 are systematically investigated, including the formation energy, voltage, theoretical capacity, electrical conductivity, Li+ diffusion, catalytic performance and Li2S oxidation decomposition. The average redox voltage of Li2Fe0.875V0.125S2 is higher than that of Li2Fe0.875Ti0.125S2. Li2Fe0.875M0.125S2 shows metallic properties. Li2Fe0.875V0.125S2 is more beneficial to the reduction reaction of Li2S2 and Li2S oxidation decomposition. Fe0.875V0.125S2 has more potential as the sulfur cathode host than Fe0.875Ti0.125S2 in LSBs. A new strategy for the selection of the sulfur cathode host material for LSBs is provided by this work.

Palygorskite-Derived Ternary Fluoride with 2D Ion Transport Channels for Ampere Hour-Scale Li-S Pouch Cell with High Energy Density

Although various excellent electrocatalysts/adsorbents have made notable progress as sulfur cathode hosts on the lithium-sulfur (Li-S) coin-cell level, high energy density (WG ) of the practical Li-S pouch cells is still limited by inefficient Li-ion transport in the thick sulfur cathode under low electrolyte/sulfur (E/S) and negative/positive (N/P) ratios, which aggravates the shuttle effect and sluggish redox kinetics. Here a new ternary fluoride MgAlF5 ·2H2 O with ultrafast ion conduction-strong polysulfides capture integration is developed. MgAlF5 ·2H2 O has an inverse Weberite-type crystal framework, in which the corner-sharing [AlF6 ]-[MgF4 (H2 O)2 ] octahedra units extend to form two-dimensional Li-ion transport channels along the [100] and [010] directions, respectively. Applied as the cathode sulfur host, the MgAlF5 ·2H2 O lithiated by LiTFSI (lithium salt in Li-S electrolyte) acts as a fast ionic conductor to ensure efficient Li-ion transport to accelerate the redox kinetics under high S loadings and low E/S and N/P. Meanwhile, the strong polar MgAlF5 ·2H2 O captures polysulfides by chemisorption to suppress the shuttle effect. Therefore, a 1.97 A h-level Li-S pouch cell achieves a high WG of 386 Wh kg-1 . This work develops a new-type ionic conductor, and provides unique insights and new hosts for designing practical Li-S pouch cells.

Small Things Make a Big Difference: Conductive Cross-Linking Sodium Alginate@MXene Binder Enables High-Volumetric-Capacity and High-Mass-Loading Li-S Battery

Binders are crucial for maintaining the integrity of an electrode, and there is a growing need for integrating multiple desirable properties into the binder for high-energy batteries, yet significant challenges remain. Here, we successfully synthesized a new binder by cross-linking sodium alginate (SA) with MXene materials (Ti3C2Tx). Besides the improved adhesion and mechanical properties, the integrated SA@Ti3C2Tx binder demonstrates much improved electronic conductivity, which enables ruling out the fluffy conductive additive from the electrode component with enhanced volumetric capacity. When SA@Ti3C2Tx is used to fabricate sulfur (S) cathodes, the conductive-additive-free electrode demonstrates extremely high capacity (1422 mAh cm-3/24.5 mAh cm-2) under an S loading of 17.2 mg cm-2 for Li-S batteries. Impressively, the SA@Ti3C2Tx binder shows remarkable feasibility in other battery systems such as Na-S and LiFePO4 batteries. The proposed strategy of constructing a cross-linking conductive binder opens new possibilities for designing high-mass-loading electrodes with high volumetric capacity.

Freestanding carbon nanofoam papers with tunable porosity as lithium-sulfur battery cathodes

To reach energy density demands greater than 3 mA h cm-2 for practical applications, the electrode structure of lithium-sulfur batteries must undergo an architectural redesign. Freestanding carbon nanofoam papers derived from resorcinol-formaldehyde aerogels provide a three-dimensional conductive mesoporous network while facilitating electrolyte transport. Vapor-phase sulfur infiltration fully penetrates >100 μm thick electrodes and conformally coats the carbon aerogel surface providing areal capacities up to 4.1 mA h cm-2 at sulfur loadings of 6.4 mg cm-2. Electrode performance can be optimized for energy density or power density by tuning sulfur loading, pore size, and electrode thickness.

Heterostructures Regulating Lithium Polysulfides for Advanced Lithium-Sulfur Batteries

Sluggish reaction kinetics and severe shuttling effect of lithium polysulfides seriously hinder the development of lithium-sulfur batteries. Heterostructures, due to unique properties, have congenital advantages that are difficult to be achieved by single-component materials in regulating lithium polysulfides by efficient catalysis and strong adsorption to solve the problems of poor reaction kinetics and serious shuttling effect of lithium-sulfur batteries. In this review, the principles of heterostructures expediting lithium polysulfides conversion and anchoring lithium polysulfides are detailedly analyzed, and the application of heterostructures as sulfur host, interlayer, and separator modifier to improve the performance of lithium-sulfur batteries is systematically reviewed. Finally, the problems that need to be solved in the future study and application of heterostructures in lithium-sulfur batteries are prospected. This review will provide a valuable reference for the development of heterostructures in advanced lithium-sulfur batteries.

Single-atom site catalysis in Li-S batteries

With their high theoretical energy density, Li-S batteries are regarded as the ideal battery system for next generation electrochemical energy storage. In the last 15 years, Li-S batteries have made outstanding academic progress. Recently, research studies have placed more emphasis on their practical application aspects, which puts forward strict requirements for the loading of S cathodes and the amount of electrolytes. To meet the above requirements, electrode catalysis design is of crucial significance. Among all the catalysts, single-atom site catalysts (SASCs) are considered to be ideal catalyst materials for the commercialization of Li-S batteries due to their high activity and highest utilization of catalytic sites. This perspective introduces the kinetic mechanism of S cathodes, the basic concept and synthesis strategy of SASCs, and then systematically summarizes the research progress of SASCs for S cathodes and, the related functional interlayers/separators in recent years. Finally, the opportunities and challenges of SASCs in Li-S batteries are summarized and prospected.

A Radical Pathway and Stabilized Li Anode Enabled by Halide Quaternary Ammonium Electrolyte Additives for Lithium-Sulfur Batteries

Passivation of the sulfur cathode by insulating lithium sulfide restricts the reversibility and sulfur utilization of Li-S batteries. 3D nucleation of Li2 S enabled by radical conversion may significantly boost the redox kinetics. Electrolytes with high donor number (DN) solvents allow for tri-sulfur (S3 ⋅- ) radicals as intermediates, however, the catastrophic reactivity of such solvents with Li anodes pose a great challenge for their practical application. Here, we propose the use of quaternary ammonium salts as electrolyte additives, which can preserve the partial high-DN characteristics that trigger the S3 ⋅- radical pathway, and inhibit the growth of Li dendrites. Li-S batteries with tetrapropylammonium bromide (T3Br) electrolyte additive deliver the outstanding cycling stability (700 cycles at 1 C with a low-capacity decay rate of 0.049 % per cycle), and high capacity under a lean electrolyte of 5 μLelectrolyte  mgsulfur -1 . This work opens a new avenue for the development of electrolyte additives for Li-S batteries.

Fast Polysulfide Conversion Catalysis and Reversible Anode Operation by A Single Cathode Modifier in Li-Metal Anode-Free Lithium-Sulfur Batteries

The two major issues confronting the commercialization of rechargeable lithium-sulfur (Li-S) batteries are the sluggish kinetics of the sulfur electrochemical reactions on the cathode and inadequate lithium deposition/stripping reversibility on the anode. They are commonly mitigated with additives designed specifically for the anode and the cathode individually. Here, we report the use of a single cathode modifier, In2 Se3 , which can effectively catalyse the polysulfide reactions on the cathode, and also improve the reversibility of Li deposition and removal on the anode through a LiInS2 /LiInSe2 containing solid electrolyte interface formed in situ by the Se and In ions dissolved in the electrolyte. The amounts of dissolved Se and In are small relative to the amount of In2 Se3 administered. The benefits of using this single modification approach were verified in Li-metal anode-free Li-S batteries with a Li2 S loading of 4 mg cm-2 and a low electrolyte/Li2 S ratio of 7.5 μL mg-1 . The resulting battery showed 60 % capacity retention after 160 cycles at the 0.2 C rate and an average Coulombic efficiency of 98.27 %, comparing very well with recent studies using separate electrode modifiers.

Recent Progress for Concurrent Realization of Shuttle-Inhibition and Dendrite-Free Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have become one of the most promising new-generation energy storage systems owing to their ultrahigh energy density (2600 Wh kg-1 ), cost-effectiveness, and environmental friendliness. Nevertheless, their practical applications are seriously impeded by the shuttle effect of soluble lithium polysulfides (LiPSs), and the uncontrolled dendrite growth of metallic Li, which result in rapid capacity fading and battery safety problems. A systematic and comprehensive review of the cooperative combination effect and tackling the fundamental problems in terms of cathode and anode synchronously is still lacking. Herein, for the first time, the strategies for inhibiting shuttle behavior and dendrite-free Li-S batteries simultaneously are summarized and classified into three parts, including "two-in-one" S-cathode and Li-anode host materials toward Li-S full cell, "two birds with one stone" modified functional separators, and tailoring electrolyte for stabilizing sulfur and lithium electrodes. This review also emphasizes the fundamental Li-S chemistry mechanism and catalyst principles for improving electrochemical performance; advanced characterization technologies to monitor real-time LiPS evolution are also discussed in detail. The problems, perspectives, and challenges with respect to inhibiting the shuttle effect and dendrite growth issues as well as the practical application of Li-S batteries are also proposed.

Coordinated Immobilization and Rapid Conversion of Polysulfide Enabled by a Hollow Metal Oxide/Sulfide/Nitrogen-Doped Carbon Heterostructure for Long-Cycle-Life Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are recognized as the prospective candidate in next-generation energy storage devices due to their gratifying theoretical energy density. Nonetheless, they still face the challenges of the practical application including low utilization of sulfur and poor cycling life derived from shuttle effect of lithium polysulfides (LiPSs). Herein, a hollow polyhedron with heterogeneous CoO/Co9 S8 /nitrogen-doped carbon (CoO/Co9 S8 /NC) is obtained through employing zeolitic imidazolate framework as precursor. The heterogeneous CoO/Co9 S8 /NC balances the redox kinetics of Co9 S8 with chemical adsorption of CoO toward LiPSs, effectively inhibiting the shuttle of LiPSs. The mechanisms are verified by both experiment and density functional theory calculation. Meanwhile, the hollow structure acts as a sulfur storage chamber, which mitigates the volumetric expansion of sulfur and maximizes the utilization of sulfur. Benefiting from the above advantages, lithium-sulfur battery with S-CoO/Co9 S8 /NC achieves a high initial discharge capacity (1470 mAh g-1 ) at 0.1 C and long cycle life (ultralow capacity attenuation of 0.033% per cycle after 1000 cycles at 1 C). Even under high sulfur loading of 3.0 mg cm-2 , lithium-sulfur battery still shows the satisfactory electrochemical performance. This work may provide an idea to elevate the electrochemical performance of LSBs by constructing a hollow metal oxide/sulfide/nitrogen-doped carbon heterogeneous structure.

In Situ Anchoring Ultrafine ZnS Nanodots on 2D MXene Nanosheets for Accelerating Polysulfide Redox and Regulating Li Plating

Lithium-sulfur (Li-S) battery is a promising energy storage system due to its cost effectiveness and high energy density. However, formation of Li dendrites from Li metal anode and shuttle effect of lithium polysulfides (LiPSs) from S cathode impede its practical application. Herein, ultrafine ZnS nanodots are uniformly grown on 2D MXene nanosheets by a low-temperature (60 °C) hydrothermal method for the first time. Distinctively, the ZnS nanodot-decorated MXene nanosheets (ZnS/MXene) can be easily filtered to be a flexible and freestanding film in several minutes. The ZnS/MXene film can be used as a current collector for Li-metal anode to promote uniform Li deposition due to the superior lithiophilicity of ZnS nanodots. ZnS/MXene powders obtained by freeze drying can be used as separator decorator to address the shuttle effect of LiPSs due to their excellent adsorbability. Theoretical calculation proves that the existence of ZnS nanodots on MXene can obviously improve the adsorption ability of ZnS/MXene with Li+ and LiPSs. Li-S full cells with composite Li-metal anode and modified separator exhibit remarkable rate and cycling performance. Other transition metal sulfides (CdS, CuS, etc.) can be also grown on 2D MXene nanosheets by the low-temperature hydrothermal strategy.

Application of Inorganic Quantum Dots in Advanced Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have emerged as one of the most attractive alternatives for post-lithium-ion battery energy storage systems, owing to their ultrahigh theoretical energy density. However, the large-scale application of Li-S batteries remains enormously problematic because of the poor cycling life and safety problems, induced by the low conductivity , severe shuttling effect, poor reaction kinetics, and lithium dendrite formation. In recent studies, catalytic techniques are reported to promote the commercial application of Li-S batteries. Compared with the conventional catalytic sites on host materials, quantum dots (QDs) with ultrafine particle size (<10 nm) can provide large accessible surface area and strong polarity to restrict the shuttling effect, excellent catalytic effect to enhance the kinetics of redox reactions, as well as abundant lithiophilic nucleation sites to regulate Li deposition. In this review, the intrinsic hurdles of S conversion and Li stripping/plating reactions are first summarized. More importantly, a comprehensive overview is provided of inorganic QDs, in improving the efficiency and stability of Li-S batteries, with the strategies including composition optimization, defect and morphological engineering, design of heterostructures, and so forth. Finally, the prospects and challenges of QDs in Li-S batteries are discussed.

Boosting Lean Electrolyte Lithium-Sulfur Battery Performance with Transition Metals: A Comprehensive Review

Lithium-sulfur (Li-S) batteries have received widespread attention, and lean electrolyte Li-S batteries have attracted additional interest because of their higher energy densities. This review systematically analyzes the effect of the electrolyte-to-sulfur (E/S) ratios on battery energy density and the challenges for sulfur reduction reactions (SRR) under lean electrolyte conditions. Accordingly, we review the use of various polar transition metal sulfur hosts as corresponding solutions to facilitate SRR kinetics at low E/S ratios (< 10 µL mg-1), and the strengths and limitations of different transition metal compounds are presented and discussed from a fundamental perspective. Subsequently, three promising strategies for sulfur hosts that act as anchors and catalysts are proposed to boost lean electrolyte Li-S battery performance. Finally, an outlook is provided to guide future research on high energy density Li-S batteries.

The Proof-of-Concept of Anode-Free Rechargeable Mg Batteries

The desperate pursuit of high gravimetric specific energy leads to the ignorance of volumetric energy density that is one of the basic requirements for batteries. Due to the high volumetric capacity, less-prone formation of dendrite, and low reduction potential of Mg metal, rechargeable Mg batteries are considered with innately high volumetric energy density. Nevertheless, the substantial elevation in energy density is compromised by extremely excessive Mg metal anode. Herein, the proof-of-concept of anode-free Mg2 Mo6 S8 -MgS/Cu batteries is proposed, in which MgS as the premagnesiation additive constantly decomposes to replenish Mg loss by electrolyte corrosion over cycling, while both Mg2 Mo6 S8 and MgS acts as the active material to reversibly provide high capacities. Besides, Mg2 Mo6 S8 shows superior catalytic activity on the decomposition of MgS and provides the strong affinity to polysulfides to restrain their dissolution. Consequently, the anode-free Mg2 Mo6 S8 -MgS/Cu batteries deliver a high reversible capacity of 190 mAh g-1 with the capacity retention of 92% after 100 cycles, corresponding to the highly competitive energy density of 420 Wh L-1 . The proposed anode-free Mg battery here spotlights the great promise of Mg batteries in achieving high volumetric energy densities, which will significantly expedite the advances of Mg batteries in practice.

Progress and Prospects of Inorganic Solid-State Electrolyte-Based All-Solid-State Pouch Cells

All-solid-state batteries have piqued global research interest because of their unprecedented safety and high energy density. Significant advances have been made in achieving high room-temperature ionic conductivity and good air stability of solid-state electrolytes (SSEs), mitigating the challenges at the electrode-electrolyte interface, and developing feasible manufacturing processes. Along with the advances in fundamental study, all-solid-state pouch cells using inorganic SSEs have been widely demonstrated, revealing their immense potential for industrialization. This review provides an overview of inorganic all-solid-state pouch cells, focusing on ultrathin SSE membranes, sheet-type thick solid-state electrodes, and bipolar stacking. Moreover, several critical parameters directly influencing the energy density of all-solid-state Li-ion and lithium-sulfur pouch cells are outlined. Finally, perspectives on all-solid-state pouch cells are provided and specific metrics to meet certain energy density targets are specified. This review looks to facilitate the development of inorganic all-solid-state pouch cells with high energy density and excellent safety.

The role of selenium vacancies functionalized mediator of bimetal (Co, Fe) selenide for high-energy-density lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are currently only in the basic research stage and have not been commercialized, which is mainly affected by the poor conductivity of sulfur/lithium sulfide (S/Li₂S), volume expansion effect of sulfur and the shuttle effect of lithium polysulfides (LiPSs). Herein, a three dimensional (3D) carbon nanotubes (CNTs) decorated cubic Co₉Se_8-x/FeSe_2-y (0 ＜ x ＜ 8, 0 ＜ y ＜ 2) composite (Co₉Se_8-x/FeSe_2-y@CNTs) is developed, and used as the functionalized mediator on polypropylene (PP) in Li-S batteries. Benefiting from the good electrical conductivity, large number of Se vacancies and the triple block/adsorption/catalytic effects of Co₉Se_8-x/FeSe_2-y@CNTs, the cell with Co₉Se_8-x/FeSe_2-y@CNTs//PP modified separator delivers a high reversible capacity (1103.5 mA h g^-1) at 1C after three cycles activation at 0.5C and remains 446 mA g h^-1 after 750 cycles with a 0.08% capacity decay rate each cycle. Moreover, at 0.2C, a high areal capacity of 3.63 mA h cm^-2 after 100 cycles with a high sulfur loading of 4.1 mg cm^-2 is obtained. The in-situ XRD tests revealing the transition path of α-S₈ → Li₂S → β-S₈ during the first charge-discharge process, then β-S₈ → Li₂S → β-S₈ conversion reaction in the next cycles, and firstly determine the sulfur-selenide active intermediates (Se_1.1S_6.9) during cycles. The work provides a new insight into the development of bimetallic selenide composites by defect engineering with highly adsorptive and catalytic properties for Li-S batteries.

Rough Endoplasmic Reticulum Inspired Polystyrene-Brush-Based Superhigh Sulfur Content Cathodes Enable Lithium-Sulfur Cells with High Mass and Capacity Loading

The development of highly sophisticated biomimetic models is significant yet remains challenging in the electrochemical energy storage field. Lithium-sulfur (Li-S) cells with high sulfur content and high-sulfur-loading cathodes are urgently required to meet the fast-growing demand for electronic devices. Nevertheless, such cathode materials generally suffer from large sulfur agglomeration, nonporous structure, and insufficient conductivity, leading to rapid capacity decay and low sulfur utilization. Herein, inspired by rough endoplasmic reticulum, a 2D polystyrene (PS)-brush-based (G-g-PS) superhigh-sulfur-content (96 wt%) composite(G-g-sPS@S) is fabricated via the vulcanization reaction. The vulcanized PS side-chains and their S₈ composites on the nanosheet surface can efficiently provide sulfur species, and the intersheet interstitial pores can provide rapid mass-transfer channels for redox reactions of sulfur species. Furthermore, the highly sulfophilic vulcanized PS side-chains are able to effectively inhibit the shuttle effect of polysulfides and regulate their redox process. With these merits, the cells with G-g-sPS@S cathodes exhibit an ultralow decay rate of 0.02% per cycle over 400 cycles at 2 C and deliver a superior areal capacity of 12.6 mAh cm^-2 even with a high sulfur loading of 10.5 mg cm^-2 .

Insights into the electrochemical properties of Li2FeS2 after FeS2 discharging

All-solid-state lithium-sulfur batteries (ASSLSBs) have high reversible characteristics owing to the high redox potential, high theoretical capacity, high electronic conductivity, and low Li⁺ diffusion energy barrier in the cathode. Monte Carlo simulations with cluster expansion, based on the first-principles high-throughput calculations, predicted a phase structure change from Li₂FeS₂ (P3̄M1) to FeS₂ (PA3̄) during the charging process. LiFeS₂ is the most stable phase structure. The structure of Li₂FeS₂ after charging was FeS₂ (P3̄M1). By applying the first-principles calculations, we explored the electrochemical properties of Li₂FeS₂ after charging. The redox reaction potential of Li₂FeS₂ was 1.64 to 2.90 V, implying a high output voltage of ASSLSBs. Flatter voltage step plateaus are important for improving the electrochemical performance of the cathode. The charge voltage plateau was the highest from Li_0.25FeS₂ to FeS₂ and followed from Li_0.375FeS₂ to Li_0.25FeS₂. The electrical properties of Li_xFeS₂ remained metallic during the Li₂FeS₂ charging process. The intrinsic Li Frenkel defect of Li₂FeS₂ was more conducive to Li⁺ diffusion than that of the Li₂S Schottky defect and had the largest Li⁺ diffusion coefficient. The good electronic conductivity and Li⁺ diffusion coefficient of the cathode implied a better charging/discharging rate performance of ASSLSBs. This work theoretically verified the FeS₂ structure after Li₂FeS₂ charging and explored the electrochemical properties of Li₂FeS₂.

Dual-Functional Lithiophilic/Sulfiphilic Binary-Metal Selenide Quantum Dots Toward High-Performance Li-S Full Batteries

The commercial viability of lithium-sulfur batteries is still challenged by the notorious lithium polysulfides (LiPSs) shuttle effect on the sulfur cathode and uncontrollable Li dendrites growth on the Li anode. Herein, a bi-service host with Co-Fe binary-metal selenide quantum dots embedded in three-dimensional inverse opal structured nitrogen-doped carbon skeleton (3DIO FCSe-QDs@NC) is elaborately designed for both sulfur cathode and Li metal anode. The highly dispersed FCSe-QDs with superb adsorptive-catalytic properties can effectively immobilize the soluble LiPSs and improve diffusion-conversion kinetics to mitigate the polysulfide-shutting behaviors. Simultaneously, the 3D-ordered porous networks integrated with abundant lithophilic sites can accomplish uniform Li deposition and homogeneous Li-ion flux for suppressing the growth of dendrites. Taking advantage of these merits, the assembled Li-S full batteries with 3DIO FCSe-QDs@NC host exhibit excellent rate performance and stable cycling ability (a low decay rate of 0.014% over 2,000 cycles at 2C). Remarkably, a promising areal capacity of 8.41 mAh cm-2 can be achieved at the sulfur loading up to 8.50 mg cm-2 with an ultra-low electrolyte/sulfur ratio of 4.1 μL mg-1. This work paves the bi-serve host design from systematic experimental and theoretical analysis, which provides a viable avenue to solve the challenges of both sulfur and Li electrodes for practical Li-S full batteries.

Li-S Chemistry of Manganese Phosphides Nanoparticles With Optimized Phase

The targeted synthesis of manganese phosphides with target phase remains a huge challenge because of their various stoichiometries and phase-dependent physicochemical properties. In this study, phosphorus-rich MnP, manganese-rich Mn₂ P, and their heterostructure MnP-Mn₂ P nanoparticles evenly dispersed on porous carbon are accurately synthesized by a convenient one-pot heat treatment of phosphate resin combined with Mn²⁺ . Moreover, their electrochemical properties are systematically investigated as sulfur hosts in lithium-sulfur batteries. Density functional theory calculations demonstrate the superior adsorption, catalysis capabilities, and electrical conductivity of MnP-Mn₂ P/C, compared with MnP/C and Mn₂ P/C. The MnP-Mn₂ P/C@S exhibits an excellent capacity of 763.3 mAh g^-1 at 5 C with a capacity decay rate of only 0.013% after 2000 cycles. A phase evolution product (MnS) of MnP-Mn₂ P/C@S is detected during the catalysis of MnP-Mn₂ P/C with polysulfides redox through in situ X-ray diffraction and Raman spectroscopy. At a sulfur loading of up to 8 mg cm^-2 , the MnP-Mn₂ P/C@S achieves an area capacity of 6.4 mAh cm^-2 at 0.2 C. A pouch cell with the MnP-Mn₂ P/C@S cathode exhibits an initial energy density of 360 Wh kg^-1 .

Dual Single-Atom Moieties Anchored on N-Doped Multilayer Graphene As a Catalytic Host for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are promising for energy storage, especially in the era of carbon neutrality. Nonetheless, the sluggish kinetics of converting soluble lithium polysulfides into solid lithium sulfide impedes its development. In this work, we design Fe and Co dual single-atom moieties anchored on N-doped multilayer graphene (FeCoNGr) as a catalytic sulfur cathode host for Li-S batteries. With an efficient catalytic role in converting soluble lithium polysulfides into solid Li2S, the FeCoNGr-based Li-S cell demonstrates a capacity of 878.7 mA h g-1 at 0.2 C and retains 77.4% of the initial value after 100 cycles. The first and retained capacities are ∼1.7 and ∼1.8 times those of the NGr (without single atoms)-based cell, respectively. Theoretical calculations reveal that the Fe-N4 moiety has a higher binding energy toward low-order lithium polysulfides, while the Co-N4 moiety has a higher binding energy toward high-order lithium polysulfides. The efficient catalytic conversion of soluble lithium polysulfides into solid lithium sulfides of FeCoNGr plays important roles in outperforming NGr. This work enhances our knowledge on the tandem role of dual single-atom moieties and confirmed the high catalytic efficiency of single-atom catalysts in Li-S batteries.

Functional CNTs@EMIM+ -Br- Electrode Enabling Polysulfides Confining and Deposition Regulating for Solid-State Li-Sulfur Battery

With an extremely high theoretical energy density, poly(ethylene oxide) (PEO)-based solid-state lithium-sulfur (Li-S) batteries are emerging as one of the most feasible and safest battery storage systems. However, the long-term cycling performance is severely impeded by polysulfides (Li₂ S_n , n = 4-8) shuttling and terrible electrode passivation from the electronic insulating Li₂ S. Here, a novel cathode through chemically grafted 1-Ethyl-3-methylimidazolium bromide (EMIM⁺ -Br^- ) to carbon nanotube (CNTs) for PEO-based Li-S batteries is reported (CNTs@EMIM-Br/S). Concretely, bi-functional mediator EMIM⁺ -Br^- not only inhibits the polysulfides shuttling by strong chemical interactions via EMIM⁺ , but also facilitates the electrochemical kinetics for promoting the formation of 3D particulate Li₂ S through high donor anion (Br^- ). Satisfactorily, dual-function CNTs@EMIM-Br/S cathode exhibits high sulfur utilization with the capacity of up to 1298 mAh g^-1 , and keeps high capacity retention of 80.2% at 0.2 C after 350 cycles, exceeding that of many reported PEO-based solid-state Li-S batteries. This work will open a new door for rationally designed architecture to enable the practical applications of advanced Li-S batteries.

Realization of a 594 Wh kg-1 Lithium-Metal Battery Using a Lithium-Free V2 O5 Cathode with Enhanced Performances by Nanoarchitecturing

To realize a high-energy lithium metal battery (LMB) using a high-capacity Li-free cathode, in this work, nanoplate-stacked V₂ O₅ with dominantly exposed (010) facets and a relatively short [010] length is proposed to be used as a cathode. The V₂ O₅ nanostructure can be fabricated via a modified hydrothermal method, including a Li⁺ crystallization inhibitor, followed by heat treatment. In particular, the enlargement of the favorable Li⁺ diffusion pathway in the [010] direction and the formation of a robust hierarchical nanoplate-stacked structure in the modified V₂ O₅ improves the electrochemical kinetics and stability; as a result, the nanoplate-stacked V₂ O₅ electrode exhibits a higher capacity and rate performance (258 mAh g^-1 at 50 mA g^-1 [0.17 C], 140 mAh g^-1 at 1 A g^-1 [3.4 C]) and cycling capability (79% capacity retention after 100 cycles at 0.5 C) compared to the previously reported V₂ O₅ nanobelt electrode. Notably, the LMB composed of Li//nanoplate-stacked V₂ O₅ full-cells shows high specific energy densities of 594.1 and 296.2 Wh kg^-1 at 0.1 and 1.0 C, respectively, and a high Coulombic efficiency of 99.6% during 50 cycles.

Uniform Lithium Deposition Induced by ZnFx(OH)y for High-Performance Sulfurized Polyacrylonitrile-Based Lithium-Sulfur Batteries

Lithium metal batteries are emerging as the next generation of high-density electrochemical energy storage systems because of the ultra-high specific capacity and ultra-low electrochemical potential of the Li metal anode. However, the uneven Li deposition on commercial Cu current collectors result in low Coulombic efficiencies (CEs) and poor cycle life. In this research, we proposed the modification of ZnFx(OH)y on Cu foils to expand the lifespan. As-generated ZnLi alloy and LiF could promote uniform Li nucleation and deposition, thus resulting in an improved Li plating/stripping CE and extended cycle life. The Li-S battery with sulfurized polyacrylonitrile cathode and Li-ZnFx(OH)y@Cu anode (N/P ratio of 1.5:1) maintains 95% capacity after 60 cycles, proving the feasibility of ZnFx(OH)y@Cu for practical applications.

Prospects of halide-based all-solid-state batteries: From material design to practical application

The safety of lithium-ion batteries has caused notable concerns about their widespread adoption in electric vehicles. A nascent but promising approach to enhancing battery safety is using solid-state electrolytes (SSEs) to develop all-solid-state batteries, which exhibit unrivaled safety and superior energy density. A new family of SSEs based on halogen chemistry has recently gained renewed interest because of their high ionic conductivity, high-voltage stability, good deformability, and cost-effective and scalable synthesis routes. Here, we provide a comprehensive review of halide SSEs concerning their crystal structures, ion transport kinetics, and viability for mass production. Furthermore, their moisture sensitivity and interfacial challenges are summarized with corresponding effective strategies. Last, halide-based all-solid-state Li-ion and Li-S pouch cells with energy density targets of 400 and 500 Wh kg-1 are projected to guide future endeavors. This work serves as a comprehensive guideline for developing halide SSEs from material design to practical application.

Nanoscale Diamane Spiral Spring for High Mechanical Energy Storage

A compact, stable, sustainable, and high-energy density power supply system is crucial for the engineering deployment of mobile electromechanical devices/systems either at the small- or large-scale. This work proposes a spiral-based mechanical energy storage scheme utilizing the newly synthesized 2D diamane. Atomistic simulations show that diamane spiral can achieve a high theoretical gravimetric energy density of about 564 Wh kg^-1 , about 14 500 times the steel spring. The interlayer friction between diamane is found to cause a strong stick-slip effect that results in local stress/strain concentration. As such, the energy storage capacity of the diamane spiral can be tuned by suppressing the influence from the interlayer friction. Simulations affirm that higher gravimetric energy density can be achieved by reducing the turn number or adopting a low friction contact pair. The fundamental principles that dominate the energy storage capacity of the spiral spring are theoretically analyzed, respectively. The obtained insights suggest that the 2D vdW solids can be promising candidates to construct spiral structures with a high gravimetric energy density. This work should be beneficial for the design of reliable, stable, and sustainable nanoscale mechanical energy storage schemes that can be used as an alternative low-carbon footage energy supplier for novel micro-/nanoscale devices or systems.

A Review of the Application of Modified Separators in Inhibiting the "shuttle effect" of Lithium-Sulfur Batteries

Lithium-sulfur batteries with high theoretical specific capacity and high energy density are considered to be one of the most promising energy storage devices. However, the "shuttle effect" caused by the soluble polysulphide intermediates migrating back and forth between the positive and negative electrodes significantly reduces the active substance content of the battery and hinders the commercial applications of lithium-sulfur batteries. The separator being far from the electrochemical reaction interface and in close contact with the electrode poses an important barrier to polysulfide shuttle. Therefore, the electrochemical performance including coulombic efficiency and cycle stability of lithium-sulfur batteries can be effectively improved by rationally designing the separator. In this paper, the research progress of the modification of lithium-sulfur battery separators is reviewed from the perspectives of adsorption effect, electrostatic effect, and steric hindrance effect, and a novel modification of the lithium-sulfur battery separator is prospected.

Regulating Lithium Salt to Inhibit Surface Gelation on an Electrocatalyst for High-Energy-Density Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have great potential as high-energy-density energy storage devices. Electrocatalysts are widely adopted to accelerate the cathodic sulfur redox kinetics. The interactions among the electrocatalysts, solvents, and lithium salts significantly determine the actual performance of working Li-S batteries. Herein, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), a commonly used lithium salt, is identified to aggravate surface gelation on the MoS₂ electrocatalyst. In detail, the trifluoromethanesulfonyl group in LiTFSI interacts with the Lewis acidic sites on the MoS₂ electrocatalyst to generate an electron-deficient center. The electron-deficient center with high Lewis acidity triggers cationic polymerization of the 1,3-dioxolane solvent and generates a surface gel layer that reduces the electrocatalytic activity. To address the above issue, Lewis basic salt lithium iodide (LiI) is introduced to block the interaction between LiTFSI and MoS₂ and inhibit the surface gelation. Consequently, the Li-S batteries with the MoS₂ electrocatalyst and the LiI additive realize an ultrahigh actual energy density of 416 W h kg^-1 at the pouch cell level. This work affords an effective lithium salt to boost the electrocatalytic activity in practical working Li-S batteries and deepens the fundamental understanding of the interactions among electrocatalysts, solvents, and salts in energy storage systems.

Realizing High Utilization of High-Mass-Loading Sulfur Cathode via Electrode Nanopore Regulation

One main challenge of realizing high-energy-density lithium-sulfur batteries is low active materials utilization, excessive use of inert components, high electrolyte intake, and mechanical instability of high-mass-loading sulfur cathodes. Herein, chunky sulfur/graphene particle electrodes were designed, where active sulfur was confined in vertically aligned nanochannels (width ∼12 nm) of chunky graphene-based particles (∼70 μm) with N, O-containing groups. The short charge transport distance and low tortuosity enabled high utilization of active materials for high-mass-loading chunky sulfur/graphene particle electrodes. The intermediate polysulfide trapping effect by capillary effect and heteroatoms-containing groups, and a mechanically robust graphene framework, helped to realize stable electrode cycling. The as-designed electrode showed high areal capacity (10.9 mAh cm^-2) and high sulfur utilization (72.4%) under the rigorous conditions of low electrolyte/active material ratio (∼2.5 μL mg^-1) and high sulfur loading (9.0 mg cm^-2), realizing high energy densities (520 Wh kg^-1, 1635 Wh L^-1).

Thiol-Containing Metal-Organic Framework-Decorated Carbon Cloth as an Integrated Interlayer-Current Collector for Enhanced Li-S Batteries

Lithium-sulfur (Li-S) batteries hold great promise for new-generation energy storage technologies owing to their overwhelming energy density. However, the poor conductivity of active sulfur and the shuttle effect limit their widespread use. Herein, a carbon cloth decorated with thiol-containing UiO-66 nanoparticles (CC@UiO-66(SH)₂) was developed to substitute the traditional interlayer and current collector for Li-S batteries. One side of CC@UiO-66(SH)₂ acts as a current collector to load active materials, while the other side serves as an interlayer to further restrain polysulfide shuttling. This two-in-one integrated architecture endows the sulfur cathode with fast electron/ion transport and efficient chemical confinement of polysulfides. More importantly, rich thiol groups in the pores of UiO-66(SH)₂ serve to tether polysulfides by both covalent interactions and lithium bonding. Therefore, the Li-S battery equipped with this integrated interlayer-current collector not only delivers an enhanced specific capability (1209 mAh g^-1 at 0.1 C) but also exhibits prominent cycling stability (an attenuation rate of 0.037% per cycle for 1000 cycles at 1 C). Meanwhile, the battery achieves a high discharge capacity of 795 mAh g^-1 at a sulfur loading of 3.83 mg cm^-2. The new metal-organic framework (MOF)-based electrode material reported in this study undoubtedly provides insights into the exploration of functional MOFs for robust Li-S batteries.

Carbon nanofiber frameworks for Li metal batteries: the synergistic effect of conductivity and lithiophilic-sites

The utilization of carbon framework to guide the growth of the Li dendrites is an important theme for Li metal batteries. The conductivity and electronegative sites of carbon materials will greatly affect the nucleation of Li metal. However, how much these two contributing factors affect the Li plating/stripping stability should be considered. This work presents N, O doped carbon nanofiber framework (CNF) membrane as the interlayer for protecting the Li anode. The amounts of N and O elements and their ratios, the conductivity, the thickness of CNF membrane and their effects on the Li plating/stripping process have been fully analyzed. The voltage profile and the stability of Li plating/stripping process are evaluated by symmetric and asymmetrical coin cells. The lithiophilic heteroatom doped surface mainly works as an excellent guide during the Li plating process, whereas the conductivity and mechanical stability of CNF equalize the current density and confine the volume change in during cycling. With the optimized CNF membrane as the interlayer, both Li metal and Li-S full cells exhibit good capacity properties and cyclic stability.

High-Density Oxygen Doping of Conductive Metal Sulfides for Better Polysulfide Trapping and Li2 S-S8 Redox Kinetics in High Areal Capacity Lithium-Sulfur Batteries

Exploring new materials and methods to achieve high utilization of sulfur with lean electrolyte is still a common concern in lithium-sulfur batteries. Here, high-density oxygen doping chemistry is introduced for making highly conducting, chemically stable sulfides with a much higher affinity to lithium polysulfides. It is found that doping large amounts of oxygen into NiCo2 S4 is feasible and can make it outperform the pristine oxides and natively oxidized sulfides. Taking the advantages of high conductivity, chemical stability, the introduced large Li-O interactions, and activated Co (Ni) facets for catalyzing Sn 2- , the NiCo2 (O-S)4 is able to accelerate the Li2 S-S8 redox kinetics. Specifically, lithium-sulfur batteries using free-standing NiCo2 (O-S)4 paper and interlayer exhibit the highest capacity of 8.68 mAh cm-2 at 1.0 mA cm-2 even with a sulfur loading of 8.75 mg cm-2 and lean electrolyte of 3.8 µL g-1 . The high-density oxygen doping chemistry can be also applied to other metal compounds, suggesting a potential way for developing more powerful catalysts towards high performance of Li-S batteries.

Rational Design Strategy of Novel Energy Storage Systems: Toward High-Performance Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMBs) are promising candidates to replace currently commercialized lithium-ion batteries (LIBs) in large-scale energy storage applications owing to their merits of abundant resources, low cost, high theoretical volumetric capacity, etc. However, the development of RMBs is still facing great challenges including the incompatibility of the electrolyte and the lack of suitable cathode materials with high reversible capacity and fast kinetics of Mg²⁺ . While tremendous efforts have been made to explore compatible electrolytes and appropriate electrode materials, the rational design of unconventional Mg-based battery systems is another effective strategy for achieving high electrochemical performance. This review specifically discusses the recent research progress of various Mg-based battery systems. First, the optimization of electrolyte and electrode materials for conventional RMBs is briefly discussed. Furthermore, various Mg-based battery systems, including Mg-chalcogen (S, Se, Te) batteries, Mg-halogen (Br₂ , I₂ ) batteries, hybrid-ion batteries, and Mg-based dual-ion batteries are systematically summarized. This review aims to provide a comprehensive understanding of different Mg-based battery systems, which can inspire latecomers to explore new strategies for the development of high-performance and practically available RMBs.

Excavating Anomalous Capacity Increase of Li-S Pouch Cells by Electrochemical Oscillation Formation

The insufficient activation of a S/C cathode makes insufficient utilization of S in Li-S pouch cells, while the deep activation of a S/C cathode in a formation process is time-consuming and produces lithium polysulfides, which corrode a Li anode. Both situations lead to a low actual capacity of the Li-S pouch cells with a high S loading but are ignored for coin cells. In this work, electrochemical oscillation (EOS) formation employing hundreds of shallow discharge/charge cycles with high frequency was used to replace the resting and/or one deep discharge/charge cycle of traditional (TD) formation protocols. By controlling the discharge/charge capacity separately, symmetric oscillation (SOS) and asymmetric oscillation (ASOS) protocols were performed to facilitate the infiltration of electrolyte into the S cathode and restrict the formed lithium polysulfide in the cathode region. For SOS formation, the batteries were discharged/charged above 2.4 V with the same (symmetric) capacity with 2.78 × 10^-3 Hz of oscillation frequency (∼1.4 mAh/g for SOS-500), in which the polysulfide dissolution was suppressed effectively. For ASOS formation, 100% discharge capacity (also ∼1.4 mAh/g for ASOS-500) and 92% charge capacity are set in each oscillation period, which leads to better activation effect but more shuttling polysulfides than SOS. Compared with SOS protocol, for ASOS protocol, more oxidative S (instead of polysulfides) inside original nonactivated cathode will be preferentially reduced in the next discharging process, but all the accumulated polysulfides during discharge of activation are oxidized into elemental S in the final charging process. These efficient formation protocols increase the practical capacity by up to 160% after 50 cycles without any change in pouch cell assembly.