Reversible electrochemical oxidation of sulfur in ionic liquid for high-voltage Al-S batteries

Elucidating Consequences of Selenium Crystallinity on Its Electrochemical Reduction in Aluminum-Selenium Batteries

Selenium (Se) is an attractive positive electrode material for rechargeable aluminum (Al) batteries due to its high theoretical capacity of 2037 mA h g-1 and its higher electronic conductivity compared to sulfur. Selenium can undergo a series of electrochemical reactions between Se(-II) and Se(IV), resulting in a six-electron capacity per Se atom. However, existing Al-Se battery literature is inconsistent regarding the different electrochemical reactions possible, while the conditions enabling the electrochemical reduction of Se to Al2Se3 are not well understood. Here, we demonstrate that this electrochemical reduction is achievable using amorphous selenium but is suppressed for crystalline selenium. We further show that the electrochemical oxidation of Se to SeCl4, which occurs at higher potentials, reduces the long-range order of crystalline Se and enables its discharge to Al2Se3. Solid-state 77Se nuclear magnetic resonance (NMR) measurements further establish that the local Se helical structures are maintained upon the loss of crystallinity.

Highly Reversible Positive-Valence Conversion of Sulfur Chemistry for High-Voltage Zinc-Sulfur Batteries

Sulfur is a promising conversion-type cathode for zinc batteries (ZBs) due to its high discharge capacity and cost-effectiveness. However, the redox conversion of multivalent S in ZBs is still limited, only having achieved S0/S2- redox conversion with low discharge voltage and poor reversibility. This study presents significant progress by demonstrating, for the first time, the reversible S2-/S4+ redox behavior in ZBs with up to six-electron transfer (with an achieved discharge capacity of ≈1284 mAh g-1) using a highly concentrated ClO4 --containing electrolyte. The developed succinonitrile-Zn(ClO4)2 eutectic electrolyte stabilizes the positive-valence S compound and contributes to an ultra-low polarization voltage. Notably, the achieved flat discharge plateaus demonstrate the highest operation voltage (1.54 V) achieved to date in Zn‖S batteries. Furthermore, the high-voltage Zn‖S battery exhibits remarkable conversion dynamics, excellent cycling performance (85.7% capacity retention after 500 cycles), high efficiency (98.4%), and energy density (527 Wh kg S -1). This strategy of positive-valence conversion of sulfur represents a significant advancement in understanding sulfur chemistry in batteries and holds promise for future high-voltage sulfur-based batteries.

Recent Progress on Rechargeable Zn-X (X=S, Se, Te, I2, Br2) Batteries

Recently, aqueous Zn-X (X=S, Se, Te, I2, Br2) batteries (ZXBs) have attracted extensive attention in large-scale energy storage techniques due to their ultrahigh theoretical capacity and environmental friendliness. To date, despite tremendous research efforts, achieving high energy density in ZXBs remains challenging and requires a synergy of multiple factors including cathode materials, reaction mechanisms, electrodes and electrolytes. In this review, we comprehensively summarize the various reaction conversion mechanism of zinc-sulfur (Zn-S) batteries, zinc-selenium (Zn-Se) batteries, zinc-tellurium (Zn-Te) batteries, zinc-iodine (Zn-I2) batteries, and zinc-bromine (Zn-Br2) batteries, along with recent important progress in the design and electrolyte of advanced cathode (S, Se, Te, I2, Br2) materials. Additionally, we investigate the fundamental questions of ZXBs and highlight the correlation between electrolyte design and battery performance. This review will stimulate an in-deep understanding of ZXBs and guide the design of conversion batteries.

Superhalide-Anion-Motivator Reforming-Enabled Bipolar Manipulation toward Longevous Energy-Type Zn||Chalcogen Batteries

Neutrophilic superhalide-anion-triggered chalcogen conversion-based Zn batteries, despite latent high-energy merit, usually suffer from a short lifespan caused by dendrite growth and shuttle effect. Here, a superhalide-anion-motivator reforming strategy is initiated to simultaneously manipulate the anode interface and Se conversion intermediates, realizing a bipolar regulation toward longevous energy-type Zn batteries. With ZnF2 chaotropic additives, the original large-radii superhalide zincate anion species in ionic liquid (IL) electrolytes are split into small F-containing species, boosting the formation of robust solid electrolyte interphases (SEI) for Zn dendrite inhibition. Simultaneously, ion radius reduced multiple F-containing Se conversion intermediates form, enhancing the interion interaction of charged products to suppress the shuttle effect. Consequently, Zn||Se batteries deliver a ca. 20-fold prolonged lifespan (2000 cycles) at 1 A g-1 and high energy/power density of 416.7 Wh kgSe-1/1.89 kW kgSe-1, outperforming those in F-free counterparts. Pouch cells with distinct plateaus and durable cyclability further substantiate the practicality of this design.

Developing high-power Li||S batteries via transition metal/carbon nanocomposite electrocatalyst engineering

The activity of electrocatalysts for the sulfur reduction reaction (SRR) can be represented using volcano plots, which describe specific thermodynamic trends. However, a kinetic trend that describes the SRR at high current rates is not yet available, limiting our understanding of kinetics variations and hindering the development of high-power Li||S batteries. Here, using Le Chatelier's principle as a guideline, we establish an SRR kinetic trend that correlates polysulfide concentrations with kinetic currents. Synchrotron X-ray adsorption spectroscopy measurements and molecular orbital computations reveal the role of orbital occupancy in transition metal-based catalysts in determining polysulfide concentrations and thus SRR kinetic predictions. Using the kinetic trend, we design a nanocomposite electrocatalyst that comprises a carbon material and CoZn clusters. When the electrocatalyst is used in a sulfur-based positive electrode (5 mg cm-2 of S loading), the corresponding Li||S coin cell (with an electrolyte:S mass ratio of 4.8) can be cycled for 1,000 cycles at 8 C (that is, 13.4 A gS-1, based on the mass of sulfur) and 25 °C. This cell demonstrates a discharge capacity retention of about 75% (final discharge capacity of 500 mAh gS-1) corresponding to an initial specific power of 26,120 W kgS-1 and specific energy of 1,306 Wh kgS-1.

Unveiling Confinement Engineering for Achieving High-Performance Rechargeable Batteries

The confinement effect, restricting materials within nano/sub-nano spaces, has emerged as an innovative approach for fundamental research in diverse application fields, including chemical engineering, membrane separation, and catalysis. This confinement principle recently presents fresh perspectives on addressing critical challenges in rechargeable batteries. Within spatial confinement, novel microstructures and physiochemical properties have been raised to promote the battery performance. Nevertheless, few clear definitions and specific reviews are available to offer a comprehensive understanding and guide for utilizing the confinement effect in batteries. This review aims to fill this gap by primarily summarizing the categorization of confinement effects across various scales and dimensions within battery systems. Subsequently, the strategic design of confinement environments is proposed to address existing challenges in rechargeable batteries. These solutions involve the manipulation of the physicochemical properties of electrolytes, the regulation of electrochemical activity, and stability of electrodes, and insights into ion transfer mechanisms. Furthermore, specific perspectives are provided to deepen the foundational understanding of the confinement effect for achieving high-performance rechargeable batteries. Overall, this review emphasizes the transformative potential of confinement effects in tailoring the microstructure and physiochemical properties of electrode materials, highlighting their crucial role in designing novel energy storage devices.

Locally Concentrated Deep Eutectic Liquids Electrolytes for Low-Polarization Aluminum Metal Batteries

Low-cost and nontoxic deep eutectic liquid electrolytes (DELEs), such as [AlCl3]1.3[Urea] (AU), are promising for rechargeable non-aqueous aluminum metal batteries (AMBs). However, their high viscosity and sluggish ion transport at room temperature lead to high cell polarization and low specific capacity, limiting their practical application. Herein, non-solvating 1,2-difluorobenzene (dFBn) is proposed as a co-solvent of DELEs using AU as model to construct a locally concentrated deep eutectic liquid electrolyte (LC-DELE). dFBn effectively improves the fluidity and ion transport without affecting the ionic dynamics in the electrolyte. Moreover, dFBn also modifies the solid electrolyte interphase growing on the aluminum metal anodes and reduces the interfacial resistance. As a result, the lifespan of Al/Al cells is improved from 210 to 2000 h, and the cell polarization is reduced from 0.36 to 0.14 V at 1.0 mA cm-2. The rate performance of Al-graphite cells is greatly improved with a polarization reduction of 0.15 and 0.74 V at 0.1 and 1 A g-1, respectively. The initial discharge capacity of Al-sulfur cells is improved from 94 to 1640 mAh g-1. This work provides a feasible solution to the high polarization of AMBs employing DELEs and a new path to high-performance low-cost AMBs.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

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

Dynamically Ion-Coordinated Bipolar Organodichalcogenide Cathodes Enabling High-Energy and Durable Aqueous Zn Batteries

Bipolar organic cathode materials (OCMs) implementing cation/anion storage mechanisms are promising for high-energy aqueous Zn batteries (AZBs). However, conventional organic functional group active sites in OCMs usually fail to sufficiently unlock the high-voltage/capacity merits. Herein, we initially report dynamically ion-coordinated bipolar OCMs as cathodes with chalcogen active sites to solve this issue. Unlike conventional organic functional groups, chalcogens bonded with conjugated group undergo multielectron-involved positive-valence oxidation and negative-valence reduction, affording higher redox potentials and reversible capacities. With phenyl diselenide (PhSe-SePh, PDSe) as a proof of concept, it exhibits a conversion pathway from (PhSe)- to (PhSe-SePh)0 and then to (PhSe)+ as unveiled by characterization and theoretical simulation, where the diselenide bonds are periodically broken and healed, dynamically coordinating with ions (Zn2+ and OTF-). When confined into ordered mesoporous carbon (CMK-3), the dissolution of PDSe intermediates is greatly inhibited to obtain an ultralong lifespan without voltage/capacity compromise. The PDSe/CMK-3 || Zn batteries display high reversibility capacity (621.4 mAh gPDSe -1), distinct discharge plateau (up to 1.4 V), high energy density (578.3 Wh kgPDSe -1), and ultralong lifespan (12 000 cycles) at 10 A g-1, far outperforming conventional bipolar OCMs. This work sheds new light on conversion-type active site engineering for high-voltage/capacity bipolar OCMs towards high-energy AZBs.

Locally Concentrated Ionic Liquid Electrolytes for Wide-Temperature-Range Aluminum-Sulfur Batteries

Aluminum-sulfur (Al-S) batteries are promising energy storage devices due to their high theoretical capacity, low cost, and high safety. However, the high viscosity and inferior ion transport of conventionally used ionic liquid electrolytes (ILEs) limit the kinetics of Al-S batteries, especially at sub-zero temperatures. Herein, locally concentrated ionic liquid electrolytes (LCILE) formed via diluting the ILEs with non-solvating 1,2-difluorobenzene (dFBn) co-solvent are proposed for wide-temperature-range Al-S batteries. The addition of dFBn effectively promotes the fluidity and ionic conductivity without affecting the AlCl4 - /Al2 Cl7 - equilibrium, which preserves the reversible stripping/plating of aluminum and further promotes the overall kinetics of Al-S batteries. As a result, Al-S cells employing the LCILE exhibit higher specific capacity, better cyclability, and lower polarization with respect to the neat ILE in a wide temperature range from -20 to 40 °C. For instance, Al-S batteries employing the LCILE sustain a remarkable capacity of 507 mAh g-1 after 300 cycles at 20 °C, while only 229 mAh g-1 is delivered with the dFBn-free electrolyte under the same condition. This work demonstrates the favorable use of LCILEs for wide-temperature Al-S batteries.

Selenium-Anchored Chlorine Redox Chemistry in Aqueous Zinc Dual-Ion Batteries

Chlorine-based batteries with Cl0 to Cl- redox reaction (ClRR) are promising for high-performance energystorage due to their high redox potential and large theoretical capacity. However, the inherent gas-liquid conversion feature of ClRR together with poor Cl fixation can cause Cl2 leakage, reducing battery reversibility. Herein, we utilize a Se-based organic molecule, diphenyl diselenide (di-Ph-Se), as the Cl anchoring agent and realize an atomic level-Cl fixation through chalcogen-halogencoordinating chemistry. The promoted Cl fixation, with two oxidized Cl0 anchoring on a single Ph-Se, and the multivalence conversion of Se contributeto a six-electron conversion process with up to 507 mAh g-1 and an average voltage of 1.51 V, as well as a high energy density of 665 Wh Kg-1 . Based on the superior reversibility of thedeveloped di-Ph-Se electrode with ClRR, a remarkable rate performance (205 mAh g-1 at 5 A g-1 ) and cycling performance (capacity retention of 77.3 % after 500cycles) are achieved. Significantly, the pouch cell delivers a record arealcapacity of up to 6.87 mAh cm-2 and extraordinary self-discharge performance. This chalcogen-halogen coordination chemistry between the Se electrode and Cl provides a new insight for developing reversible and efficientbatteries with halogen redox reactions.

Rapid-charging aluminium-sulfur batteries operated at 85 °C with a quaternary molten salt electrolyte

Molten salt aluminum-sulfur batteries are based exclusively on resourcefully sustainable materials, and are promising for large-scale energy storage owed to their high-rate capability and moderate energy density; but the operating temperature is still high, prohibiting their applications. Here we report a rapid-charging aluminium-sulfur battery operated at a sub-water-boiling temperature of 85 °C with a tamed quaternary molten salt electrolyte. The quaternary alkali chloroaluminate melt - possessing abundant electrochemically active high-order Al-Cl clusters and yet exhibiting a low melting point - facilitates fast Al3+ desolvation. A nitrogen-functionalized porous carbon further mediates the sulfur reaction, enabling the battery with rapid-charging capability and excellent cycling stability with 85.4% capacity retention over 1400 cycles at a charging rate of 1 C. Importantly, we demonstrate that the asymmetric sulfur reaction mechanism that involves formation of polysulfide intermediates, as revealed by operando X-ray absorption spectroscopy, accounts for the high reaction kinetics at such temperature wherein the thermal management can be greatly simplified by using water as the heating media.

High-Reversibility Sulfur Anode for Advanced Aqueous Battery

Despite being extensively explored as cathodes in batteries, sulfur (S) can function as a low-potential anode by changing charge carriers in electrolytes. Here, a highly reversible S anode that fully converts from S8 0 to S2- in static aqueous S-I2 batteries by using Na+ as the charge carrier is reported. This S anode exhibits a low potential of -0.5 V (vs standard hydrogen electrode) and a near-to-theoretical capacity of 1404 mA h g-1 . Importantly, it shows significant advantages over the widely used Zn anode in aqueous media by obviating dendrite formation and H2 evolution. To suppress "shuttle effects" faced by both S and I2 electrodes, a scalable sulfonated polysulfone (SPSF) membrane is proposed, which is superior to commercial Nafion in cost (US$1.82 m-2  vs $3500 m-2 ) and environmental benignity. Because of its ultra-high selectivity in blocking polysulfides/iodides, the battery with SPSF displays excellent cycling stability. Even under 100% depth of discharge, the battery demonstrates high capacity retention of 87.6% over 500 cycles, outperforming Zn-I2 batteries with 3.1% capacity under the same conditions. These findings broaden anode options beyond metals for high-energy, low-cost, and fast-chargeable batteries.

Stable Aluminum Metal Anode Enabled by Dual-Functional Molybdenum Nanoparticles

Constructing robust anode with strong aluminophilicity and rapid desolvation kinetics is essential for achieving high utilization, long-term durability, and superior rate performance in Al metal-based energy storage, yet remains largely unexplored. Herein, molybdenum nanoparticles embedded onto nitrogen-doped graphene (Mo@NG) are designed and prepared as Al host to regulate the deposition behavior and achieve homogeneous Al plating/stripping. The monodispersed Mo nanoparticles reduce the desolvation energy barrier and promote the deposition kinetics of Al. Additionally, Mo nanoparticles act as aluminophilic nucleation sites to minimize the Al nucleation overpotential, further guiding uniform and dense Al deposition. As a result, the dual-functional Mo@NG endows Al anodes with low voltage hysteresis, reversible Al plating/stripping with high coulombic efficiency, and excellent high-rate capability under 5 mA cm-2 . Moreover, the as-designed Al metal full batteries deliver a high capacity retention of 92.8% after 3000 cycles at 1 A g-1 . This work provides an effective solution to optimize the electrochemical properties of Al metal anode from the perspective of desolvation and deposition reactions, towards the development of high-safety and long-cycling aluminum-ion batteries.

Application of triphenylphosphine organic compounds constructed with O, S, and Se in aluminum ion batteries

Due to their high reactivity and theoretical capacity, chalcogen elements have been favored and applied in many battery studies. However, the high surface charge density and high solubility of these elements as electrode materials have hindered their deeper exploration due to the shuttle effect. In this article, organic structural triphenylphosphine is used as a molecular main chain structure, and chalcogen elements O, S, and Se are introduced to combine with P as active sites. This approach not only takes advantage of the beneficial effects of the aromatic ring on the physical and chemical properties of the chalcogen element but also allows for the optimization of its advantages. By utilizing Triphenylphosphine selenide (TP-Se) as the cathode material in aluminum-ion batteries(AIBs), a high-performance Al-organic battery was fabricated, which exhibited a high initial capacity of 180.6 mAh g-1 and stable cycling for up to 1000 cycles. Based on density functional theory (DFT) calculations, TP-Se exhibits a smaller energy gap, which renders it favorable for chemical reactions. Moreover, the calculated results suggest that TP-Se tends to undergo redox reactions with AlCl2+. The molecular structure of triphenylphosphine and its combination with Se offers an enticing pathway for designing cathode materials in aluminum-organic batteries.

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

Ionic liquids (ILs) consisting entirely of ions exhibit many fascinating and tunable properties, making them promising functional materials for a large number of energy-related applications. For example, ILs have been employed as electrolytes for electrochemical energy storage and conversion, as heat transfer fluids and phase-change materials for thermal energy transfer and storage, as solvents and/or catalysts for CO2 capture, CO2 conversion, biomass treatment and biofuel extraction, and as high-energy propellants for aerospace applications. This paper provides an extensive overview on the various energy applications of ILs and offers some thinking and viewpoints on the current challenges and emerging opportunities in each area. The basic fundamentals (structures and properties) of ILs are first introduced. Then, motivations and successful applications of ILs in the energy field are concisely outlined. Later, a detailed review of recent representative works in each area is provided. For each application, the role of ILs and their associated benefits are elaborated. Research trends and insights into the selection of ILs to achieve improved performance are analyzed as well. Challenges and future opportunities are pointed out before the paper is concluded.

Tellurium with Reversible Six-Electron Transfer Chemistry for High-Performance Zinc Batteries

Chalcogens, especially tellurium (Te), as conversion-type cathodes possess promising prospects for zinc batteries (ZBs) with potential rich valence supply and high energy density. However, the conversion reaction of Te is normally restricted to the Te2-/Te0 redox with a low voltage plateau at ∼0.59 V (vs Zn2+/Zn) rather than the expected positive valence conversion of Te0 to Ten+, inhibiting the development of Te-based batteries toward high output voltage and energy density. Herein, the desired reversible Te2-/Te0/Te2+/Te4+ redox behavior with up to six-electron transfer was successfully activated by employing a highly concentrated Cl--containing electrolyte (Cl- as strong nucleophile) for the first time. Three flat discharge plateaus located at 1.24, 0.77, and 0.51 V, respectively, are attained with a total capacity of 802.7 mAh g-1. Furthermore, to improve the stability of Ten+ products and enhance the cycling stability, a modified ionic liquid (IL)-based electrolyte was fabricated, leading to a high-performance Zn∥Te battery with high areal capacity (7.13 mAh cm-2), high energy density (542 Wh kgTe-1 or 227 Wh Lcathdoe+anode-1), excellent cycling performance, and a low self-discharge rate based on 400 mAh-level pouch cell. The results enhance the understanding of tellurium chemistry in batteries, substantially promising a remarkable route for advanced ZBs.

Realizing Nanolime Aqueous Dispersion via Ionic Liquid Surface Modification to Consolidate Stone Relics

After decades of research in the conservation of cultural heritage, nanolime (NL) has emerged as a potential alternative inorganic material to the frequently used organic materials. However, its poor kinetic stability in water has been a major challenge that restricted its penetration depth through cultural relics and resulted in unsatisfactory conservation outcomes. Here, for the first time, we realize NL water dispersion by modification of ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) via a sample aqueous solution deposit method. Our findings indicate that the cation of the ionic liquid (IL) binds strongly to the surface of NL particles (IL-NL) by forming hydrogen bonds with Ca(OH)₂ facets. The absorption of IL causes an unexpected significant alteration in the morphology of NL particles and results in a drastic reduction in NL's size. More importantly, this absorption endows NL excellent kinetic stability dispersed into water and implements NL water dispersion, which makes a breakthrough in terms of extreme poor kinetic stability of as-synthesized NL and commercial NL in water. The mechanism driving IL-NL water dispersion is explained by Stern theory. In the context of consolidating weathered stone, the presence of IL may delay carbonation of NL but the penetration depth of IL-NL through stone samples is three times deeper than that of as-synthesized and commercial NLs. Additionally, the consolidation strength of IL-NL is similar to that of as-synthesized NL and commercial NL. Moreover, IL-NL has no significant impact on the permeability, pore size, and microstructure of consolidated stone relics. Our research contributes to the field of NL-related materials and will enhance the dissemination and utilization of NL-based materials in the preservation of water-insensitive cultural heritage.

ZnSe/SnSe2 hollow microcubes as cathode for high performance aluminum ion batteries

Advances in cathode material design and understanding of intercalation mechanisms are necessary to improve the overall performance of aluminum ion batteries. Therefore, we designed ZnSe/SnSe₂ hollow microcubes with heterojunction structure as a cathode material for aluminum ion batteries. ZnSe/SnSe₂ hollow microcubes with an average size of about1.4 µm were prepared by selenization of ZnSn(OH)₆ microcubes successfully. The shell thickness of ZnSe/SnSe₂ hollow microcubes is about 250 nm. On one hand, the hollow cubic structure can effectively alleviate the volume effect, provide shorter ion diffusion paths, and increase the contact area with the electrolyte. On the other hand, ZnSe/SnSe₂ heterojunction structure can establish a built-in electric field to facilitate ion transport. The synergistic effect of the two leads to the improved electrochemical performance of ZnSe/SnSe₂ as the cathode of aluminum ion batteries. The material delivered a reversible capacity of 124 mAh/g after 150 cycles at a current density of 100 mA/g. Meanwhile, coulombic efficiency remained above 98% in almost all cycles. In addition, the electrochemical reaction mechanism and kinetic process of Al³⁺ and ZnSe/SnSe₂ were studied.

Dual synergistic effects assisting Cu-SeS2 electrochemistry for energy storage

Selenium sulfide (SeS2) features higher electronic conductivity than sulfur and higher theoretical capacity and lower cost than selenium, attracting considerable interest in energy storage field. Although nonaqueous Li/Na/K-SeS2 batteries are attractive for their high energy density, the notorious shuttle effect of polysulfides/polyselenides and the intrinsic limitations of organic electrolyte have hindered the deployment of this technology. To circumvent these issues, here we design an aqueous Cu-SeS2 battery by encapsulating SeS2 in a defect-enriched nitrogen-doped porous carbon monolith. Except the intrinsic synergistic effect between Se and S in SeS2, the porous structure of carbon matrix has sufficient internal voids to buffer the volume change of SeS2 and provides abundant pathways for both electrons and ions. In addition, the synergistic effect of nitrogen doping and topological defect not only enhances the chemical affinity between reactants and carbon matrix but also offers catalytic active sites for electrochemical reactions. Benefiting from these merits, the Cu-SeS2 battery delivers superior initial reversible capacity of 1,905.1 mAh g-1 at 0.2 A g-1 and outstanding long-span cycling performance over 1,000 cycles at 5 A g-1. This work applies variable valence charge carriers to aqueous metal-SeS2 batteries, providing valuable inspiration for the construction of metal-chalcogen batteries.

Reversible, Dendrite-Free, High-Capacity Aluminum Metal Anode Enabled by Aluminophilic Interface Layer

Aluminum (Al) metal is an attractive anode material for next-generation rechargeable batteries, because of its low cost and high capacities. However, it brings some fundamental issues such as dendrites, low Coulombic efficiency (CE), and low utilization. Here, we propose a strategy for constructing an ultrathin aluminophilic interface layer (AIL) to regulate the Al nucleation and growth behaviors, which enables highly reversible and dendrite-free Al plating/stripping under high areal capacity. Metallic Al can maintain stable plating/stripping on the Pt-AIL@Ti for over 2000 h at 10 mAh cm^-2 with an average CE of 99.9%. The Pt-AIL also enables reversible Al plating/stripping at a record high areal capacity of 50 mAh cm^-2, which is 1-2 orders of magnitude higher than the previous studies. This work provides a valuable direction for further construction of high-performance rechargeable Al metal batteries.

2D Mesoporous Zincophilic Sieve for High-Rate Sulfur-Based Aqueous Zinc Batteries

Sulfur-based aqueous zinc batteries (SZBs) attract increasing interest due to their integrated high capacity, competitive energy density, and low cost. However, the hardly reported anodic polarization seriously deteriorates the lifespan and energy density of SZBs at a high current density. Here, we develop an integrated acid-assisted confined self-assembly method (ACSA) to elaborate a two-dimensional (2D) mesoporous zincophilic sieve (2DZS) as the kinetic interface. The as-prepared 2DZS interface presents a unique 2D nanosheet morphology with abundant zincophilic sites, hydrophobic properties, and small-sized mesopores. Therefore, the 2DZS interface plays a bifunctional role in reducing the nucleation and plateau overpotential: (a) accelerating the Zn²⁺ diffusion kinetics through the opened zincophilic channels and (b) inhibiting the kinetic competition of hydrogen evolution and dendrite growth via the significant solvation-sheath sieving effect. Therefore, the anodic polarization is reduced to 48 mV at 20 mA cm^-2, and the full-battery polarization is reduced to 42% of an unmodified SZB. As a result, an ultrahigh energy density of 866 Wh kg_sulfur^-1 at 1 A g^-1 and a long lifespan of 10,000 cycles at a high rate of 8 A g^-1 are achieved.

Self-Adaptive Re-Organization Enables Polythiophene as an Extraordinary Cathode Material for Aluminum-Ion Batteries with a Cycle Life of 100 000 Cycles

Aluminum-ion batteries (AIBs) have attracted great attentions in recent years. Organic materials such as polythiophene (PT) are promising cathode for AIBs. However, the capacity and cyclic stability of conventional organic cathode such as PT are limited by the inadequate degree of reaction and the unstable nature of organic materials. To obtain high-performance organic cathode, a new PT with the ability of self-adaptive re-organization was prepared. During cycling, its molecular chain can be re-organized, and the polymerization mode will change from C_α -C_α (α-PT) to C_β -C_β (β-PT). This change leads to smaller steric hindrance and faster kinetics during ion insertion which can lower the reaction energy barrier and stabilize the molecular structure. Benefited by this, AIBs with this cathode can deliver a specific capacity of 180 mAh g^-1 (@2 A g^-1 ) and a superb stability of 100 000 cycles at 10 A g^-1 . High energy density and power density can also be achieved with this cathode.

Unraveling the Catalyst-Solvent Interactions in Lean-Electrolyte Sulfur Reduction Electrocatalysis for Li-S Batteries

Efficient catalyst design is important for lean-electrolyte sulfur reduction in Li-S batteries. However, most of the reported catalysts were focused on catalyst-polysulfide interactions, and generally exhibit high activity only with a large excess of electrolyte. Herein, we proposed a general rule to boost lean-electrolyte sulfur reduction by controlling the catalyst-solvent interactions. As evidenced by synchrotron-based analysis, in situ spectroscopy and theoretical computations, strong catalyst-solvent interaction greatly enhances the lean-electrolyte catalytic activity and battery stability. Benefitting from the strong interaction between solvent and cobalt catalyst, the Li-S battery achieves stable cycling with only 0.22 % capacity decay per cycle with a low electrolyte/sulfur mass ratio of 4.2. The lean-electrolyte battery delivers 79 % capacity retention compared with the battery with flooded electrolyte, which is the highest among the reported lean-electrolyte Li-S batteries.

σ-Alkynyl Adsorption Enables Electrocatalytic Semihydrogenation of Terminal Alkynes with Easy-Reducible/Passivated Groups over Amorphous PdSx Nanocapsules

Highly chemo- and regioselective semihydrogenation of alkynes is significant and challenging for the synthesis of functionalized alkenes. Here, a sequential self-template method is used to synthesize amorphous palladium sulfide nanocapsules (PdS_x ANCs), which enables electrocatalytic semihydrogenation of terminal alkynes in H₂O with excellent tolerance to easily reducible groups (e.g., C-I/Br/Cl, C═O) and the metal center deactivating skeletons (e.g., quinolyl, carboxyl, and nitrile). Mechanistic studies demonstrate that specific σ-alkynyl adsorption via terminal carbon and negligible alkene adsorption on isolated Pd²⁺ sites ensure successful synthesis of various alkenes with outstanding time-irrelevant selectivity in a wide potential range. The key hydrogen and carbon radical intermediates are validated by electron paramagnetic resonance and high-resolution mass spectrometry. Gram-scale synthesis of 4-bromostyrene and expedient preparation of deuterated alkene precursors and drugs with D₂O show promising applications. Impressively, PdS_x ANCs can be applied to the prevailing thermocatalytic semihydrogenation of functionalized alkyne using H₂.

Tuning Zn-Ion Solvation Chemistry with Chelating Ligands toward Stable Aqueous Zn Anodes

Changing the solvation sheath of hydrated Zn ions is an effective strategy to stabilize Zn anodes to obtain a practical aqueous Zn-ion battery. However, key points related to the rational design remain unclear including how the properties of the solvent molecules intrinsically regulate the solvated structure of the Zn ions. This study proposes the use of a stability constant (K), namely, the equilibrium constant of the complexation reaction, as a universal standard to make an accurate selection of ligands in the electrolyte to improve the anode stability. It is found that K greatly impacts the corrosion current density and nucleation overpotential. Following this, ethylene diamine tetraacetic acid with a superhigh K effectively suppresses Zn corrosion and induces uniform Zn-ion deposition. As a result, the anode has an excellent stability of over 3000 h. This work presents a general principle to stabilize anodes by regulating the solvation chemistry, guiding the development of novel electrolytes for sustainable aqueous batteries.

A core-shelled Sb@C nanorod cathode with a graphene aerogel interlayer for high-capacity aluminum ion batteries

Rechargeable aluminum-ion batteries, RAIBs, as a prime candidate for next-generation batteries, have attracted much attention due to their extremely high anode capacity and good safety. However, the lack of matching high-capacity cathode materials and reasonable design limit their practical development. Herein, core-shelled Sb@C nanorods are prepared by polymer coating and thermal reduction as a metal-based cathode for RAIBs. The carbon shell and graphene aerogel interlayer effectively block the diffusion and shuttling of charging products, thus exhibiting excellent electrochemical performance. This Al-Sb battery delivers an initial discharge capacity of 656 mA h g^-1 at 100 mA g^-1, a stable discharge voltage of 0.9 V, and excellent cycling stability maintained at 306 mA h g^-1 after 500 cycles at 1 A g^-1. Serial characterizations are used to monitor the structural changes of Sb in reversible reactions and to determine the configuration of the charged products, showing that the product exists in the form of [SbCl₄]⁺ cations, that is, a five-electron transfer reaction occurs with a very high theoretical capacity (1100 mA h g^-1). This study sheds light on the energy storage mechanism of a metallic Sb cathode in RAIBs, and provides new insights into the study of high-capacity cathodes and the rational design of battery structures.

Advances and challenges of aluminum-sulfur batteries

The search for cost-effective stationary energy storage systems has led to a surge of reports on novel post-Li-ion batteries composed entirely of earth-abundant chemical elements. Among the plethora of contenders in the 'beyond lithium' domain, the aluminum-sulfur (Al-S) batteries have attracted considerable attention in recent years due to their low cost and high theoretical volumetric and gravimetric energy densities (3177 Wh L^-1 and 1392 Wh kg^-1). In this work, we offer an overview of historical and present research pursuits in the development of Al-S batteries with particular emphasis on their fundamental problem-the dissolution of polysulfides. We examine both experimental and computational approaches to tailor the chemical interactions between the sulfur host materials and polysulfides, and conclude with our view on research directions that could be pursued further.

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

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

Electrocatalysis for Continuous Multi-Step Reactions in Quasi-Solid-State Electrolytes Towards High-Energy and Long-Life Aluminum-Sulfur Batteries

Aluminum-sulfur (Al-S) batteries of ultrahigh energy-to-price ratios are a promising energy storage technology, while they suffer from a large voltage gap and short lifespan. Herein, we propose an electrocatalyst-boosting quasi-solid-state Al-S battery, which involves a sulfur-anchored cobalt/nitrogen co-doped graphene (S@CoNG) positive electrode and an ionic-liquid-impregnated metal-organic framework (IL@MOF) electrolyte. The Co-N₄ sites in CoNG continuously catalyze the breaking of Al-Cl and S-S bonds and accelerate the sulfur conversion, endowing the Al-S battery with a shortened voltage gap of 0.43 V and a high discharge voltage plateau of 0.9 V. In the quasi-solid-state IL@MOF electrolytes, the shuttle effect of polysulfides has been inhibited, which stabilizes the reversible sulfur reaction, enabling the Al-S battery to deliver 820 mAh g^-1 specific capacity and 78 % capacity retention after 300 cycles. This finding offers novel insights to design Al-S batteries for stable energy storage.

Optimization of Electrolytes for High-Performance Aqueous Aluminum-Ion Batteries

Aqueous rechargeable batteries based on aluminum chemistry have become the focus of immense research interest owing to their earth abundance, low cost, and the higher theoretical volumetric energy density of this element compared to lithium-ion batteries. Efforts to harness this huge potential have been hindered by the narrow potential window of water and by passivating effects of the high-electrical band-gap aluminum oxide film. Herein, we report a high-performing aqueous aluminum-ion battery (AIB), which is constructed using a Zn-supported Al alloy, an aluminum bis(trifluoromethanesulfonyl)imide (Al[TFSI]₃) electrolyte, and a MnO₂ cathode. The use of Al[TFSI]₃ significantly extends the voltage window of the electrolyte and enables the cell to access Al³⁺/Al electrochemistry, while the use of Zn-Al alloy mitigates the issue of surface passivation. The Zn-Al alloy, which is produced by in situ electrochemical deposition, obtained from Al[TFSI]₃ showed excellent long-term reversibility for Al electrochemistry and displays the highest performance in AIB when compared to the response obtained in Al₂(SO₄)₃ or aluminum trifluoromethanesulfonate electrolyte. AIB cells constructed using the Zn-Al|Al[TFSI]₃|MnO₂ combination achieved a record discharge voltage plateau of 1.75 V and a specific capacity of 450 mAh g^-1 without significant capacity fade after 400 cycles. These findings will promote the development of energy-dense aqueous AIBs.

Nanostructure Engineering Strategies of Cathode Materials for Room-Temperature Na-S Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries are considered to be a competitive electrochemical energy storage system, due to their advantages in abundant natural reserves, inexpensive materials, and superb theoretical energy density. Nevertheless, RT Na-S batteries suffer from a series of critical challenges, especially on the S cathode side, including the insulating nature of S and its discharge products, volumetric fluctuation of S species during the (de)sodiation process, shuttle effect of soluble sodium polysulfides, and sluggish conversion kinetics. Recent studies have shown that nanostructural designs of S-based materials can greatly contribute to alleviating the aforementioned issues via their unique physicochemical properties and architectural features. In this review, we review frontier advancements in nanostructure engineering strategies of S-based cathode materials for RT Na-S batteries in the past decade. Our emphasis is focused on delicate and highly efficient design strategies of material nanostructures as well as interactions of component-structure-property at a nanosize level. We also present our prospects toward further functional engineering and applications of nanostructured S-based materials in RT Na-S batteries and point out some potential developmental directions.