Initiating a Reversible Aqueous Zn/Sulfur Battery through a "Liquid Film"

Synergistic effect between S and Te enhancing the electrochemical behavior of heteroatomic TeS-x cathodes in aqueous Zn-TeS batteries

Aqueous Zn-S batteries (AZSBs) have garnered increasing attention in the energy storage field owing to their high capacity, energy density, and cost effectiveness. Nevertheless, sulfur (S) cathodes face challenges, primarily stemming from sluggish reaction kinetics and the formation of an irreversible byproduct (SO42-) during the charge, hindering the progress of AZSBs. Herein, Te-S bonds within S-based cathodes were introduced to enhance electron and ion transport and facilitate the conversion reaction from zinc sulfide (ZnS) to S. This was achieved by constructing heteroatomic TeS-x@Ketjen black composite cathodes (HM-TeS-x@KB, where x  = 36, 9, and 4). The HM-TeS-9@KB electrode exhibits long-term cycling stability, maintaining a capacity decay rate of 0.1 % per cycle over 450 cycles at a current density of 10 A g-1. Crucially, through a combination of experimental data analysis and theoretical calculations, the impact mechanism of Te on the charge and discharge of S active materials within the HM-TeS-9@KB cathode in AZSBs was investigated. The presence of Te-S bonds boost the intrinsic conductivity and wettability of the HM-TeS-9@KB cathode. Furthermore, during the charge, the interaction of preferentially oxidized Te with S atoms within ZnS promotes the oxidation reaction from ZnS to S and suppresses the irreversible side reaction between ZnS and H2O. These findings indicate that the heteroatomization of chalcogen S molecules represents a promising approach for enhancing the electrochemical performance of S cathodes in AZSBs.

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.

Ionic Covalent Organic Framework Membrane as Active Separator for Highly Reversible Zinc-Sulfur Battery

Zinc-sulfur (Zn-S) batteries exhibit a high theoretical energy density, nontoxicity, and cost-effectiveness, demonstrating significant potential for integration into large-scale energy storage systems. However, the phenomenon of polysulfide (including dissolved S8 and Sx2-) shuttling is a major issue that results in rapid capacity decay and a short lifespan, limiting the practical performance of sulfur-based batteries. Herein, we fabricated an ionic covalent organic framework (iCOF) membrane as an active separator for the Zn-S battery. Sulfonic acid groups were introduced to the COF membrane, providing abundant negative charge sites in its pore wall. By combining size sieving and charge interaction between the polysulfide and pore wall, the iCOF membrane inhibited the crossover of polysulfides to the Zn metal anode without affecting the transport of metal ions. The Zn-S battery with the iCOF membrane as the separator shows a high-performance and low attenuation rate of 0.05% per cycle over 300 cycles at 2.5 A g-1. This study emphasizes the significance of separator design in enhancing Zn-S batteries and showcases the potential of functionalized framework materials for the development of high-performance energy storage systems.

High-Valent Thiosulfate Redox Electrochemistry for Advanced Sulfur-Based Aqueous Batteries

Sulfur-based aqueous batteries (SABs) are promising for safe, low-cost, and high-capacity energy storage. However, the low output voltage of sulfur cannot meet the demands of high-energy cathode applications due to its intrinsic negative potential (E0 = -0.51 V vs SHE) of low-valent polysulfide redox (S2-/S0). Here, instead of relying on traditional aqueous polysulfide redox, for the first time, we demonstrate a high-valent thiosulfate redox (S2O32-/S4O62-) electrochemistry, exhibiting positive redox potential (E0 > 0 V vs SHE) and reversible cation storage in aqueous environment. Operando X-ray absorption fine structure spectroscopy, in situ Raman spectroscopy, and density functional theory calculations reveal the high reversibility and dynamic charge transfer process of high-valent thiosulfate redox. Significantly, the aqueous thiosulfate redox exhibits a high operating voltage of approximately 1.4 V, a reversible capacity of 193 Ah L-1, and a long cycling life of over 1000 cycles (99.6% capacity retention). This work provides new insights into the high-valent S-based electrochemistry and opens a new pathway to achieve energetic aqueous batteries.

The emerging hybrid electrochemical energy technologies

Electrochemical energy devices serve as a vital link in the mutual conversion between chemical energy and electrical energy. This role positions them to be essential for achieving high-efficiency utilization and advancement of renewable energy. Electrochemical reactions, including anodic and cathodic reactions, play a crucial role in facilitating the connection between two types of charge carriers: electrons circulating within the external circuit and ions transportation within the internal electrolyte, which ensures the completion of the circuit in electrochemical devices. While electrons are uniform, ions come in various types, we herein propose the concept of hybrid electrochemical energy technologies (h-EETs) characterized by the utilization of different ions as charge carriers of anodic and cathodic reactions. Accordingly, this review aims to explore the fundamentals of emerging hybrid electrochemical energy technologies and recent research advancements. We start with the introduction of the concept and foundational aspects of h-EETs, including the proposed definition, the historical background, operational principles, device configurations, and the underlying principles governing these configurations of the h-EETs. We then discuss how the integration of hybrid charge carriers influences the performance of associated h-EETs, to facilitate an insightful understanding on how ions carriers can be beneficial and effectively implemented into electrochemical energy devices. Furthermore, a special emphasis is placed on offering an overview of the research progress in emerging h-EETs over recent years, including hybrid battery capacitors that extend beyond traditional hybrid supercapacitors, as well as exploration into hybrid fuel cells and hybrid electrolytic synthesis. Finally, we highlight the major challenges and provide anticipatory insights into the future perspectives of developing high-performance h-EETs devices.

Advances in Aqueous Zinc Ion Batteries based on Conversion Mechanism: Challenges, Strategies, and Prospects

Recently, aqueous zinc-ion batteries with conversion mechanisms have received wide attention in energy storage systems on account of excellent specific capacity, high power density, and energy density. Unfortunately, some characteristics of cathode material, zinc anode, and electrolyte still limit the development of aqueous zinc-ion batteries possessing conversion mechanism. Consequently, this paper provides a detailed summary of the development for numerous aqueous zinc-based batteries: 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. Meanwhile, the reaction conversion mechanism of zinc-based batteries with conversion mechanism and the research progress in the investigation of composite cathode, zinc anode materials, and selection of electrolytes are systematically introduced. Finally, this review comprehensively describes the prospects and outlook of aqueous zinc-ion batteries with conversion mechanism, aiming to promote the rapid development of aqueous zinc-based batteries.

Building a High-Potential Silver-Sulfur Redox Reaction Based on the Hard-Soft Acid-Base Theory

Sulfur holds immense promise for battery applications owing to its abundant availability, low cost, and high capacity. Currently, sulfur is commonly combined with alkali or alkaline earth metals in metal-sulfur batteries. However, these batteries universally face challenges in cycling stability due to the inevitable issue of polysulfide dissolution and shuttling. Additionally, the inferior stability of metal sulfide discharge compounds results in low S0/S2- redox potentials (<-0.41 V vs SHE). Herein, we leverage the principle of the hard-soft acid-base theory to introduce a novel silver-sulfur (Ag-S) battery system, which operates on the reaction between the soft acid of Ag+ and the soft base of S2-. Due to their high reaction affinity, the discharge compound of silver sulfide (Ag2S) is intrinsically insoluble and fundamentally stable. This not only resolves the polysulfide dissolution issue but also leads to a predominantly high S0/S2- redox potential (+1.0 V vs. SHE). We thus exploit the Ag-S reaction for a primary zinc battery application, which exhibits a high capacity of ∼620 mAh g-1 and a high voltage of ∼1.45 V. This work offers valuable insights into the application of classic chemistry theories in the development of innovative energy storage devices.

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.

The role of electrocatalytic materials for developing post-lithium metal||sulfur batteries

The exploration of post-Lithium (Li) metals, such as Sodium (Na), Potassium (K), Magnesium (Mg), Calcium (Ca), Aluminum (Al), and Zinc (Zn), for electrochemical energy storage has been driven by the limited availability of Li and the higher theoretical specific energies compared to the state-of-the-art Li-ion batteries. Post-Li metal||S batteries have emerged as a promising system for practical applications. Yet, the insufficient understanding of quantitative cell parameters and the mechanisms of sulfur electrocatalytic conversion hinder the advancement of these battery technologies. This perspective offers a comprehensive analysis of electrode parameters, including S mass loading, S content, electrolyte/S ratio, and negative/positive electrode capacity ratio, in establishing the specific energy (Wh kg-1) of post-Li metal||S batteries. Additionally, we critically evaluate the progress in investigating electrochemical sulfur conversion via homogeneous and heterogeneous electrocatalytic approaches in both non-aqueous Na/K/Mg/Ca/Al||S and aqueous Zn||S batteries. Lastly, we provide a critical outlook on potential research directions for designing practical post-Li metal||S batteries.

A Tellurium-Boosted High-Areal-Capacity Zinc-Sulfur Battery

Aqueous rechargeable zinc-sulfur (Zn-S) batteries are a promising, cost-effective, and high-capacity energy storage technology. Still, they are challenged by the poor reversibility of S cathodes, sluggish redox kinetics, low S utilization, and unsatisfactory areal capacity. This work develops a facile strategy to achieve an appealing high-areal-capacity (above 5 mAh cm-2) Zn-S battery by molecular-level regulation between S and high-electrical-conductivity tellurium (Te). The incorporation of Te as a dopant allows for manipulation of the Zn-S electrochemistry, resulting in accelerated redox conversion, and enhanced S utilization. Meanwhile, accompanied by the S-ZnS conversion, Te is converted to zinc telluride during the discharge process, as revealed by ex-situ characterizations. This additional redox reaction contributes to the S cathode's total excellent discharge capacity. With this unique cathode structure design, the carbon-confined TeS cathode (denoted as Te1S7/C) delivers a high reversible capacity of 1335.0 mAh g-1 at 0.1 A g-1 with a mass loading of 4.22 mg cm-2, corresponding to a remarkable areal capacity of 5.64 mAh cm-2. Notably, a hybrid electrolyte design uplifts discharge plateau, reduces overpotential, suppresses Zn dendrites growth, and extends the calendar life of Zn-Te1S7 batteries. This study provides a rational S cathode structure to realize high-capacity Zn-S batteries for practical applications.

Metal-cation-induced shifts in thiolate redox and reduced sulfur speciation

Sulfur-containing anions (e.g. thiolates, polysulfides) readily exchange in solution, making control over their solution speciation and distribution challenging. Here, we demonstrate that different redox-inactive alkali, alkaline earth, and transition metals (Li+, Na+, K+, Mg2+, Ca2+, Zn2+, and Cd2+) shift the equilibria of sulfur catenation or sulfur reduction/oxidation between thiolate, polysulfanide, and polysulfide anions in acetonitrile solution. The thermodynamic factors that govern these equilibria are examined by identification of intermediate metal thiolate and metal polysulfide species using a combination of NMR spectroscopy, electronic absorption spectroscopy, and mass spectrometry. Electrochemical measurements demonstrate that the metal cation of the electrolyte modulates both sulfur reduction and thiolate oxidation potentials. DFT calculations suggest that the changes in equilibria are driven by stronger covalent interactions between polysulfide anions and more highly charged cations.

Advanced cathodes for aqueous Zn batteries beyond Zn2+ intercalation

Aqueous zinc (Zn) batteries have attracted global attention for energy storage. Despite significant progress in advancing Zn anode materials, there has been little progress in cathodes. The predominant cathodes working with Zn2+/H+ intercalation, however, exhibit drawbacks, including a high Zn2+ diffusion energy barrier, pH fluctuation(s) and limited reproducibility. Beyond Zn2+ intercalation, alternative working principles have been reported that broaden cathode options, including conversion, hybrid, anion insertion and deposition/dissolution. In this review, we report a critical assessment of non-intercalation-type cathode materials in aqueous Zn batteries, and identify strengths and weaknesses of these cathodes in small-scale batteries, together with current strategies to boost material performance. We assess the technical gap(s) in transitioning these cathodes from laboratory-scale research to industrial-scale battery applications. We conclude that S, I2 and Br2 electrodes exhibit practically promising commercial prospects, and future research is directed to optimizing cathodes. Findings will be useful for researchers and manufacturers in advancing cathodes for aqueous Zn batteries beyond Zn2+ intercalation.

A High-Energy Tellurium Redox-Amphoteric Conversion Cathode Chemistry for Aqueous Zinc Batteries

Rechargeable aqueous zinc batteries are potential candidates for sustainable energy storage systems at a grid scale, owing to their high safety and low cost. However, the existing cathode chemistries exhibit restricted energy density, which hinders their extensive applications. Here, a tellurium redox-amphoteric conversion cathode chemistry is presented for aqueous zinc batteries, which delivers a specific capacity of 1223.9 mAh gTe -1 and a high energy density of 1028.0 Wh kgTe -1. A highly concentrated electrolyte (30 mol kg-1 ZnCl2) is revealed crucial for initiating the Te redox-amphoteric conversion as it suppresses the H2O reactivity and inhibits undesirable hydrolysis of the Te4+ product. By carrying out multiple operando/ex situ characterizations, the reversible six-electron Te2-/Te0/Te4+ conversion with TeCl4 is identified as the fully charged product and ZnTe as the fully discharged product. This finding not only enriches the conversion-type battery chemistries but also establishes a critical step in exploring redox-amphoteric materials for aqueous zinc batteries and beyond.

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.

Facilitating the Electrochemical Oxidation of ZnS through Iodide Catalysis for Aqueous Zinc-Sulfur Batteries

Aqueous zinc-sulfur (Zn-S) batteries show great potential for unlocking high energy and safety aqueous batteries. Yet, the sluggish kinetic and poor redox reversibility of the sulfur conversion reaction in aqueous solution challenge the development of Zn-S batteries. Here, we fabricate a high-performance Zn-S battery using highly water-soluble ZnI2 as an effective catalyst. In situ experimental characterizations and theoretical calculations reveal that the strong interaction between I- and the ZnS nanoparticles (discharge product) leads to the atomic rearrangement of ZnS, weakening the Zn-S bonding, and thus facilitating the electrochemical oxidation reaction of ZnS to S. The aqueous Zn-S battery exhibited a high energy density of 742 Wh kg(sulfur) -1 at the power density of 210.8 W kg(sulfur) -1 and good cycling stability over 550 cycles. Our findings provide new insights about the iodide catalytic effect for cathode conversion reaction in Zn-S batteries, which is conducive to promoting the future development of high-performance aqueous batteries.

DFT Model of Elemental Sulfur in Sulfolane Solutions

The structure and the thermodynamic and optical (UV) properties of elemental sulfur solution in sulfolane (Sl) have been studied using density functional theory methods. The cyclic molecular form of sulfur (S8 "crown") was found using PBE1PBE/6-311+G(d,p) approximation in combination with a polarizable continuum model (the integral equation formalism variant) to exist in sulfolane medium as a Sl-S8-Sl solvate. It has been theoretically established that sulfur can form stable (S8)n clusters in concentrated solutions. An increase in the extent of association (n) of the sulfur cluster leads to a decrease in the extinction coefficient [TD-DFT(TPSSTPSS/6-311+G(d,p))] of the most intense absorption maximum lying at about 50,000 cm-1 while maintaining the shape of the remaining part of the spectrum. The observed pattern qualitatively expresses the spectral regularities of solutions with different concentrations of sulfur in sulfolane. It has been proposed that a model of the absorption spectrum of elemental sulfur suggests a minor contribution of the S12 molecular form (G298°((S12)2) - G298°((S8)3) ≈ -15.5 kJ mol-1). The findings of the study will provide deeper insights into the transformation of molecular forms of sulfur and more precisely analyze processes involving sulfur as an acting species using electronic spectroscopy.

A triple-synergistic small-molecule sulfur cathode promises energetic Cu-S electrochemistry

Metal-sulfur batteries have received great attention for electrochemical energy storage due to high theoretical capacity and low cost, but their further development is impeded by low sulfur utilization, poor electrochemical kinetics, and serious shuttle effect of the sulfur cathode. To avoid these problems, herein, a triple-synergistic small-molecule sulfur cathode is designed by employing N, S co-doped hierarchical porous bamboo charcoal as a sulfur host in an aqueous Cu-S battery. Expect the enhanced conductivity and chemisorption induced by N, S synergistic co-doping, the intrinsic synergy of macro-/meso-/microporous triple structure also ensures space-confined small-molecule sulfur as high utilization reactant and effectively alleviates the volume expansion during conversion reaction. Under a further joint synergy between hierarchical structure and heteroatom doping, the resulting sulfur cathode endows the Cu-S battery with outstanding electrochemical performance. Cycled at 5 A g-1, it can deliver a high reversible capacity of 2,509.8 mAh g-1 with a good capacity retention of 97.9% after 800 cycles. In addition, a flexible hybrid pouch cell built by a small-molecule sulfur cathode, Zn anode, and gel electrolytes can firmly deliver high average operating voltage of about 1.3 V with a reversible capacity of over 2,500 mAh g-1 under various destructive conditions, suggesting that the triple-synergistic small-molecule sulfur cathode promises energetic metal-sulfur batteries.

Accumulative Delocalized Mo 4d Electrons to Bound the Volume Expansion and Accelerate Kinetics in Mo6S8 Cathode for High-Performance Aqueous Cu2+ Storage

Electronic structure defines the conductivity and ion absorption characteristics of a functional electrode, significantly affecting the charge transfer capability in batteries, while it is rarely thought to be involved in mesoscopic volume and diffusion kinetics of the host lattice for promoting ion storage. Here, we first correlate the evolution in electronic structure of the Mo6S8 cathode with the ability to bound volume expansion and accelerate diffusion kinetics for high-performance aqueous Cu2+ storage. Operando synchrotron energy-dispersive X-ray absorption spectroscopy reveals that accumulative delocalized Mo 4d electrons enhance the Mo-Mo interaction with distinctly contracting and uniformizing Mo6 clusters during the reduction of Mo6S8, which potently restrain lattice expansion and release space to promote Cu2+ diffusion kinetics. Operando synchrotron X-ray diffraction and comprehensive characterizations further validate the structural and electrochemical properties induced by the Cu2+ intercalation electronic structure, endowing the Mo6S8 cathode a high specific capacity with small volume expansion, fast ions diffusion, and long-term cycling stability.

Conversion-Type Cathode Materials for Aqueous Zn Metal Batteries in Nonalkaline Aqueous Electrolytes: Progress, Challenges, and Solutions

Aqueous Zn metal batteries are attractive as safe and low-cost energy storage systems. At present, due to the narrow window of the aqueous electrolyte and the strong reliance of the Zn2+ ion intercalated reaction on the host structure, the current intercalated cathode materials exhibit restricted energy densities. In contrast, cathode materials with conversion reactions can promise higher energy densities. Especially, the recently reported conversion-type cathode materials that function in nonalkaline electrolytes have garnered increasing attention. This is because the use of nonalkaline electrolytes can prevent the occurrence of side reactions encountered in alkaline electrolytes and thereby enhance cycling stability. However, there is a lack of comprehensive review on the reaction mechanisms, progress, challenges, and solutions to these cathode materials. In this review, four kinds of conversion-type cathode materials including MnO2 , halogen materials (Br2 and I2 ), chalcogenide materials (O2 , S, Se, and Te), and Cu-based compounds (CuI, Cu2 O, Cu2 S, CuO, CuS, and CuSe) are reviewed. First, the reaction mechanisms and battery structures of these materials are introduced. Second, the fundamental problems and their corresponding solutions are discussed in detail in each material. Finally, future directions and efforts for the development of conversion-type cathode materials for aqueous Zn batteries are proposed.

Hybrid Electrolyte Design for High-Performance Zinc-Sulfur Battery

Rechargeable aqueous Zn/S batteries exhibit high capacity and energy density. However, the long-term battery performance is bottlenecked by the sulfur side reactions and serious Zn anode dendritic growth in the aqueous electrolyte medium. This work addresses the problem of sulfur side reactions and zinc dendrite growth simultaneously by developing a unique hybrid aqueous electrolyte using ethylene glycol as a co-solvent. The designed hybrid electrolyte enables the fabricated Zn/S battery to deliver an unprecedented capacity of 1435 mAh g^-1 and an excellent energy density of 730 Wh kg^-1 at 0.1 Ag^-1 . In addition, the battery exhibits capacity retention of 70% after 250 cycles even at 3 Ag^-1 . Moreover, the cathode charge-discharge mechanism studies demonstrate a multi-step conversion reaction. During discharge, the elemental sulfur is sequentially reduced by Zn to S^2- ( S 8 → S x 2 - → S 2 2 - + S 2 - ) ${{\rm{S}}_8}{\bm{ \to }}{\rm{S}}_{\rm{x}}^{2{\bm{ - }}}{\bm{ \to }}{\rm{S}}_2^{2{\bm{ - }}}{\bm{ + }}{{\rm{S}}^{2{\bm{ - }}}})$ , forming ZnS. On charging, the ZnS and short-chain polysulfides will oxidize back to elemental sulfur. This electrolyte design strategy and unique multi-step electrochemistry of the Zn/S system provide a new pathway in tackling both key issues of Zn dendritic growth and sulfur side reactions, and also in designing better Zn/S batteries in the future.

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.

Initiating Reversible Aqueous Copper-Tellurium Conversion Reaction with High Volumetric Capacity through Electrolyte Engineering

Pursuing conversion-type cathodes with high volumetric capacity that can be used in aqueous environments remains rewarding and challenging. Tellurium (Te) is a promising alternative electrode due to its intrinsic attractive electronic conductivity and high theoretical volumetric capacity yet still to be explored. Herein, the kinetically/thermodynamically co-dominat copper-tellurium (Cu-Te) alloying phase-conversion process and corresponding oxidation failure mechanism of tellurium are investigated using in situ synchrotron X-ray diffraction and comprehensive ex situ characterization techniques. By virtue of the fundamental insights into the tellurium electrode, facile and precise electrolyte engineering (solvated structure modulation or reductive antioxidant addition) is implemented to essentially tackle the dramatic capacity loss in tellurium, affording reversible aqueous Cu-Te conversion reaction with an unprecedented ultrahigh volumetric capacity of up to 3927 mAh cm^-3 , a flat long discharge plateau (capacity proportion of ≈81%), and an extraordinary level of capacity retention of 80.4% over 2000 cycles at 20 A g^-1 of which lifespan thousand-fold longer than Cu-Te conversion using CuSO₄ -H₂ O electrolyte. This work paves a significant avenue for expanding high-performance conversion-type cathodes toward energetic aqueous multivalent-ion batteries.

Multifunctional Quasi-Solid-State Zinc-Sulfur Battery

The introduction of structural energy storage devices into emerging markets, such as electric vehicles, is predominately hindered by weak energy density, safety concerns, and immaturity of the field in materials. Herein, fabrication and testing of a freeze-resistant, multifunctional quasi-solid-state zinc-sulfur battery (ZnS) are reported. To this end, an electrostatic spray coating technique was used to deposit a thin layer of sulfur on the highly porous, unidirectional activated carbon nanofibers (A-CNFs) as a load-bearing cathode. This technique could fill micro- and mesopores, and microsized channels with sulfur, achieving an extensive sulfur loading of 60 wt %. Several drawbacks of structural energy storage devices (applicability under varied climate conditions, poor electrochemical performance and mechanical properties) are addressed by initiating an antifreezing hydrogel electrolyte with a failure strain of over 200%. This electrolyte possesses ethylene glycol and an I2 additive as an antifreezing agent and redox mediator, respectively. The as-assembled ZnS battery offers a high energy density of 283 Wh/kg based on the CNF-S cathode (149 Wh/kg based on the ZnS cell) and mechanical properties beyond state-of-the-art structural energy storage devices with a tensile strength of 377 MPa, Young's modulus of 16.7 GPa, and energy-to-failure of 4.5 MJ/m3. The electrochemomechanical properties of the ZnS battery were also investigated to elucidate the effects of electrochemical energy storage on mechanical properties and vice versa. Overall, the ZnS battery outperforms state-of-the-art structural energy storage devices in terms of energy storage and load-bearing capabilities.

Interspace and Vacancy Modulation: Promoting the Zinc Storage of an Alcohol-Based Organic-Inorganic Cathode in a Water-Organic Electrolyte

Expanding interspace and introducing vacancies are desired to promote the mobility of Zn ions and unlock the inactive sites of layered cathodes. However, this two-point modulation has not yet been achieved simultaneously in vanadium phosphate. Here, a strategy is proposed for fabricating an alcohol-based organic-inorganic hybrid material, VO_{1- x} PO₄ ·0.56C₆ H₁₄ O₄ , to realize the conjoint modulation of the d-interspace and oxygen vacancies. Peculiar triglycol molecules with an inclined orientation in the interlayer also boost the improvement in the conversion rate of V⁵⁺ to V⁴⁺ and the intensity of the PO bond. Their synergism can ensure steerable adjustment for intercalation kinetics and electron transport, as well as realize high chemical reactivity and redox-center optimization, leading to at least 200% increase in capacity. Using a water-organic electrolyte, the designed Zn-ion batteries with an ultrahigh-rate profile deliver a long-term durability (fivefold greater than pristine material) and an excellent energy density of ≈142 Wh kg^-1 (including masses of cathode and anode), thereby substantially outstripping most of the recently reported state-of-the-art zinc-ion batteries. This work proves the feasibility to realize the two-point modulation by using organic intercalants for exploiting high-performance new 2D materials.

Redox Catalysis Promoted Activation of Sulfur Redox Chemistry for Energy-Dense Flexible Solid-State Zn-S Battery

In aqueous Zn-ion batteries, the intercalation chemistry often foil attempts at the realization of high energy density. Unlocking the full potential of zinc-sulfur redox chemistry requires the manipulation of the feedbacks between kinetic response and the cathode's composition. The cell degradation mechanism also should be tracked simultaneously. Herein, we design a high-energy Zn-S system where the high-capacity cathode was fabricated by in situ interfacial polymerization of Fe(CN)₆^4--doped polyaniline within the sulfur nanoparticle. Compared with sulfur, the Fe^II/III(CN)₆^4/3- redox mediators exhibit substantially faster cation (de)insertion kinetics. The higher cathodic potential (Fe^II(CN)₆^4-/Fe^III(CN)₆^3- ∼ 0.8 V vs S/S^2- ∼ 0.4 V) spontaneously catalyzes the full reduction of sulfur during battery discharge (S₈ + Zn₂Fe^II(CN)₆ ↔ ZnS + Zn_1.5Fe^III(CN)₆, ΔG = -24.7 kJ mol^-1). The open iron redox species render a lower energy barrier to ZnS activation during the reverse charging process, and the facile Zn²⁺ intercalative transport facilitates highly reversible conversion between S and ZnS. The yolk-shell structured cathode with 70 wt % sulfur delivers a reversible capacity of 1205 mAh g^-1 with a flat operation voltage of 0.58 V, a fade rate over 200 cycles of 0.23%/cycle, and an energy density of 720 Wh kg_sulfur^-1. A range of ex situ investigations reveal the degradation nature of Zn-S cells: aggregation of inactive ZnS nanocrystals rather than the depletion of Zn anode. Impressively, the flexible solid-state Zn battery employing the composite cathode was assembled, realizing an energy density of 375 Wh kg_sulfur^-1. The proposed redox electrocatalysis effect provides reliable insights into the tunable Zn-S chemistry.

Non-Electrode Components for Rechargeable Aqueous Zinc Batteries: Electrolytes, Solid-Electrolyte-Interphase, Current Collectors, Binders, and Separators

Rechargeable aqueous zinc batteries (AZBs) are one of the promising options for large-scale electrical energy storage owing to their safety, affordability and environmental friendliness. During the past decade, there have been remarkable advancements in the AZBs technology, which are achieved through intensive efforts not only in the area of electrode materials but also in the fundamental understandings of non-electrode components such as electrolytes, solid electrolyte interphase (SEI), current collectors, binders, and separators. In particular, the breakthroughs in the non-electrode components should not be underestimated in having enabled the AZBs to attain a higher energy and power density beyond that of the conventional AZBs, proving their critical role. In this article, the recent research progress is comprehensively reviewed with respect to non-electrode components in AZBs, covering the new-type of electrolytes that have been introduced, attempts for the tailoring of SEI, and the design efforts for multi-functional current collectors, binders and separators, along with the remaining challenges associated with these non-electrode components. Finally, perspectives are discussed toward future research directions in this field. This extensive overview on the non-electrode components is expected to guide and spur further development of high-performance AZBs.

Synergistic dual conversion reactions assisting Pb-S electrochemistry for energy storage

Based on the analysis of three thermodynamic parameters of various M-S systems (solubility of metal sulfides [M_xS_y] in aqueous solution, volume change of the metal-sulfur [M-S] battery system, and the potential of S/M_xS_y cathode redox couple), an aqueous Pb-S battery operated by synergistic dual conversion reactions (cathode: S⇄PbS, anode: Pb²⁺⇄PbO₂) has been officially reported. Benefitting from the inherent insolubility of PbS and a conversion-type counter electrode, the aqueous Pb-S battery exhibited two advantages: it is shuttle effect free and has a dendrite-free nature. Moreover, the practical value of the Pb-S battery was further certified by the prototype S|Pb(NO₃)₂ǁZn(NO₃)₂|Zn hybrid cell, which afforded an energy density of 930.9 Wh kg⁻¹_sulfur.

As one of the most promising cathode materials for next-generation batteries, sulfur has been widely used in organic metal-sulfur batteries, especially in Li-S batteries. However, to date, Pb-S chemistry has never been officially reported. In this paper, a reliable aqueous Pb-S battery based on a dual conversion reaction was constructed. To clarify the feasibility, three important thermodynamic parameters of the Pb-S system were analyzed, including the solubility of PbS in aqueous solution, the volume change of the Pb-S battery system, and the potential of the S/PbS cathode redox couple. Here, it is demonstrated that the aqueous Pb-S battery possesses a great advantage in theory, and the inherent insolubility of PbS makes an aqueous Pb-S system without a shuttle effect. Moreover, the conversion-type counter electrode of a Pb-S system with a stable nucleation rate endows it with a dendrite-free nature, which is quite different from the traditional metal-sulfur battery with a stripping/plating–type counter electrode. Benefitting from these remarkable natures, the aqueous Pb-S battery exhibits a high discharge capacity of 1,343.9 mAh g⁻¹_sulfur with a capacity retention of 71.4% after 400 cycles. In addition, the feasibility of this Pb-S system is further demonstrated in a hybrid cell consisting of an S cathode and Zn anode, which affords an energy density of 930.9 Wh kg⁻¹_sulfur.

The key role of concentrated Zn(OTF)2 electrolyte in performance of aqueous Zn-S batteries

In this communication, the electrolyte chemistry in aqueous Zn-S batteries was illustrated systematically. Compared to Zn(AC)2 and ZnSO4, Zn(OTF)2 electrolyte can achieve better electrochemical performance due to the impact of...

Ultra-High-Capacity and Dendrite-Free Zinc-Sulfur Conversion Batteries Based on a Low-Cost Deep Eutectic Solvent

Traditional cathodes for aqueous Zn-ion batteries are afflicted by a limited specific capacity and fearful Zn dendrites. Herein, these troubles are disposed of with a conversion-type Zn-S battery and low-cost deep eutectic solvent (DES). By utilizing the optimized electrolyte, the symmetrical Zn battery can stably cycle over 3920 h, which also confers on the Zn-S battery an ultrahigh specific capacity of ∼846 mA h g_S^-1 and energy density of 259 W h kg^-1 at 0.5 A g^-1. Importantly, the conversion chemistry of S and ZnS is responsible for the superior anti-self-discharge behavior (capacity retention: 94.58 and 68.58% after standing for 72 and 288 h versus Zn//VO₂ battery: 76.82 and 47.80% after resting for 24 and 72 h versus Zn//MnO₂ battery: 95.96 and 91.57% after resting for 24 and 72 h, respectively). This work is the first authentication of Zn-S batteries based on a newly developed low-cost DES-based electrolyte, which meanwhile settles the deep-rooted low specific capacity and infamous Zn dendrite issues in conventional (de)intercalation Zn-ion batteries.

Vacancy Modulating Co3 Sn2 S2 Topological Semimetal for Aqueous Zinc-Ion Batteries

Weyl semimetals (WSMs) with high electrical conductivity and suitable carrier density near the Fermi level are enticing candidates for aqueous Zn-ion batteries (AZIBs), meriting from topological surface states (TSSs). We propose a WSM Co₃ Sn₂ S₂ cathode for AZIBs showing a discharge plateau around 1.5 V. By introducing Sn vacancies, extra redox peaks from the Sn⁴⁺ /Sn²⁺ transition appear, which leads to more Zn²⁺ transfer channels and active sites promoting charge-storage kinetics and Zn²⁺ storage capability. Co₃ Sn_1.8 S₂ achieves a specific energy of 305 Wh kg^-1 (0.2 Ag^-1 ) and a specific power of 4900 Wkg^-1 (5 Ag^-1 ). Co₃ Sn_1.8 S₂ and Zn_x Co₃ Sn_1.8 S₂ benefit from better conductivity at lower temperatures; the quasi-solid Co₃ Sn_1.8 S₂ //Zn battery delivers 126 mAh g^-1 (0.6 Ag^-1 ) at -30 °C and a cycling stability over 3000 cycles (2 Ag^-1 ) with 85 % capacity retention at -10 °C.

Sulfur-Based Aqueous Batteries: Electrochemistry and Strategies

While research interest in aqueous batteries has surged due to their intrinsic low cost and high safety, the practical application is plagued by the restrictive capacity (less than 600 mAh g^-1) of electrode materials. Sulfur-based aqueous batteries (SABs) feature high theoretical capacity (1672 mAh g^-1), compatible potential, and affordable cost, arousing ever-increasing attention and intense efforts. Nonetheless, the underlying electrochemistry of SABs remains unclear, including complicated thermodynamic evolution and insufficient kinetics metrics. Consequently, multifarious irreversible reactions in various application systems imply the systematic complexity of SABs. Herein, rather than simply compiling recent progress, this Perspective aims to construct a theory-to-application methodology. Theoretically, attention has been paid to a critical appraisal of the aqueous-S-related electrochemistry, including fundamental properties evaluation, kinetics metrics with transient and steady-state analyses, and thermodynamic equilibrium and evolution. To put it into practice, current challenges and promising strategies are synergistically proposed. Practically, the above efforts are employed to evaluate and develop the device-scale applications, scilicet flow-SABs, oxide-SABs, and metal-SABs. Last, chemical and engineering insights are rendered collectively for the future development of high-energy SABs.

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

Sulfur is an important electrode material in metal-sulfur batteries. It is usually coupled with metal anodes and undergoes electrochemical reduction to form metal sulfides. Herein, we demonstrate, for the first time, the reversible sulfur oxidation process in AlCl₃/carbamide ionic liquid, where sulfur is electrochemically oxidized by AlCl₄^- to form AlSCl₇. The sulfur oxidation is: 1) highly reversible with an efficiency of ~94%; and 2) workable within a wide range of high potentials. As a result, the Al-S battery based on sulfur oxidation can be cycled steadily around ~1.8 V, which is the highest operation voltage in Al-S batteries. The study of sulfur oxidation process benefits the understanding of sulfur chemistry and provides a valuable inspiration for the design of other high-voltage metal-sulfur batteries, not limited to Al-S configurations.

A Zn-S aqueous primary battery with high energy and flat discharge plateau

We demonstrate a disposable aqueous primary battery chemistry that comprises environmentally benign materials of the sulfur cathode and Zn anode in a 1 M ZnCl₂ aqueous electrolyte. The Zn-S battery shows a high energy density of 1083.3 Wh kg^-1 for sulphur with a flat discharge voltage plateau around 0.7 V. When operating at a high mass loading of 8.3 mg cm^-2 for sulfur in the cathode, the battery exhibits a very high areal capacity of 11.4 mA h cm^-2 and areal energy of 7.7 mW h cm^-2.

Chitosan-Assisted Fabrication of a Network C@V2O5 Cathode for High-Performance Zn-Ion Batteries

Vanadium oxide-based aqueous zinc-ion batteries exhibit promising potential due to their low cost and safety profiles. However, fabricating cathodes with outstanding electrochemical performance for Zn-ion batteries is still a challenge. Herein, network C@V₂O₅ materials were prepared using a mild chitosan-assisted hydrothermal process. Coin-type cells, using network C@V₂O₅ as a cathode, zinc film as an anode, and Zn(CF₃SO₃)₂ as an electrolyte, were also assembled, and the as-synthesized cathode delivered a high specific capacity of 361 mA h g^-1 at 0.5 A g^-1 and excellent cyclic stability. Specifically, after 2000 cycles, the capacity still remained about 71% of the initial value at 0.5 A g^-1. Moreover, ex situ X-ray diffraction (XRD) characterizations confirmed that Zn-ion storage in the cathode was achieved through the reversible intercalation/extraction of Zn²⁺ during the charge/discharge process. Therefore, the network C@V₂O₅ cathode demonstrated potential applications for zinc-ion batteries.

Self-Healing Solid Polymer Electrolyte with High Ion Conductivity and Super Stretchability for All-Solid Zinc-Ion Batteries

The zinc-ion battery (ZIB) is a novel energy storage device, an attractive alternative to the lithium-ion battery. The frequently used aqueous electrolyte suffers from many problems such as zinc dendrites and leakage, which prompts hydrogel electrolytes and solid electrolytes as good replacements. However, hydrogel electrolytes are usually unstable, owing to water volatilization. Herein, a novel solid polymer electrolyte (SPE) utilizing coordination of zinc ions is designed and then introduced into an all-solid ZIB. Benefiting from the unique coordination structure between the polymer and zinc ions, the SPE shows outstanding flexibility, high ion conductivity, and self-healing properties. In addition, the imine bonds in the polymer allow the electrolyte to degrade in acid environments, endowing its recyclability. More importantly, solid-state ZIBs based on the polymer electrolytes exhibit an impressive cycling stability (125% capacity retention after 300 cycles) and a high coulombic efficiency (94% after 300 cycles). The results demonstrate the promising potentials of the developed SPEs that can be used in all-solid ZIBs.

A COF-Like N-Rich Conjugated Microporous Polytriphenylamine Cathode with Pseudocapacitive Anion Storage Behavior for High-Energy Aqueous Zinc Dual-Ion Batteries

Conducting polymers with good electron conductivity and rich redox functional groups are promising cathode candidates for constructing high-energy aqueous zinc batteries. However, the glaring flaw of active-site underutilization impairs their electrochemical performance. Herein, we report a poriferous polytriphenylamine conjugated microporous polymer (CMP) cathode capable of accommodating Cl^- anions in a pseudocapative-dominated manner for energy storage. Its specific 3D, covalent-organic-framework-like conjugated network ensures high accessibility efficacy of N active sites (up to 83.2% at 0.5 A g^-1 ) and distinct physicochemical stability (87.6% capacity retention after 1000 cycles) during repeated charging/discharging courses. Such a robust CMP electrode also leads to a zinc dual-ion battery device with a high energy density of 236 W h kg^-1 and a maximum power density of 6.8 kW kg^-1 , substantially surpassing most recently reported organic-based zinc batteries. This study paves the way for the rational design of advanced CMP-based organic cathodes for high-energy devices.

Wearable and Fully Biocompatible All-in-One Structured ″Paper-Like″ Zinc Ion Battery

A power supply with the characteristics of portability and safety will be one of the dominating mainstreams for future wearable electronics and implantable biomedical devices. The conventional energy storage devices with typical sandwich structures have complicated components and low mechanical properties, suffering from the apparent performance degradation during deformation and hindering the possibility of implanting biomedical units. Herein, a novel all-in-one structure ″paper-like″ zinc ion battery (ZIB) was designed and assembled from an electrospun polyacrylonitrile (PAN) nanomembrane (as the separator) with in situ deposited anode (zinc nanosheets) and cathode (MnO₂ nanosheets), which ensures the monolith under different bending states by avoiding the relative sliding and detaching between the integrated layers. Benefiting from the well-designed all-in-one construction and electrodes, the resultant all-in-one ZIB (AZIB) features an ultrathin thickness (about 97 μm), superior specific capacity of 353.8 mAh g^-1 (at 0.1 mA cm^-2), and outstanding cycling stability (98.7% capacity retention after 500 cycles at 1 A cm^-2). And the achieved volumetric energy density is as high as 17.5 mWh cm^-3 at a power density of 116.4 mW cm^-3. Impressively, the concept of wearable electronic applications of the obtained AZIB was fully demonstrated with excellent flexibility and remarkable temperature resistance under various severe conditions. Our AZIB may provide a versatile strategy for applying and developing flexible wearable electronics and implantable biomedical devices.

Scalable and Controllable Synthesis of Interface-Engineered Nanoporous Host for Dendrite-Free and High Rate Zinc Metal Batteries

Rechargeable zinc (Zn)-ion batteries are regarded as highly prospective candidates for next-generation renewable and safe energy storage systems. However, the uncontrolled dendrite growth of the Zn anode impedes their practical application. Here, a scalable and controllable approach is developed for converting commercial titanium (Ti) foil to 3D porous Ti, which retains good resistance to corrosion, high electrical conductivity, and excellent mechanical properties. Benefiting from a spontaneous ultrathin zincophilic titanium dioxide (TiO₂) interfacial layer and continuous 3D structure, the 3D porous Ti can act as an effective host to achieve a 3D Ti/Zn metal anode. By ensuring homogeneous nucleation, uniform current distribution, and volume change accommodation, the dendritic growth of 3D Ti/Zn metal anode is effectively inhibited with stable Zn plating/stripping up to 2000 h with low polarization. When conjugated with a 3D sulfur-doped Ti₃C₂T_x MXene@MnO₂ nanotube cathode, a high rate and stable Zn cell is achieved with 95.46% capacity retention after 500 cycles at a high rate of 5 A g^-1. This work may also be interesting for researches in porous metals and other battery systems.

Advances and Perspectives of Cathode Storage Chemistry in Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) have captured a surge of interest in recent years as a promising alternative for scalable energy storage applications owing to the intrinsic safety, affordability, environmental benignity, and impressive electrochemical performance. Despite the facilitated development of this technology by many investigations, however, its smooth implementation is still plagued by inadequate energy density and undesirable life span, which calls for an efficient and controllable cathode storage chemistry. Here, this review focuses on the key bottlenecks by offering a comprehensive summary of representative cathode materials and comparatively analyzing their structural features and electrochemical properties. Then, we critically present several feasible electrode design strategies to guide future research activities from a fundamental perspective for high-energy-density and durable cathode materials mainly in terms of interlayer regulation, defect engineering, multiple redox reactions, activated two-electron reactions, and electrochemical activation and conversion. Finally, we outline the remaining challenges and future perspectives of developing high-performance AZIBs.

Intrinsically conducting polymers and their combinations with redox-active molecules for rechargeable battery electrodes: an update

Intrinsically conducting polymers and their copolymers and composites with redox-active organic molecules prepared by chemical as well as electrochemical polymerization may yield active masses without additional binder and conducting agents for secondary battery electrodes possibly utilizing the advantageous properties of both constituents are discussed. Beyond these possibilities these polymers have found many applications and functions for various further purposes in secondary batteries, as binders, as protective coatings limiting active material corrosion, unwanted dissolution of active mass ingredients or migration of electrode reaction participants. Selected highlights from this rapidly developing and very diverse field are presented. Possible developments and future directions are outlined.

Enhanced Redox Kinetics and Duration of Aqueous I2 /I- Conversion Chemistry by MXene Confinement

Weak binding and affinity between the conductive support and iodine species leads to inadequate electron transfer and the shuttle effect. Herein, redox kinetics and duration are significantly boosted by introducing a Nb₂ CT_X host that is classified as a layered 2D Nb-based MXene. With a facile electrodeposition strategy, initial I^- ions are electrically driven to insert in the nanosized interlayers and are electro-oxidized in situ. Linear I₂ is firmly confined inside and benefits from the rapid charge supply from the MXene. Consequently, an aqueous Zn battery based on a Zn metal anode and ZnSO₄ electrolyte delivers an ultraflat plateau at 1.3 V, which contributes to 84.5% of the capacity and 89.1% of the energy density. Record rate capability (143 mAh g^-1 at 18 A g^-1 ) and lifespan (23 000) cycles are achieved, which are far superior to those of all reported aqueous MXenes and I₂ -metal batteries. Moreover, the low voltage decay rate of 5.6 mV h^-1 indicates its superior anti-self-discharge properties. Physicochemical analyses and density functional theory calculations elucidate that the localized electron transfer and trapping effect of the Nb₂ CT_X MXene host are responsible for enhanced kinetics and suppressed shuttle behavior. This work can be extended to the fabrication of other I₂ -metal batteries with long-life-time expectations.