A High-Performance Quasi-Solid-State Aqueous Zinc-Dual Halogen Battery

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.

Activating and Stabilizing a Reversible four Electron Redox Reaction of I-/I+ for Aqueous Zn-Iodine Battery

Low capacity and poor cycle stability greatly inhibit the development of zinc-iodine batteries. Herein, a high-performance Zn-iodine battery has been reached by designing and optimizing both electrode and electrolyte. The Br- is introduced as the activator to trigger I+, and coupled with I+ forming interhalogen to stabilize I+ to achieve a four-electron reaction, which greatly promotes the capacity. And the Ni-Fe-I LDH nanoflowers serve as the confinement host to enable the reactions of I-/I+ occurring in the layer due to the spacious and stable interlayer spacing of Ni-Fe-I LDH, which effectively suppresses the iodine-species shuttle ensuring high cycling stability. As a result, the electrochemical performance is greatly enhanced, especially in specific capacity (as high as 350 mAh g-1 at 1 A g-1 far higher than two-electron transfer Zn-iodine batteries) and cycling performance (94.6 % capacity retention after 10000 cycles). This strategy provides a new way to realize high capacity and long-term stability of Zn-iodine batteries.

Halide Exchange in Perovskites Enables Bromine/Iodine Hybrid Cathodes for Highly Durable Zinc Ion Batteries

With the increasing need for reliable storage systems, the conversion-type chemistry typified by bromine cathodes attracts considerable attention due to sizeable theoretical capacity, cost efficiency, and high redox potential. However, the severe loss of active species during operation remains a problem, leading researchers to resort to concentrated halide-containing electrolytes. Here, profiting from the intrinsic halide exchange in perovskite lattices, a novel low-dimensional halide hybrid perovskite cathode, TmdpPb2[IBr]6, which serves not only as a halogen reservoir for reversible three-electron conversions but also as an effective halogen absorbent by surface Pb dangling bonds, C─H…Br hydrogen bonds, and Pb─I…Br halogen bonds, is proposed. As such, the Zn||TmdpPb2[IBr]6 battery delivers three remarkable discharge voltage plateaus at 1.21 V (I0/I-), 1.47 V (I+/I0), and 1.74 V (Br0/Br-) in a typical halide-free electrolyte; meanwhile, realizing a high capacity of over 336 mAh g-1 at 0.4 A g-1 and high capacity retentions of 88% and 92% after 1000 cycles at 1.2 A g-1 and 4000 cycles at 3.2 A g-1, respectively, accompanied by a high coulombic efficiency of ≈99%. The work highlights the promising conversion-type cathodes based on metal-halide perovskite materials.

Enhanced Energy Storage Performance through Controlled Composition and Synthesis of 3D Mixed Metal-Oxide Microspheres

Binary transition metal oxide complexes (BTMOCs) in three-dimensional (3D) layered structures show great promise as electrodes for supercapacitors (SCs) due to their diverse oxidation states, which contribute to high specific capacitance. However, the synthesis of BTMOCs with 3D structures remains challenging yet crucial for their application. In this study, we present a novel approach utilizing a single-step hydrothermal technique to fabricate flower-shaped microspheres composed of a NiCo-based complex. Each microsphere consists of nanosheets with a mesoporous structure, enhancing the specific surface area to 23.66 m2 g-1 and facilitating efficient redox reactions. When employed as the working electrode for supercapacitors, the composite exhibits remarkable specific capacitance, achieving 888.8 F g-1 at 1 A g-1. Furthermore, it demonstrates notable electrochemical stability, retaining 52.08% capacitance after 10,000 cycles, and offers a high-power density of 225 W·kg-1, along with an energy density of 25 Wh·kg-1, showcasing its potential for energy storage applications. Additionally, an aqueous asymmetric supercapacitor (ASC) was assembled using NiCo microspheres-based complex and activated carbon (AC). Remarkably, the NiCo microspheres complex/AC configuration delivers a high specific capacitance of 250 F g-1 at 1 A g-1, with a high energy density of 88 Wh kg-1, for a power density of 800 W kg-1. The ASC also exhibits excellent long-term cyclability with 69% retention over 10,000 charge-discharge cycles. Furthermore, a series of two ASC devices demonstrated the capability to power commercial blue LEDs for a duration of at least 40 s. The simplicity of the synthesis process and the exceptional performance exhibited by the developed electrode materials hold considerable promise for applications in energy storage.

Halogen-powered static conversion chemistry

Halogen-powered static conversion batteries (HSCBs) thrive in energy storage applications. They fall into the category of secondary non-flow batteries and operate by reversibly changing the chemical valence of halogens in the electrodes or/and electrolytes to transfer electrons, distinguishing them from the classic rocking-chair batteries. The active halide chemicals developed for these purposes include organic halides, halide salts, halogenated inorganics, organic-inorganic halides and the most widely studied elemental halogens. Aside from this, various redox mechanisms have been discovered based on multi-electron transfer and effective reaction pathways, contributing to improved electrochemical performances and stabilities of HSCBs. In this Review, we discuss the status of HSCBs and their electrochemical mechanism-performance correlations. We first provide a detailed exposition of the fundamental redox mechanisms, thermodynamics, conversion and catalysis chemistry, and mass or electron transfer modes involved in HSCBs. We conclude with a perspective on the challenges faced by the community and opportunities towards practical applications of high-energy halogen cathodes in energy-storage devices.

Asymmetric Anion Zinc Salt Derived Solid Electrolyte Interphase Enabled Long-Lifespan Aqueous Zinc Bromine Batteries

Organic additives with high-reduction potentials are generally applied in aqueous electrolytes to stabilize the Zn anode, while compromise safety and environmental compatibility. Highly concentrated water-in-salt electrolytes have been proposed to realize the high reversibility of Zn plating/stripping; however, their high cost and viscosity hinder their practical applications. Therefore, exploring low-concentration Zn salts, that can be used directly to stabilize Zn anodes, is of primary importance. Herein, we developed an asymmetric anion group, bi(difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide (DFTFSI- )-based novel zinc salt, Zn(DFTFSI)2 , to obtain a high ionic conductivity and a highly stable dendrite-free Zn anode. Experimental tests and theoretical calculations verified that DFTFSI- in the Zn2+ solvation sheath and inner Helmholtz plane would be preferentially reduced to construct layer-structured SEI films, inhibiting hydrogen evolution and side reactions. Consequently, the Zn| | ${||}$ Zn symmetric cell with 1M Zn(DFTFSI)2 aqueous electrolyte delivers an ultralong cycle life for >2500 h outperforming many other conventional Zn salt electrolytes. The Zn| | ${||}$ Br2 battery also exhibits a long lifespan over 1200 cycles at ~99.8 % Coulombic efficiency with a high capacity retention of 92.5 %. Furthermore, this outstanding performance translates well to a high-areal-capacity Zn| | ${||}$ Br2 battery (~5.6 mAh ⋅ cm-2 ), cycling over 320 cycles with 95.3 % initial capacity retained.

Stabilized four-electron aqueous zinc-iodine batteries by quaternary ammonium complexation

Four-electron aqueous zinc-iodine batteries (4eZIBs) leveraging the I-/I0/I+ redox couple have garnered attention for their potential high voltage, capacity, and energy density. However, the electrophilic I+ species is highly susceptible to hydrolysis due to the nucleophilic attack by water. Previous endeavors to develop 4eZIBs primarily relied on highly concentrated aqueous electrolytes to mitigate the hydrolysis issue, nonetheless, it introduced challenges associated with dissolution, high electrolyte viscosity, and sluggish electrode kinetics. In this work, we present a novel complexation strategy that capitalizes on quaternary ammonium salts to form solidified compounds with I+ species, rendering them impervious to solubilization and hydrolysis in aqueous environments. The robust interaction in this complexation chemistry facilitates a highly reversible I-/I0/I+ redox process, significantly improving reaction kinetics within a conventional ZnSO4 aqueous electrolyte. The proposed 4eZIB exhibits a superior rate capability and an extended lifespan of up to 2000 cycles. This complexation chemistry offers a promising pathway for the development of advanced 4eZIBs.

Advancements in aqueous zinc-iodine batteries: a review

Aqueous zinc-iodine batteries stand out as highly promising energy storage systems owing to the abundance of resources and non-combustible nature of water coupled with their high theoretical capacity. Nevertheless, the development of aqueous zinc-iodine batteries has been impeded by persistent challenges associated with iodine cathodes and Zn anodes. Key obstacles include the shuttle effect of polyiodine and the sluggish kinetics of cathodes, dendrite formation, the hydrogen evolution reaction (HER), and the corrosion and passivation of anodes. Numerous strategies aimed at addressing these issues have been developed, including compositing with carbon materials, using additives, and surface modification. This review provides a recent update on various strategies and perspectives for the development of aqueous zinc-iodine batteries, with a particular emphasis on the regulation of I2 cathodes and Zn anodes, electrolyte formulation, and separator modification. Expanding upon current achievements, future initiatives for the development of aqueous zinc-iodine batteries are proposed, with the aim of advancing their commercial viability.

Rechargeable Aqueous Zinc-Halogen Batteries: Fundamental Mechanisms, Research Issues, and Future Perspectives

Aqueous zinc-halogen batteries (AZHBs) have emerged as promising candidates for energy storage applications due to their high security features and low cost. However, several challenges including natural subliming, sluggish reaction kinetics, and shuttle effect of halogens, as well as dendrite growth of the zinc (Zn) anode, have hindered their large-scale commercialization. In this review, first the fundamental mechanisms and scientific issues associated with AZHBs are summarized. Then the research issues and progresses related to the cathode, separator, anode, and electrolyte are discussed. Additionally, emerging research opportunities in this field is explored. Finally, ideas and prospects for the future development of AZHBs are presented. The objective of this review is to stimulate further exploration, foster the advancement of AZHBs, and contribute to the diversified development of electrochemical energy storage.

Conversion-intercalation competing behaviour of halogen storage on graphite electrode from fluid ZnCl2/ZnBr2 hydrates

Zinc-based aqueous dual-ion batteries (ADIBs) with halogen-graphite intercalation compound positive electrodes are among the most competitive candidates for next-generation electrochemical energy storage systems. However, most of the electrolytes employed have been gel-like electrolytes; hence, a fundamental understanding of the halogen storage process using fluid hydrates will be essential for constructing efficient Zn-based ADIBs. Herein, the halogen storage mechanism on a graphite electrode from fluid ZnCl2/ZnBr2 hydrates is studied by experimental and computational methods. The results indicate that the halogen storage mechanism is a competition between conversion and intercalation. Moreover, the macroscopic electrode reaction is determined by both the ion-pair solvation state at the graphite-electrolyte interface and the subsequent reactant supply is influenced by the electrode reaction rate.

Synergistic Ion Sieve and Solvation Regulation by Recyclable Clay-Based Electrolyte Membrane for Stable Zn-Iodine Battery

The high dissolution of polyiodides and unstable interface at the anode/electrolyte severely restrict the practical applications of rechargeable aqueous Zn-iodine batteries. Herein, we develop a zinc ion-based montmorillonite (ZMT) electrolyte membrane for synergizing ion sieve and solvation regulation to achieve highly stable Zn-iodine batteries. The rich M-O band and special cation-selective transport channel in ZMT locally tailor the solvation sheath around Zn2+ and therefore achieve high transference number (t+ = 0.72), benefiting for uniform and reversible deposition/stripping of Zn. Meanwhile, the mechanisms for three-step polyiodide generation and shuttle-induced Zn corrosion are highlighted by in situ characterization techniques. It is confirmed that the strong chemical adsorption between O atoms in ZMT and polyiodides species is the key to effectively inhibit the shuffle effect and side reactions. Consequently, the ZMT-based Zn-iodine battery delivers a high capacity of 0.45 mAh cm-2 at 1 mA cm-2 with a much improved Coulombic efficiency of 99.5% and outstanding capacity retention of 95% after 13 500 cycles at 10 mA cm-2. Moreover, owing to its high durability and chemical inertness and structural stability, ZMT-based electrolyte membranes can be recycled and applied in double-sided pouch cells, delivering a high areal capacity of 2.4 mAh cm-2 at 1 mA cm-2.

Deploying Cationic Cellulose Nanofiber Confinement to Enable High Iodine Loadings Towards High Energy and High-Temperature Zn-I2 Battery

High iodine loading and high-temperature adaptability of the iodine cathode are prerequisites to achieving high energy density at full battery level and promoting the practical application for the zinc-iodine (Zn-I2 ) battery. However, it would aggravate the polyiodide shuttle effect when employing high iodine loading and working temperature. Here, a sustainable cationic cellulose nanofiber (cCNF) was employed to confine the active iodine species through strong physiochemical adsorption to enlarge the iodine loading and stabilize it even at high temperatures. The cCNF could accommodate dual-functionality by enlarging the iodine loading and suppressing the polyiodide shuttle effect, owing to the unique framework structure with abundant surface positive charges. As a result, the iodine cathode based on the cCNF could deliver high iodine mass loading of 14.1 mg cm-2 with a specific capacity of 182.7 mAh g-1 , high areal capacity of 2.6 mAh cm-2 , and stable cycling over 3000 cycles at 2 A g-1 , thus enabling a high energy density of 34.8 Wh kg-1 and the maximum power density of 521.2 W kg-1 at a full Zn-I2 battery level. In addition, even at a high temperature of 60 °C, the Zn-I2 battery could still deliver a stable cycling.

Chaotropic Electrolyte Enabling Wide-Temperature Metal-Free Battery

Metal-free aqueous batteries are promising candidates for grid-scale energy storage owing to their inherent safety, low cost, and cost effectiveness. The battery chemistry based on fast NH4+ diffusion kinetics avoids unfavorable generation of inactive metallic byproducts. However, their practical applications have been impeded by electrolyte instability and the intrinsic drawbacks of current electrodes. Herein, we propose an aqueous ammonium-iodine battery by using a chaotropic electrolyte, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) anode, and iodine composite (I2@CC) cathode. Experimental investigations and theoretical calculations reveal that the chaotropic electrolyte not only enhances electrolyte stability through modulating the H-bond structure but also facilitates the formation of a hydrophobic cationic sieve (HCS) on the anode, which ensures the electrolyte/electrode stability and high reversibility of the anode. Additionally, the Cl--containing electrolyte can support the consecutive I+/I0 reaction on the cathode by forming [IClx]1-x interhalogen. The as-assembled aqueous ammonium-iodine batteries (AIBs) based on NH4+ accommodation at the anode and I+/I0 redox reaction at the cathode can deliver superior electrochemical performance at room temperature and low temperature (-20 °C). This study provides a strategic insight into developing metal-free aqueous batteries with electrolyte modulation.

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.

Quasi-Solid Electrolyte Interphase Boosting Charge and Mass Transfer for Dendrite-Free Zinc Battery

The practical applications of zinc metal batteries are plagued by the dendritic propagation of its metal anodes due to the limited transfer rate of charge and mass at the electrode/electrolyte interphase. To enhance the reversibility of Zn metal, a quasi-solid interphase composed by defective metal-organic framework (MOF) nanoparticles (D-UiO-66) and two kinds of zinc salts electrolytes is fabricated on the Zn surface served as a zinc ions reservoir. Particularly, anions in the aqueous electrolytes could be spontaneously anchored onto the Lewis acidic sites in defective MOF channels. With the synergistic effect between the MOF channels and the anchored anions, Zn2+ transport is prompted significantly. Simultaneously, such quasi-solid interphase boost charge and mass transfer of Zn2+, leading to a high zinc transference number, good ionic conductivity, and high Zn2+ concentration near the anode, which mitigates Zn dendrite growth obviously. Encouragingly, unprecedented average coulombic efficiency of 99.8% is achieved in the Zn||Cu cell with the proposed quasi-solid interphase. The cycling performance of D-UiO-66@Zn||MnO2 (~ 92.9% capacity retention after 2000 cycles) and D-UiO-66@Zn||NH4V4O10 (~ 84.0% capacity retention after 800 cycles) prove the feasibility of the quasi-solid interphase.