Hierarchically Porous Metal-Organic Gel Hosting Catholyte for Limiting Iodine Diffusion and Self-Discharge Control in Sustainable Aqueous Zinc-I2 Batteries

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.

Armoring the cathode with starch gel enables Shuttle-Free Zinc-Iodine batteries

Zinc-iodine batteries (ZIBs) have been recognized as a promising energy storage device due to their high energy density, low cost and environmental friendliness. However, the development of ZIBs is hindered by the shuttle effect of polyiodides which results in capacity degradation and poor cycling performance. Inspired by the ability of starch to form inclusion compounds with iodine, we propose to use a starch gel on the cathode to suppress the shuttle of polyiodides. Herein, porous carbon is utilized as a host for iodine species and provides an excellent conductive network, while starch gel is used as another host to suppress polyiodides shuttle, resulting in improved battery performance. The test results demonstrate that the conversion between I-/I2/I3- in the cathode and the effective inclusion role of starch suppress the shuttle of polyiodides during the charging process. Meanwhile, based on the electrochemical tests and theoretical DFT calculations, it is found that starch has a stronger ability to adsorb polyiodides compared to carbon materials, which enables effective confinement of polyiodides. The ZIBs used the cathode with starch gel exhibit high coulombic efficiency (>95 % at 0.2 A/g) and low self-discharge (86.8 % after resting for 24 h). This strategy is characterized by its simplicity, low cost and high applicability, making it significant for the advancement of high-performance ZIBs.

Suppressing the Shuttle Effect of Aqueous Zinc-Iodine Batteries: Progress and Prospects

Aqueous zinc-iodine batteries are considered to be one of the most promising devices for future electrical energy storage due to their low cost, high safety, high theoretical specific capacity, and multivalent properties. However, the shuttle effect currently faced by zinc-iodine batteries causes the loss of cathode active material and corrosion of the zinc anodes, limiting the large-scale application of zinc-iodine batteries. In this paper, the electrochemical processes of iodine conversion and the zinc anode, as well as the induced mechanism of the shuttle effect, are introduced from the basic configuration of the aqueous zinc-iodine battery. Then, the inhibition strategy of the shuttle effect is summarized from four aspects: the design of cathode materials, electrolyte regulation, the modification of the separator, and anode protection. Finally, the current status of aqueous zinc-iodine batteries is analyzed and recommendations and perspectives are presented. This review is expected to deepen the understanding of aqueous zinc-iodide batteries and is expected to guide the design of high-performance aqueous zinc-iodide batteries.

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.

Aqueous Zinc Batteries with Ultra-Fast Redox Kinetics and High Iodine Utilization Enabled by Iron Single Atom Catalysts

Rechargeable aqueous zinc iodine (ZnǀǀI2) batteries have been promising energy storage technologies due to low-cost position and constitutional safety of zinc anode, iodine cathode and aqueous electrolytes. Whereas, on one hand, the low-fraction utilization of electrochemically inert host causes severe shuttle of soluble polyiodides, deficient iodine utilization and sluggish reaction kinetics. On the other hand, the usage of high mass polar electrocatalysts occupies mass and volume of electrode materials and sacrifices device-level energy density. Here, we propose a "confinement-catalysis" host composed of Fe single atom catalyst embedding inside ordered mesoporous carbon host, which can effectively confine and catalytically convert I2/I- couple and polyiodide intermediates. Consequently, the cathode enables the high capacity of 188.2 mAh g-1 at 0.3 A g-1, excellent rate capability with a capacity of 139.6 mAh g-1 delivered at high current density of 15 A g-1 and ultra-long cyclic stability over 50,000 cycles with 80.5% initial capacity retained under high iodine loading of 76.72 wt%. Furthermore, the electrocatalytic host can also accelerate the [Formula: see text] conversion. The greatly improved electrochemical performance originates from the modulation of physicochemical confinement and the decrease of energy barrier for reversible I-/I2 and I2/I+ couples, and polyiodide intermediates conversions.

Low-Concentration Redox-Electrolytes for High-Rate and Long-Life Zinc Metal Batteries

The uncontrolled zinc electrodeposition and side reactions severely limit the power density and lifespan of Zn metal batteries. Herein, the multi-level interface adjustment effect is realized with low-concentration redox-electrolytes (0.2 m KI) additives. The iodide ions adsorbed on the zinc surface significantly suppress water-induced side reactions and by-product formation and enhance the kinetics of zinc deposition. The distribution of relaxation times results reveal that iodide ions can reduce the desolvation energy of hydrated zinc ions and guide the deposition of zinc ions due to their strong nucleophilicity. As a consequence, the Zn||Zn symmetric cell achieves superior cycling stability (>3000 h at 1 mA cm^-2 , 1 mAh cm^-2 ) accompanied by a uniform deposition and a fast reaction kinetics with a low voltage hysteresis (<30 mV). Additionally, coupled with an activated carbon (AC) cathode, the assembled Zn||AC cell delivers a high-capacity retention of 81.64% after 2000 cycles at 4 A g^-1 . More importantly, the operando electrochemical UV-vis spectroscopies show that a small number of I₃ ^- can spontaneously react with the dead zinc as well as basic zinc saltsand regenerate iodide ions and zinc ions; thus, the Coulombic efficiency of each charge-discharge process is close to 100%.

Life cycle thinking and safe-and-sustainable-by-design approaches for the battery innovation landscape

Developments in battery technology are essential for the energy transition and need to follow the framework for safe-and-sustainable-by-design (SSbD) materials, chemicals, products, and processes as set by the EU. SSbD is a broad approach that ensures that chemicals/advanced materials/products/services are produced and used in a way to avoid harm to humans and the environment. Technical and policy-related literature was surveyed for battery technologies and recommendations were provided for a broad SSbD approach that remains firmly grounded in Life Cycle Thinking principles. The approach integrates functional performance and sustainability (safety, social, environmental, and economic) aspects throughout the life cycle of materials, products, and processes, and evaluates how their interactions reflect on SSbD parameters. 22 different types of batteries were analyzed in a life cycle thinking approach for criticality, toxicity/safety, environmental and social impact, circularity, functionality, and cost to ensure battery innovation has a green and sustainable purpose to avoid unintended consequences.

Hierarchically Porous Ferroelectric Layer with the Aligned Dipole Moment for a High-Performance Aqueous Zn Metal Battery

Rechargeable aqueous Zn metal batteries (AZMBs) are desirable because of the advantages of metallic Zn and aqueous media. However, AZMBs suffer from limited cyclability and low Coulombic efficiency, originating from uncontrolled dendrite growth and side reactions such as hydrogen gas evolution and corrosion. A hierarchically porous poly(vinylidene difluoride) (PVDF) protection layer with ferroelectric β-phases is formed on the Zn metal using a simple electrospinning method. This suppresses Zn metal failure modes such as side reactions and dendrite growth and supports rapid electrolyte accessibility. The synergetic effect of hierarchically porous structures and ferroelectricity not only facilitates a supporting matrix to form uniform nucleation sites for Zn deposition but also inhibits corrosion, allowing dendrite-free Zn deposition. This multifunctional PVDF film significantly improves the cyclability of Zn symmetric cells, allowing for up to 850 h of repeated plating/stripping cycles. Moreover, it exhibits an excellent cycle life of 1000 cycles under harsh conditions and high current densities of 4.0-10.0 mA cm^-2, which are 62-fold higher than those that the bare Zn electrode tolerates.

Recent Advances of Aqueous Rechargeable Zinc-Iodine Batteries: Challenges, Solutions, and Prospects

Aqueous rechargeable zinc-iodine batteries (ZIBs), including zinc-iodine redox flow batteries and static ZIBs, are promising candidates for future grid-scale electrochemical energy storage. They are safe with great theoretical capacity, high energy, and power density. Nevertheless, to make aqueous rechargeable ZIBs practically feasible, there are quite a few hurdles that need to be overcome, including self-discharge, sluggish kinetics, low energy density, and instability of Zn metal anodes. This article first reviews the electrochemistry in aqueous rechargeable ZIBs, including the flow and static battery configurations and their electrode reactions. Then the authors discuss the fundamental questions of ZIBs and highlight the key strategies and recent accomplishments in tackling the challenges. Last, they share their thoughts on the future research development in aqueous rechargeable ZIBs.

Long-Life Aqueous Zn-I2 Battery Enabled by a Low-Cost Multifunctional Zeolite Membrane Separator

Aqueous zinc iodide (Zn-I₂) batteries are promising large-scale energy-storage devices. However, the uncontrollable diffuse away/shuttle of soluble I₃^- leads to energy loss (low Coulombic efficiency, CE), and poor reversibility (self-discharge). Herein, we employ an ordered framework window within a zeolite molecular sieve to restrain I₃^- crossover and prepare zeolite molecular sieve particles into compact, large-scale, and flexible membranes at the engineering level. The as-prepared membrane can confine I₃^- within the catholyte region and restrain its irreversible escape, which is proved via space-resolution and electrochemical in situ time-resolution Raman technologies. As a result, overcharge/self-discharge and Zn corrosion are effectively controlled by zeolite separator. After replacing the typically used glass fiber separator to a zeolite membrane, the CE of Zn-I₂ battery improves from 78.9 to 98.6% at 0.2 A/g. Besides, after aging at the fully charged state for 5.0 h, self-discharge is restrained and CE is enhanced from 44.0 to 85.65%. Moreover, the Zn-I₂ cell maintains 91.0% capacity over 30,000 cycles at 4.0 A/g.

Triiodide-in-Iodine Networks Stabilized by Quaternary Ammonium Cations as Accelerants for Electrode Kinetics of Iodide Oxidation in Aqueous Media

The Zn-polyiodide redox flow battery is considered to be a promising aqueous energy storage system. However, in its charging process, the electrode kinetics of I^- oxidation often suffer from an intrinsically generated iodine film (I₂-F) on the cathode of the battery. Therefore, it is critical to both understand and enhance the observed slow electrode kinetics of I^- oxidation by an electrochemically generated I₂-F. In this article, we introduced an electrogenerated N-methyl-N-ethyl pyrrolidinium iodide (MEPI)-iodine (I₂) solution, designated as MEPIS, and demonstrated that the electrode kinetics of I^- oxidation were dramatically enhanced compared to an I₂-F under conventional electrolyte conditions, such as NaI. We showed that this result mainly contributed to the fast electro-oxidation of triiodide (I₃^-), which exists in the shape of a I₃^--in-I₂ network, [I₃^-·(I₂)_n]. Raman spectroscopic and electrochemical analyses showed that the composition of electrogenerated MEPIS changed from I₃^- to [I₃^-·(I₂)_n] via I₅^- as the anodic overpotential increased. We also confirmed that I^- was electrochemically oxidized on a MEPIS-modified Pt electrode with fast electrode kinetics, which is clearly contrary to the nature of an I₂-F derived from a NaI solution as a kinetic barrier of I^- oxidation. Through stochastic MEPIS-particle impact electrochemistry and electrochemical impedance spectroscopy, we revealed that the enhanced electrode kinetics of I^- oxidation in MEPIS can be attributed to the facilitated charge transfer of I₃^- oxidation in [I₃^-·(I₂)_n]. In addition, we found that the degree of freedom of I₃^- in a quaternary ammonium-based I₂-F can also be critical to determine the kinetics of the electro-oxidation of I^-, which is that MEPIS showed more enhanced charge-transfer kinetics of I^- oxidation compared to tetrabutylammonium I₃^- due to the higher degree of freedom of I₃^-.

ZIF-8 derived porous carbon to mitigate shuttle effect for high performance aqueous zinc-iodine batteries

Rechargeable aqueous zinc-iodine batteries (ZIBs) with low environmental impacts and abundant natural reserves have emerged as promising electrochemical energy storage devices. However, the shuttle effect and low conductivity of the iodine species cause poor electrochemical performance and hinder their practical application. Herein, we propose a ZIF-8 derived porous carbon (ZPC) for iodine species immobilization in ZIBs. The rich porous structure and highly conductive framework of ZPC provide efficient iodine loading and allow the fast transmission of electrons. In addition, the presence of N, Zn and ZnO in the carbon framework can build chemical anchoring with the iodine species to mitigate the shuttle effect. Thus, the ZPC/I₂ cathode exhibits a reversible capacity of 156 mAh g^-1 after 100 cycles at 100 mA g^-1 and a long-term stability of 1000 cycles at a high rate. This study will open a new paradigm for devolving highly reversible ZIBs.