An Anode-Free Zn-Graphite Battery

2D Conjugated Metal-Organic Frameworks Bearing Large Pore Apertures and Multiple Active Sites for High-Performance Aqueous Dual-Ion Batteries

2D conjugated metal-organic frameworks (2D c-MOFs) with large pore sizes and high surface areas are advantageous for adsorbing iodine species to enhance the electrochemical performance of aqueous dual-ion batteries (ADIBs). However, most of the reported 2D c-MOFs feature microporous structures, with few examples exhibiting mesoporous characteristics. Herein, we developed two mesoporous 2D c-MOFs, namely PA-TAPA-Cu-MOF and PA-PyTTA-Cu-MOF, using newly designed arylimide based multitopic catechol ligands (6OH-PA-TAPA and 8OH-PA-PyTTA). Notably, PA-TAPA-Cu-MOF exhibits the largest pore sizes (3.9 nm) among all reported 2D c-MOFs. Furthermore, we demonstrated that these 2D c-MOFs can serve as promising cathode host materials for polyiodides in ADIBs for the first time. The incorporation of triphenylamine moieties in PA-TAPA-Cu-MOF resulted in a higher specific capacity (423.4 mAh g-1 after 100 cycles at 1.0 A g-1) and superior cycling performance, retaining 96 % capacity over 1000 cycles at 10 A g-1 compared to PA-PyTTA-Cu-MOF. Our comparative analysis revealed that the increased number of N anchoring sites and larger pore size in PA-TAPA-Cu-MOF facilitate efficient anchoring and conversion of I3 -, as supported by spectroscopic electrochemistry and density functional theory calculations.

A Durable and High-Voltage Mn-Graphite Dual-Ion Battery Using Mn-Based Hybrid Electrolytes

Rechargeable Mn-metal batteries (MMBs) can attract considerable attention because Mn has the intrinsic merits including high energy density (976 mAh g-1), high air stability, and low toxicity. However, the application of Mn in rechargeable batteries is limited by the lack of proper cathodes for reversible Mn2+ intercalation/de-intercalation, thus leading to low working voltage (<1.8 V) and poor cycling stability (≤200 cycles). Herein, a high-voltage and durable MMB with graphite as the cathode is successfully constructed using a LiPF6-Mn(TFSI)2 hybrid electrolyte, which shows a high discharge voltage of 2.34 V and long-term stability of up to 1000 cycles. Mn(TFSI)2 can reduce the plating/stripping overpotential of Mn ions, while LiPF6 can efficiently improve the conductivity of the electrolyte. Electrochemical in-situ characterization implies the dual-anions intercalation/de-intercalation at the cathode and Mn2+ plating/stripping reaction at the anode. Theoretical calculations unveil the top site of graphite is the energetically favorable for anions intercalation and TFSI- shows the low migration barrier. This work paves an avenue for designing high-performance rechargeable MMBs towards electricity storage.

MXene-Stabilized VS2 Nanostructures for High-Performance Aqueous Zinc Ion Storage

Aqueous zinc-ion batteries (AZIBs) based on vanadium oxides or sulfides are promising candidates for large-scale rechargeable energy storage due to their ease of fabrication, low cost, and high safety. However, the commercial application of vanadium-based electrode materials has been hindered by challenging problems such as poor cyclability and low-rate performance. To this regard, sophisticated nanostructure engineering technology is used to adeptly incorporate VS2 nanosheets into the MXene interlayers to create a stable 2D heterogeneous layered structure. The MXene nanosheets exhibit stable interactions with VS2 nanosheets, while intercalation between nanosheets effectively increases the interlayer spacing, further enhancing their stability in AZIBs. Benefiting from the heterogeneous layered structure with high conductivity, excellent electron/ion transport, and abundant reactive sites, the free-standing VS2/Ti3C2Tz composite film can be used as both the cathode and the anode of AZIBs. Specifically, the VS2/Ti3C2Tz cathode presents a high specific capacity of 285 mAh g-1 at 0.2 A g-1. Furthermore, the flexible Zn-metal free in-plane VS2/Ti3C2Tz//MnO2/CNT AZIBs deliver high operation voltage (2.0 V) and impressive long-term cycling stability (with a capacity retention of 97% after 5000 cycles) which outperforms almost all reported Vanadium-based electrodes for AZIBs. The effective modulation of the material structure through nanocomposite engineering effectively enhances the stability of VS2, which shows great potential in Zn2+ storage. This work will hasten and stimulate further development of such composite material in the direction of energy storage.

On-Water Surface Synthesis of Vinylene-Linked Cationic Two-Dimensional Polymer Films as the Anion-Selective Electrode Coating

Vinylene-linked two-dimensional polymers (V-2DPs) and their layer-stacked covalent organic frameworks (V-2D COFs) featuring high in-plane π-conjugation and robust frameworks have emerged as promising candidates for energy-related applications. However, current synthetic approaches are restricted to producing V-2D COF powders that lack processability, impeding their integration into devices, particularly within membrane technologies reliant upon thin films. Herein, we report the novel on-water surface synthesis of vinylene-linked cationic 2DPs films (V-C2DP-1 and V-C2DP-2) via Knoevenagel polycondensation, which serve as the anion-selective electrode coating for highly-reversible and durable zinc-based dual-ion batteries (ZDIBs). Model reactions and theoretical modeling revealed the enhanced reactivity and reversibility of the Knoevenagel reaction on the water surface. On this basis, we demonstrated the on-water surface 2D polycondensation towards V-C2DPs films that show large lateral size, tunable thickness, and high chemical stability. Representatively, V-C2DP-1 presents as a fully crystalline and face-on oriented film with in-plane lattice parameters of a=b≈43.3 Å. Profiting from its well-defined cationic sites, oriented 1D channels, and stable frameworks, V-C2DP-1 film possesses superior bis(trifluoromethanesulfonyl)imide anion (TFSI-)-transport selectivity (transference, t_=0.85) for graphite cathode in high-voltage ZDIBs, thus triggering additional TFSI--intercalation stage and promoting its specific capacity (from ~83 to 124 mAh g-1) and cycling life (>1000 cycles, 95 % capacity retention).

Lamellar Nanoporous Metal/Intermetallic Compound Heterostructure Regulating Dendrite-Free Zinc Electrodeposition for Wide-Temperature Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries are attractive post-lithium battery technologies for grid-scale energy storage because of their inherent safety, low cost and high theoretical capacity. However, their practical implementation in wide-temperature surroundings persistently confronts irregular zinc electrodeposits and parasitic side reactions on metal anode, which leads to poor rechargeability, low Coulombic efficiency and short lifespan. Here, this work reports lamellar nanoporous Cu/Al2Cu heterostructure electrode as a promising anode host material to regulate high-efficiency and dendrite-free zinc electrodeposition and stripping for wide-temperatures aqueous zinc-ion batteries. In this unique electrode, the interconnective Cu/Al2Cu heterostructure ligaments not only facilitate fast electron transfer but work as highly zincophilic sites for zinc nucleation and deposition by virtue of local galvanic couples while the interpenetrative lamellar channels serving as mass transport pathways. As a result, it exhibits exceptional zinc plating/stripping behaviors in aqueous hybrid electrolyte of diethylene glycol dimethyl ether and zinc trifluoromethanesulfonate at wide temperatures ranging from 25 to -30 °C, with ultralow voltage polarizations at various current densities and ultralong lifespan of >4000 h. The outstanding electrochemical properties enlist full cell of zinc-ion batteries constructed with nanoporous Cu/Al2Cu and ZnxV2O5/C to maintain high capacity and excellent stability for >5000 cycles at 25 and -30 °C.

Backside Coating for Stable Zn Anode with High Utilization Rate

Stable Zn anodes with high utilization rate are urgently required to promote the specific and volumetric energy densities of Zn-ion batteries for practical applications. Herein, contrary to the widely utilized surface coating on Zn anodes, this work shows that a zinc foil with a backside coated layer delivers much enhanced cycling stability even under high depth of discharge. The backside coating significantly reduces stress concentration, accelerates heat diffusion, and facilitates electron transfer, thus effectively preventing dendrite growth and structural damage at high Zn utilization. As a result, the developed anode can be stably cycled for 334 h at 85.5% Zn utilization, which outperforms bare Zn and previously reported results on surface-coated Zn foils. An NVO-based full cell also shows stable performance with high Zn utilization rate (69.4%), low negative-positive electrodes ratio (1.44), and high specific/volumetric energy densities (155.8 Wh kg-1/178 Wh L-1), which accelerates the progress toward practical zinc-ion batteries.

Polymer hetero-electrolyte enabled solid-state 2.4-V Zn/Li hybrid batteries

The high redox potential of Zn0/2+ leads to low voltage of Zn batteries and therefore low energy density, plaguing deployment of Zn batteries in many energy-demanding applications. Though employing high-voltage cathode like spinel LiNi0.5Mn1.5O4 can increase the voltages of Zn batteries, Zn2+ ions will be immobilized in LiNi0.5Mn1.5O4 once intercalated, resulting in irreversibility. Here, we design a polymer hetero-electrolyte consisting of an anode layer with Zn2+ ions as charge carriers and a cathode layer that blocks the Zn2+ ion shuttle, which allows separated Zn and Li reversibility. As such, the Zn‖LNMO cell exhibits up to 2.4 V discharge voltage and 450 stable cycles with high reversible capacity, which are also attained in a scale-up pouch cell. The pouch cell shows a low self-discharge after resting for 28 days. The designed electrolyte paves the way to develop high-voltage Zn batteries based on reversible lithiated cathodes.

Toward a Metal Anode-Free Zinc-Air Battery for Next-Generation Energy Storage

Rechargeable aqueous zinc-air batteries (ZABs) promise high energy density and safety. However, the use of conventional zinc anodes affects the energy output from the battery, so that the theoretical energy density is not achievable under operation conditions. A large portion of the zinc is shielded by anode passivation during the discharge process and remains electrochemically unused, making the operation of rechargeable ZABs inefficient up to date. In a metal anode-free ZAB, there is no unnecessary excess zinc if the zinc reservoir can be precisely adjusted by electrodeposition of zinc from the electrolyte. In this respect, an anode-free battery uses the electrolyte offering a dual-mode functionality not only providing ionic conductivity but also being the source of zinc. In addition, it is shown that a defined porous anode architecture is crucial for high rechargeability in this new type of ZAB. 3D-spatially arranged carbon nanotubes as geometrically defined host structures allow a homogeneous zinc deposition from the electrolyte. Together with carbon nanohorns as an active 2e- catalyst on the cathode side, the rechargeability of this new concept reaches up to 92%.

Dual-ion conductors: from liquid to solid

The traditional working principle within lithium-ion batteries relies on Li+ shuttling between the cathode and anode, namely the rocking-chair mechanism. A single working ion constrains the possibilities for battery design and the selection of electrode materials, while realizing multiple working ions offers the potential to break through the fundamental principles of traditional battery construction. Accordingly, it is necessary to develop dual-ion conductors to enable the migration of multiple working ions. This focus article starts by introducing traditional dual-ion batteries based on liquid electrolytes and their pros and cons. Then, solidifying liquid dual-ion conductors is expected to overcome these drawbacks, so the development of solid dual-ion conductors is discussed in detail. Specifically, basic design principles of solid dual-ion conductors are briefly proposed, including constructing continuous ion transport channels and choosing appropriately sized ion carriers. The potential applications of solid dual-ion conductors are also summarized, such as stabilizing the electrode/electrolyte interface and activating additional redox couples. The goal of this article is to inspire researchers in the development of dual-ion conductors and to contribute to the advancement of all-solid-state batteries.

Sustainable Dual-Ion Batteries beyond Li

The limitations of resources used in current Li-ion batteries may hinder their widespread use in grid-scale energy storage systems, prompting the search for low-cost and resource-abundant alternatives. "Beyond-Li cation" batteries have emerged as promising contenders; however, they confront noteworthy challenges due to the scarcity of suitable host materials for these cations. In contrast, anions, the other crucial component in electrolytes, demonstrate reversible intercalation capacity in specific materials like graphite. The convergence of anion and cation storage has given rise to a new battery technology known as dual-ion batteries (DIBs). This comprehensive review presents the current status, advancements, and future prospects of sustainable DIBs beyond Li. Notably, most DIBs exhibit similar cathode reaction mechanisms involving anion intercalation, while the distinguishing factor lies in the cation types functioning at the anode. Accordingly, the review is organized into sections by various cation types, including Na-, K-, Mg-, Zn-, Ca-, Al-, NH4 + -, and proton-based DIBs. Moreover, a perspective on these novel DIBs is presented, along with proposed protocols for investigating DIBs and promising future research directions. It is envisioned that this review will inspire fresh concepts, ideas, and research directions, while raising important questions to further tailor and understand sustainable DIBs, ultimately facilitating their practical realization.

Zincophilic Metal-Organic-Framework Interface Mitigating Dendrite Growth for Highly Reversible Zinc Metal Batteries

Aqueous Zn-ion batteries are the ideal candidate for large-scale energy storage systems owing to their high safety and low cost. However, the uncontrolled deposition and parasitic reaction of Zn metal anode hinder their commercial application. Here, the 2D metal-organic-framework (MOF) nanoflakes covered on the surface of Zn are proposed to enable dendrite-free for long lifespan Zn metal batteries. The MOF can facilitate the desolvation process to accelerate reaction kinetic due to its special channel structure. The abundant zincopilicity sites of MOF can realize the homogenous Zn2+ deposition. Consequently, their synergetic effect makes the MOF protected Zn anode good electrochemical performance with a long cycle life of 1400 h at 1 mA cm-2 and a high depth of discharge of 30 mAh cm-2 (DOD ≈ 54%) continued for over 700 h. This work provides a novel strategy for high-performance rechargeable Zn-ion batteries.

Design Strategies for Aqueous Zinc Metal Batteries with High Zinc Utilization: From Metal Anodes to Anode-Free Structures

Aqueous zinc metal batteries (AZMBs) are promising candidates for next-generation energy storage due to the excellent safety, environmental friendliness, natural abundance, high theoretical specific capacity, and low redox potential of zinc (Zn) metal. However, several issues such as dendrite formation, hydrogen evolution, corrosion, and passivation of Zn metal anodes cause irreversible loss of the active materials. To solve these issues, researchers often use large amounts of excess Zn to ensure a continuous supply of active materials for Zn anodes. This leads to the ultralow utilization of Zn anodes and squanders the high energy density of AZMBs. Herein, the design strategies for AZMBs with high Zn utilization are discussed in depth, from utilizing thinner Zn foils to constructing anode-free structures with theoretical Zn utilization of 100%, which provides comprehensive guidelines for further research. Representative methods for calculating the depth of discharge of Zn anodes with different structures are first summarized. The reasonable modification strategies of Zn foil anodes, current collectors with pre-deposited Zn, and anode-free aqueous Zn metal batteries (AF-AZMBs) to improve Zn utilization are then detailed. In particular, the working mechanism of AF-AZMBs is systematically introduced. Finally, the challenges and perspectives for constructing high-utilization Zn anodes are presented.

Key to High Performance Ion Hybrid Capacitor: Weakly Solvated Zinc Cations

Zinc ion hybrid capacitors suffer from lack of reversibility and dendrite formation. An electrolyte, based on a solution of a zinc salt in acetonitrile and tetramethylene sulfone, allows smooth zinc deposition with high coulombic efficiency in a Zn||stainless steel cell (99.6% for 2880 cycles at 1.0 mA cm-2 , 1.0 mAh cm-2 ). A Zn||Zn cell operates stably for at least 7940 h at 1.0 mA cm-2 with an area capacity of 10 mAh cm-2 , or 648 h at 90% depth of discharge and 1 mA cm-2 , 9.0 mAh cm-2 . Molecular dynamics simulations reveal the reason for the excellent reversibility: The zinc cation is only weakly solvated than in pure tetramethylene sulfone with the closest atoms at 3.3 to 3.8 Å. With this electrolyte, a zinc||activated-carbon hybrid capacitor exhibits an operating voltage of 2.0 to 2.5 V, an energy-density of 135 Wh kg-1 and a power-density of 613 W kg-1 at 0.5 A g-1 . At the very high current-density of 15 A g-1 , 29.3 Wh kg-1 and 14 250 W kg-1 are achieved with 81.2% capacity retention over 9000 cycles.

Unveiling the Role of Charge Dilution and Anionic Chemistry in Enabling High-Rate p-Type Polymer Cathodes for Dual-Ion Batteries

Herein, we introduce a p-type redox conjugated covalent organic polymer (p-PNZ) as a universal and high-rate cathode for diverse dual-ion batteries. By constructing an n-type redox counterpart (n-PNZ) with an analogous reticular structure and redox-site composition, we also attain a comparative platform to probe how the redox-site nature and counterion chemistry affect the rate performance of polymer cathodes. It is disclosed that the charge dilution in p-type redox sites and bulky anions engenders their weak interaction and rapid anion diffusion in electrodes, while the trivial interaction of the solvent with anions facilitates anion desolvation and interfacial charge transfer. Thus, p-PNZ possesses rapid surface-controlled redox kinetics with a high anion diffusion coefficient regardless of its inferior porosity and conductivity relative to n-PNZ. Along with a long cycle life of over 50000 cycles, the p-PNZ-engaged Zn-based dual-ion battery with a dilute electrolyte delivers nearly constant capacities of ∼149 mAh g-1 at various rates of ≤10 A g-1─such an unusual rate capability has rarely been observed previously─and retains ∼99 mAh g-1 at 40 A g-1, surpassing the n-PNZ counterpart and most existing p-type organic cathodes. The p-PNZ cathode can also be applied to build high-rate Li-based batteries, signifying its universality, while the "ready-to-charge" character of p-PNZ enables anode-free dual-ion batteries with a high-rate capability and long lifespan.

Interfacial Designs of MXenes for Mild Aqueous Zinc-Ion Storage

Limited Li resources, high cost, and safety risks of using organic electrolytes have stimulated a strong motivation to develop non-Li aqueous batteries. Aqueous Zn-ion storage (ZIS) devices offer low-cost and high-safety solutions. However, their practical applications are at the moment restricted by their short cycle life arising mainly from irreversible electrochemical side reactions and processes at the interfaces. This review sums up the capability of using 2D MXenes to increase the reversibility at the interface, assist the charge transfer process, and thereby improve the performance of ZIS. First, they discuss the ZIS mechanism and irreversibility of typical electrode materials in mild aqueous electrolytes. Then, applications of MXenes in different ZIS components are highlighted, including as electrodes for Zn2+ intercalation, protective layers of Zn anode, hosts for Zn deposition, substrates, and separators. Finally, perspectives are put forward on further optimizing MXenes to improve the ZIS performance.

Cation Co-Intercalation with Anions: The Origin of Low Capacities of Graphite Cathodes in Multivalent Electrolytes

Dual-ion batteries involving anion intercalation into graphite cathodes represent promising battery technologies for low-cost and high-power energy storage. However, the fundamental origins regarding much lower capacities of graphite cathodes in earth abundant and inexpensive multivalent electrolytes than in Li-ion electrolytes remain elusive. Herein, we reveal that the limited anion-storage capacity of a graphite cathode in multivalent electrolytes is rooted in the abnormal multivalent-cation co-intercalation with anions in the form of large-sized anionic complexes. This cation co-intercalation behavior persists throughout the stage evolution of graphite intercalation compounds and leads to a significant decrease of sites practically viable for capacity contribution inside graphite galleries. Further systematic studies illustrate that the phenomenon of cation co-intercalation into graphite is closely related to the high energy penalty of interfacial anion desolvation due to the strong cation-anion association prevalent in multivalent electrolytes. Leveraging this understanding, we verify that promoting ionic dissociation in multivalent electrolytes by employing high-permittivity and oxidation-tolerant co-solvents is effective in suppressing multivalent-cation co-intercalation and thus achieving increased capacity of graphite cathodes. For instance, introducing adiponitrile as a co-solvent to a Mg²⁺-based carbonate electrolyte leads to 83% less Mg²⁺ co-intercalation and a ∼29.5% increase in delivered capacity of the graphite cathode.

Observation of Zn Dendrite Growth via Operando Digital Microscopy and Time-Lapse Tomography

The zinc-ion battery is one of the promising candidates for next-generation energy storage devices beyond lithium technology due to the earth's abundance of Zn materials and their high volumetric energy density (5855 mA h cm-3). To date, the formation of Zn dendrites during charge-discharge cycling still hinders the practical application of zinc-ion batteries. It is, therefore, crucial to understand the formation mechanism of the zinc dendritic structure before effectively suppressing its growth. Here, the application of operando digital optical microscopy and in situ lab-based X-ray computed tomography (X-ray CT) is demonstrated to probe and quantify the morphologies of zinc electrodeposition/dissolution under multiple galvanostatic plating/stripping conditions in symmetric Zn||Zn cells. With the combined microscopy approaches, we directly observed the dynamic nucleation and subsequent growth of Zn deposits, the heterogeneous transportation of charged clusters/particles, and the evolution of 'dead' Zn particles via partial dissolution. Zn electrodeposition at the early stage is mainly attributed to activation, while the subsequent dendrite growth is driven by diffusion. The high current not only facilitates the formation of sharp dendrites with a larger mean curvature at their tips but also leads to dendritic tip splitting and the creation of a hyper-branching morphology. This approach offers a direct opportunity to characterize dendrite formation in batteries with a metal anode in the laboratory.

Spreading the Landscape of Dual Ion Batteries: from Electrode to Electrolyte

The working mechanism of a dual-ion battery (DIB) differs from that of a lithium-ion battery (LIB) in that the anions in the electrolyte of the former can be intercalated as well. Researchers have been paying close attention to this device because of its high voltage, low price, and environmental friendliness. However, DIBs are still in their early research stages, and numerous issues need to be addressed and investigated further. Initially, this Review explains how DIBs work in principle and discusses the progress of electrode materials for cathode and anode. Furthermore, since the electrolytes used as the active material, as well as anion, solvent, and additives, have a significant impact on the DIB's capacity and voltage, the current status is also presented in terms of electrolytes, followed by an outlook on confronting the challenges. A comprehensive summary from electrode to electrolyte will guide the development of next-generation DIBs.

Surface Engineering for Ultrathin Metal Anodes Enabling High-Performance Zn-Ion Batteries

Zn-ion batteries with low cost and high safety have been regarded as a promising energy storage technology for grid storage. It is well-known that the metal anode surface orientation is vital to its reversibility. Herein, we demonstrate a facile route to control the Zn metal anode surface orientation through electrodeposition with electrolyte additives. An ultrathin (101)-inclined Zn metal anode (down to 2 μm) is obtained by adding a small amount of dimethyl sulfoxide (DMSO) in the ZnSO₄ aqueous electrolyte. Scanning electron microscopy indicates the formation of flat terrace-like surfaces, while in situ optical observations demonstrate the reversible plating and stripping. DFT calculations reveal that the large reconstruction of the Zn-(101) surface with DMSO and H₂O adsorption to lower the interface energy is the main driving force for surface preference. Raman, XPS, and ToF-SIMS characterizations are performed to unveil the surface SEI components. Exceptional electrochemical performance is demonstrated for the (101)-inclined Zn metal anode in a half cell, which could cycle for 200 h with a low overpotential (<50 mV). The Zn||V₂O full cells are assembled, showing much better cycle performance for the 5 μm (101)-inclined Zn metal anode as compared to the commercialized 10 μm Zn metal foil, with a maximum specific capacity of 359 mAh/g and >170 mAh/g after over 300 cycles. We hope this study will spur further interest in the control of surface crystallographic orientation for a stable ultrathin Zn metal anode.

Constructing robust heterostructured interface for anode-free zinc batteries with ultrahigh capacities

The development of Zn-free anodes to inhibit Zn dendrite formation and modulate high-capacity Zn batteries is highly applauded yet very challenging. Here, we design a robust two-dimensional antimony/antimony-zinc alloy heterostructured interface to regulate Zn plating. Benefiting from the stronger adsorption and homogeneous electric field distribution of the Sb/Sb₂Zn₃-heterostructured interface in Zn plating, the Zn anode enables an ultrahigh areal capacity of 200 mAh cm^-2 with an overpotential of 112 mV and a Coulombic efficiency of 98.5%. An anode-free Zn-Br₂ battery using the Sb/Sb₂Zn₃-heterostructured interface@Cu anode shows an attractive energy density of 274 Wh kg^-1 with a practical pouch cell energy density of 62 Wh kg^-1. The scaled-up Zn-Br₂ battery in a capacity of 500 mAh exhibits over 400 stable cycles. Further, the Zn-Br₂ battery module in an energy of 9 Wh (6 V, 1.5 Ah) is integrated with a photovoltaic panel to demonstrate the practical renewable energy storage capabilities. Our superior anode-free Zn batteries enabled by the heterostructured interface enlighten an arena towards large-scale energy storage applications.

Iodine Promoted Ultralow Zn Nucleation Overpotential and Zn-Rich Cathode for Low-Cost, Fast-Production and High-Energy Density Anode-Free Zn-Iodine Batteries

The anode-free design is a promising strategy to increase the energy density of aqueous Zn metal batteries (AZMBs). However, the scarcity of Zn-rich cathodes and the rapid loss of limited Zn greatly hinder their commercial applications. To address these issues, a novel anode-free Zn-iodine battery (AFZIB) was designed via a simple, low-cost and scalable approach. Iodine plays bifunctional roles in improving the AFZIB overall performance: enabling high-performance Zn-rich cathode and modulating Zn deposition behavior. On the cathode side, the ZnI₂ serves as Zn-rich cathode material. The graphene/polyvinyl pyrrolidone heterostructure was employed as an efficient host for ZnI₂ to enhance electron conductivity and suppress the shuttle effect of iodine species. On the anode side, trace I₃^- additive in the electrolyte creates surface reconstruction on the commercial Cu foil. The in situ formed zincophilic Cu nanocluster allows ultralow-overpotential and uniform Zn deposition and superior reversibility (average coulombic efficiency > 99.91% over 7,000 cycles). Based on such a configuration, AFZIB exhibits significantly increased energy density (162 Wh kg^-1) and durable cycle stability (63.8% capacity retention after 200 cycles) under practical application conditions. Considering the low cost and simple preparation methods of the electrode materials, this work paves the way for the practical application of AZMBs.