Design Strategies for High‐Energy‐Density Aqueous Zinc Batteries

Interfacial chemistry in multivalent aqueous batteries: fundamentals, challenges, and advances

As one of the most promising electrochemical energy storage systems, aqueous batteries are attracting great interest due to their advantages of high safety, high sustainability, and low costs when compared with commercial lithium-ion batteries, showing great promise for grid-scale energy storage. This invited tutorial review aims to provide universal design principles to address the critical challenges at the electrode-electrolyte interfaces faced by various multivalent aqueous battery systems. Specifically, deposition regulation, ion flux homogenization, and solvation chemistry modulation are proposed as the key principles to tune the inter-component interactions in aqueous batteries, with corresponding interfacial design strategies and their underlying working mechanisms illustrated. In the end, we present a critical analysis on the remaining obstacles necessitated to overcome for the use of aqueous batteries under different practical conditions and provide future prospects towards further advancement of sustainable aqueous energy storage systems with high energy and long durability.

Transforming Undesired Corrosion Products into a Nanoflake-Array Functional Layer: A Gelatin-Assistant Modification Strategy for High Performance Zn Battery Anodes

As corrosion products of Zn anodes in ZnSO4 electrolytes, Zn4SO4 (OH)6·xH2O with loose structure cannot suppress persistent side reactions but can increase the electrode polarization and induce dendrite growth, hindering the practical applications of Zn metal batteries. In this work, a functional layer is built on the Zn anode by a gelatin-assistant corrosion and low-temperature pyrolysis method. With the assistant of gelatin, undesired corrosion products are converted into a uniform nanoflake array comprising ZnO coated by gelatin-derived carbon on Zn foil (denoted Zn@ZnO@GC). It is revealed that the gelatin-derived carbons not only enhance the electron conductivity, facilitate Zn2+ desolvation, and boost transport/deposition kinetics, but also inhibit the occurrence of hydrogen evolution and corrosion reactions on the zincophilic Zn@ZnO@GC anode. Moreover, the 3D nanoflake array effectively homogenizes the current density and Zn2+ concentration, thus inhibiting the formation of dendrites. The symmetric cells using the Zn@ZnO@GC anodes exhibit superior cycling performance (over 7000 h at 1 mA cm-2/1 mAh cm-2) and without short-circuiting even up to 25 mAh cm-2. The Zn@ZnO@GC||NaV3O8 full cell works stably for 5000 cycles even with a limited N/P ratio of ≈5.5, showing good application prospects.

Multi-layered carbon accommodation of MnO2 enabling fast kinetics for highly stable zinc ion batteries

Large-scale durable aqueous zinc ion batteries for stationary storage are realized by spray-coating conductive PEDOT(Poly(3,4-ethylenedioxythiophene)) wrapping MnO2/carbon microspheres hybrid cathode in this work. The porous carbon microspheres with multiple layers deriving from sucrose provide suitable accommodation for MnO2 active materials, exposing more redox active sites and enhancing the contact surface between electrolyte and active materials. As a result, MnO2/microspheres are adhered to the current collector by a conductive PEDOT coating without any binder. The ternary design retards the structural degradation during cycling and shortens the electron and ion transport path, rendering the full batteries high capacity and long cycle stability. The resulting batteries perform the capacity of 277, 227, 110, 85 and 50 mAh/g at 0.2, 0.5, 1, 2 and 5 A/g, respectively. After 3000 cycles the initial capacity retains 86%, and 80% after 5000 cycles. GITT indicates PEDOT wrapping MnO2/microspheres cathode enables better ion intercalating kinetics than conventional MnO2. The work could represent a novel and significant step forward in the studies on the large-scale application of zinc ion batteries.

Construction of an n-Type Fluorinated ZnO Interfacial Phase for a Stable Anode of Aqueous Zinc-Ion Batteries

Aqueous rechargeable zinc-ion batteries have become an ideal solution for the next generation of energy storage systems due to their low cost and high safety. However, the uncontrollable zinc dendrites and harmful side reactions of metal zinc anodes hinder the further development of aqueous zinc-ion batteries. In this work, the artificial fluoride zinc oxide (F-ZnO) interface phase is integrated in situ on the surface of zinc foil. The F-ZnO interface phase significantly inhibits the side reactions on the surface of the zinc electrode by reducing the direct contact between the electrolyte and the surface of the zinc foil. In addition, F-ZnO modified by a small amount of F doping shows enhanced conductivity and electron transport capacity, avoiding the accumulation of high concentration Zn2+ on the anode surface, and ultimately promoting the efficient nucleation and orderly deposition of a zinc anode. The cycle life of the symmetrical cell based on F-ZnO is as high as 2600 cycles at an area current density of 4 mA cm-2, which is much better than that of a commercial pure Zn electrode. The modified F-ZnO@Zn anode truly achieves the purpose of prolonging the anode's life.

Host-design strategies of zinc anodes for aqueous zinc-ion batteries

Aqueous zinc ion batteries (AZIBs) have garnered considerable interest as an eco-friendly, safe, and cost-effective energy storage solution. Although significant strides have been made in recent years, there remain technical hurdles to overcome. Herein, this review summarizes in detail the primary challenges confronting aqueous zinc ion batteries, including the rampant dendrite growth, and water-induced parasitic reactions, and proposes host-engineering modification strategies focusing on optimizing the structure design of the zinc anode substrates, involving three-dimensional structure design, zincophilicity regulation, and epitaxial-oriented modification, and comprehensively analyzes the structure-activity relationship between different modification strategies and battery performance. In addition, we highlight the research trends and prospects in future anode modification for aqueous zinc-ion batteries. This work offers valuable insights into advanced Zn anode constructions for further applications in high-performance AZIBs.

Hetero-Solvation-Diluted Strongly-Coordinated Zn2+-Cosolvent Pairs Downshifting Zn Electrode Potential for High-Voltage Hybrid Batteries

Mild aqueous Zn batteries (AZBs) generally suffer a low-voltage/energy dilemma, which compromises their competitiveness for large-scale energy storage. Pushing Zn anode potential downshift is an admissible yet underappreciated approach for high-voltage/energy AZBs. Herein, with a mild hybrid electrolyte containing in situ-derived diluted strongly-coordinated Zn2+-cosolvent pairs, a considerable Zn anode potential downshift is initially achieved for high-voltage Zn-based hybrid batteries. The chosen butylpyridine cosolvent not only strongly coordinates Zn2+ ions but also acts as a hydrogen-bond end-capping agent to inhibit hydrogen evolution reaction (HER). The electrolyte environment with hetero-solvation-diluted strongly-coordinated Zn2+-cosolvent pairs remarkably lowers Zn2+ activity, responsible for the Zn electrode potential downshift (-0.330 V vs Zn), confirming to modified Nernst law (ΔE =R T n F $\frac{{RT}}{{nF}}$ ln[a(Zn2 + )/a(coordinated solvent)]). With the diluted Zn2+-containing hybrid electrolyte, the Zn//Zn symmetric cell in the hybrid electrolyte shows a long lifespan over 1270 h at a stripping/plating capacity of 0.4 mA h cm-2. Compared with in common hybrid electrolytes, the as-assembled Zn-MnO2 hybrid battery delivers a ca. 0.278 V enhanced voltage plateau (1.57 V) and a long-term cyclability of over 736 cycles. This work opens a new avenue toward Zn anode potential downshift for high-voltage AZBs, which can extend to other mild metal batteries.

Three-in-One Zinc Anodes Created by a Large-scale Two-Step Method Achieving Excellent Long-Term Cyclic Reversibility and Thin Electrode Integrity

Practical aqueous zinc-ion batteries require low-cost thin zinc anodes with long-term reversible stripping/depositing. However, thin zinc anodes encounter more severe issues than thick zinc, such as dendrites and uneven stripping, resulting in subpar performance and limited lifetimes. Here, this work proposes a three-in-one zinc anode obtained by a large-scale two-step method to address the above issues. In a three-in-one zinc anode, the copper foil as an inactive current collector solves the gradual reduction of the active area when only the pure zinc as an active current collector. This work develops an automatic electroplating device that can continuously deposit a zinc layer on a conducting foil to meet the demand for zinc-coated copper foils. The sodium carboxymethylcellulose (CMC)-zinc fluoride (ZnF2) protective layer prevents direct contact between zinc and separator, and provides a uniform and sufficient supply of zinc ions. The CMC-ZnF2-coated copper foil performs up to 3000 reversible zinc deposition/stripping cycles with a cumulative capacity of 6 Ah cm-2 and an average Coulombic efficiency of 99.94%. The Zn||ZnVO cell using the three-in-one anode achieved a high capacity retention of over 70% after 15 000 cycles. The proposed three-in-one anode and the automatic electroplating device will facilitate industrialization of practical thin zinc anodes.

Understanding the Role of Zinc Hydroxide Sulfate and its Analogues in Mildly Acidic Aqueous Zinc Batteries: A Review

Mildly acidic aqueous zinc batteries (AZBs) have attracted tremendous attention for grid storage applications with the expectation to tackle the issues of Li-ion batteries on high cost and poor safety. However, the performance, particularly energy density and cycle stability of AZBs are still unsatisfactory when compared with LIBs. To help the development of AZBs, a lot of effort have been made to understand the battery reaction mechanisms and precedent microscopic and spectroscopic analyses have shown flake-like large particles of zinc hydroxide sulfate (ZHS) and its analogues formed on the surfaces of cathodes and anodes in sulfate and other electrolyte systems during cycling. However, because of the complexity of the thermodynamics and kinetics of aqueous reactions to understand different battery conditions, controversies still exist. This article will review the roles of ZHS discussed in recent representative references aiming to shine light on the fundamental mechanisms of AZBs and pave ways to further improve the battery performance.

Tunneling Proton Grotthuss Transfer Channels by Hydrophilic-Zincophobic Heterointerface Shielding for High-Performance Zn-MnO2 Batteries

Hollandite-type manganese dioxide (α-MnO2) is recognized as a promising cathode material upon high-performance aqueous zinc-ion batteries (ZIBs) owing to the high theoretical capacities, high working potentials, unique Zn2+/H+ co-insertion chemistry, and environmental friendliness. However, its practical applications limited by Zn2+ accommodation, where the strong coulombic interaction and sluggish kinetics cause significant lattice deformation, fast capacity degradation, insufficient rate capability, and undesired interface degradation. It remains challenging to accurately modulate H+ intercalation while suppressing Zn2+ insertion for better lattice stability and electrochemical kinetics. Herein, proton Grotthuss transfer channels are first tunneled by shielding MnO2 with hydrophilic-zincophobic heterointerface, fulfilling the H+-dominating diffusion with the state-of-the-art ZIBs performance. Local atomic structure and theoretical simulation confirm that surface-engineered α-MnO2 affords to the synergy of Mn electron t2g-eg activation, oxygen vacancy enrichment, selective H+ Grotthuss transfer, and accelerated desolvation kinetics. Consequently, fortified α-MnO2 achieves prominent low current density cycle stability (≈100% capacity retention at 1 C after 400 cycles), remarkable long-lifespan cycling performance (98% capacity retention at 20 C after 12 000 cycles), and ultrafast rate performance (up to 30 C). The study exemplifies a new approach of heterointerface engineering for regulation of H+-dominating Grotthuss transfer and lattice stabilization in α-MnO2 toward reliable ZIBs.

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 trinity strategy enabled by iodine-loaded nitrogen-boron-doped carbon protective layer for dendrite-free zinc-ion batteries

Although aqueous zinc ion batteries (AZIBs) have the merits of environmental friendliness, high safety and theoretical capacity, the slow kinetics associated with zinc deposition and unavoidable interfacial corrosion have seriously affected the commercialization of aqueous zinc ion batteries. In this work, an ingenious "trinity" design is proposed by applying a porous hydrophilic carbon-loaded iodine coating to the zinc metal surface (INBC@Zn), which simultaneously acts as an artificial protective layer, electrolyte additive and anode curvature regulator, so as to reduce the nucleation overpotential of Zn and promote the preferential deposition of (002) planes to some extent. With this synergistic effect, INBC@Zn exhibits high reversibility and strong side reaction inhibition. As a result, INBC@Zn shows high symmetric cycling stability up to 4500 h at 1 mA cm-2. An ultra-long cycle stability of 1500 cycles with high Coulombic efficiency (99.8 %) is achieved in the asymmetric cell. In addition, the INBC@Zn//NVO full cells exhibit impressive capacity retention (96 % after 1000 cycles at 3 A/g). Importantly, the designed pouch cell demonstrates stable performance and shows certain prospects for application. This work provides a facile and instructive approach toward the development of high-performance AZIBs.

Modular Design of Functional Glucose Monomer and Block Co-Polymer toward Stable Zn Anodes

Aqueous Zn batteries employing mildly acidic electrolytes have emerged as promising contenders for safe and cost-effective energy storage solutions. Nevertheless, the intrinsic reversibility of the Zn anode becomes a focal concern due to the involvement of acidic electrolyte, which triggers Zn corrosion and facilitates the deposition of insulating byproducts. Moreover, the unregulated growth of Zn over cycling amplifies the risk of internal short-circuiting, primarily induced by the formation of Zn dendrites. In this study, a class of glucose-derived monomers and a block copolymer are synthesized through a building-block assembly strategy, ultimately leading to uncover the optimal polymer structure that suppresses the Zn corrosion while allowing efficient ion conduction with a substantial contribution from cation transport. Leveraging these advancements, remarkable enhancements are achieved in the realm of Zn reversibility, exemplified by a spectrum of performance metrics, including robust cycling stability without voltage overshoot and short-circuiting during 3000 h of cycling, stable operation at a high depth of charge/discharge of 75% and a high current density, >95% Coulombic efficiency over 2000 cycles, successful translation of the anode improvement to full cell performance. These polymer designs offer a transformative path based on the modular synthesis of polymeric coatings toward highly reversible Zn anode.

Carbon Nanotube Network Induces Porous Deposited MnO2 for High-Areal Capacity Zn/Mn Batteries

Mn2+/MnO2 aqueous battery is a promising candidate for large-scale energy storage owing to its feature of low-cost and abundant crustal reserves. However, the inherent MnO2 shedding issue results in a limited areal capacity and poor cycling life, which prohibits its further commercialization. In this manuscript, it is revealed that the cause of shedding is the cracking of MnO2 layer due to stress. To circumvent this challenge, carbon nanotubes framework is introduced on pristine carbon felt, which provides more deposition sites and induces the formation of a porous deposition layer. Compared to the dense deposition layer on pristine carbon felt, the porous structure can effectively avoid cracking and subsequent shedding issue. Moreover, the porous deposited layer is conducive to proton diffusion and rich in defects, which facilitates the subsequent dissolution reaction. As results, the assembled Zn/Mn battery demonstrates more than 200 cycles with the areal capacity of 15 mAh cm-2 at 40 mA cm-2. Even with a high areal capacity of 40 mAh cm-2, it can still run for more than 60 cycles. This breakthrough paves a way toward practical manganese-based batteries, bringing us closer to achieve cost-effective batteries.

Modified Ion Migration via Multi-Ion Competitive Transportation for Stable Aqueous Zn Metal Batteries

The application of metal batteries is seriously affected by active ions transport and deposition stability during operation. This article takes water-based Zn metal electrodes as an example to analyze the factors that affect ion distribution and the impact of ion distribution on electrodeposition morphology through electrochemical model simulation calculation, in situ observation and electrochemical experiment: 1) high concentration will reduce the concentration polarization and the overpotential; 2) The passage of active ions through channels are facilitated by small anion (Cl-) rather than bigger one (SO4 2-), which means small deposition overpotential; 3) The transportability-reaction properties of cations (Zn2+, Li+, Na+ and H+) depends on their concentration, solvent coordination structure, and the energy changes during redox reactions. Based on the diffusion and reaction properties, a Li+ coupled Zn2+ electrolyte is designed to achieve the rapid transportation of doped ions to cover uneven growth sites and maintain a stable interface for the steady deposition of active Zn2+, guiding the interface design for high stability metal batteries in addition to the traditional addition of organic solvents.

Langmuir-Blodgett Film Formed by Amphiphilic Molecules for Facile and Rapid Construction of Zinc-Iodine Cell

Zinc-iodine batteries (ZIBs) are promising candidates for ecofriendly, safe, and low-cost energy storage systems, but polyiodide shuttling and the complex cathode fabrication procedures have severely hindered their broader commercial usage. Herein, a protocol is developed using phospholipid-like oleylamine molecules for scalable production of Langmuir-Blodgett films, which allows the facile preparation of ZIB cathodes in less than 1 min. The resulting inhomogeneous cathode allows for the continuous conversion of iodine. Moreover, the amine group of the oleylamine molecule at the cathode is capable of producing [OA*I+]I3- charge-transfer complexes with iodine, which facilitates the rapid migration of iodine and results in a highly reversible iodine conversion process. Consequently, the as-prepared ZIBs can deliver over 2000 cycles at 0.5 mA cm-2 with a capacity retention of 75.3%. This work presents a novel, straightforward, and efficient method for the rapid construction of ZIBs.

Inducing preferential growth of the Zn (002) plane by using a multifunctional chelator for achieving highly reversible Zn anodes

Aqueous zinc-ion batteries (AZIBs) have demonstrated great potential for large-scale energy storage. However, their practical applications have been restricted by fast Zn dendrite growth and severe side reactions at the Zn/electrolyte interface. Herein, sodium gluconate is incorporated into a mild acidic electrolyte as a multifunctional additive to stabilize the Zn anode. Experiments and theoretical calculations reveal that the SG additive can induce planar growth of Zn along its (002) direction, thereby inhibiting Zn dendrite growth. This dendrite inhibition effect is attributed to the preferential adsorption of Zn2+ on the Zn (002) plane, while the Zn (100) and (101) planes are shielded by gluconate ions. Consequently, Zn||Zn symmetric cells with the electrolyte additive exhibit significantly prolonged cycle lives of 2000 h at 1 mA cm-2, 1 mA h cm-2 and 900 h at 5 mA cm-2, 2.5 mA h cm-2. Futhermore, the Zn||NH4V4O10 full cell retains 95% of its initial capacity after 2000 cycles at a current density of 5 A g-1 with an average CE of nearly 100%. This work offers a cost-effective strategy to enhance the electrochemical performance of AZIBs.

Hydrolysis of Solid Buffer Enables High-Performance Aqueous Zinc Ion Battery

Aqueous zinc (Zn) ion batteries (AZIBs) have not yet fulfilled their talent of high safety and low cost since the anode/electrolyte interface (AEI) has long been impeded by hydrogen evolution, surface corrosion, dendritic growth, and by-product accumulation. Here, the hydrolysis of solid buffers is elaborately proposed to comprehensively and enduringly handle these issues. Take 2D layered black phosphorus (BP) as a hydrolytic subject. It is reported that the phosphoric acid generated by hydrolysis in an aqueous electrolyte produces a zinc phosphate (ZPO) rich solid electrolyte interphase (SEI) layer, which largely inhibits the dendrite growth, surface corrosion, and hydrogen evolution. Meanwhile, the hydrolytic phosphoric acid stabilizes the pH value near AEI, avoiding the accumulation of alkaline by-products. Notably, compared with the disposable ZPO engineerings of anodic SEI pre-construction and electrolyte additive, the hydrolysis strategy of BP can realize a dramatically prolonged protective effect. As a result, these multiple merits endow BP modified separator to achieve improved stripping/plating stability toward Zn anode with more than ten times lifespan enhancement in Zn||Zn symmetrical cell. More encouragingly, when coupled with a V2 O5 ·nH2 O cathode with ultra-high loadings (34.1 and 28.7 mg cm-2 ), the cumulative capacities are remarkably promoted for both coin and pouch cells.

Gradient Quasi-Solid Electrolyte Enables Selective and Fast Ion Transport for Robust Aqueous Zinc-Ion Batteries

The quasi-solid electrolytes (QSEs) attract extensive attention due to their improved ion transport properties and high stability, which is synergistically based on tunable functional groups and confined solvent molecules among the polymetric networks. However, the trade-off effect between the polymer content and ionic conductivity exists in QSEs, limiting their rate performance. In this work, the epitaxial polymerization strategy is used to build the gradient hydrogel networks (GHNs) covalently fixed on zinc anode. Then, it is revealed that the asymmetric distribution of negative charges benefits GHNs with fast and selective ionic transport properties, realizing a higher Zn2+ transference number of 0.65 than that (0.52) for homogeneous hydrogel networks (HHNs) with the same polymer content. Meanwhile, the high-density networks formed at Zn/GHNs interface can efficiently immobilize free water molecules and homogenize the Zn2+ flux, greatly inhibiting the water-involved parasitic reactions and dendrite growth. Thus, the GHNs enable dendrite-free stripping/plating over 1000 h at 8 mA cm-2 and 1 mAh cm-2 in a Zn||Zn symmetric cell, as well as the evidently prolonged cycles in various full cells. This work will shed light on asymmetric engineering of ion transport channels in advanced quasi-solid battery systems to achieve high energy and safety.

High-Sulfur Loading and Single Ion-Selective Membranes for High-Energy and Durable Decoupled Aqueous Batteries

The decoupled battery design is promising for breaking the energy density limit of traditional aqueous batteries. However, the complex battery configuration and low-selective separator membranes restrict their energy output and service time. Herein, a zinc-sulfur decoupled aqueous battery is achieved by designing a high-mass loading sulfur electrode and single ion-selective membrane (ISM). A vertically assembled nanosheet network constructed with the assistance of a magnetic field enables facile electron and ion conduction in thick sulfur electrodes, which is conducive to boosting the cell-level energy output. For the tailored ISM, the Na ions anchored on its skeleton effectively prevent the crossover of OH- or Cu2+ , facilitating the transport of Na+ and ensuring structural and mechanical stability. Consequently, the Zn-S aqueous battery achieves a reversible energy density of 3988 Wh kgs -1 (by sulfur mass), stable operation over 300 cycles, and an energy density of 53.2 mWh cm-2 . The sulfur-based decoupled system may be of immediate benefit toward safe, reliable, and affordable static energy storage.

Vanadium Hexacyanoferrate Prussian Blue Analogs for Aqueous Proton Storage: Excellent Electrochemical Properties and Mechanism Insights

The significant attraction toward aqueous proton batteries (APBs) is attributable to their expedited kinetics, elevated safety profile, and economical feasibility. Nevertheless, their practical implement is significantly blocked by the unsatisfactory energy density due to the limited cathode materials. Herein, vanadium hexacyanoferrate Prussian blue analog (VOHCF) is introduced as a potentially favorable cathode material for APBs. The findings demonstrate that this VOHCF electrode exhibits a notable reversible capacity of 102.7 mAh g-1 and exceptional cycling stability, with 95.4% capacity retention over 10 000 cycles at 10 A g-1 . It is noteworthy that this is the detailed instance of VOHCF being proposed as a cathode for APBs. Combining the in situ characterization techniques and theoretical simulations, the origins of excellent proton storage performance are revealed as the multiple redox mechanisms with double active centers of ─C≡N group and V═O bond in VOHCF as well as the robust structure stability. A proton full cell with excellent performance is further achieved by coupling the VOHCF cathode and diquinoxalino[2,3-a:2',3'-c] phenazine (HATN) anode, demonstrating the great potential of VOHCF in practical applications. This work could provide fundamental understanding to the development of feasible cathode materials for proton storage device.

A Comprehensive Evaluation of Battery Technologies for High-Energy Aqueous Batteries

Aqueous batteries have garnered significant attention in recent years as a viable alternative to lithium-ion batteries for energy storage, owing to their inherent safety, cost-effectiveness, and environmental sustainability. This study offers a comprehensive review of recent advancements, persistent challenges, and the prospects of aqueous batteries, with a primary focus on energy density compensation of various battery engineering technologies. Additionally, cutting-edge high-energy aqueous battery designs are emphasized as a reference for future endeavors in the pursuit of high-energy storage solutions. Finally, a dual-compatibility battery configuration perspective aimed at concurrently optimizing cycle stability, redox potential, capacity utilization for both anode and cathode materials, as well as the selection of potential electrode candidates, is proposed with the ultimate goal of achieving cell-level energy densities exceeding 400 Wh kg-1 .

Critical Issues of Vanadium-Based Cathodes Towards Practical Aqueous Zn-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) are gaining significant attention for their numerous advantages, including high safety, high energy density, affordability, and environmental friendliness. However, the development of ZIBs has been hampered by the lack of suitable cathode materials that can store Zn2+ with high capacity and reversibility. Currently, vanadium-based materials with tunnel or layered structures are widely researched owing to their high theoretical capacity and diversified structures. However, their long-term cycling stability is unsatisfactory because of material dissolution, phase transformation, and restrictive kinetics in aqueous electrolytes, which limits their practical applications. Different from previous reviews on ZIBs, this review specifically addresses the critical issues faced by vanadium-based cathodes for practical aqueous ZIBs and proposes potential solutions. Focusing on vanadium-based cathodes, their ion storage mechanisms, the critical parameters affecting their performance, and the progress made in addressing the aforementioned problems are also summarized. Finally, future directions for the development of practical aqueous ZIB are suggested.

Tissue-Matchable and Implantable Batteries Toward Biomedical Applications

Implantable electronic devices can realize real-time and reliable health monitoring, diagnosis, and treatment of human body, which are expected to overcome important bottlenecks in the biomedical field. However, the commonly used energy supply devices for them are implantable batteries based on conventional rigid device design with toxic components, which both mechanically and biologically mismatch soft biological tissues. Therefore, the development of highly soft, safe, and implantable tissue-matchable flexible batteries is of great significance and urgency for implantable bioelectronics. In this work, the recent advances of tissue-matchable and implantable flexible batteries are overviewed, focusing on the design strategies of electrodes/batteries and their biomedical applications. The mechanical flexibility, biocompatibility, and electrochemical performance in vitro and in vivo of these flexible electrodes/batteries are then discussed. Finally, perspectives are provided on the current challenges and possible directions of this field in the future.

Coulombic Efficiency for Practical Zinc Metal Batteries: Critical Analysis and Perspectives

Climate change and energy depletion are common worries of this century. During the global clean energy transition, aqueous zinc metal batteries (AZMBs) are expected to meet societal needs due to their large-scale energy storage capability with earth-abundant, non-flammable, and economical chemistries. However, the poor reversibility of Zn poses a severe challenge to AZMB implementation. Coulombic efficiency (CE) is a quantitative index of electrode reversibility in rechargeable batteries but is not well understood in AZMBs. Thus, in this work,  the state-of-art CE to present the status quo of AZMB development is summarized.  A fictional 120 Wh kg-1 AZMB pouch cell is also proposed and evaluated revealing the improvement room and technical goal of AZMB chemistry. Despite some shared mechanisms between AZMBs and lithium metal batteries, misconceptions prevalent in AZMBs are clarified. Essentially, AZMB has its own niche in the market with unique merits and demerits. By incorporating academic and industrial insights, the development pathways of AZMB are suggested.

A Two-Dimensional Porphyrin Coordination Supramolecular Network Cathode for High-Performance Aqueous Dual-Ion Battery

Iodine has great potential in the energy storage, but high solubility of I₃ ^- has seriously delayed its promotion. Benefited from abundant active sites and the open channel, two-dimensional coordination supramolecular networks (2D CSNs) is considered to be a candidate for the energy storage. Herein, a 2D porphyrin-CSN cathode named Zn-TCPP for aqueous iodine dual-ion battery (DIB) shows an excellent specific capacity of 278 mAh g^-1 , and a high energy density of 340 Wh kg^-1 at 5 A g^-1 , as well as a durable cycle performance of 5000 cycles and a high Coulombic efficiency of 98 %. Molecular orbital theory, UV/VIS, Raman spectroscopy and density functional theory (DFT) calculations reveal charge-transfer interaction between the donor of porphyrin nitrogen and the acceptor of I₃ ^- , and computational fluid dynamics (CFD) simulations demonstrate the contribution of 2D layered network structure of Zn-TCPP to the penetration of I₃ ^- .