Protein Interfacial Gelation toward Shuttle-Free and Dendrite-Free Zn-Iodine Batteries

Cold-Optimized Zinc-Ion Batteries: Enhanced Stability at -5 °C

Aqueous zinc-ion batteries (AZIBs) have been extensively studied under room and ultralow temperature conditions. However, mechanism studies at intermediate temperature ranges remain limited. In this work, we investigate the electrochemical performance of an AZIB using a commonly employed 3 M ZnSO4 electrolyte across the intermediate temperature range of 25 to -15 °C. Notably, we find that the battery with a double hydroxide cathode exhibits optimized performance at -5 °C, demonstrating significantly enhanced cycling stability compared to 25 °C. Mechanistic studies reveal that unfavorable H+-associated reactions at both the cathode and anode are effectively alleviated at -5 °C, contributing to improved cycling stability. Spectroscopic and theoretical analyzes show that changes in the electrolyte environment at -5 °C-such as reduced electrochemical activity of H2O, increased H-bond strength, and decreased total number of H bonds-impede H+ diffusion through H-bond network via the Grotthuss mechanism. These effects collectively suppress harmful H+-associated reactions, allowing Zn2+ insertion/deinsertion to dominate the charge storage process. This work provides valuable insights into the enhanced performance of AZIBs at sublow temperatures and presents opportunities for extending battery operation in near-freezing environments.

Coordination Chemistry toward Advanced Zn-I2 Batteries with Four-Electron I-/I0/I+ Conversion

Aqueous zinc-iodine (Zn-I2) batteries with four-electron (4e) I-/I0/I+ conversion (4eZIBs) offer high energy density but face significant challenges for application, including the polyiodide shuttle effect and I+ hydrolysis for the I2 cathodes and poor reversibility for the Zn anodes. Here, we report a coordination chemistry strategy to address these issues simultaneously by introducing hexamethylenetetramine (HMTA) as an electrolyte additive. In aqueous electrolytes, HMTA undergoes protonation to form positively charged nitrogen moieties that effectively precipitate the polyiodides and I+ species (ICl2-) to mitigate the polyiodides shuttle and I+ hydrolysis. This strategy enables 4eZIBs to achieve a near-theoretical specific capacity of 425 mA h g-1 (based on the mass of iodine) and a Coulombic efficiency (CE) exceeding 99%. On the Zn anode, HMTA preferentially adsorbs onto its surface, inhibiting competitive water adsorption to suppress both Zn dendrite formation and hydrogen evolution. As a result, for the first time, we achieve durable 4eZIB performance in pouch-cell configurations with limited Zn supply. A 0.5 A h pouch cell with 15% Zn utilization exhibits a high energy density of 113.0 W h kg-1 (based on the mass of cathodes and anodes) and excellent cycling stability for over 1400 cycles, highlighting the potential of 4eZIBs for next-generation energy storage systems.

Biomimetic Localized Gel Electrolyte for Practical Zinc Anode

Incompatible electrode/electrolyte interface often leads to dendrite growth, parasitic reactions, and corrosion, posing significant challenges to the application of Zn anodes. Herein, we introduce a biomimetic antifreeze protein localized gel electrolyte (ALGE) with multifunctional capabilities to address these issues by combining electrolyte modification with interface optimization. ALGE modifies the Zn2+ solvation structure and the hydrogen-bond network adjacent to the zinc anode, effectively suppressing hydrogen evolution. Additionally, ALGE promotes (002)Zn crystal plane-dominated deposition by protein-zinc surface interactions, enabling a long-range dendrite-free deposition. The absence of by-products and inhibited corrosion further highlights the practical potential of ALGE. Symmetric cells with ALGE-modified zinc demonstrate an impressive lifespan of 610  h under a current density of 10 mA cm-2 and a capacity of 10 mAh cm-2. The pouch cell integrating a manganese dioxide cathode and ALGE-modified Zn anode retains 75.8% of its capacity after 200 cycles at 1 A g-1. This localized gel electrolyte strategy offers a practical and scalable approach to stabilizing Zn anodes for next-generation energy storage systems.

α-Methyl Group Reinforced Amphiphilic Poly(Ionic Liquid) Additive for High-Performance Zinc-Iodine Batteries

Aqueous zinc-iodine (Zn-I2) batteries are prospective on energy storage, yet the practical application is severely hindered by side reactions of Zn metal and the shuttle effects for polyiodide. Herein, a polymer additive was copolymerized by 1-vinyl-3-ethylimidazolium trifluoromethanesulfonate (VEImOTf) and methacrylamide (MAAm) (PVEMA) to alleviate the above issues. The polymer chain of PVEMA endows amphipathic properties for Zn2+ diffusion and solvation structure regulation, and the α-methyl of MAAm enhances the hydrophobic properties to avoid side reactions on Zn metal. In addition, the imidazole groups adsorb onto Zn metal with electrostatic shielding effect for further side reaction alleviation and mitigate shuttle effects by electrostatic interactions with polyiodides. Consequently, the PVEMA confers the symmetrical Zn battery with great cycling stability for over 400 h at 20 mA cm-2 and high depth of discharge (DOD) of 77.7%. The Zn-I2 batteries with PVEMA also demonstrate stable cycling performance under various current densities and temperatures.

A Ce3+/4+ Redox Couple-Promoted Aqueous Zinc-Ion Hybrid Capacitor: Design Strategies and Mechanistic Insights

Aqueous zinc-ion hybrid capacitors (ZIHCs) are emerging as promising energy storage devices owing to several desirable attributes including good safety, high power density, and good stability. However, the limited energy density mainly caused by the low specific capacity of porous carbon cathodes hinders the practical application of ZIHCs. A Ce3+/4+ redox couple-promoted aqueous ZIHC (Ce-ZIHC) is designed with the addition of Ce3+/4+ electrolyte additives. The Ce3+/4+ redox couple is shown to markedly increase the specific capacity of the porous carbon cathode energy and enhance the stability of Zn2+ stripping/plating at the Zn metal anode. Notably, the as-constructed Ce-ZIHC performs more than twice the energy density of the ZIHC with the commercial activated carbon cathode. Furthermore, the Ce-ZIHC shows a low self-discharge rate and can work stably for more than 60 000 cycles at 5.0 A g-1. This work highlights the great potential of Ce3+/4+ redox couple in improving the overall performance of ZIHCs toward practical application.

Dual-Mechanism Anchoring of Iodine Species by Pitch-Derived Porous Carbon for Enhanced Zinc-Iodine Battery Performance

Aqueous Zn-I2 battery is an overwhelming candidate for sustainable energy storage systems due to its high safety, low cost, and environmental friendliness. However, the serious self-discharge and the shuttle effect initiated by soluble polyiodides significantly hinder further development. Herein, a pitch-derived carbon (PPCMK) with a unique micro-/mesopores structure and abundant oxygen-containing functional groups is prepared, with dual-mechanism anchoring of iodine species to effectively confine the polyiodides for alleviating the above problems. The rich micropores of PPCMK (0.62 nm) function to inhibit the formation of I3 -, and the large specific surface area enables a high I2 uptake of 64.51%. Moreover, oxygen-containing functional groups of PPCMK further enhance the interaction with I3 - to strengthen the polyiodide confinement. Therefore, the Zn-I2 batteries exhibit a high specific capacity of 236.76 mAh g-1 (4 mgiodine cm-2) with an average Coulombic efficiency of 99.73% at 1 C, low self-discharge rate of 18.18% capacity loss after one-week resting, and superior durability of 20 000 cycles at 20 C with 95.08% retentive capacity. Especially, the pouch cell exhibits a superior area capacitance of 5.51 mAh cm-2 at a high-loading (30 mgiodine cm-2). This study provides an economically effective solution for the large-scale production of high-performance Zn-I2 batteries.

Interfacial Adsorption Layers Based on Amino Acid Analogues to Enable Dual Stabilization toward Long-Life Aqueous Zinc Iodine Batteries

Aqueous zinc-iodine (Zn-I2) batteries are promising candidates for large-scale energy storage due to the merits of low cost and high safety. However, their commercial application is hindered by Zn corrosion and polyiodide shuttle at I2 cathode. Herein, N,N-bis(2-hydroxyethyl)glycine (BHEG) based interfacial adsorption layers are constructed to stabilize Zn anodes and mitigate polyiodide shuttle according to ion-dipole interactions, by using a strategy of electrolyte additive. The tertiary amine (N(CH2)3) and carboxyl (─COO-) groups in the deprotonated BHEG can reversibly capture H+ and dynamically neutralize OH- ions, efficiently buffering the interfacial pH of Zn metal anodes and suppressing hydrogen evolution reactions. Additionally, the BHEG adsorption layers can repel 39.3% of H2O molecules at the Zn interface, creating a "water-deficient" inner Helmholtz plane and preventing Zn corrosion. Significantly, the N(CH2)3 groups in BHEG also inhibit polyiodide shuttle at the I2 cathode, which exhibits high adsorption energies of -0.88, -0.41, and -0.39 eV for I-, I2, and I3 -, respectively. Attributing to these benefits, the Zn-I2 battery can achieve a high areal capacity of 2.99 mAh cm-2 and an extended cycling life of 2,000 cycles, even at a high mass loading of I2 cathode (≈21.5 mg cm-2).

Hydrogel Electrolytes-Based Rechargeable Zinc-Ion Batteries under Harsh Conditions

Rechargeable zinc (Zn)-ion batteries (RZIBs) with hydrogel electrolytes (HEs) have gained significant attention in the last decade owing to their high safety, low cost, sufficient material abundance, and superb environmental friendliness, which is extremely important for wearable energy storage applications. Given that HEs play a critical role in building flexible RZIBs, it is urgent to summarize the recent advances in this field and elucidate the design principles of HEs for practical applications. This review systematically presents the development history, recent advances in the material fundamentals, functional designs, challenges, and prospects of the HEs-based RZIBs. Firstly, the fundamentals, species, and flexible mechanisms of HEs are discussed, along with their compatibility with Zn anodes and various cathodes. Then, the functional designs of hydrogel electrolytes in harsh conditions are comprehensively discussed, including high/low/wide-temperature windows, mechanical deformations (e.g., bending, twisting, and straining), and damages (e.g., cutting, burning, and soaking). Finally, the remaining challenges and future perspectives for advancing HEs-based RZIBs are outlined.

Dual-Additive Synergistic Complementation Electrolyte Engineering with "Job-Sharing" Modulation Mechanism for Long-Lifespan Zn-Iodine Batteries

The large-scale practical application of Zn-iodine batteries (ZIBs) with environmental benignity and cost-effectiveness is hindered by the challenges of poor reversibility of Zn anode and serious polyiodide shuttling. Herein, a dual-additive synergistic complementation electrolyte engineering method is proposed to promote Zn2+ transport, enhance Zn deposition reversibility, and improve iodine conversion kinetics by introducing lactulose and caffeine into 1 M ZnSO4. It is revealed that lactulose can reduce the desolvation barrier by substituting the coordinated water of Zn2+ ions and increase the Zn2+ transference number by hydrogen bond-assisted SO42-/H2O-locking. As a bilateral interfacial stabilizer, high polar caffeine is preferentially adsorbed on the Zn anode owing to its p-π conjugated structure and a "push-pull electron" effect, which renders (002)-textured Zn plating. Furthermore, the conjugated polar system of caffeine can firmly immobilize I3-, further stabilizing the I2/I- redox behavior. Consequently, the Zn//Zn cells deliver dendrite-free Zn stripping/plating cycling for 3500 h at 1 mA cm-2/1 mAh cm-2, and survive over 1300 h even at a high depth of discharge of 71.0%. This "job-sharing" modulation mechanism offers a practical strategy for the development of long-lifespan ZIBs.

Polymeric Iodine Transport Layer Enabled High Areal Capacity Dual Plating Zinc-Iodine Battery

Iodine cathode in aqueous battery has drawn great attention due to its high energy density and high safety. However, iodine has extremely low conductivity of 1×10-7 S cm-1, which usually results in low specific capacity. In this work, a PVA-hydrogel layer was designed to enhance the areal capacity of zinc-iodine cell. The areal capacity of PVA-hydrogel layer modified CNT cathode showed twice as higher capacity than that of pure CNT film in a dual-plating cell, The significant enhancement of the capacity was attributed to the fast iodine transport in the PVA-hydrogel layer. Besides, the strong interaction between PVA chain and polyiodide anions prevented the shuttle effect. The PVA modified CNT cathode could stably operate for over 3000 hours with remarkably higher capacity and cycle life. We analyzed the uniquely fast transport behavior of polyiodides in PVA hydrogel by in situ Raman spectroscopy, in situ optical micrography, as well as DFT calculations. It was found that the strong binding force together with lower dissociation energy of iodine on PVA chain is the dominate reason for reduced shuttle effect and fast polyiodide transport. As a result, the assembled PVA-I2 pouch cells showed excellent performance in both dual-plating cells and conventional-type cells.

Zinc Single-Atom Catalysts Encapsulated in Hierarchical Porous Bio-Carbon Synergistically Enhances Fast Iodine Conversion and Efficient Polyiodide Confinement for Zn-I2 Batteries

Aqueous zinc iodine (Zn-I2) batteries have attracted attention due to their low cost, environmental compatibility, and high specific capacity. However, their development is hindered by the severe shuttle effect of polyiodides and the slow redox conversion kinetics of the iodine (I2) cathode. Herein, a long-life Zn-I2 battery is developed by anchoring iodine within an edible fungus slag-derived carbon matrix encapsulated with Zn single-atom catalysts (SAZn@CFS). The high N content and microporous structure of SAZn@CFS provide a strong iodine confinement, while the Zn-N4-C sites chemical interact with polyiodides effectively mitigating the iodine dissolution and the polyiodide shuttle effect. Additionally, the uniformly distributed SAZn sites significantly enhance the redox conversion efficiency of I-/I3 -/I5 -/I2, leading to improved capacity. At a high current density of 10 A g-1, the designed Zn-I2 battery delivers an excellent capacity of 147.2 mAh g-1 and a long lifespan of over 80 000 cycles with 93.6% capacity retention. Furthermore, the battery exhibits stable operation for 3500 times even at 50 °C, demonstrating significant advances in iodine reversible storage. This synergistic strategy optimizes composite structure, offering a practical approach to meet the requirements of high-performance Zn-I2 batteries.

Iodine/Chlorine Multi-Electron Conversion Realizes High Energy Density Zinc-Iodine Batteries

Aqueous zinc-iodine (Zn-I2) batteries are promising energy storage devices; however, the conventional single-electron reaction potential and energy density of iodine cathode are inadequate for practical applications. Activation of high-valence iodine cathode reactions has evoked a compelling direction to developing high-voltage zinc-iodine batteries. Herein, ethylene glycol (EG) is proposed as a co-solvent in a water-in-deep eutectic solvent (WiDES) electrolyte, enabling significant utilization of two-electron-transfer I+/I0/I- reactions and facilitating an additional reversibility of Cl0/Cl- redox reaction. Spectroscopic characterizations and calculations analyses reveal that EG integrates into the Zn2+ solvation structure as a hydrogen-bond donor, competitively binding O atoms in H2O, which triggers a transition from water-rich to water-poor clusters of Zn2+, effectively disrupting the H2O hydrogen-bond network. Consequently, the aqueous Zn-I2 cell achieves an exceptional capacity of 987 mAh gI2 -1 with an energy density of 1278 Wh kgI2 -1, marking an enhancement of ≈300 mAh g-1 compared to electrolyte devoid of EG, and enhancing the Coulombic efficiency (CE) from 68.2% to 98.7%. Moreover, the pouch cell exhibits 3.72 mAh cm-2 capacity with an energy density of 4.52 mWh cm-2, exhibiting robust cycling stability. Overall, this work contributes to the further development of high-valence and high-capacity aqueous Zn-I2 batteries.

Breaking Mass Transport Limit for Hydrogen Evolution-Inhibited and Dendrite-Free Aqueous Zn Batteries

It is commonly accepted that batteries perform better at low current densities below the mass-transport limit, which restricts their current rate and capacity. Here, it is demonstrated that the performance of Zn metal electrodes can be dramatically enhanced at current densities and cut-off capacities exceeding the mass-transport limit by using pulsed-current protocols. These protocols achieve cumulative plating/stripping capacities of 11.0 Ah cm-2 and 3.8 Ah cm-2 at record-high current densities of 80 and 160 mA cm-2, respectively. The study identifies and understands the promoted (002)-textured Zn growth and suppressed hydrogen evolution based on the thermodynamics and kinetics of competing reactions. Furthermore, the over-limiting pulsed-current protocol enables long-life Zn batteries with high mass loading (29 mgcathode cm-2) and high areal capacity (7.9 mAh cm-2), outperforming cells using constant-current protocols at equivalent energy and time costs. The work provides a comprehensive understanding of the current-capacity-performance relationship in Zn plating/stripping and offers an effective strategy for dendrite-free metal batteries that meet practical requirements for high capacity and high current rates.

Versatile Biopolymers for Advanced Lithium and Zinc Metal Batteries

Lithium (Li) and zinc (Zn) metals are emerging as promising anode materials for next-generation rechargeable metal batteries due to their excellent electronic conductivity and high theoretical capacities. However, issues such as uneven metal ion deposition and uncontrolled dendrite growth result in poor electrochemical stability, limited cycle life, and rapid capacity decay. Biopolymers, recognized for their abundance, cost-effectiveness, biodegradability, tunable structures, and adjustable properties, offer a compelling solution to these challenges. This review systematically and comprehensively examines biopolymers and their protective mechanisms for Li and Zn metal anodes. It begins with an overview of biopolymers, detailing key types, their structures, and properties. The review then explores recent advancements in the application of biopolymers as artificial solid electrolyte interphases, electrolyte additives, separators, and solid-state electrolytes, emphasizing how their structural properties enhance protection mechanisms and improve electrochemical performance. Finally, perspectives on current challenges and future research directions in this evolving field are provided.

A tripartite synergistic optimization strategy for zinc-iodine batteries

The energy industry has taken notice of zinc-iodine (Zn-I2) batteries for their high safety, low cost, and attractive energy density. However, the shuttling of I3- by-products at cathode electrode and dendrite issues at Zn metal anode result in short cycle lifespan. Here, a tripartite synergistic optimization strategy is proposed, involving a MXene cathode host, a n-butanol electrolyte additive, and the in-situ solid electrolyte interface (SEI) protection. The MXene possesses catalytic ability to enhance the reaction kinetics and reduce I3- by-products. Meanwhile, the partially dissolved n-butanol additive can work synergistically with MXene to inhibit the shuttling of I3-. Besides, the n-butanol and I- in the electrolyte can synergistically improve the solvation structure of Zn2+. Moreover, an organic-inorganic hybrid SEI is in situ generated on the surface of the Zn anode, which induces stable non-dendritic zinc deposition. As a result, the fabricated batteries exhibit a high capacity of 0.30 mAh cm-2 and a superior energy density of 0.34 mWh cm-2 at a high specific current of 5 A g-1 across 30,000 cycles, with a minimal capacity decay of 0.0004% per cycle. This work offers a promising strategy for the subsequent research to comprehensively improve battery performance.

Physical Field Effects to Suppress Polysulfide Shuttling in Lithium-Sulfur Battery

Lithium-sulfur batteries (LSB) with high theoretical energy density are plagued by the infamous shuttle effect of lithium polysulfide (LPS) and the sluggish sulfur reduction/evolution reaction. Extensive research is conducted on how to suppress shuttle effects, including physical structure confinement engineering, chemical adsorption strategy, and the design of sulfur redox catalysts. Recently, the rational design to mitigate shuttle effects and enhance reaction kinetics based on physical field effects has been widely studied, providing a more fundamental understanding of interactions with sulfur species. Herein, the physical field effect is focused and their methods and mechanisms of interaction are summarized systematically with LPS. Overall, the working principle of LSB system, the origin of the shuttle effect, and kinetic trouble in LSB are briefly described. Then, the mechanism and application of rational design of materials based on physical field effect concepts and the external physical field-assisted LSB are elaborated, including electrostatic force, built-in electric field, spin state regulation, strain engineering, external magnetic field, photoassisted and other physical field-assisted strategies are pivotally elaborated and discussed. Finally, the potential directions of physical field effects in enhancing the performance and weakening the shuttle effect of high-energy LSB are summarized and anticipated.

Toward High-Energy-Density Aqueous Zinc-Iodine Batteries: Multielectron Pathways

Aqueous zinc-iodine batteries (ZIBs) based on the reversible conversion between various iodine species have garnered global attention due to their advantages of fast redox kinetics, good reversibility, and multielectron conversion feasibility. Although significant progress has been achieved in ZIBs with the two-electron I-/I2 pathway (2eZIBs), their relatively low energy density has hindered practical application. Recently, ZIBs with four-electron I-/I2/I+ electrochemistry (4eZIBs) have shown a significant improvement in energy density. Nonetheless, the practical use of 4eZIBs is challenged by poor redox reversibility due to polyiodide shuttling during I-/I2 conversion and I+ hydrolysis during I2/I+ conversion. In this Review, we thoroughly summarize the fundamental understanding of two ZIBs, including reaction mechanisms, limitations, and improvement strategies. Importantly, we provide an intuitive evaluation on the energy density of ZIBs to assess their practical potential and highlight the critical impacts of the Zn utilization rate. Finally, we emphasize the cost issues associated with iodine electrodes and propose potential closed-loop recycling routes for sustainable energy storage with ZIBs. These findings aim to motivate the practical application of advanced ZIBs and promote sustainable global energy storage.

Mullite Mineral-Derived Robust Solid Electrolyte Enables Polyiodide Shuttle-Free Zinc-Iodine Batteries

Zinc dendrite, active iodine dissolution, and polyiodide shuttle caused by the strong interaction between liquid electrolyte and solid electrode are the chief culprits for the capacity attenuation of aqueous zinc-iodine batteries (ZIBs). Herein, mullite is adopted as raw material to prepare Zn-based solid-state electrolyte (Zn-ML) for ZIBs through zinc ion exchange strategy. Owing to the merits of low electronic conductivity, low zinc diffusion energy barrier, and strong polyiodide adsorption capability, Zn-ML electrolyte can effectively isolate the redox reactions of zinc anode and AC@I2 cathode, guide the reversible zinc deposition behavior, and inhibit the active iodine dissolution as well as polyiodide shuttle during cycling process. As expected, wide operating voltage window of 2.7 V (vs Zn2+/Zn), high Zn2+ transference number of 0.51, and low activation energy barrier of 29.7 kJ mol-1 can be achieved for the solid-state Zn//Zn cells. Meanwhile, high reversible capacity of 127.4 and 107.6 mAh g-1 can be maintained at 0.5 and 1 A g-1 after 3 000 and 2 100 cycles for the solid-state Zn//AC@I2 batteries, corresponding to high-capacity retention ratio of 85.2% and 80.7%, respectively. This study will inspire the development of mineral-derived solid electrolyte, and facilitate its application in Zn-based secondary batteries.