Regulating Zn Ion Desolvation and Deposition Chemistry Toward Durable and Fast Rechargeable Zn Metal Batteries

Inorganic-metal hybrid coating for stabilizing and regulating aqueous zinc anodes

Aqueous zinc ion batteries (ZIBs) are expected to be the next generation of energy storage devices. However, the unwanted dendrites growth on zinc anodes, hydrogen evolution and other side reactions hinder the practical application of ZIBs. Here, we designed a novel inorganic-metal hybrid coating with an optimised electric double layer structure at the zinc anode/electrolyte interface. The hybrid coating effectively promotes ionic desolvation, reduces the nucleation overpotential, and suppresses the 2D diffusion process. Furthermore, the coating has good stability and inhibits the dendrites growth, hydrogen precipitation corrosion, and by-products generation. Consequently, the hybrid coating-modified Zn anode exhibited excellent electrochemical performance. Among them, the symmetric cell was able to cycle for 1480 h at 1 mA cm-2, 1 mAh cm-2 with an overpotential of ∼34 mV. The symmetric cell achieved a cycle life of ∼1000 h even at a high current of 3 mA cm-2. The cycling performance and multiplication rate performance in full cells were also demonstrated. This work shows the effectiveness and feasibility of hybrid coating to modulate zinc anode/electrolyte interface.

Cr2O3-x artificial interfacial layer featuring abundant nucleation sites: Facilitating rapid Zn2+ transport and highly reversible Zn anode

Interfacial engineering offers a promising solution to zinc anode instability, yet most studies focus solely on suppressing side reactions with water, overlooking the critical role of fast zinc ion kinetics. This work investigates the Cr2O3-x artificial interface layer, demonstrating its dual benefits of electrostatic shielding and enhanced Zn2+ transport kinetics. The Cr2O3-x layer exhibits excellent mechanical stability and hydrophilicity, with its negatively charged surface effectively repelling anions like SO42- and OH- to suppress side reactions. Moreover, the highly active Cr2O3-x layer accelerates Zn2+ migration, reduces nucleation energy barriers, and promotes uniform zinc deposition by facilitating Zn2+ detachment from solvated structures. As a result, the Cr2O3-x@Zn anode achieves exceptional cycling stability and remarkable reversibility, with symmetric batteries enduring over 1,800 h at 5 mA cm-2. When paired with NH4V4O10, it also demonstrates long cycle life and superior rate performance. This work sheds new light on the development of stable, high-performance zinc anodes.

Practical issues toward high-voltage aqueous rechargeable batteries

This review offers a critical and exhaustive examination of the current state and innovative advances in high-voltage Li, Na, K, and Zn aqueous rechargeable batteries, an area poised for significant technological breakthroughs in energy storage systems. The practical issues that have traditionally hampered the development of aqueous batteries, such as limited operating potential windows, challenges in stable solid-electrolyte interphase (SEI) formation, the need for active materials optimized for aqueous environments, the misunderstood intercalation chemistry, the unreliable assessment techniques, and the overestimated performance and underestimated physicochemical and electrochemical drawbacks, are highlighted. We believe that this review not only brings together existing knowledge but also pushes the boundaries by providing a roadmap for future research and development efforts aimed at overcoming the longstanding challenges faced by the promising aqueous rechargeable batteries.

Anion-endowed high-dielectric water-deficient interface towards ultrastable Zn metal batteries

To achieve reversible metallic Zn anodes for aqueous rechargeable zinc batteries, regulating the electrolyte-Zn interface is the key to addressing the side reactions on Zn. Beyond water-deficiency, design rules for constructing the highly efficient electrochemical interface are still vague. Anions, as primary electrolyte constituents, not only play a role in solvation structure, but also influence the electrolyte-Zn interface. Here, the characteristics of representative anions in current aqueous zinc electrolytes are surveyed. A candidate combining polarizability, H-bond tuning ability and high solubility is proposed to construct a high-dielectric water-deficient electrolyte-Zn interface to regulate the interfacial chemistry on Zn. The anion-dominated electrochemical interface promotes the Zn deposition kinetics and achieves uniform Zn deposition with high stability, which further enables the in situ formation of an SEI for highly stable Zn stripping/plating, e.g., at 20 mA cm-2 and 20 mA h cm-2. Furthermore, this built-in interface exhibits an effect in stabilizing the V2O5 cathode, endowing the V2O5/Zn cell with ultra-stable long-term cycling, e.g., 10 000 cycles at 10 A g-1 with a high retention rate of 89.7%. Our design offers insight into guidelines for the development of novel electrolytes towards rationally designed electrochemical interfaces.

Sulfhydryl and Sulfonic Acid Bifunctional Group Achieving (101) Crystal Preferential Reversible Zn2+ Electrodeposition Without Dendrite and Nucleation Overpotential

Disordered electrodeposition of Zn2+ resulted in serious dendrite and hydrogen evolution reactions, greatly decreasing the energy efficiency and durability of aqueous zinc ion batteries (AZIBs). Herein, sodium 2-mercaptoethanesulfonate (MSN) is proposed as a new additive to achieve induced directional electrodeposition of Zn2+ on the Zn (101) crystal surface to form a dense uniform Zn metal layer via the cooperative effect of sulfhydryl and sulfonic acid groups. Different from the reported additives, MSN molecules promote the rapid formation of the Zn2+ adsorption layer, which greatly accelerates its directed migration rate and orderly nucleation process, achieving eliminated zinc dendrites and nucleation overpotential, far superior to the reported additives. The MSN-introduced Zn||Zn symmetric battery displays amazing durability and is stably cycled for more than 3500 h at 2 mA cm-2 @ 2 mAh cm-2, and over 1 000 h even under harsh conditions (5 mA cm-2 @ 5 mAh cm-2). Furthermore, the Zn||δ-MnO2 coin battery offers a high capacity of 201.5 mAh g-1 and a low recession rate of 1% during 800 cycles at 1 A g-1, far higher than that of the blank sample (121.3 mAh g-1, 56.1%), respectively, fully demonstrating the extraordinary advantages and contributions of the new MSN molecules.

Bi-Functional Agarose-Filled Porous Polysulfone Protective Layer for Dendrite-Free Zn Anode

The uneven electric field and slow Zn2+ desolvation lead to rapid dendrite growth during Zn plating and stripping, which severely deteriorates the performance of Zn metal anodes (ZMAs) in Zn-ion batteries (ZIBs). Although polymer-based artificial protective (PBAP) layers are widely applied to homogenize the electric field of ZMAs, they often fail to promote the desolvation process that eventually induces Zn dendrite growth. Herein, a bi-functional protective layer, comprising a finger-like porous matrix of polysulfone (PSF) and a hydroxyl-rich filler of agarose (AG), is constructed to suppress Zn dendrite growth. COMSOL simulation demonstrates the ZMAs with bi-functional protective layers (Zn@PSF/AG) exhibit uniform electric field and Zn2+ distribution. Besides, the Zn@PSF/AG has both low desolvation energy and nucleation overpotential, effectively promoting the desolvation of Zn2+. Therefore, the Zn@PSF/AG symmetric cell exhibits excellent cycling performance, achieving 4200 h at 1 mA cm-2/1 mAh cm-2 and 1000 h at 5 mA cm-2/5 mAh cm-2. When coupling with ZnxV2O5 (ZnVO) cathode, the ZnVO‖Zn@PSF/AG full cell shows similarly high cycling stability, maintaining 72% of its capacity after 7000 cycles at 10 A g-1. This research highlights the positive roles of PBAP layer with multi-functional matrix-filler structure in developing long-life ZIBs.

Polyhydroxy Sodium Salt Additive to Regulate Zn2+ Solvation Structure and Zn Deposition Texture for High-Stability and Long-Life Aqueous Zinc Batteries

Electrolyte additives are commonly employed in aqueous zinc-ion batteries (ZIBs) to suppress dendrite growth, corrosion, and hydrogen evolution. However, rational design principles and systematic mechanistic studies for selecting suitable additives to regulate reversible Zn plating/stripping chemistry are worth in-depth study. Using L-ascorbic acid sodium (LAAS) as the representative, theoretical calculations combined with in situ experimental analyses manifest that polyhydroxy-sodium-salts preferentially chemisorbed on Zn surface to construct the H2O-poor interfacial microenvironment, suppressing undesirable water-related side reactions. Concurrently, sodium ions provide an armor shielding layer to regulate the electric field to guide (002) Zn deposition texture. Specifically, sodium-salts replace H2O molecules in the coordinated shell of hydrated Zn2+ ions, improving the electrochemical stability window (ESW) to extend the working voltage of the aqueous ZIBs. Therefore, Zn||Zn symmetric cell with polyhydroxy-sodium-salts additive exhibits impressive cumulative capacity of 7875 mAh cm-2 at high current density of 30 mA cm-2. Even when the discharge voltage expands to 1.8 V, Zn||V2O5 full cell realizes a capacity retention of 98.26% for over 500 cycles. This work quickens the design of advanced aqueous ZIBs by green and cheap electrolyte additive, which is expected to herald an innovative phase of research on high-stability aqueous batteries.

Promoting Migration Kinetic of Desolvated Zn2+ by Functional Interlayer Toward Superior Zn Metal Anode

The development of Zn metal anodes is challenged by non-uniformity of ion flux causing inhomogeneous deposition and strong solvation of Zn(H2O)6 2+ resulting in adverse side reactions. Applying intermediate protecting layers with high affinity to Zn2+ is a popular and effective solution, but it also limits the ion migration. A functional MXene-based interlayer is designed in this work to modify the glass fiber separator achieving balanced adsorption energy and ion migration. By coating porous silica on the MXene surface, the instinct advanatges of MXene are mostly reserved while the adsorption energy to Zn2+ is optimized. Such an interlayer enables high flux and uniformity of desolvated Zn2+, contributing to rapid deposition kinetic for excellent rate performance and inhibited side reactions for long-term cycling stability. As a result, the functionalized Zn metal anode delivers steady plating/stripping cycles for more than 5000 h at 0.1 mA cm-2 and 700 h at 5.0 mA cm-2. The Zn||MnO2 full cells with this separator also exhibit superior rate capabilities (173 mAh g-1 at 2.0 A g-1) and excellent cycle performance (254.7 mAh g-1 after 1000 cycles at 0.5 A g-1). This work provides a feasible strategy for preparing functional interlayers toward superior Zn or other metal anodes.

Suppressing Hydrogen Evolution and Dendrite Formation on a Zn Anode by Coating In2O3 with Tailored Affinity to H* and Zn

To suppress the hydrogen evolution reaction (HER) and dendrite formation on the Zn anode in aqueous Zn-ion batteries, a submicrometer In2O3 coating on the Zn anode (referred to as Zn@In2O3) was constructed via magnetron sputtering. Density functional theory (DFT) and experimental data show that the In2O3 coating suppresses the HER because of its weaker interactions with H* compared with Zn, inhibiting the Volmer step. At the same time, the In2O3 coating exhibits a moderate affinity for Zn*, higher than that on Zn but lower than that at the In2O3-Zn interface, thus facilitating the desolvation of the hydrated Zn2+ ions while promoting its deposition on the Zn substrate beneath the In2O3 coating. The resultant suppression of side reactions and dendrite growth significantly enhance the reversible plating/stripping of Zn. The optimized Zn@In2O3 stably cycles over 6400 h with a low voltage hysteresis of 9.5 mV at 1 mA cm-2 and 1 mAh cm-2 in symmetric cells. The average Coulombic efficiency of Zn plating/stripping is increased from 95.8 to 99.6% owing to the In2O3 coating. Moreover, when coupled with the Mn0.15V2O5·nH2O cathode, the Zn@In2O3 battery maintains a capacity retention of 78.6% after 2000 cycles at 5 A g-1. This facile and economical modification of Zn anodes provides an idea for realizing the practical application of AZIBs.

Fundamentals, Advances and Perspectives in Designing Eutectic Electrolytes for Zinc-Ion Secondary Batteries

Zinc-ion secondary batteries have been competitive candidates since the "post-lithium-ion" era for grid-scale energy storage, owing to their plausible security, high theoretical capacity, plentiful resources, and environment friendliness. However, many encumbrances like notorious parasitic reactions and Zn dendrite growth hinder the development of zinc-ion secondary batteries remarkably. Faced with these challenges, eutectic electrolytes have aroused notable attention by virtue of feasible synthesis and high tunability. This review discusses the definition and advanced functionalities of eutectic electrolytes in detail and divides them into nonaqueous, aqueous, and solid-state eutectic electrolytes with regard to the state and component of electrolytes. In particular, the corresponding chemistry concerning solvation structure regulation, electric double layer (EDL) structure, solid-electrolyte interface (SEI) and charge/ion transport mechanism is systematically elucidated for a deeper understanding of eutectic electrolytes. Moreover, the remaining limitations and further development of eutectic electrolytes are discussed for advanced electrolyte design and extended applications.

Synergistic Gradient Anodes for Long-Term Stability in Aqueous Zinc-Ion Batteries

The stability of aqueous zinc metal anodes is still constrained by their severe dendrite growth. Optimizing electric field distribution and crystallography to modulate the diffusion and deposition behavior of zinc ions can effectively suppress dendrite growth. However, the fabrication strategy to directly endow specific textured zinc anodes with gradient electric field distribution is still lacking. Herein, a strategy combining crystal reconstruction of commercial zinc foil with graphene oxide (GO) protective layer is proposed to construct an in situ gradient electric field-enhanced strong (002) textured GO@ZnO/Zn(002) anode. Based on the experimental and theoretical results, the GO protective layer can regulate a wide-range homogeneous Zn2+ ions flow, while the dense and uniform ZnO/Zn(002) nanoneedles /nanoparticles can enhance localized polarized electric field to accelerate rapid localized transfer of Zn2+ ions and guide them toward directional deposition along (002) plane. Therefore, the hierarchical GO@ZnO/Zn(002) anode enables the symmetric cell to operate continuously and stably for 5700 and 4200 h at 2 and 4 mA cm-2, respectively, which is comparable to or better than most high-end Zn anodes. This work presents new insights into the zinc foil reconstruction and gradient electric field fabrication strategy, offering a scalable approach for the development of long-term stable metal anodes.

Double Network Gel Electrolyte with High Ionic Conductivity and Mechanical Strength for Zinc-Ion Batteries

Gel electrolytes hold promise for stabilizing zinc-ion batteries (ZIBs), but achieving both high ionic conductivity and strong mechanical properties remains challenging. This work presents a double network gel electrolyte based on poly(N-hydroxymethyl acrylamide) (PNMA) and sodium alginate (SA), overcoming this trade-off. The PNMA network provides mechanical strength and water retention, while the SA network facilitates rapid zinc-ion (Zn2+) diffusion through tailored solvation. This double network gel exhibits a tensile strength of up to 838 kPa, significantly higher than previous reports. The SA network provides ion channels for rapid transport of hydrated Zn2+, enhancing the ionic conductivity to a ground-breaking 33.1 mS cm-1. This value is even higher than the liquid electrolytes. The growth of Zn dendrites is also suppressed due to the mechanical constraint and rapid ion conduction. In symmetrical cells, the PNMA/SA gel demonstrates exceptional cycling stability (>2000 h). Characterizations show this is because of reduced free water amount, hindering cathode material dissolution. The full cells with sodium vanadate cathode manifest a high capacity (364.8 mA h g-1 at 0.5 A g-1) and excellent capacity retention (83% after 2500 cycles at 10 A g-1). This double network design offers a way to achieve high-performance and stable ZIBs.

Biomass-derived polymer as a flexible "zincophilic-hydrophobic" solid electrolyte interphase layer to enable practical Zn metal anodes

Aqueous zinc ion batteries (AZIBs) face significant challenges stemming from Zn dendrite growth and water-contact attack, primarily due to the lack of a well-designed solid electrolyte interphase (SEI) to safeguard the Zn anode. Herein, we report a bio-mass derived polymer of chitin on Zn anode (Zn@chitin) as a novel and robust artificial SEI layer to boost the Zn anode rechargeability. The polymeric chitin SEI layer features both zincophilic and hydrophobic characteristics to target the suppressed dendritic Zn formation as well as the water-induced side reactions, thus harvesting a dendrite-free and corrosion-resistant Zn anode. More importantly, this polymeric interphase layer is strong and flexible accommodating the volume changes during repeated cycling. Based on these benefits, the Zn@chitin anode demonstrates prolonged cycling performance surpassing 1300 h under an ultra-large current density of 20 mA cm-2, and a long cycle life of 680 h with a record-high zinc utilization rate of 80 %. Besides, the assembled Zn@chitin/V2O5 full batteries reveal excellent capacity retention and rate performance under practical conditions, proving the reliability of our proposed strategy for industrial AZIBs. Our research offers valuable insights for constructing high-performance AZIBs, and simultaneously realizes the high-efficient use of cheap biomass from a "waste-to-wealth" concept.

Solidify Eutectic Electrolytes via the Added MXene as Nucleation Sites for a Solid-State Zinc-Ion Battery with Reconstructed Ion Transport

Stationary energy storage infrastructure based on zinc-ion transport and storage chemistry is attracting more attention due to favorable metrics, including cost, safety, and recycling feasibility. However, splitting water and liquid electrolyte fluidity lead to cathode dissolution and Zn corrosion, resulting in rapid attenuation of the capacity and service life. Herein, a new architecture of solid-state electrolytes with high zinc ionic conductivity at room temperature was prepared via solidification of deep eutectic solvents utilizing MXene as nucleation additives. The ionic conductivity of MXene/ZCEs reached 6.69 × 10-4 S cm-1 at room temperature. Dendrite-free Zn plating/stripping with high reversibility can remain for over 2500 h. Subsequently, the fabricated solid-state zinc-ion battery with eliminated HER and suppressed Zn dendrites exhibited excellent cycling performance and could work normally in a range from -10 to 60 °C. This design inspired by eutectic solidification affords new insights into the multivalent solid electrochemistry suffering from slow ion migration.

Regulating Desolvation Activation Energy and Zn Deposition via a CTAB-Intercalated Mg-Al-Layered Double-Hydroxide Protective Layer for Durable Zn Metal Anodes

While aqueous Zn-ion batteries (AZIBs) are widely considered as a promising energy storage system due to their merits of low cost, high specific capacity, and safety, the practical implementation has been hindered by the Zn dendrite growth and undesirable parasitic reactions. To address these issues, a unique hydrophobic-ion-conducting cetyltrimethylammonium bromide-intercalated Mg-Al-layered double-hydroxide protective layer was constructed on the Zn anode (OMALDH-Zn) to modulate the nucleation behavior and desolvation process. The hydrophobic cetyl group long chain can inhibit the hydrogen evolution reaction and Zn corrosion by repelling water molecules from the anode surface and reducing the desolvation activation energy. Meanwhile, the Mg-Al LDH with abundant zincophilic active sites can modulate the Zn2+ ion flux, enabling the dendrite-free Zn deposition. Benefiting from this interfacial synergy, a long cycle life (>2300 h) with low and stable overpotential (<18 mV at 1 mA cm-2) and excellent Coulombic efficiency (99.4%) for symmetrical and asymmetrical batteries were achieved. More impressively, excellent rate performance and long cyclic stability have been realized by OMALDH-Zn//MnO2 batteries in both coin-type and pouch-type devices. This low-cost, simple, and high-efficiency coordinated modulation method provides a reliable strategy for the practical application of AZIBs.

Water Catchers within Sub-Nano Channels Promote Step-by-Step Zinc-Ion Dehydration Enable Highly Efficient Aqueous Zinc-Metal Batteries

Zinc metal suffers from violent and long-lasting water-induced side reactions and uncontrollable dendritic Zn growth, which seriously reduce the coulombic efficiency (CE) and lifespan of aqueous zinc-metal batteries (AZMBs). To suppress the corresponding harmful effects of the highly active water, a stable zirconium-based metal-organic framework with water catchers decorated inside its sub-nano channels is used to protect Zn-metal. Water catchers within narrow channels can constantly trap water molecules from the solvated Zn-ions and facilitate step-by-step desolvation/dehydration, thereby promoting the formation of an aggregative electrolyte configuration, which consequently eliminates water-induced corrosion and side reactions. More importantly, the functionalized sub-nano channels also act as ion rectifiers and promote fast but even Zn-ions transport, thereby leading to a dendrite-free Zn metal. As a result, the protected Zn metal demonstrates an unprecedented cycling stability of more than 10 000 h and an ultra-high average CE of 99.92% during 4000 cycles. More inspiringly, a practical NH4V4O10//Zn pouch-cell is fabricated and delivers a capacity of 98 mAh (under high cathode mass loading of 25.7 mg cm-2) and preserves 86.2% capacity retention after 150 cycles. This new strategy in promoting highly reversible Zn metal anodes would spur the practical utilization of AZMBs.

Chelating Additive Regulating Zn-Ion Solvation Chemistry for Highly Efficient Aqueous Zinc-Metal Battery

Aqueous zinc-metal batteries (AZMBs) usually suffered from poor reversibility and limited lifespan because of serious water induced side-reactions, hydrogen evolution reactions (HER) and rampant zinc (Zn) dendrite growth. Reducing the content of water molecules within Zn-ion solvation sheaths can effectively suppress those inherent defects of AZMBs. In this work, we originally discovered that the two carbonyl groups of N-Acetyl-ϵ-caprolactam (N-ac) chelating ligand can serve as dual solvation sites to coordinate with Zn2+, thereby minimizing water molecules within Zn-ion solvation sheaths, and greatly inhibit water-induced side-reactions and HER. Moreover, the N-ac chelating additive can form a unique physical barrier interface on Zn surface, preventing the harmful contacting with water. In addition, the preferential adsorption of N-ac on Zn (002) facets can promote highly reversible and dendrite-free Zn2+ deposition. As a result, Zn//Cu half-cell within N-ac added electrolyte delivered ultra-high 99.89 % Coulombic efficiency during 8000 cycles. Zn//Zn symmetric cells also demonstrated unprecedented long life of more than 9800 hours (over one year). Aqueous Zn//ZnV6O16 ⋅ 8H2O (Zn//ZVO) full-cell preserved 78 % capacity even after ultra-long 2000 cycles. A more practical pouch-cell was also obtained (90.2 % capacity after 100 cycles). This method offers a promising strategy for accelerating the development of highly efficient AZMBs.

Insight into Sulfur-Containing Zwitter-Molecule Boosting Zn Anode: from Electrolytes to Electrodes

Numerous organic electrolytes additives have been reported to improve Zn anode performance in aqueous Zn metal batteries (AZMBs). However, the modification mechanism needs to be further revealed in consideration of different environments for electrolytes and electrodes during the charge-discharge process. Herein, sulfur-containing zwitter-molecule (methionine, Met) is used as an additive for ZnSO4 electrolytes. In electrolytes, Met reduces the H2O coordination number and facilitates the desolvation process by virtue of functional groups (─COOH, ─NH2, C─S─C), accelerating Zn2+ transference kinetics and decreasing the amount of active water. On electrodes, Met prefers to adsorb on Zn (002) plane and further transforms into a zincophilic protective layer containing C─SOx─C through an in situ electrochemical oxidization, suppressing H2 evolution/corrosion reactions and guiding dendrite-free Zn deposition. By using Met-containing ZnSO4 electrolytes, the Zn//Zn cells show superior cycling performance under 30 mA cm-2/30 mA h cm-2. Moreover, the full cells Zn//NH4V4O10 full cells using the modified electrolytes exhibit good performance at temperatures from -8 to 60 °C. Notably, a high energy density of 105.30 W h kg-1 can be delivered using a low N/P ratio of 1.2, showing a promising prospect of Met electrolytes additives for practical use.

Three-Phase-Heterojunction Cu/Cu2O-Sb2O3 Catalyst Enables Efficient CO2 Electroreduction to CO and High-Performance Aqueous Zn-CO2 Battery

Zn-CO2 batteries are excellent candidates for both electrical energy output and CO2 utilization, whereas the main challenge is to design electrocatalysts for electrocatalytic CO2 reduction reactions with high selectivity and low cost. Herein, the three-phase heterojunction Cu-based electrocatalyst (Cu/Cu2O-Sb2O3-15) is synthesized and evaluated for highly selective CO2 reduction to CO, which shows the highest faradaic efficiency of 96.3% at -1.3 V versus reversible hydrogen electrode, exceeding the previously reported best values for Cu-based materials. In situ spectroscopy and theoretical analysis indicate that the Sb incorporation into the three-phase heterojunction Cu/Cu2O-Sb2O3-15 nanomaterial promotes the formation of key *COOH intermediates compared with the normal Cu/Cu2O composites. Furthermore, the rechargeable aqueous Zn-CO2 battery assembled with Cu/Cu2O-Sb2O3-15 as the cathode harvests a peak power density of 3.01 mW cm-2 as well as outstanding cycling stability of 417 cycles. This research provides fresh perspectives for designing advanced cathodic electrocatalysts for rechargeable Zn-CO2 batteries with high-efficient electricity output together with CO2 utilization.

Direct Growth of a Polymer Film to Induce Horizontal Orientation of Zn4(OH)6SO4·xH2O for Stable Zn Metal Batteries

The loose and randomly oriented byproduct (i.e., Zn4(OH)6SO4·xH2O, ZHS) in situ formed on the zinc (Zn) surface is recognized to be the primary cause for dendritic Zn growth and side reactions. Switching the detrimental passivation film into a dense and kinetically favorable solid electrolyte interphase (SEI) is a straightforward strategy to tackle these issues faced by Zn metal anodes but remains largely unexplored. Herein, a new polymer film directly grown on Zn metal through room-temperature plasma-enhanced chemical vapor deposition is proposed to induce the lateral growth of ZHS nanosheets and decrease the Zn2+ desolvation barrier, thereby forming a beneficial composite SEI for suppressing Zn dendrite growth and surface corrosion. As a result of the joint effect, we realize an impressively stable cycling behavior in symmetric cell over 3400 h at 2 mA cm-2. Moreover, full cells also demonstrate prolonged lifespans. This work opens a new avenue for stabilizing Zn metal batteries by turning detrimental ZHS into a favorable interlayer.

Separator Design Strategies to Advance Rechargeable Aqueous Zinc Ion Batteries

With the increasing demand for low-cost and high-safety portable batteries, aqueous zinc-ion batteries (ZIBs) have been regarded as a potential alternative to the lithium-ion batteries, bringing about extensive research dedicated in the exploration of high-performance and highly reversible ZIBs. Although separators are generally considered as non-active components in conventional research on ZIBs, advanced separators designs seem to offer effective solutions to the majority of issues within ZIBs system. These issues encompass concerns related to the zinc anode, cathode, and electrolyte. Initially, we delve into the origins and implications of various inherent problems within the ZIBs system. Subsequently, we present the latest research advancements in addressing these challenges through separators engineering. This includes a comprehensive, detailed exploration of various strategies, coupled with instances of advanced characterizations to provide a more profound insight into the mechanisms that influence the separators. Finally, we undertake a multi-criteria evaluation, based on application standards for diverse substrate separators, while proposing guiding principles for the optimal design of separators in zinc batteries. This review aims to furnish valuable guidance for the future development of advanced separators, thereby nurturing progress in the field of ZIBs.

Controllable synthesis of electric double-layer capacitance and pseudocapacitance coupled porous carbon cathode material for zinc-ion hybrid capacitors

The designability of the porous structure of carbon material makes it a popular material for zinc-ion hybrid capacitors (ZIHCs). However, the micropore confinement effect leads to sluggish kinetics and is not well resolved yet. In this work, a pore-size controllable carbon material was designed to enhance ion accessibility. The experimental and calculated results revealed that suitable pore sizes and defects were beneficial to ion transfer/adsorption. Meanwhile, oxygen-containing functional groups could introduce a pseudocapacitance reaction. Its large specific surface area and interconnecting network structure could shorten the ion/electron transfer length to reach high ion adsorption capacity and fast kinetic behavior. When used as a zinc-ion hybrid capacitor cathode material, it showed 9.9 kW kg-1 power density and 100 W h kg-1 energy density. Even at 5 A g-1, after 50 000 cycles, there was still 93% capacity retention. Systemic ex situ characterization and first-principles calculations indicated that the excellent electrochemical performance is attributed to the electric double layer capacitance (EDLC) - pseudocapacitance coupled mechanism via the introduction of an appropriate amount of oxygen-containing functional groups. This work provides a robust design for pore engineering and mechanistic insights into rapid zinc-ion storage in carbon materials.

Hydrated Eutectic Electrolyte Induced Bilayer Interphase for High-Performance Aqueous Zn-Ion Batteries with 100 °C Wide-Temperature Range

The practical implementation of aqueous zinc-ion batteries (AZIBs) encounters challenges such as dendrite growth, parasitic reactions, and severe decay in battery performance under harsh environments. Here, a novel hydrated eutectic electrolyte (HEE) composed of Zn(ClO4 )2 ·6H2 O, ethylene glycol (EG), and InCl3 solution is introduced to effectively extend the lifespan of AZIBs over a wide temperature range from -50 to 50 °C. Molecular dynamics simulations and spectroscopy analysis demonstrate that the H2 O molecules are confined within the liquid eutectic network through dual-interaction, involving coordination with Zn2+ and hydrogen bonding with EG, thus weakening the activity of free water and extending the electrochemical window. Importantly, cryo-transmission electron microscopy and spectroscopy techniques reveal that HEE in situ forms a zincophobic/zincophilic bilayer interphase by the dissociation-reduction of eutectic molecules. Specifically, the zincophilic interphase reduces the energy barrier for Zn nucleation, promoting uniform Zn deposition, while the zincophobic interphase prevents active water from contacting the Zn surface, thus inhibiting the side reactions. Furthermore, the relationships between the structural evolution of the liquid eutectic network and interfacial chemistry at electrode/electrolyte interphase are further discussed in this work. The scalability of this design strategy can bring benefits to AZIBs operating over a wide temperature range.

Adaptive Ionization-Induced Tunable Electric Double Layer for Practical Zn Metal Batteries over Wide pH and Temperature Ranges

The violent side reactions of Zn metal in aqueous electrolyte lead to sharp local-pH fluctuations at the interface, which accelerate Zn anode breakdown; thus, the development of an optimization strategy to accommodate a wide pH range is particularly critical for improving aqueous Zn metal batteries. Herein, we report a pH-adaptive electric double layer (EDL) tuned by glycine (Gly) additive with pH-dependent ionization, which exhibits excellent capability to stabilize Zn anodes in wide-pH aqueous electrolytes. It is discovered that a Gly-ionic EDL facilitates the directed migration of charge carriers in both mildly acidic and alkaline electrolytes, leading to the successful suppression of local saturation. It is worth mentioning that the regulation effect of the additive concentration on the inner Helmholtz plane (IHP) structure of Zn electrodes is clarified in depth. It is revealed that the Gly additives without dimerization can develop orderly and dense vertical adsorption within the IHP to effectively reduce the EDL repulsive force of Zn2+ and isolate H2O from the anode surface. Consequently, they Zn anode with tunable EDL exhibits superior electrochemical performance in a wide range of pH and temperature, involving the prodigious cycle reversibility of 7000 h at Zn symmetric cells with ZnSO4-Gly electrolytes and an extended lifespan of 50 times in Zn symmetric cells with KOH-Gly electrolytes. Moreover, acidic Zn powder||MnO2 pouch cells, and alkaline high-voltage Zn||Ni0.8Co0.1Mn0.1O2 cells, and Zn||NiCo-LDH cells also deliver excellent cycling reversibility. The tunable EDL enables the ultrahigh depth of discharge (DOD) of 93%. This work elucidates the design of electrolyte additives compatible in a wide range of pH and temperature, which might cause inspiration in the fields of practical multiapplication scenarios for Zn anodes.

Stabilizing a zinc anode via a tunable covalent organic framework-based solid electrolyte interphase

Zinc (Zn) is an excellent material for use as an anode for rechargeable batteries in water-based electrolytes. Nevertheless, the high activity of water leads to Zn corrosion and hydrogen evolution, along with the formation of dendrites on the Zn surface during repeated charge-discharge (CD) cycles. To protect the Zn anode and limit parasitic side reactions, an artificial solid electrolyte interphase (ASEI) protective layer is an effective strategy. Herein, an ASEI made of a covalent organic framework (COFs: HqTp and BpTp) was fabricated on the surface of a Zn anode via Schiff base reactions of aldehyde and amine linkers. It is seen that COFs can regulate the Zn-ion flux, resulting in dendritic-free Zn. COFs can also mitigate the formation of an irreversible passive layer and the hydrogen evolution reaction (HER). Zn plating/stripping tests using a symmetrical cell suggest that HqTpCOF@Zn shows superior stability and greater coulombic efficiency (CE) compared to bare Zn. The full cell having COFs@Zn also displays much improved cyclability. As a result, the COF proves to be a promising ASEI material to enhance the stability of the Zn anode in aqueous media.

A Nature-Inspired Separator with Water-Confined and Kinetics-Boosted Effects for Sustainable and High-Utilization Zn Metal Batteries

Uncontrollable dendrite growth and sluggish ion-transport kinetics are considered as the main obstacles for the further development of high-performance aqueous zinc ion batteries (AZIBs). Here, a nature-inspired separator (ZnHAP/BC) is developed to tackle these issues via the hybridization of the biomass-derived bacterial cellulose (BC) network and nano-hydroxyapatite particles (HAP). The as-prepared ZnHAP/BC separator not only regulates the desolvation process of the hydrated Zn²⁺ ions (Zn(H₂ O)₆ ²⁺ ) by suppressing the water reactivity through the surface functional groups, alleviating the water-induced side-reactions, but also boosts the ion-transport kinetics and homogenize the Zn²⁺ flux, resulting in a fast and uniform Zn deposition. Remarkably, the Zn|Zn symmetric cell with ZnHAP/BC separator harvests a long-term stability over 1600 h at 1 mA cm^-2 , 1 mAh cm^-2 and endures stable cycling over 1025 and 611 h even at a high depth of discharge (DOD) of 50% and 80%, respectively. The Zn|V₂ O₅ full cell with a low negative/positive (N/P) capacity ratio of 2.7 achieves a superior capacity retention of 82% after 2500 cycles at 10 A g^-1 . Furthermore, the Zn/HAP separator can be totally degraded within 2 weeks. This work develops a novel nature-derived separator and provides insights in constructing functional separators toward sustainable and advanced AZIBs.