Interface Reversible Electric Field Regulated by Amphoteric Charged Protein-Based Coating Toward High-Rate and Robust Zn Anode

Organic solid-electrolyte interface layers for Zn metal anodes

Zinc ion batteries (ZIBs) have emerged as promising candidates for renewable energy storage owing to their affordability, safety, and sustainability. However, issues with Zn metal anodes, such as dendrite growth, hydrogen evolution reaction (HER), and corrosion, significantly hinder the practical application of ZIBs. To address these issues, organic solid electrolyte interface (SEI) layers have gained traction in the ZIB community as they can, for instance, help achieve uniform Zn plating/stripping and suppress side reactions. This article summarizes recent advances in organic artificial SEI layers for ZIB anodes, including their fabrication methods, electrochemical performance, and degradation suppression mechanisms.

Construction of ultrathin solid electrolyte interface on Zn anode within 1 min for high current operating condition

Organic acid treatment can facilitate the in-situ formation of a solid electrolyte interface (SEI) on Zn foil protecting the anode from corrosion. However, the generation of hydrogen (H2) during this process is inevitable, which is often considered detrimental to getting compact SEI. Herein, a H2 film-assisted method is proposed under concentrated Amino-Trimethylene-Phosphonic-Acid to construct ultrathin and dense SEI within 1 min. Specifically, the (002) crystal planes survive from the etching process of 1 min due to the adhered H2, inducing uniform deposition and enhanced corrosion-resistance. Moreover, the H2 can effectively regulate the reaction rate, leading to ultrathin SEI and initiating a morphology preservation behavior, which has been neglected by the previous reports. The quick-formed SEI has excellent compatibility, low resistance and effective isolation of electrolyte/anode, whose advantages work together with exposed (002) planes to get accustomed to high-current surge, leading to the ZAC1@Zn//ZAC1@Zn consistently cycling over 800 h at 15 mA cm-2 and 15 mAh cm-2, the ZAC1@Zn//Cu preserves high reversibility (CE 99.7 %), and the ZAC1@Zn//MVO exhibits notable capacity retention at 191.7 mAh/g after 1000 cycles.

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

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

Controllable Solid Electrolyte Interphase by Ionic Environment Regulation for Stable Zn-Ion Battery

Artificial solid electrolyte interphase in organic solutions is effective and facile for long-cycling aqueous zinc ion batteries. However, the specific effects on different ionic environments have not been thoroughly investigated. Herein, pyromellitic acid (PA) are employed as organic ligand to coordinate with Zn2+ under various ionic environments. The connection between the ionic environment and reaction spontaneity is analyzed to provide insights into the reasons behind the effectiveness of the SEI layer and to characterize its protective impact on the zinc anode. Notably, the PA solution (pH4) lacking OH- contributes to the formation of a dense and ultrathin SEI with Zn-PA coordination, preventing direct contact between the anode and electrolyte. Moreover, the presence of organic functional groups facilitates a uniform flux of Zn2+. These advantages enable stable cycling of the PA4-Zn symmetric cell at a current density of 3 mA cm-2 for over 3500 h. The PA4-Zn//MVO full cell demonstrates excellent electrochemical reversibility. Investigating the influence of the ionic environment on SEI generation informs the development of novel SEI strategies.

Dynamic Molecular Interphases Regulated by Trace Dual Electrolyte Additives for Ultralong-Lifespan and Dendrite-Free Zinc Metal Anode

Metallic zinc is a promising anode material for rechargeable aqueous multivalent metal-ion batteries due to its high capacity and low cost. However, the practical use is always beset by severe dendrite growth and parasitic side reactions occurring at anode/electrolyte interface. Here we demonstrate dynamic molecular interphases caused by trace dual electrolyte additives of D-mannose and sodium lignosulfonate for ultralong-lifespan and dendrite-free zinc anode. Triggered by plating and stripping electric fields, the D-mannose and lignosulfonate species are alternately and reversibly (de-)adsorbed on Zn metal, respectively, to accelerate Zn2+ transportation for uniform Zn nucleation and deposition and inhibit side reactions for high Coulombic efficiency. As a result, Zn anode in such dual-additive electrolyte exhibits highly reversible and dendrite-free Zn stripping/plating behaviors for >6400 hours at 1 mA cm-2, which enables long-term cycling stability of Zn||ZnxMnO2 full cell for more than 2000 cycles.

Engineering a High-Strength and Superior-Electrolyte-Wettability Silk Fibroin-Based Gel Interface Achieving Dendrite-Free Zn Anode

Zn metal anode is confronted with notorious Zn dendrite growth caused by inhomogeneous Zn2+ deposition, rampant dendrite growth, and serious interface side reactions, which significantly hinder their large-scale implication. Interface modification engineering is a powerful strategy to improve the Zn metal anode by regulating Zn2+ deposition behavior, suppressing dendrite formation, and protecting the anode from electrolyte corrosion. Herein, we have designed a high-strength and superior-electrolyte-wettability composite gel protective layer based on silk fibroin (SF) and ionic liquids (ILs) on the Zn anode surface by a straightforward spin-coating strategy. The Zn ion transport kinetics and mechanical properties were further improved by following the incubation process to construct a more well-ordered β-sheet structure. Consequently, the incubated composite gel coating serves as a command station, guiding the Zn ion's preferential growth along the (002) plane, resulting in a smooth and uniform deposition morphology. Driven by these improvements, the zinc anode modified with this composite gel exhibits a remarkably long-term cycling lifespan up to 2200 h at 2 mA cm-2, while also displaying superior rate capability. This study represents a landmark achievement in the realm of electrochemical science, delineating a clear pathway toward the realization of a highly reversible and enduring Zn anode.

Tailoring Localized Electrolyte via a Dual-Functional Protein Membrane toward Stable Zn Anodes

Considerable attention has been by far paid to stabilizing metallic Zn anodes, where side reactions and dendrite formation still remain detrimental to their practical advancement. Electrolyte modification or protected layer design is widely reported; nonetheless, an effective maneuver to synergize both tactics has been rarely explored. Herein, we propose a localized electrolyte optimization via the introduction of a dual-functional biomass modificator over the Zn anode. Instrumental characterization in conjunction with molecular dynamics simulation indicates local solvation structure transformation owing to the limitation of bound water with intermolecular hydrogen bonds, effectively suppressing hydrogen evolutions. Meanwhile, the optimized nucleation throughout the protein membrane allows uniform Zn deposition. Accordingly, the symmetric cell exhibits an elongated lifespan of 3280 h at 1.0 mA cm-2/1.0 mAh cm-2, while the capacity retention of the full cell sustains 91.1% after 2000 cycles at 5.0 A g-1. The localized electrolyte tailoring via protein membrane introduction might offer insights into operational metal anode protection.

Critical Solvation Structures Arrested Active Molecules for Reversible Zn Electrochemistry

Aqueous Zn-ion batteries (AZIBs) have attracted increasing attention in next-generation energy storage systems due to their high safety and economic. Unfortunately, the side reactions, dendrites and hydrogen evolution effects at the zinc anode interface in aqueous electrolytes seriously hinder the application of aqueous zinc-ion batteries. Here, we report a critical solvation strategy to achieve reversible zinc electrochemistry by introducing a small polar molecule acetonitrile to form a "catcher" to arrest active molecules (bound water molecules). The stable solvation structure of [Zn(H2O)6]2+ is capable of maintaining and completely inhibiting free water molecules. When [Zn(H2O)6]2+ is partially desolvated in the Helmholtz outer layer, the separated active molecules will be arrested by the "catcher" formed by the strong hydrogen bond N-H bond, ensuring the stable desolvation of Zn2+. The Zn||Zn symmetric battery can stably cycle for 2250 h at 1 mAh cm-2, Zn||V6O13 full battery achieved a capacity retention rate of 99.2% after 10,000 cycles at 10 A g-1. This paper proposes a novel critical solvation strategy that paves the route for the construction of high-performance AZIBs.

Janus interface enables reversible Zn-ion battery by regulating interfacial water structure and crystal-orientation

To tackle the shortcomings of traditional battery systems, there has been much focus on aqueous Zn-ion batteries due to various advantages. However, they still suffer from poor stability of Zn anodes. Here, a methionine additive with unique Janus properties is proposed to regulate the behavior of the interface between Zn anodes and the electrolyte environment. Systematic characterizations as well as calculations elucidate that the Janus additive is adsorbed on the Zn anode via zincophilic -NH2, changing the structure of the electric double layer and breaking the hydrogen bonding network among H2O molecules through hydrophobic S-CH3. At the same time, it can induce preferential formation of Zn(101) with high reversibility. The above two functions contribute to the dendrite inhibiting ability of Zn anodes. As validated, fabricated Zn//Zn symmetric cells achieve stable cycles of 4500 h, 1165 h, and 318 h at 1, 5 and 10 mA cm-2/mA h cm-2, respectively. Furthermore, Zn//Cu asymmetric cells with an average coulombic efficiency of 98.9% for 2200 stable cycles can be realized. Finally, Zn//MnO2 full cells exhibit 79.9% capacity retention with an ultra-high coulombic efficiency of 99.9% for 1000 cycles, much better than that of the pure Zn(ClO4)2 system, indicating the great potential of this useful strategy in aqueous batteries.

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

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

Coupling of Adhesion and Anti-Freezing Properties in Hydrogel Electrolytes for Low-Temperature Aqueous-Based Hybrid Capacitors

Solid-state zinc-ion capacitors are emerging as promising candidates for large-scale energy storage owing to improved safety, mechanical and thermal stability and easy-to-direct stacking. Hydrogel electrolytes are appealing solid-state electrolytes because of eco-friendliness, high conductivity and intrinsic flexibility. However, the electrolyte/electrode interfacial contact and anti-freezing properties of current hydrogel electrolytes are still challenging for practical applications of zinc-ion capacitors. Here, we report a class of hydrogel electrolytes that couple high interfacial adhesion and anti-freezing performance. The synergy of tough hydrogel matrix and chemical anchorage enables a well-adhered interface between hydrogel electrolyte and electrode. Meanwhile, the cooperative solvation of ZnCl2 and LiCl hybrid salts renders the hydrogel electrolyte high ionic conductivity and mechanical elasticity simultaneously at low temperatures. More significantly, the Zn||carbon nanotubes hybrid capacitor based on this hydrogel electrolyte exhibits low-temperature capacitive performance, delivering high-energy density of 39 Wh kg-1 at -60 °C with capacity retention of 98.7% over 10,000 cycles. With the benefits of the well-adhered electrolyte/electrode interface and the anti-freezing hydrogel electrolyte, the Zn/Li hybrid capacitor is able to accommodate dynamic deformations and function well under 1000 tension cycles even at -60 °C. This work provides a powerful strategy for enabling stable operation of low-temperature zinc-ion capacitors.

An Electrochemical Perspective of Aqueous Zinc Metal Anode

Based on the attributes of nonflammability, environmental benignity, and cost-effectiveness of aqueous electrolytes, as well as the favorable compatibility of zinc metal with them, aqueous zinc ions batteries (AZIBs) become the leading energy storage candidate to meet the requirements of safety and low cost. Yet, aqueous electrolytes, acting as a double-edged sword, also play a negative role by directly or indirectly causing various parasitic reactions at the zinc anode side. These reactions include hydrogen evolution reaction, passivation, and dendrites, resulting in poor Coulombic efficiency and short lifespan of AZIBs. A comprehensive review of aqueous electrolytes chemistry, zinc chemistry, mechanism and chemistry of parasitic reactions, and their relationship is lacking. Moreover, the understanding of strategies for suppressing parasitic reactions from an electrochemical perspective is not profound enough. In this review, firstly, the chemistry of electrolytes, zinc anodes, and parasitic reactions and their relationship in AZIBs are deeply disclosed. Subsequently, the strategies for suppressing parasitic reactions from the perspective of enhancing the inherent thermodynamic stability of electrolytes and anodes, and lowering the dynamics of parasitic reactions at Zn/electrolyte interfaces are reviewed. Lastly, the perspectives on the future development direction of aqueous electrolytes, zinc anodes, and Zn/electrolyte interfaces are presented.

Maximizing Electrostatic Polarity of Non-Sacrificial Electrolyte Additives Enables Stable Zinc-Metal Anodes for Aqueous Batteries

Although additives are widely used in aqueous electrolytes to inhibit the formation of dendrites and hydrogen evolution reactions on Zn anodes, there is a lack of rational design principles and systematic mechanistic studies on how to select a suitable additive to regulate reversible Zn plating/stripping chemistry. Here, using saccharides as the representatives, we reveal that the electrostatic polarity of non-sacrificial additives is a critical descriptor for their ability to stabilize Zn anodes. Non-sacrificial additives are found to continuously modulate the solvation structure of Zn ions and form a molecular adsorption layer (MAL) for uniform Zn deposition, avoiding the thick solid electrolyte interphase layer due to the decomposition of sacrificial additives. A high electrostatic polarity renders sucrose the best hydrated Zn2+ desolvation ability and facilitates the MAL formation, resulting in the best cycling stability with a long-term reversible plating/stripping cycle life of thousands of hours. This study provides theoretical guidance for the screening of optimal additives for high-performance ZIBs.

Engineering a Ni-Al Brucite-Based Interface Layer with Regulated Zn2+ Flux for Highly Reversible Zn Metal Anodes

Practical aqueous Zn-ion batteries are appealing for grid-scale energy storage with intrinsic safety and cost-effectiveness, yet their cycling stability and reversibility are limited by unwanted dendrite growth and water-induced erosions on Zn. Herein, a hydrophilic and Zn2+-conductive Ni-Al layered double hydroxide (NiAl-LDH) interphase layer is constructed on the surface of Zn, in which NiAl-LDH enables a more uniformly distributed Zn2+ concentration and interfacial electric field owing to its large internal Zn2+ channels and favorable charge redistribution effect. Consequently, the NiAl-LDH-integrated Zn anode achieves low voltage hysteresis and high reversibility of Zn plating/stripping with uniform underneath deposition behaviors. Remarkably, the resultant NiAl-2 LDH@Zn delivers superior cycling durability over 2800 h (∼4 months, 0.5 mA cm-2), realizes high reversibility with 99.4% average Coulombic efficiency over 1400 cycles, and confers stable operation of full Zn cells with high V2O5 mass loadings. This work offers a facile and instructive interface design approach for achieving highly stable Zn metal anodes.

Rational Design of Zincophilic Ag/Permselective PEDOT:PSS Heterogeneous Interfaces for High-Rate Zinc Electrodeposition

Designing artificial interface is a promising strategy to protect Zn metal anode but achieving long Zn plating/stripping lifespans and efficient nucleation/deposition kinetics, particularly at high current densities, remains a challenge. In this study, a permselective zincophilic heterogeneous interface consisting of metallic Ag layer and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is designed via a simple chemical displacement and drop casting process. The artificial interface plays a multifunctional role in inhibiting dendrite growth/side reactions by reducing the nucleation barrier through a large number of Zn nucleation sites offered by the bottom Ag layer, homogenizing electrical field/Zn2+ flux and shielding SO4 2- migration via the compact, conducting, and Zn2+ -permselective PEDOT:PSS supporting layer. Moreover, the heterogeneous interface demonstrates enhanced structural integrity owing to the binder effect of PEDOT:PSS. As a result, the modified Zn anode demonstrates a cyclic lifespan of 200 h and a reduced voltage hysteresis of ≈150 mV at 20 mA cm-2 /5 mAh cm-2 , far surpassing its counterparts. Moreover, the protected Zn anode allows the LiMn2 O4 -based full cells with remarkable rate and cycling performance. These findings provide new insight into the design of an efficient artificial interface for highly reversible and high-rate Zn electrodeposition.

Self-Assembled Protein Nanofilm Regulating Uniform Zn Nucleation and Deposition Enabling Long-Life Zn Anodes

Rechargeable zinc-ion batteries (RZIBs) have gained promising attention as a feasible alternative for large-scale energy storage by the virtue of their intrinsic security, environmental benignity, low cost, and high volumetric capacity (5849 mAh cm-3 ). Nevertheless, the deep-rooted issues of dendrite formation and side reactions in unstable Zn metal anode have impeded RZIBs from being dependably deployed in their proposed applications. Herein, silk fibroin (SF) and lysozyme (ly), as natural biomacromolecules with abundant polar groups arranged in polypeptide backbones, are in situ self-assembled on the Zn anode surface to construct a homogeneous and compact protein nanofilm. Such protein nanofilm protecting layer presents a negative charge surface and significantly regulates Zn2+ deposition behavior. Meanwhile, synergistic flexible and robust features of protein nanofilm function as artificial solid electrolyte interface (SEI), accommodates the dynamic volume deformation during deposition/dissolution, and blocks corrosion of side reactions. Consequently, the electrochemical stability of protein nanofilm-modified Zn anode is greatly improved, with an excellent extended lifespan of over 1100 h at a high current density of 10 mA cm-2 and a high cycling capacity of 10 mAh cm-2 , corresponding to a high depth of discharge (83% DODZn ). Furthermore, the highly reversible Zn electrode remarkably improved the overall performance of MnO2 ||Zn full-cells.

Trace Amounts of Triple-Functional Additives Enable Reversible Aqueous Zinc-Ion Batteries from a Comprehensive Perspective

Although their cost-effectiveness and intrinsic safety, aqueous zinc-ion batteries suffer from notorious side reactions including hydrogen evolution reaction, Zn corrosion and passivation, and Zn dendrite formation on the anode. Despite numerous strategies to alleviate these side reactions have been demonstrated, they can only provide limited performance improvement from a single aspect. Herein, a triple-functional additive with trace amounts, ammonium hydroxide, was demonstrated to comprehensively protect zinc anodes. The results show that the shift of electrolyte pH from 4.1 to 5.2 lowers the HER potential and encourages the in situ formation of a uniform ZHS-based solid electrolyte interphase on Zn anodes. Moreover, cationic NH4+ can preferentially adsorb on the Zn anode surface to shield the "tip effect" and homogenize the electric field. Benefitting from this comprehensive protection, dendrite-free Zn deposition and highly reversible Zn plating/stripping behaviors were realized. Besides, improved electrochemical performances can also be achieved in Zn//MnO2 full cells by taking the advantages of this triple-functional additive. This work provides a new strategy for stabilizing Zn anodes from a comprehensive perspective.