Rational Screening of Artificial Solid Electrolyte Interphases on Zn for Ultrahigh-Rate and Long-Life Aqueous Batteries

Non-Epitaxial Electrodeposition of Overall 99 % (002) Plane Achieves Extreme and Direct Utilization of 95 % Zn Anode and By-Product as Cathode

Zn anode protection in Zn-ion batteries (ZIBs) face great challenges of high Zn utilization rate (i.e., depth of discharge, DOD) and high current density due to the large difficulty in obtaining an extreme overall RTC (relative texture coefficient) of Zn (002) plane. Through the potent interaction of Mn(III)aq and H+ with distinct Zn crystal planes under an electric field, large-size Zn foils with a breakthrough (002) plane RTC of 99 % (i.e., close to Zn single crystal) are electrodeposited on texture-less substrates, which is also applicable from recycled Zn. The ultra-high (002) plane RTC remarkably enhances cyclic performance of the Zn anode (70 % DOD @ 45.5 mA cm-2), and the DOD is even up to 95 % (@ 28.1 mA cm-2) with an electrolyte additive of polyaniline. Furthermore, MnO2, the by-product of electrodeposition, is directly used as cathode of both coin cell and pouch battery, surpassing the cyclic performance exhibited by the majority of Zn||MnO2 batteries in previous instances. These results demonstrate the great potential of our strategy for high-performance, low-cost and large-scale ZIBs.

Formulating Self-Repairing Solid Electrolyte Interface via Dynamic Electric Double Layer for Practical Zinc Ion Batteries

Zinc ion batteries (ZIBs) encounter interface issues stemming from the water-rich electrical double layer (EDL) and unstable solid-electrolyte interphase (SEI). Herein, we propose the dynamic EDL and self-repairing hybrid SEI for practical ZIBs via incorporating the horizontally-oriented dual-site additive. The rearrangement of distribution and molecular configuration of additive constructs the robust dynamic EDL under different interface charges. And, a self-repairing organic-inorganic hybrid SEI is constructed via the electrochemical decomposition of additive. The dynamic EDL and self-repairing SEI accelerate interfacial kinetics, regulate deposition and suppress side reactions in the both stripping and plating during long-term cycles, which affords high reversibility for 500 h at 42.7 % depth of discharge or 50 mA ⋅ cm-1. Remarkably, Zn//NVO full cells deliver the impressive cycling stability for 10000 cycles with 100 % capacity retention at 3 A ⋅ g-1 and for over 3000 cycles even at lean electrolyte (7.5 μL ⋅ mAh-1) and high loading (15.26 mg ⋅ cm-2). Moreover, effectiveness of this strategy is further demonstrated in the low-temperature full cell (-30 °C).

Dynamically Favorable Ion Channels Enabled by a Hybrid Ionic-Electronic Conducting Film toward Highly Reversible Zinc Metal Anodes

Aqueous zinc ion batteries show great promise for future applications due to their high safety and ecofriendliness. However, nonuniform dendrite growth and parasitic reactions on the Zn anode have severely impeded their use. Herein, a hybrid ionic-electronic conducting ink composed of graphene-like carbon nitride (g-C3N4) and conductive polymers (CP) of poly(3,4ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is introduced to Zn anode using a scalable spray-coating strategy. Notably, the g-C3N4 promotes a screening effect, disrupting the coulombic interaction between the PEDOT+ segments and PSS- chains within CP, thereby reducing interfacial resistance and homogenizing the surface electric field distribution of the Zn anode. Furthermore, the abundant N-containing species and ─SO3 - groups in g-C3N4/CP exhibit strong zincophilicity, which accelerates the diffusion of Zn2+ and disrupts the solvation structure of Zn(H2O)6 2+, thus improving the Zn2+ transfer capability. Consequently, the g-C3N4/CP can powerfully stabilize the Zn2+ flux and thus enable a high coulombic efficiency of 99.47% for 1500 cycles and smooth Zn plating/stripping behaviors more than 3000 h at a typical current density of 1 mA cm-2. These findings shed new light on the Zn electrodeposition process under the mediation of g-C3N4/CP and offer sustainability considerations in designing more stable Zn-metal anodes with enhanced reversibility.

Cutting-Edge Progress in Aqueous Zn-S Batteries: Innovations in Cathodes, Electrolytes, and Mediators

Rechargeable aqueous zinc-sulfur batteries (AZSBs) are emerging as prominent candidates for next-generation energy storage devices owing to their affordability, non-toxicity, environmental friendliness, non-flammability, and use of earth-abundant electrodes and aqueous electrolytes. However, AZSBs currently face challenges in achieving satisfied electrochemical performance due to slow kinetic reactions and limited stability. Therefore, further research and improvement efforts are crucial for advancing AZSBs technology. In this comprehensive review, it is delved into the primary mechanisms governing AZSBs, assess recent advancements in the field, and analyse pivotal modifications made to electrodes and electrolytes to enhance AZSBs performance. This includes the development of novel host materials for sulfur (S) cathodes, which are capable of supporting higher S loading capacities and the refinement of electrolyte compositions to improve ionic conductivity and stability. Moreover, the potential applications of AZSBs across various energy platforms and evaluate their market viability based on recent scholarly contributions is explored. By doing so, this review provides a visionary outlook on future research directions for AZSBs, driving continuous advancements in stable AZSBs technology and deepening the understanding of their charge-discharge dynamics. The insights presented in this review signify a significant step toward a sustainable energy future powered by renewable sources.

Spatially Confined Engineering Toward Deep Eutectic Electrolyte in Metal-Organic Framework Enabling Solid-State Zinc-Ion Batteries

Uncontrollable interfacial side reactions generated from common aqueous electrolytes, just like the hydrogen evolution reaction (HER) and dendrite growth, have severely prevented the practical application of zinc-ion batteries (ZIBs). Solid-state ZIBs are considered to be an efficient strategy by adopting high-quality solid-state electrolytes (SSEs). Here, by confining deep eutectic electrolyte (DEE) into the nanochannels of metal-organic framework (MOF)-PCN-222, a stable DEE@PCN-222 SSE with internal Zn2+ transport channels was obtained. A distinctive ion-transport network composed of DEE and PCN-222 in the interior of DEE@PCN-222 realizes the efficient Zn2+ conduction, contributing to high ionic conductivity of 3.13×10-4 S cm-1 at room temperature, low activation energy of 0.12 eV, and a high Zn2+ transference number of 0.74. Furthermore, experimental and theoretical investigations demonstrate that DEE@PCN-222 with its unique channel structure could homogeneously regulate the Zn2+ distribution and effectively alleviate the side reactions. Highly reversible Zn plating/stripping performance of 2476 h can be realized by the SSE. The solid-state ZIBs show a specific capacity of 306 mAh g-1 and display cycling stability of 517 cycles. This unique design concept provides a new perspective in realizing the high-safety and high-performance ZIBs.

Robust bilayer solid electrolyte interphase for Zn electrode with high utilization and efficiency

Construction of a solid electrolyte interphase (SEI) of zinc (Zn) electrode is an effective strategy to stabilize Zn electrode/electrolyte interface. However, single-layer SEIs of Zn electrodes undergo rupture and consequent failure during repeated Zn plating/stripping. Here, we propose the construction of a robust bilayer SEI that simultaneously achieves homogeneous Zn2+ transport and durable mechanical stability for high Zn utilization rate (ZUR) and Coulombic efficiency (CE) of Zn electrode by adding 1,3-Dimethyl-2-imidazolidinone as a representative electrolyte additive. This bilayer SEI on Zn surface consists of a crystalline ZnCO3-rich outer layer and an amorphous ZnS-rich inner layer. The ordered outer layer improves the mechanical stability during cycling, and the amorphous inner layer homogenizes Zn2+ transport for homogeneous, dense Zn deposition. As a result, the bilayer SEI enables reversible Zn plating/stripping for 4800 cycles with an average CE of 99.95% (± 0.06%). Meanwhile, Zn | |Zn symmetric cells show durable lifetime for over 550 h with a high ZUR of 98% under an areal capacity of 28.4 mAh cm-2. Furthermore, the Zn full cells based on the bilayer SEI functionalized Zn negative electrodes coupled with different positive electrodes all exhibit stable cycling performance under high ZUR.

Bidentate Coordination Structure Facilitates High-Voltage and High-Utilization Aqueous Zn-I2 Batteries

The aqueous zinc-iodine battery is a promising energy storage device, but the conventional two-electron reaction potential and energy density of the iodine cathode are far from meeting practical application requirements. Given that iodine is rich in redox reactions, activating the high-valence iodine cathode reaction has become a promising research direction for developing high-voltage zinc-iodine batteries. In this work, by designing a multifunctional electrolyte additive trimethylamine hydrochloride (TAH), a stable high-valence iodine cathode in four-electron-transfer I-/I2/I+ reactions with a high theoretical specific capacity is achieved through a unique amine group, Cl bidentate coordination structure of (TA)ICl. Characterization techniques such as synchrotron radiation, in situ Raman spectra, and DFT calculations are used to verify the mechanism of the stable bidentate structure. This electrolyte additive stabilizes the zinc anode by promoting the desolvation process and shielding mechanism, enabling the zinc anode to cycle steadily at a maximum areal capacity of 57 mAh cm-2 with 97 % zinc utilization rate. Finally, the four-electron-transfer aqueous Zn-I2 full cell achieves 5000 stable cycles at an N/P ratio of 2.5. The unique bidentate coordination structure contributes to the further development of high-valence and high capacity aqueous zinc-iodine 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.

Guiding uniform Zn deposition with a multifunctional additive for highly utilized Zn anodes

The practical applications of aqueous zinc-ion batteries (AZIBs) have been restricted by the fast growth of Zn dendrites and severe side reactions at the Zn/electrolyte interface. Herein, a multifunctional additive, L-leucine (Leu), is incorporated into a mild acidic electrolyte to stabilize the Zn anode. The Leu molecule, featuring both carboxyl and amino groups, exhibits strong interactions with Zn2+, which can reshape the solvation structure of Zn2+ and facilitate the uniform electrodeposition of Zn. Simultaneously, the Leu molecule exhibits preferential adsorption onto the Zn surface, effectively isolating it from direct contact with water, thus suppressing unwanted side reactions. Consequently, the Zn∥Cu asymmetric cell exhibits a high and stable coulombic efficiency of 99.5% at a current density of 5 mA cm-2 for 1100 h. Importantly, the capacity retention of the Zn∥NH4V4O10 full cell based on the Leu electrolyte reaches 80% after 1200 cycles at a current density of 2 A g-1. The successful application of the low-cost Leu effectively enhances the cycling stability of the AZIBs and accelerates their applications.

Ether-Water Co-Solvent Electrolytes Enhanced Vanadium Oxide Cathode Cyclic Behaviors for Zinc Batteries

Vanadium-based compounds are fantastic cathodes for aqueous zinc metal batteries due to the high specific capacity and excellent rate capability. Nevertheless, the practical application has been hampered by the dissolution of vanadium in traditional aqueous electrolytes owing to the strong polarity of water molecules. Herein, we propose a hybrid electrolyte made of Zn(ClO4)2 salt in tetraethylene glycol dimethyl ether (G4) and H2O solvents to upgrade the cycle life of Zn//K0.486V2O5 battery. The G4 jointly solvates with Zn2+ ions and replaces a portion of the H2O molecules in the Zn2+ solvation sheath. It forms a strong bond with H2O, reducing its activity, and significantly inhibiting vanadium dissolution and water-induced parasitic reaction. Consequently, the optimized electrolyte with H2O and G4 volume ratio of 5 : 5 enhances the cycling stability of Zn//K0.486V2O5 battery, enabling it to reach up to 600 cycles. In addition, the battery demonstrates a satisfactory reversible capacity of 475.7 mAh g-1 and excellent rate performance attributed to the moderate ionic conductivity (28.8 mS cm-1) of the hybrid electrolyte. Last but not least, in the optimized electrolyte, the symmetric Zn//Zn cells deliver a long cycling performance of 400 h, while the asymmetric Zn//Cu cells shows a high average coulombic efficiency of 97.4 %.

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.

Trace Small Molecular/Nano-Colloidal Multiscale Electrolyte Additives Enable Ultra-Long Lifespan of Zinc Metal Anodes

Electrolyte additives are efficient to improve the performance of aqueous zinc-ion batteries (AZIBs), yet the current electrolyte additives are limited to fully water-soluble additives (FWAs) and water-insoluble additives (WIAs). Herein, trace slightly water-soluble additives (SWAs) of zinc acetylacetonate (ZAA) were introduced to aqueous ZnSO4 electrolytes. The SWA system of ZAA is composed of a FWA part and a WIA part in a dynamic manner of dissolution equilibrium. The FWA part exists as soluble small molecules, which efficiently regulate Zn2+ ion solvation structure, while the WIA part exists as insoluble nano-colloids, which in-situ form a thick and robust solid electrolyte interface film on zinc metal anodes (ZMAs). Such small molecular/nano-colloidal multiscale electrolyte additives of ZAA are capable to not only improve ionic conductivity and transference number but also inhibit corrosion, hydrogen evolution, and Zn dendrite on ZMAs. The SWA-based Zn∥Zn half battery delivers a superb cumulative plating capacity of 15 Ah cm-2 under 1 mAh cm-2 and 20 mA cm-2, and the SWA-based NH4V4O10∥Zn pouch cell obtains a capacity retention of 67.8% within 4000 cycles under 4 A g-1. The study provides innovative insights for rational design of electrolyte additives, which may pave the way for the practicality of AZIBs.

Planar Deposition via In Situ Conversion Engineering for Dendrite-Free Zinc Batteries

Owing to the considerable capacity, high safety, and abundant zinc resources, zinc-ion batteries (ZIBs) have been garnering much attention. Nonetheless, the unsatisfactory cyclic lifespan and poor reversibility originate from side reactions and dendrite obstacles to their practical applications. In addition to inhibiting the corrosion of aqueous electrolytes, regulating planar deposition is a key strategy to enhance their long-term stability. Herein, an in situ conversion strategy is reported to construct a protective "dual-layer" structure (VZSe/V@Zn) on zinc metal, consisting of the VSe2-ZnSe outer layer with low lattice mismatch to Zn (002) plane, and corrosion-resistant nanometallic V inner layer. Such design integrates superior interfacial ionic/electronic transfer, corrosion resistance, and unique planar deposition regulation capability. The as-prepared VZSe/V@Zn demonstrates remarkable durability of 238 h at 50 mA cm-2 with a high depth of discharge (68.3% DOD) in the Zn||Zn symmetric cell. Even in the anode-free system, the as-prepared protective layer can extend the cycle life up to 2000 cycles, with an outstanding capacity retention of 93.1% and ultra-high average coulombic efficiency of 99.998%. This work delineates an effective strategy for fabricating lattice-matching protective layers, with profound implications for elucidating zinc deposition mechanisms and paving the way for the development of high-performance zinc batteries.

Improvements and Challenges of Hydrogel Polymer Electrolytes for Advanced Zinc Anodes in Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are widely regarded as desirable energy storage devices due to their inherent safety and low cost. Hydrogel polymer electrolytes (HPEs) are cross-linked polymers filled with water and zinc salts. They are not only widely used in flexible batteries but also represent an ideal electrolyte candidate for addressing the issues associated with the Zn anode, including dendrite formation and side reactions. In HPEs, an abundance of hydrophilic groups can form strong hydrogen bonds with water molecules, reducing water activity and inhibiting water decomposition. At the same time, special Zn2+ transport channels can be constructed in HPEs to homogenize the Zn2+ flux and promote uniform Zn deposition. However, HPEs still face issues in practical applications, including poor ionic conductivity, low mechanical strength, poor interface stability, and narrow electrochemical stability windows. This Review discusses the issues associated with HPEs for advanced AZIBs, and the recent progresses are summarized. Finally, the Review outlines the opportunities and challenges for achieving high performance HPEs, facilitating the utilization of HPEs in AZIBs.

Suppressed Dissolution of Fluorine-Rich SEI Enables Highly Reversible Zinc Metal Anode for Stable Aqueous Zinc-Ion Batteries

The instability of the solid electrolyte interface (SEI) is a critical challenge for the zinc metal anodes, leading to an erratic electrode/electrolyte interface and hydrogen evolution reaction (HER), ultimately resulting in anode failure. This study uncovers that the fluorine species dissolution is the root cause of SEI instability. To effectively suppress the F- dissolution, an introduction of a low-polarity molecule, 1,4-thioxane (TX), is proposed, which reinforces the stability of the fluorine-rich SEI. Moreover, the TX molecule has a strong affinity for coordinating with Zn2+ and adsorbing at the electrode/electrolyte interface, thereby diminishing the activity of local water and consequently impeding SEI dissolution. The robust fluorine-rich SEI layer promotes the high durability of the zinc anode in repeated plating/stripping cycles, while concurrently suppressing HER and enhancing Coulombic efficiency. Notably, the symmetric cell with TX demonstrates exceptional electrochemical performance, sustaining over 500 hours at 20 mA cm-2 with 10 mAh cm-2. Furthermore, the Zn||KVOH full cell exhibits excellent capacity retention, averaging 6.8 mAh cm-2 with 98 % retention after 400 cycles, even at high loading with a lean electrolyte. This work offers a novel perspective on SEI dissolution as a key factor in anode failure, providing valuable insights for the electrolyte design in energy storage devices.

Interfacial Biomacromolecular Engineering Toward Stable Ah-Level Aqueous Zinc Batteries

Interfacial instability within aqueous zinc batteries (AZBs) spurs technical obstacles including parasitic side reactions and dendrite failure to reach the practical application standards. Here, an interfacial engineering is showcased by employing a bio- derived zincophilic macromolecule as the electrolyte additive (0.037 wt%), which features a long-chain configuration with laterally distributed hydroxyl and sulfate anion groups, and has the propensity to remodel the electric double layer of Zn anodes. Tailored Zn2+-rich compact layer is the result of their adaptive adsorption that effectively homogenizes the interfacial concentration field, while enabling a hybrid nucleation and growth mode characterized as nuclei-rich and space-confined dense plating. Further resonated with curbed corrosion and by-products, a dendrite-free deposition morphology is achieved. Consequently, the macromolecule-modified zinc anode delivers over 1250 times of reversible plating/stripping at a practical area capacity of 5 mAh cm-2, as well as a high zinc utilization rate of 85%. The Zn//NH4V4O10 pouch cell with the maximum capacity of 1.02 Ah can be steadily operated at 71.4 mA g-1 (0.25 C) with 98.7% capacity retained after 50 cycles, which demonstrates the scale-up capability and highlights a "low input and high return" interfacial strategy toward practical AZBs.

In Situ Self-Reconfiguration Induced Multifunctional Triple-Gradient Artificial Interfacial Layer toward Long-Life Zn-Metal Anodes

Aqueous Zn-ion batteries featuring with intrinsic safety and low cost are highly desirable for large-scale energy storage, but the unstable Zn-metal anode resulting from uncontrollable dendrite growth and grievous hydrogen evolution reaction (HER) shortens their cycle life. Herein, a feasible in situ self-reconfiguration strategy is developed to generate triple-gradient poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDDA-TFSI)-Zn5(OH)8Cl2·H2O-Sn (PT-ZHC-Sn) artificial layer. The resulting triple-gradient interface consists of the spherical top layer PT with cation confinement and H2O inhibition, the dense intermediate layer ZHC nanosheet with Zn2+ conduction and electron shielding, and the bottom layer Znophilic Sn metal. The well-designed triple-gradient artificial interfacial layer synergistically facilitates rapid Zn2+ diffusion to regulate uniform Zn deposition and accelerates the desolvation process while suppressing HER. Consequently, the PT-ZHC-Sn@Zn symmetric cell achieves an ultralong lifespan over 6500 h at 0.5 mA cm-2 for 0.5 mAh cm-2. Furthermore, a full battery coupling with MnO2 cathode exhibits a 17.2% increase in capacity retention compared with bare Zn anode after 1000 cycles. The in situ self-reconfiguration strategy is also applied to prepare triple-gradient PT-ZHC-In, and the assembled Zn//Cu cell operates steadily for over 8400 h while maintaining Coulombic efficiency of 99.6%. This work paves the way to designing multicomponent gradient interface for stable Zn-metal anodes.

Stable zinc anode solid electrolyte interphase via inner Helmholtz plane engineering

The inner Helmholtz plane and thus derived solid-electrolyte interphase (SEI) are crucial interfacial structure to determine the electrochemical stability of Zn-ion battery (ZIB). In this work, we demonstrate that introducing β-cyclodextrins (CD) as anion-receptors into Zn(OTf)2 aqueous electrolyte could significantly optimize the Zn anode SEI structure for achieving stable ZIB. Specifically, β-CD with macrocyclic structure holds appropriate cavity size and charge distribution to encase OTf- anions at the Zn metal surface to form β-CD@OTf- dominated inner Helmholtz structure. Meanwhile, the electrochemically triggered β-CD@OTf- decomposition could in situ convert to the organic-inorganic hybrid SEI (ZnF2/ZnCO3/ZnS‒(C-O-C/*CF/*CF3)), which could efficiently hinder the Zn dendrite growth with maintain the proper SEI mechanical strength stability to guarantee the long-term stability. The thus-derived Zn | |Zn pouch cell (21 cm2 size) with β-CD-containing electrolyte exhibits a cumulative capacity of 6450 mAh-2 cm-2 at conditions of 10 mAh cm-2 high areal capacity. This work gives insights for reaching stable ZIB via electrolyte additive triggered SEI structure regulation.

Surface Engineering on Zinc Anode for Aqueous Zinc Metal Batteries

Rechargeable aqueous zinc metal batteries (AZMBs) are considered as a potential alternative to lithium-ion batteries due to their low cost, high safety, and environmental friendliness. However, the Zn anodes in AZMBs face severe challenges, such as dendrite growth, metal corrosion, and hydrogen evolution, all of which are closely related to the Zn/electrolyte interface. This article offers a short review on surface passivation to alleviate the issues on the Zn anodes. The composition and structure of the surface layers significantly influence their functions and then the performance of the Zn anodes. The recent progresses are introduced, according to the chemical components of the passivation layers on the Zn anodes. Moreover, the challenges and prospects of surface passivation in stabilizing Zn anodes are discussed, providing valuable guidance for the development of AZMBs.

Stabilizing Zn/electrolyte Interphasial Chemistry by a Sustained-Release Drug Inspired Indium-Chelated Resin Protective Layer for High-Areal-Capacity Zn//V2O5 Batteries

For zinc-metal batteries, the instable chemistry at Zn/electrolyte interphasial region results in severe hydrogen evolution reaction (HER) and dendrite growth, significantly impairing Zn anode reversibility. Moreover, an often-overlooked aspect is this instability can be further exacerbated by the interaction with dissolved cathode species in full batteries. Here, inspired by sustained-release drug technology, an indium-chelated resin protective layer (Chelex-In), incorporating a sustained-release mechanism for indium, is developed on Zn surface, stabilizing the anode/electrolyte interphase to ensure reversible Zn plating/stripping performance throughout the entire lifespan of Zn//V2O5 batteries. The sustained-release indium onto Zn electrode promotes a persistent anticatalytic effect against HER and fosters uniform heterogeneous Zn nucleation. Meanwhile, on the electrolyte side, the residual resin matrix with immobilized iminodiacetates anions can also repel detrimental anions (SO4 2- and polyoxovanadate ions dissolved from V2O5 cathode) outside the electric double layer. This dual synergetic regulation on both electrode and electrolyte sides culminates a more stable interphasial environment, effectively enhancing Zn anode reversibility in practical high-areal-capacity full battery systems. Consequently, the bio-inspired Chelex-In protective layer enables an ultralong lifespan of Zn anode over 2800 h, which is also successfully demonstrated in ultrahigh areal capacity Zn//V2O5 full batteries (4.79 mAh cm-2).

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.

Improving Aqueous Zinc Ion Batteries with Alkali Metal Ions

Aqueous zinc (Zn) ion batteries have received broad attention recently. However, their practical application is limited by severe Zn dendrite growth and the hydrogen evolution reaction. In this study, three alkali metal ions (Li+, Na+, and K+) are added in ZnSO4 electrolytes, which are subjected to electrochemical measurements and molecular dynamics simulations. The studies show that since K+ has the highest mobility and self-diffusion coefficient among the four ions (Li+, Na+, K+, and Zn2+), it enables K+ to preferentially approach a zinc dendrite at an earlier time, driven by a negative electric field during a cathodic process. The electric double layer, with K+ around the negatively charged Zn dendrite, inhibits dendrite growth and mitigates the hydrogen evolution reaction on the Zn anode. Under this kinetic effect, the Zn-Zn symmetric cell with K+ exhibits a long cycling stability of 1000 h at 1 mA·cm-2 of 1 mAh·cm-2 and 190 h at 30 mA·cm-2 of 2 mAh·cm-2. Such a kinetic effect is also observed with additives Na+ and Li+, though less profound than that of K+.

Spontaneous grain refinement effect of rare earth zinc alloy anodes enables stable zinc batteries

Irreversible interfacial reactions at the anodes pose a significant challenge to the long-term stability and lifespan of zinc (Zn) metal batteries, impeding their practical application as energy storage devices. The plating and stripping behavior of Zn ions on polycrystalline surfaces is inherently influenced by the microscopic structure of Zn anodes, a comprehensive understanding of which is crucial but often overlooked. Herein, commercial Zn foils were remodeled through the incorporation of cerium (Ce) elements via the 'pinning effect' during the electrodeposition process. By leveraging the electron-donating effect of Ce atoms segregated at grain boundaries (GBs), the electronic configuration of Zn is restructured to increase active sites for Zn nucleation. This facilitates continuous nucleation throughout the growth stage, leading to a high-rate instantaneous-progressive composite nucleation model that achieves a spatially uniform distribution of Zn nuclei and induces spontaneous grain refinement. Moreover, the incorporation of Ce elements elevates the site energy of GBs, mitigating detrimental parasitic reactions by enhancing the GB stability. Consequently, the remodeled ZnCe electrode exhibits highly reversible Zn plating/stripping with an accumulated capacity of up to 4.0 Ah cm-2 in a Zn symmetric cell over 4000 h without short-circuit behavior. Notably, a ∼0.4 Ah Zn||NH4V4O10 pouch cell runs over 110 cycles with 83% capacity retention with the high-areal-loading cathode (≈20 mg cm-2). This refining-grains strategy offers new insights into designing dendrite-free metal anodes in rechargeable batteries.

Constructing Lysozyme Protective Layer via Conformational Transition for Aqueous Zn Batteries

The practical applications for aqueous Zn ion batteries (ZIBs) are promising yet still impeded by the severe side reactions on Zn metal. Here, a lysozyme protective layer (LPL) is prepared on Zn metal surface by a simple and facile self-adsorption strategy. The LPL exhibits extremely strong adhesion on Zn metal to provide stable interface during long-term cycling. In addition, the self-adsorption strategy triggered by the hydrophobicity-induced aggregation effect endows the protective layer with a gap-free and compacted morphology which can reject free water for effective side reaction inhibition performance. More importantly, the lysozyme conformation is transformed from α-helix to β-sheet structure before layer formation, thus abundant functional groups are exposed to interact with Zn2+ for electrical double layer (EDL) modification, desolvation energy decrease, and ion diffusion kinetics acceleration. Consequently, the LPL renders the symmetrical Zn battery with ultra-long cycling performance for more than 1200 h under high Zn depth of discharge (DOD) for 77.7%, and the Zn/Zn0.25V2O5 pouch cell with low N/P ratio of 2.1 at high Zn utilization of 48% for over 300 cycles. This study proposes a facile and low-cost method for constructing a stable protective layer of Zn metal for high Zn utilization aqueous devices.

2D Tungsten Borides Induced Interfacial Modulation Engineering Toward High-Rate Performance Zinc-Iodine Battery

Aqueous zinc-iodine batteries are promising candidates for large-scale energy storage due to their high energy density and low cost. However, their development is hindered by several drawbacks, including zinc dendrites, anode corrosion, and the shuttle of polyiodides. Here, the design of 2D-shaped tungsten boride nanosheets with abundant borophene subunits-based active sites is reported to guide the (002) plane-dominated deposition of zinc while suppressing side reactions, which facilitates interfacial nucleation and uniform growth of zinc. Meanwhile, the interfacial d-band orbits of tungsten sites can further enhance the anchoring of polyiodides on the surface, to promote the electrocatalytic redox conversion of iodine. The resulting tungsten boride-based I2 cathodes in zinc-iodine cells exhibit impressive cyclic stability after 5000 cycles at 50 C, which accelerates the practical applications of zinc-iodine batteries.

Backside Coating for Stable Zn Anode with High Utilization Rate

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

Constructing 3D Zincophilic Skeleton in Nitrogen-Doped Carbon Hybrid Fibers for Dendrite-Free Zn Anodes

The Zn dendrite growth and side reactions are two major issues for the practical use of Zn metal anodes (ZMAs). Herein, an N-doped carbon-based hybrid fiber with the 3D porous skeleton and the zincophilic Cu nanoparticles (denoted as Cu@HLCF) is developed for stable ZMAs. The zincophilic Cu particles in the skeleton work as the active sites to facilitate uniform Zn nucleation. Meanwhile, the abundant pores in the framework of the hybrid fibers provide a large space to relieve the structural stress and suppress the dendrite growth. Moreover, the good mechanical characteristics of the hybrid fiber ensure its high potential applications for flexible electronics. Theoretical analysis results disclose the strong interaction between Zn and Cu sites, and experimental results demonstrate the low voltage hysteresis, high reversibility, and dendrite-free behavior of the Cu@HLCF host for Zn plating/stripping. Moreover, the solid-state Zn-ion battery (ZIB) assembled with a Cu@HLCF/Zn anode shows the prominent flexibility, impressively reliability, and outstanding cycling capability. Therefore, this work not only provides a novel design for the efficient and stable Zn metal anode but also promotes the development of flexible power sources for flexible electronics.

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.

In Situ Grown Coordination-Supramolecular Layer Holding 3D Charged Channels for Highly Reversible Zn Anodes

Dynamic reversible noncovalent interactions make supramolecular framework (SF) structures flexible and designable. A three-dimensional (3D) growth of such frameworks is beneficial to improve the structure stability while maintaining unique properties. Here, through the ionic interaction of the polyoxometalate cluster, coordination of zinc ions with cationic terpyridine, and hydrogen bonding of grafted carboxyl groups, the construction of a 3D SF at a well-crystallized state is realized. The framework can grow in situ on the Zn surface, further extending laterally into a full covering without defects. Relying on the dissolution and the postcoordination effects, the 3D SF layer is used as an artificial solid electrolyte interphase to improve the Zn-anode performance. The uniformly distributed clusters within nanosized pores create a negatively charged nanochannel, accelerating zinc ion transfer and homogenizing zinc deposition. The 3D SF/Zn symmetric cells demonstrate high stability for over 3000 h at a current density of 5 mA cm-2.

Carbonate Ester-Based Electrolyte Enabling Rechargeable Zn Battery to Achieve High Voltage and High Zn Utilization

Owing to the high H2O activity, the aqueous electrolyte in the Zn battery exhibits a narrow electrochemical window and inevitable hydrogen evolution reaction, limiting the anode utilization ratio and performance at high voltage. Carbonate ester, the well-developed electrolyte solvent in Li-ion batteries, exhibits aprotic properties and high anodic stability. However, its use in Zn metal batteries is limited due to the low solubility of Zn salts in carbonate esters. Herein, we propose a carbonate ester-based electrolyte (EC:DMC:EMC = 1:1:1 wt %), which contains a new Zn salt (Zn(BHFip)2) characterized by low cost, easy synthesis, and excellent aprotic solvent solubility. The BHFip- anion assists in forming Zn2+ conductive SEI on the anode and decomposes at high voltage to generate a protective CEI layer on the cathode. The Zn//Zn symmetric cell using such electrolyte achieves a remarkable Zn utilization ratio of 91% for 125 h, which has rarely been reported before. Furthermore, the Zn//LiMn2O4 full cell with an average operation voltage of 1.7 V demonstrates reliable cycling for 135 cycles with an N/P ratio of 1:1. In addition, the Zn//LiNi0.5Mn1.5O4 full cell exhibits a high discharge median voltage exceeding 2.2 V for 280 cycles, with the high voltage plateau (above 2 V) constituting 82% of the total capacity.

Electrolyte and Interphase Engineering of Aqueous Batteries Beyond "Water-in-Salt" Strategy

Aqueous batteries are promising alternatives to non-aqueous lithium-ion batteries due to their safety, environmental impact, and cost-effectiveness. However, their energy density is limited by the narrow electrochemical stability window (ESW) of water. The "Water-in-salts" (WIS) strategy is an effective method to broaden the ESW by reducing the "free water" in the electrolyte, but the drawbacks (high cost, high viscosity, poor low-temperature performance, etc.) also compromise these inherent superiorities. In this review, electrolyte and interphase engineering of aqueous batteries to overcome the drawbacks of the WIS strategy are summarized, including the developments of electrolytes, electrode-electrolyte interphases, and electrodes. First, the main challenges of aqueous batteries and the problems of the WIS strategy are comprehensively introduced. Second, the electrochemical functions of various electrolyte components (e.g., additives and solvents) are summarized and compared. Gel electrolytes are also investigated as a special form of electrolyte. Third, the formation and modification of the electrolyte-induced interphase on the electrode are discussed. Specifically, the modification and contribution of electrode materials toward improving the WIS strategy are also introduced. Finally, the challenges of aqueous batteries and the prospects of electrolyte and interphase engineering beyond the WIS strategy are outlined for the practical applications of aqueous batteries.

Advancements in aqueous zinc-iodine batteries: a review

Aqueous zinc-iodine batteries stand out as highly promising energy storage systems owing to the abundance of resources and non-combustible nature of water coupled with their high theoretical capacity. Nevertheless, the development of aqueous zinc-iodine batteries has been impeded by persistent challenges associated with iodine cathodes and Zn anodes. Key obstacles include the shuttle effect of polyiodine and the sluggish kinetics of cathodes, dendrite formation, the hydrogen evolution reaction (HER), and the corrosion and passivation of anodes. Numerous strategies aimed at addressing these issues have been developed, including compositing with carbon materials, using additives, and surface modification. This review provides a recent update on various strategies and perspectives for the development of aqueous zinc-iodine batteries, with a particular emphasis on the regulation of I2 cathodes and Zn anodes, electrolyte formulation, and separator modification. Expanding upon current achievements, future initiatives for the development of aqueous zinc-iodine batteries are proposed, with the aim of advancing their commercial viability.

Surface Patterning of Metal Zinc Electrode with an In-Region Zincophilic Interface for High-Rate and Long-Cycle-Life Zinc Metal Anode

The undesirable dendrite growth induced by non-planar zinc (Zn) deposition and low Coulombic efficiency resulting from severe side reactions have been long-standing challenges for metallic Zn anodes and substantially impede the practical application of rechargeable aqueous Zn metal batteries (ZMBs). Herein, we present a strategy for achieving a high-rate and long-cycle-life Zn metal anode by patterning Zn foil surfaces and endowing a Zn-Indium (Zn-In) interface in the microchannels. The accumulation of electrons in the microchannel and the zincophilicity of the Zn-In interface promote preferential heteroepitaxial Zn deposition in the microchannel region and enhance the tolerance of the electrode at high current densities. Meanwhile, electron aggregation accelerates the dissolution of non-(002) plane Zn atoms on the array surface, thereby directing the subsequent homoepitaxial Zn deposition on the array surface. Consequently, the planar dendrite-free Zn deposition and long-term cycling stability are achieved (5,050 h at 10.0 mA cm-2 and 27,000 cycles at 20.0 mA cm-2). Furthermore, a Zn/I2 full cell assembled by pairing with such an anode can maintain good stability for 3,500 cycles at 5.0 C, demonstrating the application potential of the as-prepared ZnIn anode for high-performance aqueous ZMBs.

Synergistic Modulation of Mass Transfer and Parasitic Reactions of Zn Metal Anode via Bioinspired Artificial Protection Layer

Rechargeable aqueous zinc-ion batteries are regarded as promising energy storage devices due to their attractive economic benefits and extraordinary electrochemical performance. However, the sluggish Zn2+ mass transfer behavior and water-induced parasitic reactions that occurred on the anode-electrode interface inevitably restrain their applications. Herein, inspired by the selective permeability and superior stability of plasma membrane, a thin UiO-66 metal-organic framework layer with smart aperture size is ex-situ decorated onto the Zn anode. Experimental characterizations in conjunction with theoretical calculations demonstrate that this bio-inspired layer promotes the de-solvation process of hydrated Zn2+ and reduces the effective contact between the anode and H2 O molecules, thereby boosting Zn2+ deposition kinetics and restraining interfacial parasitic reactions. Hence, the Zn||Zn cells could sustain a long lifespan of 1680 h and the Zn||Cu cells yielded a stable coulombic efficiency of over 99.3% throughout 600 cycles under the assistance of the bio-inspired layer. Moreover, pairing with δ-MnO2 cathode, the full cells also demonstrate prominent cycling stability and rate performance. From the bio-inspired design philosophy, this work provides a novel insight into the development of aqueous batteries.

Ion Sieve Interface Assisted Zinc Anode with High Zinc Utilization and Ultralong Cycle Life for 61 Wh/kg Mild Aqueous Pouch Battery

The cycling stability of a thin zinc anode under high zinc utilization has a critical impact on the overall energy density and practical lifetime of zinc ion batteries. In this study, an ion sieve protection layer (ZnSnF@Zn) was constructed in situ on the surface of a zinc anode by chemical replacement. The ion sieve facilitated the transport and desolvation of zinc ions at the anode/electrolyte interface, reduced the zinc deposition overpotential, and inhibited side reactions. Under a 50% zinc utilization, the symmetrical battery with this protection layer maintained stable cycling for 250 h at 30 mA cm-2. Matched with high-load self-supported vanadium-based cathodes (18-20 mg cm-2), the coin battery with 50% zinc utilization possessed an energy density retention of 94.3% after 1000 cycles at 20 mA cm-2. Furthermore, the assembled pouch battery delivered a whole energy density of 61.3 Wh kg-1, surpassing the highest mass energy density among reported mild zinc batteries, and retained 76.7% of the energy density and 85.3% (0.53 Ah) of the capacity after 300 cycles.

Atomic-Level Customization of Zinc Crystallization Kinetics at the Interface for High-Utilization Zn Anodes

Understanding the crystallization occurring at the inner interfaces during electrochemical deposition is crucial for achieving a high reversibility in zinc anodes. However, design rules for crystallization kinetics still lack predictive power, particularly at the atomic scale, posing a significant challenge. Herein, we propose a crystal facet terminating agent, LaCl3, which modulates the preferential crystallization orientation of Zn by regulating its growth kinetics through the synergistic adsorption of dual ions. Interface molecular dynamics (MD) simulations and crucial experimental parameters reveal that the strong (002) facet texture of Zn deposits primarily depends on the adsorption of strong inhibitors. Specifically, the high adsorption free energy of Cl- on the Zn (002) facet and the concomitant aggregation of La3+ reduces the growth rate of the Zn (002) facet, thereby favoring its preservation as the final crystal facet. Consequently, this terminating agent enables the Zn anodes to deliver a high cumulative capacity of 12 Ah cm-2 at 40 mA cm-2, 20 mAh cm-2. The Zn||MnO2 full cell, when coupled with a high-mass-loading cathode and limited Zn supply, can maintain a practical areal capacity of 3.39 mAh cm-2. Furthermore, rigorous testing conditions and the successful scaling up to a 0.34 Ah pouch cell further confirm its promising prospects for practical applications.

Ultrathin Zincophilic Interphase Regulated Electric Double Layer Enabling Highly Stable Aqueous Zinc-Ion Batteries

The practical application of aqueous zinc-ion batteries for large-grid scale systems is still hindered by uncontrolled zinc dendrite and side reactions. Regulating the electrical double layer via the electrode/electrolyte interface layer is an effective strategy to improve the stability of Zn anodes. Herein, we report an ultrathin zincophilic ZnS layer as a model regulator. At a given cycling current, the cell with Zn@ZnS electrode displays a lower potential drop over the Helmholtz layer (stern layer) and a suppressed diffuse layer, indicating the regulated charge distribution and decreased electric double layer repulsion force. Boosted zinc adsorption sites are also expected as proved by the enhanced electric double-layer capacitance. Consequently, the symmetric cell with the ZnS protection layer can stably cycle for around 3,000 h at 1 mA cm-2 with a lower overpotential of 25 mV. When coupled with an I2/AC cathode, the cell demonstrates a high rate performance of 160 mAh g-1 at 0.1 A g-1 and long cycling stability of over 10,000 cycles at 10 A g-1. The Zn||MnO2 also sustains both high capacity and long cycling stability of 130 mAh g-1 after 1,200 cycles at 0.5 A g-1.

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.

Labile Coordination Interphase for Regulating Lean Ion Dynamics in Reversible Zn Batteries

Rechargeability in zinc (Zn) batteries is limited by anode irreversibility. The practical lean electrolytes exacerbate the issue, compromising the cost benefits of zinc batteries for large-scale energy storage. In this study, a zinc-coordinated interphase is developed to avoid chemical corrosion and stabilize zinc anodes. The interphase promotes Zn2+ ions to selectively bind with histidine and carboxylate ligands, creating a coordination environment with high affinity and fast diffusion due to thermodynamic stability and kinetic lability. Experiments and simulations indicate that interphase regulates dendrite-free electrodeposition and reduces side reactions. Implementing such labile coordination interphase results in increased cycling at 20 mA cm-2 and high reversibility of dendrite-free zinc plating/stripping for over 200 hours. A Zn||LiMn2 O4 cell with 74.7 mWh g-1 energy density and 99.7% Coulombic efficiency after 500 cycles realized enhanced reversibility using the labile coordination interphase. A lean-electrolyte full cell using only 10 µL mAh-1 electrolyte is also demonstrated with an elongated lifespan of 100 cycles, five times longer than bare Zn anodes. The cell offers a higher energy density than most existing aqueous batteries. This study presents a proof-of-concept design for low-electrolyte, high-energy-density batteries by modulating coordination interphases on Zn anodes.

Localized Anion-Cation Aggregated Aqueous Electrolytes with Accelerated Kinetics for Low-Temperature Zinc Metal Batteries

Aqueous zinc metal batteries hold great promise for large-scale energy storage because of their high safety, rich material resources and low cost. However, the freeze of aqueous electrolytes hinders low-temperature operation of the batteries. Here, aqueous localized anion-cation aggregated electrolytes composed of Zn(BF4 )2 as the salt and tetrahydrofuran (THF) as the diluent, are developed to improve the low-temperature performance of the Zn anode. THF promotes the inclusion of BF4 - in the solvation sheath of Zn2+ , facilitating the formation of ZnF2 -rich solid-electrolyte-interphase. THF also affects the hydrogen bonding between neighboring H2 O molecules, effectively lowering the freezing point. Therefore, the full cells of Zn||polyaniline (PANI) exhibit an ultralong cycle life of 8000 cycles with an average Coulombic efficiency of 99.99 % at -40 °C. Impressively, the pouch cells display a high capacity retention of 86.2 % after 500 cycles at -40 °C, which demonstrates the great prospect of such electrolytes in cold regions. This work provides new insights for the design of low-temperature aqueous electrolytes.

In Situ Etching of Multifunctional Three-Dimensional Interfacial Layers for the Construction of Porous Zn Anodes with Enhanced Surface Textures

Aqueous Zn-ion batteries offer the advantages of greater security and lower fabrication costs over their lithium-ion counterparts. However, their further advancement and practical application are hindered by the drastic decay in their performance due to the uncontrollable dendrite growth on Zn anodes. In this study, we fabricated a versatile three-dimensional (3D) interfacial layer (3D PVDF-Zn(TFO)2 (PVDF: poly(vinylidene fluoride); TFO: trifluoromethanesulfonate), which simultaneously formed porous Zn-metal anodes (PZn) with an enhanced (002) texture, via a in situ etching scheme. The 3D PVDF-Zn(TFO)2@PZn symmetrical cells leverage the advantages of surface coating and 3D porous architectures to yield extra-long cyclic lifetimes of over 5300 h (0.1 mA cm-2). The fabricated anodes were found to be compatible with MnO2 cathodes, and the resulting full batteries delivered an outstanding capacity of 336 mAh g-1 at 0.1 A g-1 and exhibited impressive long-term reversibility with a capacity retention of 78.7% for 2000 cycles. The proposed coating strategy is viable for developing porous structures with cutting-edge designs and for textured surface engineering.

Constructing Solid Electrolyte Interphase for Aqueous Zinc Batteries

Problems of zinc anode including dendrite and hydrogen evolution seriously degrade the performance of zinc batteries. Solid electrolyte interphase (SEI), which plays a key role in achieving high reversibility of lithium anode in aprotic organic solvent, is also beneficial to performance improvement of zinc anode in aqueous electrolyte. However, various studies about interphase for zinc electrode is quite fragmented, and lack of deep understanding on root causes or general design rules for SEI construction. And water molecules with high reactivity brings serious challenge to the effective SEI construction. Here, we reviewed the brief development history of zinc batteries firstly, then summarized the approaches to construct SEI in aqueous electrolyte. Furthermore, the formation mechanisms behind approaches are systematically analyzed, together with discussion on the SEI components and evaluation on electrochemical performance of zinc anode with various types of SEI. Meanwhile, the challenge between lab and industrialization are also discussed.

Guiding Zn Uniform Deposition with Polymer Additives for Long-lasting and Highly Utilized Zn Metal Anodes

The parasitic side reaction on Zn anode is the key issue which hinders the development of aqueous Zn-based energy storage systems on power-grid applications. Here, a polymer additive (PMCNA) engineered by copolymerizing 2-methacryloyloxyethyl phosphorylcholine (MPC) and N-acryloyl glycinamide (NAGA) was employed to regulate the Zn deposition environment for satisfying side reaction inhibition performance during long-term cycling with high Zn utilization. The PMCNA can preferentially adsorb on Zn metal surface to form a uniform protective layer for effective water molecule repelling and side reaction resistance. In addition, the PMCNA can guide Zn nucleation and deposition along 002 plane for further side reaction and dendrite suppression. Consequently, the PMCNA additive can enable the Zn//Zn battery with an ultrahigh depth of discharge (DOD) of 90.0 % for over 420 h, the Zn//active carbon (AC) capacitor with long cycling lifespan, and the Zn//PANI battery with Zn utilization of 51.3 % at low N/P ratio of 2.6.

Pure Amorphous and Ultrathin Phosphate Layer with Superior Ionic Conduction for Zinc Anode Protection

Fast and uniform ion transport within the solid electrolyte interphase (SEI) is considered a crucial factor for ensuring the long-term stability of metal electrodes. In this study, we present the fabrication of ultrathin artificial interphases consisting of a zinc phosphate nanofilm with pure amorphous characteristics and a surfactant overlayer. The thickness of the interphases can be precisely controlled within the range of a few tens of nanometers. We explore the impact of artificial SEI structure, including thickness and crystallinity, on its protective capabilities. The pure amorphous phosphate layer with optimized nanoscale thickness is found to provide an abundance of short and isotropic ion migration pathways and a low diffusion energy barrier. These features facilitate rapid and homogeneous Zn2+ transportation, resulting in compact and planar zinc deposition. Meanwhile, the hydrophobic alkyl moieties of the overlayer prevent disassociation of water at the interface. As a result, this nanofilm endures ultralong cycling stability with a low overpotential and enables high Zn plating/stripping reversibility. The Zn||MnO2 full cell shows a stable cycle life for 700 cycles under practical conditions of lean electrolyte, high areal capacity cathode, and limited Zn excess. These findings provide insights into the design and optimization of SEI layers for protection of metal anodes.

Recent Research Progress into Zinc Ion Battery Solid-Electrolyte Interfaces

Aqueous zinc ion batteries (ZIBs) are prospective next-generation energy storage device candidates owing to resource abundance, affordability, eco-friendliness, and safety. The solid-electrolyte interface (SEI) produced in a ZIB by electrolyte/electrode interactions significantly impacts battery performance. The SEI is known to promote dendrite growth, determine the electrochemical stability window, passivate zinc-metal-anodic corrosion, and mutate the electrolyte. Accordingly, the SEI is closely related to the overall property of a ZIB device. This review provides an overview of the impact of SEIs on ZIB performance recently and provides an SEI design strategy based on the formation mechanism, type, and characteristics of the SEI. Finally, future investigational directions for SEIs in ZIBs are expected to lead to a deep understanding of the SEI, enhance ZIB performance, and facilitate their extensive implementation.

Fast Ionic Conducting Hydroxyapatite Solid Electrolyte Interphase Enables Ultra-Stable Zinc Metal Anodes

Zn metal has been extensively utilized as an anode in aqueous zinc-ion batteries attributed to its affordable cost and superior theoretical capacity. Nevertheless, the presence of dendrites and undesirable side reactions poses challenges to its widespread commercialization. To address these issues, herein, a surface coating composed of hydroxyapatite (HAP) was developed on the Zn anode to create an artificial solid electrolyte interphase. After the application of a hydroxyapatite layer, dendrites and corrosion of the Zn anode are sufficiently inhibited. Furthermore, the hydroxyapatite interphase with a low ionic diffusion barrier enables fast anodic redox kinetics. Consequently, the Zn@HAP symmetric cell possesses a durable lifespan over 2000 h at 1 mA cm-2, while maintaining minimal polarization. Moreover, the practical feasibilities of the Zn@HAP anode are also manifested in full batteries combined with MnO2 cathodes, exhibiting exceptional cycling performance up to 500 cycles at 1 A g-1 and excellent rate capability with a retention of 109 mAh g-1 at 5 A g-1.

A biocompatible electrolyte enables highly reversible Zn anode for zinc ion battery

Progress towards the integration of technology into living organisms requires power devices that are biocompatible and mechanically flexible. Aqueous zinc ion batteries that use hydrogel biomaterials as electrolytes have emerged as a potential solution that operates within biological constraints; however, most of these batteries feature inferior electrochemical properties. Here, we propose a biocompatible hydrogel electrolyte by utilising hyaluronic acid, which contains ample hydrophilic functional groups. The gel-based electrolyte offers excellent anti-corrosion ability for zinc anodes and regulates zinc nucleation/growth. Also, the gel electrolyte provides high battery performance, including a 99.71% Coulombic efficiency, over 5500 hours of long-term stability, improved cycle life of 250 hours under a high zinc utilization rate of 80%, and high biocompatibility. Importantly, the Zn//LiMn2O4 pouch cell exhibits 82% capacity retention after 1000 cycles at 3 C. This work presents a promising gel chemistry that controls zinc behaviour, offering great potential in biocompatible energy-related applications and beyond.

Balancing Interfacial Reactions through Regulating p-Band Centers by an Indium Tin Oxide Protective Layer for Stable Zn Metal Anodes

Metallic zinc (Zn) is considered as one of the most attractive anode materials for the post-lithium metal battery systems owing to the high theoretical capacity, low cost, and intrinsic safety. However, the Zn dendrites and parasitic side reaction impede its application. Herein, we propose a new principle of regulating p-band center of metal oxide protective coating to balance Zn adsorption energy and migration energy barrier for effective Zn deposition and stripping. Experimental results and theoretical calculations indicate that benefiting from the uniform zincophilic nucleation sites and fast Zn transport on indium tin oxide (ITO), highly stable and reversible Zn anode can be achieved. As a result, the I-Zn symmetrical cell achieves highly reversible Zn deposition/stripping with an extremely low overpotential of 9 mV and a superior lifespan over 4000 h. The Cu/I-Zn asymmetrical cell exhibits a long lifetime of over 4000 cycles with high average coulombic efficiency of 99.9 %. Furthermore, the assembled I-Zn/AC full cell exhibits an excellent lifetime for 70000 cycles with nearly 100 % capacity retention. This work provides a general strategy and new insight for the construction of efficient Zn anode protection layer.

Solvation Modulation Enhances Anion-Derived Solid Electrolyte Interphase for Deep Cycling of Aqueous Zinc Metal Batteries

Stable Zn anodes with a high utilization efficiency pose a challenge due to notorious dendrite growth and severe side reactions. Therefore, electrolyte additives are developed to address these issues. However, the additives are always consumed by the electrochemical reactions over cycling, affecting the cycling stability. Here, hexamethylphosphoric triamide (HMPA) is reported as an electrolyte additive for achieving stable cycling of Zn anodes. HMPA reshapes the solvation structures and promotes anion decomposition, leading to the in situ formation of inorganic-rich solid-electrolyte-interphase. More interestingly, this anion decomposition does not involve HMPA, preserving its long-term impact on the electrolyte. Thus, the symmetric cells with HMPA in the electrolyte survive ≈500 h at 10 mA cm-2 for 10 mAh cm-2 or ≈200 h at 40 mA cm-2 for 10 mAh cm-2 with a Zn utilization rate of 85.6 %. The full cells of Zn||V2 O5 exhibit a record-high cumulative capacity even under a lean electrolyte condition (E/C ratio=12 μL mAh-1 ), a limited Zn supply (N/P ratio=1.8) and a high areal capacity (6.6 mAh cm-2 ).

Dynamic Zn/Electrolyte Interphase and Enhanced Cation Transfer of Sol Electrolyte for All-Climate Aqueous Zinc Metal Batteries

Zn metal as one of the promising anodes of aqueous batteries possesses notable advantages, but it faces severe challenges from severe side reactions and notorious dendrite growth. Here, ultrathin nanosheets of α-zirconium phosphate (ZrP) are explored as an electrolyte additive. The nanosheets not only create a dynamic and reversible interphase on Zn but also promote the Zn2+ transportation in the electrolyte, especially in the outer Helmholtz plane near ZrP. Benefited from the enhanced kinetics and dynamic interphase, the pouch cells of Zn||LiMn2 O4 using this electrolyte remarkably improve electrochemical performance under harsh conditions, i.e. Zn powders as the Zn anode, high mass loading, and wide temperatures. The results expand the materials available for this dynamic interphase, provide an insightful understanding of the enhanced charge transfer in the electrolyte, and realize the combination of dynamic interphase and enhanced kinetics for all-climate performance.