Coordination modulation of hydrated zinc ions to enhance redox reversibility of zinc batteries

Organic-inorganic hybrid cathode enabled by in-situ interface polymerization engineering boosts Zn2+ desolvation in aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) have attracted considerable attention for application in large-scale energy storage systems. However, the progress of RAZIBs has been hindered by the sluggish reaction kinetics and poor structural stability, which are closely associated with the desolvation process of hydrated Zn2+. To overcome these issues, an in situ interfacial polymerization strategy is proposed to uniformly germinate a polyaniline (PANI) layer on α-MnO2 and form an organic-inorganic hybrid cathode (MnO2@PANI). Theoretical calculations and experimental characterizations disclose that the polyaniline layer equipped with hydrophilic functional groups can effectively trap the active water molecules to break the strong attraction between H2O and Zn2+, thereby facilitating the desolvation process of hydrated Zn2+, and regulating the Zn2+ diffusion kinetics and electrode reaction kinetics on the cathode/electrolyte surface. Meanwhile, the irreversible phase evolution and dissolution of active species are largely suppressed due to the PANI shell protecting the α-MnO2 from the attack of active water molecules. As a consequence, the organic-inorganic hybrid cathode exhibits 401.9 mAh/g after 200 cycles at a current density of 0.5 A/g and long-term durability over 1000 cycles at a current density of 2.0 A/g without irreversible phase transformation. This work provides insight into the regulation of the desolvation process for high performance aqueous energy storage systems.

A processable and recyclable gelatin/carboxymethyl chitosan hydrogel electrolyte for high performance flexible zinc-ion batteries

Hydrogels are currently under extensive research as flexible quasi-solid electrolytes for zinc-ion batteries. However, the non-degradability and non-recyclability of hydrogel electrolytes pose significant issues, leading to resource wastage and plastic pollution. Moreover, the increasing needs of hydrogel electrolyte with various shapes to meet individual requirements of next-generation flexible battery raise significant challenges. In this study, we introduce the Hofmeister effect and multiple non-covalent interactions to fabricate an eco-friendly and recyclable multifunctional hydrogel electrolyte using biomass natural polymers. This is achieved by simply soaking primary hydrogel networks of carboxymethyl chitosan (CMCS) and gelatin in zinc sulfate (ZnSO4) aqueous solutions, abbreviated as GCZ-x. The GCZ-x hydrogels exhibit both stiffness and toughness due to the formation of crystalline domains and ionic crosslinks. The dynamic physical interactions and temperature and pH responsiveness of the GCZ-x hydrogels enable them excellent processability and recyclability. The zinc-ion battery with GCZ-x hydrogel as electrolyte exhibits high specific capacity and superior cyclic performance (2200 h at 0.1 A g-1) without the formation of zinc dendrites. The GCZ-x electrolyte is sustainable with high recycling rate (above 80 %). It is envisaged that the GCZ-x hydrogel electrolyte will initiate new prosperity of green zinc-ion batteries in energy-efficient and environmentally sustainable ways.

A multifunctional quasi-solid-state polymer electrolyte with highly selective ion highways for practical zinc ion batteries

The uncontrolled dendrite growth and detrimental parasitic reactions of Zn anodes currently impede the large-scale implementation of aqueous zinc ion batteries. Here, we design a versatile quasi-solid-state polymer electrolyte with highly selective ion transport channels via molecular crosslinking of sodium polyacrylate, lithium magnesium silicate and cellulose nanofiber. The abundant negatively charged ionic channels modulate Zn2+ desolvation process and facilitate ion transport. Moreover, an in-situ formed Zn-Mg-Si medium-entropy alloy on Zn anode allows for an improved Zn nucleation kinetics and homogeneous Zn deposition. These combined advantages of the polymer electrolyte enable Zn anodes to achieve an average Coulombic efficiency of 99.7 % over 2400 cycles and highly reversible cycling up to 600 h with large depth of discharge of 85.6%. The resultant Zn | |V2O5 offers a stable long-term cycling performance and its pouch cell achieves a cycling capacity of 1.13 Ah at industrial-level loading mass of 31.3 mg.

Polyelectrolyte Additive-Modulated Interfacial Microenvironment Boosting CO2 Electrolysis in Acid

Acidic CO2 electrolysis offers a promising strategy to achieve high carbon utilization and high energy efficiency. However, challenges still remain in suppressing the competitive hydrogen evolution reaction (HER) and improving product selectivity. Although high concentrations of potassium ions (K+) can suppress HER and accelerate CO2 reduction, they still inevitably suffer from salt precipitation problems. In this study, we demonstrate that the sulfonate-based polyelectrolyte, polystyrene sulfonate (PSS), enables to reconstruct the electrode-electrolyte interface to significantly enhance the acidic CO2 electrolysis. Mechanistic studies reveal that PSS induces high local K+ concentrations through the electrostatic interaction between PSS anions and K+. In situ spectroscopy reveals that PSS reshapes the interfacial hydrogen-bond (H-bond) network, which is attributed to the H-bonds between PSS anions and hydrated proton, as well as the steric hindrance of the additive molecules. This greatly weakens proton transfer kinetics and leads to the suppression of undesirable HER. As a result, a Faradaic efficiency of 93.9 % for CO can be achieved at 250 mA cm-2, simultaneous with a high single-pass carbon efficiency of 72.2 % on commercial Ag catalysts in acid. This study highlights the important role of the electrode-electrolyte interface induced by polyelectrolyte additives in promoting electrocatalytic reactions.

Ultra-fast activated NH4+-intercalated vanadium oxide cathode for high-performance aqueous zinc-ion batteries

Vanadium-based oxides hold immense promise as cathode materials for aqueous zinc-ion batteries (AZIBs); however, their practical implementation faces a significant hurdle: a prolonged activation period is typically required to achieve peak performance. This activation process, which often requires hundreds of cycles, arises from the complex behavior of mixed-valence vanadium systems. In this paper, we propose a solution based on an elegant and simple electrical activation strategy. By applying a carefully designed precycling charging protocol to NH4+-intercalated vanadium oxide (VON), we achieved activation speeds, reaching peak capacity within just several to 25 cycles-even under high current densities. The electrochemically activated material (E-VON) demonstrates performance metrics: delivering a high specific capacity of 359.1 mAh g-1 at 0.1 A g-1, maintaining a rate capability of 155.5 mAh g-1 at 10 A g-1, and showing cycling stability. The electrical activation process enhances ion transport within the VON structure and triggers a Zn2+/H+ coinsertion mechanism during cycling. This mechanism is intricately linked to the reversible formation and dissolution of a basic zinc sulfonate by-product, offering new insights into charge storage processes within vanadium-based AZIB cathodes. Our comprehensive characterization revealed how this activation strategy fundamentally transforms the structure and electrochemical behavior of materials, providing a practical pathway to overcome the longstanding limitations of traditional vanadium oxide cathodes. This study focuses on rapidly activating cathode materials, advancing the development of high-performance AZIBs.

Regulating Zn Deposition Manner by Confining the Reactivity of Free Water in the Electric Double Layer

Aqueous Zn ion batteries (AZIBs) are promising candidates of next-generation energy storage devices with high safety and theoretical capacity. However, the irreversibility of metallic Zn anode, attributed to dendrite growth and water decomposition, severely limits the cycling durability of AZIBs and restricts their further development. Herein, a facile surface engineering strategy is put forward to tackle the issue of poor reversibility of the Zn anode. Benzotriazole (BTA) is employed as a functional additive of ZnSO4 electrolyte to confine the reactivity of free water situated in the electric double layer (EDL). Experimental results and theoretical simulation reveal that BTA can preferiencially adsorb onto the Zn surface to uniform Zn2+ ion distribution and alleviate H2O-involved side reactions like hydrogen evolution, and surface passivation. Consequently, in BTA-modulated aqueous electrolyte, the lifespan of the Zn anode is extended from 170 h-1092 h at 1 mA cm-2/1 mAh cm-2. The reversibility improvement of Zn anode also benefits the cycling durability of full devices including supercapacitors and batteries. Zn||I₂ batteries assembled in as-designed electrolyte witness only 11.3 % capacity decay over 17000 cycles at 1 A g-1, far outstripping that observed in ZnSO4 counterpart (~4675 cycles). The design criteria proposed in this study offers a new concept for the development of regulation additives that confine the reactivity of free water in the electric double layer.

Carbon Dioxide Evolution in Aqueous Zinc Metal Batteries

Gas evolution reactions in aqueous zinc metal batteries (AZMBs) cause gas accumulation and battery swelling that negatively affect their performance. However, previous work often reported hydrogen as the main, if not the only, gas species evolved in AZMBs; the complexity of gas evolution has been overlooked. For the first time, this work found the CO2 evolution reaction (CER) in AZMBs, pinpointed its sources, and identified electrolyte modulation strategies. Using differential electrochemical mass spectrometry, CER was detected in V2O5||Zn full cells, instead of in asymmetric Cu||Zn cells, and it became substantial when being charged to 2.0 V. By using a carbon isotope tracing method, the primary origin of CER was identified as the electrochemical corrosion of conductive carbon at the cathode. Among six representative electrolytes, the weakly solvating electrolyte (3 m Zn(OTf)2 in acetonitrile/water) presented a high CER resistance by reducing water solvating and disturbing hydrogen bonding. This work sheds light on interfacial parasitic reactions for practical aqueous metal (Zn and Al) batteries.

Realization of Hydrogel Electrolytes with High Thermoelectric Properties: Utilization of the Hofmeister Effect

Ionic thermoelectric materials, renowned for their high Seebeck coefficients, are gaining prominence for their potential in harvesting low-grade waste heat. However, the theoretical underpinnings for enhancing the performance of these materials remain underexplored. In this study, the Hoffmeister effect was leveraged to augment the thermoelectric properties of hydrogel-based ionic thermoelectric materials. A series of PAAm-x Zn(CF3SO3)2, PAAm-x ZnSO4, and PAAm-x Zn(ClO4)2 hydrogels were synthesized, using polyacrylamide (PAAm) as the matrix and three distinct zinc salts with varying anion volumes to impart the Hoffmeister effect. Exceptionally, the most cost-effective ZnSO4 yielded the highest ionic Seebeck coefficient among the hydrogels, with PAAm-1 ZnSO4 achieving a remarkable value of -3.72 mV K-1. To elucidate the underlying mechanism, we conducted an innovative analysis correlating the Seebeck coefficient with the zinc ion transfer number. Additionally, the hydrogel materials demonstrated outstanding mechanical properties, including high elongation at break (>1400% at its peak), exceptional resilience (virtually no hysteresis loops), and robust fatigue resistance (overlapping cyclic tensile curves). This work not only advances the understanding of ionic thermoelectric materials but also showcases the potential of hydrogels for practical waste heat recovery applications.

Trace amount of taurine leveling agent for stable Zn anode

Aqueous zinc-ion batteries are highly praised for their cost-effectiveness, environmental friendliness, and high safety, making them an ideal choice for next-generation energy storage systems. However, the practical application of Zn metal anodes is constrained by well-known challenges such as dendrite growth and significant interfacial side reactions. This study introduces a trace amount of taurine (TAU) as a leveling additive into the electrolyte to optimize the microstructure of the electrolyte and the anode interface chemistry. On one hand, the preferential adsorption of TAU on the Zn surface promotes the in situ formation of a stable, protective molecular interfacial layer on the anode, which helps to refine the deposited grains and guide the uniform deposition of Zn2+. On the other hand, the introduction of TAU can regulate the hydrogen bond structure in the electrolyte, reduce the activity of water, thereby significantly inhibiting the occurrence of side reactions such as hydrogen evolution. Consequently, the Zn//Zn symmetric cell system demonstrates an extended cycle life of over 1150 cycles at a current density of 1 mA cm-2 and maintains stable cycling performance for over 600 cycles at 10 mA cm-2. Moreover, the Zn//Cu asymmetric cell system achieves over 1400 cycles of reversible deposition/dissolution at a current density of 1 mA cm-2, with a coulombic efficiency of 99.4%. The incorporation of TAU further enhances the cycle stability of the Zn//MnO2 full cell. These innovative achievements have laid a solid foundation for the broader industrial adoption of aqueous zinc-ion batteries.

Multifunctional Interface Layer Constructed by Trace Zwitterions for Highly Reversible Zinc Anodes

The inhomogeneous plating/stripping of Zn anode, attributed to dendrite growth and parasitic reactions at the electrode/electrolyte interface, severely restricts its cycling life-span. Here, trace zwitterions (trifluoroacetate pyridine, TFAPD) are introduced into the aqueous electrolyte to construct a multifunctional interface that enhances the reversibility of Zn anode. The TFA- anions with strong specific adsorption adhere onto the Zn surface to reconstruct the inner Helmholtz plane (IHP), preventing the hydrogen evolution and corrosion side reactions caused by free H2O. The Py+ cations accumulate on the outer Helmholtz plane (OHP) of Zn anode with the force of electric field during Zn2+ plating, forming a shielding layer to uniformize the deposition of Zn2+. Besides, the adsorbed TFA- and Py+ promote the desolvation process of Zn2+ resulting in fast reaction kinetics. Thus, the Zn||Zn cells present an outstanding cycling performance of more than 10000 hours. And even at 85 % utilization rate of Zn, it can stably cycle for over 200 hours at 10 mA cm-2 and 10 mAh cm-2. The Zn||I2 full cell exhibits a capacity retention of over 95 % even after 30000 cycles. Remarkably, the Zn||I2 pouch cells (95 mAh) deliver a high-capacity retention of 99 % after 750 cycles.

Electrical Double Layer and In Situ Polymerization SEI Enables High Reversible Zinc Metal Anode

Aqueous zinc-ion batteries (AZIBs) stand out among new energy storage devices due to their excellent safety and environmental friendliness. However, the formation of dendrites and side reactions on the zinc metal anode during cycling have become the major obstacles to their commercialization. This study innovatively selected Sodium 4-vinylbenzenesulfonate (VBS) as a multifunctional electrolyte additive to address the issues. The dissociated VBS- anions can not only significantly alter the hydrogen bond network structure of H2O in the electrolyte, but also preferentially adsorb on the surface of the zinc anode before H2O molecules, which will result in the development of organic anion-rich interface and alterations to the electrical double layer (EDL) structure. Furthermore, the ─C═C─ structure in VBS leads to the formation of an in situ polymerized organic anion solid electrolyte interface (SEI) layer that adheres to the surface of the zinc anode. The mechanisms work together to significantly improve the performance of Zn//Zn symmetric batteries, achieving a cycle life of over 1800 h at 1 mA cm-2 and 1 mAh cm-2. The introduction of VBS also enhances the cycling performance and capacity of Zn//δ-MnO2 full cells. This study provides a low-cost solution for the development of AZIBs.

Tunable Zn2+ de-solvation behavior in MnO2 cathodes via self-assembled phytic acid monolayers for stable aqueous Zn-ion batteries

Sluggish ion diffusion kinetics at the electrode/electrolyte interface leads to insufficient rate capability and poor structural reversibility, which are mainly attributed to the hydrated Zn2+ migration process being inhibited due to its huge de-solvation energy barriers. Herein, a self-assembly method is proposed in which a multifunctional monolayer with phytic acid (PA) is coated on the surface of MnO2 strongly attaching to the substrate with the formation of chemical bonding to effectively prevent the dissolution of PA in the electrolyte. Due to the negative charge and inherent ultra-hydrophilicity of PA, modified MnO2 demonstrates stronger adsorption of positive ions and captures reactive water molecules, easily accelerating the de-solvation process of interfacial hydrated Zn2+, efficiently achieving reversible Zn2+ insertion/extraction. Meanwhile, the coating layers can protect the substrate from attack by active water molecules, thus inhibiting cathode dissolution during battery cycling. Experimental characterization studies reveal that the protected MnO2 cathode exhibits a remarkable specific capacity of 273 mA h g-1 with a zinc intercalation capacity contribution of more than 60% at a current density of 0.1 A g-1. Additionally, even at a high current density of 1 A g-1, it maintains a capacity of 197 mA h g-1, far exceeding that of pure MnO2. Furthermore, the Zn-ion pouch cell, serving as a proof of concept, achieves an impressive energy density of 300 W h kg-1 and exhibits remarkable capacity retention of 77% even after 100 cycles. This work offers a universal strategy for expediting the de-solvation process of hydrated Zn2+ on the surface of manganese-based cathodes in aqueous zinc-ion batteries.

Porous V2CTx MXene as a High Stability Zinc Anode Protective Coating

Aqueous Zn batteries exhibit significant research potential owing to their environmental friendliness and high energy density. Nevertheless, the formation of dendrites on the zinc anode and the sluggish diffusion kinetics of zinc ions adversely affect the cycle life of zinc ion batteries. In this study, we employ porous V2CTx (MVMX) as a protective layer for the zinc anode. The uniform porous structure of MVMX promotes active site exposure and facilitates the transport of zinc ions. Remarkably, the Zn@Ti half-cell demonstrated an average CE of 99.7% in 1500 cycles. Furthermore, the Zn-Zn symmetric battery exhibited stable cycling for 1600 h at current densities of 5 mA cm-2 and 1 mAh cm-2. Additionally, the MVMX@Zn||V2O5 full cell exhibited a capacity of 198 mAh g-1 and retained a capacity of 124.75 mAh g-1 after 5000 cycles at 1 A g-1, demonstrating the potential of employing alternative MXenes for fabricating stable zinc anodes.

Sulfurized Composite Interphase Enables a Highly Reversible Zn Anode

The stability and reversibility of Zn anode can be greatly improved by in situ construction of solid electrolyte interphase (SEI) on Zn surface via a low-cost design strategy of ZnSO4 electrolyte. However, the role of hydrogen bond acceptor -SO3 accompanying ZnS formation during SEI reconstruction is overlooked. In this work, we have explored and revealed the new role of -SO3 and ZnS in the in situ formed sulfide composite SEI (SCSEI) on Zn anode electrochemistry in ZnSO4 aqueous electrolytes. Structure characterization and DFT demonstrate that the introduction of -SO3 can not only reduce the dehydration energy of [Zn(H2O)6]2+, but also enhance the stability of the ZnS/Zn interface and homogenize the ZnS/Zn interface electric field, thereby significantly improving the dynamic kinetics and uniform deposition of Zn2+. Owing to the synergistic effect of ZnS and -SO3, a high cycling stability of 1500 h with a cumulative-plated capacity of 7.5 Ah cm-2 at 10 mA cm-2 has been achieved within the symmetrical cell. Furthermore, the full cell with NH4V4O10 cathode exhibits outstanding cyclic stability, exceeding 2000 cycles at 5 A g-1 and maintaining a Coulombic efficiency of 100 %. These new insights into anionic synergistic strategy could significantly enhance the practical application of zinc-ion batteries.

Strong Replaces Weak: Hydrogen Bond-Anchored Electrolyte Enabling Ultra-Stable and Wide-Temperature Aqueous Zinc-Ion Capacitors

Despite aqueous electrolytes offer a great opportunity for large-scale energy storage owing to their safety and cost-effectiveness, their practical application suffers from the parasitic side reactions and poor temperature adaptability stemming from weak hydrogen-bond (HB) network in free water. Here, we propose the guiding thought "strong replaces weak" to design hydrogen bond-anchored electrolyte by introducing sulfolane (SL) for disrupting the regular weak HB network and contributing to superior temperature tolerance. Judiciously combined experimental characterization and theoretical calculation confirm that SL can remodel the primary solvation shell of metal ions, customize stable electrode interface chemistry and restrain the side reactions. Consequently, symmetric supercapacitor constructed by activated carbon (AC) electrodes is able to fully work within a voltage range of 2.4 V and reach high capacitance retention of 89.8 % after 60000 cycles. Additionally, Zn anodes exhibit ultra-stable Zn plating/stripping behaviors and a wide temperature range (-20-60 °C), and zinc-ion capacitor (Zn//AC) also delivers an excellent cycling stability with capacity retention of 99.7 % after 55000 cycles, implying that the designed electrolyte has practical application potential in extreme environments. This work proposes a novel critical solvation strategy that paves the route for the construction of ultra-stable and wide-temperature aqueous energy storage devices.

A tripartite synergistic optimization strategy for zinc-iodine batteries

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

Photo-Assisted Chemical Self-Rechargeable Zinc Ion Batteries with High Charging and Discharging Efficiency

Chemical self-recharging zinc ion batteries (ZIBs), which are capable of auto-recharging in ambient air, are promising in self-powered battery systems. Nevertheless, the exclusive reliance on chemical energy from oxygen for ZIBs charging often would bring some obstacles in charging efficiency. Herein, we develop photo-assisted chemical self-recharging aqueous ZIBs with a heterojunction of MoS2/SnO2 cathode, which are favorable to enhancing both the charging and discharging efficiency as well as the chemical self-charging capabilities under illumination. The photo-assisted process promotes the electron transfer from MoS2/SnO2 to oxygen, accelerating the occurrence of the oxidation reaction during chemical self-charging. Furthermore, the electrons within the MoS2/SnO2 cathode exhibit a low transfer impedance under illumination, which is beneficial to reducing the migration barrier of Zn2+ within the cathode and thereby facilitating the uniform inserting of Zn2+ into MoS2/SnO2 cathode during discharging. This photo-assisted chemical self-recharging mechanism enables ZIBs to attain a maximum self-charging potential of 0.95 V within 3 hours, a considerable self-charging capacity of 202.5 mAh g-1 and excellent cycling performance in a self-charging mode. This work not only provides a route for optimizing chemical self-charging energy storage, but also broadens the potential application of aqueous ZIBs.

3D Leaf-Like Copper-Zinc Alloy Enables Dendrite-Free Zinc Anode for Ultra-Long Life Aqueous Zinc Batteries

Metallic zinc exhibits immense potential as an anode material for aqueous rechargeable zinc batteries due to its high theoretical capacity, low redox potential, and inherent safety. However, practical applications are hindered by dendrite formation and poor cycling stability. Herein, a facile substitution reaction method is presented to fabricate a 3D leaf-like Cu@Zn composite anode. This unique architecture, featuring a 3D network of leaf-like Cu on a Zn foil surface, significantly reduces nucleation overpotential and facilitates uniform Zn plating/stripping, effectively suppressing dendrite growth. Notably, an alloy layer of CuZn5 forms in situ on the 3D Cu layer during cycling. DFT calculations reveal that this CuZn5 alloy possesses a lower Zn binding energy compared to both Cu and Zn metal, further promoting Zn plating/stripping and enhancing electrochemical kinetics. Consequently, the symmetric Cu@Zn electrode exhibits remarkable cycling stability, surpassing 1300 h at 0.5 mA cm-2 with negligible dendrite formation. Furthermore, full cells comprising Cu@Zn||VO2 exhibit superior capacity and rate performance compared to bare Zn anodes. This work provides a promising strategy for constructing highly stable and efficient Zn anodes for next-generation aqueous zinc batteries.

Nanoconfined Supercooled Water in Hydrated Two-Dimensional Polyaniline for Sub-Zero Solid-State Zinc-Ion Hybrid Capacitor

Solid-state electrochemical energy systems have attracted numerous attentions for their excellent performance, high safety, and low cost. Recently, ice of aqueous electrolytes is reported as a new kind solid-state electrolyte for low-temperature solid-state devices. However, the lack of kinetically favorable electrodes hampers the performance of this new class of icy electrolyte-based solid-state devices at sub-zero temperatures. In this work, a hydrated layered polyaniline cathode active material (h-LPANi) with nanoconfined supercooled water by metatungstate clusters is utilized to improve the performance of sub-zero solid-state zinc ion hybrid capacitors (ZIHCs). The interlayer confined hydrated network of h-LPANi improves kinetics, surpassing pristine polyaniline and conventional porous carbon-based active materials. At -15 °C, the solid-state iced ZIHCs with h-LPANi cathode demonstrate an areal energy density of 580.0 µWh cm-2 at 1.1 mW cm-2 and 155.7 µWh cm-2 at 43.3 mW cm-2, surpassing other low-temperature solid-state ZIHCs with conventional cathodes.

Zinc Chemistries of Hybrid Electrolytes in Zinc Metal Batteries: From Solvent Structure to Interfaces

Along with the booming research on zinc metal batteries (ZMBs) in recent years, operational issues originated from inferior interfacial reversibility have become inevitable. Presently, single-component electrolytes represented by aqueous solution, "water-in-salt," solid, eutectic, ionic liquids, hydrogel, or organic solvent system are hard to undertake independently the task of guiding the practical application of ZMBs due to their specific limitations. The hybrid electrolytes modulate microscopic interaction mode between Zn2+ and other ions/molecules, integrating vantage of respective electrolyte systems. They even demonstrate original Zn2+ mobility pattern or interfacial chemistries mechanism distinct from single-component electrolytes, providing considerable opportunities for solving electromigration and interfacial problems in ZMBs. Therefore, it is urgent to comprehensively summarize the zinc chemistries principles, characteristics, and applications of various hybrid electrolytes employed in ZMBs. This review begins with elucidating the chemical bonding mode of Zn2+ and interfacial physicochemical theory, and then systematically elaborates the microscopic solvent structure, Zn2+ migration forms, physicochemical properties, and the zinc chemistries mechanisms at the anode/cathode interfaces in each type of hybrid electrolytes. Among of which, the scotoma and amelioration strategies for the current hybrid electrolytes are actively exposited, expecting to provide referenceable insights for further progress of future high-quality ZMBs.

Regulation of Zn2+ Solvation Configuration in Aqueous Batteries via Selenium-Substituted Crown Ether Engineering

The efficient utilization of the metallic Zn in rechargeable aqueous Zn-ion batteries (RAZBs) struggle to suffer from parasitic Zn dendrite formation, hydrogen evolution reactions as well as severe interfacial degradation at high areal capacity loadings. This study thus proposes to employ the modified crown ether as an aqueous electrolyte additive to regulate the Zn2+ desolvation kinetic and facilitates the horizontally oriented (002) deposition of Zn, extending the lifespan of both the symmetric cell and full cell models. Specifically, zincophilic cyano and hydrophobic selenium atoms are incorporated into the crown ether supramolecule to enhance Zn2+ coordination and desolvation capability. The addition of 4-cyanobenzo-21-crown-7-selenium at a low concentration of 0.5 wt.% effectively mitigates hydrogen evolution and Zn corrosion caused by water, promoting the oriented deposition of Zn2+. The Zn||V2O5 full cell prototype, assembled with the areal capacity loadings of 2 mAh cm-2 and N/P ratio of 2.95, exhibits negligible capacity fading at 2.0A g-1 for 300 cycles, highlighting the commercial feasibility of supramolecular macrocycles additive for practical RAZBs applications.

Visualizing and Understanding the Ionic Liquid-Mediated Polybromide Electrochemistry for Aqueous Zinc-Bromine Redox Batteries

Aqueous zinc-bromine redox systems possess multiple merits for scalable energy storage. Applying bromine complexing agents shows effectiveness in alleviating the key challenge of ubiquitous crossover of reactive liquid bromine species, while the underlying microscopic mechanism requires a deep understanding to engineer better complexing electrochemistry. Herein, taking a series of quaternary ammonium ionic liquids (methyl4NBr, ethyl4NBr, propyl4NBr, and butyl4NBr) as a redox mediator model, operando optical monitoring was used to visualize the dynamic electrochemical behaviors, unveiling the ionic liquid-mediated polybromide electrochemistry with a distinct chain length effect. A longer chain length possesses a stronger electrostatic interaction in the complexing product to effectively capture Br2. Operando results reveal the liquid nature of the reversibly electrogenerated polybromide microdroplets in the butyl4NBr-added redox system, which promoted the Br3-/Br- conversion kinetics and alleviated the self-discharge for improved battery performance. This work provides direct evidence and new insights into complexing electrochemistry for advancing Zn-Br2 batteries.

Quantum Spin Exchange Interactions Trigger O p Band Broadening for Enhanced Aqueous Zinc-Ion Battery Performance

The pressing demand for large-scale energy storage solutions has propelled the development of advanced battery technologies, among which zinc-ion batteries (ZIBs) are prominent due to their resource abundance, high capacity, and safety in aqueous environments. However, the use of manganese oxide cathodes in ZIBs is challenged by their poor electrical conductivity and structural stability, stemming from the intrinsic properties of MnO2 and the destabilizing effects of ion intercalation. To overcome these limitations, our research delves into atomic-level engineering, emphasizing quantum spin exchange interactions (QSEI). These essential for modifying electronic characteristics, can significantly influence material efficiency and functionality. We demonstrate through density functional theory (DFT) calculations that enhanced QSEI in manganese oxides broadens the O p band, narrows the band gap, and optimizes both proton adsorption and electron transport. Empirical evidence is provided through the synthesis of Ru-MnO2 nanosheets, which display a marked increase in energy storage capacity, achieving 314.4 mAh g-1 at 0.2 A g-1 and maintaining high capacity after 2000 cycles. Our findings underscore the potential of QSEI to enhance the performance of TMO cathodes in ZIBs, pointing to new avenues for advancing battery technology.

In situ construction of a static-dynamic hybrid interface toward stable Zn anodes for aqueous Zn-ion batteries

Aqueous Zn-ion batteries are promising candidates for next-generation energy storage devices due to the advantages of high safety, low cost and good environmental friendliness. However, the uncontrollable dendrite growth and undesirable side reactions occurring on the Zn anode result in poor cycling stability. Herein, a Lewis base, triethanolamine, is used as the electrolyte additive to construct a hybrid solid-electrolyte interphase layer composed of a static ZnSO4·3Zn(OH)2·4H2O layer and dynamic quaternary ammonium ion adsorption layer. The static SEI layer acts as a physical barrier between the Zn anode and electrolyte, thus effectively suppressing chemical corrosion and the hydrogen evolution reaction. The dynamic layer can not only regulate the ion flux at the interface, but also promote the de-solvation of solvated Zn2+, thus leading to homogenous Zn deposition along the (002) electro-crystallization orientation. As a result, the Zn anode demonstrates an extended cycle life of 2500 h at a current density of 1.0 mA cm-2, with an areal capacity of 1.0 mA h cm-2 and a high coulombic efficiency (CE) of 98.94%. The Zn‖V2O5 cells exhibit a specific capacity of 178.4 mA h g-1 after 500 cycles, indicating both high capacity and robust cycling stability, which are essential for practical applications.

Tailoring Oxygen-Depleted and Unitary Ti3C2Tx Surface Terminals by Molten Salt Electrochemical Etching Enables Dendrite-Free Stable Zn Metal Anode

Two-dimensional Ti3C2Tx MXene materials, with metal-like conductivities and versatile terminals, have been considered to be promising surface modification materials for Zn-metal-based aqueous batteries (ZABs). However, the oxygen-rich and hybridized terminations caused by conventional methods limit their advantages in inhibiting zinc dendrite growth and reducing corrosion-related side reactions. Herein, -O-depleted, -Cl-terminated Ti3C2Tx was precisely fabricated by the molten salt electrochemical etching of Ti3AlC2, and controlled in situ terminal replacement from -Cl to unitary -S or -Se was achieved. The as-prepared -O-depleted and unitary-terminal Ti3C2Tx as Zn anode coatings provided excellent hydrophobicity and enriched zinc-ionophilic sites, facilitating Zn2+ horizontal transport for homogeneous deposition and effectively suppressing water-induced side reactions. The as-assembled Ti3C2Sx@Zn symmetric cell achieved a cycle life of up to 4200 h at a current density and areal capacity of 2 mA cm-2 and 1 mAh cm-2, respectively, with an impressive cumulative capacity of up to 7.25 Ah cm-2 at 5 mA cm-2//2 mAh cm-2. These findings provide an effective electrochemical strategy for tailoring -O-depleted and unitary Ti3C2Tx surface terminals and advancing the understanding of the role of specific Ti3C2Tx surface chemistry in regulating the plating/stripping behaviors of metal ions.

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.

A Dual Salt/Dual Solvent Electrolyte Enables Ultrahigh Utilization of Zinc Metal Anode for Aqueous Batteries

Rechargeable aqueous zinc batteries are promising in next-generation sustainable energy storage. However, the low zinc (Zn) metal anode reversibility and utilization in aqueous electrolytes due to Zn corrosion and poor Zn2+ deposition kinetics significantly hinder the development of Zn-ion batteries. Here, a dual salt/dual solvent electrolyte composed of Zn(BF4)2/Zn(Ac)2 in water/TEGDME (tetraethylene glycol dimethyl ether) solvents to achieve reversible Zn anode at an ultrahigh depth of discharge (DOD) is developed. An "inner co-salt and outer co-solvent" synergistic effect in this unique dual salt/dual solvent system is revealed. Experimental results and theoretical calculations provide evidence that the ether co-solvent inhibits water activity by forming hydrogen bonding with the water and coordination effects with the proton in the outer Zn2+ solvation structure. Meanwhile, the anion of zinc acetate co-salt enters the inner Zn2+ solvation structure, thereby accelerating the desolvation kinetics. Strikingly, based on the electrolyte design, the zinc anode shows high reversibility at an ultrahigh utilization of 60% DOD with 99.80% Coulombic efficiency and 9.39 mAh cm-2 high capacity. The results far exceed the performance reported in electrolyte design work recently. The work provides fundamental insights into inner co-salt and outer co-solvent synergistic regulation in multifunctional electrolytes for reversible aqueous metal-ion batteries.

Spin Symmetry Breaking-Induced Hubbard Gap Near-Closure in N-Coordinated MnO2 for Enhanced Aqueous Zinc-Ion Battery Performance

Transition metal oxides (TMOs) are promising cathode materials for aqueous zinc ion batteries (ZIBs), however, their performance is hindered by a substantial Hubbard gap, which limits electron transfer and battery cyclability. Addressing this, we introduce a heteroatom coordination approach, using triethanolamine to induce axial N coordination on Mn centers in MnO2, yielding N-coordinated MnO2 (TEAMO). This approach leverages the change of electronegativity disparity between Mn and ligands (O and N) to disrupt spin symmetry and augment spin polarization. This enhancement leads to the closure of the Hubbard gap, primarily driven by the intensified occupancy of the Mn eg orbitals. The resultant TEAMO exhibit a significant increase in storage capacity, reaching 351 mAh g-1 at 0.1 A g-1. Our findings suggest a viable strategy for optimizing the electronic structure of TMO cathodes, enhancing the potential of ZIBs in energy storage technology.

Additives for Aqueous Zinc-Ion Batteries: Recent Progress, Mechanism Analysis, and Future Perspectives

Aqueous zinc-ion batteries (ZIBs) stand out as a promising next-generation electrochemical energy storage technology, offering notable advantages such as high specific capacity, enhanced safety, and cost-effectiveness. However, the application of aqueous electrolytes introduces challenges: Zn dendrite formation and parasitic reactions at the anode, as well as dissolution, electrostatic interaction, and by-product formation at the cathode. In addressing these electrode-centric problems, additive engineering has emerged as an effective strategy. This review delves into the latest advancements in electrolyte additives for ZIBs, emphasizing their role in resolving the existing issues. Key focus areas include improving morphology and reducing side reactions during battery cycling using synergistic effects of modulating anode interface regulation, zinc facet control, and restructuring of hydrogen bonds and solvation sheaths. Special attention is given to the efficacy of amino acids and zwitterions due to their multifunction to improve the cycling performance of batteries concerning cycle stability and lifespan. Additionally, the recent additive advancements are studied for low-temperature and extreme weather applications meticulously. This review concludes with a holistic look at the future of additive engineering, underscoring its critical role in advancing ZIB performance amidst the complexities and challenges of electrolyte additives.

Quantifying Asymmetric Zinc Deposition: A Guide Factor for Designing Durable Zinc Anodes

Zinc metal is recognized as the most promising anode for aqueous energy storage but suffers from severe dendrite growth and poor reversibility. However, the coulombic efficiency lacks specificity for zinc dendrite growth, particularly in Zn||Zn symmetric cells. Herein, a novel indicator (fD) based on the characteristic crystallization peaks is proposed to evaluate the growth and distribution of zinc dendrites. As a proof of concept, triethylenetetramine (TETA) is adopted as an electrolyte additive to manipulate the zinc flux for uniform deposition, with a corroborating low fD value. A highly durable zinc symmetric cell is achieved, lasting over 2500 h at 10 mA cm-2 and 400 h at a large discharge of depth (10 mA cm-2, 10 mAh cm-2). Supported by the low fD value, the Zn||TETA-ZnSO4||MnO2 batteries overcome the sudden short circuit and fast capacity fading. The study provides a feasible method to evaluate zinc dendrites and sheds light on the design of highly reversible zinc anodes.

In Situ Constructing Metal-Organic Complex Interface Layer Using Biomolecule Enabling Stabilize Zn Anode

Aqueous zinc-ion batteries (ZIBs) are considered as a promising candidate for next-generation large-scale energy storage due to their high safety, low cost, and eco-friendliness. Unfortunately, commercialization of ZIBs is severely hindered owing to rampant dendrite growth and detrimental side reactions on the Zn anode. Herein, inspired by the metal-organic complex interphase strategy, the authors apply adenosine triphosphate (ATP) to in situ construct a multifunctional film on the metal Zn surface (marked as ATP@Zn) by a facile etching method. The ATP-induced interfacial layer enhances lipophilicity, promoting uniform Zn2+ flux and further homogenizing Zn deposition. Meanwhile, the functional interlayer improves the anticorrosion ability of the Zn anode, effectively suppressing corrosion and hydrogen evolution. Consequently, the as-prepared ATP@Zn anode in the symmetric cell exhibits eminent plating/stripping reversibility for over 2800 h at 5.0 mA cm-2 and 1 mAh cm-2. Furthermore, the assembled ATP@Zn||MnO2 full cells are investigated to evaluate practical feasibilities. This work provides an efficient and simple strategy to prepare stabilized Zn anode toward high-performance ZIBs.

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.

Anion Modulation of Ag-Imidazole Cuboctahedral Cage Microenvironments for Efficient Electrocatalytic CO2 Reduction

How to achieve CO2 electroreduction in high efficiency is a current challenge with the mechanism not well understood yet. The metal-organic cages with multiple metal sites, tunable active centers, and well-defined microenvironments may provide a promising catalyst model. Here, we report self-assembly of Ag4L4 type cuboctahedral cages from coordination dynamic Ag+ ion and triangular imidazolyl ligand 1,3,5-tris(1-benzylbenzimidazol-2-yl) benzene (Ag-MOC-X, X=NO3, ClO4, BF4) via anion template effect. Notably, Ag-MOC-NO3 achieves the highest CO faradaic efficiency in pH-universal electrolytes of 86.1 % (acidic), 94.1 % (neutral) and 95.3 % (alkaline), much higher than those of Ag-MOC-ClO4 and Ag-MOC-BF4 with just different counter anions. In situ attenuated total reflection Fourier transform infrared spectroscopy observes formation of vital intermediate *COOH for CO2-to-CO conversion. The density functional theory calculations suggest that the adsorption of CO2 on unsaturated Ag-site is stabilized by C-H⋅⋅⋅O hydrogen-bonding of CO2 in a microenvironment surrounded by three benzimidazole rings, and the activation of CO2 is dependent on the coordination dynamics of Ag-centers modulated by the hosted anions through Ag⋅⋅⋅X interactions. This work offers a supramolecular electrocatalytic strategy based on Ag-coordination geometry and host-guest interaction regulation of MOCs as high-efficient electrocatalysts for CO2 reduction to CO which is a key intermediate in chemical industry process.

Stabilizing Zinc Anode through Ion Selection Sieving for Aqueous Zn-Ion Batteries

Uncontrollable dendrite growth and corrosion induced by reactive water molecules and sulfate ions (SO42-) seriously hindered the practical application of aqueous zinc ion batteries (AZIBs). Here we construct artificial solid electrolyte interfaces (SEIs) realized by sodium and calcium bentonite with a layered structure anchored to anodes (NB@Zn and CB@Zn). This artificial SEI layer functioning as a protective coating to isolate activated water molecules, provides high-speed transport channels for Zn2+, and serves as an ionic sieve to repel negatively charged anions while attracting positively charged cations. The theoretical results show that the bentonite electrodes exhibit a higher binding energy for Zn2+. This demonstrates that the bentonite protective layer enhances the Zn-ion deposition kinetics. Consequently, the NB@Zn//MnO2 and CB@Zn//MnO2 full-battery capacities are 96.7 and 70.4 mAh g-1 at 2.0 A g-1 after 1000 cycles, respectively. This study aims to stabilize Zn anodes and improve the electrochemical performance of AZIBs by ion-selection sieving.

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.

Less is More: Underlying Mechanism of Zn Electrode Long-Term Stability using Sodium L-Ascorbate as Electrolyte Additive

Structured passivation layers and hydrated Zn2+ solvation structure strongly influence Zn depositions on Zn electrodes and then the cycle life and electrochemical performance of aqueous zinc ion batteries. To achieve these, the electrolyte additive of sodium L-ascorbate (Ass) is introduced into aqueous zinc sulfate (ZnSO4, ZS) electrolyte solutions. Combined experimental characterizations with theoretical calculations, the unique passivation layers with vertical arrayed micro-nano structure are clearly observed, as well as the hydrated Zn2+ solvation structure is changed by replacing two ligand water molecules with As-, thus regulating the wettability and interfacial electric field intensity of Zn surfaces, facilitating rapid ionic diffusions within electrolytes and electrodes together with the inhibited side reactions and uniform depositions of Zn2+. When tested in Zn||Zn symmetric cell, the electrolyte containing Ass is extraordinarily stably operated for the long time ≈3700 h at both 1 mA cm-2 and 1 mAh cm-2. In Zn||MnO2 full coin cells, the energy density can still maintain as high as ≈184 Wh kg-1 at the power density high up to 2 kW kg-1, as well as the capacity retention can reach up to 80.5% even after 1000 cycles at 2 A g-1, which are substantially superior to the control cells.

Electric Double Layer Oriented Eutectic Additive Design toward Stable Zn Anodes with a High Depth of Discharge

ZnSO4-based electrolytes for aqueous zinc ion batteries fail to meet practical application metrics due to hydrogen evolution reaction (HER) and dendrite growth. In this work, a highly polarized eutectic additive, glycerophosphorylcholine (GPC) is rationally designed, to regulate the electric double layer (EDL) structure for stable Zn anodes with a high depth of discharge (DOD). On one hand, GPC molecules with abundant hydroxyl groups can precisely regulate the hydrogen bond network in EDL to suppress HER. On the other hand, the enrichment of GPC at the interface is positively responsible for the negative charge density on the Zn surface, which leads to the formation of a robust ZnxPyOz-rich solid-electrolyte interphase and terminates dendrite growth in the charge-rich sites. This EDL-oriented eutectic additive engineering enables highly reversible and selectively (002)-textured Zn anodes to operate for over 1450 h at a high DOD of 45.3%. Meanwhile, a high-capacity (185.7 mAh g-1) aqueous Zn||VS2 full cell shows remarkable cycling stability over 220 cycles with an excellent capacity retention of 90.4% even at a low current density of 0.1 A g-1 (0.5 C). This work sheds light on electrolyte design and interface engineering for high-performance aqueous batteries.

Electrolyte Solvation Chemistry for Stabilizing the Zn Anode via Functionalized Organic Agents

As a potential candidate for grid-scale energy storage technology, aqueous Zn-ion batteries (ZIBs) have attracted considerable attention due to their intrinsic safety, environmental friendliness, and ease of fabrication. Nevertheless, the road to industry for this technique is hindered by serious issues, including undesired side reactions, random growth of the Zn dendrites, electrode passivation, and anode corrosion, which are associated with the high reactivity of water molecules during the electrochemical reactions. These challenges are strongly dependent on electrolyte solvation chemistry (ESC), which subsequently determines the electrochemical behavior of the metal ions and water molecules on the electrode surface. In this work, a comprehensive understanding of optimized ESC with specified functional groups on the mixing agents to stabilize the Zn anode is provided. First, the challenges facing the ZIBs and their chemical principles are outlined. Specific attention is paid to the working principles of the mixing agents with different functional groups. Then the recent progress is summarized and compared. Finally, perspectives on future research for the aqueous Zn batteries are presented from the point of view.

Unlocking Dynamic Solvation Chemistry and Hydrogen Evolution Mechanism in Aqueous Zinc Batteries

Understanding the interfacial hydrogen evolution reaction (HER) is crucial to regulate the electrochemical behavior in aqueous zinc batteries. However, the mechanism of HER related to solvation chemistry remains elusive, especially the time-dependent dynamic evolution of the hydrogen bond (H-bond) under an electric field. Herein, we combine in situ spectroscopy with molecular dynamics simulation to unravel the dynamic evolution of the interfacial solvation structure. We find two critical change processes involving Zn-electroplating/stripping, including the initial electric double layer establishment to form an H2O-rich interface (abrupt change) and the subsequent dynamic evolution of an H-bond (gradual change). Moreover, the number of H-bonds increases, and their strength weakens in comparison with the bulk electrolyte under bias potential during Zn2+ desolvation, forming a diluted interface, resulting in massive hydrogen production. On the contrary, a concentrated interface (H-bond number decreases and strength enhances) is formed and produces a small amount of hydrogen during Zn2+ solvation. The insights on the above results contribute to deciphering the H-bond evolution with competition/corrosion HER during Zn-electroplating/stripping and clarifying the essence of electrochemical window widened and HER suppression by high concentration. This work presents a new strategy for aqueous electrolyte regulation by benchmarking the abrupt change of the interfacial state under an electric field as a zinc performance-enhancement criterion.

Fullerenol as a nano-molecular sieve additive enables stable zinc metal anodes

Aqueous zinc batteries (AZBs) with the advantages of safety, low cost, and sustainability are promising candidates for large-scale energy storage devices. However, the issues of interface side reactions and dendrite growth at the zinc metal anode (ZMA) significantly harm the cycling lifespan of AZBs. In this study, we designed a nano-molecular sieve additive, fullerenol (C60(OH)n), which possesses a surface rich in hydroxyl groups that can be uniformly dispersed in the aqueous solution, and captures free water in the electrolyte, thereby suppressing the occurrence of interfacial corrosion. Besides, fullerenol can be further reduced to fullerene (C60) on the surface of ZMA, holding a unique self-smoothing effect that can inhibit the growth of dendritic Zn. With the synergistic action of these two effects, the fullerenol-contained electrolyte (FE) enables dendrite-free ZMAs. The Zn-Ti half-cell using FE exhibits stable cycling over 2500 times at 5 mA cm-2 with an average Coulombic efficiency as high as 99.8 %. Additionally, the Zn-NaV3O8 cell using this electrolyte displays a capacity retention rate of 100 % after 1000 cycles at -20 °C. This work provides important insights into the molecular design of multifunctional electrolyte additives.

Unique solvation structure induced by anionic Cl in aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIBs) have garnered significant attention in large-scale static energy storage battery systems due to their low cost, high safety and environmental friendliness. However, it has some inherent problems during operation, such as the occurrence of side reactions (hydrogen evolution reaction, HER) and anode corrosion, formation of by-products and growth of metal dendrites. To analyze the mechanism of generation from aspect of the electrolyte solvation structure and make cell efficiency further improvements based on it, so we use DFT calculations to find the most stable solvation structure in AZIBs with ZnCl2 as the electrolyte and analyze it. We define the relative concentration C r , and calculate different groups metal cation cluster structures such as [ Zn ( H 2 O ) n ] 2 + , [ ZnCl ( H 2 O ) n ] + , [ ZnCl 2 ( H 2 O ) n ] and [ ZnCl 3 ( H 2 O ) n ] - that exist at different C r . We discuss the effect of different clusters formed due to the C r variations on the battery performance in terms of three aspects: the structural conformation, the cluster characteristics (including the hydrogen bonding network, bond lengths, bond angles, as well as the electrostatic potential ESP) and the cluster performance (including the adsorption energy Ea, binding energy Eb, and desolvation energy Edes). The results shows that the electrolyte metal cation Zn2+ can be coordinated with up to six H2O molecules in first shell, and this metal cation solvation structure contributes to the occurrence and formation of side reactions and by-products, which reduces the battery efficiency. Increasing the electrolyte anion Cl- concentration by appropriately increasing the C r helps to desolvate the metal cation cluster structure, which greatly improves the battery efficiency and suppresses the side reactions and by-products. Yet the improvement effect was not obviously further improved by further increasing the Cl- concentration.

Rescuing zinc anode-electrolyte interface: mechanisms, theoretical simulations and in situ characterizations

The research interest in aqueous zinc-ion batteries (AZIBs) has been surging due to the advantages of safety, abundance, and high electrochemical performance. However, some technique issues, such as dendrites, hydrogen evolution reaction, and corrosion, severely prohibit the development of AZIBs in practical utilizations. The underlying mechanisms regarding electrochemical performance deterioration and structure degradation are too complex to understand, especially when it comes to zinc metal anode-electrolyte interface. Recently, theoretical simulations and in situ characterizations have played a crucial role in AZIBs and are exploited to guide the research on electrolyte engineering and solid electrolyte interphase. Herein, we present a comprehensive review of the current state of the fundamental mechanisms involved in the zinc plating/stripping process and underscore the importance of theoretical simulations and in situ characterizations in mechanism research. Finally, we summarize the challenges and opportunities for AZIBs in practical applications, especially as a stationary energy storage and conversion device in a smart grid.

Cation-Conduction Dominated Hydrogels for Durable Zinc-Iodine Batteries

Zinc-iodine batteries have the potential to offer high energy-density aqueous energy storage, but their lifetime is limited by the rampant dendrite growth and the concurrent parasite side reactions on the Zn anode, as well as the shuttling of polyiodides. Herein, a cation-conduction dominated hydrogel electrolyte is designed to holistically enhance the stability of both zinc anode and iodine cathode. In this hydrogel electrolyte, anions are covalently anchored on hydrogel chains, and the major mobile ions in the electrolyte are restricted to be Zn2+. Specifically, such a cation-conductive electrolyte results in a high zinc ion transference number (0.81) within the hydrogel and guides epitaxial Zn nucleation. Furthermore, the optimized Zn2+ solvation structure and the reconstructed hydrogen bond networks on hydrogel chains contribute to the reduced desolvation barrier and suppressed corrosion side reactions. On the iodine cathode side, the electrostatic repulsion between negative sulfonate groups and polyiodides hinders the loss of the iodine active material. This all-round electrolyte design renders zinc-iodine batteries with high reversibility, low self-discharge, and long lifespan.

Multifunctionalized Supramolecular Cyclodextrin Additives Boosting the Durability of Aqueous Zinc-Ion Batteries

The poor cycling stability of aqueous zinc-ion batteries hinders their application in large-scale energy storage due to uncontrollable dendrite growth and harmful hydrogen evolution reactions. Here, we designed and synthesized an electrolyte additive, N-methylimidazolium-β-cyclodextrin p-toluenesulfonate (NMI-CDOTS). The cations of NMI-CD+ are more easily adsorbed on the abrupt Zn surface to regulate the deposition of Zn2+ and reduce dendrite generation under the combined action of the unique cavity structure with abundant hydroxyl groups and the electrostatic force. Meanwhile, p-toluenesulfonate (OTS-) is able to change the Zn2+ solvation structure and suppress the hydrogen evolution reaction by the strong interaction of Zn2+ and OTS-. Benefiting from the synergistic role of NMI-CD+ and OTS-, the Zn||Zn symmetric cell exhibits superior cycling performance as high as 3800 h under 1 mA cm-2 and 1 mA h cm-2. The Zn||V2O5 full battery also shows a high specific capacity (198.3 mA h g-1) under 2.0 A g-1 even after 1500 cycles, and its Coulomb efficiency is nearly 100% during the charging and discharging procedure. These multifunctional composite strategies open up possibilities for the commercial application of aqueous zinc-ion batteries.

Highly Stable Photo-Assisted Zinc-Ion Batteries via Regulated Photo-Induced Proton Transfer

Photo-assisted ion batteries utilize light to boost capacity but face cycling instability due to complex charge/ion transfer under illumination. This study identified photo-induced proton transfer (photo-induced PT) as a significant process in photo-(dis)charging of widely-used V2O5-based zinc-ion batteries, contributing to enhanced capacity under illumination but jeopardizing photo-stability. Photo-induced PT occurs at 100 ps after photo-excitation, inducing rapid proton extraction into V2O5 photoelectrode. This process creates a proton-deficient microenvironment on surface, leading to repetitive cathode dissolution and anode corrosion in each cycle. Enabling the intercalated protons from photo-induced PT to be reversibly employed in charge-discharge processes via the anode-alloying strategy achieves high photo-stability for the battery. Consequently, a ~54 % capacity enhancement was achieved in a V2O5-based zinc-ion battery under illumination, with ~90 % capacity retention after 4000 cycles. This extends the photo-stability record by 10 times. This study offers promising advancements in energy storage by addressing instability issues in photo-assisted ion batteries.

Unraveling the "Gap-Filling" Mechanism of Multiple Charge Carriers in Aqueous Zn-MoS2 Batteries

The utilization rate of active sites in cathode materials for Zn-based batteries is a key factor determining the reversible capacities. However, a long-neglected issue of the strong electrostatic repulsions among divalent Zn2+ in hosts inevitably causes the squander of some active sites (i.e., gap sites). Herein, we address this conundrum by unraveling the "gap-filling" mechanism of multiple charge carriers in aqueous Zn-MoS2 batteries. The tailored MoS2 /(reduced graphene quantum dots) hybrid features an ultra-large interlayer spacing (2.34 nm), superior electrical conductivity/hydrophilicity, and robust layered structure, demonstrating highly reversible NH4 + /Zn2+ /H+ co-insertion/extraction chemistry in the 1 M ZnSO4 +0.5 M (NH4 )2 SO4 aqueous electrolyte. The NH4 + and H+ ions can act as gap fillers to fully utilize the active sites and screen electrostatic interactions to accelerate the Zn2+ diffusion. Thus, unprecedentedly high rate capability (439.5 and 104.3 mAh g-1 at 0.1 and 30 A g-1 , respectively) and ultra-long cycling life (8000 cycles) are achieved.

An extended substrate screening strategy enabling a low lattice mismatch for highly reversible zinc anodes

Aqueous zinc batteries possess intrinsic safety and cost-effectiveness, but dendrite growth and side reactions of zinc anodes hinder their practical application. Here, we propose the extended substrate screening strategy for stabilizing zinc anodes and verify its availability (dsubstrate: dZn(002) = 1: 1→dsubstrate: dZn(002)=n:1, n = 1, 2). From a series of calculated phyllosilicates satisfying dsubstrate ≈ 2dZn(002), we select vermiculite, which has the lowest lattice mismatch (0.38%) reported so far, as the model to confirm the effectiveness of "2dZn(002)" substrates for zinc anodes protection. Then, we develop a monolayer porous vermiculite through a large-scale and green preparation as a functional coating for zinc electrodes. Unique "planting Zn(002) seeds" mechanism for "2dZn(002)" substrates is revealed to induce the oriented growth of zinc deposits. Additionally, the coating effectively inhibits side reactions and promotes zinc ion transport. Consequently, the modified symmetric cells operate stably for over 300 h at a high current density of 50 mA cm-2. This work extends the substrate screening strategy and advances the understanding of zinc nucleation mechanism, paving the way for realizing high-rate and stable zinc-metal batteries.

Trade-Off between Rough and Smooth Electrode Surfaces toward Stable Zn Stripping/Plating in Aqueous Electrolytes

The effects of surface roughness on the performance of the Zn metal anode in aqueous electrolytes are investigated by experiments and computational simulations. Smooth surfaces can homogenize the nucleation and growth of Zn, which helps to form a flat Zn anode under high current density. In spite of these advantages, the whole surface of the smooth electrode serves as the reactive contact area for parasitic reactions, generating severe hydrogen evolution, corrosion, and byproduct formation, which seriously hinder the long-term cycle stability of the Zn anode. To trade off this double-sided effect, we identify a medium degree of surface roughness that could stabilize the Zn anode for 1000 h cycling at 1.0 mAh cm-2. The electrode also enabled stable cycling for 800 h at a high current density of 5.0 mAh cm-2. This naked Zn metal anode with optimized surface roughness holds great promise for direct use in aqueous zinc ion batteries.

Molecularly modulating solvation structure and electrode interface enables dendrite-free zinc-ion batteries

The performance of aqueous Zn ion batteries (AZIBs) is hindered by the uncontrollable growth of Zn dendrites and side reactions at the Zn anode/electrolyte interface. Here, we introduce low-cost glucosamine hydrochloride (GLA) into the ZnSO4 electrolyte system to modulate the Zn anode/electrolyte interface and the solvation structure of Zn2+, which leads to improved reversibility of Zn plating/striping. Through experimental and theoretical analyses, we demonstrate that GLA molecules could adsorp on the Zn metal surface to form a new interface with reduced active water, effectively suppressing water-induced side reactions. Moreover, after adding GLA, the flux of Zn2+ ions is regulated, the desolvation of the primary [Zn(H2O)6]2+ ions is promoted, and the Zn dendrite growth is significantly inhibited. Consequently, superior cyclic stability with a lower voltage hysteresis is simultaneously achieved in a Zn//Zn symmetric cell. When coupled with the Mn3O4 cathode, the fabricated Zn-Mn batteries with the modified ZnSO4 + GLA electrolyte system deliver boosted capacity, improved long-term cycling stability, and better self-discharge performance. This work provides insight into the development of high-efficient and low-cost electrolytes for high-performance Zn-based energy storage devices.

Establishing Ultralow Self-Discharge Zn-I2 Battery by Optimizing ZnSO4 Electrolyte Concentration

As one of promising candidates for large-scale energy-storage systems, Zn-I2 aqueous battery exhibits multifaceted advantages including low cost, high energy/powder density, and intrinsic operational safety, but also suffers from fast self-discharge and short cycle/shelf lifespan associating with I3 - shuttle, Zn dendrite growth, and corrosion. In this paper, the battery's self-discharge rate is successfully suppressed down to an unprecedent level of 17.1% after an ultralong shelf-time of 1 000 h (i.e., 82.9% capacity retention after 41 days open-circuit storage), by means of manipulating solvation structures of traditional ZnSO4 electrolyte via simply adjusting electrolyte concentration. Better yet, the optimized 2.7 m ZnSO4 electrolyte further prolongs the cycle lifespan of the battery up to >10 000 and 43 000 cycles at current density of 1 and 5 A g-1 , respectively, thanks to the synthetic benefits from reduced free water content, modified solvation structure and lowered I2 dissolution in the electrolyte. With both long lifespan and ultralow self-discharge, this reliable and affordable Zn-I2 battery may provide a feasible alternative to the centuries-old lead-acid battery.