Triple-function Hydrated Eutectic Electrolyte for Enhanced Aqueous Zinc Batteries

Triple-function eutectic solvent additive for high performance lithium metal batteries

Rational carbonate electrolyte chemistry is critical for the development of high-voltage lithium metal batteries (LMBs). However, the implementation of traditional carbonate electrolyte is greatly hindered by the generation of an unstable electrode interphase and corrosive by-product (HF). Herein, we propose a triple-function eutectic solvent additive of N-methylacetamide (NmAc) with LiNO3 to enhance the stability and compatibility of carbonate electrolyte. Firstly, the addition of NmAc significantly improves the solubility of LiNO3 in carbonate electrolyte by forming an eutectic pair, which regulates the Li+ solvation structure and leads to dense and homogenous Li plating. Secondly, the hydrolysis of acidic PF5 is effectively alleviated due to the strong complexation of NmAc with PF5, thus reducing the generation of corrosive HF. In addition, the optimized cathode electrolyte interphase layer decreases the structural degradation and transition metal dissolution. Consequently, Li||LiNi0.6Co0.2Mn0.2O2 (NCM622) cells with the designed electrolyte deliver superior long-term cycle reversibility and excellent rate capability. This study unveils the rationale for incorporating eutectic solvent additives within carbonate electrolytes, which significantly contribute to the advancement of their practical application for high-voltage LMBs.

Enabling Gradient-Structured Solid Electrolyte Interphase by a Hydrated Eutectic Electrolyte for High-Performance Zn Metal Batteries

Aqueous Zn metal batteries are attracting tremendous interest as promising energy storage systems due to their intrinsic safety and cost-effectiveness. Nevertheless, the reversibility of Zn metal anodes (ZMAs) is hindered by water-induced parasitic reactions and dendrite growth. Herein, a novel hydrated eutectic electrolyte (HEE) consisting of Zn(BF4)2·xH2O and sulfolane (SL) is developed to prevent the side reactions and achieve the outstanding cyclability of ZMAs. The strong coordination between Zn2+ and SL triggers the eutectic feature, enabling the low-temperature availability of HEEs. The restriction of BF4 - hydrolysis in the eutectic system can realize favorable compatibility between Zn(BF4)2-based electrolyte and ZMAs. Besides, the newly-established solvation structure with the participation of SL, H2O, and BF4 -, can induce in situ formation of desirable SEI with gradient structure consisting of B,O-rich species, ZnS, and ZnF2, to offer satisfactory protection toward ZMAs. Consequently, the HEE allows the Zn||Zn symmetric cell to cycle over 1650 h at 2 mA cm-2 and 1 mA h cm-2. Moreover, the Zn||NH4V4O10 full batteries can deliver a prolonged lifespan for 1000 cycles with a high capacity retention of 83.4%. This work represents a feasible approach toward the elaborate design of advanced electrolyte systems for next-generation batteries.

Low-Cost Aqueous Electrolyte with MBA Additives for Uniform and Stable Zinc Deposition

Aqueous zinc ion batteries (AZIBs) are attracting increasing research interest due to their intrinsic safety, low cost, and scalability. However, the issues including hydrogen evolution, interface corrosion, and zinc dendrites at anodes have seriously limited the development of aqueous zinc ion batteries. Here, N,N-methylenebis(acrylamide) (MBA) additives with -CONH- groups are introduced to form hydrogen bonds with water and suppress H2O activity, inhibiting the occurrence of hydrogen evolution and corrosion reactions at the interface. In situ optical microscopy demonstrates that the MBA additive promotes the uniform deposition of Zn2+ and then suppresses the dendrite growth on the zinc anode. Therefore, Zn//Ti asymmetric batteries demonstrate a high plating/stripping efficiency of 99.5%, while Zn//Zn symmetric batteries display an excellent cycle stability for more than 1000 h. The Zn//MnO2 full cells exhibit remarkable cycling stability for 700 cycles in aqueous electrolytes with MBA additives. The additive engineering via MBA achieved the dendrite-free Zn anodes and stable full batteries, which is favorable for advanced AZIBs in practical applications.

Aqueous Electrolyte With Weak Hydrogen Bonds for Four-Electron Zinc-Iodine Battery Operates in a Wide Temperature Range

In the pursuit of high-performance energy storage systems, four-electron zinc-iodine aqueous batteries (4eZIBs) with successive I-/I2/I+ redox couples are appealing for their potential to deliver high energy density and resource abundance. However, susceptibility of positive valence I+ to hydrolysis and instability of Zn plating/stripping in conventional aqueous electrolyte pose significant challenges. In response, polyethylene glycol (PEG 200) is introduced as co-solvent in 2 m ZnCl2 aqueous solution to design a wide temperature electrolyte. Through a comprehensive investigation combining spectroscopic characterizations and theoretical simulations, it is elucidated that PEG disrupts the intrinsic strong H-bonds of water by global weak PEG-H2O interaction, which strengthens the O─H covalent bond of water and intensifies the coordination with Zn2+. This synergistic effect substantially reduces water activity to restrain the I+ hydrolysis, facilitating I-/I2/I+ redox kinetics, mitigating I3 - formation and smoothening Zn deposition. The 4eZIBs in the optimized hybrid electrolyte not only deliver superior cyclability with a low fading rate of 0.0009% per cycle over 20 000 cycles and a close-to-unit coulombic efficiency but also exhibit stable performance in a wide temperature range from 40 °C to -40 °C. This study offers valuable insights into the rational design of electrolytes for 4eZIBs.

Air-Stable and Low-Cost High-Voltage Hydrated Eutectic Electrolyte for High-Performance Aqueous Aluminum-Ion Rechargeable Battery with Wide-Temperature Range

Aqueous aluminum-ion batteries (AAIBs) are considered as a promising alternative to lithium-ion batteries due to their large theoretical capacity, high safety, and low cost. However, the uneven deposition, hydrogen evolution reaction (HER), and corrosion during cycling impede the development of AAIBs, especially under a harsh environment. Here, a hydrated eutectic electrolyte (AATH40) composed of Al(OTf)3, acetonitrile (AN), triethyl phosphate (TEP), and H2O was designed to improve the electrochemical performance of AAIBs in a wide temperature range. The combination of molecular dynamics simulations and spectroscopy analysis reveals that AATH40 has a less-water-solvated structure [Al(AN)2(TEP)(OTf)2(H2O)]3+, which effectively inhibits side reactions, decreases the freezing point, and extends the electrochemical window of the electrolyte. Furthermore, the formation of a solid electrolyte interface, which effectively inhibits HER and corrosion, has been demonstrated by X-ray photoelectron spectroscopy, X-ray diffraction tests, and in situ differential electrochemical mass spectrometry. Additionally, operando synchrotron Fourier transform infrared spectroscopy and electrochemical quartz crystal microbalance with dissipation monitoring reveal a three-electron storage mechanism for the Al//polyaniline full cells. Consequently, AAIBs with this electrolyte exhibit improved cycling stability within the temperature range of -10-50 °C. This present study introduces a promising methodology for designing electrolytes suitable for low-cost, safe, and stable AAIBs over a wide temperature range.

Extended Battery Compatibility Consideration from an Electrolyte Perspective

The performance of electrochemical batteries is intricately tied to the physicochemical environments established by their employed electrolytes. Traditional battery designs utilizing a single electrolyte often impose identical anodic and cathodic redox conditions, limiting the ability to optimize redox environments for both anode and cathode materials. Consequently, advancements in electrolyte technologies are pivotal for addressing these challenges and fostering the development of next-generation high-performance electrochemical batteries. This review categorizes perspectives on electrolyte technology into three key areas: additives engineering, comprehensive component analysis encompassing solvents and solutes, and the effects of concentration. By summarizing significant studies, the efficacy of electrolyte engineering is highlighted, and the review advocates for further exploration of optimized component combinations. This review primarily focuses on liquid electrolyte technologies, briefly touching upon solid-state electrolytes due to the former greater vulnerability to electrode and electrolyte interfacial effects. The ultimate goal is to generate increased awareness within the battery community regarding the holistic improvement of battery components through optimized combinations.

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.

Toward Simultaneous Dense Zinc Deposition and Broken Side-Reaction Loops in the Zn//V2 O5 System

The Zn//V2 O5 system not only faces the incontrollable growth of zinc (Zn) dendrites, but also withstands the cross-talk effect of by-products produced from the cathode side to the Zn anode, inducing interelectrode talk and aggravating battery failure. To tackle these issues, we construct a rapid Zn2+ -conducting hydrogel electrolyte (R-ZSO) to achieve Zn deposition modulation and side reaction inhibition in Zn//V2 O5 full cells. The polymer matrix and BN exhibit a robust anchoring effect on SO4 2- , accelerating Zn2+ migration and enabling dense Zn deposition behavior. Therefore, the Zn//Zn symmetric cells based on the R-ZSO electrolyte can operate stably for more than 1500 h, which is six times higher than that of cells employing the blank electrolyte. More importantly, the R-ZSO hydrogel electrolyte effectively decouples the cross-talk effects, thus breaking the infinite loop of side reactions. As a result, the Zn//V2 O5 cells using this modified hydrogel electrolyte demonstrate stable operation over 1,000 cycles, with a capacity loss rate of only 0.028 % per cycle. Our study provides a promising gel chemistry, which offers a valuable guide for the construction of high-performance and multifunctional aqueous Zn-ion batteries.

Critical Solvation Structures Arrested Active Molecules for Reversible Zn Electrochemistry

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

Screening Selection of Hydrogen Evolution-Inhibiting and Zincphilic Alloy Anode for Aqueous Zn Battery

The hydrogen evolution reaction (HER) and Zn dendrites growth are two entangled detrimental effects hindering the application of aqueous Zn batteries. The alloying strategy is studied to be a convenient avenue to stabilize Zn anodes, but there still lacks global understanding when selecting reliable alloy elements. Herein, it is proposed to evaluate the Zn alloying elements in a holistic way by considering their effects on HER, zincphilicity, price, and environmental-friendliness. Screening selection sequence is established through the theoretical evaluation of 17 common alloying elements according to their effects on hydrogen evolution and Zn nucleation thermodynamics. Two alloy electrodes with opposite predicted effects are prepared for experimental demonstration, i.e., HER-inhibiting Bi and HER-exacerbating Ni. Impressively, the optimum ZnBi alloy anode exhibits one order of magnitude lower hydrogen evolution rate than that of the pure Zn, leading to an ultra-long plating/stripping cycling life for more than 11 000 cycles at a high current density of 20 mA cm-2 and 81% capacity retention for 170 cycles in a Zn-V2O5 pouch cell. The study not only proposes a holistic alloy selection principle for Zn anode but also identifies a practically effective alloy element.

Constructing Stable Zinc-Metal Anodes by Synergizing Hydrophobic Host with Zincophilic Interface for Aqueous Zinc Ions Batteries

Aqueous zinc (Zn) ions battery is promising for future large-scale applications of energy storage due to the abundant reserves, high capacity of metallic Zn. However, dendritic growth, severe side reactions have limited the development of Zn-metal anodes. A single skeleton structure or interface protection is difficult to simultaneously mitigate these issues. Here, a novel composite design based on the synergistic interaction between the hydrophobic host, the zincophilic interface is reported. On the one hand, the 3D substrate reduces the local current density, inhibits dendritic growth. On the other hand, the protective interface homogenizes the nucleation due to the formation of the ZnAu3 alloy layer. More importantly, the collaborative construction of the hydrophobicity, zincophilicity for the electrode alleviates the aggravated hydrogen evolution reaction (only 2.5 mmol h-1 ), simultaneously enables a low nucleation overpotential (31.7 mV) during cycling. Consequently, a high Coulombic efficiency of ≈98.25% after 300 cycles is harvested for the composite electrode. The pouch cells assembled by this anode, LiMn2 O4 cathode maintain 82 mAh g-1 capacity retention after 140 cycles. This research shows an innovative Zn-based structural design for aqueous Zn-ion batteries.

Fast Reaction Kinetics and Commendable Low-Temperature Adaptability of Zinc Batteries Enabled by Aprotic Water-Acetamide Symbiotic Solvation Sheath

Although rechargeable aqueous zinc batteries are cost effectiveness, intrinsicly safe, and high activity, they are also known for bringing rampant hydrogen evolution reaction and corrosion. While eutectic electrolytes can effectively eliminate these issues, its high viscosity severely reduces the mobility of Zn2+ ions and exhibits poor temperature adaptability. Here, we infuse acetamide molecules with Lewis base and hydrogen bond donors into a solvated shell of Zn[(H2 O)6 ]2+ to create Zn(H2 O)3 (ace)(BF4 )2 . The viscosity of 1ace-1H2 O is 0.032 Pa s, significantly lower than that of 1ace-0H2 O (995.6 Pa s), which improves ionic conductivity (9.56 mS cm-1 ) and shows lower freezing point of -45 °C, as opposed to 1ace-0H2 O of 4.04 mS cm-1 and 12 °C, respectively. The acidity of 1ace-1H2 O is ≈2.8, higher than 0ace-1H2 O at ≈0.76, making side reactions less likely. Furthermore, benefiting from the ZnCO3 /ZnF2 -rich organic/inorganic solid electrolyte interface, the Zn || Zn cells cycle more than 1300 hours at 1 mA cm-2 , and the Zn || Cu operated over 1800 cycles with an average Coulomb efficiency of ≈99.8 %. The Zn || PANI cell cycled over 8500 cycles, with a specific capacity of 99.8 mAh g-1 at 5 A g-1 at room temperature, and operated at -40 °C with a capacity of 66.8 mAh g-1 .

Trehalose in Trace Quantities as a Multifunctional Electrolyte Additive for Highly Reversible Zinc Metal Anodes

The unsatisfactory performance of Zn metal anodes significantly impedes the commercial application of aqueous zinc-ion batteries (AZIBs). Herein, we introduce a trace amount of a multifunctional trehalose additive to enhance the stability and reversibility of Zn metal anodes. The trehalose additive exhibits a stronger Zn2+ ion affinity due to abundant lone-pair electrons, disrupting hydrogen bonds in H2O, regulating solvation structures, and tuning the Zn-electrolyte interface. Consequently, the Zn metal anode demonstrates a remarkable Coulombic efficiency of 99.80% and a cycle stability exceeding 4500 h at 1 mA cm-2. Even under stringent conditions of 10 mA cm-2, the Zn metal anode maintains a cumulative capacity of 2500 mA h cm-2 without a short circuit. Furthermore, Zn//Zn symmetric batteries exhibit excellent low-temperature cycle performance (over 400 h at -10 °C). As a proof of concept, assembled Zn//NH4V4O10 and Zn//MnO2 pouch cells demonstrate an improved electrochemical performance. This work presents an electrolyte additive strategy for achieving stable zinc anode operation in AZIBs.

Constructing a Topologically Adaptable Solid Electrolyte Interphase for a Highly Reversible Zinc Anode

The performance of aqueous zinc metal batteries is significantly compromised by the stability of the solid electrolyte interphase (SEI), which is intimately linked to the structure of the electrical double layer (EDL) between the zinc anode and electrolyte. Furthermore, understanding the mechanical behavior of SEI is crucial, as it governs its response to stress induced by volume changes, fracture, or deformation. In this study, we introduce l-glutamine (Gln) as an additive to regulate the adsorbed environment of the EDL and in situ produce a hybrid SEI consisting of ZnS and Gln-related species. The results of the nanoindentation test indicate that the hybrid SEI exhibits a low modulus and low hardness, alongside exceptional shape recovery capability, which effectively limits side reactions and enables topological adaptation to volume fluctuations in zinc anodes during zinc ion plating/stripping, thereby enabling Zn//Zn symmetric cells to exhibit an ultralong cycle life of 4000 h in coin cells and a high cumulative capacity of 18,000 mA h in pouch cells. More importantly, the superiority of the formulated strategy is further demonstrated in Zn//NH4V4O10 full cells at different N/P ratios of 5.2, 4.9, 3.5, and 2.4. This provides a promising approach for future interfacial modulation in aqueous battery chemistry.

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.

Highly Solubilized Urea as Effective Proton Donor-Acceptors for Durable Zinc-Ion Storage Beyond Single-Anion Selection Criteria

Urea, as one of the most sustainable organic solutes, denies the high salt consumption in commercial electrolytes with its peculiar solubility in water. The bi-mixture of urea-H2 O shows the eutectic feature for increased attention in aqueous Zn-ion electrochemical energy storage (AZEES) technologies. While the state-of-the-art aqueous electrolyte recipes are still pursuing the high-concentrated salt dosage with limited urea adoption and single-anion selection category. Here, a dual-anion urea-based (DAU) electrolyte composed of dual-Zn salts and urea-H2 O-induced solutions is reported, contributing to a stable electric double-layer construction and in situ organic/inorganic SEI formation. The optimized ZT2 S0.5 -20U electrolytes show a high initial Coulombic efficiency of 93.2% and durable Zn-ion storage ≈4000 h regarding Zn//Cu and Zn//Zn stripping/plating procedures. The assembled Zn//activated carbon full cells maintain ≈100% capacitance over 50 000 cycles at 4 A g-1 in coin cell and ≈98% capacitance over 20 000 cycles at 1 A g-1 in pouch cell setups. A 12 × 12 cm2 pouch cell assembly illustrates the practicality of AZEES devices by designing the cheap, antifreezing, and nonflammable DAU electrolyte system coupling proton donor-acceptor molecule and multi-anion selection criteria, exterminating the critical technical barriers in commercialization.

Phase-Field Simulation of a Dynamic Protective Layer for the Inhibition of Dendrite Growth in Zinc Metal Batteries

Metallic zinc (Zn) has been considered one of the most promising anode materials for next-generation aqueous Zn batteries due to its low redox potential and high storage capacity. However, excessive dendrite formation in Zn metal, corrosion, the evolution of hydrogen gas during the cycling process, and the poor Zn-ion (Zn2+) transport from the electrolyte to the electrode limit its practical application. One of the most effective strategies to suppress Zn dendrite growth and promote Zn2+ transport is to introduce suitable protective layers between the Zn metal electrode and the electrolyte. Herein, we mathematically simulated the dynamic interactions between the Zn deposition on the anode and the resulting displacement of a protective layer that covers the anode, the latter of which can simultaneously inhibit Zn dendrite growth and enhance the Zn2+ transport through the interface between the Zn anode and the protective layer. Our simulation results indicate that a protective layer of high Zn2+ diffusivity not only improves the deposition rate of the Zn metal but also prevents dendrite growth by homogenizing the Zn2+ concentration at the anode surface. In addition, it is revealed that the anisotropic Zn2+ diffusivity in the protective layer influences the 2D diffusion of Zn2+. Higher Zn2+ diffusivity perpendicular to the Zn metal surface inhibits dendrite growth, while higher diffusivity parallel to the Zn metal surface promotes dendrite growth. Our work thus provides a fundamental understanding and a design principle for controlling anisotropic Zn2+ diffusion in the protective layer for better suppression of dendrite growth in Zn metal batteries.

Highly Reversible Zn Metal Anode with Low Voltage Hysteresis Enabled by Tannic Acid Chemistry

The zinc dendrites and side reactions formed on the zinc anode have greatly hindered the development of aqueous zinc-ion batteries (ZIBs). Herein, we introduce tannic acid (TA) as an additive in the ZnSO4 (ZSO) electrolyte to enhance the reversible Zn plating/stripping behavior. TA molecules are found to adsorb onto the zinc surface, forming a passivation layer and replacing some of the H2O molecules in the Zn2+ solvation sheath to form the [Zn(H2O)6-xTAx]2+ complex; this process effectively prevents side reactions. Moreover, the lower desolvation energy barrier of the [Zn(H2O)6-xTAx]2+ structure facilitates uniform Zn metal deposition and enables a stable plating/stripping lifespan of 2500 h with low voltage hysteresis (53 mV at 0.5 mA cm-2) as compared to the ZSO electrolyte (167 h and 104 mV). Additionally, the incorporation of the MnO2 cathode in the TA + ZSO electrolyte shows improved cycling capacity retention, from 64% (ZSO) to 85% (TA + ZSO), after 250 cycles at 1 A g-1, demonstrating the effectiveness of the TA additive in enhancing the performance of ZIBs.