Decreasing Water Activity Using the Tetrahydrofuran Electrolyte Additive for Highly Reversible Aqueous Zinc Metal Batteries

Interfacial Adsorption Layers Based on Amino Acid Analogues to Enable Dual Stabilization toward Long-Life Aqueous Zinc Iodine Batteries

Aqueous zinc-iodine (Zn-I2) batteries are promising candidates for large-scale energy storage due to the merits of low cost and high safety. However, their commercial application is hindered by Zn corrosion and polyiodide shuttle at I2 cathode. Herein, N,N-bis(2-hydroxyethyl)glycine (BHEG) based interfacial adsorption layers are constructed to stabilize Zn anodes and mitigate polyiodide shuttle according to ion-dipole interactions, by using a strategy of electrolyte additive. The tertiary amine (N(CH2)3) and carboxyl (─COO-) groups in the deprotonated BHEG can reversibly capture H+ and dynamically neutralize OH- ions, efficiently buffering the interfacial pH of Zn metal anodes and suppressing hydrogen evolution reactions. Additionally, the BHEG adsorption layers can repel 39.3% of H2O molecules at the Zn interface, creating a "water-deficient" inner Helmholtz plane and preventing Zn corrosion. Significantly, the N(CH2)3 groups in BHEG also inhibit polyiodide shuttle at the I2 cathode, which exhibits high adsorption energies of -0.88, -0.41, and -0.39 eV for I-, I2, and I3 -, respectively. Attributing to these benefits, the Zn-I2 battery can achieve a high areal capacity of 2.99 mAh cm-2 and an extended cycling life of 2,000 cycles, even at a high mass loading of I2 cathode (≈21.5 mg cm-2).

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

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

Trace alcohol ether electrolytes with dual-site hydrogen bonds and modulated solvation structures for ultralong-life zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are highly regarded for their affordability, stability, safety, and eco-friendliness. Nevertheless, their practical application is hindered by severe side reactions and the formation of zinc (Zn) dendrites on the Zn metal anode surface. In this study, we employ tetrahydrofuran alcohol (THFA), an efficient and cost-effective alcohol ether electrolyte, to mitigate these issues and achieve ultralong-life AZIBs. Theoretical calculations and experimental findings demonstrate that THFA acts as both a hydrogen bonding donor and acceptor, effectively anchoring H2O molecules through dual-site hydrogen bonding. This mechanism restricts the activity of free water molecules. Moreover, the two oxygen (O) atoms in THFA serve as dual solvation sites, enhancing the desolvation kinetics of [Zn(H2O)6]2+ and improving the deposition dynamics of Zn2+ ions. As a result, even trace amounts of THFA significantly suppress adverse reactions and the formation of Zn dendrites, enabling highly reversible Zn metal anodes for ultralong-life AZIBs. Specifically, a Zn-based symmetric cell containing 2 % THFA achieves an ultralong cycle life of 8,800 h at 0.5 mA cm-2/0.5 mAh cm-2, while a Zn//VO2 full cell containing 2 % THFA maintains a remarkable 80.03 % capacity retention rate at 5 A g-1 over 2,000 cycles. This study presents a practical strategy to develop dendrite-free, cost-effective, and highly efficient aqueous energy storage systems by leveraging alcohol ether compounds with dual-site hydrogen bonding capabilities.

Hydrogen bonding state of THF-H2O solution analyzed by 2D Raman-COS spectroscopy

In this study, three distinct hydrogen bonding (HB) states of tetrahydrofuran (THF)-aqueous solutions at varying concentrations were characterized and analyzed using Raman spectroscopy coupled with two-dimensional correlation Raman (2D-COS) analysis. Specifically, in the range of 10%≤NTHF ≤ 30%, the solution exhibits cluster structures characterized by free THF-5H2O and THF-4H2O tetrahedral configurations; in the range of 40%≤NTHF ≤ 70%, the cluster structures within the solution consisted of THF·2H2O and THF·H2O configurations, following the fragmentation of tetrahedral structures; in 80%≤NTHF, the disruption of the tetrahedral structure of water enters the second stage, resulting in the formation of 2THF·H2O and low-dimensional self-aggregated structures of THF. Combined with density functional theory, a further discussion on the changes in bond lengths and bond angles was conducted. The results indicate that with the increase of NTHF, the HB length initially shortens and then elongates, the dihedral angle first increases and then decreases, and the corresponding bond energy increases initially and then decreases.

AI-Driven Electrolyte Additive Selection to Boost Aqueous Zn-Ion Batteries Stability

In tackling the stability challenge of aqueous Zn-ion batteries (AZIBs) for large-scale energy storage, the adoption of electrolyte additive emerges as a practical solution. Unlike current trial-and-error methods for selecting electrolyte additives, a data-driven strategy is proposed using theoretically computed surface free energy as a stability descriptor, benchmarked against experimental results. Numerous additives are calculated from existing literature, forming a database for machine learning (ML) training. Importantly, this ML model relies solely on experimental values, effectively addressing the challenge of large solvent molecule models that are difficult to handle with quantum chemistry computation. The interpretable linear regression algorithm identifies the number of heavy atoms in the additive molecule and the liquid surface tension as key factors. Artificial intelligence (AI) clustering categorizes additive molecules, identifying regions with the most significant impact on enhancing battery stability. Experimental verification successfully confirms the exceptional performance of 1,2,3-butanetriol and acetone in the optimal region. This integrated methodology, combining theoretical models, data-driven ML, and experimental validation, provides insights into the rational design of battery electrolyte additives.

Manipulating the Solvation Structure and Interface via a Bio-Based Green Additive for Highly Stable Zn Metal Anode

The practical application of aqueous zinc-ion batteries (AZIBs) is limited by serious side reactions, such as the hydrogen evolution reaction and Zn dendrite growth. Here, the study proposes a novel adoption of a biodegradable electrolyte additive, γ-Valerolactone (GVL), with only 1 vol.% addition (GVL-to-H2O volume ratio) to enable a stable Zn metal anode. The combination of experimental characterizations and theoretical calculations verifies that the green GVL additive can competitively engage the solvated structure of Zn2+ via replacing a H2O molecule from [Zn(H2O)6]2+, which can efficiently reduce the reactivity of water and inhibit the subsequent side reactions. Additionally, GVL molecules are preferentially adsorbed on the surface of Zn to regulate the uniform Zn deposition and suppress the Zn dendrite growth. Consequently, the Zn anode exhibits boosted stability with ultralong cycle lifespan (over 3500 h) and high reversibility with 99.69% Coulombic efficiency. The Zn||MnO2 full batteries with ZnSO4-GVL electrolyte show a high capacity of 219 mAh g-1 at 0.5 A g-1 and improved capacity retention of 78% after 550 cycles. This work provides inspiration on bio-based electrolyte additives for aqueous battery chemistry and promotes the practical application of AZIBs.

Electrolyte and Additive Engineering for Zn Anode Interfacial Regulation in Aqueous Zinc Batteries

Aqueous Zn-metal batteries (AZMBs) have gained great interest due to their low cost, eco-friendliness, and inherent safety, which serve as a promising complement to the existing metal-based batteries, e.g., lithium-metal batteries and sodium-metal batteries. Although the utilization of aqueous electrolytes and Zn metal anode in AZMBs ensures their improved safety over other metal batteries meanwhile guaranteeing their decent energy density at the cell level, plenty of challenges involved with metallic Zn anode still await to be addressed, including dendrite growth, hydrogen evolution reaction, and zinc corrosion and passivation. In the past years, several attempts have been adopted to address these problems, among which engineering the aqueous electrolytes and additives is regarded as a facile and promising approach. In this review, a comprehensive summary of aqueous electrolytes and electrolyte additives will be given based on the recent literature, aiming at providing a fundamental understanding of the challenges associated with the metallic Zn anode in aqueous electrolytes, meanwhile offering a guideline for the electrolytes and additives engineering strategies toward stable AZMBs in the future.

Effect of Antisolvent Additives in Aqueous Zinc Sulfate Electrolytes for Zinc Metal Anodes: The Case of Acetonitrile

Aqueous zinc-ion batteries (ZIBs) employing zinc metal anodes are gaining traction as batteries for moderate to long duration energy storage at scale. However, corrosion of the zinc metal anode through reaction with water limits battery efficiency. Much research in the past few years has focused on additives that decrease hydrogen evolution, but the precise mechanisms by which this takes place are often understudied and remain unclear. In this work, we study the role of an acetonitrile antisolvent additive in improving the performance of aqueous ZnSO4 electrolytes using experimental and computational techniques. We demonstrate that acetonitrile actively modifies the interfacial chemistry during Zn metal plating, which results in improved performance of acetonitrile-containing electrolytes. Collectively, this work demonstrates the effectiveness of solvent additive systems in battery performance and durability and provides a new framework for future efforts to optimize ion transport and performance in ZIBs.

Dendrite-free zinc metal anodes enabled by electrolyte additive for high-performing aqueous zinc-ion batteries

Rechargeable aqueous zinc (Zn)-ion batteries are regarded as a suitable candidate for large-scale energy storage due to their high safety and the natural abundance of Zn. However, the Zn anode in the aqueous electrolyte faces the challenges of corrosion, passivation, hydrogen evolution reaction, and the growth of severe Zn dendrites. These problems severely affect the performance and service life of aqueous Zn ion batteries, making it difficult to achieve their large-scale commercial applications. In this work, the sodium bicarbonate (NaHCO₃) additive was introduced into the zinc sulfate (ZnSO₄) electrolyte to inhibit the growth of Zn dendrites by promoting uniform deposition of Zn ions on the (002) crystal surface. This treatment presented a significant increase in the intensity ratio of (002) to (100) from an initial value of 11.14 to 15.31 after 40 cycles of plating/stripping. The Zn//Zn symmetrical cell showed a longer cycle life (over 124 h at 1.0 mA cm^-2) than the symmetrical cell without NaHCO₃. Additionally, the high capacity retention rate was increased by 20% for Zn//MnO₂ full cells. This finding is expected to be beneficial for a range of research studies that use inorganic additives to inhibit Zn dendrites and parasitic reactions in electrochemical and energy storage applications.