Microstructural Evolution of Zinc-Ion Species from Aqueous to Hydrated Eutectic Electrolyte for Zn-Ion Batteries

Weakly solvating effect optimized hydrated eutectic electrolyte towards reliable zinc anode interfacial chemistry

The inherent issues of aqueous Zn-ion batteries, including side reactions and dendrite growth, can be effectively addressed through designing solvation structures enriched with anions to facilitate the formation of an anion-derived solid electrolyte interphase (SEI) layer. Here, the weakly solvating effect is utilized to modulate Zn2+ solvation structure for constructing an anion-derived SEI layer. Trifluoroacetamide (TFACE), with a specific weak solvating ability, serves as an ideal ligand for preparing hydrated eutectic electrolytes (HEEs) combining the anion-containing solvation structures and high ionic conductivity. The results demonstrate that coordinated anions preferentially decompose and generate an inorganic/organic hybrid SEI layer on the Zn anode, which efficiently suppresses both side reactions and dendritic growth. Such an electrolyte enables assembled Zn//polyaniline (PANI) full cells to process an impressive capacity retention, maintaining 80 % after 3000 cycles at 0.5 A g-1. This work provides a fundamental insight into building the anion-derived SEI by the weakly solvating effect and gives a viable route for designing advanced aqueous electrolytes.

Fundamentals, Advances and Perspectives in Designing Eutectic Electrolytes for Zinc-Ion Secondary Batteries

Zinc-ion secondary batteries have been competitive candidates since the "post-lithium-ion" era for grid-scale energy storage, owing to their plausible security, high theoretical capacity, plentiful resources, and environment friendliness. However, many encumbrances like notorious parasitic reactions and Zn dendrite growth hinder the development of zinc-ion secondary batteries remarkably. Faced with these challenges, eutectic electrolytes have aroused notable attention by virtue of feasible synthesis and high tunability. This review discusses the definition and advanced functionalities of eutectic electrolytes in detail and divides them into nonaqueous, aqueous, and solid-state eutectic electrolytes with regard to the state and component of electrolytes. In particular, the corresponding chemistry concerning solvation structure regulation, electric double layer (EDL) structure, solid-electrolyte interface (SEI) and charge/ion transport mechanism is systematically elucidated for a deeper understanding of eutectic electrolytes. Moreover, the remaining limitations and further development of eutectic electrolytes are discussed for advanced electrolyte design and extended applications.

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.

Electrolyte Design Strategies for Aqueous Sodium-Ion Batteries: Progress and Prospects

Sodium-ion batteries (SIBs) have emerged as one of today's most attractive battery technologies due to the scarcity of lithium resources. Aqueous sodium-ion batteries (ASIBs) have been extensively researched for their security, cost-effectiveness, and eco-friendly properties. However, aqueous electrolytes are extremely limited in practical applications because of the narrow electrochemical stability window (ESW) with extremely poor low-temperature performance. The first part of this review is an in-depth discussion of the reasons for the inferior performance of aqueous electrolytes. Next, research progress in extending the electrochemical stabilization window and improving low-temperature performance using various methods such as "water-in-salt", eutectic, and additive-modified electrolytes is highlighted. Considering the shortcomings of existing solid electrolyte interphase (SEI) theory, recent research progress on the solvation behavior of electrolytes is summarized based on the solvation theory, which elucidates the correlation between the solvation structure and the electrochemical performance, and three methods to upgrade the electrochemical performance by modulating the solvation behavior are introduced in detail. Finally, common design ideas for high-temperature resistant aqueous electrolytes that are hoped to help future aqueous batteries with wide temperature ranges are summarized.

Advanced electrolytes for high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have garnered significant attention in the realm of large-scale and sustainable energy storage, primarily owing to their high safety, low cost, and eco-friendliness. Aqueous electrolytes, serving as an indispensable constituent, exert a direct influence on the electrochemical performance and longevity of AZIBs. Nonetheless, conventional aqueous electrolytes often encounter formidable challenges in AZIB applications, such as the limited electrochemical stability window and the zinc dendrite growth. In response to these hurdles, a series of advanced aqueous electrolytes have been proposed, such as "water-in-salt" electrolytes, aqueous eutectic electrolytes, molecular crowding electrolytes, and hydrogel electrolytes. This comprehensive review commences by presenting an in-depth overview of the fundamental compositions, principles, and distinctive characteristics of various advanced aqueous electrolytes for AZIBs. Subsequently, we systematically scrutinizes the recent research progress achieved with these advanced aqueous electrolytes. Furthermore, we summarizes the challenges and bottlenecks associated with these advanced aqueous electrolytes, along with offering recommendations. Based on the optimization of advanced aqueous electrolytes, this review outlines future directions and potential strategies for the development of high-performance AZIBs. This review is anticipated to provide valuable insights into the development of advanced electrolyte systems for the next generation of stable and sustainable multi-valent secondary batteries.

Interfacial chemistry in multivalent aqueous batteries: fundamentals, challenges, and advances

As one of the most promising electrochemical energy storage systems, aqueous batteries are attracting great interest due to their advantages of high safety, high sustainability, and low costs when compared with commercial lithium-ion batteries, showing great promise for grid-scale energy storage. This invited tutorial review aims to provide universal design principles to address the critical challenges at the electrode-electrolyte interfaces faced by various multivalent aqueous battery systems. Specifically, deposition regulation, ion flux homogenization, and solvation chemistry modulation are proposed as the key principles to tune the inter-component interactions in aqueous batteries, with corresponding interfacial design strategies and their underlying working mechanisms illustrated. In the end, we present a critical analysis on the remaining obstacles necessitated to overcome for the use of aqueous batteries under different practical conditions and provide future prospects towards further advancement of sustainable aqueous energy storage systems with high energy and long durability.

Ethylene Glycol-Choline Chloride Based Hydrated Deep Eutectic Electrolytes Enabled High-Performance Zinc-Ion Battery

Aqueous rechargeable zinc-ion batteries (ARZIBs) are considered as an emerging energy storage technology owing to their low cost, inherent safety, and reasonable energy density. However, significant challenges associated with electrodes, and aqueous electrolytes restrict their rapid development. Herein, ethylene glycol-choline chloride (Eg-ChCl) based hydrated deep-eutectic electrolytes (HDEEs) are proposed for RZIBs. Also, a novel V10O24·nH2O@rGO composite is prepared and investigated in combination with HDEEs. The formulated HDEEs, particularly the composition of 1 ml of EG, 0.5 g of ChCl, 4 ml of H2O, and 2 M ZnTFS (1-0.5-4-2 HDEE), not only exhibit the lowest viscosity, highest Zn2+ conductivity (20.38 mS cm-1), and the highest zinc (Zn) transference number (t+ = 0.937), but also provide a wide electrochemical stability window (>3.2 V vs ZnǁZn2+) and enabledendrite-free Zn stripping/plating cycling over 1000 hours. The resulting ZnǁV10O24·nH2O@rGO cell with 1-0.5-4-2 HDEE manifests high reversible capacity of ≈365 mAh g-1 at 0.1 A g-1, high rate-performance (delivered ≈365/223 mAh g-1 at 0.1/10 mA g-1) and enhanced cycling performance (≈63.10% capacity retention in the 4000th cycle at 10 A g-1). Furthermore, 1-0.5-4-2 HDEE support feasible Zn-ion storage performance across a wide temperature range (0-80 °C) FInally, a ZnǁV10O24·nH2O@rGO pouch-cell prototype fabricated with 1-0.5-4-2 HDEE demonstrates good flexibility, safety, and durability.

Gyroid Liquid Crystals as Quasi-Solid-State Electrolytes Toward Ultrastable Zinc Batteries

The potential for optimizing ion transport through triply periodic minimal surface (TPMS) structures renders promising electrochemical applications. In this study, as a proof-of-concept, we extend the inherent efficiency and mathematical beauty of TPMS structures to fabricate liquid-crystalline electrolytes with high ionic conductivity and superior structural stability for aqueous rechargeable zinc-ion batteries. The specific topological configuration of the liquid-crystalline electrolytes, featuring a Gyroid geometry, enables the formation of a continuous ion conduction pathway enriched with confined water. This, in turn, promotes the smooth transport of charge carriers and contributes to high ionic conductivity. Meanwhile, the quasi-solid hydrophobic phase assembled by hydrophobic alkyl chains exhibits notable rigidity and toughness, enabling uniform and compact dendrite-free Zn deposition. These merits synergistically enhance the overall performance of the corresponding full batteries. This work highlights the distinctive role of TPMS structures in developing high-performance, liquid-crystalline electrolytes, which can provide a viable route for the rational design of next-generation quasi-solid-state electrolytes.