Production of fast-charge Zn-based aqueous batteries via interfacial adsorption of ion-oligomer complexes

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.

Positively Charged Amino Acid-Modulated Interfacial Chemistry and Deposition Textures for Highly Reversible Zinc Anodes

Interfacial active water molecule-induced parasitic reactions and stochastic Zn2+ transport-caused dendrite issue significantly impede the implementation of aqueous Zn-ion batteries. Herein, three positively charged amino acids, namely arginine, histidine, and lysine, were utilized as adsorption-type electrolyte additives to enhance the stability and reversibility of Zn anodes. Combined theoretical and experimental analyses verified that these amino acid cations can synergistically modulate the interfacial microenvironment and promote orientational Zn deposition. The adsorbed amino acid cations reconfigured the interfacial electric double layer structure, forming SO42-- and H2O-poor interfaces, thereby retarding hydrogen evolution and corrosion side reactions. Simultaneously, the preferential adsorption of the amino acid cations at specific facets induced crystallographic orientational Zn deposition along unterminated facets. Three deposition architectures, namely planar texture, subvertical alignment, and vertical erection, were obtained, all effectively inhibiting dendrite formation. Consequently, symmetric cells with the three amino acid cations exhibited high stripping/plating reversibility of over 2000 cycles at 5 mA cm-2. Moreover, MnO2-based full cells exhibited markedly improved stabilities compared with their additive-free counterparts.

Aqueous Rechargeable Zn-Iodine Batteries: Issues, Strategies and Perspectives

The static aqueous rechargeable Zn-Iodine batteries (ARZiBs) have been studied extensively because of their low-cost, high-safety, moderate voltage output, and other unique merits. Nonetheless, the poor electrical conductivity and thermodynamic instability of the iodine cathode, the complicated conversion mechanism, and the severe interfacial reactions at the Zn anode side induce their low operability and unsatisfactory cycling stability. This review first clarifies the typical configuration of ARZiBs with a focus on the energy storage mechanism and uncovers the issues of the ARZiBs from a fundamental point of view. After that, it categorizes the recent optimization strategies into cathode fabrication, electrolyte modulation, and separator/anode modification; and summarizes and highlights the achieved progress of these strategies in advanced ARZiBs. Given that the ARZiBs are still at an early stage, the future research outlook is provided, which hopefully may guide the rational design of advanced ARZiBs.

Controllable Solid Electrolyte Interphase by Ionic Environment Regulation for Stable Zn-Ion Battery

Artificial solid electrolyte interphase in organic solutions is effective and facile for long-cycling aqueous zinc ion batteries. However, the specific effects on different ionic environments have not been thoroughly investigated. Herein, pyromellitic acid (PA) are employed as organic ligand to coordinate with Zn2+ under various ionic environments. The connection between the ionic environment and reaction spontaneity is analyzed to provide insights into the reasons behind the effectiveness of the SEI layer and to characterize its protective impact on the zinc anode. Notably, the PA solution (pH4) lacking OH- contributes to the formation of a dense and ultrathin SEI with Zn-PA coordination, preventing direct contact between the anode and electrolyte. Moreover, the presence of organic functional groups facilitates a uniform flux of Zn2+. These advantages enable stable cycling of the PA4-Zn symmetric cell at a current density of 3 mA cm-2 for over 3500 h. The PA4-Zn//MVO full cell demonstrates excellent electrochemical reversibility. Investigating the influence of the ionic environment on SEI generation informs the development of novel SEI strategies.

Highly Potent and Low-Volume Concentration Additives for Durable Aqueous Zinc Batteries: Machine Learning-Enabled Performance Rationalization

The essential virtues of aqueous zinc battery chemistry stem from the energy-dense zinc metal anode and mild aqueous electrolytes. Yet, their incompatibility - as exposed by zinc's corrosion and associated dendrite problem - poses a challenge to achieving improved cycle life under practically relevant parameters. While electrolyte additives are a scalable strategy, additives that can function at low volume concentrations remain elusive. Here, through screening alkanol and alkanediol chemistries, 1,2-butanediol and pentanediol are unveiled as highly potent additives, which operate at a practical 1 volume% concentration owing to their ability to furnish dynamic solid-electrolyte interphase through pronounced interfacial filming. This unique mechanistic action renders effective corrosion and dendrite mitigation, resulting in up to five to twenty-fold zinc cyclability enhancement with a high Coulombic efficiency (up to 99.9%) and improved full-cell performance under demanding conditions, including at elevated temperatures. A machine learning-based analysis is presented to rationalize the additive performance relative to critical physicochemical descriptors, which can pave the way for a rational approach to efficient additive discoveries.

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

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

Adaptive Ion Channels Formed in Ultrathin and Semicrystalline Polymer Interphases for Stable Aqueous Batteries

Aqueous Zn batteries have recently emerged as promising candidates for large-scale energy storage, driven by the need for a safe and cost-effective technology with sufficient energy density and readily accessible electrode materials. However, the energy density and cycle life of Zn batteries have been limited by inherent chemical, morphological, and mechanical instabilities at the electrode-electrolyte interface where uncontrolled reactions occur. To suppress the uncontrolled reactions, we designed a crystalline polymer interphase for both electrodes, which simultaneously promotes electrode reversibility via fast and selective Zn transport through the adaptive formation of ion channels. The interphase comprises an ultrathin layer of crystalline poly(1H,1H,2H,2H-perfluorodecyl acrylate), synthesized and applied as a conformal coating in a single step using initiated chemical vapor deposition (iCVD). Crystallinity is optimized to improve interphase stability and Zn-ion transport. The optimized interphase enables a cycle life of 9500 for Zn symmetric cells and over 11,000 for Zn-MnO2 full-cell batteries. We further demonstrate the generalizability of this interphase design using Cu and Li as examples, improving their stability and achieving reversible cycling in both. The iCVD method and molecular design unlock the potential of highly reversible and cost-effective aqueous batteries using earth-abundant Zn anode materials, pointing to grid-scale energy storage.

Artificial bi-functional layers promoting Zn2+ desolvation and homogeneous deposition for reversible zinc metal anodes

Rechargeable aqueous zinc-ion hybrid supercapacitors (ZHSs) are drawing extensive attention because of their cost-effectiveness and diminished safety hazards. Nevertheless, large-scale application of ZHSs has been hindered by the severe side reactions and rampant dendrites growth on the surface of Zn metal anodes. Herein, we propose a three-dimensional organic-inorganic composite frame material as an artificial bi-functional layer coated on the zinc foil, featuring nitrogenous functional groups with zincophilicity (abbreviated as NCFM@Zn). The nitrogen (N) site's strong adsorption capacity and synergistic effect of the sub-nanopore size promote rapid desolvation of zinc ions and reduce side reactions, while also prolonging galvanized nucleation's Sand's time and allowing for even nucleation. Moreover, the uniform distribution of N on the layer results in homogeneous zinc ions flux and supports consistent zinc plating while inhibiting dendrites generation. As a result of this unique artificial bi-functional layer, symmetric Zn cells can survive 2500 h at 2.5 mA cm-2. High-areal-capacity zinc||activated carbon hybrid supercapacitors also demonstrate 20,000 cycles at high Coulombic efficiency, thus highlighting the utter convenience and potential of this strategy for modifying rechargeable metal hybrid supercapacitor surfaces.

Atomic Pinning of Trace Additives Induces Interfacial Solvation for Highly Reversible Zn Metal Anodes

Aqueous Zn metal batteries are considered promising energy storage devices due to their high energy density and low cost. Unfortunately, such great potential is at present obscured by two clouds called dendrite growth and parasitic reactions. Herein, trace amounts of sodium cyclamate (CYC-Na) are introduced as an electrolyte additive, and accordingly, an atomic-pinning-induced interfacial solvation mechanism is proposed to summarize the effect of trace addition. Specifically, coadsorption of -NH- and -SO3 groups overcomes the ring-flipping effect and pins the CYC anion near the Zn anode surface in parallel, which significantly modifies the Zn2+ solvation sheath at the interface. This process homogenizes the surface Zn2+ flux and reduces the H2O and SO42- content on the surface, thus eliminating byproducts and leveling Zn deposition. Cells with trace CYC-Na cycle stably for 3650 h and still cycle for 330 h at high depths of discharge of 56.9%. This work dispels the clouds for efficient trace additives for AZMBs.

An Electrochemical Perspective of Aqueous Zinc Metal Anode

Based on the attributes of nonflammability, environmental benignity, and cost-effectiveness of aqueous electrolytes, as well as the favorable compatibility of zinc metal with them, aqueous zinc ions batteries (AZIBs) become the leading energy storage candidate to meet the requirements of safety and low cost. Yet, aqueous electrolytes, acting as a double-edged sword, also play a negative role by directly or indirectly causing various parasitic reactions at the zinc anode side. These reactions include hydrogen evolution reaction, passivation, and dendrites, resulting in poor Coulombic efficiency and short lifespan of AZIBs. A comprehensive review of aqueous electrolytes chemistry, zinc chemistry, mechanism and chemistry of parasitic reactions, and their relationship is lacking. Moreover, the understanding of strategies for suppressing parasitic reactions from an electrochemical perspective is not profound enough. In this review, firstly, the chemistry of electrolytes, zinc anodes, and parasitic reactions and their relationship in AZIBs are deeply disclosed. Subsequently, the strategies for suppressing parasitic reactions from the perspective of enhancing the inherent thermodynamic stability of electrolytes and anodes, and lowering the dynamics of parasitic reactions at Zn/electrolyte interfaces are reviewed. Lastly, the perspectives on the future development direction of aqueous electrolytes, zinc anodes, and Zn/electrolyte interfaces are presented.

F-Doped Carbon Nanoparticles-Based Nucleation Assistance for Fast and Uniform Three-Dimensional Zn Deposition

Aqueous Zn metal-based batteries have considerable potential as energy storage system; however, their application is extremely limited by dendrite development and poor reversibility. In this study, to overcome both challenges, F-doped carbon nanoparticles (FCNPs) are uniformly constructed on substrates (Ti, Zn, Cu, and steel) by a plasma-assisted surface modification, which endows reversible and uniform deposition of Zn metal. FCNPs with high surface charge density act as nucleation assistors and form numerous homogenous Zn nucleation sites toward Zn 3D growth, which improves Zn plating kinetic and results in uniform Zn deposition. Furthermore, the ZnF₂  solid electrolyte interface generated during cycling contributes to rapid mass transfer and enhances Zn reversibility, but also suppresses the side reaction. Accordingly, the half-cell of P-Ti coupled with Zn exhibits an average Coulombic efficiency of 99.47% with 500 cycles. The symmetric cell of the P-Zn anode presents a lifespan of over 1500 h at the current density of 5 mA cm^-2 . Notably, the cell works for 100 h at 50 mA cm^-2 . It is believed that this ingenious surface modification broadens revolutionary methods for uniform metallic deposition, as well as the dendrite-free rechargeable batteries system.

Nonepitaxial Electrodeposition of (002)-Textured Zn Anode on Textureless Substrates for Dendrite-Free and Hydrogen Evolution-Suppressed Zn Batteries

Nontoxic and safe aqueous Zn batteries are largely restricted by the detrimental dendrite growth and hydrogen evolution of Zn metal anode. The (002)-textured Zn electrodeposition, demonstrated as an effective approach for solving these issues, is nevertheless achieved mainly by epitaxial or hetero-epitaxial deposition of Zn on pre-textured substrates. Herein, the electrodeposition of (002)-textured and compact Zn on textureless substrates (commercial Zn, Cu, and Ti foils) at a medium-high galvanostatic current density is reported. According to the systematic investigations on Zn nucleation and growth behaviors, this is ascribed to two reasons: i) the promoted nonepitaxial nucleation of fine horizontal (002) nuclei at increased overpotential and ii) the competitive growth advantages of (002)-orientated nuclei. The resulting freestanding (002)-textured Zn film exhibits significantly suppressed hydrogen evolution and prolonged Zn plating-stripping cycling life, achieving over 2100 mAh cm^-2 cumulative capacity under a current density of 10 mA cm^-2 and a high depth of discharge (DOD) of 45.5%. Therefore, this study provides both fundamental and practical insights into long-life Zn metal batteries.

Synergetic modulation on ionic association and solvation structure by electron-withdrawing effect for aqueous zinc-ion batteries

Aqueous zinc-ion batteries are emerging as one of the most promising large-scale energy storage systems due to their low cost and high safety. However, Zn anodes often encounter the problems of Zn dendrite growth, hydrogen evolution reaction, and formation of by-products. Herein, we developed the low ionic association electrolytes (LIAEs) by introducing 2, 2, 2-trifluoroethanol (TFE) into 30 m ZnCl2 electrolyte. Owing to the electron-withdrawing effect of -CF3 groups in TFE molecules, in LIAEs, the Zn2+ solvation structures convert from larger aggregate clusters into smaller parts and TFE will construct H-bonds with H2O in Zn2+ solvation structure simultaneously. Consequently, ionic migration kinetics are significantly enhanced and the ionization of solvated H2O is effectively suppressed in LIAEs. As a result, Zn anodes in LIAE display a fast plating/stripping kinetics and high Coulombic efficiency of 99.74%. The corresponding full batteries exhibit an improved comprehensive performance such as high-rate capability and long cycling life.

Electroconvective Flow in Liquid Electrolytes Containing Oligomer Additives

Metal electrodeposition in batteries is fundamentally unstable and affected by different instabilities depending on operating conditions and electrolyte chemistry. Particularly, at high charging rates, a hydrodynamic instability loosely termed electroconvection sets in, which complicates all electrochemical processes by creating a nonuniform ion flux and preferential deposition at the electrode. Here, we isolate and study electroconvection by experimentally investigating how oligomer additives in liquid electrolytes interact with the hydrodynamic instability at a cation selective interface. From electrochemical measurements and direct visualization experiments, we find that electroconvection is delayed and suppressed at all voltages in the presence of oligomers. The underlying mechanism is revealed to involve formation of an oligomer ad-layer at the interface, which in response to perturbation is believed to exert an opposing body force on the surrounding fluid to preserve the ad-layer structure and in so doing suppresses electroconvection. Our results therefore reveal that in battery electrolytes without obvious sources of bulk elasticity, surface forces produced by adsorbed polymers can be used to advantage for suppressing instability.

Development of long lifespan high-energy aqueous organic||iodine rechargeable batteries

Rechargeable aqueous metal||I₂ electrochemical energy storage systems are a cost-effective alternative to conventional transition-metal-based batteries for grid energy storage. However, the growth of unfavorable metallic deposition and the irreversible formation of electrochemically inactive by-products at the negative electrode during cycling hinder their development. To circumvent these drawbacks, herein we propose 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) as negative electrode active material and a saturated mixed KCl/I₂ aqueous electrolyte solution. The use of these components allows for exploiting two sequential reversible electrochemical reactions in a single cell. Indeed, when they are tested in combination with an active carbon-enveloped I₂ electrode in a glass cell configuration, we report an initial specific discharge capacity of 900 mAh g⁻¹ (electrode mass of iodine only) and an average cell discharge voltage of 1.25 V at 40 A g⁻¹ and 25\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}±1 °C. Finally, we also report the assembly and testing of a PTCDI|KCl-I₂|carbon paper multilayer pouch cell prototype with a discharge capacity retention of about 70% after 900 cycles at 80 mA and 25\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pm$$\end{document}±1 °C.

Aqueous I₂-based batteries are a promising system for cost-effective and environmentally-friendly electricity storage. Here, the authors propose a high-capacity and long-lasting aqueous I₂ battery system using an electrochemically active organic molecule at the negative electrode.

Hydrogels Enable Future Smart Batteries

The growing trend of intelligent devices ranging from wearables and soft robots to artificial intelligence has set a high demand for smart batteries. Hydrogels provide opportunities for smart batteries to self-adjust their functions according to the operation conditions. Despite the progress in hydrogel-based smart batteries, a gap remains between the designable functions of diverse hydrogels and the expected performance of batteries. In this Perspective, we first briefly introduce the fundamentals of hydrogels, including formation, structure, and characteristics of the internal water and ions. Batteries that operate under unusual mechanical and temperature conditions enabled by hydrogels are highlighted. Challenges and opportunities for further development of hydrogels are outlined to propose future research in smart batteries toward all-climate power sources and intelligent wearables.

Designing interphases for practical aqueous zinc flow batteries with high power density and high areal capacity

Aqueous zinc flow batteries (AZFBs) with high power density and high areal capacity are attractive, both in terms of cost and safety. A number of fundamental challenges associated with out-of-plane growth and undesirable side reactions on the anode side, as well as sluggish reaction kinetics and active material loss on the cathode side, limit practical deployment of these batteries. We investigated artificial interphases created using a simple electrospray methodology as a strategy for addressing each of these challenges. The effectiveness of the electrospray interphases in full cell zinc-iodine flow batteries was evaluated and reported; it is possible to simultaneously achieve high power density [115 milliwatts per square centimeter (mW/cm²)] and high areal capacity [25 milliampere hour per square centimeter (mA·hour/cm²)]. Last, we extended it to aqueous zinc-bromine and zinc-vanadium flow batteries of contemporary interest. It is again found that high power density (255 and 260 mW/cm², respectively) and high areal capacity (20 mA·hour/cm²) can be simultaneously achieved in AZFBs.

Halogenated Zn2+ Solvation Structure for Reversible Zn Metal Batteries

Rechargeable aqueous Zn metal batteries have become promising candidates for large-scale electrochemical energy storage owing to their high safety and affordable low cost. However, Zn metal anode suffers from dendritic growth and hydrogen evolution reaction (HER), deteriorating the electrochemical performance. Here, we demonstrate that these challenges can be conquered by introducing a halogen ion into the Zn²⁺ solvation structure. By designing an electrolyte composed of zinc acetate and ammonium halide, the electron-donating anion I^- can coordinate with Zn²⁺ and transform the traditional Zn(H₂O)₆²⁺ to ZnI(H₂O)₅⁺, in which I^- could transfer electrons into H₂O and thus suppress HER. The dynamic electrostatic shielding layer formed by concomitant NH₄⁺ can restrict the dendritic growth. As a result, the halogenated electrolyte achieves a high initial coulombic efficiency (CE) of 99.3% in the Zn plating/stripping process and remains at an average of ∼99.8% with uniform Zn deposition. Moreover, Zn-I batteries are constructed by using dissociative I^- as the cathode and carbon felt-polyaniline as the conductive and adsorptive layer, exhibiting an average CE of 98.6% without capacity decay after 300 cycles. This work provides insights into the halogenated Zn²⁺ solvation structure and offers a general electrolyte design strategy for achieving a highly reversible Zn metal anode and batteries.