Stabilizing Interface pH by Mixing Electrolytes for High-Performance Aqueous Zn Metal Batteries

Regulating Protons to Tailor the Enol Conversion of Quinone for High-Performance Aqueous Zinc Batteries

Quinone-based electrodes using carbonyl redox reactions are promising candidates for aqueous energy storage due to their high theoretical specific capacity and high-rate performance. However, the proton storage manners and their influences on the electrochemical performance of quinone are still not clear. Herein, we reveal that proton storage could determine the products of the enol conversion and the electrochemical stability of the organic electrode. Specifically, the protons preferentially coordinated with the prototypical pyrene-4,5,9,10-tetraone (PTO) cathode, and increasing the proton concentration in the electrolyte can improve its working potentials and cycling stability by tailoring the enol conversion reaction. We also found that exploiting Al2(SO4)3 as a pH buffer can increase the energy density of the Zn||PTO batteries from 242.8 to 284.6 Wh kg-1. Our research has a guiding significance for emphasizing proton storage of organic electrodes based on enol conversion reactions and improving their electrochemical performance.

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.

In Situ Grown Coordination-Supramolecular Layer Holding 3D Charged Channels for Highly Reversible Zn Anodes

Dynamic reversible noncovalent interactions make supramolecular framework (SF) structures flexible and designable. A three-dimensional (3D) growth of such frameworks is beneficial to improve the structure stability while maintaining unique properties. Here, through the ionic interaction of the polyoxometalate cluster, coordination of zinc ions with cationic terpyridine, and hydrogen bonding of grafted carboxyl groups, the construction of a 3D SF at a well-crystallized state is realized. The framework can grow in situ on the Zn surface, further extending laterally into a full covering without defects. Relying on the dissolution and the postcoordination effects, the 3D SF layer is used as an artificial solid electrolyte interphase to improve the Zn-anode performance. The uniformly distributed clusters within nanosized pores create a negatively charged nanochannel, accelerating zinc ion transfer and homogenizing zinc deposition. The 3D SF/Zn symmetric cells demonstrate high stability for over 3000 h at a current density of 5 mA cm-2.

Stabilizing Anode-Electrolyte Interface for Dendrite-Free Zn-Ion Batteries Through Orientational Plating with Zinc Aspartate Additive

The stability of aqueous Zn-ion batteries (AZIBs) is detrimentally influenced by the formation of Zn dendrites and the occurrence of parasitic side reactions at the Zn metal anode (ZMA)-electrolyte interface. The strategic manipulation of the preferential crystal orientation during Zn2+ plating serves as an essential approach to mitigate this issue. Here, Zn aspartate (Zn-Asp), an electrolyte additive for AZIBs, is introduced not only to optimize the solvation structure of Zn2+ , but also to crucially promote preferential Zn2+ plating on the (002) crystal plane of ZMA. As a result, both side reactions and Zn dendrites are effectively inhibited, ensuring an anode surface free of both dendrites and by-products. The implementation of Zn-Asp leads to significant enhancements in both Zn||Zn symmetric and Zn||Ti batteries, which demonstrate robust cyclability of over 3200 h and high Coulombic efficiency of 99.29%, respectively. Additionally, the Zn||NaV3 O8 ·1.5H2 O full battery exhibits remarkable rate capability, realizing a high capacity of 240.77 mA h g-1 at 5 A g-1 , and retains 92.7% of its initial capacity after 1000 cycles. This research underscores the vital role of electrolyte additives in regulating the preferential crystal orientation of ZMA, thereby contributing to the development of high-performing AZIBs.

Low-Temperature and High-Performance Vanadium-Based Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries have attracted attention due to their low cost and high safety. Unfortunately, dendrite growth, hydrogen evolution reactions, cathodic dissolution, and other problems are more serious; not only that, but also the cathodic and anodic materials' lattices contract when the temperature drops, and charge transfer and solid phase diffusion become slow, seriously aggravating dendrite growth. At present, there are few studies on the low-temperature system, and studies on retaining high specific capacity are even more rare. Herein, ethylene glycol (EG) and manganese sulfate (MSO) are selected as additives, and the manganese vanadate (MVO) cathode is used to find a high-performance solution at low temperature. MVO can provide higher specific capacity and better structural stability than MnO2 to adapt to a low-temperature environment. At the same time, Mn2+ in MSO can produce a cationic shield covering the initial zinc tip at an appropriate concentration to avoid the tip effect and inhibit the dissolution of MVO. EG can not only reduce the freezing point of the electrolyte but also promote the desolvation of [Zn(H2O)6]2+. The synergistic effect of the three elements prevents the dissolution equilibrium of Mn2+ in MVO from fluctuating greatly due to the change of temperature. Therefore, when we use EG@0.2 M MnSO4 + 2 M ZnSO4 (EG + 0.2Mn/2ZSO) electrolyte at -30 °C, the Zn||Zn batteries which used this type of electrolyte can remain 350 h at 1 mA cm-2 without failure. The Zn||Cu batteries can retain 100% Coulombic efficiency after more than 2000 cycles at 0.2 mA cm-2. The Zn||MVO battery can reach 231.13 mA h g-1 at its first cycle, and the capacity retention rate is still above 85% after 1000 cycles, which is higher than that of the existing low-temperature research system.

Kinetics Conditioning of (Electro) Chemically Stable Zn Anode with pH Regulation Toward Long-Life Zn-Storage Devices

The safety, low cost, and high power density of aqueous Zn-based devices (AZDs) appeal to large-scale energy storage. Yet, the presence of hydrogen evolution reaction (HER) and chemical corrosion in the AZDs leads to local OH- concentration increasement and the formation of Znx SOy (OH)z •nH2 O (ZHS) by-products at the Zn/electrolyte interface, causing instability and irreversibility of the Zn-anodes. Here, a strategy is proposed to regulate OH- by introducing a bio-sourced/renewable polypeptide (ɛ-PL) as a pH regulator in electrolyte. The consumption of OH- species is evaluated through in vitro titration and cell in vivo in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy at a macroscopic and molecular level. The introduction of ɛ-PL is found to significantly suppress the formation of ZHS and associated side reactions, and reduce the local coordinated H2 O of the Zn2+ solvation shell, widening electrochemical stable window and suppressing OH- generation during HER. As a result, the inclusion of ɛ-PL improves the cycle time of Zn/Zn symmetrical cells from 15 to 225 h and enhances the cycle time of aqueous Zn- I2 cells to 1650 h compared to those with pristine electrolytes. This work highlights the potential of kinetical OH- regulation for by-product and dendrite-free AZDs.

Design Strategies for Aqueous Zinc Metal Batteries with High Zinc Utilization: From Metal Anodes to Anode-Free Structures

Aqueous zinc metal batteries (AZMBs) are promising candidates for next-generation energy storage due to the excellent safety, environmental friendliness, natural abundance, high theoretical specific capacity, and low redox potential of zinc (Zn) metal. However, several issues such as dendrite formation, hydrogen evolution, corrosion, and passivation of Zn metal anodes cause irreversible loss of the active materials. To solve these issues, researchers often use large amounts of excess Zn to ensure a continuous supply of active materials for Zn anodes. This leads to the ultralow utilization of Zn anodes and squanders the high energy density of AZMBs. Herein, the design strategies for AZMBs with high Zn utilization are discussed in depth, from utilizing thinner Zn foils to constructing anode-free structures with theoretical Zn utilization of 100%, which provides comprehensive guidelines for further research. Representative methods for calculating the depth of discharge of Zn anodes with different structures are first summarized. The reasonable modification strategies of Zn foil anodes, current collectors with pre-deposited Zn, and anode-free aqueous Zn metal batteries (AF-AZMBs) to improve Zn utilization are then detailed. In particular, the working mechanism of AF-AZMBs is systematically introduced. Finally, the challenges and perspectives for constructing high-utilization Zn anodes are presented.

Negatively Charged Hydrophobic Carbon Nano-Onion Interfacial Layer Enabling High-Rate and Ultralong-Life Zn-Based Energy Storage

Zn-based electrochemical energy storage (EES) systems are attracting more attention, whereas their large-scale application is restricted by the dendrite and parasitic reaction-caused unstable Zn anodes. Herein, a negatively charged hydrophobic carbon nano-onion (CNO) interfacial layer is proposed to realize ultrastable and high-rate Zn anodes, enabling high-performance Zn-based EES. For the CNO interfacial layer, its hydrophobicity not only blocks active water but also reduces the Zn2+ desolvation barrier, and meanwhile, the negatively-charged CNO nanoparticles adsorb Zn2+ and repel SO4 2- to homogenize Zn2+ flux, accelerate Zn2+ desolvation and suppress the self-corrosion of Zn anodes. Besides, the conductive CNO interfacial layer increases the surface area for the Zn deposition to reduce local current density. Consequently, under the modulation of the CNO interfacial layer, Zn plating/stripping exhibits impressive reversibility with an average Coulombic efficiency of 99.4% over 800 cycles, and Zn anodes present significantly enhanced electrochemical stability and rate performance, whose operation lifetime exceeds 2000 h at 1 mA cm-2 and 350 h even at 10 mA cm-2 . Moreover, high-rate and ultralong-life Zn-ion hybrid supercapacitors are achieved with the CNO interfacial layer-modulated Zn anode and activated CNO cathode. This work provides new thinking in regulating the Zn deposition interface to realize high-performance Zn-based EES.