Benefiting from loose assembly conditions, a high level of safety and environmentally friendly characteristics, rechargeable aqueous Zn-ion batteries (AZIBs) have attracted significant attention. The electrochemical kinetics and performance of the AZIBs are greatly affected by water in electrolytes or electrode materials. The corrosion and passivation of the Zn electrode caused by the inevitable solvation process of water molecules can lead to the growth of dendrites, thus resulting in a limited cycle life. Moreover, water in the electrode material, whether in the form of structural water or co-intercalated hydrated cations, can greatly affect the electrochemical behavior due to its small size, high polarity and hydrogen bonding. Unlike previous reports, this review focuses on the roles of water molecules during electrochemical processes in AZIBs. We comprehensively summarize the influencing mechanisms of water molecules during the energy storage process from the perspectives of the electrolyte, Zn anode, and cathode materials, and further include the basic theory, modification methods, and practical applications. The mystery concerning the water molecules and the electrochemical performance of AZIBs is revealed herein, and we also propose novel insights and actionable methods regarding the potential future directions in the design of high-performance AZIBs.

Comprehensive understanding of the roles of water molecules in aqueous Zn-ion batteries: from electrolytes to electrode materials

Cotton-derived cellulose film as a dendrite-inhibiting separator to stabilize the zinc metal anode of aqueous zinc ion batteries

The rapid advance of mild aqueous zinc-ion batteries (ZIBs) is driving the development of the energy storage system market. But the thorny issues of Zn anodes, mainly including dendrite growth, hydrogen evolution, and corrosion, severely reduce the performance of ZIBs. To commercialize ZIBs, researchers must overcome formidable challenges. Research about mild aqueous ZIBs is still developing. Various technical and scientific obstacles to designing Zn anodes with high stripping efficiency and long cycling life have not been resolved. Moreover, the performance of Zn anodes is a complex scientific issue determined by various parameters, most of which are often ignored, failing to achieve the maximum performance of the cell. This review proposes a comprehensive overview of existing Zn anode issues and the corresponding strategies, frontiers, and development trends to deeply comprehend the essence and inner connection of degradation mechanism and performance. First, the formation mechanism of dendrite growth, hydrogen evolution, corrosion, and their influence on the anode are analyzed. Furthermore, various strategies for constructing stable Zn anodes are summarized and discussed in detail from multiple perspectives. These strategies are mainly divided into interface modification, structural anode, alloying anode, intercalation anode, liquid electrolyte, non-liquid electrolyte, separator design, and other strategies. Finally, research directions and prospects are put forward for Zn anodes. This contribution highlights the latest developments and provides new insights into the advanced Zn anode for future research. 

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Zinc Anode for Mild Aqueous Zinc-Ion Batteries: Challenges, Strategies, and Perspectives

https://link.springer.com/content/pdf/10.1007/s40820-021-00782-5.pdf

The widespread application of aqueous rechargeable zinc ion batteries (ARZIBs) is limited by issues from both electrodes, including poor reversibility of the zinc anode and low capacity of the cathode. Here, we report the application of a Zn2+ substituted Nafion separator (Zn-Nafion) in ARZIBs which improves the performance of both the cathode and anode. On the anode side, the Zn-Nafion separator creates a uniform electrical and Zn2+ concentration field near the zinc anode surface, resulting in limited zinc dendrite growth. Therefore, a Zn symmetric cell with a Zn-Nafion separator shows a lower polarization and longer cycle life than those applying a traditional glass fiber separator. On the cathode side, the Zn-Nafion separator increases the contribution of the H+ reaction in the H+/Zn2+ co-insertion process, and causes the randomly distributed byproducts, Zn4SO4(OH)6·nH2O platelets, to transform into a dense solid-electrolyte-interphase layer, which protects the cathode from dissolving into the electrolyte. Thus, the energy density and capacity retention of both zinc full cells (applying commercial V2O5 or α-MnO2 nanowires as the cathode) are dramatically improved by the Zn-Nafion separator. Notably, the Zn//Zn-Nafion//V2O5 cell delivers a high specific capacity of 495.8 mA h g−1 (374.4 W h kg−1) with a low cathode cost (39.23 US$ W h kg−1). Moreover, the Zn-Nafion separator can be recycled at least ten times without performance degradation, which significantly reduces the cost of the battery. The present work can provide a novel insight into cost-effective and high-performance battery technologies.

Jianshuo Zhang

Papers

A cation selective separator induced cathode protective layer and regulated zinc deposition for zinc ion batteries

Iron-doped metal-organic framework with enhanced oxygen evolution reaction activity for overall water splitting