【Background】
The application of zinc (Zn) metal batteries is hampered by thermodynamically driven hydrogen evolution reactions and kinetics-induced dendrite growth, resulting in reduced cycling stability and premature cell failure. Electrochemical reactions mostly occur in the electric double-layer region (EDL), and their properties determine the electrochemical behaviors such as deposition/stripping at the metal/electrolyte interface. Controlling the properties and charge of EDL on Zn metal surfaces can effectively inhibit thermodynamic and kinetic-induced interfacial side reactions.
【Job Introduction】
Recently, Hongfei Li's team at Southern University of Science and Technology (SUSTech) introduced a pH-mediated surface charge enhancement and ion-selectivity strategy, which uses a simple self-assembly method to construct a cysteamine (SH-CH2-CH2-NH2) molecular layer (SAL) molecular layer (SAL) on the surface of Zn metal (Zn@SCRIS-SAL). Triggered by a pH-mediated protonation effect, these layers produce a partial positive surface (-NH3+) to repel hydrated protons (H+· H2O) and zinc-philic sites (-NH2) to anchor Zn2+. The synergistic combination of these effects enables highly reversible zinc metal chemistry to effectively inhibit side reactions and dendrite growth. At a high current density of 10 mA cm-2, Zn@SCRIS-SALs in symmetrical cells exhibit stability with an ultra-long life of 2500 h. The interfacial electrochemical reaction of Zn metal/electrolyte was detected by in-situ electrochemical surface-enhanced Raman spectroscopy (EC-SERS), which strongly demonstrated that the locally enhanced positively charged surface could repel H+· H2O, thereby reducing the activity of hydrolysis at the Zn interface. Excellent reversibility was further determined by integrating Zn@SCRIS-SAL with the I2 cathode into the full cell, and the I2 cathode exhibited high capacity retention compared to bare zinc-based cells. In addition, an 80 mAh pouch battery assembled with Zn@SCRIS-SAL operated more than 2500 cycles at a surface capacity of 5.18 mA h cm-2. The article was published in the top international journal Energy & Environmental Science. Zhiquan Wei is the first author of this article.
【Content Description】
In order to achieve a practical aqueous zinc-based battery system, the stability of the zinc anode is particularly critical. All electrochemical reactions occur in the electric double-layer region (EDL), and the characteristic region determines the reversibility of the metal peeling/plating process at the metal/electrolyte interface. However, the current research work has made compromises on the performance of the Zn surface modification reconstruction interface (conductive/insulating-coating) in different aspects, and has failed to solve the thermodynamic and kinetic obstacles in the EDL region of the Zn metal/electrolyte interface at the same time. Therefore, the EDL performance of metal interfaces is largely advantageously controlled by a custom layer with highly oriented molecules and ordered end groups. In this paper, a cysteamine electrolysis system was designed to spontaneously construct a molecular layer on the surface of zinc metal. The terminal amino functional group was chosen here because it triggers a partial protonation effect in an acidic zinc salt electrolyte (weak base and strong acid nature). The protonated moiety (-NH3+) effectively repels hydrated protons, while the unprotonated moiety (-NH2) elicits more zinc-philic sites. Finally, the stable cycle of zinc metal anode is realized.
Figure 1: Structure and characterization of Zn@SCRIS-SALs. Schematic diagram of (a) and (b) self-assembly of cysteamine on a zinc metal surface. (c)-(e) Deep etching profiles obtained from XPS analysis of N, S, and Zn elements in Zn@SCRIS-SALs, respectively. AFM images show the topographic features of (f) bare zinc foil and (g) Zn@SCRIS-SALs anodes.
Figure 2: Electrochemical properties of Zn@SCRIS-SALs and bare zinc in symmetrical cells. (a) Zn||, with an area capacity of 0.5 mA h cm-2 and 1 mA cm-2CE evolution of Cu asymmetric cells, where the 0~20 h and 740~800 h regions are shown in the figure. Voltage distribution map for the selected period corresponding to zone (i) (1st, 100th, 200th, 300th cycles) and zone (ii) (1st, 200th, 400th, 800th cycles) in (b)(a) with the short circuit points marked. (c) Voltage distribution plot cyclic at a high current density of 10 mA cm-2 and an areal capacity of 1 mA h cm-2. The selection period corresponding to zones (i) (45-46 h) and zones (ii) (2498-2499 h) in (d)(c) with short-circuit point markings. (e) Plot of cyclic voltage distribution at 20 mA cm-2 with a capacity of 20 mA h cm-2, where the region (0-5 h) is in the inset. (f) Performance comparison of Zn@SCRIS-SALs anodes with other protection strategies based on different materials.
Figure 3: Exploring the zinc deposition process from a thermodynamic perspective. (a) Schematic diagram of the inhibition of HER by SCRIS-SALs at different pH conditions. (b) LSV curves of 1 M Na2SO4 and 1 M Na2SO4 plus 1 mM cysteine inhibiting water lysis at different pH conditions. (c) Gas production of bare Zn and Zn@SCRIS-SALs anodes recorded by the Operando pressure detector at 10 mA cm-2 with an area capacity of 25 mA h cm-2. (d) Light microscope images recorded in a symmetrical transparent cell after a specified period in the deposition state. (e) Schematic diagram of an in-situ EC-SERS cell with Au coated with the working electrode of the Zn anode. (f) In-situ SERS spectra of O-H stretching modes of water molecules at the surface interface of bare Zn foil and Zn@SCRIS-SALs measured at different current densities (corresponding current density-time on the right). (g) Raman displacement of the O-H tensile mode vibration peak of panel (f).
图4：Zn成核和生长机理的动力学探讨。 （a）不同pH条件下SCRIS-SALs在Zn沉积中的示意图。 （b）不同pH条件下Zn||Cu电池在5 mA cm-2和1 mAh cm-2下的首次电镀电压分布图与初始成核过程的过电位。 （c）（i）裸Zn和Zn@SCRIS-SALs阳极（（ii）pH≈5，（iii）pH≈4，（iv）pH≈3）在5 mA cm-2和1 mAh cm-2下循环100h后沉积状态的SEM图像。 （d - f）循环100 h后SCRIS-SALs在Zn表面的N 1s、S 2p和Zn 2p的XPS谱图。
Figure 5: Charge state of SCRIS-SALs on the Zn surface. (a) Zeta potential and EDLC of bare Zn and Zn@SCRIS-SALs in different pH-mediated protonation states (pH 3, 4, 5 for full protonation, partial protonation, and non-protonation, respectively). (c) Schematic diagram of the mechanism of electrostatic repulsion effect of hydrated protons and zinc-philic effect of Zn2+ on Zn@SCRIS-SALs. (d) Electrostatic potential (ESP) diagram of fully protonated (i,-NH3+) and unprotonated ((ii,-NH2) molecules with end groups. The local ESP minima on the surface is indicated by a red sphere, and the corresponding ESP value is marked with a number. DFT calculated the surfaces of bare Zn and Zn@SCRIS-SALs with fully protonated (-NH3+) and unprotonated (-NH2) end groups, (e) Zn2+ and (f) H+· Binding energy between H2O.
Figure 6: Electrochemical performance of SCRIS-SALs whole cells. (a) CV curves of Zn-I2 coin cell cells based on bare Zn and Zn@SCRIS-SALs anodes. (b) Rate performance of Zn-I2 coin cell cells based on bare Zn and Zn@SCRIS-SALs anodes at current densities (0.5, 1, 2, 4, and 8 A g-1). (c) Corresponding voltage distribution of Zn@SCRIS-SALs coin cell batteries under different currents. （d）Zn@SCRIS-SALs||AC-I2 and bare Zn||Cycling performance of AC-I2 batteries. (e) Schematic diagram of Zn@SCRIS-SALs-based Zn-I2 pouch cells. （f）Zn@SCRIS-SALs||Cycling performance of AC-I2 cells in pouch cells with an area capacity of 5 mAh cm-2, with illustrations of photographs and voltage distribution plots of Zn@SCRIS-SALs pouch cells at 1st, 1000th, 2000th, 2500th cycles.
【Conclusion】
In conclusion, we design efficient surface charge enhancement and ion-selective self-assembly layers (SCRIS-SALs) through a simple and versatile in-situ self-assembly strategy. These molecular layers with a pH-mediated state of partial protonation can confer reversibility to zinc metal anodes. Taking advantage of partial protonation, the repulsion effect and zinc-philic effect are expanded, the chemistry of the Zn interface and the deposition behavior of Zn are improved, and the cycle life is greatly extended. This is due to the significant inhibition of hydrogen evolution reactions, by-products and dendrite formation, i.e., synergistically improving the stability of interfacial thermodynamics and kinetics during galvanizing/stripping. In addition, it has been demonstrated that self-assembled surface charge enhancement layers and ion-selective layers are versatile at acidic pH, regardless of the class of zinc salt electrolytes (ZnSO4 and Zn(OTF)2). This work will provide new insights into the fine tuning of the electronic state of the interfacial layer in long-lived aqueous zinc-ion batteries.
Zhiquan Wei, Shixun Wang, Dedi Li, Shuo Yang, Songde Guo, Guangmeng Qu, Yihan Yang, Hongfei Li*, Surface Charge-Reinforced and Ion-Selective Layers for Stable Metal Zinc Anodes Chemistry, Energy Environ. Sci., 2024.
https://doi.org/10.1039/D4EE01260G
Source: Energy Scholar
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