第一作者：王佳

通讯作者：陈政，李桂村，崔光磊

单位：中国科学院青岛生物能源与过程研究所；青岛科技大学

近年来，水系锌金属电池由于其低成本、高安全性和环境友好等优点在储能领域显示了广阔的应用前景。然而，常规水系电解质中锌沉积的动力学较快，沉积的金属锌通常呈现疏松、不均匀的特点，在深度放电时疏松的金属锌易从根部脱落，变成“死锌”，最终造成金属锌负极的实际利用率较低。因此，通过调控锌离子的沉积动力学行为来实现致密且平整的锌沉积对于实现二次锌金属电池的实际应用具有重要意义。

基于此，中科院崔光磊研究员&青岛科大李桂村教授团队，在国际知名期刊Energy Storage Materials上发表题为“Eutectic electrolytes with leveling effects achieving high depth-of-discharge of rechargeable zinc batteries”的研究论文。

该研究借鉴锌电镀行业中添加表面活性剂来增加锌沉积的过电位并促进致密均匀锌沉积这一现象，选择阴离子型表面活性剂十二烷基苯磺酸锌（Zn(DBS)₂）作为锌盐代替ZnSO₄、Zn(OTf)₂、Zn(TFSI)₂等传统锌盐，通过引入乙酰胺与Zn(DBS)₂形成共晶电解质来促进其溶解，并加入少量水来降低黏度和提升离子电导率，设计了一种具有阴离子型表面活性剂特征的水合共晶电解质。

与Zn²⁺之间高结合能的DBS^–阴离子进入Zn²⁺的第一溶剂化壳层，减缓了Zn²⁺的电化学还原动力学，实现了均匀、致密且光亮的锌沉积。锌负极在50%的高放电深度下具有约600 mAh cm^–2的累积容量。此外，该电解质在锌负极限量（N/P=2）的苛刻条件下运行Zn//Na₃V₂(PO₄)₃全电池，循环后100次容量保持率为79.7%。

Schematic Zn²⁺ deposition in a conventional electrolyte and an electrolyte with levelling effect.

Zn(DBS)₂在水中表现出极低的溶解度（＜0.01 M），而具有氢键供体（-NH₂）和路易斯碱性（-C=O）的乙酰胺（Ace）是与该锌盐形成共晶电解质的理想候选者。Zn(DBS)₂/Ace低共熔体在不同摩尔比例下的DSC和红外光谱测试数据证实了Ace与Zn(DBS)₂之间氢键作用和路易斯酸碱作用，促进了该共晶电解质的形成。

在此基础上引入的少量水分子有效降低了共晶电解质的粘度，增加了离子电导率。对比同样组成的Zn(TFSI)₂电解质，Zn(DBS)₂电解质中的Zn//Zn电池在长时间静置后具有更低的电荷转移阻抗，且在Zn// Na₃V₂(PO₄)₃电池中表现出更稳定的浮充电流。

Figure 1. Preparation and characterization of the eutectic electrolyte. (a) Optical images of dissolution phenomenon of Zn(DBS)₂ in H₂O (left) and a mixture of H₂O and Ace (right). (b) DSC curves of eutectic electrolytes with different Zn(DBS)₂/Ace molar ratios. Ace alone is also included as a comparison. (c) FTIR results of eutectic electrolytes with different Zn(DBS)₂/Ace molar ratios. (d) Variation of viscosity and conductivity for the 0.5 M Zn(DBS)₂/H₂O-Ace with different Zn(DBS)₂/Ace molar ratios at room temperature. (e) Evolution of interfacial charge transfer resistance in the assembled Zn//Zn cells using Zn(DBS)₂ electrolyte and Zn(TFSI)₂ electrolyte respectively. (f) Time dependence of the floating currents of fully charged Zn//Na₃V₂(PO₄)₃ cells hold at a constant voltage of 1.7 V using different electrolytes.

要点二：共晶电解质的电化学性能

使用Zn(DBS)₂电解质的Zn//Cu电池在低放电深度（0.5%~1% DODZn）下的平均库伦效率达到99.1%，Zn//Zn电池稳定循环接近2000h。为了在接近实际应用的条件下评估锌负极的可逆性，Zn//Cu电池在50% DODZn 的苛刻条件下进行测试。在5 mAh cm^–2的高面容量下，使用Zn(DBS)₂电解质的Zn//Cu电池实现约600 mAh cm^–2的累积容量，比Zn(TFSI)₂的电解质高出23倍。N/P=2的严苛条件下Zn//Na₃V₂(PO₄)₃全电池在100次循环后容量保持率为79.7%。

Figure 2. Electrochemical reversibility and stability of Zn anodes in different electrolytes. (a) Coulombic efficiency (CE) of Zn plating/stripping on Cu foil at a current density of 0.5 mA cm⁻² (1 mAh cm⁻² for each half cycle, corresponding to 1% DODZn). (b) Galvanostatic cycling of symmetrical Zn//Zn cells at a current density of 0.5 mA cm⁻² (0.5 mAh cm⁻² for each half cycle, corresponding to 0.5% DODZn). The cycling performances of Zn//Cu cells at a current density of 1 mA cm⁻² and 50% DODZn with different areal capacities of (c) 1 mAh cm⁻², (d) 2.5 mAh cm⁻² and (e) 5mAh cm⁻². (f) Relationship between areal capacity, cumulative galvanic capacity, and cycle life. (g) The cycling performance and corresponding CE of Zn//NVP cells with the N/P ratio of 2 at a current density of 0.3 mA cm⁻².

要点三：锌沉积层的形态和结构特征

利用多尺度的显微观察技术，对不同电解质中锌沉积的形貌进行了表征。Zn(TFSI)₂电解质中的锌沉积层显示出不均匀的黑色颗粒外观，对应的SEM图像中可以看到疏松多孔的结构，反观Zn(DBS)₂电解质中光亮的锌沉积层，层状的六边形板块致密堆叠。这种平整无孔隙的结构阻挡了电解液与底部沉积的金属锌的直接接触，抑制了“死锌”的生成，保证了在高放电深度下锌沉积/剥离的高度可逆性。

Figure 3. Morphology and crystallography characterizations of Zn electrodeposits from different electrolytes. Typical SEM images of Zn deposits on Cu substrate with (a) Zn(TFSI)₂ electrolyte and (b) Zn(DBS)₂ electrolyte, respectively. The Zn deposits were obtained by plating at a current density of 0.5 mA cm² with areal capacity of 4 mAh cm². The insets display the optical photos of Zn deposits on Cu foil. (c) X-ray diffraction (XRD) patterns of Zn deposits obtained in different electrolytes. Cross-sectional SEM images and EDS-mapping of Zn deposits obtained in (d) Zn(TFSI)₂ electrolyte and (e) Zn(DBS)₂ electrolyte, respectively. Confocal laser scanning microscopy (CLSM) images and root mean square (RMS) roughness of Zn deposits obtained in (f) Zn(TFSI)₂ electrolyte and (g) Zn(DBS)₂ electrolyte. Atomic force microscopy (AFM) to obtain topographic surface images and roughness (Sq) of Zn deposits in (h) Zn(TFSI)₂ electrolyte and (i) Zn(DBS)₂ electrolyte.

要点四：Zn²⁺电化学还原的动力学和成核过电位

在Zn(DBS)₂电解质中，锌电化学沉积的交换电流密度大幅降低，减轻了电极表面锌离子的浓度梯度，有利于平整、致密的锌沉积。较小的交换电流密度代表了电极表面较慢的反应动力学，伴随着锌沉积过电位的增加。此外，Zn(DBS)₂电解质中锌沉积的成核过电位也增加，这有利于尺寸较小的晶核分布，原理与电镀领域中涉及的光亮剂相似。计时安培法证实Zn(DBS)₂电解质中锌沉积可以更加快速的完成成核并进行稳定的生长。

Figure 5. Kinetics of Zn electrodeposition in different electrolytes. (a) The exchange current density (j0) for Zn plating/stripping based on Tafel analysis, which is performed using Zn plate as the working and counter electrode, Ag/AgCl as the reference electrode at a scan rate of 0.2 mV s⁻¹. Tafel plots were obtained by plotting the overpotential of Zn plating/stripping to the natural log of the current density in the CV curve. j0 was calculated by the slope that extracted from the linear fitting of the overpotential to the applied current. (b) Voltage profiles of Zn plating and stripping processes in 3rd cycle in different electrolytes at a current density of 0.5 mA cm⁻² and areal capacity of 1 mAh cm⁻². The cut-off voltage is set as 0.5 V. (c) Voltage profile of Zn plating on a Cu foil in the first cycle at a current density of 0.5 mA cm⁻². (d) Chronoamperograms of Zn plating at an overpotential of −200 mV with Zn foil as the working and the counter electrode, Ag/AgCl as the reference electrode.

要点五：溶剂化结构分析

基于分子动力学模拟的结果，Zn(DBS)₂电解质中的第一溶剂化壳层为[Zn(H₂O)₄(Ace)(DBS^–)]⁺，而Zn(TFSI)₂电解质中为[Zn(H₂O)₅(Ace)]²⁺。此外，通过DFT计算比较了两种电解质中锌离子与第一溶剂化壳层中阴离子、溶剂分子的结合能，[Zn(H₂O)₄(Ace)(DBS^–)]⁺中Zn²⁺具有最高的结合能。由于DBS^–参与Zn²⁺的第一溶剂化壳层，增加了Zn²⁺的去溶剂化能，因此锌沉积的过电位增加，相应的交换电流密度降低。Zn²⁺沉积的动力学降低了反应界面和体相电解质之间的活性锌物种的浓度梯度，最终导致了致密和均匀的锌沉积。

Figure 6. Theoretical simulations of solvation structures of different electrolytes. Radial distribution functions (RDFs) and coordination number (CN) for (a) Zn²⁺-O(H₂O), (b) Zn²⁺-O(Ace) and (c) Zn²⁺-O(DBS⁻/TFSI⁻) from molecular dynamics (MD) simulations of Zn(DBS)₂ electrolyte and Zn(TFSI)₂ electrolyte. The vertical dashed line is the cutoff radius in calculating CN. (d) Total binding energies of the most probable solvated Zn complexes in Zn(DBS)₂ electrolyte and Zn(TFSI)₂ electrolytes obtained from DFT calculations.

Eutectic electrolytes with leveling effects achieving high depth-of-discharge of rechargeable zinc batteries

陈政副研究员简介： 陈政，中国科学院青岛能源所副研究员。2017年于中科院大连化物所获得物理化学博士学位，随后加入中国科学院青岛能源所固态能源系统技术中心。主要研究方向为发展适用于规模储能的低成本、高安全特征的水系电池和双离子电池，相关研究工作发表在Angew. Chem. Int. Ed.、ACS Energy Lett.、ChemSusChem、Energy Storage Materials等期刊。

2005年于中国科学院化学所获得有机化学博士学位。2005年9月至2009年先后在德国马普协会高分子所和固态所从事博士后研究。2009年至今，任职于中国科学院青岛生物能源与过程研究所。在能源材料、化学、器件等方面的国际权威杂志Nat. Commun.、J. Am. Chem. Soc.、Joule、Angew. Chem. Int. Ed.、Adv. Mater.、Environ. Energy Sci.等发表文章260多篇，他引超20000次。

王佳：青岛科技大学材料工程专业硕士研究生