【作者】 陈志辉；

【导师】 惠静姝； 邵元龙；

【作者基本信息】 苏州大学 ， 新能源科学与工程， 2024， 硕士

【摘要】 近年来,能源需求推动着新能源储能体系的发展,电化学储能器件由于其广泛的适用性而得到人们的关注。在众多电化学储能器件中,目前主要使用的是有机系的锂离子电池,但是有机电解液存在的有毒、易燃等缺点,阻碍了锂离子电池进一步拓展应用场景。相较而言,水系电化学储能体系具备高安全性、绿色环保等特性,成为符合人们期待的新一代储能体系。在水系电化学储能体系中,水系锌离子电池有以下优点:锌（Zinc,Zn）金属负极具有较低的氧化还原电位（-0.76 V vs.标准氢电极（Standard Hydrogen Electrode,SHE））和较高的理论容量(820 m Ah g^-1和5854 m Ah cm^-3)。水系电解液的本征离子电导率较高,能够实现更高的功率密度。由于水系锌离子电池常采用水系锌盐作为电解质,因而该类电池具有高安全性,能够避免发生燃烧爆炸等安全问题。此外,水系锌离子电池还兼具高自然丰度（大约比锂金属资源丰度高300倍）和环境友好性等优势。总的来说,水系锌离子电池具有作为大规模、商业化储能体系的应用潜力。然而,锌离子电池负极面临着显著的枝晶生长、腐蚀以及析氢等界面问题,显著影响了锌离子储能体系的稳定性。因此,合理对电极结构和电解质组分进行设计和改进是提升水系锌离子电池储能特性的关键。基于锌离子电池目前面临的问题,本文将从以下两个方面来进行优化:（1）设计合适的锌负极结构,通过构建高导电的三维定向孔道集流体,改善锌负极电子和离子传输性能,实现孔道内的均匀锌沉积;（2）优选合适的电解质添加剂来控制循环过程中pH的改变,从根本上抑制界面副反应的发生。本文的具体研究内容如下:（1）基于MXene/PVA气凝胶集流体构建无枝晶锌负极。基于MXene纳米片与聚乙烯醇（Polyvinyl alcohol,PVA）间的强氢键作用构建了复合水凝胶,并通过定向冷冻冰模板法和冷冻干燥得到了定向孔道的三维集流体（MPA）。高导电的三维定向孔道结构能够有效实现电子的快速传输,定向孔道也能引导Zn²⁺的传输,实现均匀的电场和离子场分布。因此,在MPA上可以观察到平整的Zn沉积,Zn||MPA非对称电池在循环880圈中能实现99.71%的高库伦效率（Coulombic Efficiency,CE）。此外,通过扫描电化学显微镜等表征技术检测到了在锌沉积过程中MPA电极表面原位生成的Zn F₂固体电解质层,其可作为保护层抑制副反应的发生。通过在MPA上预沉积Zn得到Zn@MPA复合锌负极,由其组装的对称电池在10 m A cm^-2的高电流密度和1m Ah cm^-2的容量下可以稳定循环320 h。最后组装的全电池在高电流密度下呈现良好的循环稳定性,在5 A g^-1的高电流密度下循环800圈仍能具有93.86%的容量保持率,表现出良好的电化学性能。（2）采用甘氨酸作为pH缓冲功能添加剂实现高可逆的锌负极循环。采用甘氨酸（Glycine,Gly）作为电解质添加剂,基于Gly本征的pH缓冲特性,用于缓解锌负极在电化学反应过程中由于析氢反应造成的局部pH升高。并且Gly具备良好的亲锌性,能够吸附在锌负极表面作为保护层防止其受到腐蚀。通过对比不同电解质体系的电化学性能,表明Gly可以作为具备pH缓冲功能的添加剂来稳定电极-电解质界面,从而有效抑制副反应和锌枝晶生长,提高锌离子电池的循环稳定性。在Zn||Cu非对称电池中,在循环900次循环中的平均库伦效率达到99.47%。Zn||Zn对称电池在2m A cm^-2的电流密度和1 m Ah cm^-2的容量下能稳定循环1000 h。最后,使用Gly添加剂的电解液中全电池在循环2000圈后依然能保持109.97 m Ah g^-1的容量。这些优异的性能表现得益于Gly添加剂对电极-电解质界面稳定性的促进作用。更多还原

【Abstract】 In recent years,the global energy demand has driven the development of advanced energy storage systems.The electrochemical energy storage devices have attracted numerous attentions due to their wide range of applications.Among many types of devices,organic lithium-ion batteries are definitely the leading technology.However,due to the flammability and explosiveness for organic electrolytes,safety remains a critical concern of lithium-ion battery systems.As a comparison,water-based electrochemical energy storage systems have inherent characteristics of high safety and environmentally friendliness,making them important candidates for advanced energy storage devices.As one of the most promising aqueous electrochemical energy storage systems,zinc-ion batteries offer several advantages.They utilize zinc（Zn）metal as the anode,which provides the benefits of a low redox potential in aqueous electrolyte,and a high theoretical capacity.Based on the fast ion diffusion coefficient,aqueous zinc ions can exhibit high power density.The use of an aqueous zinc salt as electrolyte,can effectively prevent explosion caused by short circuit.The high natural abundance of zinc and its environmental friendliness make zinc relatively inexpensive to purchase and process.In summary,aqueous zinc-ion batteries are an attractive large-scale energy storage system.However,the metallic anode still faces significant dendrite growth,corrosion,and hydrogen evolution reactions,which will significantly affect the stability of the zinc-ion energy storage system.Therefore,the rational design of electrodes and electrolytes is one of the key factors to improving the electrochemical performance of aqueous zinc-ion batteries.Based on the current limitations of zinc-ion batteries,this thesis will focus on modifying and optimizing zinc-ion batteries from following two aspects:（1）Optimization the zinc anode structure to improve electron and ion transportation by constructing a highly conductive three-dimensional current collector with directional pores to achieve uniform zinc deposition.（2）Optimization the electrolyte composition to inhibit side reactions by stabilizing the pH of the electrolyte system.The specific research details of this paper are explained as follows:（1）Construction of dendrite-free zinc anode based on MXene/PVA aerogel current collector.Based on the strong hydrogen bonding between MXene nanosheets and polyvinyl alcohol（PVA）,composite hydrogels were constructed.Three-dimensional current collectors（MPA）with directional pores were obtained using a templated freeze-drying method.This highly conductive 3D directional channel structure can effectively facilitate the rapid transportation of electrons and guide the fast diffusion of Zn²⁺.Thus,a flat and homogeneous Zn deposition can be achieved on the MPA.The Zn||MPA asymmetric cells exhibited a high coulombic efficiency of 99.71%over 880 cycles.In addition,the Zn F₂ solid electrolyte layer was observed to form on the MPA surface during the zinc deposition process,which was evidenced by scanning electrochemical microscopy.This interphase layer can serve as a protective barrier to prevent the occurrence of side reactions.By pre-depositing Zn on the MPA,the Zn@MPA composite zinc anode was obtained.The assembled symmetrical cell can be stably cycled for 320 h.The assembled full cell exhibited good cycling stability at high current density and maintained good capacity retention at 93.86%after 800 cycles(at a high current density of 5 A g^-1).These results demonstrate excellent electrochemical performance achieved through a specially designed anode structure.（2）Glycine is used as a pH buffer functional additive to achieve highly reversible zinc anode cycling.Glycine（Gly）was used as an electrolyte additive in this study.Based on the intrinsic pH buffer capability of Gly,it was used to alleviate the pH increase caused by the inevitable hydrogen evolution reaction during the cycling of the zinc anode.In addition,Gly has excellent zincophilic properties,which allow it to preferentially adsorb to the surface of the zinc anode,protecting itfrom corrosion.By comparing the properties of different electrolyte systems,it was shown that Gly can be used as a functional additive to buffer electrolyte pH and stabilize the electrode/electrolyte interphase.Therefore,the use of Gly additives can effectively inhibit side reactions and zinc dendrite growth,and enhance the cycling stability of zinc-ion batteries.In the Zn||Cu asymmetric cells,the average coulombic efficiency reached 99.47%after 900 cycles.Finally,the full-cell battery in the electrolyte with Gly additive maintained a capacity of 109.97 m Ah g^-1 after 2000 cycles.更多还原