锌离子电池作为一种新型电化学储能体系，因具有安全环保、成本低廉等优势有望在大规模储能领域得到应用。然而，目前锌离子电池的发展面临着两个突出问题：一是常规报道的锌离子电池正极材料通常面临较快的容量衰减或者剧毒性；二是锌金属负极在循环过程中容易产生危险的锌枝晶，严重危害电池的循环寿命。针对上述问题，主要有两个方面的解决思路：一方面，通过对传统电极材料（例如MnO2）改性优化，进一步提升其电化学性能；另一方面，积极探索新型材料（例如MOFs）在锌离子电池中的运用，开发出适用于锌离子电池的高性能电极材料，拓宽锌离子电池研究体系。这两个方面的研究工作对于构筑高性能锌离子电池至关重要。 本论文针对传统MnO2正极材料面临的循环性能差的问题，创新性的提出了对苯二甲酸（H2BDC）电极安全添加剂。通过实验发现10 wt%质量分数的H2BDC添加到γ-MnO2正极后，γ-MnO2正极材料循环100周后的容量保持率由31.6%提升到了78%，展现出更加优异的循环稳定性。进一步通过对添加剂作用机制的探究，发现H2BDC添加剂能有效抑制电化学反应体系中pH的剧烈升高，显著抑制放电过程中碱式硫酸锌杂质的形成，优化电池的电化学性能。 本论文还对MOFs材料在锌离子电池中的运用进行了探究。合成了五种不同MOFs材料，并将其作为锌离子电池正极进行了电化学性能表征，发现Mn(BTC)材料展现出最优的Zn2+存储能力，首周循环能实现112 mAh g-1的放电比容量。同时对Mn(BTC)的储锌机理进行了深入研究，发现Mn(BTC)正极在充电过程中存在向MnO2和Zn(BTC)材料的转化机制。此外，ZIF-8 MOFs材料被用来构筑高性能锌负极，通过在锌箔表面均匀涂覆一层ZIF-8材料制备了ZIF-8@Zn负极，ZIF-8涂层的独特多孔结构可以引导锌离子在锌负极表面进行均匀的沉积和溶解。结果显示ZIF-8@Zn负极表现出优异的电化学稳定性，其循环寿命是纯锌箔的8倍。最后，基于Mn(BTC)正极和ZIF-8@Zn负极构建了高性能的锌离子电池体系，通过对电解液的调控优化，全电池表现出稳定的循环性能，在循环900周后容量没有明显衰减。该研究为设计高性能储能系统提供了新的思路。
As a new electrochemical energy storage system, zinc-ion battery (ZIB) is highly promising for large-scale energy storage applications due to their high safety, environmental friendliness and low cost. However, the current development of zinc-ion batteries is impeded by two problems: commonly reported cathode materials usually suffer from rapid capacity fading or high toxicity，and the formation of zinc dendrites on Zn anode seriously shortens the cycling life of ZIBs. To solve these problems, two measures should be carried out: firstly, material modification is an effective method to optimize the electrochemical performance of currently reported cathode materials such as MnO2. Besides, exploring new materials such as metal-organic frameworks materials (MOFs) may open opportunities for addressing these problems. Above measures are critical to realize high-performance ZIBs.To improve the cycling stability of MnO2 cathode, terephthalic acid (H2BDC) was proposed as positive safety additives in ZIBs. When H2BDC additives with mass ratio of 10% were added into γ-MnO2 positive material, the capacity retention rate of γ-MnO2 cathode after 100 cycles increased from 31.6% to 78%, showing an excellent cycle stability. Further mechanism investigation revealed that the H2BDC additive effectively suppress the sharp increase of pH in the electrolyte and significantly inhibit the formation of basic zinc sulfate impurities during the discharge process, so the electrochemical performance of ZIBs is effectively optimized. Besides, MOFs electrodes were also explored in this study. Five MOFs materials were synthesized and used as cathodes in zinc-ion battery, electrochemical characterizations show that Mn(BTC) MOFs cathode exhibited the best Zn2+-storage capacity of 112 mAh g-1. Furthermore, the energy storage mechanism of Mn(BTC) cathode was carefully studied and a special conversion mechanism from Mn(BTC) cathode to MnO2 and Zn(BTC) MOFs materials during charging process was discovered. Besides, ZIF-8 MOFs materials were used to construct high-performance Zn anodes. A ZIF-8 modified Zn (ZIF-8@Zn) anode was prepared by uniformly coating ZIF-8 MOFs materials on the surface of Zn foil. Unique porous structure of the ZIF-8 coating guided uniform Zn stripping/plating on Zn anodes, the ZIF-8@Zn anodes exhibited stable Zn stripping/plating behaviors, with 8 times longer cycle life than bare Zn foils. Based on the above, a high-performance zinc-ion battery system was constructed using the Mn(BTC) cathode and ZIF-8@Zn anode. Benefiting from the optimization of electrolyte, the full battery displayed an excellent long-cycling stability without obvious capacity fading after 900 charge/discharge cycles. This work opens up a new door for designing high-performance energy storage systems.
