有机高电压醌氰类锂离子电池正极材料的研究

In Lithium Ion Batteries (LIBs), typical cathode materials are inorganic compounds composed of transition metals such as manganese, cobalt, and nickel. These metals are expensive and resource limited, therefore it is detrimental to the large-scale applications of LIBs. Organic cathode materials are promising alternatives because of their abundant resources and diverse structures. However, the low redox potentials of most organic cathode materials lead to limited energy and power density for organic LIBs. In addition, organic cathode materials are easy to dissolve into electrolyte, which result in poor cycling performance. Due to these two problems, the practical application of organic batteries has been significantly restrained. In this project, we focus on the development of high-potential organic cathode materials based on tetracyanoquinodimethane (TCNQ) and their analogues. We aim to develop a series of high-potential organic cathode materials by designing and selecting materials out of several electron-withdrawing substituted TCNQs, and investigate the correlation between their molecular structures and corresponding electrochemical performance. In-situ characterizations will be employed to clarify their redox reaction mechanisms. To suppress the solution problem, oxide/polymer composite solid electrolytes will be employed, meanwhile, the electrochemical performance will be optimized so as to fabricate high-potential, long cycle-life organic tetracyanoquino LIBs. This project is expected to provide theoretical insights and scientific basis for the development of high-potential organic cathode materials, thus promote the practical applications of organic batteries.

锂离子电池正极材料主要为基于Co/Mn/Ni等过渡金属元素的无机化合物，资源有限、价格昂贵，不利于其大规模应用。有机正极材料具有来源丰富、结构多样的特点，是无机正极材料的良好替代。然而，有机正极材料的氧化还原电位普遍较低，导致有机电池的能量密度和功率密度具有一定的局限性；另外，有机正极材料在电解液中易溶解流失导致电池循环性能较差。这两大问题限制了有机电池的应用。本项目拟以电压相对较高的醌氰类化合物为研究对象，通过设计筛选不同吸电子基团取代的醌氰化合物以发展一系列有机高电压正极材料，并揭示该类材料结构和电化学性能间的关系；通过原位表征技术阐明醌氰类正极材料的氧化还原反应机理；为抑制材料的溶解流失，拟使用氧化物/聚合物复合固态电解质组装电池，优化电池性能，构建高电压、长循环有机醌氰锂离子电池。本项目的实施将为有机高电压正极材料的发展提供理论指导和科学依据，推进有机电池的应用。

锂离子电池正极材料主要为基于Co/Mn/Ni等过渡金属元素的无机化合物，资源有限、价格昂贵，不利于其大规模应用。有机正极材料具有来源丰富、结构多样的特点，是无机正极材料的良好替代。然而，有机正极材料的氧化还原电位普遍较低，导致有机电池的能量密度和功率密度具有一定的局限性；另外，有机正极材料在电解液中易溶解流失导致电池循环性能较差。这两大问题限制了有机电池的应用。本项目考察了醌氰类化合物TCNQ、FTCNQ、F4TCNQ、TCAQ在锂离子电池中的电化学性能，通过对比使用商用电解液、离子液体、高浓度电解液，分析了取代基对醌氰化合物氧化还原电压和循环稳定性的影响；为降低材料在电解液中的溶解性，使用PEO-LLZTO复合电解质组装有机半固态电池，为彻底解决有机电极材料的溶解问题，使用卤化物全固态电解质组装了全固态有机锂电池；使用原位/非原位表征方法研究醌氰类化合物的反应机理。实验结果表明，随着F取代基数量的增加，TCNQ类化合物的氧化还原电压升高，比容量降低；PEO-LLZTO复合电解质中PEO的分子量对有机固态电池的性能有显著影响，Mw=400,0000的PEO基复合电解质能实现F4TCNQ/Li电池稳定循环100圈后容量保持率在80%以上，比容量80 mAh g-1；我们使用全固态卤化物电解质Li3InCl6组装了全固态TCNQ/Li电池，电池在0.1C电流密度下比容量为250 mAh g-1，循环23圈后容量保持率为60%。有机全固态卤化物电池的稳定性稍差可能是由于有机固体颗粒与电解质粉末间的接触存在较大的界面阻抗，有关全固态有机锂电池性能提升的方法和科学依据仍需要进一步的研究。本项目的实施为有机高电压正极材料的发展提供了理论指导和科学依据，推进了有机电池的应用。