Zwitterionic polymer-based electrolyte engineering for alkali metal ion batteries

锂离子电池在现代社会中无处不在，为从可穿戴/手持设备到电动汽车的各种设备供电。然而，确保未来可靠且具有成本效益的电化学储能将取决于使用各种电池化学物质，包括那些利用更丰富的碱金属离子（如钠）的电池化学物质。对于每一种正在开发的电池来说，最大化某些目标离子的运动和确保高度的用户安全是两个至关重要的目标。在这个项目中，研究人员将研究一类具有两性离子侧基的高度稳定聚合物促进钠离子和锂离子选择性运输的能力。两性离子是一类既带正电荷又带负电荷的分子。适量的不易燃的室温熔盐（离子液体）将在这些电解质中共同配制，以增强整体离子运动，同时保持安全操作。这项研究将对两性离子化学、离子液体含量和碱金属阳离子同一性在确定未来电池电解质理想化学成分中的作用产生重要的新见解。通过为代表性不足的学生提供指导的本科生和研究生研究经验，并参与K-12外展活动，该项目还将通过为不同经验水平的不同学生群体提供变革性的教育和培训经验，从而造福社会。该项目的主要目的是研究分子间相互作用和选择性碱金属阳离子（锂，钠）在两性离子聚合物/盐电解质中的转运，这些电解质含有大约5- 80wt .%的离子液体（IL）质量分数。这是一个存在于传统聚合物电解质和富含il的离子凝胶之间的未被开发的成分空间。研究目标将通过寻求多种合成策略来制备这种电解质，利用几种多核核磁共振和FTIR/拉曼光谱技术探测各种带电物质之间的相互作用，通过交流阻抗谱和直流极化测试测量总离子电导率和碱金属阳离子转移值，并对对称碱金属电极电池中反复带板循环的电化学稳定性进行了研究。假设沿聚合物上悬垂的两性离子官能团可能会产生碱金属阳离子运输的高迁移率途径，这为研究降低这种新型电解质中IL含量的影响提供了动力。该项目将是第一个使用不同的两性离子聚合物化学直接比较钠离子和锂离子传输的项目，这将为未来设计用于“超锂离子”电池的聚合物电解质提供有用的信息。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Lithium-ion batteries are ubiquitous in modern society, powering everything from wearable/handheld devices to electric vehicles. Securing the future of reliable and cost-effective electrochemical energy storage, however, will depend on using a variety of battery chemistries, including those that utilize more abundant alkali metal ions such as sodium. For every battery that is developed, maximizing the motion of certain target ions and ensuring a high degree of user safety are two critically important goals. In this project, the investigators will examine the ability of a class of highly stable polymers featuring zwitterionic side groups to promote increased selective transport of sodium and lithium cations. Zwitterions are a class of molecules which contain both a positive and a negative charge. Moderate amounts of a nonflammable, room temperature molten salt (an ionic liquid) will be co-formulated in these electrolytes to enhance overall ionic motion while maintaining safe operation. This study will produce important new insights into the roles of zwitterion chemistry, ionic liquid content, and alkali metal cation identity in determining ideal chemical compositions for future battery electrolytes. Through mentored undergraduate and graduate research experiences for underrepresented students and participation in K-12 outreach activities, this project will also benefit society by enabling transformative educational and training experiences for a diverse group of students at multiple experience levels.The main objective of this project is to examine the intermolecular interactions and selective alkali metal cation (lithium, sodium) transport within zwitterionic polymer/salt electrolytes that contain ionic liquid (IL) mass fractions of approximately 5-80 wt.%. This is an underexplored compositional space that exists between conventional polymer electrolytes and IL-rich ionogels. The research objectives will be accomplished by pursuing multiple synthetic strategies to prepare such electrolytes, probing interactions between the various charged species using several multinuclear NMR and FTIR/Raman spectroscopy techniques, measuring total ionic conductivities and alkali metal cation transference number values via AC impedance spectroscopy and DC polarization tests, and interrogating electrochemical stability upon repeated strip-plate cycling in symmetric alkali metal electrode cells. It is hypothesized that high-mobility pathways for alkali metal cation transport may be created along the pendant zwitterionic functional groups on the polymer, which provides a motivation for examining the effects of reducing the IL content among this novel class of electrolytes. This project will be among the first to directly compare sodium versus lithium cation transport using different zwitterionic polymer chemistries, which will provide useful information for the future design of polymer-based electrolytes for “beyond-Li ion” batteries.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.