Zwitterionic polymer-based electrolyte engineering for alkali metal ion batteries

锂离子电池在现代社会无处不在，为从可穿戴/手持设备到电动汽车的一切设备提供动力。然而，确保可靠和经济高效的电化学能量存储的未来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的电池，如钠。对于每一种开发的电池来说，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，研究人员将检验一类具有两性离子侧基的高度稳定的聚合物促进钠和锂离子选择性传输的能力。两性离子是一类既含有正电荷又含有负电荷的分子。适量的不可燃、室温熔盐(一种离子液体)将在这些电解液中共同配制，以增强整体离子运动，同时保持安全运行。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特性在确定未来电池电解液的理想化学成分中的作用产生重要的新见解。通过为未被充分代表的学生提供指导的本科生和研究生研究经验以及参与K-12外展活动，该项目还将通过使不同的学生群体在多个经验水平上获得变革性的教育和培训体验而受益于社会。该项目的主要目标是研究含有大约5-80wt.%的离子液体(IL)质量分数的两性离子聚合物/盐电解质中的分子间相互作用和选择性的碱金属阳离子(锂、钠)迁移。这是一个未被开发的组成空间，存在于传统的聚合物电解质和富含IL的离子凝胶之间。研究目标将通过寻求制备此类电解液的多种合成策略来实现，使用几种多核核磁共振和FTIR/拉曼光谱技术来探测不同带电物种之间的相互作用，通过交流阻抗谱和直流极化测试来测量总离子电导率和碱金属阳离子迁移数值，以及在对称碱金属电极电池中反复进行带板循环时的电化学稳定性。假设碱金属离子迁移的高迁移率途径可能是沿着聚合物的侧链上的两性离子官能团建立的，这为考察降低这类新型电解液中IL含量的效果提供了动力。该项目将是第一个使用不同的两性离子聚合物化学物质直接比较钠和锂离子传输的项目之一，这将为未来设计用于“超越锂离子”电池的基于聚合物的电解液提供有用的信息。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.