Impact of Ion Transport and Dissociation on Polymer Electrolyte Battery Rate Capability

对于先进的电动和混合动力运输应用，需要固体聚合物电解质来实现电池容量的变革性增加。然而，目前的聚合物电解质存在离子传输速率低的问题，最常见的特征是导电性。这个基础工程科学项目将评估这样一个假设，即电导率本身不是衡量电池充放电能力的良好指标，而同样关键的组成部分是聚合物电解液中的离子传输。这样的理解将使电动汽车电池的下一代固体电解液的智能设计成为可能。新型聚合物电解质的研究将采用通常不适用于电解液的实验技术。这些技术提供了实时的离子浓度和离子形态的直接测量，这两者对于准确和完整地表征电池中的聚合物电解液性能都很重要。该项目的研究人员分别结合了工程和化学方面的互补专业知识，将通过尖端的时间分辨测量和新的合成聚电解质来进一步了解离子传输和电池性能，这些合成聚电解质是为探测这些系统中的结构-性质关系而量身定做的。对于教育和外展活动，该项目包括与这项研究相关的动手电池活动，这些活动将在经济困难的中学进行。参与这项研究的学生将接受培训，掌握合成开发新的精密聚电解质系统和锂电池商业开发所需的技能。这项研究的目标是全面了解聚合物电解液的传输情况，以及它与电池性能的关系。具体目标是(1)使用几种互补技术来全面描述一组聚合物电解液中的传输，(2)研究离子形态和电解液结构对传输行为的作用，以及(3)确定聚合物电解液电池的极限电流，并与基于对传输的完全理解的速率预测进行比较。使用表面增强拉曼光谱来评估离解状态，使用X射线散射来检查离子结构的连通性，将实现对输运基础的物理洞察。本工作将在目前标准的聚合物电解液--含锂双三氟甲基磺酰亚胺(LiTFSI)盐的聚环氧乙烷(PEO)上进行。纳米结构的影响将用一种机械强度很强的含PEO的嵌段共聚物和LiTFSI来检验。我们将使用与PEO混合的精密聚电解质来研究阴离子连接性对离解状态的影响，以及它与阳离子结构的可公度性。最后，对聚合物电解液电池的极限电流进行了连续水平的测量和预测。该项目包含了对锂电池聚合物电解液传输的彻底评估，这可能会改变理解是什么限制了这些电池的放电率的范式。将利用前沿技术和新材料的组合来获得关于运输的物理基础的知识。一个经过验证的聚合物电解液电池模型将被开发并公开上市。它将帮助电池社区确定下一代固体电解液的目标传输特性。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。

Solid, polymer electrolytes are needed to enable transformative increases in battery capacity for advanced electric and hybrid-electric transportation applications. However, the current polymer electrolytes suffer from low ion transport rates, most commonly characterized by conductivity. This fundamental engineering science project will evaluate the hypothesis that conductivity alone is not a good metric for battery rate capability and that an equally critical component is ion transport in the polymer electrolytes. Such understanding will allow intelligent design of the next generation of solid electrolytes for electric vehicle batteries. Novel polymer electrolytes will be studied with experimental techniques not typically applied to electrolytes. The techniques provide direct measurement of ion concentration in real time and ion speciation, both of which are important for accurate and complete characterization of polymer electrolyte performance in a battery. The investigators of this project combine complementary expertise in engineering and chemistry, respectively, which will be used to further the understanding of ion-transport and battery performance through cutting-edge, time-resolved measurements and new synthetic polyelectrolytes tailored to probe structure-property relationships in these systems. For educational and outreach activities, this project includes hands-on battery activities related to this research that will be presented at economically disadvantaged middle schools. Students involved in this research will be trained with skills needed in the synthetic development of new precision polyelectrolyte systems and commercial development of lithium batteries. The goal of this research is to develop a complete picture of transport in polymer electrolytes and how it connects to battery performance. The specific aims are (1) to fully characterize transport in a systematic set of polymer electrolytes using several complementary techniques, (2) to investigate the role of ion speciation and electrolyte structure on transport behavior, and (3) to determine limiting currents for polymer-electrolyte batteries and compare to rate predictions based on a complete understanding of transport. Physical insight into the underpinnings of transport will be achieved using surface-enhanced Raman spectroscopy to evaluate dissociation state and x-ray scattering to examine the connectivity of ionic structure. This work will be conducted on the current standard polymer electrolyte, poly(ethylene oxide) (PEO) containing lithium bis-trifluoromethanesulfonimide (LiTFSI) salt. The effect of nanostructure will be examined using a mechanically strong PEO-containing block copolymer with LiTFSI. Precision polyelectrolytes blended with PEO will be used to draw conclusions about the effect of anion connectivity on dissociation state and its commensurability with the cation structure. Finally, limiting currents of polymer electrolyte batteries will be measured and predicted with continuum-level simulations. This project encompasses a thorough evaluation of transport in polymer electrolytes for lithium batteries which could shift the paradigm in understanding what limits the discharge rate in these batteries. Knowledge will be gained of the physical underpinnings of transport using a combination of frontier techniques and novel materials. A validated polymer electrolyte battery model will be developed and made publicly available. It will assist the battery community in determining target transport properties for the next generation of solid electrolytes.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.