CAREER: Engineering Structure and Ionic Conductivity in Li7La3Zr2O12 Nanowire-Based Solid Electrolytes

非技术描述：锂离子电池在笔记本电脑和手机中无处不在，在不久的将来可能会在交通应用中获得更多用途。然而，这些电池受到安全问题的困扰，这些问题源于用于在电池内传输锂离子的易燃液体电解液。具有良好的热稳定性、化学稳定性和离子传输性能的陶瓷锆酸镧锂(LLZO)是最有希望成为更安全的替代电解液的候选材料之一。尽管如此，仍然需要进行大量的基础研究，以提高对LLZO中几个关键问题的理解，并如何提高其性能。本项目研究具有独特纳米性质的新型LLZO纳米线结构和复合材料，可以改善其对锂离子的导电性，并集成到更安全的全固态电池中。该项目还支持教育和外联活动，这些活动的重点是通过实践经验改善理工科女学生的学习渠道和留住女学生，增加对工程学概念的理解和留住，并激发学生的研究兴趣。通过电池相关挑战向当地中学女生提供与电动汽车相关问题的背景知识，并为高中生、本科生和研究生提供研究机会是范例活动。教育工作包括与韩国教师进行国际教学方法交流，以了解促进女学生成就的策略，以及如何在以学生为中心的学习环境中最好地吸引来自不同背景的学生。技术细节：该研究项目旨在将使用静电纺丝制备的LLZO纳米线材料的成分、晶界结构和晶相与离子导电性联系起来。纳米线固体电解质可以提供与块状材料相比有益和有利的特性--即结晶的较温和的焙烧条件、亚稳定相的稳定以及获得独特结构(如核壳复合材料)的机会。这些特性可以提高离子传导性、烧结能力以及将电解液集成到全固态电池中。纳米线被用来了解LLZO的相稳定性、晶化和烧结过程。核壳纳米线结构被用来研究复合材料中的界面性质和输运，以了解如何最大化锂离子的高导电路径和均匀地改变晶界。此外，详细的原位和像差校正的透射电子显微镜被用来了解电纺纳米线的结晶、杂质向晶界的偏析、纳米线网络中的烧结以及电解液/阴极界面的互扩散等过程。这一信息与纳米线固体电解质材料的离子导电性和电化学循环测试相关联，并与块状材料进行了比较。从这项工作中获得的见解是能够更好地控制成分、亚稳相的稳定、烧结过程和锂离子传输，这最终可以导致更高的离子导电性陶瓷电解质。

NON-TECHNICAL DESCRIPTION: Lithium ion batteries are ubiquitous in laptops and cell phones and may gain more use in transportation applications in the near future. However, these batteries suffer from safety issues originating from the flammable liquid electrolyte that is used to transport lithium ions within the battery. One of the most promising candidates for a safer, replacement electrolyte is the ceramic lithium lanthanum zirconate (LLZO), which has good thermal/chemical stability and ionic transport properties. Nonetheless, there is still much fundamental research needed in order to improve understanding of several critical issues in LLZO and how to improve its performance. This project investigates novel LLZO nanowire structures and composites with unique nanoscale properties that can improve their conductivity for lithium ions and integration into safer, all-solid-state batteries. This project also supports education and outreach activities that focus on improving the pipeline and retention of female students in science and engineering through hands-on experiences that will increase understanding and retention of engineering concepts and stimulate the students' interests in research. Outreach to local middle school girls through a battery-related challenge to provide context on issues related to electric cars and research opportunities to high school, undergraduate, and graduate students are example activities. Educational efforts include international exchange of teaching methodologies with faculty in South Korea to understand strategies that promote female student achievement, as well as how to best engage students from diverse backgrounds in student-centered learning environments.TECHNICAL DETAILS: This research project aims to correlate composition, grain boundary structure, and crystal phase with ionic conductivity in LLZO nanowire materials prepared using electrospinning. Nanowire solid electrolytes can offer characteristics that are beneficial and advantageous compared to bulk materials - namely milder calcination conditions for crystallization, stabilization of metastable phases, and opportunities for unique structures such as core-shell composites. These characteristics can lead to properties that improve the ionic conductivity, sintering ability, and integration of the electrolytes into all-solid-state batteries. The nanowires are used to understand the LLZO phase stability, crystallization, and sintering processes. Core-shell nanowire structures are used to investigate interfacial properties and transport in composites to understand how to maximize highly conducting pathways for lithium ions and uniformly modify grain boundaries. Additionally, detailed in situ and aberration-corrected transmission electron microscopy is used to understand processes such as crystallization of electrospun nanowires, impurity segregation to grain boundaries, sintering in networks of nanowires, and interdiffusion at the electrolyte/cathode interface. This information is being correlated with ionic conductivity and electrochemical cycling tests on the nanowire solid electrolyte materials and compared to bulk materials. The insights gained from this work are enabling better control of composition, stabilization of metastable phases, sintering processes, and Li ion transport, which can ultimately lead to higher ionic conductivity ceramic electrolytes.