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运输中得到更多的应用。然而，这些电池的安全问题来自于用于在电池内运输锂离子的易燃液体电解质。作为一种更安全的替代电解质，最有希望的候选者之一是陶瓷锆酸锂镧（LLZO），它具有良好的热/化学稳定性和离子传输性能。尽管如此，为了提高对LLZO中几个关键问题的理解以及如何提高其性能，仍需要进行许多基础研究。该项目研究新颖的LLZO纳米线结构和复合材料，具有独特的纳米级性能，可以提高锂离子的导电性，并集成到更安全的全固态电池中。该项目还支持教育和外展活动，重点是通过实践经验改善理工科女学生的输送和保留，这将增加对工程概念的理解和保留，并激发学生对研究的兴趣。通过与电池相关的挑战，向当地的中学女生提供与电动汽车相关的问题的背景，并为高中、本科生和研究生提供研究机会，这些都是示例活动。教育方面的努力包括与韩国教师进行教学方法的国际交流，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：本研究项目旨在将静电纺丝制备的LLZO纳米线材料的成分、晶界结构和晶相与离子电导率联系起来。与块状材料相比，纳米线固体电解质可以提供有益和有利的特性，即更温和的结晶煅烧条件，亚稳相的稳定，以及独特结构（如核壳复合材料）的机会。这些特性可以提高离子电导率、烧结能力，并使电解质集成到全固态电池中。纳米线被用来了解LLZO的相稳定性、结晶和烧结过程。核壳纳米线结构用于研究复合材料的界面特性和传输，以了解如何最大化锂离子的高导电途径并均匀地改变晶界。此外，详细的原位和像差校正透射电子显微镜用于了解电纺丝纳米线的结晶、杂质向晶界的偏析、纳米线网络的烧结以及电解质/阴极界面的相互扩散等过程。这些信息与纳米线固体电解质材料的离子电导率和电化学循环测试相关联，并与块状材料进行比较。从这项工作中获得的见解可以更好地控制成分，稳定亚稳相，烧结过程和Li离子传输，这最终可以导致更高的离子电导率的陶瓷电解质。

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.