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

Arizona State University, Scottsdale AZ

Investigators

Abstract

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.