Deciphering the Competing Mechanisms of Li Microstructure Formation in Solid Electrolytes with Nuclear Magnetic Resonance Spectroscopy (NMR) and Imaging (MRI)

该项目解决了电池技术中广泛使用的一个关键挑战：在电池内部形成称为树突的微小结构。这些树突会导致短路，限制固态电池的功率和寿命，而固态电池对可持续能源的未来至关重要。该团队的目标是了解这些树突是如何形成的，并制定缓解策略。研究重点是固态电池的重要组成部分Li7La3Zr2O12 （LLZO）。通过使用核磁共振（NMR）和磁共振成像（MRI）等先进技术，研究小组希望揭示树突形成的根本原因。这种理解对于设计寿命更长、效率更高的电池至关重要。这项研究的结果将增强我们对电池技术的理解，并有助于开发更高效和可持续的能源存储解决方案，直接造福整个社会。该项目还旨在开发新的工具来研究广泛的功能材料，为多个领域的科学知识做出贡献。此外，它将开设一门关于先进磁共振技术的新课程，并通过几个教育和推广平台扩大代表性不足的群体对科学研究的参与。通过解决与可充电电池相关的主要挑战，该项目将促进科学技术的进步，提高国民福利。固体电解质中li微结构的形成会导致电池短路，限制全固态电池（assb）的功率密度和寿命。与广泛研究的液体系统不同，固体中的枝晶形成非常复杂，难以表征。本项目提出了固体电解质中枝晶形成的两种机制：电极-电解质界面上不均匀的Li电镀（机制1）和固体电解质中晶界处Li+离子的还原（机制2）。虽然机制1已经使用电子和光学显微镜进行了探索，但机制2由于在非侵入性探测大块固体方面的挑战而仍然知之甚少。为了解决这个问题，该提案采用了核磁共振波谱（NMR）和成像（MRI）技术。具体而言，该项目旨在使用示踪交换核磁共振确定锂枝晶的来源，使用无创7Li/6Li MRI创建固体电解质中枝晶的3D图像，并使用原位核磁共振和核磁共振监测实时枝晶形成，并辅以电子顺磁共振研究。所选择的材料体系Li7La3Zr2O12 （LLZO）及其衍生物代表了具有已知枝晶形成问题的突出的氧化物基固体电解质。本研究旨在区分不同的机制，并确定与ASSB电化学循环相关的不同条件下具有空间和时间分辨率的主导机制。对具有不同电子导电性的LLZO衍生物的研究将有助于深入了解电子导电性在确定枝晶形成机制及其分布中的作用。这项工作的结果将有助于理解和减轻与枝晶相关的挑战，最终推动更安全、更高效的固态电池的发展。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARY This project tackles a critical challenge in battery technology that is widely used daily: the formation of tiny structures, called dendrites, within batteries. These dendrites can cause short circuits, limiting the power and lifespan of solid-state batteries, which are crucial for powering a sustainable energy future. The team aims to understand how these dendrites form and develop mitigating strategies. The research focuses on Li7La3Zr2O12 (LLZO), an important component in solid-state batteries. By using advanced techniques like nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI), the team hopes to uncover the root causes of dendrite formation. This understanding is vital for designing batteries with longer lifespans and higher efficiency.The outcomes of this research will enhance our understanding of battery technology and contribute to developing more efficient and sustainable energy storage solutions, directly benefiting society at large. The project also aims to develop new tools to study a broad range of functional materials, contributing to scientific knowledge in multiple fields. Moreover, it will establish a new course on advanced magnetic resonance techniques and broaden the participation of underrepresented groups in scientific research via several educational and outreach platforms. By addressing the major challenges associated with rechargeable batteries, this project will promote the progress of science and technology and advance the national welfare. PART 2: TECHNICAL SUMMARYLi microstructure formation in solid electrolytes results in battery short circuits, limiting the power density and lifespan of all-solid-state batteries (ASSBs). Unlike extensively studied liquid systems, dendrite formation in solids is complex and challenging to characterize. This project proposes two mechanisms for dendrite formation in solid electrolytes: non-uniform Li plating at the electrode-electrolyte interface (Mechanism 1) and reduction of Li+ ions at grain boundaries within solid electrolytes (Mechanism 2). While Mechanism 1 has been explored using electron and optical microscopy, Mechanism 2 remains less understood due to challenges in noninvasively probing bulk solids. To address this, the proposal employs nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI) techniques. Specifically, the project aims to determine the source of Li dendrites using tracer-exchange NMR, create 3D images of dendrites within solid electrolytes using noninvasive 7Li/6Li MRI, and monitor real-time dendrite formation using in situ NMR and MRI, complemented by electron paramagnetic resonance studies. The chosen material system, Li7La3Zr2O12 (LLZO) and its derivatives represent a prominent oxide-based solid electrolyte with known dendrite formation issues. The research aims to distinguish between the proposed mechanisms and determine the dominant one with spatial and temporal resolution under varied conditions relevant to ASSB electrochemical cycling. Investigations on LLZO derivatives with diverse electronic conductivities will provide insights into the role of electronic conductivity in determining dendrite formation mechanisms and their distribution. The outcomes of this work will contribute to understanding and mitigating dendrite-related challenges, ultimately advancing the development of safer and more efficient solid-state 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.