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

第一部分： 非技术概述该项目解决了日常广泛使用的电池技术中的一个关键挑战：在电池内形成称为树突的微小结构。这些树枝状晶体会导致短路，限制固态电池的功率和寿命，而固态电池对于为可持续能源的未来提供动力至关重要。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。该研究的重点是固态电池的重要成分Li 7 La 3 Zr 2 O 12（LLZO）。通过使用核磁共振（NMR）和磁共振成像（MRI）等先进技术，该团队希望揭示树突形成的根本原因。这种理解对于设计更长寿命和更高效率的电池至关重要。这项研究的成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储能解决方案，直接造福于整个社会。该项目还旨在开发新的工具来研究各种功能材料，为多个领域的科学知识做出贡献。此外，它还将开设一门关于先进磁共振技术的新课程，并通过若干教育和外联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。 第二部分： 固体电解质中Li微结构的形成导致电池短路，限制了全固态电池（ASSB）的功率密度和寿命。与广泛研究的液体系统不同，固体中的枝晶形成是复杂且具有挑战性的。该项目提出了固体电解质中枝晶形成的两种机制：电极-电解质界面处的不均匀Li电镀（机制1）和固体电解质内晶界处Li+离子的还原（机制2）。虽然机制1已被探索使用电子和光学显微镜，机制2仍然不太了解，由于在非侵入性探测散装固体的挑战。为了解决这个问题，该提案采用了核磁共振光谱（NMR）和成像（MRI）技术。具体而言，该项目旨在使用示踪剂交换NMR确定Li树突的来源，使用非侵入性7 Li/6Li MRI创建固体电解质内树突的3D图像，并使用原位NMR和MRI监测实时树突形成，并辅以电子顺磁共振研究。所选择的材料系统Li 7 La 3 Zr 2 O 12（LLZO）及其衍生物代表了具有已知枝晶形成问题的突出的基于氧化物的固体电解质。该研究的目的是区分所提出的机制，并确定在不同的条件下与ASSB电化学循环相关的空间和时间分辨率的主导机制。LLZO衍生物具有不同的电子电导率的调查将提供洞察电子电导率在确定枝晶形成机制及其分布的作用。这项工作的成果将有助于理解和缓解枝晶相关的挑战，最终推动更安全，更高效的固态电池的发展。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.