CAREER: Electro-Chemo-Mechanics of Li and Na Metal: Toward Dendrite- and Damage-Free Metallic Anodes of Rechargeable Batteries

非技术综述：充电电池在日常生活中随处可见。事实上，锂电池已经成为便携式电子产品和电动汽车的首选电源。尽管如此，商用电池使用的材料能量密度相对较低；它们增加了车辆的重量，并在便携式电子产品中占据了巨大的体积，但必须每隔几个小时充电一次。由于其巨大的能量密度，基于金属锂和钠的超越锂离子的电池已经出现，为满足日益增长的需求做好了准备。然而，这些系统存在严重的退化和安全问题，阻碍了它们的实际使用。因此，必须进行基于材料和力学的研究，才能实现安全和持久的操作。因此，该项目的目标是结合合金材料的发现，了解锂和钠金属阳极的功能和结构行为之间的相互作用。这些研究将指导适当的充电条件、施加的压力和防止损坏的材料特性。总体而言，电池的进步将通过减少有害排放、改善安全、加强基础设施和确保能源独立而使美国受益。将锂阳极商业化将极大地提高便携式电子产品和电动汽车的能量密度(最高可达~4倍)，而将钠阳极商业化则可能实现电网规模的可再生能源存储。这项提议的更广泛的目标包括利用现有的项目，为退伍军人和代表性不足的少数族裔提供研究经验。该项目还将开发沉浸式增强/虚拟现实(AR/VR)学习模块，以加强学生对能量存储和转换材料中力学、微结构、化学和电场之间的相互作用的理解。技术总结：虽然锂和钠的电化学已经得到了广泛的研究，但上述问题的核心是材料的力学问题：在操作过程中会发生不稳定的变形，产生树枝晶和损坏。使问题复杂化的是，由于锂和钠在空气中的极端化学反应能力，人们对锂和钠的基本机械性能知之甚少，例如钠的室温塑性性能和变形机制仍基本未知。关于电沉积过程中产生的应力、随时间/温度变化的行为、断裂和疲劳行为、合金如何改变性能以及它们对微观结构稳定性的相应影响，人们更是知之甚少。本项目将通过测试以下假设来填补这些基础知识的空白：(1)与时间相关的塑性变形主导着锂和钠金属的机械行为；(2)特定合金增强了蠕变阻力，促进了结构稳定性；(3)在电沉积过程中产生的应力可能会损害周围的层和金属本身；以及(4)施加在电极堆上的预载荷促进了微观结构的稳定沉积。为了验证这些假设，该项目将利用独特的实验设备并开发理论模型，将电化学循环过程中机械性能、应力和变形的演变与化学和微观结构的变化联系起来。从这一建议的教育角度来看，教科书很少涉及电化学-化学-力学中的耦合现象。该项目将开发AR/VR模块来填补这些空白，这些模块将被纳入本科生/研究生课程，在K-12外联活动中展示，与K-12教师分享，并在网上提供。该项目还将使材料和机械专业的学生能够在传统上不对该学科开放的领域(电化学)工作，以鼓励跨学科的研究事业。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Summary:Rechargeable batteries are everywhere in daily life. Indeed, lithium-based batteries have become the power source of choice in portable electronics and electric vehicles. Still, commercial batteries utilize materials with relatively low energy densities; they add substantial weight to vehicles and occupy huge volumes in portable electronics but must be re-charged every few hours. Owing to their enormous energy densities, batteries 'beyond lithium-ion' based on metallic lithium and sodium have emerged, primed to meet growing demands. However, these systems suffer from severe issues of degradation and safety that have precluded their practical use. Materials and mechanics-based studies are thus necessary to enable safe and durable operation. Accordingly, the goal of this project is to provide understanding of the interplay between functional and structural behavior of lithium and sodium metal anodes, combined with materials discovery of alloys. These studies will guide appropriate charging conditions, applied pressures, and material properties that prevent damage. Overall, advances in batteries will benefit the USA by reducing harmful emissions, improving safety, enhancing infrastructure, and securing energy independence. Commercializing lithium anodes would dramatically increase energy densities (up to ~4x) of portable electronics and electric vehicles, while commercializing sodium anodes may enable grid-scale storage of renewable energy. The broader objectives of this proposal include leveraging established programs to provide research experiences for military veterans and underrepresented minorities. The project will also develop immersive augmented/virtual reality (AR/VR) learning modules to enhance students’ understanding of the interplay among mechanics, microstructure, chemistry, and electric fields in materials for energy storage and conversion. Outreach activities will involve K-12 students and teachers to increase awareness of clean energy technologies.Technical Summary:While the electrochemistry of lithium and sodium has received extensive study, at the heart of the issues outlined above lies a mechanics of materials problem: unstable deformation occurs during operation, producing dendrites and damage. Complicating this matter is that due to their extreme chemical reactivity in air, relatively little is known regarding even the basic mechanical properties of lithium and sodium, e.g., sodium’s room temperature plastic properties and deformation mechanisms remain largely unknown. Even less is known regarding stresses developed during electrodeposition, time/temperature-dependent behavior, fracture and fatigue behavior, how alloys modify properties, and their corresponding influence on microstructural stability. This project will fill in these gaps in fundamental knowledge through testing the following hypotheses: (1) time-dependent plastic deformation dominates the mechanical behavior of lithium and sodium metal; (2) specific alloys enhance creep resistance, promoting structural stability; (3) stresses develop during electrodeposition that can damage surrounding layers and the metals themselves; and (4) pre-loads applied to electrode stacks promote microstructurally stable deposition. To test these hypotheses, this project will utilize unique experimental facilities and develop theoretical models to connect the evolution of mechanical properties, stress, and deformation to chemical and microstructural changes during electrochemical cycling. From the educational perspective of this proposal, textbooks seldom cover coupled phenomena in electro-chemo-mechanics. This project will develop AR/VR modules to fill these voids, which will be integrated into undergraduate/graduate curricula, shown at K-12 outreach activities, shared with K-12 teachers, and made available online. This project will also enable students in materials and mechanics to work in areas not conventionally open to the discipline (electrochemistry) to encourage interdisciplinary research careers.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.