Surface Coating for High-Capacity Electrodes in Li-ion Batteries: in-situ TEM Characterization and First-Principles Modeling

可充电锂离子电池通过存储风能和太阳能等间歇性可再生能源产生的电力，或为使用可再生能源充电的零排放电动汽车提供动力，有助于实现可持续能源系统。然而，以高储能容量为目的的锂离子电池在反复充放电循环过程中功率容量损失迅速。本项目旨在通过使用透射电子显微镜（TEM）对充电和再充电过程中电池电极结构变化的微观研究来阐明容量损失的潜在机制，从而实现纳米尺度的可视化。微观研究将得到数学建模研究的补充，这些研究旨在预测观察到的行为。与该项目相关的教育活动侧重于通过普渡大学的女性工程项目协调中学生关于电池技术的实践推广活动。本研究的总体目标是通过原位透射电子显微镜（TEM）实验和第一性原理建模来研究高容量锂离子电池电极上的金属氧化物涂层如何影响电荷容量衰减。表面涂层可以通过调节电化学锂化过程和修复变形动力学来潜在地减轻电极的降解。然而，人们对涂层材料的电化学力学行为知之甚少。为了对这些过程有一个基本的了解，研究计划有两个主要目标。第一个目标是合成金属氧化物包覆纳米线的核壳结构，利用实时原位透射电镜直接观察锂化反应及其相关的形态演变和相变。第二个目标是执行第一性原理原子建模，以发展对锂离子插入和提取对电子结构，晶格结构和结构稳定性影响的补充基本理解。通过这些目标，提出的研究将确定扩散反应和相变的热力学，结构演化动力学，离子传输和界面反应，以及涂层材料中锂化相的力学性能。从这项工作中获得的知识将有助于大容量锂离子电池涂层材料的选择，并推进对锂离子电池循环性能内在机制的基本理解。

Rechargeable lithium ion batteries help to enable sustainable energy systems by storing electricity generated by intermittent renewable resources such as wind and solar energy, or by powering zero-emission electric vehicles charged by electricity from renewable resources. However, lithium ion batteries designed for high energy storage capacity suffer from rapid power capacity loss over repeated charge and discharge cycles. This project seeks to elucidate of the underlying mechanisms of capacity loss through microscopic investigation of the changes in battery electrode structure during charging and recharging using transmission electron microscopy (TEM), which enables visualization at the nanometer scale. The microscopic study will be complimented by mathematical modeling studies that seek to predict the observed behavior. The educational activities associated with this project focus on hands-on outreach activities for middle school students on battery technology, coordinated through the Women in Engineering program at Purdue University. The overall goal of this research is to investigate how metal oxide coatings on high-capacity, lithium ion battery electrodes affect charge capacity fade through in-situ transmission electron microcopy (TEM) experiments and first-principles modeling. Surface coatings can potentially mitigate the degradation of electrodes through regulation of the electrochemical process of lithiation and the remediation of deformation dynamics. However, the electro-chemo-mechanical behavior of the coating materials is poorly understood. To develop a fundamental understanding of these processes, the research plan has two major objectives. The first objective is to synthesize core-shell structures of metal oxide-coated nanowires to directly observe the lithiation reaction and the morphological evolution and phase transitions associated with it using real-time, in situ TEM. The second objective is to perform first-principles atomistic modeling to develop a complimentary fundamental understanding of the effects of lithium ion insertion and extraction on electronic structure, crystal lattice structure, and structural stability. Through these objectives, the proposed research will determine the thermodynamics of diffusive reactions and phase transitions, the kinetics of structural evolution, ionic transport, and interfacial reactions, as well as the mechanical properties of the lithiated phases in the coating materials. The knowledge gained from this work will facilitate the selection of coating materials for high-capacity lithium ion batteries, and advance fundamental understanding of the intrinsic mechanisms underlying the cyclic performance of Li-ion batteries.