Corrosion and Passivation Mechanisms of Li-Ion Battery Cathodes from Ab Initio Interfacial Reaction Dynamics

氧化还原活性材料的腐蚀和表面钝化是电化学能量储存和催化中的一个交叉主题，但其过程及其基本分子基础仍然知之甚少。活性金属溶解是锂离子电池（LIB）阴极退化的主要原因之一，无论其晶体结构和化学组成如何。该研究项目的结果将为解释和预测降解行为所需的腐蚀和钝化机制的分子起源提供基本见解。所获得的知识将使开发一个改进的方法基础，攻击其他缓慢和罕见的事件现象相关的电化学interfaces.To捕捉的LIB溶解过程的瞬态性质和帐户的电子结构的变化动态，原子从头算分子动力学（AIMD）模拟将采用。这种计算与增强的自由能采样技术相结合，可以提供关键的洞察力的动力学，机制和动力学的统计罕见的事件在一个单一的事件水平。所获得的结果可以用来解释实验结果，往往是具有挑战性的解释，并提出抑制表面降解和钝化的方法。拟议的研究的主要目标是建立一个详细的原子理解的反应动力学在锂离子电池阴极/电解质界面，重点是过渡金属溶解和电解质分解。该研究计划集中在三种重要的氧化物基锂离子电池正极材料，即尖晶石型LiM 2 O 4，层状氧化物LiMO 2和磷橄榄石LiMPO 4（M = Mn，Co，Ni，Fe）化合物。重点将是在化学丰富的环境中研究界面反应，考虑多相电解质溶液，多组分阴极材料，结构异质性和高温效应。该研究将侧重于了解以下方面的作用：1）阴极材料的表面化学，包括过渡金属的反硝化反应; 2）复杂的混合电解质化学，涉及两种或多种组分，存在水分; 3）局部结构异质性，如氧空位的存在和不同的电荷状态（锂含量）。该项目的科学目标是通过对基本反应步骤的详细表征，解开阴极化学/结构与混合电解质化学之间的密切关系。一组简单的描述符将被确定，可用于预测阴极在复杂的LIB环境中腐蚀的倾向。该项目将为本科生和研究生提供独特的机会，包括STEM中代表性不足的群体的成员，以研究第一原理技术在界面反应动力学中的应用。该项目的主要成果将被纳入课程材料中，并在纳米物理高中夏令营中向高中生展示。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智力价值和更广泛的影响审查标准进行评估来支持。

Corrosion and surface passivation of redox-active materials is a crosscutting theme in electrochemical energy storage and catalysis, but the processes and their fundamental molecular underpinnings remain poorly understood. Active metal dissolution is one of the main reasons for degradation of Li-ion battery (LIB) cathodes, regardless of their crystal structure and chemical composition. The results of this research project will provide fundamental insights into the molecular origins of corrosion and passivation mechanisms necessary to explain and predict degradation behavior. The knowledge obtained will enable the development of an improved methodological foundation to attack other slow and rare event phenomena related to electrochemical interfaces.To capture the transient nature of the LIB dissolution process and account for changes in the electronic structure dynamically, atomistic ab initio molecular dynamics (AIMD) simulations will be employed. Such calculations in combination with enhanced free-energy sampling techniques can provide key insights into the dynamics, mechanism and kinetics of statistically rare events at a single event level. The obtained results can be used to explain experimental findings that are often challenging to interpret and to propose ways to inhibit surface degradation and passivation. The primary objective of the proposed research is to build a detailed atomistic understanding of reaction dynamics at LIB cathode/electrolyte interfaces focusing on transition-metal dissolution and electrolyte decomposition. The research plan focuses on three important classes of oxide-based LIB cathode materials, namely, spinel-type LiM2O4, layered-oxide LiMO2 and phospho-olivine LiMPO4 (M = Mn, Co, Ni, Fe) compounds. The emphasis will be on studying interfacial reactions in the chemically rich environments considering multiphase electrolyte solutions, multi-component cathode materials, structural heterogeneities and elevated temperature effects. The research will focus on understanding the role of: 1) surface chemistry of cathode materials including transition-metal disproportionation reactions; 2) complex mixed electrolyte chemistry involving two or more components in the presence of moisture; and 3) local structural heterogeneities such as the presence of oxygen vacancies and varying state of charge (Li content). The scientific goal of the project is to untangle the intimate relationships between cathode chemistry/structure and mixed electrolyte chemistry through a detailed characterization of elementary reaction steps. A set of simple descriptors will be determined that can be used to predict the propensity of the cathodes to corrode in complex LIB environments. The project will provide unique opportunities for undergraduate and graduate students, including members of underrepresented groups in STEM, to work on the application of first-principles techniques in interfacial reaction dynamics. Key results from the project will be incorporated into course materials and presented to high school students at a Nanophysics High School Camp.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.