Investigation of Degradation Mechanisms in Layered Oxide Cathodes for Na Ion Batteries

非技术摘要锂离子电池广泛用作便携式电子产品和电动汽车的电源。然而，锂的稀缺性可能会限制锂离子电池在未来的应用。钠离子电池是一种很有前途的替代储能技术，因为它在能量和功率密度等所有性能类别上都具有与锂离子电池竞争的潜力。更重要的是，钠天然丰富，钠离子电池的制造成本可以低得多。然而，钠离子电池的循环寿命较差，这在很大程度上是由于阴极的退化和失效。本研究从体相和微观两个方面研究了层状氧化物正极材料的降解机理。在材料研究部固态和材料化学计划的支持下，目标是了解电池循环过程中正极材料的结构演变，并开发减轻电极退化的方法，以提高钠离子电池的循环寿命。该项目涉及实验和建模之间的密切合作。为培养研究生和本科生提供研究机会。该项目还涉及针对高中生的课程开发。技术摘要钠离子电池是一种很有前途的低成本储能装置。然而，阴极的严重退化会极大地限制钠离子电池的循环寿命。该项目旨在以层状金属氧化物为模型体系，阐明钠离子电池正极材料的退化机理。研究假设认为，机械退化是导致层状氧化物阴极容量衰减和循环稳定性差的主要原因。合成了模型化合物，如氧化锰钠，并在半电池中进行了电化学测试。用原位X射线衍射仪研究了块体正极材料的结构变化，用原位透射电子显微镜观察了材料的微观结构变化。在实验观察和分析的基础上，建立了多尺度化学力学模型，对阴极的降解机理进行了合理的描述和预测。该研究不仅为设计出循环寿命长的高性能钠离子电池电极材料提供了可能，而且为推进固体化学的基础研究开发了新的现场实验技术。

Non-Technical AbstractLithium ion batteries are widely used as power sources in portable electronics and electric cars. However, the scarcity of lithium potentially limits the application of lithium ion batteries in future. Sodium ion battery is a promising alternative energy storage technology due to its potential to compete with lithium ion batteries in all performance categories, such as energy and power densities. More importantly, sodium is naturally abundant and sodium ion batteries can be manufactured at much lower cost. However, sodium ion batteries suffer from poor cycle life, largely due to the degradation and failure of the cathode. This research studies the degradation mechanism of the layered oxide cathode materials at bulk and microscopic scales. With support from the Solid State and Materials Chemistry Program in the Division of Materials Research, the goal is to understand the structural evolution of the cathode materials during battery cycling and to develop means of mitigating electrode degradations for improving the cycle life of sodium ion batteries. The project involves close collaborations between experiment and modeling. Research opportunities are provided to train both graduate and undergraduate students. The project also involves the course development for high school students. Technical AbstractSodium ion battery is a promising energy storage device with low cost. However, the severe degradation of cathodes can drastically limit the cycle life of sodium ion batteries. The project aims to elucidate the degradation mechanisms in the cathode of sodium ion batteries using the layered metal oxides as model systems. The research hypothesis is that the mechanical degradations are primarily responsible for the capacity fade and accordingly poor cycle stability in layered oxide cathodes. Model compounds, such as sodium manganese oxide, are synthesized and electrochemically tested in half cells. In situ X-ray diffraction is used to study the structural change of the bulk cathode materials, and in situ transmission electron microscopy is used to observe the microscopic structural changes. Based on the experimental observations and analyses, multiscale chemomechanical models are developed to rationalize and predict the degradation mechanism of the cathodes. This research not only enables the design of high performance electrode materials for sodium ion battery with long cycle life, but also develops novel in situ experimental techniques to advance the fundamental research of solid state chemistry.