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

锂离子电池广泛用作便携式电子设备和电动汽车的电源。然而，锂的稀缺性潜在地限制了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有可能与锂离子电池竞争。更重要的是，钠是天然丰富的，钠离子电池可以以低得多的成本制造。然而，钠离子电池的循环寿命很差，这主要是由于阴极的退化和失效。本研究从体相和微观两个层面对层状氧化物正极材料的降解机理进行了研究。在材料研究部门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阴极材料的结构演变，并开发减轻电极降解的方法，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。提供研究机会，以培养研究生和本科生。该项目还涉及高中学生的课程开发。钠离子蓄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。该项目的目的是阐明在钠离子电池阴极的降解机制，使用层状金属氧化物作为模型系统。研究假设是机械退化是层状氧化物阴极容量衰减和相应的循环稳定性差的主要原因。模型化合物，如钠锰氧化物，在半电池中合成和电化学测试。利用X射线衍射原位分析了阴极材料的结构变化，利用透射电子显微镜原位观察了阴极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，以合理化和预测阴极的降解机理。该研究不仅可以设计出高性能、长循环寿命的钠离子电池电极材料，而且还可以开发新的原位实验技术，推动固态化学的基础研究。

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.