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

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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.