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|Title:||ALS-CXRO Seminar | Jordi Cabana|
|When:||02/27/2013 3:00 PM - 4:00 PM|
|Description:||ALS-CXRO Seminar Series|
Wed, February 27, 2013
Peter Fischer/Jinghua Guo
Multiscale phase transformations in battery electrodes: visualization and consequences
Battery electrodes are hierarchically complex structures formed by different components whose distribution determines the final properties. These structures must enable fast ion and electron transport. As a consequence, they are usually composite films of a redox active material with carbon and a polymer binder, cast onto a metal foil current collector. Ion transport is ensured by the presence of pores that provide points of contact between the electrolyte and the active material throughout the depth of the electrode. Because these hierarchies are assembled at scales much larger than a few nanometers, tools that can probe multiple levels of complexity are required to fully determine the parameters that control performance.
Since reactions at an electrode involve redox phase transformations, the state of charge can easily be correlated to composition. Spectroscopic and diffraction tools are widely available that can produce this chemical information. In this talk, I will discuss examples of the characterization of phase transformations using synchrotron-based tools. Insight was gathered from the atomic to the atomic to the electrode level, and from bulk to interfaces, at high chemical and spatial resolution. Because thermodynamic pathways can be controlled by the presence of electrical potential, the harvesting of a sample from a cycled battery, while providing a useful preliminary insight, can lead to misleading results due to the relaxation of components into a different state that is more stable under open circuit conditions. Therefore, measurements performed during device operation, where feasible, were performed. The mechanisms of transformation will be discussed in the context of their impact on electrode properties.