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Materials Research Lecture
Wednesday June 3, 2009
4:00 PM
106 Spalding Lab, Hartley Memorial Seminar Room

Direct In-situ Measurements of Lithium Transport Rates in a Li-ion Cell
Steve Harris, General Motors

Description/Abstract:
Degradation and failure in Li-ion batteries can often be viewed as a problem with Li+ transport (“It didn’t get to the right place at the right time.”) But while there are many studies that measure macroscopic cell current and voltage (AC and DC) under a variety of conditions, until now there have been no direct in-situ experimental measurements of Li+ transport rates through an electrode of an operating Li-ion battery. Furthermore, the highly complex 3-dimensional microstructure of the electrode is not normally characterized experimentally beyond a measurement of porosity and a fitted value for tortuosity. As a result, determination of failure mechanisms tends to rely on inference and observed correlations from macroscopic data or microscopic post-mortem analyses. Li+ transport rates and spatial profiles may be predicted for a fresh cell using a 1-dimensional model fitted to macroscopic data such as current vs voltage. But such models are challenged to predict battery failure in the absence of in-situ microscale data. In this work we describe the first such direct in-situ measurements of Li+ spatial maps and transport rates in operating electrodes. We also provide initial 3-dimensional microstructural information about battery electrodes. A comparison between our results and the predictions of a standard model shows qualitative agreement in some cases and qualitative disagreement in others.

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