171st Special MMU Seminar


Multiscale Characterization of Material Degradation in Li-Ion Batteries

Professor S. S. Babu
The Ohio State University
Columbus, Ohio 43221, USA
Date: Tuesday, May 1, 2012
Time: 16:00 - 17:00
Place: 7th floor small seminar room

Degradation of LiFePO4 cathode within full-scale lithium ion batteries was investigated through systematic multi-scale characterization techniques to understand the physical changes in the LiFePO4 cathodes while subjected to charge-discharge characteristics that are typical to automotive applications. The thermal diffusivity of cathodes increased during the cycling of the batteries. The SEM micrographs revealed the coarsening of the nanoparticles in the aged samples as compared to the un-aged sample by about 6 times. To evaluate the corresponding electrical properties of the LiFePO4 cathode a semi-quantitative study of change in the surface resistance using AFM was conducted. The increased surface resistance was considered as the combined effect of the physical changes, such as coarsening of the nanoparticles, and nanocrystalline deposit over the cathode surface. To extend the studies to smaller scale lengths, the coarsening phenomenon of the LiFePO4 nanoparticles were studied using STEM. Using electron energy loss spectroscopy, indirect evidence for lithium loss in aged samples was obtained. As the EELS data was insufficient to predict the distribution of Li, a Neutron Depth Profiling technique was used to map the concentration of Li in the cathode sample. The Li concentration in the aged sample dropped considerably as compared to un-aged cathode. The impact of these observations on the overall performance of Li-ion batteries for automotive applications will be discussed.