Faber Research Group

Microstructural Evolution and Degradation Mechanisms in Lithium-Ion Batteries
Graduate Student: Zhao Liu

Lithium-ion batteries (LIBs), one of the promising electrochemical storage device options, are used worldwide for cellular phones, laptop computers, camcorders, full hybrid electric vehicles, next generation electric vehicles, etc. since first commercialized by Sony in 1991. As the third lightest element in the periodic table, lithium has low redox potential, which enables LIB technology to provide much higher specific energy densities and specific power than batteries, such as those based on nickel-cadmium, lead-acid or nickel-metal hydrides. Also, LIBs are much lighter compared to these other portable EES devices. In addition, the relatively high operating voltage makes LIB suitable for many specialized applications.

Despite the remarkable performance of LIBs, maximizing battery longevity with high capacity is still a major challenge partly due to electrode degradation as a function of repeated cycling. In general, cycling-induced degradation may result, in part, from the electrode microstructural changes. The repeated intercalation/de-intercalation of lithium ions results in the development of strain and stress in active electrode materials, which can cause plastic deformation and fracture that lead to capacity fade and eventual cell failure. Additionally, chemical reactions between the electrolyte and electrode alter the electrode microstructure via active material dissolution, surface layer formation, which also induces capacity fade. Therefore, good understanding of the impact of the microstructural changes in LIB degradation is needed and will facilitate the process of materials selection and designing mechanically robust electrodes.

My research project focuses on understanding the LIB degradation by observing and quantifying the LIB electrode microstructure evolution using a combination of three-dimensional (3D) characterization tools, which include focus-ion beam scanning electron microscopy and X-ray computed tomography, and X-ray diffraction techniques. Microstructural parameters will be extracted from the 3D reconstruction of commercial or lab-made LIB electrodes with different cycling conditions. Electrochemical test data are combined with statistical analysis on the microstructural parameters to study the correlations between the capacity fade and microstructure changes. X-ray diffraction techniques will be used to monitor the strain and stress changes, phase evolution and crack generation during the battery operation, and will link these changes to the LIB performance.

Funding provided by the National Science Foundation, DMR-0907639 and DMR-1121262