Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


Dissertation_Samartha_FINMRR.pdf (9.48 MB)

ETD Abstract Container

Abstract Header

Multiscale characterization of aging mechanisms in commercial LiFePO4 battery cathodes

Channagiri, Samartha A
http://rave.ohiolink.edu/etdc/view?acc_num=osu1468233768

Abstract Details

2016, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
Aging mechanisms in LiFePO4 batteries have been studied extensively in literature at a system level. For a complete understanding of the aging mechanism in these batteries, an approach is needed wherein every component of the cell (electrodes, electrolyte, separators, current collector etc.) is analyzed over a range of length scales, from microstructure to system levels. In this study, we chose to focus on the cathode and perform multi-scale characterization on it to understand what phases form as the battery is aged. We studied both microstructure and electronic structure evolution with aging in the cathodes using a variety of techniques involving X-rays and electron microscopy. Findings at the micrometer and nanometer length scales were linked to macroscopic aging phenomena such as capacity loss in the battery with aging. Directions for future work have been provided, based on findings from the current study. X-ray micro CT (XMT) and X-ray diffraction (XRD) were used to study the porosity and FePO4 phase fraction in the cathode respectively, and how this evolves with aging. Results of XMT analysis suggested an increase in porous weight fraction in the cathode with high charge-discharge rate cycling. The results of XRD analysis suggested an increase in FePO4 phase fraction in the cathode with aging, indicating a loss of available lithium for cycling. Together, they suggest a loss of active three phase boundary in the cathode with aging, responsible for the observed capacity loss at the system level as the battery is cycled thousands of times. We utilized Scanning Transmission Electron Microscopy - Electron Energy Loss Spectroscopy (STEM-EELS) to obtain microstructure and electronic structure information of the cathode at the nanometer length scale. Using Lorentz oscillator modelling, the STEM-EELS data was used to track electronic structure across the cathode and several cathodes aged differently based on cycling temperature, charge-discharge rate and capacity retention. The trends showed that electronic structure homogenizes across a sample as the battery is aged to its End-of-Life (80% capacity retention). Further probing of this effect using higher spatial and energy resolution demonstrated that although electronic structure across the cathode is homogenized with aging, the trends are more complex and varied. These trends in electronic structure were linked to the formation of anti-site defects and metastable phases as the battery is aged. It was suggested that future work must focus on probing the formation and evolution of defect structures and metastable phases in the cathode as it is aged. An in-operando measurement of the structural and chemical changes occurring in the cathode with aging using an in-situ battery set-up in the TEM was suggested as the best option for future studies.
David McComb (Advisor)
239 p.
Energy; Materials Science
Lithium Iron Phosphate, aging, cathode, transmission electron microscopy, electron energy loss spectroscopy, X-ray micro computed tomography, X-ray diffraction

Recommended Citations

Citations

  • Channagiri, S. A. (2016). Multiscale characterization of aging mechanisms in commercial LiFePO4 battery cathodes [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1468233768

    APA Style (7th edition)

  • Channagiri, Samartha. Multiscale characterization of aging mechanisms in commercial LiFePO4 battery cathodes. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1468233768.

    MLA Style (8th edition)

  • Channagiri, Samartha. "Multiscale characterization of aging mechanisms in commercial LiFePO4 battery cathodes." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1468233768

    Chicago Manual of Style (17th edition)

osu1468233768
2,250
© 2016, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.