Date of Award

8-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Roberto Benson

Committee Members

Claus Daniel, Claudia Rawn, Thomas Zawodzinski

Abstract

Current demands on lithium ion battery (LIB) technology include high capacity retention over a life time of many charge and discharge cycles. Maximizing battery longevity is still a major challenge partly due to electrode degradation as a function of repeated cycling. The intercalation of lithium ions into an active material causes the development of stress and strain in active electrode materials which can result in fracture and shifting that can in turn lead to capacity fade and eventual cell failure. The processes leading to active material degradation in cycling LIBs has been studied using a combination of acoustic emission (AE) and in situ X-ray diffraction (XRD) techniques. Safe, low cost custom electrochemical cells were designed and developed for use in battery AE and XRD experiments. These tools were used to monitor the time of material fracture through AE and link these events to lattice strain and phase composition as determined by XRD. Both anode and cathode materials were studied with an emphasis on graphite, silicon, and Li(Mn1.5Ni0.5)O4, and tin. A thermal analogy model for lithiation/delithiation induced fracture of spherical particles capable of predicting when AE should be detected in a cell containing a composite silicon electrode. The results of this work were used to develop an understanding of when and how active materials are degrading as well as to suggest methods of improving their performance and operational longevity.

Comments

Kevin James Rhodes was born in 1982 in El Paso, TX. He earned his bachelor’s degree in Biomedical Engineering with dual minors in Chemistry and Materials Science & Engineering in 2006 as well as his master’s degree in Polymer Engineering in 2008, both from the University of Tennessee, Knoxville. While pursuing a PhD in Materials Science and Engineering, Kevin was an active student member of the Electrochemical Society, Materials Research Society, and American Crystallographic Association. During this time he also taught classes in chemistry and materials science at Pellissippi State Community College and the University of Tennessee. He performed his doctoral research focused on materials degradation in lithium ion batteries at Oak Ridge National Laboratory under the guidance of Dr. Claus Daniel. In 2011 he prepared a dissertation on this work and submitted it as the final criteria for graduation. Upon completion of this doctoral degree, Kevin accepted a research engineer position in the energy storage division of Ford Motor Company.

Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS