Date on Master's Thesis/Doctoral Dissertation

8-2015

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Mechanical Engineering

Degree Program

Mechanical Engineering, PhD

Committee Chair

Berfield, Thomas

Committee Co-Chair (if applicable)

Park, Sam

Committee Member

Park, Sam

Committee Member

Sun, Zhihui

Committee Member

Williams, Stuart

Subject

Electrodes--Design and construction; Energy storage

Abstract

During lithiation and detlithiation, substantial volumetric changes occur within the electrode materials used for rechargeable lithium batteries. The magnitude of these deformations is inherently linked to the electrical capacity of the battery electrical capacity, which tends to degrade with repeated cycling. In this dissertation, the relationship between electrical discharge capacity and mechanical deformation state is examined using in-situ imaging of the working electrode surface within a custom CR2032 coin cell lithium battery. Digital image correlation is used to quantify electrode strains throughout the discharge-charge process. The effect of constraint due to substrate stiffness is investigated for two film materials: traditional graphite and a carbon nanotube based composite. Results for all cases show that as discharge capacity decreases with repeated cycling, increasing residual electrode strains are observed. The thin, compliant foil substrates allowed over double the bi-axial strain state to be induced within electrodes, compared to that found for the thick copper disk substrates under the same electrical cycling conditions. While this work shows that substrates play a significant role in strain development, additional tests are done to investigate the effects of adhesion quality between electrode films and substrates on electrochemical performance of lithium batteries. These effects are probed using a laser spallation technique to quantify the adhesion strength between film and substrate layer. The benefits of surface treatment designed to improve adhesion are also investigated. At last, delamination test of graphite electrode film “sandwiched” by copper substrate are performed. And the results show that surface treatment by mechanical or chemical manner can improve the adhesion dramatically.

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