Access Type

Open Access Dissertation

Date of Award

January 2014

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Electrical and Computer Engineering

First Advisor

Mark Ming-Cheng Cheng

Abstract

Development of lithium ion batteries (LIBs) with higher capacity has been booming worldwide, as growing concerns about environmental issues and increasing petroleum costs. The demands for the LIBs include high energy and power densities, and better cyclic stability in order to meet a wide range of applications, such as portable devices and electric vehicles. Silicon has recently been explored as a promising anode material due to its low discharge potential (<0.4 V) and high specific capacity (4200 mAh g-1). The capacity of silicon potentially exceeds more than 10 times of the conventional graphite anode (372 mAh g-1). However, the silicon anode experiences huge volume expansion (400%) and contraction during electrochemical cycles, resulting in pulverization and disintegration of the active material. For the improvement of the battery performance, understanding of the failure mechanism associated with the stress evolution during cycling is critical.

This study aims (1) to develop high performance anode materials and (2) to analyze the mechanism of the capacity fading using a novel in-situ characterization technique in order to optimize the electrode design for better operation of the battery. The silicon nitride thin film anodes were investigated for the improvement of cycling performance. In addition, the rate performance was enhanced by controlling the parameters in film deposition. Si-based thin films undergo large stresses induced by the volume changes, which results in material degradation and capacity fading. Hence, the in-situ measurement of the electrochemical processes is critical to clarify how the electrode degrades with time under cycling. For the in-situ measurement, a white light interferometry (WLI) and laser vibrometer were used to gather quantitative data. Amorphous silicon (a-Si) was explored for the stress measurement.

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