Date of Award

2020

Document Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Mechanical and Aerospace Engineering

Committee Chair

George J. Nelson

Committee Member

Guangsheng Zhang

Committee Member

Yu Lei

Subject(s)

Lithium ion batteries., Tin alloys., Anodes--Materials.

Abstract

There is capability for advancement of the electrochemical capacity of lithium ion battery (LIB) electrodes by utilizing the high capacity of tin (Sn) in Sn alloy electrodes. However, the destructive effects of volumetric expansion must be mitigated in order to sustain this high capacity during extended cycling. One of the ways these effects can be mitigated is by alloying Sn with more malleable metals. Through this approach the electrode can attempt to accommodate the severe volumetric expansion and related strain. In order to evaluate the effectiveness of alloy electrodes, ex situ X-ray microtomography data of cycled Cu6Sn5 pellets was used to quantify the microstructural changes that occur during lithiation and delithiation. The microtomography data was segmented into three distinct phases to evaluate phase size distribution (PSD), surface area to volume ratio, tortuosity, connectivity, and interface area between phases. When evaluating the PSD of each electrode sample, it can be seen that the electrodes lithiated and then delithiated showed the most substantial reduction in overall phase sizes compared to the other samples. This suggests that full lithiation of the Sn present in the alloy electrodes followed by partial delithiation of the Li4.4Sn to Li2CuSn can cause substantial microstructural changes related to volume expansion on lithiation and structural collapse upon delithiation. When considering other microstructural characteristics, the tortuosity for the electrodes and then delithiated show the highest tortuosity factor compared to other samples. These results show that in addition to the mechanical degradation of the electrodes, excessive volume expansion can also influence transport networks in the active material and supporting phases of the electrode. While based on studies the active-inactive alloy Cu6Sn5 for lithium ion battery applications, the insights obtained are expected to be applicable to other alloy electrodes and battery chemistries.

Share

COinS
 
 

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.