Chao Ji

Graduation Semester and Year

2013

Language

English

Document Type

Thesis

Degree Name

Master of Science in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Bo Yang

Abstract

Lithium-ion batteries are currently widely used in electronics, electrical vehicles and other devices/machines. Along with the mounting demand for much improved performance in these developing technological fields, silicon was recognized to possess much higher energy capacity when used as an anode than graphite that is currently used. However, there occurs colossal volume expansion of silicon anode during the lithiation process. The material consequently suffers enormous stresses, especially, at the interface with a current collector, which deteriorate the device quickly during cycling. To prevent the active material (Si) from falling off from a current collector, nanoengineering strategies have been suggested, including nanostructuring and composition grading.In the present thesis, we carry out a chemoelastoplastic analysis of a copper-graded silicon nanorod. From the end in contact with a current collector (taken to be copper), the nanorod composition starts with 100 % copper but is graded with decreasing copper content and increasing silicon content until a certain length in a grading zone. Beyond the grading zone, the composition is pure silicon. The deformation and stress due to steady-state insertion of lithium ions are examined by applying a finite element method. The effects of plasticity, finite strain and finite rotation are taken into account, which are significant in this system with volume expansion of ~ 400 %. The results show that the grading zone can mitigate the stresses both in the rod and at the interface with a current collector. Rods with longer length of a grading zone enjoy lower stresses. This study in part lays out a base for designing graded silicon nanorods for improved performance in lithium-ion battery application.

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

Download

Share

COinS