Degree Type

Thesis

Date of Award

2017

Degree Name

Master of Science

Department

Mechanical Engineering

Major

Mechanical Engineering

First Advisor

Abhijit Chandra

Second Advisor

Pranav Shrotriya

Abstract

Lithium-ion battery electrodes tend to fracture due to extensive mechanical stress and/or thermally fail by due to overheating. In our present research, we have studied the mechanical and thermal aspect of lithium battery electrodes. Two significant tasks were performed for this project. First, a numerical model was developed for analyzing the crack propagation during lithiation of crystalline silicon. We investigated the influence of mechanical properties of lithiated silicon on the fracture of silicon nanoparticles during lithiation. A chemo-mechanical model was used to determine the lithium distribution and associated stress states during lithiation. The concentration gradient of lithium and an elastic-plastic material response was utilized to determine the stress distribution. The stress distribution was utilized to determine the crack driving forces for radial crack propagation. The crack driving forces were computed for different mechanical response of lithiated silicon. The results showed lower modulus of lithiated silicon made the particle susceptible to fracture, and were validated from prior experiments. These results conclude that accurate mechanical characterization of lithiated silicon is necessary to model the fracture response of silicon particles and improving the mechanical properties will suppress crack growth in a silicon nanoparticle electrode during charging. The second work was based on a thermal parametric analysis of lithium battery electrode materials. Different electrode materials were tested for their thermal performance and life. A material selection analysis was performed based on a multiscale thermo-chemical model. The heat generation associated with lithium transport and mechanical deformation was computed based on polarization, entropic and joule heating. The formulation for the heat generation and dissipation were used to create a set of four material indices that categorize the electrode materials based on their thermal performance and ability to prevent runaway under condition of excess loading. The results predicted that lithium ferrous phosphate and silicon are the best cathode and anode materials, respectively. Heat generation by different materials was validated against past experimental data. We conclude that at high charging rates the polarization heat generation becomes dominant. We believe that particle size optimization and chemical structure modifications could be plausible options for improving thermal performance of electrode materials.

Copyright Owner

Abhishek Sarkar

Language

en

File Format

application/pdf

File Size

53 pages

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