THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING 

GEORGIA INSTITUTE OF TECHNOLOGY   

Under the provisions of the regulations for the degree
 

DOCTOR OF PHILOSOPHY
 

on Friday, October 8, 2021

1:00 PM

via

BlueJeans Video Conferencing

https://bluejeans.com/452083282/9438

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Stephanie Elizabeth Sandoval

"Investigation of Fundamental Lithium Growth Dynamics in Lithium Metal Batteries"

Committee Members:

Prof. Matthew McDowell, Advisor, MSE/ME

Prof. Juan-Pablo Correa-Baena, MSE

Prof. Tom Fuller, ChBE

Prof. Seung Soon Jang, MSE

Prof. Natalie Stingelin, MSE/ChBE

Abstract:

Lithium metal batteries (LMBs) offer higher energy density that are attractive to the industry; however, the uncontrollable growth of Li throughout cycling limits the electrochemical performance of LMBs. To enable LMBs, it is necessary to understand the nucleation and growth of Li and explore methods to spatially control its growth.  The goal of this research is to understand the fundamental nucleation and growth dynamics of lithium (Li) metal in liquid and solid-state batteries in the presence of alloy thin films, as well as the effects of these processes on electrochemical behavior.

In liquid electrolyte LMBs, electrodeposited Li metal is difficult to control and often leads to dendritic growth. While several studies have focused on understanding the growth dynamics of dendrites, the work presented here investigates the fundamental nucleation of Li and the evolution of its growth across the electrode. It further investigates how interfacial alloy layers affect the growth and evolution of lithium metal during electrodeposition and stripping from stainless steel current collectors by combining electrochemical methods with operando optical microscopy. We find that thin silver films enable improved Coulombic efficiency (CE) for lithium cycling in multiple electrolyte systems compared to bare current collectors or other alloy layers. Operando optical microscopy reveals reduced growth of dendritic Li on silver-coated current collectors at high current densities compared to bare current collectors, as well as different dendrite growth and stripping dynamics.

Unlike liquid electrolytes, Li deposition in solid-state batteries (SSBs) is heavily dictated by the interfacial contact between the solid-state electrolyte (SSE) and the electrode. As Li is deposited, the solid-solid interface undergoes expansion of which the SSE struggles to accommodate. Upon stripping of Li, void formation is often found at the solid-solid interface which result in localized current densities and over time, Li dendrites. Similar to our study in liquid electrolytes, the work to be studied in this second objective focuses on understanding the electrochemical and morphological evolution of the electrodeposited Li in SSBs via ex situ techniques, focusing on its effects on the contact evolution. Preliminary work shows that the use of alloy interfacial layers offers favorable Li growth conditions and can enable higher CE compared to nonalloy electrodes. It will be important to further investigate the role that alloy interlayers play in the electrochemical behavior and contact evolution in SSBs.

Further work proposed here aims to further understand the effects of Li nucleation and growth and its cycling effects through quantifying the 3D structure of Li at the solid-solid interfaces at various stages of deposition and stripping. This third objective builds upon the electrochemical and structural understanding on the nucleation and growth behavior of Li and focuses on understanding how local changes in Li morphology and the structure of the interface affect the dynamic evolution of Li throughout cycling in SSBs. Cryo-focused ion beam (cryo-FIB) tomography will be used to probe local areas of the solid-state cell to create 3D reconstructions of the solid-solid interface. Alloy and nonalloy electrodes will be studied at various points throughout cycling. This work will provide insight to affects that Li deposition and stripping have on the solid-solid interface. Through understanding the growth and stripping behaviors of Li metal, we can engineer interfaces to provide spatial control of Li, thus enabling these high energy density batteries.