Georgia Institute of Technology Materials Science and Engineering

Committee Members: 

Prof. Matthew McDowell, Advisor, ME/MSE Prof. Meilin Liu, MSE Prof. Faisal Alamgir, MSE Prof. Juan-Pablo Correa-Baena, MSE Prof. Tom Fuller, ChBE

"Probing Interfacial Dynamics in Solid-State Lithium Metal Batteries”

Abstract:

Solid-state batteries (SSBs) are a promising technology to surpass the energy density and safety of conventional lithium-ion batteries. These devices replace the flammable liquid electrolyte with a more stable solid-state electrolyte (SSE) that can conduct lithium ions. The high stiffness and strength of SSEs are also thought to be important for enabling the high-capacity lithium metal anode, which is plagued by dendrite formation and dead lithium in liquid electrolytes. Despite advances towards SSEs with high ionic conductivity, the understanding and control over solid electrode/SSE interfaces have emerged as major challenges in the development of SSBs. Chemo-mechanical degradation is expected to be more severe in SSBs compared to conventional liquid-electrolyte-batteries because the SSE cannot reconfigure like liquids. Understanding chemical transformations at interfaces, mechanical damage, and lithium filament growth is therefore critical for engineering SSBs.

Most SSEs are unstable in contact with lithium metal and decompose to form an interphase layer at the interface, with the transport properties of the decomposed phases playing a crucial role in determining whether this process is continuous or passivating. In the first section of this proposal, we investigate how mixed ionic-electronic conducting interphases formed at Li/SSE interfaces impact cell stability. We find that these interphases lead to continuous electrochemical decomposition of the SSE during cycling. The evolution of the interphase results in volume expansion within the SSE, which is relieved by fracture and crack growth. Cycling at faster rates causes the interphase to grow non-uniformly and accelerate cell failure.

The second section of this proposal uses operando synchrotron X-ray tomography to image Li/SSE interfaces during cycling. Taking advantage of the high spatial and temporal resolution of the synchrotron beamline, we are able to track dynamic phenomena at these interfaces, such as the decomposition of the SSE and the loss of interfacial contact. We develop segmentation routines to isolate the volumes of different phases, allowing us to perform quantitative analysis on how they change throughout cycling and correlate these changes to the measured electrochemistry. Our results suggest that the loss of interfacial contact over time is the dominant mechanism for cell failure, despite significant side reactions and volume changes throughout the cell.

The remainder of my thesis will focus on two thrusts. First, I will conduct additional operando synchrotron X-ray tomography experiments to image lithium deposition at Li/SSE interfaces. Second, I will characterize various Li/SSE interfaces over a broad range of temperatures between -60 °C and 150 °C to understand how failure mechanisms at these interfaces are dependent on temperature. The combination of my previous work and proposed work will provide a general framework for understanding the stability of Li/SSE interfaces, which is necessary to develop SSBs with high energy density.