Ph.D. Defense
Donald Bistri
(Advisor: Prof. Claudio Di Leo)
"Continuum Modeling of Electro-Chemo-Mechanical Phenomena in next-generation all-Solid-State Batteries"
Thursday, May 11th
1:00 p.m.
Guggenheim, BuildingRoom 442
Zoom Meeting Link: https://gatech.zoom.us/j/92449561219
Meeting ID: 924 4956 1219
Abstract
Solid-State-Batteries (SSBs) present a promising technology for next-generation batteries due to their superior properties including increased energy density and safer electrolyte design. Traditional SSB-architecture features a Lithium-metal anode, a solid-state composite cathode and a stiff ceramic electrolyte. While an attractive alternative, commercialization of SSBs faces many challenges and depends on the resolution of a series of chemo-mechanical issues across its constituents. Critical chemo-mechanical problems in SSBs involve growth induced fracture of solid-state electrolyte (SSE) due to metal deposition, interphase formation at the anode/SSE interface and damage of the various phases in composite electrodes. Computational modeling of these phenomena for SSBs is at its infancy and constitutes the focus of this thesis, with a special emphasis on mechanical integrity of composite electrodes and growth-induced fracture of SSE.
Both cathode and anode may consist of a composite of active particles surrounded by a ceramic SSE matrix. During cycling, active particles undergo electrochemically induced expansion/ contraction against the stiff SSE, which can lead to fracture across the constituents. Developing models for these systems requires then an understanding of three critical components: i) the behavior of the active particles themselves, ii) the behavior of SSE, and iii) the combined behavior of the composite. Towards modeling the role of mechanical damage on electrochemical performance of composite electrodes, we propose a novel chemo-mechanically coupled interface element, analogous to conventional cohesive elements used in fracture mechanics. The framework enables for modeling galvanostatic charging of composite electrodes and concurrently captures the continuous evolution of mechanical stresses, interfacial damage and non-uniform current distribution across particles in a microstructure. We specialize on a LCO-LGPS composite cathode for aSSBs and study the evolution of interfacial damage under varying material and microstructural properties. Specifically, we investigate electrolyte compositions with varying SSE stiffness and active particle volumetric expansion to model their effect on interfacial stresses, mechanical damage, and overall electrochemical response of the system. Subsequently, we discuss how variations in microstructural composition alter the state of interfacial damage. Both packing effects and particle size distribution are discussed to understand from a design perspective how these factors can impact integrity of the interface and overall electrochemical performance.
Towards modeling the phenomena of metal filament growth in aSSBs, we formulate a thermodynamically-consistent continuum electro-chemo-mechanical theory which couples phase-field damage and electrochemical reactions. The theory is applied to model the morphology of metal filaments growth under varying chemo-mechanical conditions. The proposed framework is fully coupled with electrodeposition impacting mechanical deformation, stress generation and subsequent SSE fracture. Conversely, electrodeposition kinetics are affected by mechanical stresses through a thermodynamically consistent, physically motivated driving force that distinguishes the role of chemical, electrical and mechanical contributions. The theory captures the interplay between crack propagation and electrodeposition by tracking the damage and reaction fields using separate phase-field variables such that filament growth is preceded by and confined to damaged regions within the SSE. An attractive feature of such approach is its ability to simulate the nucleation, propagation and branching of cracks and Li filaments in arbitrary orientations. While the framework is general in nature, we specialize it towards modeling the growth of Li-metal filaments in an inorganic LLZO electrolyte. We demonstrate the capacity of the framework to capture both intergranular and transgranular crack and Li filament growth, both of which have been experimentally observed in the literature. In modeling this system, we elucidate the manner in which mechanics and fracture of the SSE impact electrodeposition kinetics and Li filament growth. From a manufacturing standpoint, we additionally elucidate the role of mechanical boundary conditions (i.e. mechanical confinement of SSBs) on the rate of crack propagation across the electrolyte versus the rate of electrodeposition of Li-metal within cracks. Under specific mechanical boundary conditions, we demonstrate the capacity of the framework to capture the experimentally observed phenomenon of the crack front propagating ahead of the Li-metal filament, with the cracks traversing the entire electrolyte before Li reaches the cathode
Committee
- Prof. Claudio Di Leo – Guggenheim School of Aerospace Engineering (advisor)
- Prof. Christos Athanasiou – Guggenheim School of Aerospace Engineering
- Prof. Matthew McDowell – Woodruff School of Mechanical Engineering
- Prof. Julian Rimoli – Guggenheim School of Aerospace Engineering
- Prof. Ting Zhu – Woodruff School of Mechanical Engineering