MULTISCALE MODELING OF LITHIUM METAL ANODE FOR NEXT-GENERATION BATTERY DESIGN
Open Access
- Author:
- Liu, Zhe
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 04, 2019
- Committee Members:
- Long-Qing Chen, Dissertation Advisor/Co-Advisor
Long-Qing Chen, Committee Chair/Co-Chair
Chao-Yang Wang, Committee Member
Ismaila Dabo, Committee Member
Adrianus C Van Duin, Outside Member
John C Mauro, Program Head/Chair - Keywords:
- Lithium ion battery
Lithium metal anode
Dendrite growth
Phase-field modeling
Electrodeposition
Density functional theory - Abstract:
- Achieving smooth Li-plating without dendrite growth remains to be a grand challenge for developing the next-generation batteries based on Li metal anode. One of the main reasons is our inability to directly model and predict the atomistic and mesoscale mechanisms underlying the complex electroplating process involving concurrent ionic transport, redox reaction, and development of morphological instability. This dissertation presents a phase-field-based multiscale modeling framework to fundamentally understand the dendrite growth mechanism, theoretically interpret the experimental phenomena, and guide the Li metal battery design. The stability and functionality of the solid electrolyte interphase (SEI), i.e. the passivation layer between anode and electrolyte, play critical roles in maintaining a decent battery cycle life as well as calendar life. This becomes even more critical for Li metal anode, which is subjected to large volumetric and interfacial variations during Li plating and stripping. However, there is currently a lack of comprehensive understanding of Li metal/SEI interfaces and their electrochemical and mechanical properties, as well as the SEI growth mechanism at Li metal anode. In this thesis, we employed combined atomistic calculations and experimental techniques to study SEI. Using density function theory (DFT) calculations, we evaluated the interfacial energetics, density of states (DOS), and electrostatic potential profiles of two interfaces, LiF/Li and Li2CO3/Li, at Li metal anode. The calculation results suggest higher interface mechanical stability at the Li2CO3/Li interface but better electron tunneling leakage resistance at the LiF/Li interface. Experimentally, we employed an isotope-assisted time-of-flight secondary ion mass spectrometry (TOF SIMS) method to reveal a “bottom-up” formation mechanism of SEI growth. It is found that the topmost SEI near the electrolyte formed first and the SEI near the electrode formed later during the initial formation cycle. This growth mechanism was then correlated to the electrolyte one-electron and two-electron reduction reaction dynamics, which in turn explains the formation of two-layered organic-inorganic SEI composite structure. These results provide physical interpretation for the mesoscale phenomena and thus valuable insights for advanced electrode protective coating design. Continuum models have been widely used in attempts to understand and solve the Li dendrite growth problem at mesoscale. However, the limited availability and the accuracy of input physical parameters often limit the predictive power of existing continuum simulations. We hereby developed a multiscale model for a metal electrodeposition process based on the phase-field method and transition state theory by connecting the atomic level charge-transfer physics to the mesoscale morphological evolution. With this model, we discovered that the difference in cation de-solvation-induced exchange current is mainly responsible for the dramatic difference in dendritic Li-plating and smooth Mg-plating. This study not only reveals the physical origin of Li dendrite growth, but also provides a strategy to design dendrite-free Li-ion battery anodes guided by this multiscale model integrating the phase-field method and atomistic calculations. All-solid-state battery is a promising solution to suppress Li dendrite growth. However, recent experimental observation of mechanically-hard ceramic solid electrolytes such as LLZO indicates intergranular dendrite penetration. To understand the Li plating behavior in solid electrolytes, we further extended the multiscale phase-field model of Li dendrite growth by incorporating multiphase solid mechanics and explicit dendrite nucleation. This model helps elucidate the mechanism of major failure modes in a wide range of existing solid electrolyte systems, such as dendrite penetration, intergranular growth and isolated nucleation.