Abstract
Storage particles in lithium-ion batteries swell upon insertion of lithium, generating elastic stresses sufficient to crack them. This phenomenon is studied using a phase field method for fracture encompassing elasticity, lithium insertion and extraction and lithium diffusion within the particle. It is shown that high C-rates, large particles and large swelling strains motivate particle fracture and comminution. In addition, a model is developed for the redox kinetics at an interface between a single ion conducting solid electrolyte and a lithium metal anode with inclusion of the effect of the mechanical stress across the interface, thereby extending the Butler-Volmer equation. This formulation is then used to assess the morphological stability of sinusoidal roughness on the surface of the lithium metal electrode when it is being plated from the single ion conducting solid electrolyte, to which it is bonded. It is found that long wavelength roughness exceeding a critical value will always grow in amplitude. The critical value of the wavelength is proportional to the elastic shear modulus of the electrolyte, and inversely proportional to the current density in and the resistivity of the solid electrolyte. Therefore, any wavelength of roughness can be induced to increase in amplitude if the current density is high enough. The extended Butler-Volmer equation is also used to assess cracking of the solid electrolyte caused by insertion of lithium into a pre-existing flaw. It is found that lithium insertion from the solid electrolyte into the pre-existing flaw causes the lithium to yield plastically, and that pressure in the lithium in the crack builds up very rapidly. This pressure can cause the crack to propagate, thereby inducing dendrite growth that can short circuit the cell. This will occur unless the pressure in the lithium in the crack blocks the redox reaction that is inserting the lithium into it. In addition, the question of whether the lithium can extrude from the crack into the lithium electrode is investigated. It is found that it is likely that the lithium is contained within the crack, thereby enabling it to propagate the dendrite-flaw.
Biography
Robert McMeeking earned a BSc in Mechanical Engineering with First Class Honours at the University of Glasgow, Scotland in 1972. He completed his Ph.D. in solid mechanics at Brown University in 1976 and then was Acting Assistant Professor at Stanford University for 2 years. Thereafter he joined the faculty of the Theoretical and Applied Mechanics Department in the University of Illinois at Urbana-Champaign. He moved to the University of California, Santa Barbara (UCSB) in 1985 as Professor of Materials and of Mechanical Engineering, and was Chair of the Department of Mechanical Engineering 1992-1995 and again during 1999-2003. McMeeking is currently Tony Evans Distinguished Professor of Structural Materials and Distinguished Professor of Mechanical Engineering at UCSB. He is also Sixth Century Professor of Engineering Materials at the University of Aberdeen in Scotland and Leibniz Professor at the Leibniz Institute for New Materials in Saarbrücken, Germany. He has published approximately 300 papers on such subjects as plasticity, fracture mechanics, computational methods, glaciology, tough ceramics, composite materials, materials processing, powder consolidation and sintering, ferroelectrics, microstructural evolution, nanotribology, actuating structures, blast and fragment protection of structures, fluid structure interactions arising from underwater blast waves, the mechanics of the cell and its cytoskeleton, lithium-ion batteries and fuel-cells, embrittlement of alloys and ceramics, adhesion, toughening of elastomers, and the viscoelasticity and fracture of multi-network polymers. McMeeking was Editor-in-Chief of the Journal of Applied Mechanics from 2002 to 2012, and is currently Secretary of the Congress Committee of the International Union of Theoretical and Applied Mechanics and President of the International Congress on Fracture. He is a member of the U.S. National Academy of Engineering, Fellow of the American Society of Mechanical Engineers, Fellow of the U.K. Royal Academy of Engineering and Fellow of the Royal Society of Edinburgh. He held a Humboldt Award for Senior Scientists in 2006, again in 2013, and received a Humboldt Alumni Award in 2018. He was given the Brown Engineering Alumni Medal in 2007, the 2014 William Prager Medal of the Society of Engineering Science, and the 2014 Timoshenko Medal of the American Society of Mechanical Engineers. In 2018 McMeeking was awarded the honorary degree of Doctor of Engineering by the University of Glasgow.