Associate Professor of ME, Neil Dasgupta, and Michael Thouless, Arthur F. Thurnau Professor of ME, are the recipients of the 2020 William N. Findley Award. This award is given bi-annually from the department's External Advisory Board in recognition of research involving fatigue in metals and plastics, creep in metals and plastics, or yielding of metals.
Dasgupta and Thouless's paper entitled, "Lithium mechanics: roles of strain rate and temperature and implications for lithium metal batteries," published in the Journal of The Electrochemical Society was selected for this year's award.
The lack of a reliable rechargeable lithium metal (Li-metal) anode is a critical bottleneck for next-generation batteries. The unique mechanical properties of lithium influence the dynamic evolution of Li-metal anodes during cycling. While recent models have aimed at understanding the coupled electrochemical-mechanical behavior of Li-metal anodes, there is a lack of rigorous experimental data on the bulk mechanical properties of Li. This work provides comprehensive mechanical measurements of Li using a combination of digital-image correlation and tensile testing in inert gas environments. The deformation of Li was measured over a wide range of strain rates and temperatures, and it was fitted to a power-law creep model. Strain hardening was only observed at high strain rates and low temperatures, and creep was the dominant deformation mechanism over a wide range of battery-relevant conditions. To contextualize the role of creep on Li-metal anode behavior, examples are discussed for solid-state batteries, "dead" Li, and protective coatings on Li anodes. This work suggests new research directions and can be used to inform future electrochemical-mechanical models of Li-metal anodes.