Elastic, plastic, and creep mechanical properties of lithium metal

Abstract

With the potential to dramatically increase energy density compared to conventional lithium ion technology, lithium metal solid-state batteries (LMSSB) have attracted significant attention. However, little is known about the mechanical properties of Li. The purpose of this study was to characterize the elastic and plastic mechanical properties and creep behavior of Li. Elastic properties were measured using an acoustic technique (pulse-echo). The Young’s modulus, shear modulus, and Poisson’s ratio were determined to be 7.82 GPa, 2.83 GPa, and 0.381, respectively. To characterize the stress–strain behavior of Li in tension and compression, a unique load frame was used inside an inert atmosphere. The yield strength was determined to be between 0.73 and 0.81 MPa. The time-dependent deformation in tension was dramatically different compared to compression. In tension, power law creep was exhibited with a stress exponent of 6.56, suggesting that creep was controlled by dislocation climb. In compression, time-dependent deformation was characterized over a range of stress believed to be germane to LMSSB (0.8–2.4 MPa). At all compressive stresses, significant barreling and a decrease in strain rate with increasing time were observed. The implications of this observation on the charge/discharge behavior of LMSSB will be discussed. We believe the analysis and mechanical properties measured in this work will help in the design and development of LMSSB.