Characterization of Stress-Diffusion Coupling in Lithiated Germanium by Nanoindentation

Abstract

There is currently a growing demand for low-cost, high-performance electrochemical energy storage solutions to consumer electronics, vehicle electrification and stationary power management. The successful development and deployment of such solutions necessitate a fundamental understanding of the mechanical properties of electrochemical materials, as well as the intricate coupling between the electro-chemo-mechanical processes in these materials. In this work, we performed a combined experimental and modelling investigation of the stress-diffusion coupling behavior of lithiated germanium (Ge) for its use in high-performance lithium-ion batteries. Thin films of Ge were fabricated using sputtering deposition and then electrochemically lithiated, after which they were subjected to nanoindentation at varying load levels to study indentation-induced creep deformation. Concurrently, a continuum chemo-mechanical model of the nanoindentation test was developed and used to investigate the fundamental mechanisms underlying the stress-gradient-driven creep deformation. The stress-diffusion coupling coefficient and diffusivity of lithium in Ge were obtained by quantitatively comparing the simulated nanoindentation response with the experimental measurements. This integrative experimental and computation work provides important insights into the chemo-mechanical coupling process in high-performance rechargeable battery electrodes.