Nanomanufacturing: Size-Dependent Lithium Solubility in Alloy Anodes
Abstract: It is well known that when the length scale of materials decreases from macroscale to nanoscale, the fraction of surface atoms with respect to the bulk increases, resulting in an increase in the excess surface energy. Therefore, the overall Gibbs free energy of nanostructured materials is higher than that of their bulk counterparts (Gibbs-Thomson Effect). Understanding the impact of the excess surface energy on the charge storage mechanism of nanostructured materials used as battery electrodes is critical. In the first part of this talk, I will show that the excess surface energy in nanoporous alloy anodes used to store lithium causes both the solubility limit of lithium in these alloys to increase with decreasing size, and the charge storage mechanism to proceed through a nonequilibrium phase transformation pathway, unlike their bulk counterparts. The formation of nonequilibrium phases and complex phase morphologies contributes to stress and interfacial energy that can lead to early cell failure [1]. In the second part of this talk, I will use model nanoporous gold anodes to investigate the degradation behavior of nanostructured alloy anodes during cycling. Transmission electron microscopy and small-angle X-ray scattering are performed across several length scales on nanoporous alloy anodes cycled to various sequential charge states. By coupling these data sets, we propose a general model for the degradation of the solid-electrolyte interphase (SEI) and changes in anode morphology during the early stages of cycling in nanoporous alloy anodes: (i) during lithiation, active material nanoparticles created by material pulverization during volume expansion become trapped in a thick SEI layer; and (ii) during delithiation, a bimodal, hierarchical nanoporous morphology forms, and the SEI and nanoparticles formed during lithiation delaminate from the framework due to volume contraction [2].
Dr. Eric Detsi is an Associate Professor in Materials Science and Engineering at the University of Pennsylvania and Undergraduate Chair. He received his B.Sc. (2006), M.Sc. (2008), and Ph.D. (2012) degrees in Applied Physics at the University of Groningen in the Netherlands. Before joining Penn, he conducted research at the Department of Chemistry at UCLA (2013-2016) as a Dutch Science Foundation Rubicon Postdoctoral. His current research involves using liquid metals and non-precious nanoporous materials such as nanoporous zinc, magnesium, aluminum, silicon, antimony, and tin for electrochemical energy conversion and storage.
