Insights into the Degradation Mechanism of Nanoporous Alloy-Type Li-Ion Battery Anodes

While nanostructured alloy-type anodes are considered potential high-capacity alternatives to intercalation-type graphite anodes, large volume changes inherent to alloy-type anode cycling result in poor cycling performance. In this work, model nanoporous gold anodes are used to investigate the degradation behavior of nanostructured alloy-type anodes during cycling. Transmission electron microscopy and small-angle X-ray scattering are performed across several length scales on 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 morphology during the early stages of cycling in nanoporous alloy-type anodes: (1) during lithiation, active material nanoparticles created by material pulverization during volume expansion become trapped in a thick SEI layer; and (2) during delithiation, a bimodal, hierarchical nanoporous morphology forms, and the SEI and nanoparticles formed during lithiation delaminate from the framework due to volume contraction.