Insights Into the Degradation Mechanisms of Nanoporous Alloy-Type Lithium-Ion Battery Anodes: A Transmission Electron Microscopy and Small-Angle X-Ray Scattering Study

Abstract

Alloy-type lithium-ion battery anodes undergo extremely large volume changes of up to ~300% when lithiated.1 The stresses which arise during volume expansion cause pulverization, which typically cuts off electronic pathways to the active material and leads to battery failure. Previous work has demonstrated that nanostructuring alloy-type anodes into nanoporous metals, which consist of bicontinuous networks of active material and pore space, can extend the lifetime of the anode significantly.1,2 Despite these advances, the fundamental mechanisms by which nanoporous alloy-type materials degrade are not well-understood. In this presentation, I will discuss how we elucidated the (de)lithiation behavior and structural degradation of nanoporous alloy-type anodes using both transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). In particular, we observed the evolution of morphological and microstructural features of nanoporous gold by galvanostatically (de)lithiating it to various states of charge, studying its real-space structure with TEM, and corroborating this with statistically representative reciprocal-space information from SAXS. During lithiation, nanoporous gold develops a thick solid electrolyte interphase region which contains trapped nanoparticles of pulverized active material. When delithiated, the volume contraction causes the SEI along with the trapped nanoparticles to break from the surface, resulting in active material loss and battery failure. In addition, we observed the development of a second porous length scale smaller pores on the nanoporous gold ligaments during delithiation, resulting in a hierarchical nanoporous structure. With this insight, we propose a new model for the degradation of nanostructured alloy-type anodes.3 Key Words: TEM, SAXS, Nanoporous Metals, Energy Storage, Alloy-typeReferences(1) Cho, J. Porous Si Anode Materials for Lithium Rechargeable Batteries. J. Mater. Chem. 2010. https://doi.org/10.1039/b923002e.(2) Cook, J. B.; Detsi, E.; Liu, Y.; Liang, Y.-L.; Kim, H.-S.; Petrissans, X.; Dunn, B.; Tolbert, S. H. Nanoporous Tin with a Granular Hierarchical Ligament Morphology as a Highly Stable Li-Ion Battery Anode. ACS Appl. Mater. Interfaces 2017, 9 (1), 293–303. https://doi.org/10.1021/acsami.6b09014.(3) Corsi, J. S.; Welborn, S. S.; Stach, E. A.; Detsi, E. Insights into the Degradation Mechanism of Nanoporous Alloy-Type Li-Ion Battery Anodes. ACS Energy Lett. 2021, 1749–1756. https://doi.org/10.1021/acsenergylett.1c00324. Figure 1