Identifying Limitations of the Lithium Metal Anode through Laser Plasma Focused Ion Beam Cross-Sectional Imaging

Implementation of lithium metal anodes for high energy density battery applications requires an understanding of the lithium-electrolyte interfacial chemistry to determine possible failure mechanisms. To validate lithium performance, lithium/copper half cells are often cycled in coin cell configurations. After cycling, the electrodes may be characterized after disassembly, however the intricacies at the interface will be disrupted through this process. Through Laser Plasma Focused Ion Beam (Laser PFIB) cross-sectioning, the intact electrode/electrolyte (separator)/electrode stack can be imaged without disrupting the matrix of intermixed solid electrolyte interphase (SEI) and lithium metal. Previously, separator shredding during cycling was identified as a failure mechanism through cross-sectional images obtained using the Laser PFIB.¹ Here, we focus on the lithium electrodeposition/dissolution behaviors in solvate-, carbonate-, and bisalt-based electrolytes after the 1^st and 101^st electrodeposition steps. Due to the highly porous nature of electrodeposited lithium metal, it is found that at best the capacity reaches only about half the theoretical value (1044 mAh/cm³ vs 2045 mAh/cm³). Furthermore, electrolytes shown to cycle with high-efficiency exhibit failure pathways due to increased resistance resulting from continuous SEI evolution or lithium metal consumption at the counter electrode. After cycling, it is found that the practical capacity of lithium metal is reduced to 144 to 342 mAh/cm³, less than the theoretical capacity of graphite (558 mAh/cm³).<br/><br/>This work was funded by Sandia National Laboratories’ Laboratory Directed Research and Development program. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the U.S. DOE or the United States Government.<br/><br/>1. Jungjohann, K. L.; Gannon, R. N.; Goriparti, S.; Randolph, S. J.; Merrill, L. C.; Johnson, D. C.; Zavadil, K. R.; Harris, S. J.; Harrison, K. L., Cryogenic Laser Ablation Reveals Short-Circuit Mechanism in Lithium Metal Batteries. <i>ACS Energy Letters </i><b>2021,</b> <i>6</i>, 2138-2144.