MSE Early Distinguished Scholar Award Seminar: Investigating the Interfacial Evolution of Lithium Metal in Anode-Free Solid-State Batteries

Abstract: Lithium-ion batteries have powered consumer electronics for decades, and continued advancements have enabled the rapid growth of the electric vehicle market. However, increased energy density and specific energy are necessary to facilitate further expansion of electric vehicles and to enable emerging technologies such as electric flight. “Anode-free” battery architectures are a particularly promising technology as they feature no active material at the anode current collector and therefore substantially increase the volumetric energy density compared to standard lithium-ion batteries. While promising, challenges arise from limited lithium-ion inventory in the cell and the uncontrolled morphological evolution of lithium. Thus, to advance this technology, it is critical to understand how lithium deposits and strips on current collectors throughout cycling while also investigating methods to spatially control these processes. Previous work examined the effects of alloy interlayers in liquid electrolyte systems via operando optical microscopy, finding that silver interlayers enable higher Coulombic efficiencies (CEs) than bare current collectors and cause different deposition and stripping dynamics. Silver layers have also shown beneficial effects in enabling long-term cycling of solid-state batteries (SSBs).

In this seminar, we will examine the evolution of lithium metal in anode-free SSBs and the effects of alloy interlayers as probed through electron microscopy and x-ray computed tomography (CT). Improved CEs are observed using silver and gold interlayers compared to bare copper. Performance improvements are investigated using focused ion beam (FIB) and x-ray CT to probe the buried solid-solid interface. We observe non-uniform growth on bare copper throughout cycling while uniform lithium growth is observed in silver- and gold- modified interfaces. Interestingly, we observe distinct morphological evolution comparing both alloy interlayers, which also affects cycling behavior. Electrochemical impedance spectroscopy (EIS) is used to understand and investigate the influence of the alloy interlayers and correlate to morphology evolution. We observe that over the first five cycles, bare copper electrodes exhibit a relatively large increase in impedance while the alloy modified interfaces display a small shift in impedance throughout cycling. Operando EIS measurements taken during deposition and stripping show large contact loss signatures for the bare Cu while the alloy modified interfaces lack such a signature. Additionally, we will explore different lithium growth modes as captured through operando x-ray CT, where both uniform and dendritic lithium growth have been observed. Overall, this work provides new understanding of interfacial modification at solid-solid interfaces in SSBs, which will be important for engineering anode-free SSBs.

Bio: Stephanie Sandoval is a postdoctoral scholar at Georgia Tech. She completed her Ph.D. in materials science and engineering in Professor Matthew McDowell’s group at Georgia Tech in 2023, where her doctoral work focused on probing the growth evolution of lithium metal in anode-free batteries through electron microscopy and synchrotron x-ray computed tomography. She earned her B.S. in electrical engineering from the University of Arkansas in 2018. Throughout her Ph.D., Sandoval was awarded several fellowships, including NSF GRFP, Alfred. P. Sloan Fellowship, the National GEM Fellowship and the DOE SCGSR.