Is All Lithium Created Equal? Effects of Processing Conditions on Lithium Microstructure and Battery Performance

Despite growing interest in rechargeable lithium metal batteries, the influence of anode microstructure on battery performance is often overlooked, largely due to lithium's air sensitivity and low atomic number (<i>Z</i> = 3), which makes it difficult to apply standard characterization methods such as scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). To address this knowledge gap, the present study employs a set of complementary techniques─including SEM, EBSD, and X-ray diffraction (XRD)─to assess the morphology and microstructure of thermally evaporated and commercial lithium films. These investigations show that crystallographic texturing of evaporated lithium is weakly influenced by the substrate's composition and grain orientation, whereas grain size and structure are heavily dependent on film thickness. Significant microstructural variations are also observed for lithium films acquired from three commercial vendors, likely due to differences in manufacturing and processing conditions. Electrochemical measurements demonstrate that the anode's microstructure has a major impact on lithium electroplating/stripping in cells containing either oxide or polymer solid electrolytes. When tested under low stack pressure (<1 MPa), lithium/electrolyte interfacial contact loss was the primary failure mode, and thicker, coarse-grained lithium films (55 vs 4 μm average grain size) significantly enhanced cycling stability for both electrolyte classes. Notably, a direct correlation between microstructure and device performance could not be established for cells containing commercial lithium sources due to variations in other key properties such as the films' surface chemistry and purity. Collectively, these findings highlight the need to better understand and control the anode's microstructure to enable next-generation lithium metal batteries.