Intrinsic variability of lithium metal foils and its impact on rechargeable battery performance

Lithium metal anodes (LMAs) offer unrivaled theoretical capacity and the lowest electrochemical potential among practical anode materials, making them central to high energy density battery chemistries. Yet in most studies, the lithium foil itself is treated as a nominally interchangeable component, and the impact of its intrinsic variability on cell behavior remains poorly quantified. Here we systematically investigate how initial-state properties of commercial lithium foils influence electrochemical performance. Using a diverse sample set of 17 foils spanning manufacturing routes, thicknesses, and storage histories, we quantify key bulk, surface, and microstructure descriptors. By utilizing a combination of electrochemical measurements, surface optical and wetting characterization, and structural and chemical analyses, we correlate initial state descriptors to plating/stripping behavior in Li||Cu cells and capacity retention in Li||NMC622 full cells. Our results reveal that lithium inventory, surface passivation state, and microstructure each play distinct and complementary roles in governing cell performance. True lithium inventory primarily dictates the onset of lithium depletion. Optical lightness and electrolyte contact angle, which reflects the degree of surface passivation, correlates with the overpotential in electrochemical process; microstructural features such as grain size and texture influence stripping/plating homogeneity and the evolution of interfacial morphology. On this basis, we propose a practical workflow and set of screening criteria for lithium-foil quality assessment prior to cell assembly, combining simple, experimentally accessible metrics with targeted structural and chemical analysis when needed. The framework provides mechanistic insight into how variability in commercial lithium foils translates into cell-level behavior and offers actionable guidance for material selection, processing, and storage in lithium-metal battery development.