Optical Detection and Modeling of Lithium Deposition on Copper Current Collectors

ABSTRACT Understanding lithium (Li) deposition on copper (Cu) substrates is essential for improving the performance and lifetime of zero–excess lithium metal batteries. In this study, Li deposition was investigated under realistic coin–cell conditions using complementary scanning electron microscopy and laser scanning microscopy. A semi–automatic image processing workflow enabled quantitative analysis of Li surface coverage and deposit height as functions of current density and deposited charge. Depending on the applied current, Li morphology evolved from isolated hemispherical islands at low current densities to stripe–like structures aligned with the substrate grooves at higher currents. Deposits on rough, dendritic Cu exhibited more compact and vertically oriented morphologies compared to smooth Cu foil. Based on the experimental observations, a phenomenological geometric model was developed to describe Li growth dynamics. The complex transition from isolated island growth to coalesced film formation was captured by a novel combination of a hemispherical growth model and an Avrami–type model with an effective exponent of , which is consistent with numerical simulations. This geometric framework successfully rationalizes the observed dependence of Li morphology and surface coverage on deposition parameters, providing fundamental insights into Li nucleation and growth mechanisms relevant for anode–free battery design.