Origin and mitigation of premature dead Li formation at the current collector interface in high energy batteries

Abstract

Lithium metal battery (LMB) performance is strongly influenced by both Li deposition and stripping processes, which are closely related to the properties of the solid-electrolyte interphase (SEI). While most research focuses on optimizing Li deposition morphology, the stripping process and factors impacting its efficiency are often overlooked. In this study, we use cryo-electron microscopy (cryo-EM) and energy-dispersive X-ray spectroscopy (EDS) to analyze the structural and compositional properties of SEI films formed on both Li and Cu, investigating their respective roles in the stripping process. Our findings reveal that low-performing electrolytes exhibit dissimilar Li and Cu SEI compositions, which promote severe pinching near the base of the deposited Li metal, resulting in incomplete stripping and reduced Coulombic efficiency. In contrast, high-performing electrolytes display similar Li and Cu SEI compositions, which support uniform stripping and improve battery performance. This work highlights the critical role of achieving Li and Cu SEI compositional similarity to enhance stripping efficiency, offering valuable insights for future electrolyte design.