Role of tin seed layers in SEI evolution and lithium electrodeposition.

Metal batteries employing lithium or sodium anodes offer exceptional energy density but are limited by interfacial instability and uneven metal deposition, particularly in anode-free designs where lithium is plated onto a bare current collector. Here, we demonstrate a rapid and scalable method for depositing tin seed layers on copper current collectors using a replacement reaction commonly employed in the electronics industry, enabling coating from aqueous solutions at room temperature. The resulting tin layer acts as an electronically conductive lithophilic seed that potentially improves solid-solid wetting between lithium and the current collector, promoting more uniform lithium electrodeposition in anode-free cells. The mechanistic roles of the tin seed layer and the solid-electrolyte interphase (SEI) are investigated through lithium-tin alloying and de-alloying processes combined with cyclic voltammetry (CV), scanning electron microscopy (SEM), X-ray diffraction (XRD), and scanning electrochemical microscopy (SECM). Here, we show that the tin seed layer fundamentally alters the interfacial electrochemistry of copper, enabling faster charge transport across the SEI.