This is the peer reviewed version of the following article: Fu, L., Wang, X., Wang, L., Wan, M., Li, Y., Cai, Z., Tan, Y., Li, G., Zhan, R., Seh, Z. W., Sun, Y., A Salt‐in‐Metal Anode: Stabilizing the Solid Electrolyte Interphase to Enable Prolonged Battery Cycling. Adv. Funct. Mater. 2021, 2010602. https://doi.org/10.1002/adfm.202010602, which has been published in final form at https://doi.org/10.1002/adfm.202010602. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.