Water as Additive Directing Lithium Electrodeposition

Abstract

Electroplating of flat lithium layers is key for batteries using metallic lithium as the anode. For this, an intriguing growth mode is a self-assembled, compact, columnar morphology of electrodeposited lithium. Here, we demonstrate the electrodeposition of columnar lithium from LiTFSI and LiClO4 salts using water as an additive, excluding commonly found explanations of LiF directing growth. We independently investigate the effect of water during electrochemical formation and growth, showing that it is required continuously. The process is studied in situ using a rotating ring-disk electrode. We observe a dynamic passivation process, attributed to the continuous formation/ dissolution of LiOH and Li2O surface layers, accompanied by H-2 evolution and likely LiH formation. Notably, hydrogen is produced in the LiF-based mechanism, suggesting that it is an integral component for directing growth. This homogenizes our results with the literature, providing mechanistic insights on the role of water for the design of electrodeposited lithium morphologies and surface chemistry.