A salt-derived solid electrolyte interphase by electroreduction of water-in-salt electrolyte for uniform lithium deposition

Abstract Notorious growth of dendritic lithium with low Coulombic efficiency causes safety and stability issues, which hinder practical applications. To control the lithium deposition so that one has a dendrite-free lithium metal anode with high Coulombic efficiency is highly desirable but challenging. Here, this work reports a copper substrate covered by a salt-derived solid electrolyte interphase that produced by electroreduction of a highly concentrated water-in-salt electrolyte to realize stable lithium deposition. Quite distinct from the resistive layer comprised principally of solvent-derived organic species (such as lithium alkyl carbonates) that produced in conventional dilute electrolyte, this salt-derived solid electrolyte interphase is rich in inorganic components (mainly Li2SxOy and LiF), which effectively reduce the overpotential and facilitate fast Li+ transport. In addition, a small number of reduced fluorine organic anions -CFx stabilize the space charge to give a uniform distribution of Li+. Such a solid electrolyte interphase on the copper substrate is able to modulate the lithium plating/stripping to produce uniform spherical lithium deposition with no dendrites, and a high Coulombic efficiency (≈98.2%) is achieved. This work provides a unique strategy to enlarge the functions of the lithium salt decompositions on the protection of lithium metal anodes.