Modification of solid electrolyte interphase on deposited lithium metal by large separation between the electrodes in ether-based electrolytes

A thorough understanding of the lithium deposition behavior will facilitate the commercialization of lithium metal anodes. Despite enormous effort, an understanding of the lithium deposition behavior and surface film formation remains a significant challenge. A fundamental investigation of lithium deposition behavior as a function of separation between the counter electrode and the working electrode (2 mm) has been conducted for ether-based electrolytes. The effect of distance is compared with a conventional coin cell with a narrow gap between the electrodes (25 µm). The investigation reveals that lithium deposition in the two cells generates different chemical compositions of solid electrolyte interphase (SEI) on deposited lithium although the morphology of lithium deposition is similar. In the coin cell, a SEI containing a diverse mixture of compounds including LiF, Li2CO3, lithium alkyl carbonates, and Li2O is generated upon deposition of lithium. However, in 2 mm separated cell, the deposited lithium has an SEI dominated by LiF. It is suggested that the large separation between the electrodes suppresses an interaction of the highly concentrated lithium ions released from the counter electrode, which results in different SEI composition compared with the coin cell. The fundamental findings of this work provide insight for further understanding of the correlation between lithium deposition behavior and electrode separation in ether-based electrolytes.