Elucidation of the Losses in Cycling Lithium-Metal Anodes in Carbonate-Based Electrolytes

Abstract

Because of their higher energy density, compared to lithium-ion batteries, rechargeable lithium-metal batteries have been considered one of the most attractive next-generation energy-storage systems. Uneven deposition of lithium during charge results mainly from two processes. At the peak of lithium dendrites (or lithium hump) a fresh SEI is formed. This freshly formed SEI has a higher concentration of defects, thus higher lithium-ion conductivity. Another mechanism is the preferential lithium-ion conduction at the grain boundaries (GB) in the SEI, at which the concentration of lithium-ion defects is higher than in the bulk of the crystals. During discharge (lithium dissolution), dead lithium, (lithium particles that are electrically disconnected from the current collector) is formed. In this work we studied the effects of several parameters, in carbonate-based electrolytes, on the properties of the SEI and on capacity losses. The effects of vinyl carbonate (VC) and fluoroethylene carbonate (FEC) additives, current density and cycle number on the total capacity loss (QTL, Q deposition—Q dissolution), the capacity needed to repair the SEI after dissolution of lithium (QSEI repair), two types of dead lithium, roundtrip coulombic efficiency and on the correlation among them, will be discussed. Elucidation of these phenomena will lead to the improvement of the lithium deposition/dissolution (charge and discharge) processes in lithium-metal rechargeable batteries.