Tuning the Reactivity of Electrolyte Solvents on Lithium Metal by Vinylene Carbonate

Abstract

Organic solvents undergo degradation reactions when in contact with lithium metal. These reactions form a layer of decomposition products that partly prevents further electrolyte decomposition—passivation. Still, the chemical processes in this system are complex and have not yet been fully understood though it is of high relevance for lithium metal batteries. Scanning Electrochemical Microscopy (SECM) in feedback mode as well as GC-MS are used for analyzing the interface as well as soluble decomposition products. SECM data show that the native interface thickness on metallic lithium from ethylene carbonate (EC) and ethyl methyl carbonate (EMC) electrolyte solutions is reduced by approx. 98% by adding 5 wt% vinylene carbonate (VC) to the solution. The addition of VC changed significantly the dynamics of the growth of the deposition layer. GC-MS studies of the EC:EMC electrolyte solution proof an ongoing reaction of the metallic lithium with the electrolyte even after several days. In comparison, the addition of VC appears to stabilize the interface and no decomposition products could be identified. It is concluded that the addition of VC to the electrolyte solution from EC:EMC prevents the trans-esterification of EMC by surface passivation and not by scavenging alkoxides as claimed in literature.