Investigation of Electron Transfer Properties of the SEI on Metallic Lithium Electrodes by SECM at Open Circuit

The electron transfer at metallic lithium was characterized using the feedback mode of scanning electrochemical microscopy (SECM) and 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB) as redox mediator at open circuit. As a result the solid electrolyte interphase (SEI) at Li is not passivating towards DBDMB as redox mediator. In comparison to charged graphite composite electrodes, the electron transfer rate is smaller at Li and the ranges for the electron transfer rates at both electrodes overlap. Both, graphite composite and Li electrodes show a local variation of electron transfer rates and temporal changes within a time span of hours. In addition, significant short term changes of SEI passivity occur at both electrodes. However, the frequency of such events is smaller for metallic Li then on graphite.