Formation of a Lithium-Plated Reference Electrode in Lithium-Ion Cells: Characterization Using Dynamic Impedance and Simulation Using Electrochemical Model

Abstract

Metallic lithium plated onto a micro-sized substrate is widely used as the reference electrode (RE) for inter-electrode separation in lithium-ion cells. The formation process of lithium plating is crucial to the stability of the obtained RE. Dynamic electrochemical impedance spectroscopy (DEIS) is used as a tool to monitor the formation process. A new semi-circle in the spectrum attributed to the emergence of the solid/electrolyte interphase (SEI) film manifests immediately at the moment the formation starts. Ohmic resistances, SEI film resistances and charge transfer resistances all gradually decrease during the formation process, and arrive at their constant values after about 2x104 s. An analytical phenomenological model and a two-dimensional (2D) electrochemical model, accounting for the growth of RE size and the concomitant decrease of electrolyte porosity, are developed to explain the impedance evolution during the formation process and to optimize the plating protocol.