Determination of the Exchange Current Density With Polymer Electrolytes and Its Correlation With Coulombic Efficiency

Polymer electrolytes are promising materials to enable practical lithium-metal batteries for high-energy-density energy storage. Yet, parasitic side reactions at the lithium|polymer interface and inhomogeneous lithium deposition, compromising cycling reversibility and safety, remain a challenge. Despite the key role of the interfacial reactivity, there is a lack of quantitative and comparable information on interfacial charge–transfer kinetics with polymer electrolytes, and their impact on the lithium plating/stripping behavior remains unclear. Therefore, in this work, we apply a validated method for quantifying interfacial charge–transfer kinetics via the exchange current density j0 to a series of polyethylene oxide (PEO)-based polymer electrolytes to clarify how the electrolyte composition influences interfacial kinetics. By combining the j0 analyses with measurements of the solid electrolyte interphase resistance and lithium cycling reversibility, we identify a consistent trend in which smaller j0 and higher RSEI values correlate with higher Coulombic efficiencies. This indicates that moderated interfacial kinetics and a sufficiently passivating interphase favor higher plating/stripping reversibility. The results provide a coherent dataset of interfacial charge–transfer parameters for polymer electrolytes and highlight the importance of deliberate electrolyte and interphase design for achieving highly reversible lithium-metal cycling in polymer-based electrolyte systems.