Guide for characterizing polymeric electrolytes in rechargeable solid-state Li and Na batteries

Solid polymer electrolytes (SPEs) present a promising alternative for rechargeable batteries with aprotic liquids. Although SPEs were extensively researched for several decades, recent studies have gained momentum in response to growing demand for safer battery options. While various electrochemical and spectral methods for characterizing polymeric electrolytes were proposed, a comprehensive guide to support future investigations appears lacking. Here, we propose a working protocol to derive parameters that characterize SPEs as crucial components of battery systems. An overview of various methods is provided, with particular emphasis on simple impedance measurements for extracting electrochemical parameters. We underscore the significance of considering the interfaces within the battery, specifically the electrolyte-anode and electrolyte-cathode interfaces. Post-mortem analysis is discussed along with the challenges it entails. A summary table detailing the extracted parameters, the corresponding characterization methods, and their applications is provided.