Toward Efficient Development and Reliable Benchmarking of Novel CAM Coatings for Solid State Batteries

Electro-chemo-mechanical degradation phenomena at the CAM|solid electrolyte interface lead to both impedance growth and capacity fading in solid state batteries (SSBs). Driven by this, protective coatings on cathode active materials (CAMs) have emerged as a key strategy to mitigate interfacial degradation in SSB composite cathodes. Currently, the development of novel protective CAM coatings is hindered by poor comparability and benchmarking issues, due to non-standardized testing protocols. Moreover, even within a single laboratory, coating optimization remains challenging, as performance strongly depends on processing parameters that cannot be efficiently explored through long-term cycling alone. Here, we present a systematic benchmarking approach to isolate and quantify the coating effect on interfacial stability. Our two-step workflow combines X-ray photoelectron spectroscopy (XPS) for pre-characterization of coating coverage and thickness with a standardized, time-efficient electrochemical testing protocol that delivers quantitative results within one week. We demonstrate that even short-term benchmarking can reveal significant performance differences across coatings and process routes. In addition, we critically discuss challenges associated with long-term testing and impedance analysis, as well as general considerations regarding interlaboratory benchmarking and the comparability of CAM coatings. Overall, the proposed approach provides a framework to guide coating optimization and accelerate the development of stable, high-performance SSBs.