Le-Yen Lin, Chia‐Chin Chen
High Resolution Image Download MS PowerPoint Slide Solid-state battery electrodes rely on complex multiphase architectures, comprising active materials, solid electrolytes, and carbon additives, to sustain mixed ionic–electronic transport. However, such inherent structural heterogeneity gives rise to intricate electrode kinetics that conventional homogeneous models fail to capture, obscuring critical transport bottlenecks and hindering rational electrode design. Here, we establish a physically grounded framework that elucidates the microstructural origin of electrochemical impedance and lithium transport kinetics by explicitly accounting for geometric heterogeneity and interfacial carrier selectivity. By developing a generalized transmission line model, we quantitatively resolve the non-ideal transport behavior intrinsic to composite electrodes. Furthermore, simulation-derived lithium mapping reveals that particle geometry governs a dimensional transition in diffusion pathways, while non-ideal contacts induce current redirection, phenomena that are invisible to macroscopic averaging. Our approach provides a mechanistic foundation for interpreting mixed ion–electron transport in complex electrochemical systems and offers critical design principles for optimizing fast-charging solid-state batteries.