Constriction and contact impedance of ceramic solid electrolytes

The development of solid-state batteries (SSBs) is hindered by degradation at solid-solid interfaces due to void formation and contact loss, resulting in increased impedance. Here, we systematically investigate the roles of real and unrecoverable interfacial contact areas at the electrode/Li$_6$PS$_5$Cl interface in driving the impedance rise. By controlling contact geometries and applied pressures, we identify their distinct contributions to the impedance spectra and quantify their influence on the interfacial resistance and transport. Experiments reveal that interfacial resistance varies strongly with recoverable contact area and applied pressure following power law scaling, with exponents of -1 and -0.5, respectively. Moreover, distributed contacts result in lower impedance due to smaller potential gradients and a more uniform potential distribution. Continuum simulations of the contact geometries predict interfacial resistances in agreement with experiments. Our work highlights the influence of unrecoverable and recoverable contact losses on SSB impedance while quantifying the effectiveness of mitigation strategies.