Understanding Li$^+$ transport at polymer||inorganic interfaces is crucial for developing composite electrolytes in solid-state batteries. In our investigation, we employed impedance spectroscopy and established a multilayer methodology for assessing Li$^+$ transport at this interface. The inorganic phase chosen was Li 6.25 Al 0.25 La 3 Zr 2 O 12 ( Al−LLZO), and the organic phase comprised a Poly(ethylene oxide) (PEO) network with dangling chains. Li$^+$ incorporation in the polymer, as a free either salt or associated with anion grafting onto the PEO network, was explored. Additionally, the PEO network was either pressure-adhered to the inorganic surface (ex-situ configuration) or synthesized onto the Al−LLZO surfaces (in situ configuration) to investigate processing effects on Li$^+$ transport. Using a Transmission Line Model for impedance data analysis, our study identified two key elements governing Li$^+$ transport at the interface: R$_i$, representing resistance along the ionic pathway, and R$_t$ and C$_t$, describing distributed resistance and capacitance within the interface. We observed that R$_i$ is influenced by the polymerization process in the presence of Al−LLZO ceramic, while R$_t$ remains constant regardless of the synthesis method. This suggests varying Li$^+$ concentrations at the interphase in the in situ configuration, while interface/interphase heterogeneity remains consistent across configurations. The estimated activation energy indicates more energetically favorable direct Li$^+$ transport in the in−situ configuration.