Characterization of Li+ Transport through the Organic-Inorganic Interface by using Electrochemical Impedance Spectroscopy

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 Li6.25Al0.25La3Zr2O12 (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.