Role of Scaffold Architecture and Excess Surface Polymer Layers in a 3D-Interconnected Ceramic/Polymer Composite Electrolyte

3D-interconnected ceramic/polymer composite electrolytes offer promise to combine the benefits of both ceramic and polymer electrolytes. However, an in-depth understanding of the role of the ceramic scaffold's architecture, and the associated polymer/ceramic interfaces on the electrochemical properties of such composite electrolytes is still incomplete. Here, these factors are systematically evaluated using an interconnected composite electrolyte with a tunable and well-defined architecture. The ionic conductivity of the ceramic scaffold is strongly dependent on its porosity and tortuosity, as demonstrated experimentally and via theoretical modeling. The connectivity of the ceramic framework avoids the high interfacial impedance at the polymer/ceramic electrolyte interface within the composite. However, this work discovers that the interfacial impedance between the bulk composite and excess surface polymer layers of the composite membrane dominates the overall impedance, resulting in a 1-2 order drop of ionic conductivity compared to the ceramic scaffold. Despite the high impedance interfaces, an improved Li+ transference number is found compared to the neat polymer (0.29 vs 0.05), attributed to the ceramic phase's contributions toward ion transport. This leads to flatter overpotentials in lithium symmetric cell cycling. These results are expected to guide future research directions toward scalable manufacturing of composite electrolytes with optimized architecture and interfaces.

Automated summary

3D-interconnected ceramic/polymer composite electrolytes show potential in combining the advantages of both ceramic and polymer electrolytes. This study systematically evaluates the role of ceramic scaffold architecture and polymer/ceramic interfaces on the electrochemical properties of such composite electrolytes. The findings suggest that the ionic conductivity of the ceramic scaffold is influenced by its porosity and tortuosity, while the interfacial impedance between the bulk composite and excess surface polymer layers dominates the overall impedance. Despite the impedance interfaces, an improved Li+ transference number is observed, leading to flatter overpotentials in lithium symmetric cell cycling.