A Rheological Study of Ion-Conducting Ceramic-Polymer Composites as Hybrid Solid-State Electrolytes

As the search for the next generation of Lithium-ion batteries continues, solid state electrolytes, especially those based on highly ion-conductive inorganic oxides and polymers, have garnered considerable attention. Lithium lanthanum zirconium oxide (LLZO) and polyethylene oxide (PEO) have been under particular scrutiny. Hybrid electrolytes composed of ceramic and polymer materials have complementary strengths and weaknesses: LLZO is highly ion-conductive, but mechanically brittle, while PEG is less conductive, but mechanically flexible for easy processing. Yet they are intrinsically incompatible, which leads to poor interfacial contact and ion transport. In this work, we investigate the effect of an interfacial copolymer layer based on polydopamine (PDA) to enhance the LLZO-PEO interaction. Specifically, we hae synthesized PDA-co-PEO polymers of varied molecular weight and characterize the structure and property relationship of LLZO-PDA-PEO composites. To optimize the processibility of casting such hybrid composite films, we have examined their viscoelastic characteristics of composite slurries against varied PDA-PEO molecular weight. Also as increasing the concentration of added PDA-PEO copolymer, a transition from critical gel to viscoelastic solid is observed. We further correlate their viscoelastic properties with measured electrochemical properties of cast composite films to determine optimal additive conditions for LLZO-PEO solid electrolytes for lithium ion battery applications.