Metal oxide cluster-integrated polymer networks for robust solid-state single-ion conduction at high temperatures†

Ion conduction at high temperatures is critical for the improvement of working efficiency and stability of energy-conversion and -storage devices. Ceramics and highly rigid polymers are generally applied for achieving this; however, their poor processability and mechanical properties hinder their extensive applications. Herein, a sub-nanometer anionic metal oxide cluster ({V₆O₁₃[(OCH₂)₃CR]₂}²⁻) was covalently integrated into polymer networks for high-temperature solid-state conduction of H⁺ and Li⁺ single-ion electrolytes. The hexavanadate cluster was functionalized with acrylate groups, and it served as a nanoscale bifunctional crosslinker to copolymerize with poly(ethylene glycol) methacrylate for the fabrication of polymer networks. The associated counter-cations of the immobilized hexavanadate could be fully solvated in the melts of poly(ethylene glycol) for realizing high mobilities, contributing to promising single-ion conductivities and achieving an Li⁺ transference number of 0.84. According to dielectric spectroscopy studies, the transport of Li⁺ ions was directly mediated by side chain dynamics. The counter-cations could be feasibly switched for the conduction of various cations, such as H⁺ and Li⁺. Meanwhile, the covalent and supramolecular interactions between the polymer and inorganic hexavanadate afforded enhanced stability and robust ionic conduction at temperatures as high as 200 °C. Thus, this work provides versatile platform chemical systems for robust solid-state single-ion conduction at high temperatures.