High Ion Conducting Nanohybrid Solid Polymer Electrolytes <i>via</i> Single-Ion Conducting Mesoporous Organosilica in Poly(ethylene oxide)

Abstract

A novel mesoporous silica-based single-ion conductor for lithium-ion batteries was prepared via two-step selective functionalization of designated silica precursors into the inner pore wall of mesoporous silica. 2-[(Trifluoromethanesulfonylimido)-N-4-sulfonylphenyl]ethyl (TFSISPE) group was first incorporated as a silica precursor having an anionic weak-binding imide group, and a dense brush of oligo-poly(ethylene glycol) (oligo-PEG) moieties, solvating Li+, was cografted to produce functionalized mesoporous silica (FMS-TFSISPE) nanoparticles. FMS-TFSISPE showed a 2D hexagonal nanopore structure and a regular spherical shape with an average diameter of 50 nm. Poly(ethylene oxide) (PEO) was used to form a dispersion of the mesoporous silica nanoparticles into the polymer matrix. This new polymer–mesoporous silica nanohybrid solid electrolyte with the sole mobile Li ions (FMS-TFSISPE-PEO) exhibits attractive electrical, mechanical, and electrochemical properties. The ionic conductivity and storage modulus both increase simultaneously upon addition of FMS-TFSISPE nanoparticles. A 30 wt % amount of FMS-TFSISPE nanoparticles leads to the highest ionic conductivity (σDC ∼ 10–3 S/cm at 25 °C) and storage modulus (G′ ∼ 104 Pa at 30 °C) with a high lithium-ion transference number (tLi+ ∼ 0.9). Compared to conventional nonporous silica nanoparticles-incorporated PEO matrix (SiO2-TFSISPE-PEO), FMS-TFSISPE-PEO exhibits 2 orders of magnitude higher ionic conductivity with lower activation energy, suggesting that the facile transportation of lithium ions is achieved through the continuous weak-binding and solvating nanopore channel of the mesoporous silica retaining a high surface area and pore volume.