Lithium-Conducting Self-Assembled Organic Nanotubes

Abstract

<p>Supramolecular polymers are compelling platforms for the design of stimuli-responsive materials with emergent functions. Here, we report the assembly of an amphiphilic nanotube for Li-ion conduction that exhibits high ionic conductivity, mechanical integrity, electrochemical stability, and solution processability. Imine condensation of a pyridine-containing diamine with a triethylene glycol functionalized isophthalaldehyde yields pore-functionalized macrocycles. Atomic force microscopy, scanning electron microscopy, and <i>in solvo</i> X-ray diffraction reveal that macrocycle protonation under their mild synthetic conditions drives assembly into high-aspect ratio (>10<sup>3</sup>) nanotubes with three interior triethylene glycol groups. Electrochemical impedance spectroscopy demonstrates that lithiated nanotubes are efficient Li<sup>+</sup> conductors, with an activation energy of 0.42 eV and a peak room temperature conductivity of 3.91 × 10<sup>-5</sup> S cm<sup>-1</sup>. <sup>7</sup>Li NMR and Raman spectroscopy demonstrate that lithiation occurs exclusively within the nanotube interior and implicates the glycol groups in facilitating efficient Li<sup>+</sup> transduction. Linear sweep voltammetry and galvanostatic lithium plating-stripping tests reveal that this nanotube-based electrolyte is stable over a wide potential range and supports long-term cyclability. These findings demonstrate how coupling synthetic design and supramolecular structural control can yield high-performance ionic transporters that are amenable to device relevant fabrication. More broadly, these results demonstrate the technological potential of chemically designed self-assembled nanotubes. </p>

Divergent Nanotube Synthesis through Reversible Macrocycle Assembly

“…Compared to results for bulk PEO, which has a room temperature conductivity on the order of 10 −8 to 10 −6 S cm −1 , 53 the high conductivity realized within this nanotube highlights the benefit of immobilizing the glycol residues within a well-defined, layered nanotube scaffold. Furthermore, the observed conductivity surpasses the room temperature conductivity of many polymers and framework materials designed for Li + conduction, 40,54 further demonstrating the promise of designed nanotubes in ion-transport applications. Variable-temperature EIS on the lithiated nanotubes yielded an activation energy (E a ) of 0.42 eV (Figure 8C), which is substantially lower than a framework material with a similar functionality (0.87 eV).…”

“…To this end, we designed an amphiphilic nanotube with three interior triethylene glycol groups (STEG-NTs, Figure 8A). 40 Given the long-range order of the nanotubes and the propensity of glycol groups to coordinate Li + , we hypothesized that these supramolecular assemblies would exhibit solid-state Li-ion conduction. Upon lithiating the nanotubes with 1.5 equiv of Li + per macrocycle, a room temperature conductivity of 3.91 × 10 −5 S cm −1 was observed (Figure 8B).…”

“…38 The resulting nanotubes had various pore shapes, channel sizes, and site-specific chemical functionalities, which enabled systematic studies into their ability to conduct protons or Li ions. 38,40 More broadly, this synthetic methodology offers a unified approach to elucidate structure−property relationships underlying emergent nanotube properties and application performance. This Account details the underlying principles of tailored nanotube synthesis and presents new opportunities for expanding the chemical design and technological relevance of synthetic 1D architectures.…”