Co-solvent induced piezoelectric γ-phase nylon-11 separator for sodium metal battery

Abstract

Nylon-11, the most studied member of the odd-numbered nylon family, is a promising functional material for future electronic devices or energy storage systems. To utilize nylon-11 in those applications, it is necessary to control the formation of the applicable metastable crystal phases such as the piezoelectric γ-phase or ferroelectric δ′-phase. Herein, we describe a facile method of fabricating metastable γ-phase nylon-11 fibers via electrospinning with a tailored solvent system. By using a solvent mixture of 1,1,1,3,3,3-hexafluoro-2-propanol and trifluoroacetic acid [HFIP:TFA (75:25 mol%)], we could fully eliminate the formation of the most stable α-phase and create metastable γ-phase nylon-11 fibers. The electrospun γ-phase nylon-11 fibrous membrane displayed a typical piezoelectric response when it experienced a periodic external force. Furthermore, the γ-phase nylon-11 fibrous membrane exhibited higher thermal stability, electrolyte wettability, and ionic conductivity than the conventional Celgard separator. Consequently, it achieved decent performance when applied as a separator in a sodium metal half-cell. This study indicates that piezoelectric γ-phase nylon-11 fibrous membranes have great potential for further development in energy harvesting and storage, especially as piezo-separators in self-charging power cells.