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

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. A facile way to produce the pseudo-hexagonal γ-phase nylon-11 nonwoven fibers by electrospinning process with tailored HFIP:TFA (75:25 mol%) solvent mixture was demonstrated. The non-woven mat type γ-phase nylon-11 fibrous membrane allows us to fabricate the piezoelectric device, exhibiting decent electrical output current densities under a periodic vertical pressure. Furthermore, γ-phase nylon-11 fibrous membrane provides stable electrochemical performance when being applied as separator in Na metal battery, suggesting its potential in the energy harvesting and storage fields. [Display omitted] •A metastable pseudo-hexagonal γ-phase Nylon-11 fibers was successfully fabricated using the tailored co-solvent system.•The electrospun γ-phase Nylon-11 fibrous membrane exhibited a piezoelectric response under a periodic external pressure.•The γ-phase Nylon-11 separator showed a decent Na metal battery performance.