Multi-scale alignment in highly piezoelectric polyacrylonitrile nanofibers separator for advanced self-charging supercapacitor

Self-charging supercapacitor (SCSPC) is an integrated device that can convert mechanical energy into electrical energy and store it to power microelectronics without need a rectifier for DC conversion. Here, we report a multi-alignment design idea for polyacrylonitrile (PAN) piezoelectric nanofiber instead of traditional polyvinylidene fluoride (PVDF) as a separator in SCSPCs, which greatly improves device self-charging performance and index. The combination of synergistic effect of polarization and the stretching process in electrospinning technology can achieve PAN nanofibers orderly arrangement at macroscopic level and alignment of conformation and cyano groups at microstructural level, resulting in excellent hydrophilicity (contact angle 0 °), high piezoelectric property (3.80 μW at a load resistance of 1 MΩ), high mechanical property (7.77 MPa), and outstanding cycling stability (unchanged after 22,000 cycles). As a result, the SCSPCs based on PAN piezoelectric separator has a high conversion efficiency of 12.53%, an energy density of 37.60 mJ cm−2 at power density of 1.01 mW cm−2, and a capacitance retention 91.7% after 5000 compressive cycles. The SCSPC@PAN with working area of 4 × 4 cm2 was attached on elbow, shoes, and bicycle tire to collect biomechanical energy and covert mechanical energy into electrical energy and store. Two SCSPC@PAN in series attached on one shoe can light 3.0 V LEDs after working for 40 min. This multi-scale alignment design idea and understanding the relationship between structure of PAN piezoelectric membrane and properties of SCSPC@PAN would provide important basis for design advanced piezoelectric separator for SCSPCs.