Abstract:

Objective This study aims to address the poor hydrophilicity, low voltage, and rigid structure of piezoelectric separators in self-charging systems that lead to energy loss. The research focuses on substituting traditional polyvinylidene fluoride (PVDF) with polyacrylonitrile (PAN) piezoelectric nanofiber membranes in self-charging supercapacitor (SCSPC), in order to enhance the piezoelectric and self-charging performance of the devices. This innovation is crucial for advancing flexible and integrated energy storage solutions.

Method The study employed electrospinning technology to produce PAN and PVDF nanofiber membranes. The process involved the polarization and stretching of PAN fibers to achieve excellent hydrophilicity, high piezoelectric performance, and superior mechanical properties. The electrochemical performance of the resulting SCSPC was evaluated through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) tests, and piezoelectric output measurements. The structural and morphological properties of the fibers were analyzed using scanning electron microscopy (SEM) and dynamic contact angle testing.

Results The PAN nanofibers exhibited significant improvements over PVDF in several aspects. For morphology and mechanical properties, the PAN fiber membrane had a uniform diameter (450 nm), higher porosity (60%), and greater mechanical strength (8.2 MPa) compared to the PVDF counterpart (2.7 MPa). The higher porosity facilitated efficient electrolyte infiltration, and the superior mechanical strength ensured durability under mechanical stress. In terms of hydrophilicity, the PAN membranes demonstrated exceptional hydrophilicity with a contact angle of 0°, compared to the hydrophobic nature of PVDF whose contact angle 121°. This feature would enhance the ionic conductivity within the SCSPC. On piezoelectric performance, the PAN-based devices generated a higher piezoelectric voltage output (4.4 V) and maintained stability over 20 000 cycles, while the PVDF devices showed lower output of 2.9 V and reduced stability after 13 000 cycles. For electrochemical performance, the PAN-based SCSPC exhibited a high specific capacitance of 138 mF/cm² at a current density of 2 mA/cm², significantly outperforming the PVDF-based SCSPC whose specific capacitance was 42 mF/cm². The designed PAN-based devices retained 94.2% of their capacitance after 5 000 compression cycles, compared to 55.1% for the PVDF-based devices uder the same cyclic loading. In terms of self-charging capability, the self-charging voltage of the PAN-based SCSPC reached 132.8 mV under mechanical stress, far exceeding that of the PVDF-based systems (84.6 mV) and traditional piezoelectric nanogenerators with rectifiers (32.3 mV). This demonstrates efficient mechanical-to-electrical energy conversion without additional rectifiers, reducing energy loss.

Conclusion The study highlights the superior performance of the PAN piezoelectric nanofiber membranes over the traditional PVDF membranes in SCSPC. The enhanced hydrophilicity, mechanical strength, piezoelectric output, and electrochemical stability of PAN-based devices demonstrate their potential for flexible, high-performance energy storage applications. The findings suggest that the PAN nanofiber membranes are promising candidates for developing advanced self-charging technologies, overcoming the limitations of conventional materials and paving the way for practical applications in wearable and portable electronics. This research provides a foundational understanding for the future design and implementation of efficient, self-powered energy systems.

Key words: piezoelectric separator, electrospinning, self-charging supercapacitor, polyacrylonitrile, nanogenerator