A robust, efficient ion transport polytetrafluoroethylene fibrous membrane-based separator with superior stability for ultralong-life zinc ion hybrid supercapacitors

Abstract

Zinc ion hybrid supercapacitors (ZHSCs) can function as a promising electrochemical energy storage system because they combine the high power characteristic of supercapacitors with the high energy capacity of zinc-ion batteries. However, Zn dendrite formation severely restricts the cycle life of ZHSCs. It has been demonstrated that separators with high mechanical strength significantly prolong the cycle life of zinc-metal anodes. Herein, a hydrophilic polytetrafluoroethylene (PTFE)-based separator with high mechanical strength was fabricated by introduction of a mixture of sodium dodecyl sulfate (SDS), polyacrylic acid (PAA), and titanium dioxide (TiO₂) nanoparticles into a PTFE fibrous membrane via a simple suction filtration method. The SDS/PAA/TiO₂/PTFE separator with a thickness of approximately 56 μm possessed high tensile strength (stress 81.2 MPa at 17.5% strain), superior to that of glass fiber (GF) separators (stress 0.3 MPa at 1.0% strain), and suppressed dendrite growth. Also, the SDS/PAA/TiO₂/PTFE separator exhibited promising electrolyte affinity, satisfactory electrolyte uptake (348%), high ionic conductivity of up to 15 × 10⁻³ S cm⁻¹ in 2 M ZnSO₄ aqueous electrolyte, and appropriate porosity (55%). As a result, the ZHSCs based on PAA/SDS/TiO₂/PTFE separator exhibited outstanding electrochemical performance with specific capacitance (65 F g⁻¹) and excellent cycling stability (98.03% retention at 8000 cycles). This work provides new perspectives into the design of PTFE-based separators, and will expand the applications of PTFE by the use of a novel composite separator for the rapid charging of safe electrochemical energy storage devices.