Desenvolvimento e caracterização de membranas PVDF HFP/LiClO4 para aplicações em eletrólitos de estado sólido

Abstract

This work aims at the preparation, characterization, and analysis of PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene)) films doped with lithium perchlorate (LiClO₄) at different concentrations (0%, 2.5%, 5%, 7.5%, 10%, and 12.5% relative to PVDF HFP). Doping with LiClO₄ aims to improve the ionic conductivity of the material, making it potentially suitable for applications in electrochemical devices such as batteries and supercapacitors. PVDF-HFP offers several advantages, such as good flexibility, high thermal stability, and chemical resistance, in addition to good processability, which make it an ideal material for solid-state batteries and other energy storage systems. Its semicrystalline structure and polymeric characteristics allow good control over ionic conductivity, especially when doped with compounds such as LiClO₄, which enhances the electrochemical properties and broadens its applicability in high-performance devices. The films were characterized by means of several analytical techniques: X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), mechanical tensile testing, Fourier-transform infrared spectroscopy (FTIR), and electrical impedance spectroscopy (EIS). XRD analysis was used to investigate the crystalline structure of the films and the formation of the β-phase, associated with improved piezoelectric and conductivity properties. FTIR enabled the analysis of the chemical bonds and interactions between PVDF-HFP and LiClO₄, providing important information about the doping mechanisms and the resulting structural modifications. EIS provided quantitative information on the conductivity of the films; the sample with 7.5% LiClO₄ exhibited the best performance, with the lowest resistance, on the order of 2.0×10⁴ Ω, making it suitable for solid-state battery applications. The thermal analyses (TGA and DSC) demonstrated the high thermal stability of the membranes, with the main decomposition above 450 °C, and indicated that the sample with 7.5% LiClO₄ has the lowest crystallinity of the series, in agreement with its superior conductive performance. The tensile tests revealed that LiClO₄ reduces the stiffness and increases the flexibility of the membranes, with the 7.5% composition also providing the best compromise between mechanical strength and flexibility. These analyses allowed a comprehensive evaluation of the behavior of LiClO₄-doped PVDF-HFP, highlighting its physical, mechanical, and electrical properties for use in advanced electrochemical devices.