Electrochemical and physical properties of poly(acrylonitrile)/poly(vinyl acetate)-based gel electrolytes for lithium ion batteries

Polymeric gel electrolytes have been extensively studied for application in lithium ion batteries, since the electrolyte can be fabricated as a thin film leading to major performance improvements. This is mainly due to the higher ionic mobility and the higher concentration of charge carriers, yielding ionic conductivities of about 10−3 S cm−1 at room temperature and sufficient mechanical strength. PAN-based gels have been studied together with a wide range of plasticizers and tested in lithium battery systems with excellent results. Based on these results, we developed PAN-based gels with EC:PC and EC:DMC mixtures as plasticizers, LiClO4 or LiBF4 as the ionic salt and the copolymer PAN–PVA as the polymeric matrix to be used as separator and electrolyte in lithium ion batteries. The choice of the copolymer was made due to its hydrophobic properties, low cost and easy access, since it is widely used in textile industries as precursor for acrylic fibers manufacture. These new electrolytes were characterized by electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in order to determine their stability window and conductivity. The charge/discharge performance of the PAN–PVA-based gel electrolytes was investigated for two different systems: Li/gel/LiMn2O4 and Li/gel/Pani (Pani = polyaniline). FT-IR analyses showed that PAN–PVA is not a passive polymer host but an active component in the gel, where Li+ ions are located close to C= O groups of the plasticizers and C≡N groups of PAN. In addition to ionic conductivities higher than 10−3 S cm−1, these gels presented excellent electrochemical and chemical stabilities, which means a slight increased performance when compared to PAN-based gels only, and suitable charge/discharge profiles.