Ionic conductive cellulose-based hydrogels for Al-air batteries: Influence of the charged-functional groups on the electrochemical properties

Abstract

Gel electrolytes for aluminum-air (Al-air) primary batteries were prepared based on hydroxyethyl cellulose (HEC) and acrylate monomers bearing differently charged functional groups (i.e., -COOCH2CH2N+(CH3)3Cl−, -COO- and -COOCH2CF3). The acrylate monomers were grafted from HEC backbone and crosslinked using methylenebisacrylamide (MBA) to obtain hydrogels with tuned mechanical (15–75 kPa), morphological (pore size 35–125 μm) properties and varied swelling degrees at alkaline electrolyte (900–2500%). Electrochemical measurements were performed on Al-air cells assembled from Al anode, gel electrolytes (in 1 M NaOH) and carbon-based air-cathodes containing silver fine particles (Ag-FPs). Hydrogels with quaternary ammonium salt (HEC-AEtMACl) showed very long discharge time (6.5 h) compared to 1.8 h with the fluorinated hydrogels (HEC-TFEMA) and 1.1 h with carboxylated hydrogels (HEC-AA). Also, HEC-AEtMACl showed the highest current peak (3.9 μA at 1.4 V). Polarization curves proved that the anodic polarization behavior is dominant resulting from the anodic parasitic reaction. The Electrochemical Impedance Spectroscopy (EIS) evidenced that HEC-TFEMA has ionic conductivity (34.4 mScm−1) higher than that of HEC-AEtMACl. However, the highest specific capacity was observed to HEC- AEtMACl 0.928 mA h/cm2 compared to 0.26 and 0.15 mA h/cm2 for HEC-TFEMA and HEC-AA respectively.