Physically cross-linked xanthan hydrogels as solid electrolytes for Al/air batteries

This paper presents the results of an experimental study aimed at preparing high-conductivity solid electrolytes for Al-air primary cells, starting from an eco-friendly polysaccharide (xanthan) and KOH or HCl concentrated solutions (up to 11 M). Xanthan permits all-solid-state Al-air cells to be prepared with both KOH and HCl solutions but, differently from the already acquired knowledge, the best performance are obtained with acid electrolytes. The results evidence that different formation mechanisms can explain the ionic conductivities of acid and alkaline gels, and then the cell discharge performance. However, the cell capacities at higher current density are enhanced with acid hydrogels, thanks to the capability of xanthan to inhibit the anodic self-corrosion in an acid medium. In particular, a solid electrolyte prepared with 5 M HCl solution and a xanthan/liquid ratio of 0.7 g/ml provides a cell capacity higher than 70 mAh cm(-2) at discharge current density of 10 mA cm(-2), corresponding to 2.2 Ah g(Al)(-1) consumed (or 1430 Wh kg(-1)).