Performance research of the aluminum-air battery with the alkaline PVA/PVP hybrid hydrogel electrolyte

Abstract

Aluminum-air batteries (AABs) own many benefits including high energy densities, rich aluminum reserves, and environmental friendliness. For an AAB as a power source for the low-power microelectronics, the aqueous electrolyte leakage is its underlying problem. To tackle this issue, AABs adopt the hydrogel electrolytes. The hybrid hydrogels are prepared by physically crosslinking the polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) substances through thrice freezing-thawing processes. First, the four hydrogels with the different PVA:PVP mass ratios are characterized by the SEM, FTIR, and XPS tests. These results demonstrate the PVA/PVP hybrid hydrogels successfully introduce the PVP substance. The swelling rate of the PVA/PVP hydrogels increases with the PVP addition and the water retention ratio is the largest at 4:1 PVA:PVP ratio. By soaking these hybrid hydrogels into 6 mol L⁻¹ KOH electrolyte for 24 h, the alkaline PVA/PVP hydrogel electrolytes are formed. At the 4:1 PVA:PVP mass ratio, the alkaline stability of the hydrogels is strongest and its ionic conductivity (403.2 ± 2.1 mS cm⁻¹) is highest. Then, under the various PVA:PVP mass ratios, KOH concentrations, and PVA/PVP hydrogel electrolyte thicknesses, the PVA/PVP-based AAB performance is assessed. At the 4:1 PVA:PVP mass ratio, 8 mol L⁻¹ KOH solution, and 6 mm thick hydrogel electrolyte, the AAB achieves an optimal performance. Its peak power density is 47.0 ± 2.2 mW cm⁻² and limiting current density is 117.0 ± 9.2 mA cm⁻². Finally, the AAB stack from two PVA/PVP-based AABs connecting in series can light 40 LEDs.