Starch Gel Electrolyte and its Interaction with Trivalent Aluminum for Aqueous Aluminum-Ion Batteries: Enhanced Low Temperature Electrochemical Performance.

This study explores trivalent Al interaction with aqueous starch gel in the presence of two different anions through salting effect. Salting-out nature of Al 2 (SO 4 ) 3 ·18H 2 O with starch gel causes precipitation of starch; this happens due to competitive anion-water complex formation over starch-water interaction, thereby reducing polymer solubility. Salting-in effect of AlCl 3 with starch gel happens through Al 3+ cation interaction with hydroxyl group of starch and increases polymer solubility, making gel electrolyte viable for battery applications. Prepared gel electrolyte exhibits ionic conductivity of 1.59 mS cm -1 and a high t Al 3+ value of 0.77. The gel electrolyte's performance is studied using two different cathodes, the Al|MoO 3 cell employing starch gel electrolyte achieves discharge capacity of 193 mA h g -1 and Al|MnO 2 cell achieves discharge capacity of 140 mA h g -1 @0.1 A g -1 for first cycle. The diffusion coefficient of both cells using starch gel electrolyte is calculated and found to be 2.1 × 10 -11  cm 2 s -1 for Al|MoO 3 and 3.1 × 10 -11 cm 2 s -1 for Al|MnO 2 cells. The Al|MoO 3 cell at lower temperature shows improved electrochemical performance with a specific capacity retention of ≈87.8% over 90 cycles. This kind of aqueous gel electrolyte operating at low temperature broadens the application for next generation sustainable batteries.