Rechargeable Zinc-Electrolytic Manganese Dioxide (EMD) Battery with a Flexible Chitosan-Alkaline Electrolyte

A high-performing flexible chitosan-based gel electrolyte with poly­(vinyl alcohol) (PVA) additive was prepared and swelled in varying concentrations of potassium hydroxide (KOH) solutions. A highest ionic conductivity of 457 mS/cm was recorded for the sample with a 2.1 swelling ratio, obtained by soaking in a 5 M KOH solution for 45 min. Stability test results demonstrated the prepared electrolyte to be strong and ductile along with stability under 50 °C and 2 V. Zn-EMD batteries were constructed with the prepared electrolyte using an optimized assembly technique employed to achieve good interfacial contact between the layers. Continuous charge–discharge tests were performed on the batteries at a current density of 0.1 A/g in specific limited and extended potential regions (low: 0.4–1.2 V and high: 0.4–1.6 V) to explore their performance and reversibility. Results indicated that the batteries cycled in the low region had higher capacity retention due to lower δ-MnO₂ formations when compared to those in the high region cycling. To fully understand its performance capability, the battery was further tested extensively. Results indicated a good rate and initial bending performance of the battery with a maximum specific capacity of 310 mAh/g at 0.1 A/g. Additionally, the battery tested at 0.5 A/g showed an average specific capacity of 175 mAh/g over 300 cycles with a 96.5% Coulombic efficiency. Attaining energy densities between 150.4 and 252.4 Wh/kg (w.r.t. active cathode mass) is possible for these batteries, thus encouraging their use in varied applications. Utilizing chitosan gel electrolyte and limited voltage window testing, the prepared Zn-EMD alkaline batteries are among the first reported polymer-based alkaline electrolyte Zn rechargeable batteries with no cathode additives.