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 degrees 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 delta-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.