Rechargeable\nZinc-Electrolytic Manganese Dioxide (EMD)\nBattery with a Flexible Chitosan-Alkaline Electrolyte

Abstract

A high-performing flexible chitosan-based\ngel electrolyte with\npoly­(vinyl alcohol) (PVA) additive was prepared and swelled in varying\nconcentrations of potassium hydroxide (KOH) solutions. A highest ionic\nconductivity of 457 mS/cm was recorded for the sample with a 2.1 swelling\nratio, obtained by soaking in a 5 M KOH solution for 45 min. Stability\ntest results demonstrated the prepared electrolyte to be strong and\nductile along with stability under 50 °C and 2 V. Zn-EMD batteries\nwere constructed with the prepared electrolyte using an optimized\nassembly technique employed to achieve good interfacial contact between\nthe layers. Continuous charge–discharge tests were performed\non the batteries at a current density of 0.1 A/g in specific limited\nand extended potential regions (low: 0.4–1.2 V and high: 0.4–1.6\nV) to explore their performance and reversibility. Results indicated\nthat the batteries cycled in the low region had higher capacity retention\ndue to lower δ-MnO₂ formations when compared to those\nin the high region cycling. To fully understand its performance capability,\nthe battery was further tested extensively. Results indicated a good\nrate and initial bending performance of the battery with a maximum\nspecific capacity of 310 mAh/g at 0.1 A/g. Additionally, the battery\ntested at 0.5 A/g showed an average specific capacity of 175 mAh/g\nover 300 cycles with a 96.5% Coulombic efficiency. Attaining energy\ndensities between 150.4 and 252.4 Wh/kg (w.r.t. active cathode mass)\nis possible for these batteries, thus encouraging their use in varied\napplications. Utilizing chitosan gel electrolyte and limited voltage\nwindow testing, the prepared Zn-EMD alkaline batteries are among the\nfirst reported polymer-based alkaline electrolyte Zn rechargeable\nbatteries with no cathode additives.