(Invited) A Sustainable and Reliable Electrolyte Toward Safe Zn-MnO2 Alkaline Rechargeable Batteries

Abstract

Zinc-Manganese Dioxide (Zn-MnO2) rechargeable batteries has spurred interest due to lower cost, high specific capacity, increased safety while using in small electronic devices and wearable technology. Zn-MnO2 alkaline batteries form inactive compounds during charging and discharging that hinder their ability to be utilized in rechargeable settings. Design and development of functional electrolyte to replace traditional electrolyte have become an effective way to inhibit irreversible compound formations and Zn dendrite growth, avoid leakage issues and metallic packaging. However, many challenges such as reliable and reproducible ionic conductivity and ion transference number of free-standing electrolyte films at lower thickness (150 µm), and interfacial contact resistance between electrolyte and electrode layer still exist. Our assumption is producing reliable and consistent ionic conductivity and ion transference number of electrolytes at lower thickness (150 µm) will help in providing the faster redox reaction kinetics at electrolyte-electrode interface. Moreover, by reducing the interfacial contact resistance between electrolyte and electrode interface will help in reducing the charge transfer resistance and zincate ion movements and results in improving the reversible life cycle of batteries. Many electrolytes fabricated utilize two different solutions that are mixed separately, forming either a liquid or a solid electrolyte after curing. Due to separate mixing, both solutions are never fully incorporated into one another, causing discrepancies in the consistency of the electrolyte. Here, we propose to use sustainable chitosan, which utilized 5:1 ratio of naturally occurring Chitosan (Chi) and Polyvinyl Alcohol (PVA) respectively. The Chi and PVA solution were premixed using ultrasonic bath and vacuum suction was used to remove extra bubbles formation due to mixing of Chi and PVA. This new process of electrolyte formation was compared between different thickness (120 µm, 150 µm, and 250µm), and the best electrolyte was then compared to the old process of mixing the solutions separately for electrolyte formation. The different thickness electrolytes were soaked into Potassium Hydroxide (KOH) and compared on their Ionic Conductivity, Ionic Conductance, Ion Transference Number, PH, and Swelling Ratio. To reduce the interfacial contact resistance between electrolyte and electrode, free standing electrolyte layer will be dipped into Chi solution and then put in contact with electrodes. These electrolytes were then used in the fabrication of Zn-MnO2 batteries and measure their performance using cyclic voltammetry and galvanostatic charge-discharge.