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

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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 gel polymer electrolyte (GPE) 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 (250 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 (250 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. Additionally, by improving the mechanical strength and flexibility of free-standing GPE layer will be helpful to suppress the dendrite formation. Our assumption is well-arranged continuous porous structure of GPE will result in easy movement of ions and well absorption and retention of alkaline or acidic salt solution. It will also provide mechanical strength to the overall gel films at lower thickness to reduce dendrite formation. To fabricate well-arranged continuous porous GPE structure, we propose to use freeze casting method.Here, we propose to use naturally occurring sustainable chitosan, with different additives like PVA, PAAK to form GPE using freeze casting method. The different thickness electrolytes were soaked into alkaline solution e.g. Hydroxide (KOH) and fluorinate compounds 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 Chitosan solution and then put in contact with electrodes. We will also perform SEM to observe the arrangement of polymer chain using freeze casting method. These electrolytes were then used in the fabrication of Zn-MnO2 batteries and measure their performance using cyclic voltammetry and galvanostatic charge-discharge.