Invitation: PhD Dissertation Defense of Usman Ali Khan
Hello ME Community,
You are invited to join the PhD Dissertation Defense of Usman Ali Khan, on Friday, August 7, beginning at 11:00am. The defense will be presented in person in the Engineering Building room 210-I (Mechanical Engineering Conference Room) with some committee members participating remotely.
Advisor: Dr. Deepa Madan
Title: Toward Safer and Greener Flexible Batteries: Freeze-Dried BiodegradableChitosan Based Sponge-Hydrogels as Quasi Solid Electrolytes
Abstract:
Advancing zinc-based batteries in wearable applications requires solid-state electrolytes that are environmentally compatible, mechanically robust, and ionically conductive. Freeze-drying of natural biopolymer systems offers a viable and promising route to achieve safer and flexible electrolytes with functional structure integrity suitable for flexible devices. In this work, we develop a biodegradable sponge-hydrogel electrolyte composed of chitosan with polyvinyl alcohol (PVA) and potassium polyacrylate (PAAK) additives, immersed in potassium hydroxide solution, for integration into flexible Zn-MnO2 cells. The electrolyte compositions and hydrogel thicknesses were systemically variedto identify an optimized formulation, CH8-PK10 (800 mg chitosan with 10% PAAK,0.28mm thickness), which exhibited a favorable combination of ionic conductivity, structural integrity, and mechanical strength. The freeze-drying approach generated a tailored porous network in CH8-PK10 with 80.2% pore distribution and an average pore size of ~12μm, enabling efficient ion transport, swelling behavior, and electrolyte uptake. CH8PK10 has a moderate amorphous structure with hydrogen and ionic crosslinking that resulted in the highest ionic conductivity (376mScm⁻¹), swelling ratio (258%), and tensile strength (7.54MPa) among the tested compositions. Thermal analysis revealed distinctwater-binding transitions and major degradation at ~250-300oC, with ~42%residual mass at 400oC, consistent with a densely cross-linked polymer matrix. The optimized hydrogel also demonstrated flame resistance and biodegradability in soil tests, supporting its suitability for safe and environmentally responsible applications. Electrochemical evaluation confirmed a wide stability window (0–2V), reversible redox behavior, an initial discharge capacity of ~150mAhg⁻¹ with >93% coulombic efficiency, and retention of ~50mAhg⁻¹ after short-term cycling. Overall, CH8–PK10 presents a practical quasi-solid electrolyte for flexible Zn–MnO₂ alkaline batteries.