Kan-Ju Lin

Lithium ion battery have been widely used in electronic gadgets due to its high energy/power density. Current electrolytes for Li-ion batteries are mostly organic solvents. Although they are good conducting medium for Li ion, the organic solvents are toxic and volatile. Besides, those liquid electrolytes require hard casing and separator to ensure good contacts among battery elements, therefore the flexibility of the battery as well as the gadget is limited. The problem aforementioned can be solved if a non-toxic polymer electrolyte is used.

PEO-salt electrolytes have two drawbacks: 1) ionic conductivity is small, and 2) concentration polarization in PEO degrades cell performance after several charge/discharge cycle. It reduces the capacity of the battery by creating depletion regions near electrodes. Many studies focused on improving the conductivity of polymer electrolytes. Using larger anions to decrease the attraction between anion and cation, therefore resulting in higher ratio of solvated Li ion in PEO. Another highly focused research area is to dope ceramic fillers to provide extra Lithium hopping sites.

Our research collaboration focuses on the second drawback. The material in which only cations conduct is called a single-ion conductor. In single-ion conductors, anions are covalently bound to the polymer backbone, therefore the transference number is unity. By reducing anion mobility, single ion conductors prevent concentration polarization and improve the lifetime of batteries. The single-ion conductor is a type of ionomer. In contrast to most ionomers, an ionomer with PEO as the non-ionic part can solvate the cations. The conductivity for PEO-based ionomer is nevertheless less promising, and people haven't paid much attention on this material.
Our collaboration aim to understand the morphology, structure and dynamics of PEO-based Li, Na, and Cs samples. By systematically varying the PEO spacer length and ion type, logistic analyses could be made.

Courtesy of Kokonad Sinha