Position title: Postdoc
Department of Chemistry
1101 University Avenue, Madison, WI 53706
University of Wisconsin-Madison, PostDoc, 2019 – current
University of Illinois at Urbana-Champaign, Ph. D. in Chemistry, 2019
University of Evansville, B.S in Chemistry and Physics, 2014
Polymer Electrolytes in Lithium Ion Batteries
Change of Li+ ion transference number with different degree of polymerization and different types of solvent
Increasing use of consumer electronics and electrification of vehicles has caused demand for lithium-ion batteries with improved energy density and charging rates to grow. As the charging rate for a lithium-ion battery increases, the fraction of the total charge available decreases, and increasing the transference number increases the fraction of total charge available for a given charging rate. However, conventional liquid electrolytes have lithium transference numbers less than 0.5, which indicates the anion carries most of the current.
Several strategies have been proposed to increase the lithium transference number, but perhaps the simplest suggestion is to replace the anion species with a polyelectrolyte. The hypothesis is the polyelectrolyte will have a smaller mobility than the anion without appreciably decreasing the conductivity of the solution. However, molecular-level understanding of counterion dynamics in polyelectrolyte solutions is underdeveloped. Our work uses molecular dynamics simulations of coarse-grained polyelectrolyte solutions to analyze the ion transference number in solution.
We have focused on evaluating the effects of chain length and solvent type on transference numbers. Including an explicit solvent (martini polarizable water) gives smaller transference numbers than an implicit solvent, and the chain length causes the transference number to increase in both solvents. However, the shape of the transference number as a function of chain length curve in implicit solvent is different compared to explicit solvent.
Additionally, we are performing atomistic simulations of LiTFSI and LiOTf in ethylene carbonate to analyze how sulfonate groups affect ion pairing in organic solvents. The sulfonate group is of interest, because common polyelectrolytes (e.g. polystryrene sulfonate) use sulfonate groups. However, simulations suggest the Li ion strongly binds to the sulfonate group, because it can interact with the three oxygen atoms. This strong binding of Li to the sulfonate group is in agreement with experiments for both molecular anions and polyanions. These simulation results can be used to guide experimental design of electrolytes with high lithium ion transference numbers.