Solvent Effects on the Transference Number of Dilute Polyelectrolyte Solutions

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. However, lithium-ion batteries have several issues including long charging times, but high transference electrolytes are a potential route to circumvent this issue and increase the battery energy density. Traditional liquid electrolytes have lithium transference numbers less than 0.5, which indicates the anion carries most of the current. In order to increase this transference number, it has been suggested to use polyelectrolyte solutions in which the polyanion mobility is less than the lithium ion mobility, but molecular-level understanding of counterion dynamics in polyelectrolyte solutions is underdeveloped. Our work uses molecular dynamics simulations of coarse-grained polymer models to elucidate how chain length and solvent type affect the ion transference number in solution. These simulations show ion transference numbers are smaller in explicit solvent compared to implicit solvent, while increasing chain length causes the transference to increase. These simulation results can be used to guide experimental design of electrolytes with high lithium ion transference numbers.