478259 Ion Transport with Large Anions for Battery Electrolyte Applications

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Sophia Y. Chan1, Hilda G. Buss2 and Bryan D. McCloskey2, (1)Chemical and Biomolecular Engineering, University of California Berkeley, Berkeley, CA, (2)Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, CA

Efficient operation of lithium-ion batteries strongly depends on effective transport of the electrochemically active lithium cation from one electrode to the other. In uncharged systems, the diffusion coefficient of the species of interest is sufficient to describe transport in the system. However, in these electrolyte solutions, transport of the lithium cation is additionally dependent on the diffusion coefficient of its counterion. Electrolytes with ion conductivities consisting solely of cation motion have a cation transference number of unity (t+ = 1). They pose an attractive alternative to the conventional lithium salt electrolytes because of their ability to eliminate concentration gradients, which cause polarization loss and limit porous cathode utilization. To approach t+ = 1, we use a large polymer anion and lithium cation in a solvent of high dielectric constant to maximize solute-solvent interactions. A solution of 0.1 M of lithiated poly(allyl-glycidyl-ether) (PAGE, MW 4500) in dimethyl sulfoxide (DMSO) achieves ionic conductivities of 5.6 x 10-4 S cm-1 at room temperature and up to 10-3 S cm-1 at 70oC, comparable to LiTFSI's conductivities of 2.1 x 10-3 to 4.1 x 10-3 S cm-1 (25 – 70oC). Cation transference numbers of lithiated PAGE (0.8 – 0.9) compared to those of LiTFSI (0.33) show a clear increase in lithium transference with the polymer electrolyte, which would significantly improve electrochemical performance of future lithium-based batteries. To better understand the ion transport of ions in lithiated PAGE solutions, we present rheology of uncharged pre-lithiated parent polymer and extract the transition concentration from dilute to semi-dilute, C*. This change in regimes may help explain the trends in the diffusion coefficients of the lithiated PAGE used for calculating transference numbers and provide insight into design and formulation for better battery electrolytes.

Keywords: battery polymer electrolyte, transference number, ionic conductivity, diffusion coefficient

 


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