Nonaqueous Polyelectrolyte Solutions as Liquid Electrolytes with High Lithium Ion Transference Number and Conductivity

Abstract

Although the small-molecule lithium salt solutions currently employed in lithium-ion batteries display high ionic conductivity, σ, most of the initial current is carried by the electrochemically inactive anion, resulting in concentration polarization of the salt during cycling. Liquid electrolytes with high Li + transference number, t +, and high σ could improve battery performance by limiting these concentration gradients. We propose lithium-neutralized polyanions in solution as an intriguing strategy to attain both high t + and high σ at room temperature and validate the approach using a model system. Pulsed field gradient nuclear magnetic resonance spectroscopy (PFG-NMR) is used to attain self-diffusion coefficients of the ions and hence t + . Conductivity calculated from PFG-NMR showed good agreement with conductivity measured using a conductivity meter. Although the polyelectrolyte solutions exhibit maxima in conductivity at around 0.5 M Li + (1.5 mS/cm), t + continuously increases with concentration, achieving 0.98 at 1.0 M Li + in solutions containing the highest molecular weight polyanion studied.