title: Visualization of Steady-State Ionic Concentration Profiles Formed in Electrolytes during Li-Ion Battery Operation and Determination of Mass-Transport Properties by in Situ Magnetic Resonance Imaging.
abstract: Accurate modeling of Li-ion batteries performance, particularly during the transient conditions experienced in automotive applications, requires knowledge of electrolyte transport properties (ionic conductivity κ, salt diffusivity D, and lithium ion transference number t(+)) over a wide range of salt concentrations and temperatures. While specific conductivity data can be easily obtained with modern computerized instrumentation, this is not the case for D and t(+). A combination of NMR and MRI techniques was used to solve the problem. The main advantage of such an approach over classical electrochemical methods is its ability to provide spatially resolved details regarding the chemical and dynamic features of charged species in solution, hence the ability to present a more accurate characterization of processes in an electrolyte under operational conditions. We demonstrate herein data on ion transport properties (D and t(+)) of concentrated LiPF6 solutions in a binary ethylene carbonate (EC)-dimethyl carbonate (DMC) 1:1 v/v solvent mixture, obtained by the proposed technique. The buildup of steady-state (time-invariant) ion concentration profiles during galvanostatic experiments with graphite-lithium metal cells containing the electrolyte was monitored by pure phase-encoding single point imaging MRI. We then derived the salt diffusivity and Li(+) transference number over the salt concentration range 0.78-1.27 M from a pseudo-3D combined PFG-NMR and MRI technique. The results obtained with our novel methodology agree with those obtained by electrochemical methods, but in contrast to them, the concentration dependences of salt diffusivity and Li(+) transference number were obtained simultaneously within the single in situ experiment.
authors.affiliation: Department of Chemistry, McMaster University , Hamilton, Ontario, Canada L8S 4L8.
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Krachkovskiy
authors.affiliation: Department of Chemistry, McMaster University , Hamilton, Ontario, Canada L8S 4L8.
authors.forename: J David
authors.initials: JD
authors.lastname: Bazak
authors.affiliation: Department of Chemistry, McMaster University , Hamilton, Ontario, Canada L8S 4L8.
authors.forename: Peter
authors.initials: P
authors.lastname: Werhun
authors.affiliation: Department of Physics, University of New Brunswick , Fredericton, New Brunswick, Canada E3B 5A3.
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Balcom
authors.affiliation: General Motors Global Research and Development, 30500 Mound Road, Warren, Michigan 48092-2031, United States.
authors.forename: Ion C
authors.initials: IC
authors.lastname: Halalay
authors.affiliation: Department of Chemistry, McMaster University , Hamilton, Ontario, Canada L8S 4L8.
authors.forename: Gillian R
authors.initials: GR
authors.lastname: Goward