5 research outputs found
Visualization of Steady-State Ionic Concentration Profiles Formed in Electrolytes during Li-Ion Battery Operation and Determination of Mass-Transport Properties by <i>in Situ</i> Magnetic Resonance Imaging
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 <i>D</i>, and lithium ion transference
number <i>t</i><sup>+</sup>) 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 <i>D</i> and <i>t</i><sup>+</sup>. 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 (<i>D</i> and <i>t</i><sup>+</sup>)
of concentrated LiPF<sub>6</sub> 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<sup>+</sup> 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<sup>+</sup> transference number
were obtained simultaneously within the single <i>in situ</i> experiment