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.

Despite the significance of nickel compounds, NMR spectroscopy of the active nickel isotope Ni remains a largely unexplored field. While nickel(0) compounds have been studied byNi NMR in solution, solid-state experiments have been limited to Knight shift studies of nickel metal and nickel intermetallics. In conjunction with an NMR study of their ligands and Ni relativistic computations, the firstNi solid-state NMR (SSNMR) spectra of diamagnetic compounds are reported here. Specifically, bis(1,5-cyclooctadiene)nickel(0) [Ni(cod)], tetrakis(triphenylphosphite)nickel(0) [Ni[P(OPh)]], and tetrakis(triphenylphosphine)nickel(0) [Ni(PPh)] were studied. Ni SSNMR spectra of Ni(cod) were used to determine its isotropic chemical shift (δ = 965 ± 10 ppm), span (Ω = 1700 ± 50 ppm), skew (κ = -0.15 ± 0.05), quadrupolar coupling constant (C = 2.0 ± 0.3 MHz), quadrupolar asymmetry parameter (η = 0.5 ± 0.2), and the relative orientation of the chemical shift and electric field gradient tensors. A solution study of Ni(cod) in CD yielded a narrow Ni signal, and the temperature dependence of δ(Ni) was assessed (δ being 936.5 ppm at 295 K). The solution is proposed as a secondary chemical shift reference for Ni NMR in lieu of the extremely toxic Ni(CO) primary reference. For Ni[P(OPh)], Ni SSNMR was used to infer the presence of two distinct crystallographic sites and establish ranges for δ in the solid state, as well as an upper bound for C (3.5 MHz for both sites). For Ni(PPh), line shape fitting provided a δ value of 515 ± 10 ppm, Ω of 50 ± 50 ppm, κ of 0.5 ± 0.5, C of 0.05 ± 0.01 MHz, and η of 0.0 ± 0.2. The study of Ni(PPh), in particular, demonstrates the utility of Ni SSNMR given the lack of a previously reported crystal structure and transient nature of Ni(PPh) in solution.

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