Disentangling cation effects on ion mobility and structure in ionic liquid electrolytes
Data files
Feb 12, 2026 version files 837.69 KB
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Nordness_et_al_2026_raw_data.zip
827.24 KB
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README.md
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Abstract
Ionic liquids (ILs) are low-temperature molten salts, and therefore the transport of ions within ILs is dominated by ion-ion interactions. However, the influence of organic IL cations on key electrolyte properties, such as ion dissociation and overall transport behavior, in lithium-salt-doped ILs remains poorly understood. Moreover, despite their critical role in designing IL-based electrolytes for energy storage applications, ion-ion interactions and ion-specific transport under an applied electrical potential are seldom quantified, largely due to the unique experimental and computational challenges involved. Herein, we compare transport properties obtained using 1H, 7Li, and 19F pulsed-field gradient nuclear magnetic resonance (PFG NMR) and electrophoretic NMR (eNMR) with those measured by electrochemical impedance spectroscopy (EIS). Non-equilibrium molecular dynamics (MD) simulations and eNMR confirm the presence of negatively charged [Li(TFSI)n](1-n) aggregates that migrate towards the positive electrode, resulting in negative lithium transference numbers. Equilibrium MD simulations reveal a vehicular Li ion transport mechanism facilitated by long-lived aggregates with Li+ cations strongly bound to multiple TFSI– anions. Finally, we observe an inverse relationship between the apparent charge of the TFSI– anion in the neat IL, which is dictated by the IL cation, and Li+ transport in the salt-doped systems. This highlights the opportunity to tune electrolyte performance by tailoring cation chemistry.
This README.md file was generated on 2026-01-22 by Leo W. Gordon.
GENERAL INFORMATION
Date of data collection: 2022-2024
Geographic location of data collection: Santa Barbara, CA, USA; Austin, TX, USA
METHODOLOGICAL INFORMATION
- Description of methods used for collection/generation of data: See supporting information from published main text: 10.1088/2515-7655/ae3c3f.
- Methods for processing the data: See supporting information from published text: 10.1088/2515-7655/ae3c3f.
- Instrument- or software-specific information needed to interpret the
data: N/A - Standards and calibration information, if appropriate: N/A
- Environmental/experimental conditions: See supporting information from published text: 10.1088/2515-7655/ae3c3f.
- Describe any quality-assurance procedures performed on the data: See supporting information from published text: 10.1088/2515-7655/ae3c3f.
- People involved with sample collection, processing, analysis and/or
submission: Oscar A. Nordness, Leo W. Gordon, Zidan Zhang, Venkat Ganesan, Raphaële J. Clément
DATA & FILE OVERVIEW
File List: Sub-files are contained within Nordness_et_al_2026_raw_data.zip and are discretized by result. Structure is as follows: upper-case letter = description and figure reference; lower-case letter = file name; roman numerals = variables and column names.
A. Mobilities determined by eNMR and PFG NMR, with associated errors (Data for Figures 1, S7, S9)
a. Experimental Mobilities.csv
i. Variables:
- Ionic liquid (units=none);
- Mobility (units=meters^2/volt/second);
- Mobility error (units=meters^2/volt/second)
ii. Column Names:
- IL;
- μ_eNMR_cat_neat / m$2$ V${-1}$ s$^{-1}$;
- μ_eNMR_cat_neat_err / m$2$ V$^{-1}$ s${-1}$;
- μ_eNMR_an_neat / m$2$ V${-1}$ s$^{-1}$;
- μ_eNMR_an_neat_err / m$2$ V$^{-1}$ s${-1}$;
- μ_eNMR_cat / m$2$ V${-1}$ s$^{-1}$;
- μ_eNMR_cat_err / m$2$ V$^{-1}$ s${-1}$;
- μ_eNMR_an / m$2$ V${-1}$ s$^{-1}$;\
- μ_eNMR_an_err / m$2$ V$^{-1}$ s${-1}$;
- μ_eNMR_Li / m$2$ V${-1}$ s$^{-1}$;
- μ_eNMR_Li_err / m$2$ V$^{-1}$ s${-1}$;
- μ_PFG_cat_neat / m$2$ V${-1}$ s$^{-1}$;
- μ_PFG_cat_neat_err / m$2$ V$^{-1}$ s${-1}$;
- μ_PFG_an_neat / m$2$ V${-1}$ s$^{-1}$;
- μ_PFG_an_neat_err / m$2$ V$^{-1}$ s${-1}$;
- μ_PFG_cat / m$2$ V${-1}$ s$^{-1}$;
- μ_PFG_cat_err / m$2$ V$^{-1}$ s${-1}$;
- μ_PFG_an / m$2$ V${-1}$ s$^{-1}$;
- μ_PFG_an_err / m$2$ V$^{-1}$ s${-1}$;
- μ_PFG_Li / m$2$ V${-1}$ s$^{-1}$;
- μ_PFG_Li_err / m$2$ V$^{-1}$ s${-1}$
B. Self diffusivities determined by PFG NMR, with associated errors (Data for Figures 4, S7, S8).
a. Experimental Self-diffusivities.csv
i. Variables:
- Ionic liquid (units=none);
- Diffusivity (units=meters^2/second);
- Diffusivity error (units=meters^2/second)
ii. Column Names:
- IL;
- D_Cation_Neat_PFG_($m2s{–1}$);
- D_Cation_Neat_PFG_err_($m2s{–1}$);
- D_TFSI_Neat_PFG_($m2s{–1}$);
- D_TFSI_Neat_PFG_err_($m2s{–1}$);
- D_Cation_PFG_($m2s{–1}$);
- D_Cation_PFG_err_($m2s{–1}$);
- D_TFSI_PFG_($m2s{–1}$);
- D_TFSI_PFG_err_($m2s{–1}$);
- D_Li_PFG_($m2s{–1}$);
- D_Li_PFG_err_($m2s{–1}$)
C. Experimental and simulated transference numbers, with associated errors (Data for Figure 2).
a. Transference.csv
i. Variables:
- Ionic liquid (units=none);
- Transference number (units=none)
ii. Column Names:
- ILs;
- Cation_PFG;
- Cation_PFG_err;
- Anion_PFG;
- Anion_PFG_err;
- Li_PFG;
- Li_PFG_err;
- Cation_eNMR;
- Cation_eNMR_err;
- Anion_eNMR;
- Anion_eNMR_err;
- Li_eNMR;
- Li_eNMR_err;
- Cation_MD;
- Cation_MD_err;
- Anion_MD;
- Anion_MD_err;
- Li_MD;
- Li_MD_err
D. Inverse Haven ratios for neat and salt-doped electrolytes determined from eNMR and PFG NMR measurements, with associated errors (Data for Figure 3).
a. Inverse Haven Ratios.csv
i. Variables:
- Ionic liquid (units=none);
- inverse Haven ratio (units=none)
ii. Column Names:
- IL;
- H_inv_neat;
- H_inv_neat_err;
- H_inv;
- H_inv_err
E. Experimentally determined apparent charges of ions, with associated errors (Data for Figure 3).
a. Apparent Charge.csv
i. Variables:
- Ionic liquid (units=none);
- Apparent charge (units=none)
ii. Column Names:
- IL;
- Apparent charge cation neat;
- Apparent charge cation neat err;
- Apparent charge anion neat;
- Apparent charge anion neat err;
- Apparent charge cation binary;
- Apparent charge cation binary err;
- Apparent charge anion binary;
- Apparent charge anion binary err
F. Probability distribution for the number of TFSI– ions coordinated to Li+, with associated errors (Data for Figure 4).
a. P_n.csv
i. Variables: Probability distribution (units=none)
ii. Column Names:
- n;
- C_4C_1pyrr;
- C_4C_1pyrr_std;
- C_4C_1im;
- C_4C_1im_std;
- C_4C_1pip;
- C_4C_1pip_std
G. Liquid-state 1H NMR spectra of neat ILs (Data for Figure S5).
a. Neat_1H_ILs.csv
i. Variables:
- shift (units=ppm);
- Normalized intensity (units=none)
ii. Column Names:
- Im_shift / ppm;
- Im_Normalized intensity;
- Pyrr_shift / ppm;
- Pyrr_Normalized intensity;
- Pip_shift / ppm;
- Pip_Normalized intensity
H. Liquid-state 19F NMR spectra of neat ILs (Data for Figure S5).
a. Neat_19F_ILs.csv
i. Variables:
- shift (units=ppm);
- Normalized intensity (units=none)
ii. Column Names:
- Im_shift / ppm;
- Im_Normalized intensity;
- Pyrr_shift / ppm;
- Pyrr_Normalized intensity;
- Pip_shift / ppm;
- Pip_Normalized intensity
I. Liquid-state 1H NMR spectra of salt-doped ILs (Data for Figure S6).
a. Doped_1H_ILs.csv
i. Variables:
- shift (units=ppm);
- Normalized intensity (units=none)
ii. Column Names:
- Im_shift / ppm;
- Im_Normalized intensity;
- Pyrr_shift / ppm;
- Pyrr_Normalized intensity;
- Pip_shift / ppm;
- Pip_Normalized intensity
J. Liquid-state 19F NMR spectra of salt-doped ILs (Data for Figure S6).
a. Doped_19F_ILs.csv
i. Variables:
- shift (units=ppm);
- Normalized intensity (units=none)
ii. Column Names:
- Im_shift / ppm;
- Im_Normalized intensity;
- Pyrr_shift / ppm;
- Pyrr_Normalized intensity;
- Pip_shift / ppm;
- Pip_Normalized intensity
K. Liquid-state 7Li NMR spectra of salt-doped ILs (Data for Figure S6).
a. Doped_7Li_ILs.csv
i. Variables:
- shift (units=ppm);
- Normalized intensity (units=none)
ii. Column Names:
- Im_shift / ppm;
- Im_Normalized intensity;
- Pyrr_shift / ppm;
- Pyrr_Normalized intensity;
- Pip_shift / ppm;
- Pip_Normalized intensity
L. Non-equilibrium MD simulation results, with associated errors (Data for Figures S7, S12).
a. Simulated Mobilities.csv
i. Variables:
- Ionic liquid (units=none);
- Mobility (units=meters^2/volt/second);
- Mobility error (units=meters^2/volt/second)
ii. Column Names:
- ILs;
- Cation_sim_(m$2$V${-1}$s$^{-1}$);
- Cation_sim_err_(m$2$V$^{-1}$s${-1}$);
- TFSI_sim_(m$2$V${-1}$s$^{-1}$);
- TFSI_sim_err_(m$2$V$^{-1}$s${-1}$);
- Li_sim_(m$2$V${-1}$s$^{-1}$);
- Li_sim_err_(m$2$V$^{-1}$s${-1}$)
M. Equilibrium MD simulation results, with associated errors (Data for Figures S8, S12).
a. Simulated Diffusivities.csv
i. Variables:
- Ionic liquid (units=none);
- Diffusivity (units=meters^2/second);
- Diffusivity error (units=meters^2/second)
ii. Column Names:
- ILs;
- D_Cation_($m2s{–1}$);
- D_Cation_err_($m2s{–1}$);
- D_TFSI_($m2s{–1}$);
- D_TFSI_err_($m2s{–1}$);
- D_Li_($m2s{–1}$);
- D_Li_err_($m2s{–1}$)
N. Persistence times for Li-TFSI solvation structures, with associated errors (Data for Figure S10).
a. Persistence Times.csv
i. Variables:
- Ionic liquid (units=none);
- Persistence time, intermittent (units=nanoseconds);
- Persistence time, intermittent error (units=nanosecond)
- Persistence time, Li[TFSI]2 vehicle (units=nanoseconds);
- Persistence time, Li[TFSI]2 vehicle error (units=nanosecond)
ii. Column Names:
- IL;
- tau_intermittent_(ns);
- err_tau_intermittent_(ns);
- tau_Li_TFSI_2_remaining_(ns);
- err_tau_Li_TFSI_2_remaining_(ns)
O. Persistence lengths for Li-TFSI solvation structures, with associated errors (Data for Figure S10).
a. Persistence Lengths.csv
i. Variables:
- Ionic liquid (units=none);
- Persistence length, intermittent (units=Angstroms);
- Persistence length, intermittent error (units=Angstroms)
- Persistence length, Li[TFSI]2 vehicle (units=Angstroms);
- Persistence length, Li[TFSI]2 vehicle error (units=Angstroms)
ii. Column Names:
- IL;
- Persistence_length_intermittent_(Angstroms);
- err_Persistence_length_intermittent_(Angstroms);
- Persistence_length_continuous_(Angstroms);
- err_Persistence_length_continuous_(Angstroms);
- Persistence_length_Li_TFSI_2_remaining_(Angstroms);
- err_Persistence_length_Li_TFSI_2_remaining_(Angstroms)
P. Persistence ratios for Li-TFSI solvation structures, with associated errors (Data for Figure S10).
a. Persistence Ratios.csv
i. Variables:
- Ionic liquid (units=none);
- Persistence ratio, intermittent (units=none);
- Persistence ratio, intermittent error (units=none)
- Persistence ratio, Li[TFSI]2 vehicle (units=none);
- Persistence ratio, Li[TFSI]2 vehicle error (units=none)
ii. Column Names:
- IL;
- Persistence_ratio_intermittent;
- err_Persistence_ratio_intermittent;
- Persistence_ratio_Li_TFSI_2_remaining;
- err_Persistence_ratio_Li_TFSI_2_remaining
Q. Radial distribution functions for Li-TFSI interactions (Data for Figure S11).
a. G_r_Li-TFSI.csv
i. Variables: Interspecies distance (units=nanometers)
ii. Column Names:
- r/nm;
- c4c1im;
- c4c1pyrr;
- c4c1pip
R. Radial distribution functions for Li-Cation interactions (Data for Figure S11).
a. G_r_Li-Cation.csv
i. Variables: Interspecies distance (units=nanometers)
ii. Column Names:
- r/nm;
- c4c1im;
- c4c1pyrr;
- c4c1pip
S. Radial distribution functions for Cation-TFSI interactions (Data for Figure S11).
a. G_r_Cation-Anion.csv
i. Variables: Interspecies distance (units=nanometers)
ii. Column Names:
- r/nm;
- c4c1im;
- c4c1pyrr;
- c4c1pip
Relationship between files, if important: Data in file C was calculated using values from files A, B, L, and M. Data in files D and E was calculated using values from files A and B.
PFG NMR:
All NMR measurements were performed on a Bruker Avance III 300 spectrometer with a 7.05 T super-wide bore (150 mm) superconducting magnet equipped with a Bruker Diff50 probe (maximum gradient strength of 28.98 T m–1), operating at 300.15 MHz for 1H, 116.65 MHz for 7Li, and 282.40 MHz for 19F. All measurements were performed at 313.15 K following at least 30 minutes of equilibration with the sample temperature controlled using dry N2 at a flow rate of 800 L h–1. 313.15 K was chosen as an application-relevant temperature that would allow for faster ionic mobility through a decreased viscosity and, therefore, more accurate measurements. Self-diffusion coefficients of the IL (C4C1im, C4C1pyrr, and C4C1pip) and Li+ cations, and TFSI– anion, were obtained from 1H, 7Li, and 19F PFG NMR experiments, respectively. Diffusivities were determined using a variable gradient strength stimulated echo pulse sequence designed to minimize signal loss from short transverse relaxation times (T2). The self-diffusion coefficient of species i was determined by fitting the observed signal intensity as a function of the variable gradient strength using the Stejskal−Tanner equation.
eNMR:
eNMR measurements were performed using a double stimulated echo convection-compensating
pulse sequence, in which the polarity of the DC potential pulse was reversed halfway through the pulse sequence. Applied potentials and gradient strengths were varied from 0 to 90 V, and from 0.2 to 3 T m–1, respectively.
Equilibrium MD simulations:
Equilibrium atomistic molecular dynamics (MD) simulations were performed for C4C1im, C4C1pyrr, and C4C1pip ionic liquids at 313 K, each containing LiTFSI at a molar fraction of 0.1 (defined as the ratio of the number of Li+ ions to the total number of cations). Bonded (bond, angle, dihedral) and nonbonded interactions were described using the CL&P force field for C4C1im and C4C1pyrr, and the OPLS-AA force field for C4C1pip.
Full methods can be found in the Supplementary Information of the published paper.
Non-equilibrium MD simulations:
Non-equilibrium molecular dynamics (NEMD) simulations were performed to evaluate ionic drift
and transport under an applied external electric field. External electric fields ranging from 0.02 to 0.10 V nm–1 were applied along a fixed direction, with increments of 0.02 V nm–1. All parameters, including force fields, cutoffs, and thermostat/barostat settings, were identical to those used in the equilibrium simulations.