Haven Ratio Research Articles

A kinetic Monte Carlo study for Haven ratio of proton transport in perovskite ceramics

A kinetic Monte Carlo study for Haven ratio of proton transport in perovskite ceramics

Charge Transport and Glassy Dynamics in Blends Based on 1-Butyl-3-vinylbenzylimidazolium Bis(trifluoromethanesulfonyl)imide Ionic Liquid and the Corresponding Polymer.

Charge transport, diffusion properties, and glassy dynamics of blends of imidazolium-based ionic liquid (IL) and the corresponding polymer (polyIL) were examined by Pulsed-Field-Gradient Nuclear Magnetic Resonance (PFG-NMR) and rheology coupled with broadband dielectric spectroscopy (rheo-BDS). We found that the mechanical storage modulus increases with an increasing amount of polyIL and is a factor of 10,000 higher for the polyIL compared to the monomer (= Pa at 100 rad s−1 and 298 K). Furthermore, the ionic conductivity of the IL is a factor higher than its value for the polymerized monomer with S cm−1 at K. Additionally, we found the Haven Ratio ( obtained through PFG-NMR and BDS measurements to be constant around a value of for the IL and blends with 30 wt% and 70 wt% polyIL. These results show that blending of the components does not have a strong impact on the charge transport compared to the charge transport in the pure IL at room temperature, but blending results in substantial modifications of the mechanical properties. Furthermore, it is highlighted that the increase in might be attributed to the addition of a more mobile phase, which also possibly reduces ion-ion correlations in the polyIL.

Superionicity in Ionic-Liquid-Based Electrolytes Induced by Positive Ion-Ion Correlations.

In ionic-liquid (IL)-based electrolytes, relevant for current energy storage applications, ion transport is limited by strong ion-ion correlations, generally yielding inverse Haven ratios (ionicities) of below 1. In particular, Li is transported in anionic clusters into the wrong direction of the electric field, requiring compensation by diffusive anion fluxes. Here, we present a concept to exploit ion-ion correlations in concentrated IL electrolytes beneficially by designing organic cations with a Li-coordinating chain. 1H NMR and Raman spectra show that IL cations with seven or more ether oxygens in the side chain induce Li coordination to organic cations. An unusual behavior of an inverse Haven ratio of >1 is found, suggesting an ionicity larger than that of an ideal electrolyte with uncorrelated ion motion. This superionic behavior is consistently demonstrated in both NMR transport/conductivity measurements and molecular dynamics (MD) simulations. Key to this achievement is the formation of long-lived Li-IL cation complexes, which invert the Li drift direction, yielding positive Li+ ion mobilities for the first time in a single IL-solvent-based electrolyte. Onsager correlation coefficients are derived from MD simulations and demonstrate that the main contributions to the inverse Haven ratio, which induce superionicity, arise from enhanced Li-IL cation correlations and a sign inversion of Li-anion correlation coefficients. Thus, the novel concept of coordinating cations not only corrects the unfortunate anionic drift direction of Li in ILs but even exploits strong ion correlations in the concentrated electrolyte toward superionic transport.

Water-In-Salt LiTFSI Aqueous Electrolytes (2): Transport Properties and Li+ Dynamics Based on Molecular Dynamics Simulations.

The transport properties of water-in-salt lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) aqueous electrolytes were studied using classical molecular dynamics (MD) simulations. At high salt concentrations of 20 m, the calculated viscosity, self-diffusion coefficients, ionic conductivity, the inverse Haven ratio, and the Li+ apparent transference number all agree with previous experimental results quantitatively. Furthermore, analyses show that the high apparent transference number for Li+ is due to the fact that the dynamics of TFSI- decrease more quickly with increasing salt concentration than the dynamics of Li+ ions due to the formation of a TFSI- network. In addition, it was shown that the conduction of Li+ ions through the highly concentrated electrolyte occurs mainly via a hopping mechanism instead of a vehicular mechanism hypothesized in earlier studies of this system.

Cooperative excitations in superionic PbF2.

Links between dynamical Frenkel defects and collective diffusion of fluorides in β-PbF2 are explored using Born-Oppenheimer molecular dynamics. The calculated self-diffusion coefficient and ionic conductivity are 3.2 × 10-5 cm2 s-1 and 2.4 Ω-1 cm-1 at 1000 K in excellent agreement with pulsed field gradient and conductivity measurements. The calculated ratio of the tracer-diffusion coefficient and the conductivity-diffusion coefficient (the Haven ratio) is slightly less than unity (about 0.85), which in previous work has been interpreted as providing evidence against collective 'multi-ion' diffusion. By contrast, our molecular dynamics simulations show that fluoride diffusion is highly collective. Analysis of different mechanisms shows a preference for direct collinear 'kick-out' chains where a fluoride enters an occupied tetrahedral hole/cavity and pushes the resident fluoride out of its cavity. Jumps into an occupied cavity leave behind a vacancy, thereby forming dynamic Frenkel defects which trigger a chain of migrating fluorides assisted by local relaxations of the lead ions to accommodate these chains. The calculated lifetime of the Frenkel defects and the collective chains is approximately 1 ps in good agreement with that found from neutron diffraction. This article is part of the Theo Murphy meeting issue 'Understanding fast-ion conduction in solid electrolytes'.

Nonlinear ion mobility at high electric field strengths in the perovskites SrTiO3 and CH3NH3PbI3

As the characteristic dimensions of perovskite devices shrink to the nanoscale, operating voltages of a few volts lead to huge field strengths and, consequently, to the possibility of field-enhanced ion mobility. In this paper, the electrochemical mobility of $X$ anions (${u}_{X}$) along $\ensuremath{\langle}100\ensuremath{\rangle}$ in the $AB{X}_{3}$ perovskite structure was investigated as a function of electric field strength $E$ and temperature $T$ by means of classical molecular dynamics simulations. Two different cases were examined: one representative of inorganic perovskites, oxide-ion mobility (${u}_{\text{O}}$) in cubic ${\mathrm{SrTiO}}_{3}$; and the other representative of hybrid inorganic-organic perovskites, iodide-ion mobility (${u}_{\mathrm{I}}$) in cubic ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbI}}_{3}$. In both cases, isothermal mobilities are, as expected, independent of field at low values ($E<{10}^{0}$ MV ${\mathrm{cm}}^{\ensuremath{-}1}$) but become field dependent at higher values. Data obtained for ${u}_{\text{O}}(E,T)$ can be described quantitatively with an analytical treatment incorporating a modified Haven ratio for a dilute solution. In contrast, ${u}_{\text{I}}(E,T)$ displays complex behavior. At high fields, the degree of field enhancement is underestimated by the analytical treatment, while in the field-independent regime, the data imply that moderate fields decrease ${u}_{\mathrm{I}}$. Our study thus demonstrates that for cubic, inorganic $AB{X}_{3}$ perovskites ${u}_{X}(E,T)$ along $\ensuremath{\langle}100\ensuremath{\rangle}$ can now be predicted quantitatively, but for hybrid perovskites substantially more complex models are required.

From ionic to superionic conductivity: The influence of cation order on sodium diffusion in Na3Zr2Si2PO12

For many solid electrolytes, the introduction of structural disorder is beneficial for the ionic conductivity, since it breaks the localisation of the mobile species. Yet, in the case of the Na+ superionic conductor (NASICON) structure, we show that an ordered configuration of the cations can both diminish or escalate the ionic conductivity. Here, the key factor is the arrangement of the P5+ ions with respect to the sodium diffusion channels. Engineering this factor, NASICON can be tuned from a poor, two-dimensional conductor to a superionic, three-dimensional conductor. Since experimentally only general Si/P lattice positions can be determined, the distribution of P5+ in current samples is not known. Based on our calculations of conductivities and activation energies, we conclude that experimental samples possess no long-range cation order yet. Consequentially, we propose that NASICON type materials have not been utilised to their fullest extend. By tailoring their cation order, an increase in ionic conductivity of nearly a factor of four can be enabled. Supporting this statement, we present a systematic study on the influence of cation order on the tracer diffusion coefficient Dtr, the sodium diffusion pathways, the charge diffusion coefficient Dσ, the ionic conductivity σ, the Haven ratio HR and the activation energy EA obtained by Molecular Dynamics simulations.

Ion Transport and Mechanical Properties of Non-Crystallizable Molecular Ionic Composite Electrolytes

Polymer electrolytes show promise as alternatives to conventional electrolytes in energy storage and conversion devices but have been limited due to their inverse correlation between ionic conductivity and modulus. In this study, we examine surface morphology, linear viscoelastic, dielectric and diffusive properties of molecular ionic composites (MICs), materials produced through the combination of a rigid and charged double helical polymer, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), and ionic liquids (ILs). To probe temperature extremes, we incorporate a non-crystallizable IL to allow measurements from −90 to 200 °C. As we increase the PBDT weight percentage, shear moduli increase and do not decay up to 200 °C while maintaining room temperature ionic conductivity within a factor of 2 of the neat IL. We connect diffusion coefficients of IL ions with ionic conductivity through the Haven ratio across a wide temperature range and analyze trends in ion transport based on a relatively high an...

Ion Mobilities, Transference Numbers, and Inverse Haven Ratios of Polymeric Ionic Liquids.

We probe the ion mobilities, transference numbers, and inverse Haven ratio of ionic liquids and polymerized ionic liquids as a function of their molecular weight using a combination of atomistic equilibrium and nonequilibrium molecular dynamics simulations. In contrast to expectations, we demonstrate that the inverse Haven ratio increases with increasing degree of polymerization (N) and then decreases at larger N. For a fixed center of mass reference frame, we demonstrate that such results arise as a consequence of the strong cation-cation correlated motions, which exceed (in magnitude) the self-diffusivity of cations. Together, our findings challenge the premise underlying the pursuit of pure polymeric ionic liquids as high transference number, single-ion conducting electrolytes.

Dynamic Ion Correlations in Solid and Liquid Electrolytes: How Do They Affect Charge and Mass Transport?

AbstractSolid and liquid electrolytes for electrochemical energy storage and conversion cells, such as batteries, supercapacitors and fuel cells, contain often high concentrations of mobile ions. Therefore, the ion dynamics in these electrolytes is characterized by pronounced directional correlations between successive ion movements, which exert a strong influence on charge and mass transport. In this manuscript, we review the relevant transport properties of (i) single‐ion conducting solid electrolytes and of (ii) liquid electrolytes with a single type of cations and a single type of anions. All transport quantities are based on Onsager's linear irreversible thermodynamics and are defined in the laboratory frame of reference, so that they can be easily related to correlations functions of the equilibrium ion dynamics by means of linear response theory. In the case of single‐cation conducting solid electrolytes, we discuss how the complex interplay between cation‐cation and cation‐lattice interactions leads to a competition between cation self‐correlations and distinct‐cation correlations. In the case of liquid electrolytes, we describe how cation‐cation, anion‐anion, and cation‐anions correlations influence the various transport quantities, such as total ionic conductivity, Haven ratio, salt diffusion coefficient and cation transference numbers. Moreover, we discuss how, in dilute liquid electrolytes, ion correlations can be governed by ion pair formation. Finally, the competition between cation/anion and cation/polymer chain interactions can lead to negative cation transference numbers in polymer electrolytes, i. e. to cations migrating towards the positive electrode. Taken together, these case studies showcase how ion correlations in electrolyte systems can strongly influence the overall efficiency of energy storage and conversion devices due to transport limitations.

Comparison of Correlated Li+ Diffusion from Molecular Dynamics of Promising Solid Electrolytes

Li-ion batteries (LIBs) have been steadily improving since the first LIBs were commercially developed in the 1990s. Batteries with higher volumetric and gravimetric energy density using all-solid-state materials could revolutionize the LIB market. However, known superionic solid electrolytes are limited by a number of materials properties. Engineering better materials is especially limited by the lack of understanding of diffusion mechanisms, demanding novel analysis of diffusion using molecular dynamics. Molecular dynamics (MD) provides insight into correlated motion between Li-ions and correlated motion with the lattice. Correlated motion of Li-ions is common in the most promising superionic electrolytes. The results presented will be a broad survey of correlated motion using novel analysis tools developed by the authors and their collaborators. Diffusion in some of the most promising electrolytes, such as lithium borohydrides, lithium germanium thiophosphate, amorphous lithium thiophosphate, lithium lanthanum zirconium oxide, and the lithium rich anti-perovskites will be compared. Molecular dynamics of these systems will be performed either by ab-initio MD or classical MD. The Haven ratio and the Distinct Van Hove Analysis will be presented for each material. The novel analysis will focus on computational atomistic insights into the diffusion mechanisms of Li-ions, especially correlated motion.

An electrostatic spectral neighbor analysis potential for lithium nitride

Machine-learned interatomic potentials based on local environment descriptors represent a transformative leap over traditional potentials based on rigid functional forms in terms of prediction accuracy. However, a challenge in their application to ionic systems is the treatment of long-ranged electrostatics. Here, we present a highly accurate electrostatic Spectral Neighbor Analysis Potential (eSNAP) for ionic α-Li3N, a prototypical lithium superionic conductor of interest as a solid electrolyte or coating for rechargeable lithium-ion batteries. We show that the optimized eSNAP model substantially outperforms traditional Coulomb–Buckingham potential in the prediction of energies and forces, as well as various properties, such as lattice constants, elastic constants, and phonon dispersion curves. We also demonstrate the application of eSNAP in long-time, large-scale Li diffusion studies in Li3N, providing atomistic insights into measures of concerted ionic motion (e.g., the Haven ratio) and grain boundary diffusion. This work aims at providing an approach to developing quantum-accurate force fields for multi-component ionic systems under the SNAP formalism, enabling large-scale atomistic simulations for such systems.

(Invited) Elucidating Ion Transport Mechanisms in Polymerized Ionic Liquids

Poor ionic conductivity typically hinders the utilization of ion containing polymers from functioning as a single ion conductor for energy storage or conversion applications. A provocative sub class of these materials are polymerized ionic liquids (polyILs) which have the potential to combine the desirable ion transport of an ionic liquid with the favorable mechanical properties of a polymer. However, the room temperature conductivity of polyILs is usually 2 or 3 orders of magnitude lower than that of low molecular weight ionic liquids, yet a decoupling of conductivity and structural dynamics in polyILs demonstrates the opposite at the normalized glass transition temperature (T g/T). This seemingly conflicting observation can be reconciled by the fact that polyILs have higher T g and lower dielectric permittivity at the same T g/T than their molecular counterparts. Moreover, ionic conductivity of polyILs is found to be significantly slower than ion diffusion. Inverse Haven ratio shows a strong temperature dependence: saturating at 0.2 at higher temperature and decreasing at lower T. Pronounced reduction in conductivity is attributed to the cross correlation between the mobile ions since the ion pair diffusion is infeasible in polyILs. This speculation remains unverified. We have recently undertaken atomistic molecular dynamics (MD) simulations to elucidate transport mechanism in polyILs and demonstrate the dynamical heterogeneity and cooperative motion of ion transport in polyILs establishing for the first time quantitative evidence of mobile ion hopping. The hopping of anions is found to be dominantly interchain in nature and is generally facilitated by five associating cations from two different chains. Intrachain hopping was found to be much less significant being mediating with fewer chains. The mobile anions tend to form string-like structures and move cooperatively; and the string length of concerted motion of mobile anions increases with decreasing temperature. Our results reveal the important role of a distance criterion in defining hopping events to correctly elucidate the components of the ion transport mechanism. This molecular-level information will provide an important step in both rationalizing experimental observations and the design of novel ion-containing polymers with superior transport properties.

Density Functional Theory Descriptors for Ionic Liquids and the Introduction of a Coulomb Correction.

As a result of continuing ionic liquid research, it becomes clearer that charge transfer in ionic liquids has a physical reality. In a recent publication, we demonstrated the utility of simple density functional theory descriptors to estimate charge transfer for a large number of ion combinations, which is possible because the ions are treated separately. A major disadvantage found was that the charge transfer was systematically overestimated. In this work, we introduce a correction to account for the losses in Coulomb attraction when charge is transferred from the anion to the cation. We find that accounting for these losses is important to describe charge transfer in ionic liquids appropriately. The advantage that the calculations can be performed separately on the individual, isolated ions is maintained. The corrected as well as the uncorrected charge transfer have been calculated for over 4000 cation-anion combinations at the R(O)B3LYP/6-311+G(2d,p)//RB3LYP/6-31+G(d,p) level of theory. With the correction, the absolute values for the charge transfer are no longer unrealistically high and agree well with other charge transfer estimates from the literature. In general, the cumulative nature of the Haven ratio is now correctly mirrored in the relationship between the corrected theoretical charge transfer and the experimental estimate from the Nernst-Einstein relation. Earlier findings on the similarities between ether-functionalized and nonfunctionalized ionic liquids are confirmed. However, we also observe inconsistencies when using the experimental charge transfer estimates together with the ionicity interpretation of the Haven ratio. These can be interpreted as a hint toward the latter premise being wrong.

Density Functional Theory Descriptors for Ionic Liquids and the Charge-Transfer Interpretation of the Haven Ratio.

One of the few properties common to all ionic liquids is their inherent electrical conductivity, which makes them promising candidates for advanced electrochemical applications. A central finding in this respect is that the measured conductivity is almost always lower than the one obtained from the Nernst-Einstein relation. There has been much dispute about whether correlated motion, charge transfer, or some sort of aggregation is the reason for this difference. In this work, we apply density functional theory-based descriptors to estimate the charge transfer in ionic liquids, which allow predictions for a large number of systems with minimal effort. The theoretical charge transfer was obtained from vertical ionization potentials and electron affinities at the RB3LYP/6-311+G(2d,p)//RB3LYP/6-31+G(d,p) level of theory. To be able to compare and classify the values obtained with this approach, another measure for charge transfer, available directly from the Nernst-Einstein relation, is introduced. The two quantities show significant correlation for some subsets of ionic liquids for which a sufficient amount of information is available. Additionally, the purely theoretical charge-transfer values allow for identifying interesting systems that should be the subject of further investigation.

Monte Carlo Simulation of Correlation Effects in a Random SC Alloy via Interstitialcy Mechanisms

In this paper some recent progress in the area of Monte Carlo simulation of diffusion via the interstitialcy mechanism in a randomly ordered binary alloy is reviewed. Topics discussed include the calculation of tracer correlation factorsfA and fBas a function of composition and jump frequency ratiowA/wBand interstitialcy correlation factors fI; which play a crucial role in the interpretation of ion-conductivity data. The percolation behavior of fI when wA ≪ wB is analysed in detail and limits of the tracer diffusivity ratios bD A/bD B for alloy compositions below thepercolation threshold are presented. Allowance for non-collinear jumps (partly) replacing concurrent collinear site exchanges leads to a reduction of diffusion correlation effects.This goes along with a shift of the diffusion percolation threshold to lower concentrations of the (more) mobile component B. Even stronger changes of mass and charge transport compared to an exclusively collinear interstitialcy scheme are observed for additional contributions of direct interstitial jumps. It is remarkable that for both extensions of interstitialcy-mediated diffusion the Haven ratio appears to be greater than unity in certain compositionranges poor in B.

Diffusion coefficient of lithium ions in garnet-type Li6.5La3Zr1.5Ta0.5O12 single crystal probed by 7Li pulsed field gradient-NMR spectroscopy

Diffusion coefficient of lithium ions in Li6.5La3Zr1.5Ta0.5O12 (LLZTO) single crystal is measured using 7Li pulsed field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy in the temperature range from 298 K to 353 K. The Li diffusion coefficient in LLZTO is evaluated to be 1.9 × 10−13 m2 s−1 at 298 K with the activation energy of 0.43 eV. The ionic conductivity of LLZTO single crystal is measured by impedance spectroscopy, which gives 7 × 10−4 S cm−1 at 298 K with the activation energy of 0.43 eV. The diffusion coefficient obtained by PFG-NMR is lesser than the diffusion coefficient calculated from ionic conductivity using Nernst-Einstein relation. The small discrepancy gives the Haven ratio of 0.4, which suggests a correlated migration of the lithium ions in the tetrahedral and octahedral sites in LLZTO. To compare the present result with previous reports, the diffusion time (Δ) dependence is carefully checked in PFG-NMR not only for the single crystal but also the crushed powdered samples, which revealed no significant dependence in the single crystal but small dependence in the crushed samples which may be due to the restricted diffusion in the powder grains.

Analysis of the statistical and convergence properties of ionic transport coefficients with application to the solid electrolyte Li2OHCl

The challenge of computing ionic transport coefficients from first principles is to achieve the necessary convergence with respect to system size, simulation time, and configurational sampling. Unfortunately current computer resources are not yet available for such convergence studies at the fully first principles level. In this work, a lattice kinetic Monte Carlo model is used to study the convergence properties of transport coefficients, using the Li sub-lattice of the Li ion electrolyte Li2OHCl as an example system. The specific transport coefficients representing tracer diffusion, effective diffusion, and mobility are carefully studied for their convergence properties. Additionally, ion pair correlations of the effective diffusion are recast as a sum over events which allows for a detailed study of the nature of the correlation in terms of time and spatial separation. This experience suggests a general method of performing simulations by using first a kinetic Monte Carlo model followed by a first principles molecular dynamics study. For the Li2OHCl system, the kinetic Monte Carlo results provide both a reference for the Haven ratio due to purely geometric effects and a measure of the computational effort needed to obtain meaningful molecular dynamics results. The combination of the two methods provides further evidence of anti-correlated Li-ion motion in this system as predicted in a previous study.

Mass Transfer Parameters and Ionic Association of Dual-Cation Electrolyte for Hybrid Capacitor System

[Introduction] Hybrid capacitors, which combine an activated carbon (AC) electrode with a large-capacity faradic (psuedocapacitive or battery) electrode, are the focus on an increase in energy density of electric double layer capacitors (EDLCs). One representative faradic electrode material for such hybrid systems is lithium titanate (Li4Ti5O12, LTO), which was used as a negative electrode in one of the first hybrid systems1) and has been extensively investigated since then 2). In this connection, we have reported a dual-cation electrolyte system composed of lithium tetrafluoroborate (LiBF4) and spiro-(1,1’)-bipyrrolidium tetrafluoroborate (SBPBF4) dissolved in propylene carbonate (PC), where the latter cation gives high ionic conductivity in the PC-based electrolytes3). The dual-cation electrolyte system raised rate capability of LTO/AC hybrid capacitors to a level comparable to EDLCs, thanks to the enhancement of LTO reaction kinetic. Still, the detailed mechanism of improved rate capability by dual-cation system has not been completely understood. The difficulty of the analysis lies in the electrolyte containing multiple ion spices, whose contribution to the rate capability cannot be simply divided into individuals.The purpose of this study was to evaluate the contribution of individual ionic species by using pulsed gradient spin-echo (PGSE) NMR technique. Specifically, by determining the self-diffusion coefficient of dual cation electrolyte system, we attempted to break down the ionic conductivity of the whole electrolyte system into individual ionic species and to calculate a carrier number of ions. [Experimental]Electrolytes used in this report were prepared by dissolving 1 M LiBF4 and x M SBPBF4 in PC (0<x<3). All the electrolyte was prepared by mixing components with magnetic stirrer overnight in the Ar-filled glove box. PGSE-NMR was conducted to determine self-diffusion coefficients of Li+(7Li), SBP+(1H) and BF4 -(19F) in electrolytes with maximum gradient strength of 13.5 T/m at different durations. The interval between pulse gradients was set as 50 ms. Ionic conductivity of prepared electrolytes was measured by electrochemical impedance spectroscopy (EIS). [Results and discussion]Self-diffusion coefficients of different ions obtained from PGSE-NMR were plotted in Figure 1, with different concentration of SBPBF4 (0, 1, 2, and 3 M) in the 1 M LiBF4/PC electrolyte. Diffusion coefficients for all three ions decreased with an increment of added SBPBF4 concentration, while the value of SBP+ is higher compared to other two ions, especially Li+, in all cases. Based on obtained self-diffusion coefficients, we calculated the transport number t x of ions (x = Li+, SBP+, or BF4 -) according to the following equation(1) t x = N x D x /(N[Li+]D[Li+] + N[BF4 -] D[BF4 -] + N[SBP+] D[SBP+]) (1)where N x and D x is a concentration and self-diffusion coefficient of corresponding ions, respectively. Using this t x, we further calculated ionic conductivity of each ion by simply multiplying electrolyte ionic conductivity by t x. The evaluated values are shown in Figure 2. Like diffusion coefficients shown in Figure 1, Li+ ionic conductivity decreased with an increment of SBPBF4 concentration. Interestingly, cations ionic conductivity, which is sum of Li+ and SBP+, kept increased with an addition of SBPBF4. In order to discuss cations dissociation in electrolytes with presentence of SBPBF4, we evaluated number of carrier for Li+ based on the peak shifts observed in 7Li NMR spectra and theory of Haven ratio where degree of dissociation is considered as λEIS/λNMR. Here again, with a SBPBF4 concentration increase, number of Li+ carrier decreased, while number of SBP+ carrier increased. In conclusion, a dual-cation electrolyte (Li+ and SBP+) decreases Li+ ionic conductivity and its number of carrier, however, increases the two parameters for the SBP+. The present result suggests that the presence of highly conductive and dissociated SBP+ accelerates charge compensation of LTO reaction, and thus enhanced its rate capability. [References]1) G.G. Amatucci et al., J. Electrochem. Soc., 148 (8) A930 (2001).2) K. Naoi et al., Acc. Chem. Res., 46 (5), 1075 (2013).3) T. Ueda et al., 5th International Conference on Advanced Capacitors (ICAC 2016), 2O-03, Otsu, Japan (2016). Figure 1

Transport properties of protic and aprotic guanidinium ionic liquids.

Ionic liquids (ILs) are a promising class of solvents, functional fluids and electrolytes that are of high interest for both basic as well as applied research. For further fundamental understanding of ILs and a successful implementation in technical processes, a deeper insight into transport properties and their interrelations is of particular importance. In this contribution we synthesised a series of mostly novel protic and aprotic ILs based on the tetramethylguanidinium (TMG) cation that is a derivative of the superbase guanidine. Different substitution patterns and anions from acids with broadly varied pKa values were investigated. We measured general properties, such as thermal transitions and densities of these ILs, as well as their transport quantities by means of rheology, impedance spectroscopy and NMR diffusometry. Different models for the correlation of the transport properties, namely the Nernst–Einstein, Walden and Stokes–Einstein–Sutherland relations were applied. The deviation from ideal behaviour of fully dissociated electrolytes, often termed as ionicity, was quantified by the reciprocal Haven ratio, fractional Walden rule and ionicity obtained from the Walden plot. Velocity cross-correlation coefficients were calculated to gain further insight into the correlation between ion movements. Both protic and aprotic TMG ILs show transport properties comparable to other ILs with similar molecular weight and high ionicity values especially in contrast to other protic ILs. Lowest ionicity values were found for the protic ILs with smallest ΔpKa values between constituting acid and base. This can either be explained by stronger hydrogen bonding between cation and anion or lower anti-correlations between the oppositely charged ions. These results aim to provide insight into the properties of this interesting cations class and a deeper understanding of the transport properties of ILs and their interrelations in general.