Physico-Chemical Properties of LiFSI Solutions I. LiFSI with

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Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Physico-Chemical Properties of LiFSI Solutions I. LiFSI with Valeronitrile, Dichloromethane, 1,2-Dichloroethane, and 1,2-Dichlorobenzene Johannes Neuhaus, Erik von Harbou,* and Hans Hasse Laboratory of Engineering Thermodynamics (LTD), University of Kaiserslautern, Erwin-Schrödinger Strasse 44, D-67663 Kaiserslautern, Germany

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S Supporting Information *

ABSTRACT: Lithium bis(fluorosulfonyl)imide (LiFSI) is a novel electrolyte for lithium-ion batteries. Valeronitrile (VN) is a good solvent for LiFSI, and dichloromethane (DCM), 1,2-dichloroethane (DCE), and 1,2-dichlorobenzene (DCB), are interesting antisolvents for crystallization. Physico-chemical data for the design of LiFSI production processes, in which these components are used, is lacking. Therefore, the solubility of LiFSI in VN, as well as in binary solvent mixtures VN + (DCM, DCE, DCB) was measured at temperatures between 278 and 343 K and concentrations of LiFSI up to 0.52 mol mol−1. Furthermore, vapor−liquid equilibria of the systems VN−DCE (at 200 mbar) and VN−DCB (at 200, 300, and 450 mbar) were studied. Also, the density and shear viscosity of solutions of LiFSI in VN were measured at temperatures between 293 and 333 K and concentrations of LiFSI up to 0.5 mol mol−1.

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INTRODUCTION Lithium-ion batteries (LiB) are widely used for storing electricity. The benchmark for electrolytes, that are used in LiB is presently lithium hexafluorophosphate (LiPF6). An interesting candidate, which might replace LiPF6 in the future, is lithium bis(fluorosulfonyl)imide (LiFSI). It has a higher electrolytic conductivity and better stability regarding hydrolysis compared to LiPF6 and is, hence, highly attractive for LiB.1−3 The production of LiFSI is a sophisticated task.4−7 Crystallization is an important step in these processes and needed to meet the high-purity requirements of the battery industry.8 Crystallization is commonly induced either by cooling, evaporation of solvent, or the application of an antisolvent. To identify solvents and solvent mixtures of interest for the production of LiFSI, a literature and patent study and a subsequent screening was performed prior to the experimental study. In the literature, there are only few reports on solid− liquid equilibria in systems containing LiFSI. Data on solid− liquid equilibria of LiFSI in acetonitrile is reported by Han et al.3 Kubota et al.9 studied the solid−liquid equilibria of LiFSI in alkali bis(fluorosulfonyl)imides M-FSI with M = (Na, K, Rb, Cs). To our knowledge, these are the only previous publications in the field which report quantitative data. In contrast to the literature, there is a vast quantity of promising solvents that are proposed in patents. In general, the patents propose solvents of the aromatic hydrocarbon type (chlorobenzene, dichlorobenzene, toluene, xylene), of the nitrile type (acetonitrile, butyronitrile, valeronitrile), and carbonate alkyl type (diethyl carbonate, dimethyl carbonate, ethylene carbonate, propylene carbonate).4 Of the © XXXX American Chemical Society

proposed solvents, the nitrile and carbonate alkyl types are generally good solvents for LiFSI, whereas the aromatic hydrocarbon type solvents are potential antisolvents.4,7,10−13 The usage of dichlorobenzene as an antisolvent is highlighted in the patent by Rhodia S.A.4 It also proved to be promising in the preliminary screening and was therefore selected for the present study. In the screening, it was found that not only aromatic dichorinated solvents are good antisolvents but also dichlorinated alkanes. Therefore, also dichloromethane (DCM) and 1,2-dichloroethane (DCE) were included in the present study. The study of Han et al.3 shows that nitriles are interesting good solvents for LiFSI. However, acetonitrile, as studied by Han et al.,3 is not the most attractive nitrile for dissolving LiFSI. It has a high vapor pressure and is a good solvent for water and both are unwelcome. These drawbacks can be overcome easily by selecting nitriles with longer alkyl chains, such as butyronitrile or valeronitrile, as they are also suggested in the patent literature.4 For the present study, valeronitrile was selected, in continuation of our previous work.14 Hence, the present experimental study was carried out with valeronitrile (VN) as a good solvent for LiFSI and three dichlorinated solvents that are potential antisolvents (dichloromethane (DCM), 1,2-dichloroethane (DCE), and 1,2-dichlorobenzene (DCB)).13 In the present work, the solubility of LiFSI in VN, as well as in the binary solvent mixtures VN + DCM, Received: July 9, 2018 Accepted: January 18, 2019

A

DOI: 10.1021/acs.jced.8b00590 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Overview of Some Pure Component Physico-Chemical Properties15−53a

The numbers for ρ, η, and ϵ for VN, DCM, DCE, and DCB refer to the liquid state at 298.15 K and ambient pressure. For multiple references, the presented numbers are the arithmetic mean of the selected literature data. a

flushed with dry air. The measurements were carried out at ambient pressure. The apparatus was calibrated with dry air and degassed deionized liquid water. The temperature was measured with a built-in thermometer for which the manufacturer reports a standard uncertainty of ±0.1 K. The results for the density which are reported here are the arithmentic mean of the three repeated measurements. Their relative standard deviation was ≤0.15%. As this exceeds the uncertainty of the calibration, the relative standard uncertainty of the density data is estimated to be about ±0.15%. Shear Viscosity. The shear viscosity of the mixtures was determined with a falling sphere viscosimeter (HAAKE, Type B). The measurements were carried out at ambient pressure. The temperature was controlled externally with a thermostat (Julabo F32 HE, temperature stability ±0.01 K). The temperature was measured with a platinum resistance thermometer (Pt100), which was calibrated in our laboratory using a certified standard. The standard uncertainty of the temperature measurement is ±0.1 K. The apparatus was calibrated with degassed deionized liquid water and three different certified standards (D5, N14, and N100) purchased from Paragon Scientific Ltd.. All measurements were repeated three times and the arithmetic mean of the results is reported. The relative standard deviations of the three results was below ±0.5%. That number is taken for the relative standard uncertainty of the measurement of the shear viscosity higher than 1.5 mPa s. For lower viscosities, we estimate the relative standard uncertainty to be 2.5%. Solid−Liquid Equilibrium. The solid−liquid equilibrium was determined by isothermal titration. The titrations were carried out in nine identical glass vials (Erlenmeyer flasks, 100 mL). Each glass vial was equipped with a magnetic stirrer and a platinum resistance thermometer (Pt100). The nine glass vials were submersed in an insulated oil bath to control the temperature of the samples. The temperature of the oil bath was controlled using a thermostat (Julabo F32 HE, temperature stability ±0.01 K). The platinum resistance thermometers were calibrated in our laboratory using a certified standard. The maximum difference between the temperature of the nine samples was always below ±0.1 K. The standard uncertainty of the temperature measurement is estimated to be ±0.2 K. The sample vials were prepared as follows. LiFSI salt and solvent (either a pure substance or a mixture with known composition) were filled in the glass vials and hermetically sealed in

VN + DCE, and VN + DCB were studied. This is complemented by data on vapor−liquid equilibria in the systems VN + DCE and VN + DCB, and data on the density and the shear viscosity of solutions of LiFSI in VN. Also, such data were previously unavailable.

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EXPERIMENTAL SECTION

Lithium bis(fluorosulfonyl)imide (LiFSI, ≥0.999 g g−1) was supplied by Budan Process UG. Valeronitrile (≥0.995 g g−1), dichloromethane (anhydrous, ≥0.998 g g−1), 1,2-dichloroethane (anhydrous, 0.998 g g−1), and 1,2-dichlorobenzene (anhydrous, 0.99 g g−1) were purchased from Sigma-Aldrich. All chemicals were used as received. The water content of the pure components was determined by coulometric Karl Fischer titration (Metrohm 831 KF coulometer) and was found to be below 50 × 10−6 g g−1 for all solvents and below 30 × 10−6 g g−1 for LiFSI. Some relevant physico-chemical properties of the studied solvents are shown in Table 1, wherein M is the molar mass, Tnmp and Tnbp are the normal melting point and the normal boiling point, respectively, ρ is the density, η is the shear viscosity, and ϵ is the dielectric constant. Sample Preparation. All chemicals were handled in an inert gas glovebox (GS Glovebox Technik) that maintained a nitrogen atmosphere with a water content of less than 2 × 10−6 g g−1. A laboratory balance (Mettler-Toledo AG204) with an accuracy of ±0.0001 g according to calibration protocol was used for the gravimetrical sample preparation. The total mass of each sample was larger than 30 g. The standard uncertainty of the mass fraction is estimated to be ±0.0002 g g−1 for all components. The samples were hermetically sealed in 40 mL glass vials for the measurements of the density and shear viscosity and in 100 mL Erlenmeyer flasks for the measurements of the solid−liquid equilibrium. For the measurements of the vapor−liquid equilibrium solvent mixtures with more than 150 mL where prepared. Further details are given in the following section. Measurements. Density. The density of the mixtures was measured with a vibrating tube densimeter (Anton Paar DMA 4500M). The measurements were conducted according to the ASTM method D4052. All experiments were carried out three times. Before and after each set of these three measurements, the apparatus was cleaned with toluene, water, and ethanol and B



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represent the concentration dependence of the density of a solution of a strong electrolyte in a solvent. The resulting relation is often linear in a wide concentration range. Thus, the specific density ρ of the electrolyte solution is described in this work as a function of the true mole fraction of Li+-ions xLi+. However, as the maximum concentration of Li+ in solution was very high, a quadratic term was added resulting in the correlation given in eq 1.

the glovebox. The amount of LiFSI and solvent was determined gravimetrically using a laboratory balance (Mettler-Toledo balance AG204, accuracy of ±0.0001 g). The amount of LiFSI was chosen large enough so that not all LiFSI was dissolved. To ensure the equilibration of the samples, the glass vials were placed in the oil bath of the desired temperature and continuously stirred for at least 12 hours. After the equilibration, solvent was added stepwise using a syringe. The added amount of solvent was determined by weighing the syringe before and after the addition of solvent using a laboratory balance (MettlerToledo balance AG204, accuracy ±0.0001 g). Beginning with larger amounts of solvent, the mass of solvent was lowered gradually so that only single droplets (≈2−4 mg) were added in the proximity of the solubility limit. The delay time between two injections was at least 30 min to ensure equilibration of the samples. Close to the solubility limit the equilibration delay was increased to 60 min. The solubility limit was determined by visual observation of the dissolution of the last LiFSI crystal. For each SLE data point, the measurement was performed as described above in three different glass vials. The data of the SLE reported in this work represent the arithmetic mean of the three results. The standard deviation of the mole fraction of LIFSI did not exceed ±0.0033 mol mol−1. To check the accuracy of the described experimental procedure the solubility of potassium chloride and sodium acetate in water was determined. In the Supporting Information, the results from the present work are compared to data from the literature. The maximal absolute deviation between our values and the literature values is ±0.0014 mol mol−1. The standard uncertainty of data for the mole fraction of LIFSI at the solubility limit is estimated to be smaller than ±0.0033 mol mol−1. Vapor−Liquid Equilibrium. The isobaric measurements of the vapor−liquid equilibrium were carried out in a circulation still, that was initially developed by Rafflenbeul and Hartmann.54 The experimental apparatus used in the present work and the operation procedure are described in previous work.55,56 The equilibrium temperature as well as the composition of the coexisting phases were determined for different compositions of the stock solution at constant pressure. The temperature was determined with a platinum resistance thermometer (Pt100) which was calibrated in our laboratory using a certified standard. The standard uncertainty of the temperature data is ±0.1 K. The pressure was determined with a capacitive pressure sensor (Wika, P-30) with a certified accuracy of ±0.05% in the experimental range. The composition of the samples was determined by gas chromatography (Agilent Technologies 7890A; for details, see Supporting Information). The standard uncertainty of the concentration measurements was determined with test samples of which the composition was known from the gravimetrical sample preparation. The maximal relative uncertainty is ±0.3%. Further, the experimental setup was tested by the measurement of the pure vapor pressures of VN and DCB at pressures between 50 and 1000 mbar. The results from the pure vapor pressure measurements of the present work are compared to data from the literature in the Supporting Information. The relative standard uncertainty of the vapor pressure measurements is ±2% for pressures below 150 mbar and ±1% for pressures above 150 mbar.

2 ij x Li+ yz ij x Li+ yz jij ρ zyz j z j z jj z = + + A A A j z j z z 0 1 2 −1 −1 j g cm−3 z k mol mol { k mol mol { k {

(1)

where A0 is the density of the pure solvent VN. The temperature dependence of the parameters Ai is described by iT y Ai = ai + bijjj zzz kK {

(2)

with i = (0, 1, 2). ai and bi are adjustable parameters. It is assumed that LiFSI is always fully dissociated in the solutions. Shear Viscosity. The dependence of the shear viscosity η of solutions of LiFSI in VN on the composition and the temperature is described by eq 3: 2 i x LiFSI yz ij x LiFSI yz i η yz z j z zz = A 0 + A1jjj + lnjjj A 2j −1 z −1 z k mPa s { k mol mol { k mol mol {

(3)

where xLiFSI is the apparent mole fraction of LiFSI and the Ai are empirical temperature-dependent functions i b y i c y Ai = ai + jjjj i zzzz + jjjj i zzzz k T /K { k T /K {

2

(4)

with i = (0, 1, 2). ai, bi and ci are adjustable parameters. Solid−Liquid Equilibrium. VN is a good solvent for LiFSI whereas the solubility of LiFSI in the other studies solvents is negligible. The temperature dependence of the solubility of LiFSI in VN is correlated using 2 jij x LiFSI zyz = a + a ijj T yzz + a ijj T yzz j 0 1j z 2j z −1 z kK { kK { k mol mol {

(5)

where xLiFSI is the apparent mole fraction of LiFSI and a0, a1, and a2 are adjustable parameters. The solubility of LiFSI in the binary solvent mixtures VN− DCM, VN−DCE, and VN−DCB is described with a mixing rule. VN k x LiFSI = x ̃VNx LiFSI + xk̃ x LiFSI + x ̃VNxk̃ Bk

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CORRELATIONS Density. In previous work of our group,57,58 it was found that it is convenient to use the true mole fraction of cations to

(6)

Figure 1. Specific density of solutions of LiFSI in VN as a function of the mole fraction of Li+-ions and the temperature. Symbols: experimental data. Surface: correlation (eq 1 with parameters from Table 3). C



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Table 2. Experimental Data of the Density of Solutions of LiFSI in VN at p = 101.3 kPaa ρ/g cm−3 −1

xLiFSI/mol mol 0.0000 0.1000 0.1997 0.2999 0.4076

283.15 K

293.15 K

303.15 K

313.15 K

323.15 K

333.15 K

0.8077 0.9279 1.0535 1.1664 1.2773

0.7991 0.9191 1.0444 1.1572 1.2678

0.7904 0.9103 1.0353 1.1480 1.2584

0.7817 0.9015 1.0262 1.1388 1.2490

0.7729 0.8926 1.0171 1.1297 1.2398

0.7642 0.8838 1.0081 1.1206 1.2306

Standard uncertainties u are u(xLiFSI) = 0.0001 mol mol−1, u(T) = 0.1 K, ur(ρ) = 0.0015, and u(p) = 3 kPa.

a

Table 3. Parameters of the Correlation Function (Equation 1) for the Density of Solutions of LiFSI in VN a0

b0

a1

b1

a2

1.0544

−0.0009

1.2873

−0.0002

1.3820

b2

Figure 3. Solid−liquid equilibrium in the system LiFSI + VN. Symbols: experimental data. Line: correlation (eq 5 with parameters from Table 7).

Figure 2. Shear viscosity of solutions of LIFSI in VN as a function of the apparent mole fraction of LiFSI and temperature. Symbols: experimental data. Surface: correlation (eq 3 with parameters from Table 5).

Table 6. Experimental Data of the Solid-Liquid Equilibrium of Solutions of LiFSI in VN at p = 101.3 kPaa

Table 4. Experimental Data of the Shear Viscosity of Solutions of LiFSI in VN at p = 101.3 kPaa η/mPa s xLiFSI/mol mol−1

293.15 K

313.15 K

333.15 K

0.0000 0.0499 0.1000 0.1997 0.2999 0.3443 0.4076 0.4999

0.7191 1.3359 2.5207 11.6691 41.8164 65.0317 123.6403 382.1727

0.5654 0.9852 1.7228 6.6061 21.0746 30.4693 53.2010 117.8338

0.4567 0.7657 1.2756 4.2145 12.2087 16.8805 27.4998 59.3869

a Standard uncertainties u are u(xLiFSI) = 0.0001 mol mol−1, u(T) = 0.1 K, ur(η ≤ 1.5 mPa s) = 0.025, ur(η ≥ 1.5 mPa s) = 0.005, and u(p) = 3 kPa.

T/K

xLiFSI/mol mol−1

278.15 283.15 288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15 343.15

0.40483 0.41004 0.41532 0.42197 0.43017 0.43873 0.44589 0.45515 0.46418 0.47363 0.48227 0.49241 0.51718

Standard uncertainties u are u(T) = 0.2 K, u(xLiFSI) = 0.0033 mol mol−1, and u(p) = 3 kPa. Liquid phase data. The solid phase is pure LiFSI. a

Table 7. Parameters of the Correlation Function (Equation 5) for the Solid−Liquid Equilibrium of Solutions of LiFSI in VN

with k = (DCM, DCE, DCB). xLiFSI is the apparent mole fraction of LIFSI. x̃i is the mole fraction of solvent i in the LiFSI-free mixture of solvent i in VN. Bk is a temperature-dependent function

iT y Bk = b0, k + b1, k jjj zzz (7) kK { with k = (DCM, DCE, DCB). b0,k and b1,k are adjustable parameters.

a0

a1

a2

0.84081

−0.004239

9.60 × 10−06

As the solubility of LiFSI in the pure solvents DCM, DCE, and DCB is negligible (see Results and Discussion), eq 6 can be simplified to eq 8 VN x LiFSI = x ̃VNx LiFSI + x ̃VN(1 − x ̃VN)Bk

(8)

Table 5. Parameters of the Correlation Function (Equation 3) for the Shear Viscosity of Solutions of LiFSI in VN a0

b0

c0

a1

b1

c1

a2

b2

−4.1074

1107.48

43.29

−27828

5793132

−63.45

43977

−8102575

D

c2



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Table 8. Experimental Data of the Solid−Liquid Equilibrium of Solutions of LiFSI in DCM, DCE, and DCB at 293.15 K and p = 101.3 kPaa system −1

xLiFSI/mol mol

LiFSI-DCM

LiFSI-DCE

−6

−6

≤59 × 10

≤68 × 10

Table 9. Experimental Data of the Solid−Liquid Equilibrium of Solutions of LiFSI in VN−DCB at p = 101.3 kPaa LiFSI−VN−DCM

LiFSI-DCB −6

≤137 × 10

Standard uncertainties u are u(xLiFSI) = 0.0001 mol mol−1, u(T) = 0.2 K, and u(p) = 3 kPa. The solubility limit was not reached in all three systems. The soluble mole fraction of LiFSI is below the shown values. a

T/K

xLiFSI/mol mol−1

283.15

0.29103 0.22908 0.15909 0.30987 0.24217 0.16255

293.15

0.49163 0.41486 0.30664 0.47856 0.40782 0.30537 LiFSI−VN−DCE

T/K

xLiFSI/mol mol−1

278.15

0.15043 0.22310 0.28790 0.15062 0.23044 0.30073 0.17301 0.26010 0.33199 0.18394 0.28020 0.36000

293.15

313.15

333.15

xVN/mol mol−1

xVN/mol mol−1

0.28036 0.38844 0.46998 0.28029 0.38477 0.46152 0.27291 0.36994 0.44088 0.2693 0.35989 0.42240 LiFSI−VN−DCB

xDCM/mol mol−1 0.21734 0.35606 0.53428 0.21157 0.35001 0.53208 xDCM/mol mol−1 0.56921 0.38847 0.24212 0.56908 0.38480 0.23775 0.55408 0.36996 0.22712 0.54676 0.35991 0.21760

T/K

xLiFSI/mol mol−1

xVN/mol mol−1

xDCM/mol mol−1

293.15

0.29557 0.23505 0.15291 0.32373 0.26130 0.17481 0.35649 0.28048

0.46903 0.39473 0.28291 0.45028 0.38118 0.27560 0.42889 0.36645

0.23540 0.37022 0.56418 0.22599 0.35752 0.54960 0.21462 0.35308

313.15

333.15

Standard uncertainties u are u(xi) = 0.0033 mol mol−1, u(T) = 0.2 K, and u(p) = 3 kPa. Liquid phase data. The solid phase is pure LiFSI. Liquid phase data. The solid phase is pure LiFSI a

Table 10. Parameters of the Correlation (Equation 8) for the Solid−Liquid Equilibrium of Solutions of LiFSI in VN−DCM, VN−DCE, and VN−DCB b0

b1

0.00208 −0.19021 0.00145

−0.55234 0.00096 −0.35831

ij ps yz Bi lnjjjj i zzzz = Ai + Ci + k mbar {

Figure 4. Solid−liquid equilibria in the systems (a) LiFSI + VN + DCM, (b) LiFSI + VN + DCE, and (c) LiFSI + VN + DCB. Symbols: experimental data. Lines: correlation of experimental data (eq 8 with parameters from Table 10).

T K

(10)

where Ai, Bi, and Ci are adjustable parameters. The nonrandom two-liquid (NRTL) model59 is applied to describe the liquid phase activity coefficient of species i. The nonrandomness parameters αij are set to 0.3 for all investigated systems. The temperature dependence of the binary interaction parameters τij is correlated with

Vapor−Liquid Equilibrium. The vapor−liquid equilibrium (VLE) of the binary mixtures VN−DCE and VN− DCB is described by the extended Raoult’s law pis xiγi = pyi

system LiFSI−VN−DCM LiFSI−VN−DCE LiFSI−VN−DCB

(9)

psi

where is the vapor pressure of component i, xi, and yi are the mole fraction of component i in the liquid and vapor phase, γi is the activity coefficient of component i, and p is the pressure. The temperature dependence of the vapor pressure of the pure component psi is correlated using

τij = aij +

bij T/K

(11)

where aij and bij are adjustable parameters. E



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RESULTS AND DISCUSSION

Density. Figure 1 shows the experimental data for the density of solutions of LiFSI in VN together with their correlation by eq 1. The numerical experimental data is presented in Table 2 and the correlations parameters in Table 3. The correlation describes the experimental data within the experimental uncertainty. Figure 1 shows that the density depends linear on the temperature and on the mole fraction of Li+-ions. Thus, the chosen correlation (see eq 1) can describe the experimental results well. Shear Viscosity. Figure 2 shows the experimental data for the shear viscosity of solutions of LiFSI in VN together with their correlation by eq 3. The numerical experimental data is presented in Table 4 and the correlations parameters in Table 5. The mean relative deviation of the experimental data and the correlation is 3.5% and the maximal absolute deviation is 1.6 mPa s. As expected, both the temperature and the concentration of LiFSI have a strong influence on the viscosity. A very strong increase of the viscosity for low temperatures and high concentrations of LiFSI is observed. The temperature dependence of the viscosity is more important in regions where the viscosity is high. The increase in viscosity with increasing concentration of LiFSI can be explained by the strong ion-dipole coordination of the Li+-ions and the aprotic valeronitrile molecules that leads to large, poorly mobile complexes.

Figure 5. Comparison of the solid−liquid equilibria in the systems LiFSI + VN + DCM (blue circle, 298.15 K), LiFSI + VN + DCE (yellow square, 293.15 K), and LiFSI + VN + DCB (red triangle, 298.15 K). Symbols: experimental data. Lines: correlation of experimental data at 293.15 K (eq 8 with parameters from Table 10).

Parameter Estimation. All adjustable parameters were determined from fits to experimental data from the present work. As goal function the sum of the squared relative deviations between the experimental results and the correlation results of all data points was used. The optimization was carried out in Mathworks Matlab 2016b using the solver lsqnonlin.

Figure 6. Vapor−liquid equilibrium in the system VN + DCE at 200 mbar, (a) T−xy and (b) K-factor. Symbols: experimental data. Lines: NRTL model with parameters from Table 13.

Figure 7. Vapor−liquid equilibrium in the system VN + DCB at 200 mbar (blue), 300 mbar (yellow), and 450 mbar (red), a) T−xy and b) K-factor. Symbols: experimental data. Lines: NRTL model with parameters from Table 13. F



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Solid−Liquid Equilibria. Binary Systems. Figure 3 shows the experimental data of the solubility of LiFSI in VN together with their correlation by eq 5. The numerical experimental data is presented in Table 6 and the correlation parameters in Table 7. The correlation describes the experimental data for LiFSI in solutions of VN within the experimental uncertainty. The solubility of LiFSI increases with increasing temperature. The steady increase of the solubility indicates that in the investigated temperature range no transition of the solid phase occurs. In an additional experiment, the coexisting phases obtained from a supersaturated solution were separated and the crystalline solid phase was washed with dichloromethane, vacuum-dried, and dissolved in dry methanol. The obtained sample was analyzed in a nuclear magnetic resonance (NMR) spectrometer (Bruker Avance 3 HD 400 MHz-NMR equipped with a cryogenic probe). The acquired 1H-, 13C-, and 19F-NMR spectra confirmed that the crystalline solid phase was pure LiFSI (xVN < 1 × 10−5 mol mol−1, estimated from the limit of detection). The solubility of LiFSI in DCM, DCE or DCB measured with the same titration method at 293.15 K was was found to be in the ppm range. Results are presented in Table 8. In addition, equilibrated liquid phases of the SLEs (LiFSI−DCM, LiFSI−DCE, LiFSI−DCB) at 298 K were analyzed with quantitative 7Li- and 19F-NMR spectroscopy. The concentrations of LiFSI in the solvents were below the detection limit, which is approximately 1 × 10−5 mol mol−1. These results show that DCM, DCE, and DCB are good antisolvents for LiFSI. Ternary Systems. Figure 4 shows the experimental data for the solubility of LiFSI in different ternary systems together with the corresponding correlations using eq 8 (panel a, LiFSI + VN + DCM; panel b, LiFSI + VN + DCE; panel c, LiFSI + VN + DCB). The numerical experimental data are presented in Table 9 and the correlation parameters in Table 10. The correlations describe the experimental data well for all systems. The absolute deviations are in a band of ±0.005 mol mol−1. Qualitatively, the three systems show similar behavior. For increased temperature the solubility of LiFSI increases. Likewise, the solubility of LiFSI is reduced upon addition of DCM, DCE, or DCB to solutions of LiFSI in VN. The resulting curves are slightly bent, which was the reason for introducing the nonlinear term in eq 8. Figure 5 depicts the direct comparison of the solubility of LiFSI in the binary solvents for similar temperatures (VN−DCM,

Table 12. Experimental Data of the Vapor−Liquid Equilibrium in the Binary System VN + DCB at 200, 300, and 450 mbara p = 200 mbar T/K 363.51 364.47 365.65 366.51 367.42 367.44 368.54 369.24 371.58 373.64 376.79 380.95 385.42 390.12 391.66 393.53 T/K 374.68 375.25 376.03 377.26 379.70 383.06 383.94 385.46 385.20 389.69 394.33 399.50 401.82 403.73

Table 11. Experimental Data of the Vapor−Liquid Equilibrium in the Binary System VN + DCE at 200 mbara T/K

xDCE/mol mol−1

yDCE/mol mol−1

317.11 319.02 320.92 323.02 329.53 334.30 339.32 346.71 350.92 354.24 356.54 358.52

0.9793 0.9701 0.9603 0.9450 0.8943 0.8352 0.7573 0.5973 0.4726 0.3656 0.2634 0.1600

0.8370 0.7801 0.7250 0.6697 0.5128 0.4122 0.3083 0.1900 0.1303 0.0883 0.0594 0.0338

xVN/mol mol−1

yVN/mol mol−1

0.9592 0.9062 0.8456 0.7970 0.7297 0.7476 0.6916 0.6546 0.5529 0.4701 0.3572 0.2006 0.1207 0.0569 0.0392 0.0216 p = 300 mbar xVN/mol mol−1

0.9855 0.9650 0.9406 0.9220 0.8949 0.9007 0.8735 0.8590 0.8133 0.7680 0.6769 0.5258 0.3824 0.2192 0.1635 0.0954 yVN/mol mol−1

0.9645 0.9323 0.8746 0.8109 0.6841 0.5390 0.5126 0.4684 0.4667 0.3324 0.2163 0.1216 0.0835 0.0511 p = 450 mbar

0.9855 0.9731 0.9500 0.9271 0.8616 0.7930 0.7788 0.7491 0.7455 0.6303 0.4984 0.3393 0.2710 0.1892

T/K

xVN/mol mol−1

yVN/mol mol−1

386.37 386.88 387.69 389.94 392.28 395.22 396.28 397.25 400.54 404.53 406.96 410.15 412.25 414.30 418.21 420.56

0.9738 0.9465 0.8969 0.7913 0.6853 0.5698 0.5165 0.4785 0.3655 0.2727 0.2079 0.1522 0.1122 0.0805 0.0375 0.0161

0.9887 0.9768 0.9545 0.9089 0.8609 0.8010 0.7731 0.7514 0.6737 0.5749 0.5087 0.4097 0.3415 0.2663 0.1342 0.0612

a

Standard uncertainties u are ur(xi) = 0.003, ur(p) = 0.01, and u(T) = 0.1 K.

293.15 K; VN−DCE, 298.15 K; and VN−DCB, 293.15 K). Interestingly, all three systems show the same dependence of the solubility of LiFSI on the concentration of the antisolvent

a

Standard uncertainties u are ur(xi) = 0.003, ur(p) = 0.01, and u(T) = 0.1 K. G



Article

(i.e., DCM, DCE, or DCB). A rational for that finding might be that DCM, DCE, and DCB have a similar polarity (ϵ about 10), which is much lower than that of VN (ϵ about 20 cf. Table 1). Vapor−Liquid Equilibria. Figures 6 and 7 show the experimental data of the binary VLE of the systems VN + DCE (at 200 mbar) and VN + DCB (at 200, 300, and 450 mbar) together with the NRTL-model. The numerical experimental data are presented in Tables 11 and 12. The NRTL parameters and Antoine’s equation parameters are reported in Tables 13 and 14, respectively. The NRTL model describes the experiTable 13. Parameters of the NRTL Model with τij = aij + of the Binary Solvent Mixtures VN−DCE and VN-DCB component i

VN

VN + DCB indicate that these components can be separated easily by distillation. The present data can be used for designing LiFSI production processes in which LiFSI is dissolved in VN and obtained as a pure component using DCM, DCE, or DCB as antisolvents. This paper is Part I of a series of two papers reporting on properties of LiFSI solutions. In Part II, results for the solvents methyl tert-butyl ether (MTBE), water, and anisole are presented.

■

S Supporting Information *

bij

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b00590.

T/K

Sample description table; overview of experimental data of the solid−liquid equilibria of the test systems KClH2O and NaOAc-H2O, and the experimental data from literature;61−63 overview of experimental data of the pure vapor pressure measurements of VN and DCB, and experimental data from literature;17,64−67 parameters of the gaschromatographic analysis (Gaschromatograph: Agilent Technologies 7890A) of the coexisting phases in the experimental measurement of the vapor−liquid equilibrium in the binary solvent systems VN−DCE and VN−DCB. (PDF)

VN

component j

DCB

DCE

aij aji bij bji αij = αji

−4842.895 4827.537 12.71602 −11.84822 0.3

−123.290 417.091 −0.71910 −0.21092 0.3

Table 14. Parameters of the Antoine’s Equation (Equation 10) for the Pure Component Vapor Pressures of VN and DCB from the Present Worka component

VN

DCB

DCE60

A B C T

17.2158 −3824.91 −41.794 [329 K, 411 K]

15.4903 −3071.63 −95.342 [360 K, 453 K]

7.0253 1271.3 222.927 [242 K, 372 K]

a

ASSOCIATED CONTENT

(

Parameters of the Antoine’s equation log

p mmHg

)

(

= A − B/ C +

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +49-631/2054685. Fax: +49-631/205-3835. ORCID

T °C 60

)

Johannes Neuhaus: 0000-0003-1528-4811 Erik von Harbou: 0000-0001-9228-8942

for the pure component vapor pressures of DCE taken from DDB.

Notes

The authors declare no competing financial interest.

mental data well for all systems. For VN + DCE, the absolute deviations are in a band of 0.0042 mol mol−1 with a mean average deviation of 0.0017 mol mol−1. For VN + DCB, the absolute deviations are in a band of 0.0276 mol mol−1 with a mean average deviation of 0.0060 mol mol−1. No azeotropes are observed. VN is the high-boiling component in the system VN + DCE, whereas it is the low-boiling component in the system VN + DCB. In both cases, VN and the other solvent can be separated easily by distillation. This can also be seen in the K-factors, which are in addition a measure for the consistency of the experimental data.

■

REFERENCES

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■

CONCLUSIONS In the present work, a systematic investigation of the density, shear viscosity, and solid−liquid equilibrium of solutions of LiFSI in VN was carried out at ambient pressure, temperatures between 278 and 333 K, and mole fractions of LiFSI up to 0.52 mol mol−1. In addition, the solid−liquid equilibria in solutions of LiFSI in binary solvent mixtures VN + DCM, VN + DCE, and VN + DCB, as well as the isobaric vapor−liquid equilibria in the systems VN + DCE and VN + DCB were investigated experimentally. Empirical correlations are provided that are faithful representations of the experimental data. Our findings show that LiFSI is highly soluble in the aprotic VN and almost insoluble in DCM, DCE, and DCB, so that the latter components are good antisolvents for crystallization. Pure LiFSI can be obtained from such solutions by crystallization. The vapor−liquid equilibria of the binary mixtures VN + DCE and H



Article

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J


Physico-Chemical Properties of LiFSI Solutions I. LiFSI with

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