20
Figure 4: Stejskal-Tanner plots of integrals obtained from PFGSE data of LiPF6 in DMC, 50:50 EC:DMC, and PC. 1 in dark orange and light orange 7
Li data is shown in blue, 19 broadband benchtop NMR spectrometer. F in gray, and 31 H data is shown P in green. All data were acquired on a single X-Pulse
A large transference number can reduce concentration polarisation of electrolytes during charge–discharge steps, producing higher power density. Optimally, t+ should be close to 1 for a lithium-ion battery.
As an example, Lithium hexafl uorophosphate salt (LiPF6) was studied in three different electrolyte solvents: DMC, a 50:50
As an example, Lithium hexafluorophosphate salt (LiPF6
) was studied in three different electrolyte
mixture of EC and DMC, and propylene carbonate (PC). The PFGSE spectra are shown in Figure 3.
solvents: DMC, a 50:50 mixture of EC and DMC, and propylene carbonate (PC). The PFGSE spectra are shown in Figure 3.
19F 7Li Table 2: Parameters measured by NMR for three electrolyte systems: LiPF6 11 9 7 5 3 1 -45 -50 -55 -60 -65 -70 -75 δ 19F / ppm -80 -85 -90 -95 -100 -105 25 20 15 10 5 δ 7Li / ppm 0 -5 -10 -15 -20 11 9 7 5 3 1 -40 -45 -50 -55 -60 -65 -70 -75 δ 19F / ppm -80 -85 -90 -95 -100 -105 9 8 7 6 5 4 3 δ 7Li / ppm 2 1 0 -1 -2 -3
same rate. In fact, the diffusion behaviours were identical within the precision of the method. However, as expected, the diffusion behaviour of the smaller Li+ ion differed signifi cantly from that of 19
F in the larger [PF6]− ion. In addition, the markedly different quantitative results in Table 2 for the same Li+
11 9 7 5 3 1 -45 -50 -55 -60 -65 -70 -75 δ 19F / ppm -80 -85 -90 -95 -100 -105 11 10 9 8 7 6 5 4 3 2 δ 7Li / ppm 1 0 -1 -2 -3 -4 -5 -6 -7 -8 and [PF6] − ions in Figure 3. Stacked PFGSE spectra from 10 to 100% of the full gradient
Figure 3: Stacked PFGSE spectra from 10 to 100% of the full gradient strength for LiPF6 solvents, measured at 39.5°C.
strength for LiPF6 in three different alkyl carbonate solvents, measured at 39.5°C.
in three different alkyl carbonate
the three solvent systems demonstrate the importance of solvent choice in battery design. Conductivity differed by approximately a factor of three between electrolytes using PC and DMC solvents, while cation transference changed far less. Moreover, the difference in diffusion behavior for DMC as a pure solvent, compared to the 50:50 mixture with EC, demonstrates the effects of environment on solvent molecules.
Conclusion 5
Benchtop NMR has become a powerful laboratory technique for lithium-ion battery analysis. It quickly and easily distinguishes between the diffusion behavior of different electrolyte solvents, as well as between diffusion of the ionic species and the solvent. Important parameters such as conductivity and ion transference numbers are easily determined from the NMR data. Together, these provide a detailed quantitative analysis of individual components and ultimately of the electrolyte system performance. The X-Pulse broadband benchtop NMR spectrometer therefore provides critical data for electrolyte design in any laboratory environment.
Figure 4: Stejskal-Tanner plots of integrals obtained from PFGSE data of LiPF6 in DMC, 50:50 EC:DMC, and PC. 1 in dark orange and light orange 7
Li data is shown in blue, 19 broadband benchtop NMR spectrometer. F in gray, and 31 H data is shown P in green. All data were acquired on a single X-Pulse
Figure 4. Stejskal-Tanner plots of integrals obtained from PFGSE data of LiPF6 in DMC, 50:50 EC:DMC, and PC. 1
All data were acquired on a single X-Pulse broadband benchtop NMR spectrometer.
and light orange 7 Sample
D+
Li data is shown in blue, 19 , cation
D- x10−10 m2 , anion s−1 DMC EC:DMC PC 5.16 2.74
5.68 (19 5.81 (31
4.45 @ 39.5°C
F) P)
12.7 6.42 (EC) 2.56 7.38 (DMC) D, solvent Conductivity x10-3 Sm-1 3.91 2.54 0.48 Table 2: Parameters measured by NMR for three electrolyte systems: LiPF6
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0.38 1.24 2.30 1.28 0.35 constants were determined for the cation, anion, and solvent, along with conductivity and the cation transference (t+
in DMC, in 50:50 EC:DMC, and in PC. Diffusion ).
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H data is shown in dark orange F in grey, and 31
P in green. Transference (t+
)
Moreover, other benchtop NMR applications signifi cantly improve quality control and raw materials checking for next generation batteries.
More applications notes and case studies can be downloaded at
https://nmr.oxinst.com/batteries.
Figure 4 reveals the differences in diffusion behaviour among components of a single electrolyte solution, as well as differences among the same species in different solvent conditions. Because 31 is part of the same [PF6]− ion as 19
F, the two should diffuse at the constants were determined for the cation, anion, and solvent, along with conductivity and the cation transference (t+ Table 2. Parameters measured by NMR for three electrolyte systems:
in DMC, in 50:50 EC:DMC, and in PC. Diffusion ).
LiPF6 in DMC, in 50:50 EC:DMC, and in PC. Diffusion constants were determined for the cation, anion, and solvent, along with conductivity and the cation transference (t+).
6 P
Sample
D+
, cation
D- x10−10 m2
, anion s−1 DMC EC:DMC PC 5.16 2.74 1.24
5.68 (19 5.81 (31
4.45 2.30 @ 39.5°C
F) P)
12.7 6.42 (EC) 7.38 (DMC) 2.56
D, solvent
Conductivity x10-3 Sm-1
Transference (t+
)
3.91 2.54 1.28
0.48 0.38 0.35
LiPF6 in DMC
LiPF6 in EC:DMC
LiPF6 in PC
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