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Interaction of High Flash Point Electrolytes and PE-Based Separators for Li-Ion Batteries.

Hofmann A, Kaufmann C, Müller M, Hanemann T - Int J Mol Sci (2015)

Bottom Line: Cell testing of Li/NMC half cells reveals that those cell results cannot be inevitably deduced from physicochemical electrolyte properties as well as contact angle analysis.On the other hand, techniques are more suitable which detect liquid penetration into the interior of the separator.It is expected that the results can help fundamental researchers as well as users of novel electrolytes in current-day Li-ion battery technologies for developing and using novel material combinations.

View Article: PubMed Central - PubMed

Affiliation: Institut für Angewandte Materialien-Werkstoffkunde, Karlsruher Institut für Technologie (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany. andreas.hofmann2@kit.edu.

ABSTRACT
In this study, promising electrolytes for use in Li-ion batteries are studied in terms of interacting and wetting polyethylene (PE) and particle-coated PE separators. The electrolytes are characterized according to their physicochemical properties, where the flow characteristics and the surface tension are of particular interest for electrolyte-separator interactions. The viscosity of the electrolytes is determined to be in a range of η = 4-400 mPa∙s and surface tension is finely graduated in a range of γL = 23.3-38.1 mN∙m(-1). It is verified that the technique of drop shape analysis can only be used in a limited matter to prove the interaction, uptake and penetration of electrolytes by separators. Cell testing of Li/NMC half cells reveals that those cell results cannot be inevitably deduced from physicochemical electrolyte properties as well as contact angle analysis. On the other hand, techniques are more suitable which detect liquid penetration into the interior of the separator. It is expected that the results can help fundamental researchers as well as users of novel electrolytes in current-day Li-ion battery technologies for developing and using novel material combinations.

No MeSH data available.


Related in: MedlinePlus

DSC measurements of mixtures M-n (n = 1–6) in closed cup during cooling (a) and heating (b) at 10 K·min−1 (exo down).
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ijms-16-20258-f003: DSC measurements of mixtures M-n (n = 1–6) in closed cup during cooling (a) and heating (b) at 10 K·min−1 (exo down).

Mentions: The oxidative stability of the electrolytes was measured against Pt working electrodes. The measurements reveal an excellent oxidative stability of >5 V vs. Li/Li+ for all electrolyte mixtures (a detailed diagram is shown in supporting information (Figure S1)). Therefore, all electrolyte mixtures should withstand cell voltages up to 4.2 V vs. Li/Li+ and therefore should be suitable as electrolytes for NMC-based Li-ion cells based on its potential window. All mixtures are in liquid state at room temperature and the melting point is depressed compared to pure solvents when LiTFSA is added. It should be mentioned that the melting point is better described by the onset than the peak maximum in DSC measurements, albeit the determination of the onset is complicated by solid–solid transitions or recrystallizations. The temperature dependency of the density values is depicted in Figure 2, where the lowest value is received for the nitrile based electrolyte M-5 and the highest value for ionic liquid based mixture M-4. The temperature dependence for all mixtures is in similar order of magnitude, which can be quantified by the quotient d20 °C/d80 °C = 1.047 ± 0.006 for all mixtures. DSC measurements of the electrolyte mixtures are depicted in Figure 3. The maximum temperature of mixture M-1 during the measurement is set to 100 °C because of the low boiling point component dimethyl carbonate, whereas the other mixtures are investigated up to 200 °C (closed cup). It is supposed that within a cooling rate of 5 to 20 K∙min−1 the formation of a non-crystalline phase in case of mixture M-5 is favored, thus no crystallizing point can be detected. In this case, a distinct recrystallization during heating is found. Electrolytes M-3 and M-6 exhibit a recrystallization (Figure 3b, exo-peak) during heating as well, when the cooling is performed at 5 to 20 K∙min−1. It should be noted that the appearance of exothermal features in the DSC trace of sample M-1, M-3, M-5 and M-6 indicate the presence of amorphous phases. The DSC measurements reveal that all electrolyte mixtures are in liquid state at room temperature. Temperature-dependent viscosity and conductivity measurements are shown in Figure 4 for all mixtures. The detailed values are listed in Table S1.


Interaction of High Flash Point Electrolytes and PE-Based Separators for Li-Ion Batteries.

Hofmann A, Kaufmann C, Müller M, Hanemann T - Int J Mol Sci (2015)

DSC measurements of mixtures M-n (n = 1–6) in closed cup during cooling (a) and heating (b) at 10 K·min−1 (exo down).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4613202&req=5

ijms-16-20258-f003: DSC measurements of mixtures M-n (n = 1–6) in closed cup during cooling (a) and heating (b) at 10 K·min−1 (exo down).
Mentions: The oxidative stability of the electrolytes was measured against Pt working electrodes. The measurements reveal an excellent oxidative stability of >5 V vs. Li/Li+ for all electrolyte mixtures (a detailed diagram is shown in supporting information (Figure S1)). Therefore, all electrolyte mixtures should withstand cell voltages up to 4.2 V vs. Li/Li+ and therefore should be suitable as electrolytes for NMC-based Li-ion cells based on its potential window. All mixtures are in liquid state at room temperature and the melting point is depressed compared to pure solvents when LiTFSA is added. It should be mentioned that the melting point is better described by the onset than the peak maximum in DSC measurements, albeit the determination of the onset is complicated by solid–solid transitions or recrystallizations. The temperature dependency of the density values is depicted in Figure 2, where the lowest value is received for the nitrile based electrolyte M-5 and the highest value for ionic liquid based mixture M-4. The temperature dependence for all mixtures is in similar order of magnitude, which can be quantified by the quotient d20 °C/d80 °C = 1.047 ± 0.006 for all mixtures. DSC measurements of the electrolyte mixtures are depicted in Figure 3. The maximum temperature of mixture M-1 during the measurement is set to 100 °C because of the low boiling point component dimethyl carbonate, whereas the other mixtures are investigated up to 200 °C (closed cup). It is supposed that within a cooling rate of 5 to 20 K∙min−1 the formation of a non-crystalline phase in case of mixture M-5 is favored, thus no crystallizing point can be detected. In this case, a distinct recrystallization during heating is found. Electrolytes M-3 and M-6 exhibit a recrystallization (Figure 3b, exo-peak) during heating as well, when the cooling is performed at 5 to 20 K∙min−1. It should be noted that the appearance of exothermal features in the DSC trace of sample M-1, M-3, M-5 and M-6 indicate the presence of amorphous phases. The DSC measurements reveal that all electrolyte mixtures are in liquid state at room temperature. Temperature-dependent viscosity and conductivity measurements are shown in Figure 4 for all mixtures. The detailed values are listed in Table S1.

Bottom Line: Cell testing of Li/NMC half cells reveals that those cell results cannot be inevitably deduced from physicochemical electrolyte properties as well as contact angle analysis.On the other hand, techniques are more suitable which detect liquid penetration into the interior of the separator.It is expected that the results can help fundamental researchers as well as users of novel electrolytes in current-day Li-ion battery technologies for developing and using novel material combinations.

View Article: PubMed Central - PubMed

Affiliation: Institut für Angewandte Materialien-Werkstoffkunde, Karlsruher Institut für Technologie (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany. andreas.hofmann2@kit.edu.

ABSTRACT
In this study, promising electrolytes for use in Li-ion batteries are studied in terms of interacting and wetting polyethylene (PE) and particle-coated PE separators. The electrolytes are characterized according to their physicochemical properties, where the flow characteristics and the surface tension are of particular interest for electrolyte-separator interactions. The viscosity of the electrolytes is determined to be in a range of η = 4-400 mPa∙s and surface tension is finely graduated in a range of γL = 23.3-38.1 mN∙m(-1). It is verified that the technique of drop shape analysis can only be used in a limited matter to prove the interaction, uptake and penetration of electrolytes by separators. Cell testing of Li/NMC half cells reveals that those cell results cannot be inevitably deduced from physicochemical electrolyte properties as well as contact angle analysis. On the other hand, techniques are more suitable which detect liquid penetration into the interior of the separator. It is expected that the results can help fundamental researchers as well as users of novel electrolytes in current-day Li-ion battery technologies for developing and using novel material combinations.

No MeSH data available.


Related in: MedlinePlus