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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

Scanning electron microscopy (SEM) picture of the surface of separator COD-20 (a) and COATED (b).
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ijms-16-20258-f005: Scanning electron microscopy (SEM) picture of the surface of separator COD-20 (a) and COATED (b).

Mentions: For this study, a polyethylene (PE) separator (COD-20) and a particle-coated PE separator (COATED) are used in comparison. Main characteristics are summarized in Table 3. The specific surface of both separators was measured (Table 3), where it differs by a factor of ~2 based on the additional weight of the ceramic layer. Both commercial separators are analyzed via scanning electron microscope (SEM) to visualize their surface structure (Figure 5). The cross section of the separator COATED is depicted in Figure 6. Both separators are composed of a polyethylene based porous membrane with its typical porous structure (Figure 5a). Based on the SEM images, the pore sizes can be estimated to be ~100–200 nm, which is much larger (~factor 100–500) than any hydrodynamic diameter of cationic Li+ species or anionic salts that are discussed in literature [38,39,40]. The separator COATED is covered by irregular shaped particles (size ≤ 2 µm) on its surface (Figure 5b), which are mainly identified as Al2O3 particles in energy dispersive X-ray spectroscopy (EDS) analysis. Traces of the elements Na and C were also observed, among others, on the surface of separator COATED, which can be explained by impurities and organic binder compounds. In the cross section image (separator COATED, Figure 6), it is seen that the surface of the porous PE membrane is completely covered by a porous particle coating with a thickness of 2–3 µm on each side. The permeability of air is almost identical for both separators, which reveals that the coating does not affect the gas permeability. It should be mentioned that PE melts at ~137 °C (provided as shut-down temperature), which influences the separator characteristics severely. The temperatures, which are applied during drying procedures, are therefore carefully controlled and not exceeded above 80 °C to ensure not to destroy the porosity fine structure.


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)

Scanning electron microscopy (SEM) picture of the surface of separator COD-20 (a) and COATED (b).
© Copyright Policy
Related In: Results  -  Collection

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

ijms-16-20258-f005: Scanning electron microscopy (SEM) picture of the surface of separator COD-20 (a) and COATED (b).
Mentions: For this study, a polyethylene (PE) separator (COD-20) and a particle-coated PE separator (COATED) are used in comparison. Main characteristics are summarized in Table 3. The specific surface of both separators was measured (Table 3), where it differs by a factor of ~2 based on the additional weight of the ceramic layer. Both commercial separators are analyzed via scanning electron microscope (SEM) to visualize their surface structure (Figure 5). The cross section of the separator COATED is depicted in Figure 6. Both separators are composed of a polyethylene based porous membrane with its typical porous structure (Figure 5a). Based on the SEM images, the pore sizes can be estimated to be ~100–200 nm, which is much larger (~factor 100–500) than any hydrodynamic diameter of cationic Li+ species or anionic salts that are discussed in literature [38,39,40]. The separator COATED is covered by irregular shaped particles (size ≤ 2 µm) on its surface (Figure 5b), which are mainly identified as Al2O3 particles in energy dispersive X-ray spectroscopy (EDS) analysis. Traces of the elements Na and C were also observed, among others, on the surface of separator COATED, which can be explained by impurities and organic binder compounds. In the cross section image (separator COATED, Figure 6), it is seen that the surface of the porous PE membrane is completely covered by a porous particle coating with a thickness of 2–3 µm on each side. The permeability of air is almost identical for both separators, which reveals that the coating does not affect the gas permeability. It should be mentioned that PE melts at ~137 °C (provided as shut-down temperature), which influences the separator characteristics severely. The temperatures, which are applied during drying procedures, are therefore carefully controlled and not exceeded above 80 °C to ensure not to destroy the porosity fine structure.

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