Li-Nafion Membrane Plasticised with Ethylene Carbonate/Sulfolane: Influence of Mixing Temperature on the Physicochemical Properties

Abstract

The use of dipolar aprotic solvents to swell lithiated Nafion ionomer membranes simultaneously serving as electrolyte and separator is of great interest for lithium battery applications. This work attempts to gain an insight into the physicochemical nature of a Li-Nafion ionomer material whose phase-separated nanostructure has been enhanced with a binary plasticiser comprising non-volatile high-boiling ethylene carbonate (EC) and sulfolane (SL). Gravimetric studies evaluating the influence both of mixing temperature (25 to 80 °C) and plasticiser composition (EC/SL ratio) on the solvent uptake of Li-Nafion revealed a hysteresis between heating and cooling modes. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the saturation of a Nafion membrane with such a plasticiser led to a re-organisation of its amorphous structure, with crystalline regions remaining practically unchanged. Regardless of mixing temperature, the preservation of crystallites upon swelling is critical due to ionomer crosslinking provided by crystalline regions, which ensures membrane integrity even at very high solvent uptake (≈200% at a mixing temperature of 80 °C). The physicochemical properties of a swollen membrane have much in common with those of a chemically crosslinked polymer gel. The conductivity of ≈10−4 S cm−1 demonstrated by Li-Nafion membranes saturated with EC/SL at room temperature is promising for various practical applications.

Modification of the Physical Properties of a Nafion Film Due to Inclusion of n-Dodecyltriethylammonium Cation: Time Effect

“…Thus, the H + /DTA + exchange does not alter significantly the crystalline regions, suggesting a reorganization of the amorphous structure. Similar findings were previously reported for lithiated Nafion membranes [33]. The incorporation of DTA + into Nafion membranes was further studied by the FTIR (Figure S1, Supplementary Information).…”

Patterning and a Composite Protective Layer Provide Modified Li Metal Anodes for Dendrite-Free High-Voltage Solid-State Lithium Batteries

“…Furthermore, the XRD patterns of Nafion and LiNf each featured a sharp peak at 17.1°, consisting of two characteristic peaksa broad amorphous (16°) and a sharp crystalline (17.6°) peakfrom the polyfluorocarbon chains. The corresponding crystalline peaks indexed to the (100) plane of the hexagonal structure of Nafion. , The diffraction angles of the amorphous and crystalline peaks in Nafion and LiNf shifted from 16 to 16.4° and from 17.6 to 17.3°, respectively. Thus, the degree of crystallinity of the Nafion polymer decreased significantly after exchanging protons (H + ) for Li + ions .…”

“…The corresponding crystalline peaks indexed to the (100) plane of the hexagonal structure of Nafion. , The diffraction angles of the amorphous and crystalline peaks in Nafion and LiNf shifted from 16 to 16.4° and from 17.6 to 17.3°, respectively. Thus, the degree of crystallinity of the Nafion polymer decreased significantly after exchanging protons (H + ) for Li + ions . The maximum of the amorphous peak shifted to a higher angle (16.6°) in the XRD pattern of the VGCF@PDA/LiNf samples, while the graphitic carbon peak also shifted to a lower angle (26.5°), resulting from a further decrease in the degree of crystallinity of the polymer chain.…”

“…Thus, the degree of crystallinity of the Nafion polymer decreased significantly after exchanging protons (H + ) for Li + ions. 31 The maximum of the amorphous peak shifted to a higher angle (16.6°) in the XRD pattern of the VGCF@PDA/LiNf samples, while the graphitic carbon peak also shifted to a lower angle (26.5°), resulting from a further decrease in the degree of crystallinity of the polymer chain. These findings confirmed the synthesis of the polymer composite protective layer for modification of the Li metal surface.…”

“…The corresponding crystalline peaks indexed to the (100) plane of the hexagonal structure of Nafion. 30,31 The diffraction angles of the amorphous and crystalline peaks in Nafion and LiNf shifted from 16 to 16.4°and from 17.6 to 17.3°, respectively. Thus, the degree of crystallinity of the Nafion polymer decreased significantly after exchanging protons (H + ) for Li + ions.…”