Poly(ethylene oxide) (PEO)-based polymer fibers, containing different amounts of the conductive salt LiBF and the plasticizer succinonitrile, were prepared by an electrospinning process. This process resulted in fiber membranes of several square centimeters area and an overall thickness of ∼100 μm. All membranes are characterized by scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, impedance spectroscopy, cyclic voltammetry (CV), and solid-state NMR spectroscopy, to evaluate the influence of the preparation process and the composition on the conductivity of the materials. Impedance spectroscopy was used to measure the conductivities and activation barriers for the different membranes. The highest conductivity of 2 × 10 S/cm at room temperature and 9 × 10 S/cm at 328 K is reached for a PEO/SN/LiBF (36:8:1) membrane, featuring an activation energy of 31 kJ/mol. Li mobilities, as deduced from the evaluation of the temperature dependence of the Li NMR line width and the overall electrochemical performance, are found to be distinctively superior to nonspun samples, synthesized via conventional solution casting. The same trend was found for the conductivities. NMR spectroscopy clearly substantiated that the mobility of the PEO segments drastically increases with the addition of succinonitrile pushing the conductivity to reasonable high values. In CV experiments the reversible Li transport through the dry membrane was evaluated and proved. This study shows that electrospinning provides a direct synthesis of solvent-free solid-state electrolyte membranes, ready to use in electrochemical applications.
NaCd4P3 and NaCd4As3 were synthesized via short-way transport using the corresponding elements and CdI2 as mineralizer. At room temperature, the two β-polymorphs adopt the RbCd4As3 structure type which has been recently reported for alkali metal (A)-d(10) transition metal (T)-pnictides (Pn). The title compounds crystallize rhombohedrally in space group R3̅m at room temperature and show reversible phase transitions to incommensurately modulated α-polymorphs at lower temperatures. The low-temperature phases are monoclinic and can be described in space group Cm(α0γ)s with q vectors of q = (-0.04,0,0.34) for α-NaCd4P3 and q1 = (-0.02,0,0.34) for α-NaCd4As3. Thermal properties, Raman spectroscopy, and electronic structures have been determined. Both compounds are Zintl phases with band gaps of 1.05 eV for β-NaCd4P3 and ∼0.4 eV for β-NaCd4As3.
Thin membranes of lithium‐bis(trifluoromethan)sulfonimide@poly (ethylene oxide) (or Li(TFSI)@PEO) were fabricated by electrospinning from acetonitrile solutions of the starting materials at room temperature. Membranes were tested with and without succinonitrile (SN), acting as a plasticizer to enhance the ion mobility in the systems. Our experiments substantiate, that SN does influence the electrochemical performance and physical properties of the membranes. Homogeneous amorphous membranes were only realized for SN‐containing samples, while phase segregation and crystallization occurred for SN‐free representatives. Membranes of different compositions were tested and the optimum molar mixture of PEO:SN:Li(TFSI), in terms of membrane conductivity, was identified as 36:8:1. Conductivities up to up to 2.8 × 10–4 S·cm–1 were determined by impedance spectroscopy for this membrane. Used as solid electrolytes without the aid of any additional electrolyte in symmetric Li vs. Li cells, a reasonable stability upon Li cycling could be observed. Here we illustrate that electrospun plasticizer‐modified Li(TFSI)@PEO membranes show high conductivities at very low conductive salt concentrations, compared with solution casted or hot pressed representatives. This feature renders these materials as potential candidates for separators in all solid‐state batteries or related energy storage applications.
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