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Effect of nanostructured Al2O3 on poly(ethylene oxide)-based solid polymer electrolytes

  • Patrick Walke , Anna Kirchberger , Felix Reiter , Daniel Esken and Tom Nilges EMAIL logo
Published/Copyright: September 21, 2021
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Zeitschrift für Naturforschung B
From the journal Zeitschrift für Naturforschung B Volume 76 Issue 10-12

Abstract

In this study, we investigated the effect of nanostructured Al2O3 particles on Li ion conducting, poly(ethylene oxide) (PEO)-based membranes prepared by electrospinning, solution casting and hot pressing. Pure PEO:LiBF4 solid polymer electrolytes (SPEs) and also plasticizer containing membranes were investigated with various amounts of Al2O3. In a first step, the best-performing composition of pure PEO:LiBF4 concerning the resulting ionic conductivity was identified and used as a standard for further experiments. In the following, the influence of the preparation method, the nature of the Al2O3, and the type of the plasticizer additives on the thermal and electrochemical properties for this standard composition were investigated. The Al2O3 composition was varied between 1 and 5 wt%. The ionic conductivity of bare electrospun PEO:LiBF4 SPE standard material has been improved by a factor ten to 1.9 × 10−6 S cm−1 at T = 293 K when 5 wt% of Al2O3 is added. For solution-casted PEO:LiBF4 standard compositions 18:1 with an initial ionic conductivity of 6.7 × 10−8 S cm−1, the addition of 2 wt% Al2O3 increased the performance to 1.4 × 10−7 S cm−1, both at T = 293 K. If succinonitrile and Al2O3 was admixed to the solution casted standard material, the ionic conductivity was further increased to reach 5.5 × 10−5 S cm−1 at T = 293 K. This material with a composition of 18:3:1 + 2 wt% Al2O3, outperforms the standard material by three orders of magnitude.

Keywords: aluminum oxide; electrospinning; impedance spectroscopy; poly (ethylene oxide); solid polymer electrolytes

1 Introduction

The importance of safe and environmentally friendly high-power solid polymer electrolytes (SPEs) is considered to be consistently growing, facing the ongoing changes in energy storage technology. The progress in solid lithium electrolyte technologies regarding environmental considerations, commercial applicability, and energy density with a large electrochemical window is aiming at a commercial product with high performance. The goal is to create an alternative to the widely used liquid lithium accumulators. Solid polymer electrolytes, when compared to liquid electrolytes show a drastically reduced danger of flammability, no significant tendency for short circuits as a result of depressed dendrite growth, and eliminated battery bloating upon the emerge of potentially hazardous vapors. A solid electrolyte construction also possesses advantages for the use in electromobility or in portable devices as the rigid casing for the liquid reservoir is unnecessary. This is the consequence of the reduced heat dissipation, which allows a light flexible battery construction in smallest spaces [1], [2], [3].

On the downside, solid state electrolytes have currently one major drawback compared to liquid counterparts: the low conductivity at room temperature [1, 4]. One common option to tackle this problem is the addition of ceramic additives like Li super ionic conductors (LISICON) [5], Na super ionic conductor (NASICON) [6], [7], [8], lithium phosphorus oxynitride (LIPON) [9], [10], [11], TiO2 [10], [11], [12], SiO2 [11], [12], [13], [14], [15], [16], ZnO [17], BaTiO3 [18, 19], lithium lanthanum titanate (LLTO) [20], lithium lanthanum zirconium tantalum oxide (LLZTO) [21], [22], [23] or Al2O3 [1, 7, 11, 12, 16, 24] to polymer electrolytes. Thereby, an increase of conductivity of SPEs of up to 1.5 × 10−4 S cm−1 was reported using combinations of Al2O3 fillers and plasticizers [21, 24], [25], [26]. The enhancement of conductivity of SPEs with fillers was observed and a further conductivity increase is expected which could enable widespread commercial application. Further, the stability of the electrochemical window can be enlarged by the use of fillers [20, 27]. The interactions of the ceramics embedded in the polymer with the conductive salts are not yet fully understood and make a specific optimization of the electrolytes complicated. The addition of fillers and thereby the smaller volume fractions of polymers raise the hope to minimize the interfacial barrier of the Li+ transport from the superionic particles of the ceramic fillers to the polymer [10].

In contrast to the conduction mechanism for polymers including ceramic fillers, the conductivity mechanism of lithium ions in polyethylene oxide (PEO) is well studied [28, 29]. PEO serves as an interesting polymer for SPEs due to its ability to provide solvation of the lithium ions and owing to its flexible backbone to accelerate ion motion. We therefore decided to investigate this polymer and commercially available, nanostructured filler material Al2O3 as a suitable combination for SPEs.

2 Results and discussion

Ceramic filler tends to improve the electrochemical performance of SPEs [30]. Figure 1 shows different possible Li+ conduction pathways with a low A), moderate B) and high amount of filler C).

Figure 1: Illustration of the different conduction pathways in a SPEs based on PEO with a growing amount of ceramic fillers. Figure adapted from literature [30].
Figure 1:

Illustration of the different conduction pathways in a SPEs based on PEO with a growing amount of ceramic fillers. Figure adapted from literature [30].

Taking this general mechanism into account we started a systematic investigation of PEO-based Li ion conducting SPEs with various amounts of polymer, conducting salt, and plasticizer in order to address the different situations arising from Al2O3 usage. Another aspect deals with the influence of the preparation method on the electrochemical performance.

2.1 Adjustment of the molar ratio of the components used for PEO:LiBF4 membranes

In a first step, the molar ratio of PEO:LiBF4 was varied to find the composition with the highest ionic conductivity, which was chosen for further experiments as standard. Membranes prepared via electrospinning were compared regarding the crystallinity, thermal properties and conductivities derived from PEIS. As seen before by Freitag et al., the Li ion conductivity in electrospun membranes rises with the LiBF4 content in the membranes [2]. In addition to the two plasticizer-free compositions examined in previous work (PEO:LiBF4 36:1 and 18:1), a third molar ratio (PEO:LiBF4 27:1) was also tested in this study to prove the concept.

The ionic conductivity at T = 293 K raised from 1.5 × 10−7 S cm−1 for the PEO:LiBF4 36:1 membrane, to 5.0 × 10−7 S cm−1 for the PEO:LiBF4 18:1 one. As the ionic conductivity raised with temperature, the values 4.6 × 10−6 S cm−1 and 1.9 × 10−5 S cm−1 were achieved at 328 K, respectively. For the SPE with a molar composition of 27:1 the value lies in between for both temperatures (compare Figure 2a). X-ray powder diffraction (P-XRD) data of the prepared membranes illustrated the amorphous character of all samples. Samples with a molar composition of PEO:LiBF4 36:1 (compare Figure 2b) showed a few reflections at 19.2° in 2θ and between 22.8 and 23.8° in 2θ, which we assigned to a crystalline phase of PEO, as described in literature [31].

Figure 2: a) Ionic conductivities in a temperature range from 293 to 328 K, b) X-ray powder diffraction (P-XRD) from 5 to 60° in 2θ and c) DSC in the temperature range from 173 to 523 K of electrospun PEO:LiBF4 SPEs with different molar compositions of 36:1, 27:1 and 18:1.
Figure 2:

a) Ionic conductivities in a temperature range from 293 to 328 K, b) X-ray powder diffraction (P-XRD) from 5 to 60° in 2θ and c) DSC in the temperature range from 173 to 523 K of electrospun PEO:LiBF4 SPEs with different molar compositions of 36:1, 27:1 and 18:1.

The thermal properties of the prepared membranes were investigated via Differential Scanning Calorimetry (DSC) in a temperature range from 173 to 523 K. It was found that the melting point (T m) was not significantly influenced by the concentration of the conducting salt. In contrast, the glass transition temperature (T g) was shifted to a significantly lower temperature for the PEO:LiBF4 18:1 sample (T g = 176 K) compared to the one of pure PEO (T g = 223 K) and was later found to show the highest ionic conductivity, as shown in Figure 2a.

2.2 Screening of the preparative methods for optimized PEO:LiBF4 membranes

To validate the positive effect of the electrospinning in the preparation process of a SPE, the electrospun sample with the highest Li ion mobility (PEO:LiBF4 18:1) was compared to membranes of the same composition prepared by solution casting and hot pressing. Thereby, it can be seen that the SPEs prepared by electrospinning showed a higher ionic conductivity than those prepared by the other techniques in the measured temperature range. While hot pressed membranes with a molar composition of PEO:LiBF4 18:1 denoted an ionic conductivity from 2.5 × 10−8 S cm−1 at 293 K to 1.3 × 10−6 S cm−1 at 328 K, the solution casted membranes with the same molar ratio showed 6.7 × 10−8 S cm−1 and 3.0 × 10−6 S cm−1 at the same temperature. These conductivities were about one order of magnitude lower than those observed for the electrospun membrane PEO:LiBF4 18:1 (compare Figure 3a). The interested reader is referred to the literature regarding the reason for the conductivity improvement in the case of electrospun polymer electrolytes [2, 3]. For the products of all preparative methods, the crystallinity of the obtained membranes was investigated via P-XRD. While the electrospun sample was, as discussed before, amorphous, the SPEs obtained from hot pressing and solution casting showed significant amounts of crystalline PEO phase (compare Figure 3b). This agrees with the specific conductivities that were derived from impedance data. Electrospun membranes showed the highest conductivity, followed by solution casted and hot pressed ones. It is reported in the literature that crystallized PEO tends to shows lower ion mobility compared to amorphous PEO [32].

Figure 3: a) Ionic conductivities in a temperature range from 293 to 328 K, b) P-XRD from 5 to 60° in 2θ and c) DSC in the temperature range from 173 to 523 K of PEO:LiBF4 18:1 SPEs prepared by electrospinning (ES), solution casting (SC) and hot pressing (HP).
Figure 3:

a) Ionic conductivities in a temperature range from 293 to 328 K, b) P-XRD from 5 to 60° in 2θ and c) DSC in the temperature range from 173 to 523 K of PEO:LiBF4 18:1 SPEs prepared by electrospinning (ES), solution casting (SC) and hot pressing (HP).

For the examination of the thermal properties of PEO:LiBF4 18:1 samples prepared by different methods via DSC, the first heating cycle with a scan rate of 10 K min−1 was used for comparison as the unique fiber structure of the electrospun SPE was destroyed after the sample is molten once. The difference in melting temperature for the tested compounds is negligible (compare Figure 3c), all values were found between 329 and 331 K. In contrast, T g for the ES 18:1 (T g = 176 K) sample was significantly lower compared to T g of the SC 18:1 sample (T g = 227 K), while the highest T g of 248 K was found for HP 18:1. This illustrates that the PEO matrix of the SPEs offers the highest chain mobility when prepared by electrospinning, thus leading to the highest specific ionic conductivity of the ES 18:1 membrane compared to those prepared by other techniques.

As hot pressed samples in general show the poorest performance and the preparative method, as performed in our facilities, is not suitable for producing homogenous membranes with inorganic particles, hot pressing therefore was not used for further experiments in this study.

2.3 Plasticizer-free PEO:LiBF4 membranes with nanostructured Al2O3 as an additive

Using the PEO:LiBF4 18:1 standard, Al2O3-nanostructured particles were added in different amounts to the electrospinning solutions. We used 1 to 5 wt% of Al2O3 in our experiments. All electrospun membranes were subjected to electrochemical characterization by impedance analyses. The results showed a positive effect on the conductivity in a temperature range from 293 to 328 K if 3 to 5 wt% of nanostructured Al2O3 particles were added. Amounts of more than 5 wt% Al2O3 were not applied because such materials are not electrospinnable anymore. The highest conductivities were found for an electrospun PEO:LiBF4 18:1 sample with 3 wt% Al2O3 ranging from 1.9 × 10−6 S cm−1 at 293 K to 2.4 × 10−4 S cm−1 at 328 K. In contrast, SPEs with 1 and 2 wt% of Al2O3 showed decreased ionic conductivities in comparison to the membranes free of inorganic additives (compare Figure 4a). The crystallinity of all membranes was checked via P-XRD. PEO tends to show at least some hints of ordering when Al2O3 is admixed. While a particle-free membrane with a molar composition of PEO:LiBF4 18:1 displays no sharp reflections between 5 and 60° in 2θ, all diffractograms of electrospun membranes containing 1 to 5 wt% of nanostructured Al2O3 particles showed at least the main reflections of partially ordered PEO between 18 and 24° 2θ. Nevertheless, the ES polymer fibers were dominated by amorphous phase fractions as compared with the SC and HP ones, and therefore conductivities were still higher than those from solution casted or hot pressed membranes (compare Figure 4c).

Figure 4: a) Ionic conductivity of electrospun PEO:LiBF4 18:1 membranes in a temperature range from 298 to 328 K. b) P-XRD from 5 to 60° in 2θ of electrospun (ES) PEO:LiBF4 18:1 membranes with different Al2O3 content, ranging from 0 to 5 wt%. c) Ionic conductivity of solution casted (SC) PEO:LiBF4 18:1 membranes in a temperature range from 298 to 328 K and d) P-XRD from 5 to 60° in 2θ of solution casted (SC) PEO:LiBF4 18:1 membranes with different Al2O3 content, ranging from 0 to 5 wt%.
Figure 4:

a) Ionic conductivity of electrospun PEO:LiBF4 18:1 membranes in a temperature range from 298 to 328 K. b) P-XRD from 5 to 60° in 2θ of electrospun (ES) PEO:LiBF4 18:1 membranes with different Al2O3 content, ranging from 0 to 5 wt%. c) Ionic conductivity of solution casted (SC) PEO:LiBF4 18:1 membranes in a temperature range from 298 to 328 K and d) P-XRD from 5 to 60° in 2θ of solution casted (SC) PEO:LiBF4 18:1 membranes with different Al2O3 content, ranging from 0 to 5 wt%.

We performed similar sets of experiments for solution-casted (SC) membranes with the standard composition PEO: LiBF4 18:1 and nanostructured Al2O3 filler. For all tested amounts of nanostructured particles, ranging from 0 to 5 wt%, the ionic conductivities were significantly lower compared to the ones of electrospun membranes (compare Figure 4a and c). In this set of experiments, the membranes with an Al2O3 content of 2 wt% performed best with an ionic conductivity of 1.4 × 10−7 S cm−1 at 293 K, rising to 8.2 × 10−6 S cm−1 at 328 K.

Like for Al2O3 free samples, the P-XRD patterns collected of SC membranes (Figure 4d) indicated a higher amount of ordered polymer (compare Figure 4b). To check if the nanostructured Al2O3 particles were not agglomerated and equally distributed over the polymer membranes, the particle size distribution in the solutions was determined by dynamic light scattering (DLS) before, and Al distribution via energy dispersive X-ray spectroscopy (EDX) after membrane preparation. The influence of the Ultra Turrax mixing on the particle size distribution was investigated. The mean particle diameter of the aggregates was reduced from 1858 to 277.5 nm when using 0.035 g of agglomerated Al2O3 in 10 mL acetonitrile. The particle size distribution was also narrowed (compare Figure 5a). It is important to break Al2O3 agglomerates as effectively as possible prior to usage because we observed less reproducible results with agglomerated Al2O3 samples. The distribution across a solution casted membrane with the composition of PEO:SN:LiBF4 18:1 + 5 wt% Al2O3 is shown in Figure 5b and c. The EDX mapping of Al showed a homogenous distribution of Al across the whole membrane.

Figure 5: a) Dynamic light scattering (DLS) particle size distribution before and after Ultra Turrax (UT) mixing for 2 × 2 min at 10,000 rpm in acetonitrile. b) SEM at 440× magnification and c) EDX Al-mapping at 440× magnification showing the same area of a solution casted PEO:LiBF4 18:1 SPE with 5 wt% Al2O3.
Figure 5:

a) Dynamic light scattering (DLS) particle size distribution before and after Ultra Turrax (UT) mixing for 2 × 2 min at 10,000 rpm in acetonitrile. b) SEM at 440× magnification and c) EDX Al-mapping at 440× magnification showing the same area of a solution casted PEO:LiBF4 18:1 SPE with 5 wt% Al2O3.

2.4 Plasticizer-containing PEO:SN:LiBF4 membranes with nanostructured Al2O3 as an additive

Succinonitrile (SN) was added in a molar ratio of PEO:SN:LiBF4 18:3:1 as a supplement to the added nanostructured Al2O3 particles [2]. Adding 1 to 5 wt% Al2O3 to ES SPE membranes lead to, a reduction of the ionic conductivity in all cases compared with Al2O3-free samples. The membrane with 1 wt% nanostructured inorganic filler performed best. This material is characterized by the highest ionic conductivity of 2.5 × 10−6 S cm−1 at 293 K which raised to 5.8 × 10−4 S cm−1 at 328 K (compare Figure 6a). For all other compositions, the specific ionic conductivities were similar, ranging from 1.1 × 10−6 S cm−1 for ES PEO:SN:LiBF4 18:3:1 + 4 wt% Al2O3 to 2.5 × 10−6 S cm−1 for a ES PEO:SN:LiBF4 18:3:1 + 1 wt% Al2O3, both at 293 K. It appeared that for plasticizer-containing ES membranes the addition of Al2O3 showed no positive effect on the ionic conductivity. Pure ES PEO:SN:LiBF4 18:3:1 SPE showed an ionic conductivity of 2.5 × 10−5 S cm−1 at 293 K. This conductivity is comparable to a HP PEO:LiTFSI 16:1 sample (5,000,000 g mol−1 PEO, 298 K) for which a value of 1.0 × 10−5 S cm−1 was found [33].

Figure 6: a) Ionic conductivity of electrospun (ES) PEO:SN:LiBF4 18:3:1 membranes in a temperature range from 298 to 328 K and b) P-XRD from 5 to 60° in 2θ of electrospun (ES) PEO:SN:LiBF4 18:3:1 membranes with different Al2O3 content, ranging from 0 to 5 wt%. c) Ionic conductivity of solution casted (SC) PEO:SN:LiBF4 18:3:1 membranes in a temperature range from 298 to 328 K. d) P-XRD from 5 to 60° in 2θ of solution casted (SC) PEO:SN:LiBF4 18:3:1 membranes with different Al2O3 content, ranging from 0 to 5 w%.
Figure 6:

a) Ionic conductivity of electrospun (ES) PEO:SN:LiBF4 18:3:1 membranes in a temperature range from 298 to 328 K and b) P-XRD from 5 to 60° in 2θ of electrospun (ES) PEO:SN:LiBF4 18:3:1 membranes with different Al2O3 content, ranging from 0 to 5 wt%. c) Ionic conductivity of solution casted (SC) PEO:SN:LiBF4 18:3:1 membranes in a temperature range from 298 to 328 K. d) P-XRD from 5 to 60° in 2θ of solution casted (SC) PEO:SN:LiBF4 18:3:1 membranes with different Al2O3 content, ranging from 0 to 5 w%.

For all SPEs, the X-ray diffraction patterns indicated a higher degree of ordering when SN was admixed. Besides the main reflections of a crystalline PEO phase, no hints for any other ordered system was found (compare Figure 6d).

If we took a look on the SC membranes, the same trend of reduced ionic conductivity upon Al2O3 intake was observed. With higher Al2O3 contents of 3–5 wt%, we saw an even stronger depression of the conductivity than for the ES membranes. Ionic conductivities were spread over a wide range, from 1.8 × 10−9 S cm−1 for SC PEO:SN:LiBF4 18:3:1 + 3 wt% Al2O3 to 4.2 × 10−7 S cm−1 for a SC PEO:SN:LiBF4 18:3:1 + 5 wt% Al2O3 membrane, both at 293 K (compare Figure 6). Only the 1 and 2 wt% SC samples outperformed a pure ES PEO:SN:LiBF4 18:3:1 membrane by almost half an order of magnitude. Conductivities were 5.5 × 10−5 S cm−1 for SC PEO:SN:LiBF4 18:3:1 + 2 wt% and 2.3 × 10−5 S cm−1 for ES PEO:SN:LiBF4 18:3:1.

The XRD patterns of the SC PEO:SN:LiBF4 18:3:1 + x wt% Al2O3 SPEs (x = 1–5) samples showed higher ordering of PEO chains for all tested compositions.

Obviously, the increasing amount of Al2O3 in plasticizer-containing ES membranes seemed not to affect the PEO chain mobility, and as a consequence the conductivity was almost identical. This situation changed drastically in the case of SC membranes. Here we saw a spread of conductivity over almost five orders of magnitude, dependent on the Al2O3 content. Low Al2O3 contents of 1–2 wt% were beneficial and pushed conductivities in the same region as observed for ES materials. Obviously, the underlying conduction mechanism according to Figure 1 seemed not to change significantly for ES materials while this supposed to be the case for SC materials. Which mechanism occurs in both cases is subject to further investigations.

In the light of scalability and larger scale industrial fabrication of polymer electrolytes such an observed behavior might be beneficial because SC is less costly and much easier scalable than ES. In general, the crystallinity of the final material must be reduced for both preparative methods to further optimize the materials. Also, Al2O3-dependent mechanical properties need to be determined to address further optimization potential.

3 Conclusion

The application of commercially available, nanostructured Al2O3 as an inorganic additive to SPEs is found to be beneficial. Important positive issues are to break agglomerates of nanostructured particles prior to mixing with polymers and to realize homogenous distribution in the final product. For plasticizer- and filler-free membranes with a molar composition of PEO:LiBF4 18:1, the electrospun membranes performed with a ten times higher ionic conductivity compared to membranes prepared by solution casting or hot pressing over the temperature range from 293 to 328 K. Conductivities at 293 K were 5.0 × 10−7 S cm−1 for ES, 6.7 × 10−8 S cm−1 for SC, and 2.5 × 10−8 S cm−1 for HP, respectively. As hot pressed material showed the lowest ionic conductivity and this preparative method itself was not suitable to ensure homogenous distribution of inorganic filler particles in a polymer matrix, the effect of Al2O3 addition was not investigated.

For electrospun SPEs, the addition of 3–5 wt% nanostructured Al2O3 enhanced the ionic conductivity at 293 K to 1.9 × 10−6 S cm−1 for a composition of PEO:LiBF4 18:1 + 5 wt% Al2O3. A similar positive effect was observed for solution casted samples with a composition of PEO:LiBF4 18:1 + x wt% Al2O3 (x = 1–5), with conductivities reaching 1.4 × 10−7 S cm−1 at 293 K for the x = 2 sample. Thus, the addition of nanostructured Al2O3 can improve the ionic conductivities of SPEs independent of the solution-based preparative method of choice, but still electrospun SPEs outperform these materials with ten times higher conductivities. If succinonitrile (SN), a well-known plasticizer for PEO systems, was added to the system the ionic conductivity was increased to 2.5 × 10−5 S cm−1 at 293 K for a electrospun PEO:SN:LiBF4 18:3:1 Al2O3-free membrane. Adding SN to PEO:SN:LiBF4 + x wt% Al2O3 systems, did not further increase the ionic conductivity for electrospun SPEs. The most effective optimization of the ionic conductivity was found for solution casted SPEs when SN and Al2O3 were added simultaneously as plasticizer and inorganic filler, respectively. The highest ionic conductivity for solution casted PEO:SN:LiBF4 + Al2O3 was observed at 2 wt% showing 5.5 × 10−5 S cm−1 at 293 K, which translates to a 1000 times conductivity improvement compared to the initial solution casted PEO:LiBF4 membrane.

For all samples, the usage of nanostructured Al2O3 as filler had no significant effect on the temperature range of application, in which the SPEs could be used. We found no significant depression of the melting temperature which would limit the upper application range. The tendency to long range ordering of polymer chains within the membranes, as illustrated from P-XRD, was not increased with up to 5 wt% inorganic filler content, which renders a usage of Al2O3 as a filler material possible.

4 Experimental

4.1 Synthesis of membranes

4.1.1 Electrospinning (ES) and solution casting (SC)

To prepare a polymer solution suitable for electrospinning and solution casting, PEO (Sigma Aldrich, 300,000 g mol−1) was stirred in acetonitrile (Sigma Aldrich, purified) until it was fully dissolved (ca. 1 h). Succinonitrile (Sigma Aldrich) was added to the solution. In a last step, the LiBF4 was admixed. Subsequently, the solution was stirred for 12 h to ensure full homogenization. To examine the effect of different amounts of nanostructured Al2O3 (AEROXIDE® Alu 130, Evonik), the desired amount was suspended via UltraTurrax mixing (2 × 2 min, 10,000 rpm) in the solvent used. All steps were carried out under dry conditions in an inert atmosphere (O2 < 10 ppm; H2O < 0.1 ppm). For detailed quantities and molar ratios of all starting materials, see Table 1. Each sample composition is given in molar ratios, in the case of PEO based on the repetition unit.

Table 1:

Synthesis parameters for membrane preparation.

Sample composition PEO (g) SN (g) LiBF4 (g) Al2O3 (g) MeCN (mL)
PEO:LiBF 4
 ES 36:1 0.700 – 0.041 – 10
 ES 27:1 0.700 – 0.055 – 10
 ES/SC 18:1 0.700 – 0.083 – 10
 HP 18:1 0.700 – 0.083 – –
 ES/SC 18:1 + 1 wt% Al2O3 0.700 – 0.083 0.007 10
 ES/SC 18:1 + 2 wt% Al2O3 0.700 – 0.083 0.014 10
 ES/SC 18:1 + 3 wt% Al2O3 0.700 – 0.083 0.021 10
 ES/SC 18:1 + 4 wt% Al2O3 0.700 – 0.083 0.028 10
 ES/SC 18:1 + 5 wt% Al2O3 0.700 – 0.083 0.035 10
PEO:SN:LiBF 4
 ES 18:3:1 0.700 0.212 0.083 – 10
 ES/SC 18:3:1 + 1 wt% Al2O3 0.700 0.212 0.083 0.007 10
 ES/SC 18:3:1 + 2 wt% Al2O3 0.700 0.212 0.083 0.014 10
 ES/SC 18:3:1 + 3 wt% Al2O3 0.700 0.212 0.083 0.021 10
 ES/SC 18:3:1 + 4 wt% Al2O3 0.700 0.212 0.083 0.028 10
 ES/SC 18:3:1 + 5 wt% Al2O3 0.700 0.212 0.083 0.035 10

The solution was casted on a glass (SC samples) or taken up by syringe and transferred to an electrospinning apparatus (ES samples) as described in the literature [2]. During the electrospinning, a voltage of 18–22 kV was applied, the distance between the tip of the cannular and the grounded collector averaged 20 cm, while the solution was pumped with a feedrate of 1.5–3 mL.

4.1.2 Hot pressing (HP)

As a solvent-free preparation method hot pressing was used. Starting materials were homogenized in a mortar und placed in a self-made pressing tool under inert atmosphere. The pressing tool was placed in a hydraulic press at 5 t and 363 K for 2 h. The obtained membranes were dried for 24 h under vacuum at r.t.

4.2 Powder X-ray diffraction

All samples were checked for crystallinity by powder X-ray diffraction performed by a STOE STADIP diffractometer using CuKα 1 radiation (λ = 1.54051 Å), fitted with a germanium monochromator and a DECTRIS Mythen 1K solid state detector system. Data was collected between 5 and 80° in 2θ. A disk of 10 mm diameter was punched out of the membranes, placed between Scotch Magic Tape and mounted in a flat-bed sample holder. All experiments were carried out at r.t.

4.3 Thermal analysis

The thermal behavior of the solid polymer electrolytes was investigated by differential scanning calorimetry (DSC) in aluminum crucibles with a Netzsch Maia DSC 200 F3 calorimeter, in a temperature range of 123–523 K, with a heating rate of 10 K min−1 under continuous nitrogen flow.

4.4 Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX)

For SEM imaging and EDX analysis, samples were fixed on a graphite sample holder and brought into the vacuum chamber of a JOEL JCM-6000 NeoScop™ with an internal JOEL JED-2200 EDS unit. An acceleration voltage of 15 kV was applied.

4.5 Electrochemical analysis

Ionic conductivity values of PEO:SN:LiBF4 + x wt% Al2O3 membranes were calculated from potentiostatic electrochemical impedance spectroscopy data (PEIS) obtained with a Metrohm Autolab B.V. PGSTAT204 potentiostat including a FRA 32 M module. Samples were placed between two stainless steel electrodes in rhd TSC standard battery cells. PEIS data were recoded applying an amplitude of 20 mV, in the frequency range of 1 MHz to 0.1 Hz, at temperatures from 293–328 K in steps of 5 K. The resulting Nyquist plots were fitted using the software Nova 2.0 [34]. The thickness of the samples was determined after the measurements with a micrometer screw (Holex, 0–25 mm, 0.001 mm accuracy).

4.6 Dynamic light scattering

Dynamic light scattering (DLS) was performed on a Malvem Zetasizer Nano ZS instrument in disposable poly(styrene) cuvettes at a wavelength of 633 nm. Particle sizes between 0.4 and 10,000 nm were measured. The Al2O3 particles were dispersed and measured in acetonitrile at T = 25 °C.

Dedicated to: Professor Richard Dronskowski of the RWTH Aachen on the occasion of his 60th birthday.

Corresponding author: Tom Nilges, Chemistry Department, Technische Universität München, Lichtenbergstraße 4, 85748 Garching bei München, Germany, E-mail:
Patrick Walke and Anna Kirchberger contributed equally to this study.

Acknowledgment

This project was part of a collaboration with Evonik Operations GmbH. We thank Evonik for providing nanostructured Al2O3 (AEROXIDE® Alu 130), extruded polymer samples and helpful discussions.

  1. Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

  2. Research funding: None declared.

  3. Conflict of interest statement: The authors declare no conflicts of interest regarding this article.

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Received: 2021-07-08
Accepted: 2021-07-31
Published Online: 2021-09-21
Published in Print: 2021-11-25

© 2021 Walter de Gruyter GmbH, Berlin/Boston

Articles in the same Issue

  1. Frontmatter
  2. In this issue
  3. Laudatio/Preface
  4. Celebrating the 60th birthday of Richard Dronskowski
  5. Review
  6. Orbital-selective electronic excitation in phase-change memory materials: a brief review
  7. Research Articles
  8. Solving the puzzle of the dielectric nature of tantalum oxynitride perovskites
  9. d- and s-orbital populations in the d block: unbound atoms in physical vacuum versus chemical elements in condensed matter. A Dronskowski-population analysis
  10. Single-crystal structures of A 2SiF6 (A = Tl, Rb, Cs), a better structure model for Tl3[SiF6]F, and its novel tetragonal polymorph
  11. Na2La4(NH2)14·NH3, a lanthanum-rich intermediate in the ammonothermal synthesis of LaN and the effect of ammonia loss on the crystal structure
  12. Linarite from Cap Garonne
  13. Salts of octabismuth(2+) polycations crystallized from Lewis-acidic ionic liquids
  14. High-temperature diffraction experiments and phase diagram of ZrO2 and ZrSiO4
  15. Thermal conversion of the hydrous aluminosilicate LiAlSiO3(OH)2 into γ-eucryptite
  16. Crystal structure of mechanochemically prepared Ag2FeGeS4
  17. Effect of nanostructured Al2O3 on poly(ethylene oxide)-based solid polymer electrolytes
  18. Sr7N2Sn3: a layered antiperovskite-type nitride stannide containing zigzag chains of Sn4 polyanions
  19. Exploring the frontier between polar intermetallics and Zintl phases for the examples of the prolific ALnTnTe3-type alkali metal (A) lanthanide (Ln) late transition metal (Tn) tellurides
  20. Zwitterion coordination to configurationally flexible d 10 cations: synthesis and characterization of tetrakis(betaine) complexes of divalent Zn, Cd, and Hg
  21. An approach towards the synthesis of lithium and beryllium diphenylphosphinites
  22. Synthesis, crystal and electronic structure of CaNi2Al8
  23. Crystal and electronic structure of the new ternary phosphide Ho5Pd19P12
  24. Synthesis, structure, and magnetic properties of the quaternary oxysulfides Ln 5V3O7S6 (Ln = La, Ce)
  25. Synthesis, crystal and electronic structure of BaLi2Cd2Ge2
  26. Structural variations of trinitrato(terpyridine)lanthanoid complexes
  27. Preparation of CoGe2-type NiSn2 at 10 GPa
  28. Controlled exposure of CuO thin films through corrosion-protecting, ALD-deposited TiO2 overlayers
  29. Experimental and computational investigations of TiIrB: a new ternary boride with Ti1+x Rh2−x+y Ir3−y B3-type structure
  30. Synthesis and crystal structure of the lanthanum cyanurate complex La[H2N3C3O3]3 · 8.5 H2O
  31. Cd additive effect on self-flux growth of Cs-intercalated NbS2 superconducting single crystals
  32. 14N, 13C, and 119Sn solid-state NMR characterization of tin(II) carbodiimide Sn(NCN)
  33. Superexchange interactions in AgMF4 (M = Co, Ni, Cu) polymorphs
  34. Copper(I) iodide-based organic–inorganic hybrid compounds as phosphor materials
  35. On iodido bismuthates, bismuth complexes and polyiodides with bismuth in the system BiI3/18-crown-6/I2
  36. Synthesis, crystal structure and selected properties of K2[Ni(dien)2]{[Ni(dien)]2Ta6O19}·11 H2O
  37. First low-spin carbodiimide, Fe2(NCN)3, predicted from first-principles investigations
  38. A novel ternary bismuthide, NaMgBi: crystal and electronic structure and electrical properties
  39. Magnetic properties of 1D spin systems with compositional disorder of three-spin structural units
  40. Amine-based synthesis of Fe3C nanomaterials: mechanism and impact of synthetic conditions
  41. Enhanced phosphorescence of Pd(II) and Pt(II) complexes adsorbed onto Laponite for optical sensing of triplet molecular dioxygen in water
  42. Theoretical investigations of hydrogen absorption in the A15 intermetallics Ti3Sb and Ti3Ir
  43. Assembly of cobalt-p-sulfonatothiacalix[4]arene frameworks with phosphate, phosphite and phenylphosphonate ligands
  44. Chiral bis(pyrazolyl)methane copper(I) complexes and their application in nitrene transfer reactions
  45. UoC-6: a first MOF based on a perfluorinated trimesate ligand
  46. PbCN2 – an elucidation of its modifications and morphologies
  47. Flux synthesis, crystal structure and electronic properties of the layered rare earth metal boride silicide Er3Si5–x B. An example of a boron/silicon-ordered structure derived from the AlB2 structure type
https://doi.org/10.1515/znb-2021-0091
Keywords for this article
aluminum oxide; electrospinning; impedance spectroscopy; poly (ethylene oxide); solid polymer electrolytes

Articles in the same Issue

  1. Frontmatter
  2. In this issue
  3. Laudatio/Preface
  4. Celebrating the 60th birthday of Richard Dronskowski
  5. Review
  6. Orbital-selective electronic excitation in phase-change memory materials: a brief review
  7. Research Articles
  8. Solving the puzzle of the dielectric nature of tantalum oxynitride perovskites
  9. d- and s-orbital populations in the d block: unbound atoms in physical vacuum versus chemical elements in condensed matter. A Dronskowski-population analysis
  10. Single-crystal structures of A 2SiF6 (A = Tl, Rb, Cs), a better structure model for Tl3[SiF6]F, and its novel tetragonal polymorph
  11. Na2La4(NH2)14·NH3, a lanthanum-rich intermediate in the ammonothermal synthesis of LaN and the effect of ammonia loss on the crystal structure
  12. Linarite from Cap Garonne
  13. Salts of octabismuth(2+) polycations crystallized from Lewis-acidic ionic liquids
  14. High-temperature diffraction experiments and phase diagram of ZrO2 and ZrSiO4
  15. Thermal conversion of the hydrous aluminosilicate LiAlSiO3(OH)2 into γ-eucryptite
  16. Crystal structure of mechanochemically prepared Ag2FeGeS4
  17. Effect of nanostructured Al2O3 on poly(ethylene oxide)-based solid polymer electrolytes
  18. Sr7N2Sn3: a layered antiperovskite-type nitride stannide containing zigzag chains of Sn4 polyanions
  19. Exploring the frontier between polar intermetallics and Zintl phases for the examples of the prolific ALnTnTe3-type alkali metal (A) lanthanide (Ln) late transition metal (Tn) tellurides
  20. Zwitterion coordination to configurationally flexible d 10 cations: synthesis and characterization of tetrakis(betaine) complexes of divalent Zn, Cd, and Hg
  21. An approach towards the synthesis of lithium and beryllium diphenylphosphinites
  22. Synthesis, crystal and electronic structure of CaNi2Al8
  23. Crystal and electronic structure of the new ternary phosphide Ho5Pd19P12
  24. Synthesis, structure, and magnetic properties of the quaternary oxysulfides Ln 5V3O7S6 (Ln = La, Ce)
  25. Synthesis, crystal and electronic structure of BaLi2Cd2Ge2
  26. Structural variations of trinitrato(terpyridine)lanthanoid complexes
  27. Preparation of CoGe2-type NiSn2 at 10 GPa
  28. Controlled exposure of CuO thin films through corrosion-protecting, ALD-deposited TiO2 overlayers
  29. Experimental and computational investigations of TiIrB: a new ternary boride with Ti1+x Rh2−x+y Ir3−y B3-type structure
  30. Synthesis and crystal structure of the lanthanum cyanurate complex La[H2N3C3O3]3 · 8.5 H2O
  31. Cd additive effect on self-flux growth of Cs-intercalated NbS2 superconducting single crystals
  32. 14N, 13C, and 119Sn solid-state NMR characterization of tin(II) carbodiimide Sn(NCN)
  33. Superexchange interactions in AgMF4 (M = Co, Ni, Cu) polymorphs
  34. Copper(I) iodide-based organic–inorganic hybrid compounds as phosphor materials
  35. On iodido bismuthates, bismuth complexes and polyiodides with bismuth in the system BiI3/18-crown-6/I2
  36. Synthesis, crystal structure and selected properties of K2[Ni(dien)2]{[Ni(dien)]2Ta6O19}·11 H2O
  37. First low-spin carbodiimide, Fe2(NCN)3, predicted from first-principles investigations
  38. A novel ternary bismuthide, NaMgBi: crystal and electronic structure and electrical properties
  39. Magnetic properties of 1D spin systems with compositional disorder of three-spin structural units
  40. Amine-based synthesis of Fe3C nanomaterials: mechanism and impact of synthetic conditions
  41. Enhanced phosphorescence of Pd(II) and Pt(II) complexes adsorbed onto Laponite for optical sensing of triplet molecular dioxygen in water
  42. Theoretical investigations of hydrogen absorption in the A15 intermetallics Ti3Sb and Ti3Ir
  43. Assembly of cobalt-p-sulfonatothiacalix[4]arene frameworks with phosphate, phosphite and phenylphosphonate ligands
  44. Chiral bis(pyrazolyl)methane copper(I) complexes and their application in nitrene transfer reactions
  45. UoC-6: a first MOF based on a perfluorinated trimesate ligand
  46. PbCN2 – an elucidation of its modifications and morphologies
  47. Flux synthesis, crystal structure and electronic properties of the layered rare earth metal boride silicide Er3Si5–x B. An example of a boron/silicon-ordered structure derived from the AlB2 structure type
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