PDF Publication Title:
Text from PDF Page: 009
Molecules 2022, 27, 6949 9 of 17 We speculated that fluorinated DME should exhibit a wider ESW and calculated the HOMO–LUMO energy gap of fluorinated DME with the Na-ion system under the same environment (Figure 4a). The results revealed that the energy gap is already larger than the fluorinated EC when the fluorination degree reached 3 F or more. The change in the energy gap differs from the existing pattern, and “unidirectional variational”, “oscillating”, and “convergent” were not observed during the fluorination process. The oscillation of the energy gap disappeared gradually until the fluorination degree was above 6 F and started to increase gradually, reaching the maximum value at 10 F fluorination. In the case of strong fluorination above 6 F, the fully fluorinated DME exhibited the largest ESW, but in the case of weak fluorination below 6 F, -CF2CF2- and CF3CF1CF2- exhibited large HOMO–LUMO energy gaps. The shift in the absorption peak in NMR spectral of 19F was recorded with the number of F atoms (Figure 4b) to assess the effect of fluorination on the solvent molecule and the anion–cation bonding environment of the salt. An upfield shift was observed in the NMR absorption peak of 19F with the increase in the number of F atoms. This result implied a strong ionic solvation and contributed to the enhanced pairing of Na-ion with the anion of sodium salt. Furthermore, the shift intensity fluctuated to some extent in the fluorinated interval from 4 F to 6 F, whereas the shift intensity of fluorination from 6 F to 10 F (∆ = 9 ppm) was considerably smaller than that from 1 F to 3 F (∆ = 82 ppm) and almost ceased to change. The shift in the absorption peak revealed the tendencies of “unidirectional variational”, “oscillating”, and “convergent.” Finally, the difficulty of NaF formation in SEI was investigated because it considerably affects electrolyte performance. More NaF can restrain the growth of dendrite and reduce the loss of electrolyte active material during charge/discharge cycles [45]. In this study, the shorter the BNa-F bond length is, the longer the BC-F bond length is, and the larger the BNa-O and BNa-F bond angles αO-Na-F are. Thus, this phenomenon implies a higher inclination of NaF formation (Table 1). Unexpectedly, the combination of lower degree fluorination, -CF1, and -CF1CF1- appeared conducive for NaF formation, and a higher degree of fluorination results in an opposite trend. Although the lower degree of fluorination has the tendency for NaF formation, the number of F atoms of a single-solvent molecule is considerably less than that of the strongly fluorinated molecule, which may generate more NaF components during the electrochemical cycle. This result proves that fluorination could regulate charge transfer and promote NaF formation. Furthermore, based on the previous discussion, weakly fluorinated solvents were considerably weaker than strongly fluorinated solvents in terms of solvation ability, reductive activity, ESW, and other factors. Therefore, deep flu- orination, such as CF3CF1CF1-, CF3CF2CF2-, CF3CF1CF2CF3, and CF3CF2CF2CF3, remains the best fluorination strategy. Because of the complexity of the problem, Pearson correlation (PC) analysis [46] was used to understand the close relationship among properties and the types, numbers, and positions of the three units. The Pearson correction coefficient is between −1 and 1, with −1 indicating a perfectly negative linear correlation, 1 indicating a perfectly positive linear correlation, and 0 indicating no linear relationship at all. The Pearson correction coefficient is calculated as follows: where x and y denote two random variables, i denotes the index in the regression sample, and n denotes the number of samples. In this study, we define four correlation strengths “strong”, “medium”, “weak”, and “negligible”, corresponding to the cases when the absolute values of the PC coefficients fall in the intervals (0.8, 1.0), (0.4, 0.8), (0.2, 0.4), and (0.0, 0.2), respectively (abbreviated as S, M, W, and N, respectively) to improve readability. Figure 5a displays the PC coefficients of several variables in the heat map, with the labels “nF”, “n-CF1 ”, “n-CF2 ”, and “n-CF3 ” denoting the number of F atoms in each of the three units. ∑n (xi − x)(yi − y) i=1 PCxy = ∑n (xi −x)2∑n (yi −y)2, (3) i=1 i=1PDF Image | First-Principles-Based Optimized Design of Fluoride Electrolytes
PDF Search Title:
First-Principles-Based Optimized Design of Fluoride ElectrolytesOriginal File Name Searched:
molecules-27-06949.pdfDIY PDF Search: Google It | Yahoo | Bing
Salgenx Redox Flow Battery Technology: Salt water flow battery technology with low cost and great energy density that can be used for power storage and thermal storage. Let us de-risk your production using our license. Our aqueous flow battery is less cost than Tesla Megapack and available faster. Redox flow battery. No membrane needed like with Vanadium, or Bromine. Salgenx flow battery
CONTACT TEL: 608-238-6001 Email: greg@salgenx.com (Standard Web Page)