퍼킨엘머코리아(유)에서 제공한 'Propylene Carbonate-Based Electrolytes for Sodium Ion Cells: GC-MS Study of Degradation Products'에 관한 응용자료의 주요 내용은 다음과 같다.
Introduction
Rechargeable batteries are of high current interest as a storage medium for electrical energy. Although lithium-ion batteries are state of the art today, alternatives are also being intensively evaluated. Sodium-ion batteries are currently being investigated as a promising candidate to replace Li-ion batteries due to the high availability of Na compared to Li, similar cell structure and ease of transport. However, only a few solvent systems have been described so far, mostly based on the current Li-ion electrolytes, which consist of carbonate-based solvent mixtures. It is necessary for an ideal electrolyte for sodium-based batteries to meet similar characteristics as Li-ion cells: low cost, electrochemical stability, chemical stability, non-toxicity, scalability, and thermal stability.
Propylene carbonate (PC) cannot be used without further effort in the case of lithium-ion cells, as it leads to exfoliation of the graphite which is typically used. For this reason, ethylene carbonate (EC) is commonly used in mixtures in the case of lithium-ion cells. Mixtures with linear carbonates (e.g., dimethyl carbonate, ethyl methyl carbonate), which facilitate the required mobility of the ions in the solvent mixture, are also commonly used. In the case of sodium ion cells, the use of propylene carbonate becomes possible since hard carbon is stable to propylene carbonate. The handling of PC is also more convenient since, unlike EC, it is liquid at room uploaderature.
A series of electrolytes for Na-ion batteries based on propylene carbonate are investigated in this study with respect to their compatibility with sodium metal. GC-MS was used to quality control and semi-quantify the formation of decomposition products. In detail, the electrolytes shown in Table 1 were examined in detail.
Experimental Data and GC-MS Setup
Sample Preparation
The solvent and sodium operations were carried out in an argon-filled glovebox at oxygen and water contents less than 0.5 ppm. The electrolyte solvents were dried using molecular sieve and/or sodium. All items were dehydrated at 75°C for 48h in vacuum. All samples were compared and corrected with the pure diluent solvent (MTBE or dichloromethane) and the pure electrolyte solvent. Impurities in the electrolyte solvents were analyzed based on the tentative assignment using the NIST search (EI fragmentation match) when possible and by measuring the pure substance. All solvents and materials used in the study are listed in Table 2.
25μl of each of the electrolyte samples were taken and diluted with dichloromethane or MTBE. Any precipitate that formed was removed (via centrifugation) and the sample was then loaded into a GC vial and measured. All samples were taken in duplicate and measured in duplicate. In order to be able to clearly assign signals to the sample, a second dilution (10μl in 1ml solvent) was prepared and this was also measured in duplicate.
In the study, the electrolyte mixtures with selected classes of organic solvents were evaluated according to their physicochemical as well as electrochemical properties. The stability of the electrolyte formulations towards sodium metal studied in detail by gas chromatography. The reactivity towards sodium is compared between mixtures with and without NaClO4 and the degradation products are analyzed by gas chromatography. It is shown that NaClO4 plays a crucial role in the decomposition of the electrolyte.
GC-MS Setup
The gas chromatography experiments were performed using a Clarus 690 GC equipped with a liquid autosampler, a flame ionization detector (FID), and an SQ8T MS detector. The FID was used for quantification, while the MS was used for identification. The signals from the FID were used to determine the peak area. Table 3 lists all the details of the GC method as well as the MS method, while Table 4 summarizes the consumables used for the investigations.
Results and Discussion
The study investigated the compatibility of electrolytes with elemental sodium. In the first step, all pure solvents were examined. The corresponding results are shown in Table 5. GC-MS was used to detect decomposition products and aging products and to perform a semi-quantitative determination of the contained degradation products. The analysis of the corresponding products was performed by MS. The simultaneous measurement by using FID allowed the semi- quantitative estimation over a wide range of concentrations. This was done by normalizing the decomposition products to the total solvent quantity (PC+X). Since these were present in much greater concentration and in a similar magnitude ratio in all electrolytes, this allows the amount of decomposition products to be at least estimated.
It has been observed that the samples containing the linear carbonates (EM-2 and EM-3) turned intensely brownish within 20 d in the presence of conducting salt (NaClO4) and Na.
A slight color change still occurred with EM-5 (pale yellowish) and EM-6 (yellowish). It was also noticeable that the surface of the Na flask turned orange in the case of the glycol-ether mixture, indicating a high degree of surface reactions. The pure solvents (without conducting salt), the PC+G2 (pale reddish) and PC+SL (yellowish) mixtures exhibited a slight color change only.
Figure 1 shows the chromatograms of the six electrolyte samples after they were stored above Na for 122 days. In addition to the pure solvents and the signal of the diluent (MTBE), decomposition products of varying intensity can be identified depending on the electrolyte sample. An overview of selected degradation products is shown in Table 6. Within the study it was possible to determine and specify coupling products (A-C, Figure 2) in the electrolyte mixtures of linear and cyclic carbonates.
Figure 2a/2b show the semi- quantitative analysis of the data. It can be clearly seen that in the case of EMC, two products are formed with relatively large amounts. These were identified as DMC and DEC(diethyl carbonate, see Table 6). Here, a transesterification takes place when sodium metal is present which might be based on alkoxide formation. At the same time, decomposition products are formed in all samples, in electrolyte-specific amounts. Only little decomposition products are formed in case of EM-4 (EC+PC+1M NaClO4).
Conclusion
In this study, selected electrolytes are investigated, namely mixtures of PC, PC + DMC, PC + EMC, PC + EC, PC + diglyme, and PC + SL. NaClO4 is chosen as conducting salt and applied in concentrations of 1 M. The solubility of NaClO4 in all mixtures is sufficient for preparation of homogeneous liquid electrolytes. The stability of the electrolyte mixtures is investigated by storage of the samples over sodium metal.
Decomposition products are detected and compared with a semi-quantitative approach. These measurements reveal a more sufficient stability in case of cyclic carbonates, whereas mixtures between linear and cyclic carbonates tend to form coupling products. Electrochemical as well as physicochemical properties can be found in the referenced publication for more details.
Acknowledgements
The study was carried out at PerkinElmer’s Reference Laboratory of the Karlsruhe Institute of Technology under the supervision of Dr. Andreas Hofmann (andreas.hofmann2@kit.edu).
'Propylene Carbonate-Based Electrolytes for Sodium Ion Cells: GC-MS Study of Degradation Products'에 관한 궁금한 내용은 본 원고자료를 제공한 퍼킨엘머코리아(유)를 통하여 확인할 수 있다.
Reference(참고문헌): A. Hofmann, Z. Wang, S.P. Bautista, M. Weil, F. Müller, R. Löwe,L. Schneider, I.U. Mohsin, T. Hanemann. Comprehensive characterization of propylene carbonate based liquid electrolyte mixes for sodium-ion cells. Electrochimica Acta, 2022, 403, https://doi.org/10.1016/j.electacta.2021.139670.
Model Name(모델명): GCMS2400
The Person in Charge(담당자): Young-Jae.Yu
Maker(제조사): PerkinElmer
Country of Origin(원산지): Singapore
e-mail: Youngjae.yu@perkinelmer.com
Data Services(자료제공): PerkinElmer
<이 기사는 사이언스21 매거진 2025년 2월호에 게재 되었습니다.>
Experimental Data and GC-MS SetupSample PreparationThe solvent and sodium operations were carried out in an argon-filled glovebox at oxygen and water contents less than 0.5 ppm. The electrolyte solvents were dried using molecular sieve and/or sodium. All items were dehydrated at 75°C for 48h in vacuum. All samples were compared and corrected with the pure diluent solvent (MTBE or dichloromethane) and the pure electrolyte solvent. Impurities in the electrolyte solvents were analyzed based on the tentative assignment using the NIST search (EI fragmentation match) when possible and by measuring the pure substance. All solvents and materials used in the study are listed in Table 2.25μl of each of the electrolyte samples were taken and diluted with dichloromethane or MTBE. Any precipitate that formed was removed (via centrifugation) and the sample was then loaded into a GC vial and measured. All samples were taken in duplicate and measured in duplicate. In order to be able to clearly assign signals to the sample, a second dilution (10μl in 1ml solvent) was prepared and this was also measured in duplicate.
In the study, the electrolyte mixtures with selected classes of organic solvents were evaluated according to their physicochemical as well as electrochemical properties. The stability of the electrolyte formulations towards sodium metal studied in detail by gas chromatography. The reactivity towards sodium is compared between mixtures with and without NaClO4 and the degradation products are analyzed by gas chromatography. It is shown that NaClO4 plays a crucial role in the decomposition of the electrolyte.
GC-MS SetupThe gas chromatography experiments were performed using a Clarus 690 GC equipped with a liquid autosampler, a flame ionization detector (FID), and an SQ8T MS detector. The FID was used for quantification, while the MS was used for identification. The signals from the FID were used to determine the peak area. Table 3 lists all the details of the GC method as well as the MS method, while Table 4 summarizes the consumables used for the investigations.Results and DiscussionThe study investigated the compatibility of electrolytes with elemental sodium. In the first step, all pure solvents were examined. The corresponding results are shown in Table 5. GC-MS was used to detect decomposition products and aging products and to perform a semi-quantitative determination of the contained degradation products. The analysis of the corresponding products was performed by MS. The simultaneous measurement by using FID allowed the semi- quantitative estimation over a wide range of concentrations. This was done by normalizing the decomposition products to the total solvent quantity (PC+X). Since these were present in much greater concentration and in a similar magnitude ratio in all electrolytes, this allows the amount of decomposition products to be at least estimated.It has been observed that the samples containing the linear carbonates (EM-2 and EM-3) turned intensely brownish within 20 d in the presence of conducting salt (NaClO4) and Na.A slight color change still occurred with EM-5 (pale yellowish) and EM-6 (yellowish). It was also noticeable that the surface of the Na flask turned orange in the case of the glycol-ether mixture, indicating a high degree of surface reactions. The pure solvents (without conducting salt), the PC+G2 (pale reddish) and PC+SL (yellowish) mixtures exhibited a slight color change only.
Figure 1 shows the chromatograms of the six electrolyte samples after they were stored above Na for 122 days. In addition to the pure solvents and the signal of the diluent (MTBE), decomposition products of varying intensity can be identified depending on the electrolyte sample. An overview of selected degradation products is shown in Table 6. Within the study it was possible to determine and specify coupling products (A-C, Figure 2) in the electrolyte mixtures of linear and cyclic carbonates.Figure 2a/2b show the semi- quantitative analysis of the data. It can be clearly seen that in the case of EMC, two products are formed with relatively large amounts. These were identified as DMC and DEC(diethyl carbonate, see Table 6). Here, a transesterification takes place when sodium metal is present which might be based on alkoxide formation. At the same time, decomposition products are formed in all samples, in electrolyte-specific amounts. Only little decomposition products are formed in case of EM-4 (EC+PC+1M NaClO4).
ConclusionIn this study, selected electrolytes are investigated, namely mixtures of PC, PC + DMC, PC + EMC, PC + EC, PC + diglyme, and PC + SL. NaClO4 is chosen as conducting salt and applied in concentrations of 1 M. The solubility of NaClO4 in all mixtures is sufficient for preparation of homogeneous liquid electrolytes. The stability of the electrolyte mixtures is investigated by storage of the samples over sodium metal.Decomposition products are detected and compared with a semi-quantitative approach. These measurements reveal a more sufficient stability in case of cyclic carbonates, whereas mixtures between linear and cyclic carbonates tend to form coupling products. Electrochemical as well as physicochemical properties can be found in the referenced publication for more details.AcknowledgementsThe study was carried out at PerkinElmer’s Reference Laboratory of the Karlsruhe Institute of Technology under the supervision of Dr. Andreas Hofmann (andreas.hofmann2@kit.edu).'Propylene Carbonate-Based Electrolytes for Sodium Ion Cells: GC-MS Study of Degradation Products'에 관한 궁금한 내용은 본 원고자료를 제공한 퍼킨엘머코리아(유)를 통하여 확인할 수 있다.Reference(참고문헌): A. Hofmann, Z. Wang, S.P. Bautista, M. Weil, F. Müller, R. Löwe,L. Schneider, I.U. Mohsin, T. Hanemann. Comprehensive characterization of propylene carbonate based liquid electrolyte mixes for sodium-ion cells. Electrochimica Acta, 2022, 403, https://doi.org/10.1016/j.electacta.2021.139670.Model Name(모델명): GCMS2400The Person in Charge(담당자): Young-Jae.YuMaker(제조사): PerkinElmerCountry of Origin(원산지): Singaporee-mail: Youngjae.yu@perkinelmer.comData Services(자료제공): PerkinElmer<이 기사는 사이언스21 매거진 2025년 2월호에 게재 되었습니다.>