期刊
ACS APPLIED MATERIALS & INTERFACES
卷 11, 期 36, 页码 32844-32855出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsami.9b06760
关键词
sodium-ion batteries; diglyme-based electrolytes; OEMS; dilatometry; conductive salts
资金
- DFG [630743]
- BMBF [01DR18003]
- MINECO
- JST
We study the stability of several diglyme-based electrolytes in sodium|sodium and sodium|graphite cells. The electrolyte behavior for different conductive salts [sodium trifluoromethanesulfonate (NaOTf), NaPF6, NaClO4, bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI)] is compared and, in some cases, considerable differences are identified. Side reactions are studied with a variety of methods, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, online electrochemical mass spectrometry, and in situ electrochemical dilatometry. For Na|Na symmetric cells as well as for Na|graphite cells, we find that NaOTf and NaPF6 are the preferred salts followed by NaClO4 and NaFSI, as the latter two lead to more side reactions and increasing impedance. NaTFSI shows the worst performance leading to poor Coulombic efficiency and cycle life. In this case, excessive side reactions lead also to a strong increase in electrode thickness during cycling. In a qualitative order, the suitability of the conductive salts can be ranked as follows: NaOTf >= NaPF6 > NaClO4 > NaFSI >> NaTFSI. Our results also explain two recent, seemingly conflicting findings on the degree of solid electrolyte interphase formation on graphite electrodes in sodium-ion batteries [Maibach, J.; ACS Appl. Mater. Interfaces 2017, 9, 12373-12381; Goktas, M.; Adv. Energy Mater. 2018, 8, 1702724]. The contradictory findings are due to the different conductive salts used in both studies.
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