Designing fluorine-free electrolytes for stable sodium metal anodes and high-power seawater batteries via SEI reconstruction

Fluorine (F) is regarded as a key element in electrolytes for sodium metal anodes (SMAs) because of the formation of NaF containing solid–electrolyte interphase (SEI) layers; however, the high-cost and HF formation issues experienced by F-based electrolytes should be addressed. Herein, F-free, cost-...

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Published in:Energy & environmental science 2022-10, Vol.15 (10), p.4109-4118
Main Authors: Kim, Jinuk, Kim, Jioh, Jeong, Jooyoung, Park, Jiwon, Park, Cheol-Young, Park, Sewon, Lim, Shin Gwon, Lee, Kyu Tae, Choi, Nam-Soon, Byon, Hye Ryung, Jo, Changshin, Lee, Jinwoo
Format: Article
Language:English
Subjects:
Anodes
Batteries
Chemical analysis
Chemical reduction
Diethylene glycol
Dimethyl ether
Electrolytes
Fluorine
Ions
Mass spectrometry
Mass spectroscopy
Reconstruction
Seawater
Secondary ion mass spectrometry
Sodium
Sodium fluoride
Sodium hydrides
Water analysis
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Summary:Fluorine (F) is regarded as a key element in electrolytes for sodium metal anodes (SMAs) because of the formation of NaF containing solid–electrolyte interphase (SEI) layers; however, the high-cost and HF formation issues experienced by F-based electrolytes should be addressed. Herein, F-free, cost-effective 1 M NaBH 4 /ether-based electrolytes are proposed, motivated by the recent speculation that NaH is a “good SEI layer.” The time-of-flight secondary ion mass spectrometry (TOF-SIMS) results of sodium metal electrodes after galvanostatic cycling demonstrated that NaH is a major component of the SEI layer. In addition, the native oxide surface of sodium was converted into NaH and NaBO 2 after soaking in the electrolytes, implying that “SEI reconstruction” occurred by chemical reduction. Accordingly, significantly longer cyclability was obtained in the Na‖Na symmetric cell (1200 h, 1 mA cm −2 , 1 mA h cm −2 ) than in F-based electrolytes. In seawater batteries (SWBs), 1 M NaBH 4 /DEGDME (diethylene glycol dimethyl ether) delivers higher power density (2.82 mW cm −2 vs. 2.27 mW cm −2 ) and cyclability (300 h vs. 50 h) under 1 mA cm −2 than 1 M NaOTf/TEGDME (tetraethylene glycol dimethyl ether), which is commonly used in SWBs. In conclusion, two novel contributions of this study include the demonstration that NaH can work as a “good SEI layer” apart from NaF and the proposal of a cost-effective, F-free electrolyte for practical and large-scale SWBs.
ISSN:1754-5692
1754-5706
DOI:10.1039/D2EE01295B