Understanding the thermal instability of fluoroethylene carbonate in LiPF 6 -based electrolytes for lithium ion batteries

Citation data:

Electrochimica Acta, ISSN: 0013-4686, Vol: 225, Page: 358-368

Publication Year:
2017
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Abstract Views 37
Captures 39
Readers 39
Citations 10
Citation Indexes 10
Repository URL:
http://scholarworks.unist.ac.kr/handle/201301/21198
DOI:
10.1016/j.electacta.2016.12.126
Author(s):
Kim, Koeun; Park, Inbok; Ha, Se-Young; Kim, Yeonkyoung; Woo, Myung-Heui; Jeong, Myung-Hwan; Shin, Woo Cheol; Ue, Makoto; Hong, Sung You; Choi, Nam-Soon
Publisher(s):
Elsevier BV; PERGAMON-ELSEVIER SCIENCE LTD
Tags:
Chemical Engineering; Chemistry; Lithium-ion battery; LiPF6-based electrolyte; Fluoroethylene carbonate; Lewis acid; Thermal instability
article description
The cycling and storage performances of LiCoO 2 (LCO)-LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM)/pitch-coated silicon alloy-graphite (Si-C) full cells with ethylene carbonate (EC)–based and fluoroethylene carbonate (FEC)–based electrolytes are investigated at elevated temperatures. Excess FEC (used as a co-solvent in LiPF 6 -based electrolytes), which is not completely consumed during the formation of the solid electrolyte interphase (SEI) layer on the electrodes, is prone to defluorination in the presence of Lewis acids such as PF 5 ; this reaction can generate unwanted HF and various acids (H 3 OPF 6, HPO 2 F 2, H 2 PO 3 F, H 3 PO 4 ) at elevated temperatures. Our investigation reveals that the HF and acid compounds that are formed by FEC decomposition causes significant dissolution of transition metal ions (from the LCO-NCM cathode) into the electrolyte at elevated temperatures; as a result, the reversible capacity of the full cells reduces because of the deposition of the dissolved metal ions onto the anode. Moreover, we demonstrate possible mechanisms that account for the thermal instability of FEC in LiPF 6 -based electrolytes at elevated temperatures using model experiments.