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In situ formation of protective coatings on sulfur cathodes in lithium batteries with LiFSI-based organic electrolytes

: Kim, Hyea; Wu, Feixiang; Lee, Jungtae; Nitta, Naoki; Lin, Huanting; Oschatz, Martin; Cho, Wonil; Kaskel, Stefan; Borodin, Oleg A.; Yushin, Gleb N.


Advanced energy materials 5 (2015), Nr.6, Art. 1401792, 8 S.
ISSN: 1614-6840
ISSN: 1614-6832
Fraunhofer IWS ()
batteries; dissolution; cathodes; electrolytes; protective coatings

Development of sulfur cathodes with 100% coulombic efficiency (CE) and good cycle stability remains challenging due to the polysulfide dissolution in electrolytes. Here, it is demonstrated that electrochemical reduction of lithium bis(fluorosulfonyl)imide (LiFSI) based electrolytes at a potential close to the sulfur cathode operation forms in situ protective coating on both cathode and anode surfaces. Quantum chemistry studies suggest the coating formation is initiated by the FSI(-F) anion radicals generated during electrolyte reduction. Such a reduction additionally results in the formation of LiF. Accelerated cycle stability tests at 60 °C in a very simple electrolyte (LiFSI in dimethoxyethane with no additives) show an average CE approaching 100.0% over 1000 cycles with a capacity decay less than 0.013% per cycle after stabilization. Such a remarkable performance suggests a great promise of both an in situ formation of protective solid electrolyte coatings to avoid unwanted side reactions and the use of a LiFSI salt for this purpose.