Journal
CHEMSUSCHEM
Volume 8, Issue 11, Pages 1892-1900Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cssc.201500263
Keywords
electrochemistry; electrolytes; lithium ion cells; safety; solvent effects
Funding
- Deutsche Forschungsgemeinschaft (Sachbeihilfe) [HO 5266/1-1]
- Brennstoffzellen- und Batterie-Allianz Baden-Wurttemberg [Forschungsaversum 2013/1305]
- ARC by the German Research Foundation [SPP1473 WeN-DeLIB]
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In this study, novel electrolyte mixtures for Li-ion cells are presented with highly improved safety features. The electrolyte formulations are composed of ethylene carbonate/dimethyl sulfone (80:20 wt/wt) as the solvent mixture and LiBF4, lithium bis(trifluoromethanesulfonyl)azanide, and lithium bis(oxalato)borate as the conducting salts. Initially, the electrolytes are characterized with regard to their physical properties, their lithium transport properties, and their electrochemical stability. The key advantages of the electrolytes are high flash points of >140 degrees C, which enhance significantly the intrinsic safety of Li-ion cells containing these electrolytes. This has been quantified by measurements in an accelerating rate calorimeter. By using the newly developed electrolytes, which are liquid down to T=-10 degrees C, it is possible to achieve C-rates of up to 1.5C with >80% of the initial specific capacity. During 100 cycles in cell tests (graphite||LiNi1/3Co1/3Mn1/3O2), it is proven that the retention of the specific capacity is >98% of the third discharge cycle with dependence on the conducting salt. The best electrolyte mixture yields a capacity retention of >96% after 200cycles in coin cells.
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