LiFSA and Urea/Dimethylurea Eutectic Electrolytes for Lithium Metal Batteries

Eutectic electrolytes are attracting increasing attention
as liquid
electrolytes for secondary batteries as they are potentially lower
cost, less/nonflammable, and more environmentally benign than the
current state-of-the-art. We have successfully developed eutectic
electrolytes combining the LiN(SO2F)2 (LiFSA)
with urea and dimethyl urea and investigated the physicochemical properties,
solution structures, and applicability of these binary and ternary
melts to lithium batteries. Solution structure analysis and electrochemical
measurements suggest that reducing free solvent enhances anodic stability,
while mitigating solvent clustering through hydrogen bonding improves
cathodic stability. Moreover, LiFSA concentrated electrolytes of LiFSA/urea/dimethylurea
(1:1:1) and LiFSA/dimethylurea (1:2) exhibited excellent compatibility
with lithium metal due to the formation of an organic–inorganic
hybrid solid electrolyte interphase. These electrolytes enable the
reversible plating and stripping of lithium metal, as well as the
stable operation of 4 V-class lithium metal batteries.