The lithium-sulfur (Li-S) battery is a promising next-generation energy storage technology because of its high theoretical energy and low cost. Extensive research efforts have been made on new materials and...
The
electrolyte is a crucial component of lithium–sulfur
(Li–S) batteries, as it controls polysulfide dissolution, charge
shuttling processes, and solid-electrolyte interphase (SEI) layer
formation. Experimentally, the overall performance of Li–S
batteries varies with choice of solvent system and Li-salt used in
the electrolyte, and a lack of predictive understanding about the
effects of individual electrolyte components inhibits the rational
design of electrolytes for Li–S batteries. Here we analyze
the role of the counteranions of common Li salts (such as TfO–, FSI–, TFSI–,
and TDI–) when dissolved in DOL/DME (1:1 by vol.)
for use in Li–S batteries. The evolution of ion–ion
and ion–solvent interactions due to various anions was analyzed
using 17O NMR and pulsed-field gradient (PFG) NMR and then
correlated with electrochemical performance in Li–S cells.
These data reveal that the formation of the passivation layer on the
anode and the loss of active materials from the cathode (evidenced
by polysulfide dissolution) are related to anion mobility and affinity
with lithium polysulfide, respectively. For future electrolyte design,
anions with lower mobility and weaker interactions with lithium polysulfides
may be superior candidates for increasing the long-term stability
of Li–S batteries.
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