Journal
ACS NANO
Volume 11, Issue 10, Pages 10462-10471Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.7b05664
Keywords
aqueous electrolytes; batteries; molecular dynamics simulations; spectroscopy; conductivity
Categories
Funding
- Department of Energy Advanced Research Projects Agency - Energy [DEAR0000389]
- U.S. Office of Naval Research
- National Institutes of Health [MD007599]
- ARL [W911NF-16-2-0187]
- RISEN at Hunter College [GM060665]
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Using molecular dynamics simulations, small-angle neutron scattering, and a variety of spectroscopic techniques, we evaluated the ion solvation and transport behaviors in aqueous electrolytes containing bis(trifluoromethanesulfonyl)imide. We discovered that, at high salt concentrations (from 10 to 21 mol/kg), a disproportion of cation solvation occurs, leading to a liquid structure of heterogeneous domains with a characteristic length scale of 1 to 2 nm. This unusual nano-heterogeneity effectively decouples cations from the Coulombic traps of anions and provides a 3D percolating lithium- water network, via which 40% of the lithium cations are liberated for fast ion transport even in concentration ranges traditionally considered too viscous. Due to such percolation networks, superconcentrated aqueous electrolytes are characterized by a high lithium-transference number (0.73), which is key to supporting an assortment of battery chemistries at high rate. The in-depth understanding of this transport mechanism establishes guiding principles to the tailored design of future superconcentrated electrolyte systems.
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