title: Ultraconcentrated Sodium Bis(fluorosulfonyl)imide-Based Electrolytes for High-Performance Sodium Metal Batteries.
abstract: We present an ultraconcentrated electrolyte composed of 5 M sodium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane for Na metal anodes coupled with high-voltage cathodes. Using this electrolyte, a very high Coulombic efficiency of 99.3% at the 120th cycle for Na plating/stripping is obtained in Na/stainless steel (SS) cells with highly reduced corrosivity toward Na metal and high oxidation durability (over 4.9 V versus Na/Na+) without corrosion of the aluminum cathode current collector. Importantly, the use of this ultraconcentrated electrolyte results in substantially improved rate capability in Na/SS cells and excellent cycling performance in Na/Na symmetric cells without the increase of polarization. Moreover, this ultraconcentrated electrolyte exhibits good compatibility with high-voltage Na4Fe3(PO4)2(P2O7) and Na0.7(Fe0.5Mn0.5)O2cathodes charged to high voltages (>4.2 V versus Na/Na+), resulting in outstanding cycling stability (high reversible capacity of 109 mAh g-1over 300 cycles for the Na/Na4Fe3(PO4)2(P2O7) cell) compared with the conventional dilute electrolyte, 1 M NaPF6in ethylene carbonate/propylene carbonate (5/5, v/v).
authors.affiliation: School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulsan 44919, South Korea.
authors.forename: Jaegi
authors.initials: J
authors.lastname: Lee
authors.affiliation: School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulsan 44919, South Korea.
authors.forename: Yongwon
authors.initials: Y
authors.lastname: Lee
authors.affiliation: School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulsan 44919, South Korea.
authors.forename: Jeongmin
authors.initials: J
authors.lastname: Lee
authors.affiliation: Battery Research Center, Korea Electrotechnology Research Institute , Changwon 642-120, South Korea.
authors.forename: Sang-Min
authors.initials: SM
authors.lastname: Lee
authors.affiliation: Battery Research Center, Korea Electrotechnology Research Institute , Changwon 642-120, South Korea.
authors.forename: Jeong-Hee
authors.initials: JH
authors.lastname: Choi
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, South Korea.
authors.forename: Hyungsub
authors.initials: H
authors.lastname: Kim
authors.affiliation: Department of Chemical and Biological Engineering, Seoul National University , Seoul 151-742, South Korea.
authors.forename: Mi-Sook
authors.initials: MS
authors.lastname: Kwon
authors.affiliation: Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, South Korea.
authors.forename: Kisuk
authors.identifier: http://orcid.org/0000-0002-8696-1886
authors.initials: K
authors.lastname: Kang
authors.affiliation: Department of Chemical and Biological Engineering, Seoul National University , Seoul 151-742, South Korea.
authors.forename: Kyu Tae
authors.identifier: http://orcid.org/0000-0003-2769-3372
authors.initials: KT
authors.lastname: Lee
authors.affiliation: School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST) , 50 UNIST-gil, Ulsan 44919, South Korea.
authors.forename: Nam-Soon
authors.identifier: http://orcid.org/0000-0003-1183-5735
authors.initials: NS
authors.lastname: Choi
keywords: high-voltage cathodes; interfaces; liquid electrolytes; sodium bis(fluorosulfonyl)imide; sodium metal batteries