Fluorine-free "solvent-in-salt" sodium battery electrolytes: solvation structure and dynamics
Journal article, 2024

The solvation structure, dynamics, and transport properties, as well as thermal and electrochemical stabilities of "solvent-in-salt" (SIS) electrolytes, also known as highly concentrated electrolytes, are far from fully understood. Furthermore, these special types of electrolytes are almost without exception based on fluorinated salts. In contrast, here we report on fluorine-free SIS electrolytes comprising ambient temperature liquid sodium bis(2-(2-ethoxyethoxy)ethyl)phosphate (NaDEEP) salt and tris(2-(2-ethoxyethoxy)ethyl)phosphate (TEOP) solvent, for which the ionic conductivities and ion diffusivities are altered profoundly as the salt concentration is increased. A careful molecular level analysis reveals a microstructure with a "solvent-rich" phase with almost an order of magnitude faster ion diffusion than in a "salt-rich" phase. Aggregated ionic structures in these SIS electrolytes lead to higher ionic conductivities alongside lower glass transition temperatures, <-80 degrees C, but also agreeable thermal stabilities, up to 270 degrees C, and improved anodic stabilities, possibly up to 7.8 V vs. Na/Na+ and at least >5 V vs. Na/Na+. Altogether, this provides a foundation for both better understanding and further development of fluorine-free SIS electrolytes for sodium batteries.

Author

Yanqi Xu

Luleå University of Technology

Andrei Filippov

Luleå University of Technology

Sourav Bhowmick

Luleå University of Technology

Patrik Johansson

Chalmers, Physics, Materials Physics

Faiz Ullah Shah

Luleå University of Technology

Energy Advances

27531457 (eISSN)

Vol. 3 3 564-573

Biomass Derived Fluorine-Free Ionic Liquids Based Electrolytes Enabling Sustainable Batteries (BioSusBat)

Formas (2020-00969), 2021-01-01 -- 2024-12-31.

Subject Categories

Inorganic Chemistry

Physical Chemistry

Materials Chemistry

DOI

10.1039/d4ya00002a

More information

Latest update

4/2/2024 1