Potassium-ion batteries using KFSI/DME electrolytes: Implications of cation solvation on the K+-graphite (co-)intercalation mechanism
Journal article, 2022

Recently potassium-ion batteries have been proposed as a promising next generation battery technology owing to cost effectiveness and a wide range of electrode materials as well as electrolytes available. Potassium bis(fluorosulfonyl)imide (KFSI) in monoglyme (DME) is one potential electrolyte, wherein the K+ solvation heavily depends on the salt concentration and strongly affects the electrochemistry. Pure K+ intercalation occurs for highly concentrated electrolytes (HCEs), while co-intercalation is dominant for less concentrated electrolytes. The mechanisms are easily distinguished by their galvanostatic curves as well as by operando XRD. Here Raman spectroscopy coupled with computational chemistry is used to provide in-depth knowledge about the cation solvation for a wide concentration range, all the way up to 5 M KFSI in DME. Starting from pure DME experimental and computed Raman spectra provides a detailed conformational assignment enabling us to calculate the solvation number (SN) of K+ by DME as a function of salt concentration for all the electrolytes. For low to medium KFSI concentrations, the SN is approximately constant, ca. 2.7, and/as there is a surplus of DME solvent available, while for HCEs, with much less DME available, the SN is <2. This reduced SN results in a thermodynamically more favored desolvation at the graphite surface, leading to intercalation, as compared to the higher SN of conventional electrolytes leading to co-intercalation, as observed also by electrochemical cycling.

Graphite

Intercalation mechanism

K-ion batteries

Solvation

Raman spectroscopy

Author

Phuong Nam Le Pham

University of Montpellier

Alistore - European Research Institute

Vincent Gabaudan

University of Montpellier

Athmane Boulaoued

Chalmers, Physics, Materials Physics

Gustav Åvall

Chalmers, Physics, Materials Physics

Fabrice Salles

University of Montpellier

Patrik Johansson

Alistore - European Research Institute

Chalmers, Physics, Materials Physics

L. Monconduit

Centre national de la recherche scientifique (CNRS)

University of Montpellier

Alistore - European Research Institute

L. Stievano

University of Montpellier

Alistore - European Research Institute

Centre national de la recherche scientifique (CNRS)

Energy Storage Materials

2405-8297 (eISSN)

Vol. 45 291-300

Highly concentrated electrolytes

Swedish Energy Agency (39909-1), 2015-02-01 -- 2019-09-30.

Next generation batteries for hybrid and electric vehicles

Swedish Energy Agency (37671-1), 2013-12-01 -- 2017-12-31.

Subject Categories

Inorganic Chemistry

Physical Chemistry

Theoretical Chemistry

DOI

10.1016/j.ensm.2021.11.046

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7/4/2024 6