Highly Concentrated Electrolytes: Electrochemical and Physicochemical Characteristics of LiPF6 in Propylene Carbonate Solutions
Journal article, 2021

Highly concentrated electrolytes (HCEs) based on LiPF6 in propylene carbonate (PC) have been examined as lithium-ion battery electrolytes. These HCEs have lower ionic conductivities and higher viscosities than ethylene carbonate (EC) electrolytes with 1.2 M LiPF6, but they have higher Li+ ion transference numbers. Electrochemical cycling behaviour of LiNi0.8C0.015Al0.05O2//graphite cells with 3.2 M LiPF6 in PC resembles that of cells with EC-based electrolytes; the HCE cells have higher impedance, which can be lowered by increasing test temperature. By employing Raman and infrared spectroscopy, combined with density functional theory and ab initio molecular dynamics simulations, we reveal that the Li+ solvation structure and speciation are key factors that determine cell performance. Two distinct regimes are observed as a function of salt concentration-in the conventional regime, the solvation number (SN) is mostly constant, while in the HCE regime it decreases linearly. Graphite exfoliation is suppressed only at very high salt concentrations (>2.4 M), where [PC](free)/[Li+] < 1 and [PF6-](free) > [PC](free). Results from the Advanced Electrolyte Model indicate that Li+ desolvation improves at higher LiPF6 concentrations, thereby mitigating PC co-intercalation into the graphite. However, Li+ ion transport is hindered in the HCEs, which increases impedance at both the oxide-positive and graphite-negative electrodes.

Author

Gustav Åvall

Chalmers, Physics, Materials Physics

Joachim Wallenstein

Chalmers, Physics, Materials Physics

Gang Cheng

Wildcat Discovery Technologies

Argonne National Laboratory

Kevin L. Gering

Idaho National Laboratory

Patrik Johansson

Chalmers, Physics, Materials Physics

Alistore - European Research Institute

Daniel P. Abraham

Argonne National Laboratory

Journal of the Electrochemical Society

0013-4651 (ISSN)

Vol. 168 5 050521

Next generation batteries for hybrid and electric vehicles

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

Highly concentrated electrolytes

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

Subject Categories

Inorganic Chemistry

Materials Chemistry

Other Chemical Engineering

Areas of Advance

Transport

Energy

Materials Science

DOI

10.1149/1945-7111/abfdc3

More information

Latest update

8/17/2021