Key Parameter for Acetonitrile Electrolytes Identified

Study Demonstrates the Crucial Role of the Additive Vinylene Carbonate

Due to its low viscosity and high ionic conductivity, the electrolyte solvent acetonitrile (AN) is particularly suitable for lithium ion batteries that are designed for fast charging and low temperature applications. One of the biggest challenges, however, is its instability towards the graphite anode. Acetonitrile can decompose before a sufficiently protective solid electrolyte interphase (SEI) has formed between the electrolyte and the electrode during the battery’s first charge and discharge cycle. The resulting lithium plating rapidly degrades the cell performance. A team from MEET Battery Research Center at the University of Münster has therefore investigated how the electrolyte additive vinylene carbonate (VC) can contribute to the formation of a sufficient SEI in lithium ion batteries containing acetonitrile.

Mass-to-Surface-Area Ratio Crucial

The study shows that 27.5 percent by volume (vol.-%) of acetonitrile can be used in the electrolyte when the additives VC and ethylene sulfite (ES) are added appropriately. “We identified not the amount of VC, but rather the ratio of VC mass to the graphite surface area (VC/GRSA) as the decisive factor to enable targeted SEI formation,” explains MEET scientist Maik Stamm. The research team determined that a value of 59.06 milligrams of VC per square meter of graphite surface area (mg/m²) is required for the necessary protective layer to be formed. As a result, more acetonitrile can be used in lithium ion batteries while substantially reducing the electrolyte volume, without causing lithium plating during cell formation.

© Journal of The Electrochemical Society

Dr Philip Niehoff, deputy head of the research division “Cell System”, emphasizes: “Our study provides important insights for improving electrolytes with acetonitrile on a scalable basis. In subsequent research, we need to further validate our results using larger cell formats and long-term cycles.”

Detailed Results Online Available

The entire study has been published by the authors Maik Stamm, Kai Büscher and Dr Philip Niehoff, MEET Battery Research Center, as well as Prof. Dr Martin Winter, MEET Battery Research Center and Helmholtz Institute Münster of Forschungszentrum Jülich, in the “Journal of The Electrochemical Society”.