Typical measurements of parasitic heat flow in lithium-ion cells can determine the magnitude of heat flow but cannot differentiate between different types of reactions. This causes difficulty when comparing cells that contain different coatings and solvent systems, which may affect parasitic reaction pathways. In this work, a new technique to measure the rate and net enthalpy change (△H) of parasitic reactions in lithium ion cells is introduced. Isothermal microcalorimetry and precision current measurements are used to make in-situ, non-destructive measurements of heat flow and parasitic current during high-voltage holds. The results are used to determine △H of parasitic processes in NMC532/graphite pouch cells. Effects of positive electrode coating, solvent, and upper cutoff voltage are explored. Solvent systems of organic carbonates with and without methyl acetate, and fluorinated carbonates are also investigated. Each solvent system yielded a unique trend of △H with increased voltage, and results were consistent between pair cells. Cells with organic carbonates showed consistent △H between voltages, while cells containing methyl acetate showed decreasing H. Cells containing fluorinated carbonates showed increasing △H with increased voltage. The observed trends in △H and solvent systems as well as future developments of this method are discussed.
|Journal||Journal of the Electrochemical Society|
|State||Published - 2018|
Bibliographical noteFunding Information:
The authors thank NSERC and Tesla Canada for funding this work under the auspices of the Industrial Chairs program. SAO and APK thank the NSF (award CHE-1300653) for financial support. SLG thanks the NSERC PGS-D program and the Walter C. Sumner foundation for support. The authors thank Dr. Jing Li formerly at BASF and Dr. Deijun Xiong at Shenzhen CapChem for providing some of the electrolyte components used in this work. The authors thank Dr. Chris Burns of Novonix for providing the Novonix charger for high-precision voltage-hold testing. Lastly, we thank Dr. Jian Tu of LiFUN for providing expertise in cell assembly.
© The Author(s) 2018. Published by ECS.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry