Improving technology of Li-Ion Cells for Rechargeable batteries

 

by Sloan Cinelli

The lithium-ion battery is the power source for most modern electric vehicles. Each battery is made up of many smaller units, called cells. The electrical current reaches these cells via conductive surfaces, including aluminum and copper. There is a positive electrode, the cathode, and a negative electrode, the anode. The battery is filled with a transport medium, the electrolyte, so the lithium ions carrying the battery’s charge can flow freely from one electrode to the other. This electrolyte solution needs to be extremely pure in order to ensure efficient charging and discharging.

Virtually every lithium ion cell produced today uses ethylene carbonate (EC), and most battery scientists believe it is essential. Petibon et al. (2016) tested electrolyte systems other than this within Li-Ion battery cells. Surprisingly, totally removing all ethylene carbonate from typical organic carbonate-based electrolytes and adding small amounts of electrolyte additives creates cells that are better than those containing ethylene carbonate. Petibon et al. (2016) used different surface coatings, electrolyte additives, and new solvent systems, and the impact was substantial.

Petibon et al. tested the conductivity, self-heating rate, volume change, discharge capacity, and polarization growth of cells with differing electrolyte solutions. They found that the removal of ethylene carbonate has been shown to enhance high voltage performance of cells at both room temperature and high temperature. Also, the addition of a co-additive helps to lower the polarization growth during high voltage cycling, also improving the safety. Lowering the polarization decreases the mechanical side-effects, where isolating barriers develop at the interface between the electrolyte and the electrode. Overall, it is shown that several compounds are able to suffice for the ethyl carbonate electrolyte, including vinylene carbonate and ethyl methyl carbonate. These results clearly show that large amounts of EC are not needed, and are actually detrimental to the cycle of cells operated with a high voltage.

Petibon, R., Xia, J., Ma, L., Bauer, M. K. G., Nelson, K. J., Dahn, J. R., 2016. Electrolyte Systems for High Voltage Li-Ion Cells. Journal of The Electrochemical Society 163, 13.

http://jes.ecsdl.org/content/163/13/A2571.full

 

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