Measuring the Parasitic Heat Flow of Lithium Ion Pouch Cells Containing EC-Free Electrolytes

A recent study has shown that removing ethylene carbonate (EC) from electrolytes in Li[Ni0.4Mn0.4Co0.2]O-2/graphite lithium ion pouch cells significantly increases the cycle life and lifetime at high voltage operation. This work investigates the performance of EC-free electrolytes by adding small amounts of electrolyte additives to 1 M LiPF6 ethyl-methyl carbonate in Li[Ni0.4Mn0.4Co0.2]O-2/graphite pouch cells and measuring the parasitic heat flow during high voltage operation. EC-free electrolytes yielded higher parasitic heat flow at lower voltages but performed better than EC-containing electrolyte above 4.3 V. Additionally, EC-free electrolytes were able to recover to a lower parasitic heat flow after high voltage exposure than those containing EC. Most EC-free electrolytes had lower impedance and acceptable gas evolution compared to electrolytes containing EC throughout the experiment. EC-free electrolytes shed light on a new area of high voltage electrolyte development, using a simple and cost effective chemistry. (C) The Author(s) 2017. Published by ECS.